B.Parker reported the ILC QD0 baseline design, its prototype R&D and ATF2 SC Q utilization and the cryogenics system in details. It is a very compact magnet at L*=4.5m with the 14mrad crossing. One of major requirement is "50nm (vertical) stability" for the fast feedback system so that present design avoids "flowing" helium; concept will be tested with QD0 R&D Prototype.
Total heat load is estimated to be 15W for magnet coils to be 4.5K at ILC, which is consisted of 7W=2x3.5W from coil-supports, 3.5W from warm-to-cold transition, 1W from 80K shield and etc. . Under this condition, we found that a conduction cooled ILC QD0 is not practical since 20 cryocollers of 0.75W@3.5K are needed without safety margin.
R&D plan involves making and testing a full length QD0 prototype with its service cryostat (2K).
Addressing a question of "How does ATF2 SC Q fit with ILC R&D plan?", he explained as;
"We have pushed back the ILC QD0 R&D Prototype (specifically the magnet cryostat work)
in order to enable timely production of an ATF2 SC Q magnet. The ATF2 magnet allows a
scaled optics test of the ILC FF design and when connected to the ILC Service Cryostat at
BNL give us early feedback on ILC-style operation (chance to refine design before testing a
full length R&D prototype). Since the ILC Service Cryostat cannot be conveniently used at
ATF2 (and is needed at BNL anyway) we have made sure that the ATF2 magnet design is
compatible both with He-II operation at BNL and 4.2K LHe operation at ATF2. As discussed
later we have recently augmented the ATF2 quadrupole and sextupole coil designs (as
requested) to reduce their operating currents to about 300 A (was 800 A before) and the
heat shield for conduction cooling from an upper stage of a cryocooler (previously had
assumed LN2 cooling at ATF2). While the detailed mechanics of the ATF2 coils are
unavoidably different from an ILC QD0, the coils do have the same integrated corrector
design (dipole, skew-dipole, quad, skew-quad and skew-sextupole coils) so we can shift the
magnetic centers electrically; aside from increasing the clear aperture and available
strength (compared to the existing ATF2 FF), testing these "magnetic centering"
degrees of freedom and demonstrating that we can incorporate them with the existing
beam based feedback system is perhaps the most important test of these magnets at ATF2."
ATF2 SC Q has 57.2mm diameter inner worm bore. ATF2 coil winding has been started. As requested by KEK, two more coil layers will be added for 300A operation with 100A correction coils. So, there are four 300A and ten 100A current leads plus a number of instrumentation leads.
BNL would like to propose sharing responsibilities; i.e. BNL produces ATF2 magnet and cryostat and KEK produces a 4.2K He interface and a new box with cryocoolers, control valves, current leads etc . The task sharing will be discussed in more details at LCWA09, Albuquerque.
N.Kimura briefly reported cryogenics issues and examples of baby-sitter cryocooled magnet at KEK and a ultra low vibration cryogenics system.
Relevant issues of cryogenics at ATF2 are listed below;
S.Boogert updated the calibration scheme/system and the I-Q phase variations during May and June, 2009.
So far, the calibration tone signals ( CAL tone) have been injected directly into SLAC electronics. In the c-band calibration system, CAL and LO signals are locked in phase. Therefore, both the phases and the I-Q phases are very stable. On the other hand, the S-band system has unlocked LO so that the phase is constantly changing. However, the I-Q phase, i.e. the position, is stable. So, the S-band electronics has been completed. Also the calibration system was upgraded for more realistic cavity signals and control CAL tone with CSY CAMAC module, where 4 circulators are used, i.e. 2 for S-band and 2 for C-band. After discussion with Doug, it turns out the SLAC electronics already have a "reverse" calibration path via the cavity so the C-band circulators/phase shifters are not required, this might be interesting only for S-band BPMs. Doug might try to make a measurement in his November visit.
Variation of the I-Q phases at QM16FF was measured in both directions, i.e. x and y, after the calibration on 13th May through 18th June, i.e. for more than a month. They are indeed stable within 0.1 radian which corresponds to the cosine scale stability of less than 1%.
We will determine a phase relationship between calibration tone and beam by tracking changes even after long shutdowns. We will apply the measured phase shift from CAL tone to beam data without beam calibration in order to see the performance/ stability in October-November for faster start up.
I will suggest to try high resolution operation by removing attenuators in November when Alexey and Doug will be present. The most important parameter is the decay constant. Centering beam position in BPMs is also needed to reduce saturation and finer adjustment of I-Q phase is also needed.
Y. PAPAPHILIPPOU reported a possible proposal of testing SC wiggler to reduce emittance for CLIC which requires several times smaller emittance than ILC.
Two wiggler prototypes of 2.5T, 5cm period and 2.8T, 4cm period will be produced at BINP and CERN/Un.Karlruhe, respectively. We would like to install them at ANKA, CESR-TA and ATF for beam measurements (IBS and wiggler dominated regime) . Wiggler effect is calculated for typical ATF2 parameters, excluding the effect of coupling and IBS. The length of wiggler is 2m. We found strong dependence of emittance on the wiggler peak field and weaker dependence on the period length. In particular, a 4T wiggler can reduce the emittance by more than 30% and the two wigglers can reduce by a factor of 2, where the gap must be around 5mm.
In next steps, IBS and coupling will be included for the emittance reduction, and the effect to dynamic aperture will be studied. Also, technical issues of space, radiation absorption and cryogenics system will be evaluated.