Dear Peter, Thank you for discussion of the polarimeter range of energies with colleagues. These opinions are certainly important. A short document may also be useful and could be discussed with GDE and Research Director. However it is essential to understand, at this stage, what exactly we are paying for keeping compatibility with any particular option. This is the charge from the Project Managers. In that regard, we need to look at the design and cost in details. With respect to the original polarimeter with fixed field -- was there any dependence of the apertures and magnet sizes (pole width) on the energy range? If so, that probably did affect the cost? Fixed field operation vs scaled field need to be compared from various points of view. Approach to giga-Z also need to be coherent. Are there going to be a need to upgrade other systems to allow giga-Z? If so, depending on the level of efforts, one can also plan to upgrade the polarimeter chicane. This is a question between initial investment to get project going and later improvements. I hope that tomorrow we will fix the date for the fist meeting on the polarimetery requirements, where you would present the talk. The most likely date is 29th. Thank you Andrei -----Original Message----- From: Peter Schuler [mailto:schuler@mail.desy.de] Sent: Monday, November 19, 2007 2:55 PM To: Seryi, Andrei Cc: Woods, Michael B.; Moffeit, Kenneth C.; Woodley, Mark; Jenny List; Grahame Blair; Walker, Nicholas John; Angal-Kalinin, D(Deepa); Ties Behnke; Klaus Moenig; Gudrid Moortgat; Peter.Schuler@desy.de Subject: polarimeter energy range >> We have to question the basic assumption that you mentioned below, in >> particular >> >> "all the way from Giga-Z energies up to 500 GeV, which is our charge." >> >> The ILC parameter's document does not include Giga-Z. >> The range of the energy for physics is 200 to 500 GeV CM, and 90GeV >> CM is mentioned as needed for calibration. Dear Andrei, yes, I know, Giga-Z is not part of the ILC baseline program, but it is an important option for the future which could extend the rich harvest from LEP and SLD in a very cost effective way. It would therefore seem smart to design machine and detector hardware from the outset with foreseeable extensions and options in mind, provided this can be achieved without undue additional cost. This is my personal opinion, but other people share this view. I have quizzed a few of my colleagues on this particular subject and found general support for my quest. See some of the appended mail reactions. The upstream Compton polarimeter as we had planned and designed it with a fixed-field spectrometer chicane was perfectly capable to cover the full ILC energy potential, including the Giga-Z option, and that at zero additional cost! It is the combination with several other machine elements, which originally had separate locations in the BDS beamline, and in particular your plan to operate the chicane with scaled-field, that would force us to abandon polarimetry at Giga-Z. I would not raise such clamor, if I had the impression that it would take but a few minor adjustments of this combined function animal to permit polarimetry for optional extensions of the ILC program at a later stage. If such adjustments of the beamline can be realized at all and at reasonable cost, it would seem better to plan this from the very beginning. Anyway, that's my honest opinion. If you want to reduce the debate to the question: "Can we do decent polarimetry with a >>scaled-field<< chicane in the restricted baseline energy range between 200 and 500 GeV CM" then the answer is affirmative. But there is hopefully more to the ILC than its baseline program. Regards, Peter ********************************************************************* * * * K. Peter Schuler Tel.: +49-40-8998-2015 * * DESY-HERMES Fax +49-40-8998-4034 * * Notke Strasse 85 * * D-22603 Hamburg e-mail Peter.Schuler@desy.de * * Germany * * * ********************************************************************* Date: Mon, 19 Nov 2007 14:35:31 +0100 (CET) From: Klaus Moenig To: Ties Behnke Cc: Peter Schuler , "Walker, Nicholas John" , Gudrid Moortgat , Jenny List , Peter.Schuler@desy.de Subject: Re: Giga-Z policy Dear Peter et al., I agree completly with your and Ties' point of view. GigaZ is an option that may become important at a later state and the agreement was that options should be kept open as long as the possible physcs case exists. A few more specific words to GigaZ: It is true that the eaverage polarisation can be obtained with the Blondel scheme. However several relative effects still need to be obtained from polarimeters. The most important is the difference beween the absolute value of the left and right handed polarisation state. However also all correlations, like long term time correlations or variations inside a train need to be measured with polarimeters. Depending on the physics scenario GigaZ may be a very cost effective possiblity to get essential information, we should not close this option now! I also support Ties' idea to write a short document to bring these arguments to the attention of the GDE. Best wishes, Klaus ================================================ Klaus Moenig e-mail: Klaus.Moenig@desy.de DESY, Zeuthen or: Klaus.Moenig@CERN.ch Tel.: +49 33762 77271 Fax: +49 33762 77330 Mob.: +49 160 8550906 ================================================ On Fri, 16 Nov 2007, Ties Behnke wrote: > Dear Peter, > > I fully agree with your point of view, that we should maintain the > capabilities of the accelerator to operate at the Z for a GigaZ > physics program. Polarisation is indeed a major part of the GigaZ program. > It might even have some importance for the lower intensity calibration > runs at the Z, though this still needs to be worked out in more > detail. > > I would find it a major mistake if at this stage we make it impossible > or at least very difficult and expensive to make this option a reality > at some later stage. > > I would suggest that - maybe with the help of Klaus and others - we > try to make a point about the importance of this option, and possible > implications, and try to work out the role the polarimeters play in > this. This little document could then be the basis for any further > discussions with the working group and - eventually - the GDE. > > Cheers, Ties > > Ties Behnke > DESY FLC > Tel +49 40 8998 4918 > e-mail Ties.Behnke@desy.de > > > On Fri, 16 Nov 2007, Peter Schuler wrote: > >> >> Ties, >> >> I need some policy advice about the Giga-Z option at the ILC. >> >> The interpretation of such policy may impact in a major way the >> capabilities and in particular the energy range of our Upstream >> Compton Polarimeter. >> >> As you may glance from the appended communication from Andrei Seryi >> below, we may be forced to abandon our polarimetry capability below >> beam energies of 100 GeV. This loss in energy coverage does not >> originate from intrinsic features of the polarimeter itself, but is >> caused by combination with several other machine elements which >> originally had separate locations in the BDS beamline. >> >> I know of course that Giga-Z is not part of the ILC baseline program, >> but an option for future possible extension of the physics program. >> I believe, however, that is is an important option that should not be >> precluded or seriously hampered solely on the basis of initial cost >> and economy considerations. >> >> My understanding is that pecision polarimetry plays a vital role >> particularly for the Giga-Z option. With that in mind it does not >> seem wise to curtail the energy coverage of the upstream polarimeter >> in an irreversible way. >> >> I would appreciate your advice and guidance in this matter. >> >> Regards, Peter >> >> ********************************************************************* >> * * >> * K. Peter Schuler Tel.: +49-40-8998-2015 * >> * DESY-HERMES Fax +49-40-8998-4034 * >> * Notke Strasse 85 * >> * D-22603 Hamburg e-mail Peter.Schuler@desy.de * >> * Germany * >> * * >> ********************************************************************* >> >> ---------- Forwarded message ---------- >> Date: Thu, 15 Nov 2007 22:02:20 -0800 >> From: "Seryi, Andrei" >> To: "Woodley, Mark" , >> Peter Schuler >> Cc: "Moffeit, Kenneth C." , >> Grahame Blair , >> "Angal-Kalinin, D (Deepa)" , lc-pol@desy.de, >> Jenny List , "Seryi, Andrei" >> >> Subject: RE: MPS collimator in polarimeter chicane >> >> >> Dear Peter, >> >> We have to question the basic assumption that you mentioned below, in >> particular "all the way from Giga-Z energies up to 500 GeV, which is our charge." >> >> The ILC parameter's document does not include Giga-Z. >> The range of the energy for physics is 200 to 500 GeV CM, and 90GeV >> CM is mentioned as needed for calibration. >> >> Could you please show, at the phone meeting that is being planned, >> more detailed description of what is happening with space >> distribution of Compton spectrum versus the energy range and what >> happens if the field is scaled, in the 200-500GeV CM range of energies. >> >> Please also plan to show what is suggested plan of operation, what >> bunches are measured, how it affects the laser design, cost, etc. >> >> We really need to understand, justify and document all requirements >> that are driving the design. >> >> Best regards >> Andrei >> >> >> >> >> >> -----Original Message----- >> From: Woodley, Mark >> Sent: Thursday, November 15, 2007 12:07 AM >> To: 'Peter Schuler' >> Cc: Seryi, Andrei; Moffeit, Kenneth C.; 'Grahame Blair' >> Subject: RE: MPS collimator in polarimeter chicane >> >> Hi Peter, >> >> The first ILC BDS design which included upstream polarimetry had two interaction regions. Since a requirement of an upstream polarimeter chicane is that it be oriented parallel to it's respective IP beam trajectory, we had to include two polarimeter chicanes, one in each beamline downstream of the "split". Since we wanted only one fast extraction / tuneup dump line at the end of the linac, we logically put that line upstream of the "split" where, by necessity, we included a dedicated diagnostic chicane (energy scaled, of course). All well and good. >> >> In the cost-cutting excercise after the BCD cost estimate came out, the second interaction region was eliminated. We found ourselves with a BDS design that had two chicanes in a row (diagnostic followed by polarimeter), and cost managers complaining that the Beam Delivery system was too long. The "imposition of unification" was all but inevitable at that point. I did my best with the design, but admittedly it was a rush job and obviously my ignorance of the needs of your group (and Grahame's) led to a design that's unacceptable from anyone's point of view. >> >> So much for history. This area obviously requires one or more reiterations of the design, and it's on my list of "things to do" for BDS. We will make a design that works for everyone, and this will obviously require us to work closely together so that the implications of design choices/compromises are understood and agreed upon by one and all before they're cast in concrete. >> >> I'll let you know when the redesign effort begins ... until then, any clever ideas would be welcome! >> >> -Mark >> >>> -----Original Message----- >>> From: Peter Schuler [mailto:schuler@mail.desy.de] >>> Sent: Wednesday, November 14, 2007 2:13 PM >>> To: Woodley, Mark >>> Cc: Seryi, Andrei; Peter.Schuler@desy.de >>> Subject: MPS collimator in polarimeter chicane >>> >>> >>> Hi Mark, >>> >>> we are still struggling with the chicane "unification" issues that >>> were imposed on us a year ago. See page 14 of your presentation from >>> a year ago >>> >>> www.slac.stanford.edu/~mdw/ILC/2006e/doc/BDS2006e.ppt >>> >>> which prophetically highlights already the major problems with this >>> combined scheme. One of these issues has to do with the laser wire >>> photon detector, which does not have sufficient beam clearence, at >>> least at the highest foreseen beam energy of 500 GeV. The other >>> issue has to do with the MPS energy collimator. >>> >>> Here I would just to discuss just some of the engineering issues >>> connected with the 3 meter long energy collimator. >>> >>> Before this unification was decided a year ago, this collimator was >>> presumably sitting happily in its own dedicated chicane, which >>> almost certainly would have been a chicane with energy-scaled field >>> so that the transverse position and the opening of the collimator >>> aperture would remain fixed and constant for all beam energies. >>> >>> Even under the relaxed conditions of a dedicated scaled-field >>> chicane, it would not seem entirely trivial to feed the beam through >>> a narrow channel of 3 meter length and 2 mm width, which is what it >>> boils down to for +-10% of energy collimation with a constant >>> dispersion of 10 mm. >>> But maybe I am misunderstanding here something about the >>> significance of the length of 3 meters. This seems totally excessice >>> in terms of electromagnetic shower containment. Maybe you can tell >>> me what drives this length requirement. Also I suppose some tapering >>> of the collimator gap would be necessary to discourage wake field effects. >>> >>> But now back to our unhappy joint function chicane. Unfortunately, >>> this cannot be a field-scaled chicane, as querried in one of your >>> recent weekly discussion sessions. At least not as long as it is >>> supposed to be suitable for polarimetry at all envisioned beam >>> energies all the way from Giga-Z energies up to 500 GeV, which is >>> our charge. >>> >>> The great advantage of a chicane spectrometer for Compton >>> polarimetry is solidly rooted on >>fixed-field<< operation, which >>> accommodates nearly universal mapping of the Compton spectrum into a >>> detector hodoscope for all beam energies. In particular, the region >>> of the so-called Compton edge near the minimum scattered electron >>> energy is vital for excellent Compton polarimetry, since the >>> analyzing power reaches its maximum there. With our fixed field >>> chicane, most of the Compton spectrum is well separated from the >>> beam line. With a scaled-field chicane, the separation diminishes >>> for lower beam energies and operation at Giga-Z energy would render >>> the polarimeter useless, as virtually the entire Compton spectrum >>> vanishes in the beam pipe. >>> >>> So, the conclusion is, we cannot operate the polarimeter with a >>> scaled- field chicane. We must operate with fixed field, the value >>> of which is the maximum tolerable at 500 Gev from emittance blowup >>> considerations. >>> >>> So then, what consequences does this fixed field operation have for >>> the energy collimator? Very unpleasant consequences: >>> >>> (1) The lateral position of the collimator aperture changes >>> (together with the chicane dispersion) with beam energy. The offset >>> from the neutral beam location varies accordingly: >>> >>> beam energy (GeV) 500 250 100 45.6 >>> hor. offset (mm) 10 20 50 110 >>> >>> (2) Furthermore, not only the position of the collimator aperture, >>> but also the width of the aperture is energy dependent. For an >>> energy collimation of +-10%, we will need the following apertures: >>> >>> beam energy (GeV) 500 250 100 45.6 >>> delta x aperture (mm) +-1 +-2 +- 5 +-11 >>> >>> In other words, we will need a collimator with adjustable jaws that >>> >>> (a) works under beamline vacuum >>> (b) can accomodate the apertures and aperture offsets as listed >>> above >>> (c) is tapered and meshes with our 200 mm wide wide vacuum chamber >>> in such a way as to control wakefield effects >>> >>> While (a) and (b) appear to be manageable, we currently have no idea >>> on how to tackle (c). >>> >>> I had reviewed our polarimeter situation at LCWS-2007 here in >>> Hamburg, where you can find further details about our original >>> vacuum chamber ideas, which unfortunately have become totally >>> obsolete because of the collimator structure: >>> >>> www.desy.de/~schuler/LCWS-2007/Upstr_Pol_Update_rev.pdf >>> >>> Of course, we would appreciate any good ideas to resolve these >>> problems. >>> >>> Cheers, Peter >>> >>> ********************************************************************* >>> * * >>> * K. Peter Schuler Tel.: +49-40-8998-2015 * >>> * DESY-HERMES Fax +49-40-8998-4034 * >>> * Notke Strasse 85 * >>> * D-22603 Hamburg e-mail Peter.Schuler@desy.de * >>> * Germany * >>> * * >>> ******************************************************************** >>> *