A draft meeting memo of the ATF2 tolerance meeting, 10:30am-noon, 29th May
2005, KEK
Andrei Seryi and Toshiaki Tauchi
Participants:
From KEK : T.Tauchi, R.Sugahara, S.Kuroda, J.Urakawa, K.Yokoya
From NIRS: M.Kumada, K.Abe
From SLAC: A.Seryi, M.Ross, T.Raubenheimer
0. Very nice work of James Jones was discussed at the meeting. His presentation
can be downloaded from a webpage of
http://acfahep.kek.jp/subg/ir/nanoBPM/nano.project/third/talks/james.ppt at
the home page of the 3rd mini-workshop on Nano project at ATF
(http://acfahep.kek.jp/subg/ir/nanoBPM/nano.project/third/third.htm). This
discussions then followed by discussion of optics and magnets. Brief
comments form this meeting are summarized below.
1. Tolerance for the multipoles:
(1) Need to express the results in convenient for magnet designers units
(e.g. b/B at 1cm radius?), compare results from James with results from
Kuroda-san.
(2) Need to get all results from James as a table.
(3) Need to create a table of tolerances to be included into the proposal
text. Simulations need to be redone for "optimal optics" to which the new
diagnostics would be added.
(4) Need to compare the calculated tolerances with the measured values for
the BT quads (although the measurements were not very reliable, see below).
If the sextupole errors are the biggest effect and tighter than what is
measured, then need to evaluate if such errors can be corrected by the
nominal sextupoles of the beamline.
2. Position tolerances:
(1) Static tolerances for beam size increase agree with analytical
calculations by FFADA program.
(2) At the goal A of ATF2, jitter tolerances are namely of less than ~30% of
the beam jitter. With about 20magnets in the beamline, this would be
approximately equivalent to 7% jitter from each individual quad. The FD may
indeed be considered separately.
(3) At the goal B (2nm stability at IP), the tolerances could be the same
as those of the goal A, and beam stability (of 2%, for goal B) would be provided by intratrain feedback, where we need to be sure that
jitter stability of the kicker is sufficiently good, and not as much about
the vibration stability. However, ILC-like fast kicker will not be
installed at beginning of operation with the goal B. The fast kicker must be
checked separately from the ATF2 program, since it might take significant
time in order to achieve the target performance. Therefore, the jitter
shall be controlled at 5% if the technologies; e.g. feedforward system, very
stable power supplies and support system, are available. So, it could be
expressed that with about 20magnets in the beamline, this would be
approximately equivalent to 1% jitter from each individual quad. However,
this requirement might be too much simplified. We need a realistic
simulation to estimate "the jitter tolerances" at each magnet with James's
program.
(4) In the simulations of orbit correction one can optimize locations and
number of correctors and aim to zero the orbit through sextupoles. The
optimal orbit correction should relax the tolerances significantly. Also,
we discussed on a correction scheme based on the magnet-movers. One of the
approaches, at ATF2, would be to allow redundancy, so we would have all magnets
on movers and also would have several correctors. The correctors would allow
faster response, and thus we would not depend on the question whether the
FFTB-movers are fast enough to perform the orbit correction.
(5) In simulations of knobs, one could use all sextupoles and create knobs
for all terms including coupling. The waist scan can also be done with
sextupole knobs. Knobs should relaxed the tolerances even further.
3. Quadrupole magnets:
Base design on BT quads type A. Multipoles of such magnets were measured
but the measurements were not reliable. Need to re-measure. One possibility
is to remove a quad from the beamline during summer shutdown. Junji thinks
that a prototype for such quad was manufactured and should be available
somewhere. It needs to be located, and then it can be used for measurements.
Quads order from IHEP will proceed regardless of the timeline (1-3) choice.
If more quads are needed for extended diagnostics, they will be added to the
order.
4. Power supplies:
Criterion of 2% effect on the beam imposed as tight as 1E-5 of field
strength error for final quad. This is difficult but the FFTB power
supplies achieved that level. The essential part is special
controller/regulator of the power supply. These devices were made at SLAC.
They are rather independent of the power supply. Tor said that we can quite
quickly find out if the power supplies would be available.
5. Optics modifications:
(1) Concentrate on "optimal" design (straight)
(2) change bends from sector bends to rectangular
(3) use 0.8m (as used in ATF) instead of 1m for better field stability and
more space
(4) provide space near octupoles and study is we really need them
(5) extend diagnostics section (use up to ~10m additional space)
(6) QM14 is the strongest quad, and is close to max field of BT quads,
need to check if its strength can be reduced by reoptimization the matching
section