Agenda and Summary:
1) BDS tuning -- Glen White
2) Consideration for compact SC FD for ATF2 upgrade -- Brett Parker
BDS tuning
Glen reported about status of BDS tuning studies. Glen is using 20mrad BDS deck
plus extraction line starting with expected post-survey magnet and BPM alignment
tolerances, magnet errors and BPM resolutions. The BPM-to-magnet alignment is
performed using quad-shunting technique. The beamline is steered and then
orthogonal knobs for correction of IP aberrations using Sextupole movers are
used. Studies are performed with
Lucretia code.
At the moment the rms of tuned beam size is about twice the
nominal for 100 seeds. However, there are number modifications planned which
will improve convergence and make simulations more realistic. In the quad
shunting procedure, one need to limit strength change to no more than 20% or so,
to avoid quad center shift. Orbit at the end of BDS reaches 50microns, which may
affect beam sizes and would need to be fixed. Alignment of octupoles and
sextupoles -- if they are co-wound, as in FD, and their centers coincide, one
would need to measure offset of sextupoles only. In addition to knobs with
sextupole offsets, one need to use also knobs from coupling correction section,
to access all coupling planes. The magnet strength error of 0.1% in all magnets
need to be reconsidered -- at least for FD this error may be somewhat too high.
In addition, it is planned to simulate 2 beams and tune on
luminosity (pair signals), include LINAC to get real bunch shapes, include
ground motion, and so on. Studies will continue according to the described plan.
Consideration for compact SC FD for ATF2 upgrade
Brett presented design considerations for SC final doublet for ATF2. This SC doublet could be considered for second stage of ATF2, for upgrade. The FD could be designed with the same approach as for ILC: QD0 and QF1 with skew and dipole correctors and combined sextupole-octupole packages with skew sextupoles. The coils would be wound on a single tube with 30mm radius of the aperture, and placed in a common cryostat. For ATF2, the superfluid He is not essential -- normal He can be used. To match the design to low energy of ATF2, the coils would be wound with single wire (not with 7 strand cable), which would also decrease the needed current, make current leads easier, and would also allow to have six layers and allow to measure and correct the field harmonics during manufacturing.
Andrei Seryi, 11/08/05