ILC Beam Delivery System (BDS), Baseline/Alternatives Configuration Document (BCD/ACD).   Evolving document.

BDS BCD/ACD is being created by WG4, following the work and discussion at Snowmass 2005, and after Snowmass.

Created: September 7, 2005. Last updated: December 4, 2005, 4:55 PM PST
Saved previous version (November 17, 2005). Changes.

Please check this address http://www-project.slac.stanford.edu/ilc/acceldev/beamdelivery/bds_bcd_acd.htm for the most up-to-date version of this document.  This document is linked to "ILC Wiki" at http://www.linearcollider.org/wiki/doku.php?id=bcd:beam_delivery:beam_delivery_home

Contents

Beam parameters
Overview of baseline
        Baseline for two IRs: two BDSs, 20/2mrad, 2 detectors, 2 longitudinally separated IR halls
        Discussion of alternative configuration for two IRs case
        Discussion of configuration for single IR case
        http://www-project.slac.stanford.edu/ilc/acceldev/beamdelivery/bds_bcd_acd.htm#alternative_1_z_eq_0
        Alternative 2: single IR/BDS, collider hall long enough for two push-pull detectors
        Ranking of BDS configurations (20,14,2,0mr) for various criteria
                Rank 1
                Rank 2
                Rank 3
                Special Rank
        R&D specific to 20 and 2mrad baseline and 14mrad and head-on alternatives
                20mrad baseline
                14mrad alternative
                2mrad baseline
                Head-on alternative (el.-separator)
                Head-on alternative (rf kicker)
Overview of BDS and its subsystems
        Beamline sequence and design features
        Tune-up extraction line, MPS, E-error and betatron error diagnostics
        Collimation and Backgrounds
        IR and IR magnets for 20mrad
                Intermediate crossing angle 14 mrad
        20mrad Extraction Line
        2mrad Extraction Line
        Crab cavity system
        Feedback system
                BDS stability
        Beam dump system
        Beam Energy Measurements
        Luminosity Measurements
        Beam Polarization Measurements
Multi-TeV issues
Sections not yet described
References

Introduction

This text represents recommendations from WG4 to GDE towards the ILC BCD/ACD, and is based on pre-Snowmass BCD [Pre_Snowmass_BCD] and on the materials discussed during Snowmass 2005 [WG4_Snowmass_Agenda,WG4_Snowmass_Summary]. This text will evolve and will be updated to include new results of post-Snowmass work. (In particular, the recent progress reported at Nanobeam workshop in October 2005 is included.) The goal of this document is to describe the Beam Delivery baseline configuration, give justifications for baseline, describe R&D needed for baseline; as well as describe possible alternatives and benefits they can provide, describe R&D needed for alternatives. This document will address the questions [Snowmass_decision_list] posed by GDE during Snowmass (the responses are highlighted below as {GDE#N}), as described in [WG4_20050823] and [WG4_20050825] but will go beyond this list, approaching the complete document as outlined in [WG4_20050825_BCD], building the foundation for RDR.
 

Beam parameters

The present BDS design is being evaluated for various ILC parameter sets [Raubenheimer_20050228]. The nominal parameters for 500GeV and 1TeV CM are acceptable. However, the parameter sets which have large beamstrahlung, may turn out to be problematic  from the point of view of extraction line energy acceptance and from background (pairs hitting vertex) point of view. In particular, the high Lumi 1TeV parameter set is not working and an alternative set was suggested [Seryi_20050817]. This alternative set pushes the vertical emittance and thus affects DR & LET working groups. Similarly, an alternative parameter set for high L 500GeV CM could be suggested. Some other parameter (e.g. Low P) may have the same problems with high beamstrahlung and associated power loss in extraction line (is being evaluated). In terms of the effect of different parameter sets on background, the low Q option is most preferable (but may be a concern for DR working group, as it pushes number of bunches), while the large Y size, low P and high L are much less preferable, especially at 1TeV. In particular, these three sets seem to exceed the tolerance on hits of the first layer of vertex detector (assuming CCD technology -- this may affect choice of technology for vertex detector) [Kozanecki_20050824].
    The maximal energy to which the hardware, layout, design of BDS beamlines (including in particular the extraction lines and SC quad) is specified, need to be defined. This is important, in particular, because higher energy can be reached in the linac with reduced current, provided that cavities can withstand increased gradient. Should this max energy be strictly 500GeV, 1TeV, or 35/31.5*1TeV? This affects, and feedback expected from, other working groups, in particular Parameters.  {This is response to GDE#2}

Required R&D
    -- continue studies of various parameter sets, including alternative sets, on BDS and detector performance
    -- develop alternative high Lumi parameter set for 500GeV CM
    -- study how the limit of max operating energy is affecting BDS design optimization 

Overview of baseline

The recommendation for the BDS baseline have been chosen taking into account the recommendation of the particle physics community [ILCSC_scope], which requested that  ILC will have two interaction regions, which could possibly focus on different physics programs, and allow for different approaches to the search for new physics. The paradigm of two IRs (and, independently, two detectors) is being recently revisited, and is being discussed by the whole community. Possible configurations for the case of a single IR will be discussed below.
 

Baseline for two IRs: two BDSs, 20/2mrad, 2 detectors, 2 longitudinally separated IR halls
    {GDE#5 & GDE#15}
    The baseline configuration for the case of two IRs consists of two Beam Delivery Systems with crossing angle 20mrad and 2mrad, two detectors, two independent and longitudinally separated IR halls [WG4_Snowmass_Summary]. The large crossing angle IR features stable and mature design, separate incoming & extraction beamlines which allow achieving high luminosity, potentially cleaner downstream diagnostics, expect to provide good operational margins and flexibility, minimizing the risk to achieve nominal parameters, is upgradeable for gamma-gamma, but has somewhat larger backgrounds. The small crossing angle IR is a more recent design, it provides better background and better detector hermeticity, relies much less on crab crossing technique, but achieve lower luminosity than other IR, the downstream diagnostics may have higher background, the design is more constrained and operation may be more difficult.
    Longitudinal separation of collider halls in the baseline configuration (dZ about 130m) provide possibility to build or upgrade one detector while another is taking data. This decision may affect other groups. In particular, with collider hall separated longitudinally and with undulator e+ source, there may be difficulties providing collisions at both detectors with different ( /2 or *2 ) time separation if the fast (train to train) interleaved operation is considered. However, assuming that fast interleaved operation is excluded, and that DR need to have turn-around for feed-forward, it should be possible to provide collisions in both IRs regardless of train structure (this may need building additional turn-around beamlines). {GDE#17}
    The linacs in the baseline layout are pointing to the large crossing angle IR. This is configuration choice which does not a priori preclude multi-TeV upgrade. This may be a necessary but not sufficient condition to provide multi-TeV compatibility. Other requirements will be discussed below in the section "Multi-TeV issues".
    Design of the optics for the baseline is in advanced stage. Optics files for both IRs, for incoming and extraction beamlines are available [BDS_optics]. Geant or equivalent models of IR regions are being developed [BDS_IR_models] .
    The R&D which a specific to the baseline configuration choice are briefly the following. The compact SC quads and crab cavity for 20mrad IR, and large aperture SC quads and special extraction septum quads for 2mrad IR. The compact SC quads are being developed at BNL and recently demonstrated and exceeded the design gradient with 38cm short prototype [Parker_20050816], while the work on a longer prototype and preparation for stability study of such quad are under way. The crab-cavity design will build up upon the 3.9GHz deflection cavity being developed at Fermilab. Development of large aperture SC magnets within LARP program and at Saclay are relevant for 2mrad IR design [Napoly_20050816], while r&d on extraction magnets for 2mrad IR yet has to be started. (See more details on these r&d in sections "R&D specific to..." as well as in "IR magnets",  "Crab cavity systems", etc).
 

Discussion of alternative configuration for two IRs case
    {GDE#5 & GDE#15}
    While the group has consensus on the baseline for the case of two IRs being 20/2mrad configuration, discussion for single IR case is ongoing. First of all, either 20mrad or 2mrad could be a candidate for a single IR.
    In addition, several alternatives were discussed at Snowmass. The earlier design of head-on scheme, where a number of problems were identified by the TRC study [ILC_TRC2], has recently been reconsidered with attempts to improve it. In one case the electrostatic separator was suggested to be replaced by an rf-kicker [Iwashita_20050818], which however introduced severe MPS concerns and other issues. In another case, the extraction optics was modified so that the kick required from electrostatic separator was reduced about twice [Keller_20050818], improving its feasibility even at 1TeV. There are number of issues with this design: full design of extraction line is absent; it is not clear if downstream diagnostics would be possible; requirements on pressure (~1nTorr) in the separator are tight; radiative bhabha’s are hitting the separator plates; there are parasitic bunch crossing. Would these issues be solved, and required r&d successful (see below) the head-on configuration may give somewhat simpler design of the forward region and somewhat smaller background; simpler FD and extraction magnets; absence of the need for crab crossing. At Snowmass, the group did not achieve consensus whether the issues outweigh possible benefits, therefore the head-on configuration remained an alternative choice to be studied in more details.
    One more alternative, which can replace either 20mrad or 2mrad IR in the two IR baseline, or which can be considered for single IR scenario, is an intermediate crossing angle (10-15mrad) solution. This configuration was suggested as candidate for further studies. It follows recommendations of both the WG4 and the three detector concept groups to aim for the smallest possible crossing angle at the IP that does not compromise ILC performance [Tauchi_20050816]. It would be based on the same compact SC quad design developed for 20mrad, will allow maintaining separate incoming & extraction beamlines and thus to achieve high luminosity and be flexible in operation, should allow for clean downstream diagnostics, it may not preclude multi-TeV with proper linac layout & parameters, and the backgrounds may be very similar as in 2mrad. Also, the intermediate crossing angle solution would ease the crab cavity and would allow removing the need for DID (Detector Integrated Dipole) which may improve background and ease operation of TPC (Time Projection Chamber). Reverse polarity DID may also become possible, which could further improve background. The intermediate crossing angle solution, however, is unlikely to be gamma-gamma compatible, at least not with those luminosity numbers presently quoted.
    After Snowmass the group concentrated its work on the design for the intermediate crossing angle. The complete design of 14mrad alternative was presented at Nanobeam 2005 in October, including optics of incoming and extraction line, design of FD magnets, Geant model of IR and background simulations (showing that the background in 14mrad can be as low as in 2mrad) as well as considerations for upgrade scenarios from single 14mrad IR to two IRs. (The accessible crossing angle depends on L*. The 14mrad design matches L*=3.5m, while with L*=4.5m the angle could be 11mrad). This design is described in the section Intermediate crossing angle 14mrad.
    The additional r&d needed for head-on alternatives include feasibility study, prototyping and beam tests of electrostatic separator or rf-kicker. This may require several years. The r&d for alternatives need to be compared with r&d needed for baseline. In particular, the large bore SC quads for head-on may be similar as quads for 2mrad; and the r&d for intermediate 10-12mrad is synergic with r&d for 20mrad baseline. See more in "R&D specific to...".

Discussion of configuration for single IR case
    The community as a whole, and WG4 in particular, have started discussion of the single IR configuration at Snowmass. This question may be decoupled from the question of the number of detectors if a push-pull detector configuration would be possible. The staging scenario, when second IR is built much later, during upgrade, should also be discussed in this context.
    The main argument for single IR case is the cost of additional beamlines, detector and civil construction. In the staged scenario, one would also need to consider that second IR and detector could benefit from experience gained with the first IR and could be designed using deeper knowledge of the physics needs, resulted from early run of first IR.
    The cost of BDS is dominated by cost of beamline components and detector, so the cost benefit from reducing number of IRs would be well predictable. The conventional facility cost saving is most significant for deep tunnel configuration, while in the near surface configuration, especially with single collider hall, the cost difference of tunnels for 2nd IR may be rather small, since construction technology may anyway require removing soil in the entire BDS area wider than tunnel separation, and then rebuilding the tunnel structure. In this case, one can envision either building tunnels for two IRs at start, and not using one of them, or including provisions in the tunnel design (special tunnel stubs) which would facilitate building additional IR tunnels in future. Thus, one or two IRs decision is very site specific, and in particular in the shallow site case, it may be deferred.
    With respect to IR design for the single IR case, it is important to note that with two IR configuration, which complement each other, one may allow (i.e. the overall performance would not be compromised) one of IRs be more risky in terms of machine performance in expectation of better backgrounds and detector hermeticity. However, in the case of single IR configuration, one need to put the overall performance, reliability and operability on the first place. With single IR the optimal baseline may be neither 20mrad nor 2mrad. The intermediate crossing angle with compact SC quads may turn out to be the best choice. At Snowmass, the group suggested that it needs more time (2-3month) for design study of intermediate crossing angle (which was designed and presented at Nanobeam 2005 in October), and that wider discussion is needed to come up with recommendation for the baseline for the single IR case.
    Taking these considerations into account, the group suggested, at Snowmass, to study the following two alternatives for IR configurations, as described below.
    With respect to the choice of the angle for the single IR -- all versions (20,14,2,0mrad, see Ranking and R&D lists below) should be considered at this moment. The group is stressing its support of the baseline with two IRs and feels that making a choice of a particular configuration for single IR at this moment is not necessary and may be counterproductive [WG4_mtg_20051110].

Alternative 1: two BDSs, 20/2mrad, 2 detectors in single IR hall @ Z=0
    In this case, the difference from the baseline is that there is no second interaction hall and both detector are housed in the single large hall without longitudinal offset of IPs. The single collider hall gives civil engineering savings, and absence of longitudinal separation of IPs would ease handling of different bunch patterns. However, detectors are placed in the same collider hall and there may be issues of vibration and operational & installation constraints for the running detector while another one is assembled or upgraded. Moreover, transverse separation of the IPs (equal to 21m in the baseline) may have to be increased to fit the detector sizes and about five meters of removable shielding. Increasing transverse separation may involve lengthening the BDS. 
 

Alternative 2: single IR/BDS, collider hall long enough for two push-pull detectors
    In this case, there is single IR, single BDS, and long (in direction transverse to the beam) collider hall that can house two push-pull detectors. The pro arguments are again the cost savings, ease of handling of different bunch patterns. The con arguments are again the vibration issues and operational & installation constraints. One need to stress also that even if the crossing angle of the single IR is compatible with gamma-gamma, the gamma-gamma may not be feasible since it would need long & invasive modifications of IR implying very long switch-over time, which may not be scientifically affordable. One the positive note one need to stress that this configuration could be transformed adiabatically or upgraded into alternative 1, if required by physics. In that case the additional tunnels for second IR could be built with desired configuration (small, intermediate or large angle, for e+e- or gamma-gamma) and that 2nd IR could be optimized using experience gained with 1st IR. Again, the question of one or two detectors is decoupled from the question of one or two IRs if push-pull technology is feasible and short switch-over time can be provided. Number of studies are needed to understand technical feasibility & implication of supporting two push-pull detectors (e.g. constructability of long IR hall, whether Final Doublet needs to be part of detector for faster detector exchange, etc.).
 

Ranking of BDS configurations – 20mrad, 14mrad, 2mrad, and head-on (with reduced strength electrostatic separator and with rf kicker) – for various criteria

Ranking example: "best A, B and C, then D, worst E". In this case all A,B,C have the same high rank, D would be intermediate rank (separated by "then"), and E would be the worst rank.

Rank 1 – directly affecting energy and luminosity reach, background and precision measurements of beam properties, or a single point failure:

• Luminosity reach – best 14 and 20mr, worst 2mr and head on
  • In 2mr and head-on, to extract the disrupted beam, it is bent by a separator, rf kicker or field off-center of the final quadrupole. Large energy spread of disrupted beam causes beam losses and limits the luminosity reach by more than a factor of two in comparison with 20 and 14mr
• Crab-crossing – best head-on, then 2mr, then 14mr, worst 20mr
  • No need for crab cavity in head-on
  • Small to moderate luminosity loss (5%, 10% or 30% for low Q, nominal or large sigma Y parameters) in 2mr without crab cavity. Full recovery requires crab cavity that would need to be placed a km away from IP which may be an issue for phase stabilization, however the needed kick and phases stability are ten times more relaxed than in 20mr. Partial luminosity recovery may be done with dispersion at the IP, without crab-cavity, for the cost of larger energy spread in the beam and induced energy bias of luminosity spectrum
  • Crab cavity is essential for 14 or 20mr. Luminosity loss without crab cavity is 60-75-90% in 14mr and 75-85-95% in 20mr (for low Q, nominal or large sigma Y parameters)
  • Warm NC transverse cavities are in use now, SC cavities are not yet. A deflecting SC CKM cavity is being built at FNAL. Crab cavity system can be built and experimentally verified during TDR phase, before start of ILC operation. 
• Fast feedback hardware and its integration into IR  – best 20 and 14mr, then head-on, worst 2mr
  • In 20 and 14mr, feedback BPMs and kickers do not see other beam
  • In head-on with shared aperture, BPM sees other beam and need to be directional, there may be losses of low energy beam tail on the kicker.
  • In 2mrad, the feedback BPM has to be placed in front of FD, where disrupted beam envelope is still small, there is offset of outgoing beam in the BPM, the kicker should be large aperture, there are potential losses on the kicker.
  • Performance of IP feedback, with all effects of beam losses included, is difficult to guarantee from simulations (which have advanced significantly) or from simplified beam tests. Eventual verification cannot be done before start of ILC operation.
• Hermeticity & min veto angle – best head-on and 2mr, then 14mr, worst 20mr
  • The configuration with separate apertures for incoming and outgoing beams has a larger un-instrumented area in the forward region by comparison with a single aperture.
  • The minimum accessible veto angle is defined by the radial extent of the aperture required for the exiting beam (which is determined by the collimation aperture, L* and the strength of the solenoid field) and can be made equal regardless of the crossing angle choice.
  • The detection efficiency for small angle electrons from copious 2-photon processes is reduced for crossing angle configurations with two holes, which results in higher backgrounds for interesting (SUSY) physics processes whose signature in the detector is missing energy. This loss of efficiency can be compensated by higher luminosity.
• Pairs background – best head-on, 2mr and 14mr, worst 20mr
  • In small angle cases the pairs produced in beam-beam collisions are not dispersed by crossing the solenoid field and background is smallest
  • In larger crossing angle cases pairs traverse solenoid field and disperse more. In optimized 20mr configuration the background can be two times higher than in 2mr or head-on
  • Use of DID increases background, while anti-DID reduces background
  • In 14mr the effective crossing angle can also be zeroed for outgoing beam with use of anti-DID, and background can be as good as in head-on or 2mr
• Flexibility of extraction optics and possibility of downstream diagnostics – best 20 and 14mr, then 2mr, worst head-on
  • Extraction optics is independent of incoming optics and downstream diagnostics design in the 20 and 14mr options
  • Extraction optics in 2mr depends on shared FD magnets, in particular relying on focusing arising from going through final sextupole SD0 with an offset. Design of downstream diagnostics exists. 
  • Extraction optics in head-on depends on shared FD magnets and QD2A quad. Early focusing of disrupted beam by FD sextupoles, as in 2mr, cannot be done in head-on. Investigation of feasibility of downstream diagnostics remain to be done.
• Losses and background conditions in downstream diagnostics – best 20 and 14mr, then 2mr, worst head-on
  • Losses are smallest in 20 and 14mrad extraction line
  • In 2mrad extraction line, need to collimate several tens of kW in vicinity of downstream diagnostics
  • For head-on, there is no design of downstream diagnostics at the moment. 
• Losses in extraction affecting IR background - best 20 and 14mr, worst 2mr and head-on
  • In 2mrad and head-on extraction line, there are higher losses which may create, e.g., neutron flux to detector

Rank 2 – may affect energy, luminosity and background indirectly, e.g. via reliability of operation (integrated luminosity):

• Parasitic crossings – best 20,14,2mr, worst head-on
  • For bunch spacing considered for ILC, there are no parasitic crossings for 20,14,2mr
  • For head-on with electrostatic separator, there are parasitic crossings, especially an issue with halved bunch spacing
• Vertical orbit correction in IP – best head on and 2mr, then 14mr, worst 20mr
  • Vertical orbit is flat or negligible in head-on and 2mr
  • Vertical orbit through detector solenoid is nonzero, and IP vertical angle is 70-100 micro-radians in 14-20mr (relative vertical angle between e+e- is still zero).
  • If required for accurate polarization measurements, the vertical angle can be compensated with DID field or less locally with FD correctors, without DID.
  • If the vertical IP angle is not corrected, one can also tilt the beam orbit in downstream polarimeter, to match the IP angle.
  • In case when angle at IP or in downstream polarimeter will be corrected, such correction is energy dependent (if DID or anti-DID is used, its setting is independent on energy, and proportional to detector field). 
• Tracking, in particular TPC operation and calibration – best head on and 2mr, worst 14 and 20mr
  • If DID or anti-DID is used, TPC calibration may be more complex. The calibration procedure can be eased with modified DID, which provides significantly reduced transverse field in the center (|z|<0.5m) of the detector
• Radiation in solenoid field – best head on and 2mr, then 14mr, worst 20mr
  • Vertical trajectory deviation in detector solenoid is proportional to crossing angle and synchrotron radiation effects grow as fifth power of the angle, independent on energy. The effect on the luminosity is less than one percent when crossing angle is less than 32mrad (SiD), 27mrad (GLD) and 21mrad (LDC).
• Extraction line clearance for beamstrahlung photons – best 20 and 14mr, worst head-on and 2mrad
  • The aperture opening for beamstrahlung photons is +-1.25mrad in 20 and 14mr IR, while it is +-0.5mrad in 2mrad, leading to higher losses on photon collimators and more stringent steering constraints. In head-on with separator, the photons collimated to 0.38mrad at 80m from the IP.
• Photon losses in FD, direct sight to vertex – best 20,14 and head-on, worst 2mr
  • In 2mr, photons from beam halo hit poles of warm quad QF1 in FD. There is a direct sight to vertex detector from QF1 poles. For certain assumptions about beam halo, photons and neutrons backscattered from QF1 to vertex contribute about 10% in comparison with beam-beam pairs
• Extraction devices affecting MPS – best 20,14, worst 2mr and head on
  • In 2mr, because of the large size of outgoing beam, there is difficulty to locate protection collimator on both sides of FD in its vicinity
  • In 2mr, quench of QD0, which provides extraction angle, may cause the beam to hit near IR beamlines
  • In head-on with electrostatic separator, a breakdown would cause beam to hit collimators on another side.
  • In head-on with RF kicker, its failure may cause the beam to hit the IR region. The dark current from parasitic rf-buckets can be swept to IR region if BDS energy collimator is opened to more than 2% energy acceptance. 
• Extraction devices affecting collision stability – best 20,14 & 2mr, worst head-on
  • In head on with separator, its field needs to be stable at the level of 1E-5, to prevent beam separation at the IP
  • In head on with rf kicker, its field needs to be zero within 5E-6 at the moments of passage of incoming bunches

Rank 3 – affecting only cost, difficulty of r&d and of the design:

• Difficulty of final doublet magnets – best 20 and 14mr, then head-on, worst 2mr
  • The 20 and 14mr SC magnets are based on direct wind technology which was used for HERA upgrade, for BEPC upgrade, etc.
  • The head-on SC FD quads may benefit from LARP and Saclay multi-year programs which may come with a prototype in 2006
  • The 2mrad SC FD magnets must have larger aperture than for head-on, especially for sextupole. The 2mrad QD0 need to have 3mm thin tungsten liner, to reduce the energy density due to radiative Bhabhas.
• Length of extraction line – best 20 and 14mrad, worst 2mr and head on
  • Min length of extraction line defined from min transverse separation from incoming beam is about 400m in 20 and 14mr and about 800m in 2mr and head-on
• Difficulty of final doublet integration in detector – best 20, 14mr and head on, worst 2mr
  • The external size of FD cryostats with supports fits to r =20cm envelope in the detector for 20,14mr and head-on
  • For 2mr, with larger aperture magnets, the external size will be larger and the envelope radius will be increased to about  r=25cm or more
• Special extraction magnets – best 20 and 14, then head on, worst 2mr
  • The 2mr require special septum quads with large aperture for extracted beam and zero field region for incoming beam
• Special coils for detector solenoid – best 2mr and headon, worst 14 and 20mr
  • DID or anti-DID coils need to be included in detector solenoids for 14 or 20mr
  • An accurate 3D field map with (anti-)DID must be measured, for several settings

Special Rank  – compatibility with other physics programs and upgrades
(Relative weight of this category should be discussed and determined by the whole community):

• Compatibility with gamma-gamma – best 20mr, worst head-on, 2mr, 14mr
  • The +-10mrad extraction cone acceptance for gg can be provided in 20mr for L* of about 4.5m (with latest self-shielding quads). Smaller angle is not compatibility with gg
• Compatibility with e-e- – best 20 and 14mr, then head-on, worst 2mr
  • The 20 and 14mr can provide same beta-functions at IP, collision angle can be corrected
  • In head-on with electrostatic separator, a defocusing quad is relied upon to increase the extraction angle. In e-e-, its polarity needs to be changed, leading to modification of FF optics. Impact of this change was not studied.
  • Most difficult for e-e- is 2mrad, where, to preserve focusing of outgoing beam by FD sextupoles, the polarity of FD need to be changed, leading to thirty times higher Y beta function at IP 
• Compatibility with multi-TeV – best 20mr and 14mr, worst head on and 2mr
  • Parasitic crossings in CLIC-like scheme require crossing angle of 20mr and 14mr may be also fine (with new CLIC parameters, TBC)
  • Small crossing angles not compatible with multi-TeV, because of parasitic beam-beam crossings and because one cannot separate the outgoing beam

R&D specific to 20 and 2mrad baseline and 14mrad and head-on alternatives

Common items are not listed (see subsystems chapters below). Items listed mean detail engineering & prototyping, except when it says “study, evaluate or design” which means paper & engineering study. Text in () gives present status. If parenthesis () are absent, the activity still need to be started. Ranking of the R&D items (e.g. as TRCs R1-R3) is planned to be done.

20mrad baseline:

• Prototype compact SC quads (short BNL prototype tested, self shielded quad tested)
• Crab cavity system and phase stabilization (3.9GHz FNAL cavity developed, redesign coupler to open aperture)
• Study integration of DID into solenoid (preliminary consideration for SiD done [Smith_Wands_2005])
• Study vertical orbit correction & polarimetry (preliminary considerations done)
• Study TPC calibrations procedures with DID
• Stability of compact SC FD (preparations at BNL)
• Design crossing angle IR with all acc. (bpms, kickers, supports) and mdi (lumi, beamcal) components, vacuum chamber w. assembly considerations
• Study performance of downstream diagnostics in presence of beamstrahlung cone

14mrad design alternative:

• All items are same as for 20mrad, plus
• Integration of final quads into common cryostat (eng. studies at start)

2mrad baseline:

• Large aperture SC quads (r=35mm), may use NbTi for long L*, likely need Nb3Sn for L*=3.5m and E upgrade (LARP and European programs for LHC ongoing, design must be accommodated to ILC requirements)
• Large aperture SC sextupoles (r=90mm)
• Design tungsten liner into the QD0, to reduce energy density due to radiative Bhabhas
• Study integration of large aperture quads and sextupoles within the detector
• Pocket coil warm quads QF1 (first look done)
• Evaluate neutron and photon backscattering due to synchrotron radiation (produced upstream and by bending in FD) and charged halo particles impinging on apertures of FD and extraction line, in particular on the face of QF1
• Special extraction septum quads
• Crab cavity system and phase stabilization (less critical than for larger crossing angle) (3.9GHz FNAL cavity developed, redesign coupler to open aperture)
• Phase stability of crab cavities separated by a km
• Study consequence of 0.5mrad photon aperture (1.25mrad in 20mrad)
• Study possibilities to place protection collimators in FD and MPS issues
• Study performance of downstream diagnostics in presence of tens of kW losses on nearby collimators
• Feedback kicker inbore of large aperture sextupole or near
• Study effect of losses in extraction beamline to IR background
• Stability of larger aperture SC FD
• Design straight IR with all acc. (bpms, kickers, supports) and mdi (lumi, beamcal) components, vacuum chamber w. assembly considerations
• Design region of in, out and photon beam separation with all accelerator and vacuum components

Head-on design alternative (with electrostatic separator, reduced strength):

• Large aperture SC quads (r>24mm), may use NbTi for long L*, likely need Nb3Sn for L*=3.5m and E upgrade (LARP and European programs for LHC ongoing, design must be accommodated to ILC requirements)
• Large aperture SC sextupoles (r>24mm?)
• Study parasitic collisions at nominal and upgrade cases
• Study possibility to shorten the FD to increase separation at parasitic collisions
• Electrostatic separator feasibility and stability (CERN separators in ILC requirements, beam tests?)
• Beam, photons & radiative bhabha’s losses on separator plates and protection collimators (plan beam test at ESA?)
• Low vacuum (1nTorr) in electrostatic separators
• Extraction septum quads
• Design extraction line, study feasibility of downstream diagnostics

Head-on design alternative (with rf kicker):

• List is similar as for previous case of head-on with separator, where the electrostatic separator items replaced by:
• RF kicker feasibility and stability (tests at Kyoto so far show too low Q factor, to be continued)
• Study MPS issues with RF kicker (to be continued)
• Study possibility of full elimination of dark current in parasitic rf buckets (by collimation below 2% at 250GeV beam, 1% at 500GeV beam)

Overview of BDS and its subsystems

The following sections review properties of beamlines and systems such as feedbacks, beam dumps, and other, highlight baseline choices and existing alternatives, and list the required R&D.

Beamline sequence and design features
    The sequence of beamline sections in the baseline optics is the following: linac, beam emittance diagnostics and coupling correction section, tune-up and emergency extraction beamline, beam switch yard, upstream polarization diagnostics section, betatron collimation, energy collimation, upstream energy spectrometer, final focus proper with secondary clean-up collimation and with tail-folding octupoles, the final doublet, extraction beamline with downstream energy and polarization diagnostics, beam dump. The final focus optics is with local chromaticity correction {GDE#40}. The range of L* (distance from IP to final quadrupole) considered for studies is 3.5 to 4.5m {GDE#34}. The betatron collimation precedes the energy collimation so that off-energy debris from betatron collimation could be cleaned out in the downstream energy collimator {GDE#37}. The tail-folding octupoles are included into baseline and allow to open the collimation gaps by about a factor of three, which provides an additional safety factor, but they are not relied upon in the baseline. {GDE#35}
    The considered BDS baseline assumes that there is no vertical angle between linac and BDS and the nearest region of vertical bends is at least one kilometer away from beginning of BDS. This is a safety factor that would ease extension of BDS if, for example, additional collimation sections found to be necessary {GDE#4}.
    The baseline assumes that there is no undulator source at the end of the linac, before BDS. The recommendation by WG3a to place the undulator source at the very end of the linac contradicts the considered BDS baseline. Would it indeed be placed there, the number of adverse effects and integration issues will arise (see snapshot of discussion here [BDS_mtg_20051101]), requiring detailed studies. {GDE#8}
    R&D planned at the ATF2 facility will give opportunity to gain experience with local chromaticity correction optics, instrumentation and other BDS aspects.

Tune-up extraction line, MPS, E-error and betatron error diagnostics

Updated November 9, 2005.

The beamline described in this section is located at the end of the main linac at the entry to the BDS and serves several purposes:

• provide MPS protection for BDS components with a system of renewable/consumable collimators
• measure the beam emittance using a system of laserwires
• provide for correction of transverse coupling using a system of orthogonal skew quadrupoles
• monitor incoming betatron orbit errors using BPM measurements; monitor incoming energy errors in a chicane
• when necessary, abort the beam to a dump using a system of kickers and a high-bandwidth extraction line
• during linac tuning, send the full beam to the extraction line continuously using pulsed bends

Corresponding to these goals, this beamline is subject to the following design choices:

• minimum allowable beam size at the laserwire locations and properties of the laser system; required precision of emittance measurements
• maximum allowable amplitude of incoming betatron orbit errors which should be handled by the kicker system
• maximum number of errant bunches which can be allowed into the BDS which could hit the betatron spoilers
• maximum number of errant bunches which can be allowed into the BDS which could hit the energy spoiler

Required R&D
    -- Develop laserwire with one micron spot-size, tripled light, f/1 optics
    -- Study detection of laserwire signal with scattered photons or electrons
    -- Design a system of consumable (renewable?) devices to limit the amplitude of betatron orbit errors
    -- Design a system to reliably determine betatron and energy errors
 

Collimation and Backgrounds

Section updated September 19, 2005. Primary authors responsible for this section: N.Mokhov, F.Jackson

Overview

The baseline collimation design for the ILC BDS is an adaptation of the NLC scheme [LCC52,LCC111]. The design implies a betatron collimation section followed by energy collimators. Octupole pairs are located to perform beam-tail folding which relaxes collimation requirements {GDE#35}. The collimation system [Mokhov_Conf_05_154] consists of spoiler/absorber pairs, arranged to survive impact from errant bunches which escape the machine protection fast extraction system. Additional protection collimators are located elsewhere in the BDS providing local protection of components and absorption of scattered halo particles, while synchrotron radiation masks in the immediate vicinity of the interaction point (IP) protect the collider detector components. The BDS crossing angle does not greatly affect the design of the collimation system, but may impact issues affecting the collimation depth.

Betatron and Energy Collimation Scheme

In the baseline design, degraded energy particles originating from betatron collimation section (and not absorbed there) may be collected by the energy collimator {GDE#37}. Alternative ordering of betatron and energy collimation sections in this design has not been studied. However, a comparison has been done of the collimation designs of NLC and TESLA, which have opposite ordering of energy collimation and betatron collimation. In this study [LCC111] the NLC collimation performance was found to be superior.

Existing Status of R & D

The spoilers are 0.5 to 1 X0 (radiation length) thick, absorbers and synchrotron radiation masks are 30 X0, and protection collimators (PC) are 15 X0. The betatron collimation with 'survivable' spoilers included into baseline has advantage that these spoilers can withstand hit of two bunches at 250 GeV/beam, matching the emergency extraction design goal [Keller_20041015]. They can survive one bunch at 500 GeV. The survivable spoilers are more demanding for the optics (more difficult tuning, tighter tolerances). The alternative is to use consumable spoilers which ease the optics, but require more R & D in terms of renewable spoiler design, development of damage detection, study of MPS issues, etc.

The studies of the dynamic heat load show that most of energy among the beam line elements is deposited in the protection collimators PC1, PC5, PC8 and PC9. The residual activation and radiation damage in the magnets downstream of those is in excess of the limits if the length of the PCs is kept 15 X0 as originally proposed. For example, an averaged residual dose on-contact after 30 days of irradiation and one day of cooling on the front surface of the first quadrupole downstream of PC1 is as high as 7.7 mSv/hr compared to the limit of 1 mSv/hr. The absorbed dose in quadrupole coils reaches 300 MGy/yr compared to the coil insulation limit of about 4 MGy, meaning a lifetime of only a few days. This forced us to increase the PC's length to 45 X0 (about 60 cm of copper) resulting in the coil lifetime of at least several years. Dynamic heat load distribution obtained with the MARS15 code after the collimator optimization gives acceptable loads for the magnets, about 50 W/m for spoilers, and about 10 kW/m for the protection collimators PC1, PC5, PC8 and PC9. (The loss and radiation numbers correspond to conservative assumption of  0.1% for the beam halo population.)

Collimation depths (based on halo synchtrotron radiation clearance through IR apertures) have been studied for the current 20mrad and 2mrad final doublet designs  [Jackson_20050816,Carter_20050816]. Although the aperture constraints are different in each case (extraction quadrupoles for 20mrad, beam calorimeter for 2 mrad), the collimation depths are the roughly the same in both (~10 sigx in the x plane and ~60-80 sigy in the y plane). In the 20 mrad deck these correspond to betatron spoiler gaps of ~1 mm in the x plane, ~ 0.5 mm in the y plane.

The performance of the 20 mrad collimation system has been studied in halo tracking simulations [Jackson_20050816,Carter_20050816,Drozhdin_BDIR2005]. These demonstrate a reasonable performance of the collimation system. Some halo repopulation outside the collimation depth is evident, particularly in the x-plane, which can be remediated by reducing the spoilers x-apertures. The 2 mrad lattice has not yet been studied, or optimized for collimation yet.

Future R & D Required

The most important R & D subjects affecting the collimation baseline are as follows:

• Development of a fast extraction system (tune-up extraction beamline) to provide the necessary protection for the collimators. Experimental studies of collimator survivability may be performed via material damage beam tests at the SLAC end-station-A [Woods_20050302].
• Optimization of the current optics designs at different crossing angles, to minimize non-linear transport between the betatron spoilers and the final doublet.
• Reduction of radiation loads at normal operation and beam accidents.
• Further study of the use of octupole tail-folding (examined previously for the NLC [LCC118]), possibly with beam tests to verify the principle. (Initial studies of tail folding octupoles for ILC done, see [Seryi_20051102]).
• Evaluation of wakefield effects in the baseline design(s). For previous BDS designs, predicted vertical jitter amplification and emittance dilution were found to be significant [TRC2_p340]. In addition, wakefield measurements are planned at the SLAC end-station-A to optimize collimator geometry, and improve analytical methods of estimating collimator wakefields [Collwake_beamtest_request]. (Initial studies of collimator wakefield in ILC done, see [Jackson_20051102]).
• Benchmarking of simulation codes. To see how much our understanding of collimation performance is affected by simulation conventions and approximations.
• Muon flux attenuation studies (see next section).

R&D for alternative with consumable spoilers
    -- renewable spoiler design and prototyping
    -- development of damage detection
    -- study of MPS issues

Reduction of background fluxes at detectors

Muons

A lot of muons are generated - predominantly as Bethe-Heitler pairs - in electromagnetic showers induced in the collimators and other BDS elements during the beam halo cleaning. Fluxes of these muons accompanied by other secondary particles, could exceed the tolerable levels at the detector by a few orders of magnitude [Mokhov_Conf_05_154]. Calculated with the MARS code muon flux equals to 4.1 1/cm^2 s^-1, or 7600 muons in the tunnel aperture for 150 bunches from one beam (with halo population 0.1%). This is to be compared to a few muons allowed in such a sensitivity window. The mean energy of these muons is about 27~GeV. About 700000 photons and 200000 electrons accompany these muons at the detector. The fluxes doubles for energetic muons for two beams.

Magnetized spoilers sealing the tunnel would reduce muon fluxes substantially. MARS calculations were performed for two iron spoilers 9 and 18 m thick at 648 and 331 m from the IP, respectively [Mokhov_Conf_05_154]. The square spoilers are extended by 0.6 m in the tunnel walls and dirt on each side. The field of 1.5 T is used in opposite polarity on left and right sides to compensate it at the beam pipe center. Central gaps are 10 cm wide and 1 m high with 0.8 T field. The gap between the parts is as the beam pipe. This set of spoilers reduces muon background load on the detector from 7600 to 2.2, i.e. to about an acceptable level. Other particle fluxes coming from the tunnel are also down in about the same proportion.

Two alternatives to the muon tunnel spoilers need to be investigated: muon attenuator (about 120m long collar at with 1T field, 0.6m OD) and wide-aperture magnets.

Future R & D Required

The most important R & D subjects in this area are as follows:

• Build consistent, realistic BDS+detector integrated models, with detailed magnetic field maps, tunnel and experimental halls. Add engineering realism wherever possible.
• Generate/refine sub-detector tolerance tables on three levels: (1) pile-up; (2) pattern recognition; (3) radiation damage.
• Study backgrounds for 3 detector concepts and 2 crossing angles: (1) sensitivity windows with respect to tagged origin an bunch crossing; (2) tag origin of backgrounds for all particle types; (3) further explore mitigation methods such as better collimation performance, low-Z masks, muon tunnel spoilers, attenuators or wide-aperture magnets.
• Code/model benchmarking; interfacing; BDIR code/model/map depository.

Extraction

(Text of this subsection may need to be moved to extraction section).
MARS simulations confirm that synchrotron photons produced from the beam core and halo upstream of the IP are collimated by the photon masks and - with an appropriate design - their contribution to backgrounds and radiation loads to extraction line components is negligible. Same with beamstrahlung photons which form a very narrow beam. e+e- pairs and synchrotron photons generated by disrupted beam remain the main source of the IP backgrounds and radiation loads to detector, final focus and extraction components.

At high luminosity and 120-nm vertical offset total radiation load in extraction beam line is 13.3 kW with a 600 W/m peak. Without a vertical offset, these numbers are a factor of ten lower. This is to be compared to estimated tolerance levels of 10 W/m for superconducting magnets and a few hundred W/m for conventional magnets.

IR and IR magnets for 20mrad

Section updated December 2, 2005, with IR magnets description by B.Parker. Need to expand IR description. Primary authors responsible for this section: B.Parker, Y.Nosochkov, K.Tsuchiya, T.Mihara

The compact SC quads provide possibility to focus the incoming and outgoing beam independently, maximizing the luminosity performance and minimizing the losses of the disrupted beam. Expanded description of compact superconducting magnets for 20mrad baseline IR (or for intermediate crossing angle) is given in [Parker_20050915]. This includes description of BNL direct wind technology [BNL_direct_wind], details of engineering design, characteristics of the quads for incoming and outgoing beamlines, plans for stability study of such magnet, etc. A short 38cm prototype of SC QD0 has been built and successfully tested [Parker_20050816,Parker_20050915], exceeding the expectation for the design gradient.
    A self-shielded design of QD0 has been recently suggested, which allows reduction of crossing angle [Parker_20050818,Parker_20050823,Parker_20050913], and will be used for development of intermediate crossing angle alternatives. The cancellation of the external field with a shield coil has been successfully demonstrated in the recent tests at BNL.
    The 14mrad IR based on self shielded compact quad was designed, see section Intermediate crossing angle 14mrad.

Intermediate crossing angle 14 mrad
    Design of intermediate crossing angle (14mrad at L*=3.51m) has been presented in mid October at Nanobeam 2005. The design includes optics of incoming and extraction line, see [Nanobeam_Markiewicz_20051019] and [SLAC_PUB_11591], design of FD magnets [Nanobeam_Parker_20051018, Nanobeam_Parker_20051021], IR optics optimization and background simulations [Nanobeam_Seryi_IR_20051019], as well as considerations for civil engineering upgrade scenarios from single 14mrad IR to two IRs [Nanobeam_Seryi_Civil_20051019] with small or larger crossing angle of the second IR. The IR final quads are based on self-shielding concept [Parker_20050818, Parker_20050823] which eliminates the field interference between beamlines. The IR magnets are shown in Fig.1 and Fig.2 (taken from B.Parker summary [Nanobeam_Parker_20051021]) and are based on tested prototype, see Fig.3. The 14mrad crossing angle reduces the SR effects, allowing greater flexibility in optimization of vertical orbit and background, which now can be as low as in 2mrad IR, see Fig.4 and [Nanobeam_Markiewicz_20051019, Nanobeam_Seryi_IR_20051019]. 

20mrad Extraction Line

Section updated September 25, 2005. Primary authors responsible for this section: Y.Nosochkov

The 20 mrad extraction design [Nosochkov_20050817_20mrad] is based on the independent beamline for the spent beams, without shared FF magnets. The outgoing primary e+(e-) beam and the beamstrahlung photons are transported through the same extraction magnets to a shared 18.3 MW dump. The optics consists of the initial DFDF quadrupole system followed by the two vertical diagnostic chicanes and two protection collimators before the dump. The first four quadrupoles after IP will be superconducting followed by warm magnets downstream. A 2 m space after the last SC quadrupole is reserved to accommodate the crab-cavity on the incoming line. The extraction apertures and quadrupole focusing are optimized for a large energy acceptance to minimize the disrupted beam loss caused by overfocusing in the low energy tail. The magnet apertures are sufficient for a photon beam with up to ±1.25 mrad angle at IP. The optics provides the 2nd focal point with the required beam size of s < 100 µm for the Compton polarimeter diagnostics [Moffeit_SLACPUB11322]. The extraction magnets are compatible with up to 1 TeV CM beams.

The first SC extraction quadrupole QDEX1 is placed side-by-side with the first SC incoming quadrupole QD0 at L* = 3.51 m after IP. This choice is based on the SC compact quadrupole design [Parker_20050915] which makes it possible to have independent SC coils with a small transverse separation. The QDEX1 has a low strength to limit its residual field on the incoming line and built-in correction coils to compensate for QD0 residual field on the extraction line. The first diagnostic chicane will serve as the energy spectrometer. It will include wiggler magnets to produce synchrotron radiation at ±2 mrad directions to measure the average beam energy using SR stripe detectors. The polarization measurement will be performed by a Compton polarimeter, with the Compton IP located at the 2nd focus at center of the second chicane. The horizontal angular amplification term R22 from the IP to the Compton IP is adjusted close to -0.5 for maximum sensitivity to the measured effects. A long 170 m drift is included before the dump to increase the undisrupted beam size. Further increase of this size is required for a realistic dump design [Walz_20050817]. This can be achieved by a longer drift and/or the use of beam rastering. The two collimators before the dump serve to limit the size of the disrupted beam and the beamstrahlung photons to the 15×15 cm size of the dump window [Walz_20050817].

It has been shown that the effect of detector solenoid on the extraction optics and beam loss can be compensated using dipole and quadrupole correcting coils on the first SC quadrupoles [Nosochkov_20050510]. The particle tracking [Nosochkov_20050817_20mrad, Drozhdin_20mr_extr, Ferrari_20050831] showed that the primary beam loss in magnets is acceptable in the 0.5 TeV and 1 TeV CM nominal luminosity options. The power loss in the 0.5 TeV CM high luminosity option and the two alternative 1 TeV CM high luminosity options [Seryi_20050817] may be acceptable, provided that the loss of ~500 W/m in warm magnets is acceptable. The 0.5 TeV CM high luminosity option will require a larger aperture in the 3rd and 4th SC quadrupoles to reduce loss to 2 W/m in these quadrupoles. The maximum loss of the charged and photon beams on the collimators is 5 kW and 200 kW (per collimator) in the nominal and high luminosity options, respectively.

R&D (magnets):
1. SC compact quadrupole with correcting coils.
2. Large aperture warm chicane bends.

R&D (optics): to be updated! Some work done and presented at Nanobeam, see [Nanobeam_Markiewicz_20051019]
1. Design extraction optics for 14 mrad crossing angle and position of the first extraction quadrupole at 6 m after IP. (DONE)
2. Increase free space for the SC crab-cavity. (DONE)
3. Include BPMs and correctors where needed.
4. Evaluate effects of magnet field and alignment errors on beam loss and diagnostics, specify tolerances, provide correction.
5. Specify realistic magnet parameters: field and length for required aperture.
6. Include solenoid, anti-solenoid and DID fields, provide correction.
7. Include diagnostic wigglers and weak bends.
8. Consider protection collimators for magnets with large power loss.
 

2mrad Extraction Line

Section updated September 19, 2005. Minor updates November 9. Primary authors responsible for this section: D.Angal-Kalinin, R.Appleby, K. Kubo, N.Mokhov

The 2 mrad extraction optics [Angal-Kalinin_20050816] is based on large aperture superconducting QD0 magnet (the technology of this magnet is described in BCD for 2 mrad IR magnets) and a warm pocket coil quadrupole QF1 [Spencer_Parker_20050524]. Very large aperture superconducting sextupoles are required to provide focussing to the low energy tail particles, the studies of such large bore sextupoles have already started [Kashikhin_20050419]. L* of 4.5m has been considered in this case to accommodate the superconducting large aperture magnets. The final doublet is optimized for both the incoming as well as the outgoing beam. The collimation depth for this doublet is sufficient [Jackson_private_comm]. The large aperture special magnets; either warm Panofsky or the superconducting super septum [Spencer_Parker_20050524] starting at a distance of ~36 m from the IP contain the extracted beam and the beamstralung cone. Separate warm magnets start from ~47m. The optics contains energy cleanup chicane in the vertical plane, followed by the energy spectrometry and polarimeter chicanes [Moffeit_20050422,Nosochkov_20050817]. The beam is made parallel to the IP at the second focus for polarimetry. A long drift space after the polarimetry chicane provides enough separation (~3.5m) between the incoming and extracted beams for the beam dump. This drift also helps to increase the beam size of undisrupted beam at the window. However, additional sweeping/rastering mechanism needs to be included in this design to achieve the beam sizes as required for the beam dump and beam window [Maslov_TESLA2001_07,Walz_20050809]. Throughout the extraction line, dedicated collimation sections have been provided to control beam loss. The optics design has been optimized to localize beam losses on the collimators and minimize them on magnets [Drozhdin_20mr_extr]. Estimated beam loss rates on the extraction line magnets can reach tens to hundreds of Watts per meter [Mokhov_private_comm]. A table of tolerable beam losses and radiation loads on superconducting and conventional magnets of types envisioned in the extraction line needs to be generated [Mokhov_private_comm]. Detector Integrated Dipole is not required for 2 mrad case and the orbit and angle correction will be done by moving the final doublet.
    The possible locations of the IP feedback BPMs need to be identified, taking into account also the background conditions [Hartin_20050818]. For 2mrad, the feedback BPM may need to be located in front of the FD, where the envelope of outgoing beam is still small. The outgoing beam comes to this BPM with an offset and is separated in time from incoming beam. One need to study the possibility to detect the BPM signal in this situation. Preliminary study show that using directional stripline BPMs one can achieve sufficient separation between signals [BDS_mtg_smith_20050329].
    For the IP feedback, a kicker need to be included into FD as close as possible to QD0 (to maximize the feedback capture range) [BDS_mtg_seryi_20051004]. For 2mrad case, the kicker aperture should be about 180mm. Preliminary studies show that the kicker is feasible [BDS_mtg_smith_20051101].

The optics studies indicate that it is possible to get a good bandwidth for the final focus optics for the long doublet used in this case [Seryi_20050811]. The preliminary studies also indicate that it is possible to use the 2 mrad extraction scheme for the e-e- operation [Seryi_20050812].

In 2mrad FD, energy deposition in SC QD0 due to radiative Bhabhas need to be mitigated. These particles are deposited along the QD0, primarily in the horizontal plane, in a narrow vertical stripe. The energy density exceeds the safe limit of 0.5mW/g by about a factor of three, for the nominal 500GeV CM parameters. For 1TeV case the density is ~2 higher. This issue can be solved with use of 3mm thin tungsten liner, which reduces the energy density by about a factor of ten [BDS_mtg_keller_20050726].

R&D, prototypes required:
1. Super septum and Panofsky quadrupoles
2. Large aperture sextupoles [final doublet quadrupoles including pocket coil quadrupole need to be mentioned in IR magnets section of the BCD]
3. Detector integration of large aperture quadrupoles and sextupoles within the detector [based on the feedback on detector opening procedure].
4. Study possibility to integrate feedback BPM into FD and detect its signal in presence of large offset and of the incoming beam.
5. Integration of the large aperture feedback kicker into FD.
6. Design tungsten liner for QD0, to reduces energy density due to radiative Bhabhas [this should appear in IR magnet section]
 

Further Studies :
1. Generate a table of tolerable beam losses and radiation loads on superconducting and conventional magnets
2. Optimization of the extraction optics and collimator designs to minimize the losses on the extraction line magnets
3. Possible range of 3.5m<L*<5m
4. Orbit and angle correction at the IP
5. Include solenoid field in to the simulations
6. Design final doublet with QD0 gradient of 250T/m based on the Nb3Ti technology
7. Mitigation of radiation loads on incoming and outgoing beam SC magnets
 

Crab cavity system

Section updated September 20, 2005. Minor updates November 9. Primary authors responsible for this section: G.Burt, P.Goudket, H.Padamsee, L.Bellatoni

Overview:
For a large crossing angle at the IP a crab cavity system is required in the baseline to increase the luminosity by horizontally rotating the bunch by half the crossing angle, without deflecting the bunch or greatly increasing the beam emittance. In the 20 mrad case the luminosity loss without a crab cavity is 80% [Burt_EuroTeV].
    In 2mrad case, the loss is 10-15% with nominal parameters [Burt_EuroTeV] and the loss can reach about 30% for large sigma Y parameter set [Seryi_20050310]. Luminosity loss in 2mrad can be avoided with use of dispersion at the IP, however it requires introducing additional correlated energy spread and causes higher energy bias (100-200ppm) of the luminosity spectrum [Seryi_20050310]. Therefore, crab cavity considered essential for 2mrad as well.
    The crab-cavity will be placed near FD in 20mrad case, and approximately in the region of QF5 quadrupole (about 400m from IP) in 2mrad case (for the reason of transverse separation with another beam, see [BDS_mtg_seryi_20041207]). To avoid deflecting the bunch the phase of the cavities must be highly stable.
    The ILC bunches require, at 500GeV and for a 20mrad crossing angle, a transverse kick equivalent to approximately 6.5MV for 3.9GHz cavities (19.5MV for 1.3GHz). The phase jitter between crab cavities should be less than 0.07 degrees for a 3.9GHz system or 0.02 degrees for a 1.3GHz system, with a 20mrad crossing angle [Burt_EuroTeV].
 

Cavity baseline:
Fermilab 3.9GHz CKM superconductive cavity [McAshan_TM2144,Solyak_LINAC04] three/four 9-cell cavities running at 6MV/m placed near the Final Doublet. The total length of this cavity should be about 4m long and has an aperture diameter of 30mm.
    Issues: This cavity may not be rigid enough to keep microphonics to the required level. Lower order mode coupler lies 11mm from centre of the beampipe. ILC application requires redesign of coupler to open the aperture.
    Justification: This cavity has been under development for several years, and its research program is at an advanced stage.
    R&D required: Cryostat design including cavity tuner, x-y tuner and roll tuner. Effective damping of LOM, damping of modes (SOM) within pass-band of primary deflecting mode and reliable separation of unwanted polarization of deflecting mode, beam pipe HOM coupler for high frequency modes above beam pipe cut-off frequency, search for trapped modes, beam loading. Multipacting simulations in cavity and coupler regions for the deflecting mode operation. Microphonics/rigidity. Evaluation of losses in the crab cavity region as a function of aperture. Evaluation of crab cavity length on extraction line design.
    Alternatives: 13 cell CKM, CKM with larger aperture (~5m), NC (normal conducting) cavity (4.5metres) [Adolphsen_20050301], 1.3GHz cavity (~9 meters), 3.9GHz redesigned lower loss shape (~3.5 meters), stiffening rings.
 

Phase control and Distribution baseline:
Fast phase control based on FPGA (field-programmable gate array) with vector-sum phase control driven by two 3kW klystrons with one modulator.
    Issues: The use of two klystrons can induce jitter due to the klystrons phase stability.
    Justification: This is a well-developed and tested fast phase control system.
    R&D required: Working system built at the operating frequency. Piezo tuners. Distribution test; the full length of line should be tested for phase jitter. Cavity phase stability tests: The phase jitter between two or more cavities should be tested both with and without a beam at full power.
    Alternatives: High power ferrite phase shifters driven by a single high power klystron, 2nd klystron phase control at high power, individual cavity phase control, RF reference distribution using fiber optics [Naito_PAC2001], use of IOTs (inductive output tube) instead of klystrons if the frequency is appropriate.

Feedback system

The fast beam-beam intra-train feedback is a must and is baseline, as well as slower train-by-train feedback. The alternative is to consider additional intra-train feedback loops at the entrance to BDS and throughout the linac. Baseline configuration of final doublet does not have any active means of its mechanical stabilization, but includes vibration measurement of FD as part of the baseline. This would give diagnostic for fast beam-beam feedback, may reduce commissioning time and may improve feedback convergence time. Possible implementations include accelerometer on cryostat, interferometry from cold mass to cryostat and interferometry from the cold mass to an external reference (invasive but by far the best). One of the most challenging tasks in design of fast feedback is its integration into IR, taking into account background conditions [Hartin_20050818], realistic constraints on kicker location and apertures [BDS_mtg_seryi_20051004, BDS_mtg_smith_20051101] and all engineering details of FD.
    The needed r&d includes prototype of the intra-train feedback, being done  at ATF and ATF2 [Nanobeam_Burrows_20051021], beam-test of BPMs in realistic background conditions planned to be performed at ESA, design work on incorporating kicker and BPM hardware into the final doublet, developments of methods to monitor FD stability, e.g. by means of interferometry (tests ongoing at UBC and planned at ATF). For the alternative configuration when additional feedbacks are used, feasibility studies and optimization will be necessary. 

BDS stability

The issue which define whether ILC can work with baseline feedback configuration (intratrain feedback at IP only) depends on the achieved ILC stability. The need for a stability specifications for ILC was one of the actions items identified at Snowmass, at the joint WG1/WG4 meeting. The ILC stability goals were discussed at Nanobeam 2005 workshop on October 17-21, see [Nanobeam_Seryi_20051017]. Suggested stability goals for the beam jitter, in a brief summary, are the following: up to 50% sigma at the end of linac (or in BDS diagnostics); up to 100% sigma at the end of BDS, before FD; several sigmas at IP. These goals will be consistent with baseline feedback configuration. The beam stability goals translates to required stability of the tunnel floor and give limit to additional noise due to beamline components, namely:
    -- Tunnel floor stability (site + noise of nearby ILC equipment):
                Linac area: up to ground motion model K or C
                BDS area: up to ground motion B*3 or gm C/3
and
    -- Additional noise due to beamline components:
                Linac area: up to 30 nm
                BDS area : up to 10 nm
                FD : up to ~100nm
Exceeding these stability limits will likely require using multiple intratrain feedbacks along the machine.  These stability requirements need to to be discussed and set consistently by the DR, Linac and BDS groups.
    Stability and background vibration were studied at many sites, including most of the sample sites under considerations. Data can be found in [CERN_SL_94_41] for LEP tunnel data, [PRSTAB_e031001]  for data near Fermilab. Data for DESY site as well as recent comparison of different sites can be found in [Amirikas_Nanobeam05].

R&D required :
    -- studies of stability of sites (preliminary data exist for most of the sample sites)
    -- investigation and minimization of vibration produced by conventional facility, power supplies, and other in- and near-tunnel equipment
    -- studies and minimization of noises generated at or amplified by the beamline elements in linac and BDS, in particular linac quads in the cryostats and BDS magnets
    -- studies and optimization of stability properties of final doublet. 

Beam dump system

Section updated December 2, 2005. Primary authors responsible for this section: R.Appleby, D.Walz, R.Sugahara/S.Ban

The baseline beam dump is based on water vortex design rated for 18MW beam [Walz_20050817, Appleby_20050914]. The choice of a water dump for the baseline has many advantages: the water dump has been studied in detail for accelerator projects and a lower power (2MW) beam dump was used at the SLC [Walz_IEEE1965]. Furthermore the problems of the larger dump design have been noted, and the studies indicate there are no “show-stoppers”. The water dump for the TESLA project was studied in detail at DESY [Bialowons_TESLA200104]. The alternatives suggested in the ACD require more R+D to be sufficiently mature for a baseline design. The beam dump is common for charged beam and photons for the 20mrad interaction region layout, while for 2mrad layout the photon dump is separate (rated to about 1MW).
    There are separate beam dumps rated for full power for all beam lines including tune-up lines, for a total of six beam dumps in the baseline. The tune-up dumps are sufficiently remote from the IP, so that the collider halls can be accessed for detector maintenance while the linac is being tuned, and full beam sent to tune-up dump. 
    Discussion of pro/cons of separate full power tune-up dumps have started [BDS_mtg_20051129]. Technically, the elimination of two full power tune-up dumps should be possible, there will be impact on availability which may be partly mitigated by reduced power tune-up dumps (~0.5MW), the cost saving need to be further evaluated, detailed design would need to be made.
    The water flow is sufficient to avoid volume boiling of the water (for disrupted beam). The vacuum/water boundary consists of a suitably thin window. The cyclic stress of the window is controlled by limiting the temperature rise per pulse of the water system. The undisrupted beam size is allowed to increase in the extraction line, to avoid damaging the window, which required lengthening the extraction line by a hundred meters or so. Preventing water boiling due to undisrupted beam has to be done by sweeping the beam in the final part of the extraction line, as it require large increase of the beam size, which cannot be realistically done with lengthening the drift length. The water circuit consists of two closed loops and an external water circuit. The inner water loop is pressurized to 10bar and has a volume of around 18 cubic meters. The length of the dump, including all shielding, is about 25m longitudinally and about 15m transversely.

The required R+D items for the baseline are a study of window survivability, and the corresponding computation of the displacement per atom (DPA). A window replacement procedure and schedule can then be developed. A prototype of the window and a beam test are also necessary. The required test beam must give similar energy densities in the window as the full ILC machine. Furthermore, some studies of pressure wave formation maybe necessary.

The alternative beam dump design is the gas dump [Leuschner_20030916]. This consists of about 1km of a noble gas (Ar looks the most promising) enclosed in a water cooled iron jacket. The gas core acts as a scattering target, blowing the beam up and distributing the energy into the surrounding iron. This gas dump design may ease some issues such as radiolysis and tritium production, and a gas profile can be exploited to produce a uniform energy deposition along the length of the dump. However, other issues arise such as particle beam heating of the gas and ionization effects [Agapov_20050914]. Further studies needed to understand feasibility and benefits of the gas dump. A further possibility is a gas/water hybrid dump, involving the use of a shorter gas dump as a passive beam expander, followed by a small water dump. This option also required further study. A further possibility is for a rotating solid dump immersed in water, or a dump based on some kind of liquid metal.

The required R+D items for the alternative design are studies of gas heating, including ionization effects, and a study of radiation and activation effects. A study of the gas dump windows is also required. A smaller scale prototype of the dump, and some test beam, would also be required.
 

Beam Energy Measurements

Section updated September 19, 2005. Primary authors responsible for this section: E.Torrence, S.Boogert

Overview

Precision absolute beam energy measurements are required by the ILC physics program to set the absolute energy scale for measurements of particle masses. In both direct reconstruction and threshold scans, the center-of-mass collision energy needs to be measured to an absolute accuracy below 200 ppm to keep collision energy uncertainties from dominating experimental uncertainties of 50 MeV for both the Higgs and top quark masses. To reach this goal, a target uncertainty of 100 ppm on the absolute beam energy has been set.

In addition to the absolute beam energy measurement, relative measurements of the beam energy pulse-to-pulse along the train at the 100 ppm level are seen to be critically important to keep the variation in beam energy at an acceptable level and mitigate the impact of correlations between beam energy variations and other beam parameters such as luminosity or polarization. Relative measurements of the disrupted energy spectrum made downstream of the interaction point are also seen as useful to provide direct information about the collision process and provide data to validate models of beam-beam effects in the collision process.

To achieve the challenging goal of a 100 ppm absolute beam energy measurement, two independent and complimentary detectors are planned for each beam. Upstream from the IP, a spectrometer with a four-magnet chicane and precision RF-BPMs will be used. This device, an evolution of the LEP-II energy spectrometer [cite], is designed to be capable of making high-precision bunch-to-bunch relative measurements in addition to measuring the absolute beam energy scale. Downstream from the IP, a spectrometer using synchrotron radiation in the style of the SLC WISRD [cite] is planned. This device can also monitor the energy spectrum of the disrupted beams during collisions.

Upstream Measurements

This section may be edited further.

The upstream energy spectrometer is an evolution of the LEP-II spectrometer design. A four-magnet chicane in the instrumentation region (figure link) provides a point of dispersion which can be measured using triplets of high-precision RF BPMs. To avoid emmittance dilution, the maximum bend angle for this chicane is expected to be less than 100 micro-Radians. With a characteristic spectrometer length of about 10 meters, the maximum displacement of the beam will be a few millimeters. To achieve the required spectrometer performance, then, this displacement must be measured to an accuracy and precision below 100 nanometers.

Rather than require the BPMs to achieve this accuracy over a large dynamic range, the design includes precision actuators and movers to keep the beam nearly centered in the BPMs at all times. These actuators, then provide the bulk of the position information, which only small corrections being provided by the BPMs themselves. One key aspect of this design is the ability to calibrate the straight-line reference line on a time scale which is comparable to the mechanical and electrical stability of the system. This straight-line reference can be derived by ramping the chicane magnets and either making measurements with zero field, or reversing the field polarity an making position measurements at positive and negative deflection angles. The details of this calibration procedure and requirements on the magnet system still need to be specified in detail.

The nanoBPM project has demonstrated RF BPM precision and stability below 50 nm for several hours [cite], although with somewhat reduced aperture as would be foreseen in the upstream spectrometer. Using this experience, designs for the spectrometer BPMs are currently being developed. It is important to investigate the sensitivity of these devices to the details of beam tilt, beam size, bunch length, backgrounds, etc. Beam tests of these devices are foreseen to begin at SLAC ESA in the end of 2005.

Downstream Measurements

The downstream energy spectrometer is an evolution of the SLC WISRD design. A three-magnet chicane in the extraction line provides the necessary beam deflection, while the trajectory of the beam in the chicane is measured using synchrotron radiation produced in wiggler magnets imaged ~70 meters downstream at a secondary focus near the polarimeter chicane.

The layout of the instrumentation chicanes and detectors for both the energy spectrometer and polarimeter is indicated for 2 mRad and 20 mRad extraction lines. With a 3 mRad bend angle in the energy chicane and about 70 meters between the chicane and the synchrotron radiation detector plane, the effective single-beam dispersion at the detector plane is nearly 1 GeV/mm.

To achieve a 100 ppm accuracy, a position-sensitive detector for synchrotron radiation with a pitch of order 100 microns is necessary. While the WISRD used a fine wire array to achieve similar performance, the Oregon group (Torrence) is pursuing R&D into using the Cherenkov radiation produced by secondary electrons in quartz fibers. The advantages of this approach over wires are simplicity in readout, speed, radiation hardness, and potentially reduced cross-talk between channels. Any radiation hard position sensitive detector (like diamond strips) could potentially be used.

Future R&D Required

The immediate R&D required for the spectrometers is listed here:

• Specification of upstream spectrometer calibration and operational procedure.
• Design of spectrometer-specific RF BPM. Underway by several groups.
• Stability and performance tests for BPMs and associated readout electronics. Related activity underway at ATF as part of the nBPM program. BPM tests scheduled to start at SLAC ESA at the end of 2005.
• Detailed simulation of downstream spectrometer performance including realistic magnetic fields and backgrounds.
• Design and evaluation of large-wavelength, large-aperture wiggler magnets.
• Test of downstream spectrometer quartz fiber readout scheme, scheduled for SLAC ESA starting in Fall 2005.

For the longer term, a full-scale prototype of both a BPM-based and synchrotron radiation-based spectrometer are foreseen for SLAC ESA.

References need to be fixed.

Luminosity Measurements

Section updated September 30, 2005. Primary authors responsible for this section: W.Lohmann, M.Woods

The luminosity of a linear collider will be measured with a precision of 10^-3 or better by measuring the Bhabha rate in the polar region from 30-90 mrad in the LUMICAL detector [Stahl_LCDET200504].  At 500 GeV center-of-mass energy, the expected rate in this region is ~10 Bhabhas per bunch train.  At smaller polar angles of 5-30 mrad the rate or energy deposition of beamstrahlung e⁺e^- pairs can be measured in the BEAMCAL detector for a fast luminosity diagnostic.  The expected rate in BEAMCAL is 15,000 pairs (and 50 TeV energy deposition) per bunch crossing. 

BEAMCAL is expected to be useful for machine tuning and can be used for the fast IP feedback [Burrows_LCWS05] planned to stabilize the colliding beams.  In addition to its total energy or rate signals for a luminosity diagnostic, the spatial distributions of pairs in BEAMCAL may be useful for determining some of the beam collision parameters such as spotsizes and bunch lengths [White_Stahl_Yamamoto].

LumiCal and BeamCal are positioned inside the Detector just in front of the first quadrupole magnets.[Moenig_200408]  LUMICAL is planned to be a segmented silicon-tungsten calorimeter.  BEAMCAL must be very radiation hard and a finely segmented diamond-tungsten calorimeter is planned, though other technologies are also studied.  BEAMCAL should also provide good hermeticity and efficiency for detecting high energy electrons; these are needed to suppress brackgrounds from copious 2-photon events in new particle searches (ex. SUSY).  A possible layout of the very forward region of an ILC detector [Abramowicz_NSCI2004], in this case designed for head-on collisions or a small crossing angle, is shown in Figure 1.

R&D Required

• LUMICAL:  compare precision achievable for different crossing angle geometries and study effects of non-uniformities in the azymuthal distributions of the Bhabha signal and backgrounds from pairs
• LUMICAL:  adequate event rate for 10^-3 precision can be achieved by going to larger polar angles where there is less effect from a finite crossing angle, but the theoretical uncertainties in the Bhabha rates can be larger at high polar angles.  10^-4 relative precision is desired for the Giga-Z option; pair backgrounds for for Giga-Z will be significantly reduced but still need to understand azymuthal effects for the Bhabha signal rate systematics.  These issues need further study.
• BEAMCAL:  study possible systematics for its use determining beam parameters and how this is affected by a crossing angle
• BEAMCAL:  check that optimizing the pair signal also optimizes the e+e- luminosity for different aberration tuning scans
• BEAMCAL:  detector requirements and capabilities for electron identification given the high flux and energy deposition of beamsstrahlung pairs; also effect from crossing angle on hermeticity and electron id.
• BEAMCAL:   detailed detector design and prototype:  radiation-hard, hermetic, electron id
• Other Detectors:  radiative Bhabha [Napoly_CERN2000135] and wide-angle beamsstrahlung photon detectors [Bonvicini_PHREV1999]

Beam Polarization Measurements

Section updated September 30, 2005. Primary authors responsible for this section: K.C. Moffeit, K. Moenig, K.P. Schuler, M. Woods

Overview

            Precise polarimetry with 0.25% accuracy is needed.[Moortgat-Pick_hep-ph0507011]  Compton polarimeters are being designed to achieve this and have been included in the baseline beam delivery design.[Moffeit_SLACPUB11322,Meyners_LCWS05]  Preliminary designs for polarimeter diagnostic chicanes are included upstream and downstream of the IP for both the 2mrad and 20mrad IR designs. Detailed studies are underway to refine these designs and evaluate their performance capabilities.  To achieve the best accuracy for polarimetry and to aid in the alignment of the spin vector, it is desirable to implement polarimeters both upstream and downstream of the IR.  The beam optics need to be designed such that the polarization vector can be fully longitudinal simultaneously at the collider IP and the two polarimeter IPs.

            The upstream polarimeter measures the undisturbed beam during collisions. The relatively clean environment allows a laser system that measures every single bunch in the train and a large lever arm in analyzing power for a multi-channel polarimeter, which facilitates internal systematic checks.

            The downstream polarimeter measures a priory the polarization of the outgoing beam after collision. The average depolarization for colliding beams is 0.3%, and for the outgoing beam 1%.  Due to a clever choice of the extraction line optics the beam can, however, be focused such that its polarization is very similar to the luminosity-weighted polarization. The polarization of the undisturbed beam can be measured as well with non-colliding beams. The much higher background requires a high power laser that can only probe one or a few bunches per train and the lever arm in analyzing power is smaller.

Upstream Measurements

            The upstream polarimeters are located ~1400 meters before the e+e- IP. The design has evolved from an earlier study for the TESLA machine.[Gharibyan_LCDET200147]  Most major aspects of this work, except for the spectrometer configuration, remain valid for the ILC. In particular it is foreseen to use a similar laser as will be used for the electron source.  A prototype for such a laser was developed by Max-Born Institute,[Schreiber_NIM2000] for the TTF injector, and is well adapted to the ILC pulse structure.

             Dedicated 4-magnet chicane spectrometers will be employed, similar to those at the extraction line polarimeters. This will eliminate some of the operational shortcomings inherent in the original TESLA design that relied on beamline magnets in the existing BDS lattice. A schematic layout of the chicane spectrometer is shown in Figure 1.The horizontal width of the good field region of the individual dipoles is chosen to accommodate a maximum dispersion of 11 cm for the lowest expected beam energy of 45.6 GeV for the Giga-Z option. The laser beam enters and exits between the inner two dipoles, which must be separated by some 8 meters for a vertical beam crossing of 10 mrad. A possible optical arrangement was given at LCWS-05.[Meyners_LCWS05]

            Compton electrons generated at the laser IP at mid-chicane will propagate essentially along the electron beam direction . The third dipole D3 will fan out the Compton electron spectrum, while the fourth dipole can be used to restore the angular direction, if it has sufficient width. The Compton electrons are detected behind the last dipole in a gas Cerenkov hodoscope with 20 identical channels.[Meyners_LCWS05]

Downstream Measurements

The layout for the 20 mrad crossing angle interaction region shown in Figure 2 has the Compton interaction point approximately 142 meters downstream from the e+e- Interaction Point. All bends are in the vertical plane. The extraction line apertures are designed to accommodate the ±0.75mrad cone of beamsstrahlung photons produced in the e+e- interaction and the low energy disrupted electrons. The 2 mrad crossing angle extraction line first moves the extracted beam away from the incoming beam line and then bends the beam back to the direction it had at the e+e- interaction point . This is done in the horizontal plane as shown in Figure 3. The Compton polarimeter is located 226 meters downstream from the 2 mrad crossing angle e+e- interaction point and the polarimeter chicane bends in the vertical plane.

The Compton interaction point is located at a secondary focus in the middle of a chicane with 20 mm dispersion, but with no net bend angle with respect to the primary IP.[Moffeit_SLACPUB10669] At the middle of the chicane the Compton scattering occurs and the scattered electron is confined to a cone having a half-angle of 2µrad and is effectively collinear with the initial electron direction. The beam-beam depolarization effects are measured in the extraction line polarimeter directly by comparing beams in and out of collision. Also, spin precession effects due to the final focus optics and beam-beam deflections can be studied by correlating the polarization and Interaction Point beam position monitor measurements.

             A 532-nm (2.33eV) circularly polarized laser beam collides with the electron beam in the middle of the Polarimeter Chicane .  Compton-scattered electrons near the kinematic edge at 25.1 GeV are detected in segmented detectors near the last chicane magnet.

R&D Required for Baseline Design

• Comparison of extraction line polarimeters for 2mrad and 20mrad IRs
       - backgrounds (synchrotron radiation, disrupted electron beam, beamsstrahlung, radiative Bhabhas)
       - sensitivity to misalignments of spin orientation, collision offsets
       - compatibility with energy spectrometer
       - requirements and feasibility for chicane magnets
• spin alignment procedures and uncertainties; sensitivity to crossing angle and DID
• develop detailed Compton laser, IP and detector designs

R&D Required for Alternative Configuration

• evaluate use of a Fabry-Perot cavity for the laser at the Compton IP at the upstream polarimeter [Variola_LCWS05]; this technology may have better applications for the laser systems for a Compton-based polarized positron source or a gamma-gamma collider

Multi-TeV issues

The ILC BDS is being designed to be optimal up to 500GeV CM (1TeV CM in upgrade).
    Realizing that the question of multi-TeV upgrade goes much beyond the scope of the working group, the group suggests that serious consideration need to be given by the whole community to studying the advantages and disadvantages of not precluding the multi-TeV compatibility.

Technical implications and cost impact due to multi-TeV constraints will have to be studied. Such constraints were discussed in the recently (November 10, 2005) published report [CERN_Open_2005_024] and includes:
    -- crossing angle about 20mrad required
    -- horizontal bend between high energy end on the linac and beam delivery should be less than 2mrad, zero for vertical
    -- strongly prefer laser straight linac tunnels
    -- provision to add tunnel alcoves every 600m to house a drive beam return loop and 2MW drive beam dump
    -- strongly prefer ground motion to be no worse than model A or B
    -- surface space 1200x250m in IP region to house the drive beam generation complex
    -- provision to connect to power grid with capacity 450MW
    -- main beam dumps for 20MW, very similar to ILC

Several of these constraints are related to BDS. In particular, the linacs need to be pointing to the larger crossing angle IR. In the present baseline with two IRs with 20/2mrad, satisfying this constraint does not affect the performance and does not necessarily affects the cost. This layout choice, however, may affect site selection, for example because the orientation of linacs at angle widens the site, and this could make it more difficult to place the collider under a straight power-line (may be partly mitigated by horizontal back kinks at the middle of the linac). The linacs-at-an-angle layout may complicate, but would not make impossible moving the IP many km downstream, if such possibility would ever be needed.  The laser straight tunnel may have cost impact in comparison with tunnel which follows earth curvature closer to  surface. These and other configuration issues, technical and cost implications need to be studied seriously and the impact will be clearly strongly site dependent.

Number of sections were not yet described. These sections and authors name are listed in [WG4_20050825_BCD]:

IR & IR magnets for 20 mrad and alternative 10-12mrad (partly written)
IR & IR magnets for 2 mrad and alternative 0mrad
Beam switchyard (partly written)
Diagnostics section (partly written)
Detector integration (DID, magnets, assembly, support, push-pull issues)
Detector performance (Backgrounds)
Final focus optics (performance, chromaticity compensation, antisolenoids, DID)
Magnets nomenclature, stability, etc.
Standard components (BPMs, current monitors, loss monitors, vacuum, )
Tolerances & tuning
Gamma-gamma & e-e-
Summary of technical risk, R&D needed for baseline & alternatives (partly written)
 

References

1. [Pre_Snowmass_BCD] Pre-Snowmass draft BDS BCD. http://www-project.slac.stanford.edu/ilc/acceldev/beamdelivery/bds_bcd.htm
2. [WG4_Snowmass_Agenda] WG4 Agenda at Snowmass 2005. http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/agenda
3. [WG4_Snowmass_Summary] WG4 Summary of first week at Snowmass, August 19, 2005. http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug19_wg4_1st_week_summary.ppt
4. [Snowmass_decision_list] Snowmass decision spreadsheet, assembled by T.Himel, http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/GG3/tom_himel20050824165242.xls
5. [WG4_20050823] WG4 plenary discussion of responses to GDE questions, August 23, 2005. http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug23_wg4_gde_questions.ppt
6. [WG4_20050825] WG4 responses to GDE questions, August 25, 2005. http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug25_wg4_gde_questions.ppt
7. [WG4_20050825_BCD] TOC of BDS BCD/ACD and list of authors, as discussed at Snowmass. http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/BDS_BCD_ACD.doc
   see also the modified list
   http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/modified_BDS_BCD_ACD_sept8.doc
8. [Raubenheimer_20050228] T.Raubenheimer, ILC Suggested Beam Parameters Range,  http://www-project.slac.stanford.edu/ilc/acceldev/beampar/Suggested%20ILC%20Beam%20Parameter%20Space.pdf, Feb.28, 2005.
9. [Seryi_20050817] Alternative 1TeV High Luminosity parameters, A.Seryi, Snowmass 2005, http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/GG1/aug17_seryi_high_lumi_pars.ppt
10. [Kozanecki_20050824]  Normalized backgrounds in ILC tracking detectors, W.Kozanecki, Snowmass 2005, http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug24_WK_BgdTol_Snow05.ppt
11. [ILCSC_scope] ILCSC scope document, September 2003, http://www.fnal.gov/directorate/icfa/LC_parameters.pdf
12. [BDS_optics] Optics files for BDS baseline:
    Incoming beamlines: http://www.slac.stanford.edu/~mdw/ILC/
    Extraction beamlines: http://www.slac.stanford.edu/~yuri/ILC/Decks/
13. [BDS_IR_models] Geant models of IR regions for BDS baseline: link?
14. [Parker_20050816] Compact SC quads, B.Parker, Snowmass 2005,  http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug16_wg4_parker_CompactQD0.pdf
15. [ILC_TRC2] Report of 2nd ILC Technical Review Committee, SLAC-R-606, Feb 2003.
16. [Iwashita_20050818] Update on rf kicker 0-degree scheme, Y.Iwashita, Snowmass 2005,   http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug18_RFKickerUpdate1.pdf
17. [Keller_20050818] Zero-degree extraction with an electrostatic separator, L.Keller, Snowmass 2005, http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug18_ElectrostaticSeparator.ppt
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24. [Keller_20041015] L.Keller, ILC-Americas workshop, October 15, 2004,  http://www-project.slac.stanford.edu/ilc/meetings/workshops/US-ILCWorkshop/talks/ILC_MPS.ppt
25. [Jackson_20050816] http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug16_collimation_summary_jackson_snow05.ppt
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28. [Woods_20050302] M.Woods, Update on ESA beam tests, March 2, 2005,  http://www.slac.stanford.edu/xorg/lcd/ipbi/monthlymeetings/02mar2005/woods/ESA_beamtests.pdf
29. [LCC118] LCC-118 http://www-project.slac.stanford.edu/lc/ilc/TechNotes/LCCNotes/lcc_notes_index.htm
30. [TRC2_p340] ILC TRC, Second report, Section 7.3.2.6, p340, http://lcdev.kek.jp/TRCII/PAPERS/TRC03C7.PDF
31. [Collwake_beamtest_request] Collimation wakefield beam test request, April 25, 2005,
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32. [Angal-Kalinin_20050816] D.Angal-Kalinin, Status of Optics, Snowmass 2005, http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug16_snowmass_optics_summary.ppt
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35. [Jackson_private_comm] F.Jackson, private communication
36. [Moffeit_20050422] K. Moffeit, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-04-22/index.htm
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49. [McAshan_TM2144] M. McAshan, R. Wanzenberg, RF Design of a Transverse Mode Cavity for Kaon Separation, FERMILAB-TM-2144, May 2001
50. [Solyak_LINAC04] N. Solyak et al., Test Results of the 3.9GHz Cavity at Fermilab, Proc. LINAC04, THP85
51. [Adolphsen_20050301] C. Adolphsen, Options for ILC Crab Cavity, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-03-01/index.htm
52. [Naito_PAC2001] T. Naito et al., RF Reference Distribution Using Fibre Optic Links at KEKB Accelerator, Proc. PAC2001, Chicago
53. [Appleby_20050914] Overview of ILC dump issues, Rob Appleby, LC-ABD dump meetings, 14th September 2005, http://www.astec.ac.uk/lc-abd/ral.14.09.05/ral.14.09.05.htm
54. [Walz_IEEE1965] Walz et al, in IEEE Trans.Nucl.Sci.12:367-371, 1965 (issue No.3)
55. [Bialowons_TESLA200104] Bialowons et al, TESLA note 2001-04
56. [Leuschner_20030916] Another idea of a LC dump, Albrecht Leuschner, 16th September 2003, http://tesla.desy.de/new_pages/hamburg_meeting_9_2003/pdf/wg2/gasdump_talk_16sep03.pdf
57. [Agapov_20050914] Some thoughts about gas dumps, Ilya Agapov, LC-ABD dump meeting, 14th September 2005, http://www.astec.ac.uk/lc-abd/ral.14.09.05/Gas-Dump-14-09-05.pdf
58. [Stahl_LCDET200504]  Luminosity Measurement via Bhabha Scattering Precision Requirements for the Luminosity Calorimeter, A. Stahl, LC-DET-2005-004, 2005
59. [Burrows_LCWS05]  Interaction Point Feedback System R&D, Philip Burrows, presentation at LCWS05.
60. [White_Stahl_Yamamoto]  Reconstruction of IP Beam Parameters at the ILC from Beamstrahlung, G. White, SLAC-PUB-11341, 2005;       Diagnostics of Colliding Bunches from Pair Production and Beam Strahlung at the IP, A. Stahl, LC-DET-2005-003, 2005.  Beam Profile Monitor, H. Yamamoto, presentation at SLAC MDI Workshop, 2005. 
61. [Moenig_200408]  K. Moenig, talk at the Workshop "Instrumentation of the Forward Region of a Linear Collider Detector", August 2004, DESY-Zeuthen, Germany.
62. [Abramowicz_NSCI2004]  H. Abramowicz et al., IEEE Trans. Nucl. Sci. 51, 2983 (2004).
63. [Napoly_CERN2000135]  Luminosity Monitor Options for TESLA, O. Napoly and D. Schulte, CERN-OPEN-2000-135, 2000. 
64. [Bonvicini_PHREV1999]  Measurement of Colliding Beam Parameters with Wide Angle Beamstrahlung, G. Bonvicini, D. Cinabro, and E. Luckwald, Phys.Rev.E59:4584-4593,1999. e-Print Archive: physics/9812020.   Diagnostics with Beamstrahlung Electrons and Photons, C. Grah, presentation at SLAC MDI Workshop, 2005.
65. [Moortgat-Pick_hep-ph0507011]  The role of polarized positrons and electrons in revealing fundamental interactions at the Linear Collider,      G. Moortgat-Pick et al.  e-Print Archive: hep-ph/0507011 (submitted to Physics Reports).
66. [Moffeit_SLACPUB11322]  Polarization Setup and Polarimetry for 2 IRs, and Status of Downstream Polarimeter Designs,  K.C Moffeit, M. Woods, Y. Nosochkov , K.P. Schuler, K. Moenig, and W. Oliver,. SLAC-PUB-11322, 2005.
67. [Meyners_LCWS05]  Upstream Polarimetry with 4-magnet Chicane, N. Meyners, V. Gharibyan, K.P. Schuler, presentation at LCWS05.
68. [Gharibyan_LCDET200147]  The TESLA Compton Polarimeter, V. Gharibyan, N. Meyners, K.P. Schüler, LC-DET-2001-047, http://www.desy.de/~lcnotes
69. [Schreiber_NIM2000]  Running Experience with the Laser System for the rf Gun Based Injector at the TESLA Test Facility Linac, S. Schreiber et al., Nucl. Instr. Meth. A 445 (2000) 427.
70. [Moffeit_SLACPUB10669]  Studies for a Downstream Compton Polarimeter at the ILC, K.C. Moffeit and M. Woods, SLAC-PUB-10669, 2004.
71. [Variola_LCWS05]  A Fabry-Perot Cavity for FLC Polarimetry, A. Variola, presentation at LCWS05.
72. [Nosochkov_20050817_20mrad] Y. Nosochkov, http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug17_nosochkov_extraction20mrad.pdf
73. [Nosochkov_20050510] Y. Nosochkov, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-05-10/index.htm
74. [Ferrari_20050831] A. Ferrari, http://www-project.slac.stanford.edu/ilc/acceldev/beamdelivery/bcd_docs/Ferrari-050831-update.pdf
75. [Nanobeam_Seryi_20051017] A.Seryi, Issues of stability and ground motion in ILC, Nanobeam workshop, October 17, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-P-03.ppt and http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-10-25/index.htm
76. [Nanobeam_Markiewicz_20051019] T.Markiewicz, T.Maruyama, Y.Nosochkov, Status of 14mrad extraction line, Nanobeam workshop, October 19, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG2a-03.ppt
77. [Nanobeam_Seryi_IR_20051019] B.Parker, A.Seryi, IR optics optimization, DID and anti-DID, Nanobeam workshop, October 19, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG2a-04.ppt
78. [Nanobeam_Seryi_Civil_20051019] A.Seryi, BDS civil layouts and upgrade path from single IR to two IRs, Nanobeam workshop, October 19, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG2a-05.ppt
79. [Nanobeam_Markiewicz_IR_20051019] T.Markiewicz, IR Design Issues Requiring More Discussion, Nanobeam workshop, October 19, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG2a-08.ppt
80. [Nanobeam_Parker_20051018] B.Parker, Recent Progress Designing Compact Superconducting Final Focus Magnets for the ILC, Nanobeam workshop, October 18, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG2d-01.pdf
81. [Nanobeam_Jain_20051018] A.Jain, et al., Vibration Measurements in a RHIC Quadrupole at Cryogenic Temperatures, Nanobeam workshop, October 18, 2005, http://atfweb.kek.jp/nanobeam/files/presen/presen-WG2d-05.ppt (This is PDF file, not PPT. Save it, rename to pdf and open in Acrobat).
82. [Nanobeam_Parker_RnD_20051018] B.Parker, A.Jain, R&D Activities Regarding ILC Compact Superconducting Final Focus Magnets, Nanobeam workshop, October 18, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG2d-07.pdf
83. [Nanobeam_Angal_Kalinin_20051019] D.Angal-Kalinin, Update on 2mrad design, Nanobeam workshop, October 19, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG2a-11.ppt
84. [Nanobeam_Mattison_20051020] T.Mattison, ILC fast abort systems, Nanobeam workshop, October 20, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG2a-12.pdf
85. [Nanobeam_Seryi_20051021] A.Seryi, Summary of working group on BDS and IR, Nanobeam workshop, October 21, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-S-02.ppt
86. [Nanobeam_Burrows_20051021] P.Burrows, Summary of working group on stabilization and feedback, Nanobeam workshop, October 21, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-S-03.ppt
87. [Nanobeam_Parker_20051021] B.Parker, Summary of working group on magnets, Nanobeam workshop, October 21, 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-S-05.pdf 
88. [Blair_Snowmass_20050817] G.Blair, ILC Laser wires, Snowmass 2005, http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/GG2/grahame_blair20050818043011.ppt
89. [Woodley_20050927] M.Woodley, BSY emittance, diagnostic section, BDS meeting September 27, 2005, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-09-27/index.htm
90. [Nanobeam_Blair_20051018] G.Blair, Simulation of ILC Laser Wire, Nanobeam, October 18 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG1-02.ppt
91. [Nanobeam_AngalKalinin_20051018] D.Angal-Kalinin, Laser-wire location in ILC Diagnostics section, Nanobeam, October 18 2005, http://atfweb.kek.jp/nanobeam/files/presen//presen-WG1-01.ppt
92. [Seryi_20050310] A.Seryi, Test of using IR dispersion to recover luminosity loss in 2mrad, March 10, 2005, bcd_docs/ip_disp_2mrad_20050310_seryi.pdf
93. [BDS_mtg_20051101] Discussion of e+ source location at BDS meeting on November 1, 2005, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-11-01/index.htm
94. [Jackson_20051102] F. Jackson, Collimation studies,  Meeting at Daresbury devoted to Collimation for ILC, November 2-3, 2005,  http://www.astec.ac.uk/ap/collider/collimmeet02Nov05/fjackson_collim_mtg_02Nov05_BCD.ppt
95. [Seryi_20051102] A. Seryi, Collimation optics issues,  Meeting at Daresbury devoted to Collimation for ILC, November 2-3, 2005, http://www.astec.ac.uk/ap/collider/collimmeet02Nov05/seryi_ilc_collimation_2Nov05.ppt
96. [BDS_mtg_seryi_20041207] A.Seryi, Crab cavity location for 2-mrad x-ing, BDS meeting, December 7, 2004, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2004-12-07-Nosochkov,Pivi,Markiewicz,Seryi/index.htm
97. [BDS_mtg_smith_20050329] S.Smith, Independent Measurement of Two Beams in an IP Feedback BPM in 2mrad, BDS meeting, March 29, 2005, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-03-29/index.htm
98. [BDS_mtg_smith_20051101] S.Smith, Kicker for fast feedback, BDS meeting, November 1, 2005, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-11-01/index.htm
99. [Hartin_20050818] T.Hartin, IP FB BPM background environment and BDS design, Snowmass 2005, August 18, http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug18_hartin_fbk_bpm.ppt
100. [BDS_mtg_seryi_20051004] A.Seryi, Comments on feedback kicker location, BDS meeting, October 4, 2005, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-10-04/index.htm
101. [CERN_Open_2005_024]  H.H. Braun, J.-P. Delahaye, D. Schulte, ILC Compatibility with Possible Multi-TeV Upgrade, CLIC Note 644, November 2005, http://doc.cern.ch/archive/electronic/cern/preprints/open/open-2005-024.pdf
102. [WG4_mtg_20051110] Phone meeting of WG4 representatives, November 10, 2005, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-11-10/index.htm
103. [BDS_mtg_keller_20050726] L.Keller, T.Maruyama, Energy deposition in SC QD0 for 2mrad, BDS meeting, July 26, 2005, http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-07-26/index.htm
104. [CERN_SL_94_41]  V. Juravlev, et al., Seismic vibration studies for future linear colliders, CERN-SL-94-41, 1994, http://www.slac.stanford.edu/~seryi/gm/gm_papers/as_lep.html
105. [PRSTAB_e031001] B. Baklakov, et al., Ground vibration measurements for Fermilab future collider projects, 1998, http://prst-ab.aps.org/abstract/PRSTAB/v1/i3/e031001
106. [Amirikas_Nanobeam05] R. Amirikas, A. Bertolini, W. Bialowons, H. Ehrlichmann, Ground Vibration Measurements and Site Comparison, Nanobeam 2005, http://atfweb.kek.jp/nanobeam/files/proc//proc-WG2b-01.pdf and also see http://vibration.desy.de/
107. [SLAC_PUB_11591] Y.Nosochkovy , T.Markiewicz, T.Maruyama, A.Seryi, B.Parker, ILC Extraction Line for 14 mrad Crossing Angle, Nanobeam 2005, SLAC-PUB-11591, bcd_docs/nanobeam_14mrad.pdf
108. [Tauchi_20050816] T.Tauchi, Summary of Detector concept responses to MDI questions, Snowmass 2005,  http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/aug17_tauchi_machine.parameter.pdf 
109. [BDS_mtg_20051129] Discussion of pro/cons of separate tune-up dumps. BDS meeting Nov.29, 2005. http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-11-29/index.htm
110. [BNL_direct_wind] BNL direct wind technology. See http://www.bnl.gov/magnets/Linear_Collider/Magnet_Construction.asp for examples of ILC magnets prototypes and http://www.bnl.gov/magnets/BEPCII/Overview.asp where BEPC-II magnets built with direct wind technique are described.  
111. [Smith_Wands_2005] Richard P. Smith and Robert H. Wands, A Five Tesla Solenoid with Detector Integrated Dipole for the Silicon Detector at the International Linear Collider, 2005, http://ilc.fnal.gov/detector/rd/solenoid/MT_19_Paper.pdf

refs not used yet:
[X] WG4 Post-Snowmass Summary, draft. http://www-project.slac.stanford.edu/ilc/acceldev/beamdelivery/snowmass_wg4_summary.htm