ATF2 SC-Q Meeting

October 29 7:00- 8:00, Webex

Participants : Brett Parker, Andrew Marone, (BNL), Nobuhiro Kimura, Takayuki Tomaru, Toshiaki Tauchi(KEK), Philip Bambade(KEK/LAL), Glen White, Mark Woodley (KEK/SLAC), Eduardo Marin, Rogelio Thomas(CERN), Cherrill Spencer, Min-Huey Wang (SLAC)

Recent studies at KEK, Nobuhiro KIMURA (Cryogenics Science Center / KEK)

N.Kimura estimated head loads based on Brett's spread sheet. The triple copper leads (room temperature to 277K) get 80W. The HTC leads ( 77K to 4K) get 1.3W. We may need one more cryo-cooler.
Q to BNL: Can you provide decay times for each coil in order to estimate heat load in bypass leads attached to the HTC ?
A : Yes, it will be estimated by capacitances of coils.
Q to BNL: Can we pass the CAD drawings to the company for designing the connection box ?
A : Yes, while they are not complete at 100%, but they should provide the basis.

Benefits for QF1 Replacement and Estimates of SC Magnet correction Coil Strengths, Glen White ( KEK/ SLAC)

file : ( odf, 18 pages, 5.5MB )

G.White reported analysis of multipole components in final doublet magnets from simulation studies and estimation of required SC QF1 trim corrector currents.

MADX and Lucretia simulations show that the skew component of 12-pole cannot be corrected and causes the vertical beam size growth as a function of horizontal emittance. At the nominal emittance of 6um (normalized one, i.e. γ&epsilonx at the beam intensity of 1 x 1010/bunch), &sigmay becomes about 90nm (MAPCLASS re-match) while 37nm can be achieved at γ&epsilonx=3um at the beam intensity of 1 x 109/bunch .

There are three possible mitigations as follows; (1) Doubling horizontal beta function at IP while it is undesirable for deviating ILC parameters, (2) Build new skew-dodecupole magnet placed close to QF1FF while it does not help for pushed &beta optics and the other effect must be studied as well, and (3) Use new BNL SC quad to replace the QF1FF.

Next, he reported estimation of current requirement for correction coils of sextupole-based tuning and BBA/steering. The maximum ranges of positioning the magnetic centers are &Deltax=2.25mm, &Deltay=1.5875mm and &Delta&phi=13.2mrad in horizontal, vertical and rolling about longitudinal axis, respectively, which correspond to those of the cam-based mover system. Estimated requirements of currents are listed in a following table;

Corrector CoilCurrent (A)
Normal Quad17.1 + 17.1
Skew Quad12.9 + 12.9
Dipole41.9
Skew Dipole30
Skew Sextupole9.6
There are detailed calculations in the slides.

C : The current estimation is well matched to the 100A leads.
Q : What is the nominal current of sextupole ? Is there limit ?
A : It corresponds to normal operation with the nominal optics.
Q to Brett : How do you know the multipole components in the SC-Q ?
A : They were calculated at r=28mm. Since usual ones are done at r=1cm, they are conservative values.

Impact on the beam size using a SC QF1 on ATF2 Ultra-Low beta FFS, Eduardo Marin (CERN)

file : ( odf, 10 pages, 832KB )

E.Marin reported possible solutions in case of the ultra-low beta optics for future plan as well as the current issue on the QF1 multipole components which G.White described.

The solutions are listed below together with brief explanations.

  1. Reducing emittance (&epsilonx) by a SC Wiggler in DR
    The emittance can be reduced by 30% and 50% with one and two SC wigglers of 4T in the DR, where &sigmay/&sigmax become 40nm/2.7um and 28nm/2.2um, respectively.
  2. Correction by a Dodecapole magnet
    A dodecapole (1.58 x 106m-5) can reduce the IP beam sizes to &sigmay/&sigmax=44.4nm/3.9um. So, it is not sufficient.
  3. Replacing QF1 by a SC Q
    By the BNL SC-Q with 0.02% multipole component at r=28mm (aperture), the IP beam sizes can be reduced to &sigmay/&sigmax=37.13nm/3.21um, i.e. it is the designed one.
  4. Correction by an Octupole magnet
    An octupole ( -44.2m-3 ) can reduce the IP beam sizes to &sigmay/&sigmax=28.8nm/3.4um.
  5. Designing a new ATF2 UltraLow β*ylattice
    Increasing β*x to 8.4608mm and decreasing β*y to 31.5737um, the IP beam sizes can be reduced to &sigmay/&sigmax=23.8nm/4.4um. However, simulations show that 83% of measurements by Shintake monitor have the vertical beam sizes of less than 29nm and 28nm in RMS and Gaussian fit, respectively.

In future, we will study a more realistic tuning including mispowerings, ground motion etc. . Also, we will study at intermediate vertical beam size stages.

Q : Can you apply the same technique to the present optics by using MAPCLASS with relaxing &betax at QF1 ?
A : Yes, we will study.
Q : Tuning time is also important parameter to be minimized both for the nominal and ultra low &beta optics.
A : Present number of iterations is about 20,000 for the ultra low &beta optics.
Q : Is the last solution with increasing β*x good for the CLIC study?

Finally, Brett commented that he found inconsistency in the spread sheet of the correction coils. He will correct it in next week.

As discussed at previous meeting, one optics expert is invited in person at the meeting, BNL, 24th November. We would like to ask G.White for the expert. He will ask SLAC for this support.

Next webex meeting will be held at 9pm (KEK), 9am(BNL), 6am(SLAC), 1pm(CERN) , 10 November.
URL : http://ilcagenda.linearcollider.org/conferenceDisplay.py?confId=4274 .