1. Movers
- Stewart presented options from Micos and
distributed a set of notes on this
- given the cost ($10K per axis), we think for the first round we would
not implement rotation stages;
a horizontal translation stage can take a 100-kg load, while a vertical
stage can only take 30 kg
which seems marginal; I would suggest we do a single horizontal stage
on the middle bpms and consider
a second horizontal stage for one of the outer bpms. Need to look into
what angular range is interesting to
implement in the beam optics; should consider adding local correctors
on either side of the bpm girder to
span a range of say +- 200-400 microradians.
- Stewart is waiting to hear back from Newport on alternative movers;
also Hildreth looked at stages by MDC,
but was skeptical they would be useful for our application (http://www.mdcvacuum.com/)
- the linear translation stage by Micos has a dynamic range of 55mm and
readback accuracy of 100 nm;
we'd prefer a shorter range (say 5mm) with closer to 10-nm accuracy if
that is possible;
- are dc-drive linear actuators an option? Stewart can you look at
specs for
http://www.physikinstrumente.com/micropositioners/M230t.html
and
http://www.aerotech.com/products/pdf/ANT-25LA.pdf
- or maybe look into optical linear encoders?2. Interferometer
- Mike H. reported that the Zygo laser is Class II
- Mike H. described optical interferometer truss systems to pin down
transverse motion; Joe Frisch proposed
a 14-arm optical truss and Mike H. described a 6-arm (local) optical
truss; we discussed the complexity
of the interferometer systems that would give real transverse
displacement info of the middle bpm
- Woods/Arnold are skeptical of utility of inteferometer system --
easier to do a beam test; and not clear
that an interferometer system could allow meaningful corrections and is
difficult to implement;
need clearer drawings of a proposed system and how it might be used
- D. Miller and S. Boogert will follow up with Armin Reichold to better
understand the LICAS system and how
it might be imployed for our application
3. STS-2 seismometer measurements
- Streckheisen STS-2 seismometer measurements are
described in Appendix C of the NLC ZDR,
http://www.slac.stanford.edu/accel/nlc/zdr/Snowmass96/ZDRAPPC.PDF
It works down close to 0.01Hz
and so could characterize
motion with required accuracy of sub-10 nanometers out to 100 seconds. Can
probably look at
evolution of motion between 1-100s to extrapolate further, perhaps with
some use of the
ATL scaling law. 100
seconds may get us out to time scales we might consider for the
calibration period.
And can use these devices to
measure: i) on floor, ii) on girders, iii) on BPM stages and iv) maybe on
the
BPMs. SLAC owns 2 STS-2 units
and has a portable PC-based DAQ for it with Labview. Could think
about borrowing a third STS-2
as well; perhaps Fermilab has one.
4. BPM assemblies.
Yury has located a 4th BPM assembly. Actually 2 such
assemblies have been located and we
will bring them to ESA to join the existing ASSET girder with 3 such BPM
assemblies on it. We'll take one of
the additional ones and Marc Ross will take the other for use at KEK ATF.
5. Nano-BPM at ATF.
Mike and Ray met with Marc Ross to discuss relation of T-474
at SLAC with nano-bpm
program at KEK ATF. With the cold technology choice, the bpm
resolution requirements are relaxed (I believe
10 micron resolution for Linac BPMs is adequate); one of the
most, if not the most, stringent requirement might
be for the energy spectrometer and there's interest in nano-bpm
for the energy spectrometer application. Marc
thinks some tests are more meaningful at ATF where smaller beam
sizes and jitter are available. He questioned
probing 100-nm effect when the spotsizes are close to 1 mm in ESA.
On the other hand the higher beam energy
at ESA is an advantage for suppressing effects from stray fields.
For reference, at LEP-II the beam sizes and
centering were at the 1-mm level and needed to get to 1-micron level
to probe 100 ppm effects. In ESA, we
can probably get close to 200-micron level rms spotsize and below that
for centering the bpms. Also in ESA we
will use the rf cavity bpms which should be much better than the button
bpms used at LEP for sensitivity to
higher-order effects. Summary was that Marc, Ray and myself
felt that both programs should be pursued.
6. BPM gain calibration procedure.
Can bootstrap from the
accuracy of the bpm mover/encoder system to
required accuracy. For BPM offsets of 100 microns will
need to understand gain to 0.1% level. Can calibrate
this using the mover, for example 500 micron motion and
500nm readut will give gain to 0.1%. Can then use this
to bootstrap to other bpms using an upstream corrector
to move beam in all bpms.
7. Chicane design.
- can we get larger spectrometer angle? For LEP-II this
was 3.77 mrad and current proposal for ILC is x20
smaller at 0.18 mrad. I think it's
easy to effectively double this by taking measurements at both
+0.18 mrad and -0.18 mrad. Also 0.18
mrad was selected so that only 0.5% emittance growth occurred
at 1 TeV ECM. At 500 GeV ECM and
below we can easily go to +-0.36 mrad for example, which would
allow 400-nm tolerance on bpm motion
compared to 100 nm.
8. Spectrometer magnet, ramping and calibration scheme.
- if we can ramp the spectrometer magnet in less than 1
minute then can get frequent calibrations and significantly
reduce sensitivity to drifts in bpm
motion. I checked with Cherill Spencer at SLAC for warm magnets and
can expect to be able to ramp to say
1 Tesla in 30-40 seconds. Eddy currents take 10s of seconds to
stabilize. During ramping and
stabilization of eddy currents we can rely on i) magnetic measurements in
Test Lab and ii) in situ measurements
with NMR probes and coil pickups. I talked to John Weisend at SLAC
about ramping cold magnets and he
thought this could also be done in under 1 minute, citing the ramping
of Tevatron magnets for former fixed
target program at Fermi for example. There are also eddy currents to
worry about for cold magnets as well
in the flux return. I don't see superconducting to have a strong
advantage here, since don't need
particularly high fields and it adds complexity, including for in situ
Bdl monitoring. So I think we could
envision ramp times between +,- and 0 states of less than 1 minute;
then could have flat stable operation
in each of +,-,0 configs for a few minutes. And the STS-2 seismometer
measurements can be used in the ESA
test program to characterize bpm motion on the relevant time scales of
1-2 minutes.
9. Connection with collimator wakefield measurements
- the bpm girder is a good diagnostic for collimator
wakefield measurements; these measurements previously
have been done at Sector 2 at SLAC;
we can measure wakefield kicks with similar accuracy with the T-474
girder in ESA and the setup is much
more accessible; Woods is discussing this at SLAC with P. Tenenbaum
and T. Markiewicz; D. Miller and D.
Ward will discuss as well with Nigel Watson in UK
10. UK visit to SLAC
- possibly adjacent to trip UK physicists make to KEK
for run in late November/early December for nanobpm
11. Budgeting for FY05/06.
SLAC ILC group has asked for a more detailed proposal for
work/funding in FY05/06; due in ~1 week
- I presented a talk to
this group on Wednesday and talk is available at
http://www-project.slac.stanford.edu/ilc/talks/technologytalks.htm
- also I put some
background refs at
http://www.slac.stanford.edu/~mwoods/ILC/ipbi/Documentation_refs.html
- need more details
on system configuration, schematics, cost spreadsheet, run plan details,
next steps for FY06 (and beyond);
Mike and Ray are working on this, but please feed us input. We'll be
putting in additional cost estimates for
i) temperature stabilization for T-474 electronics
ii) interferometer? Only include if have a viable schematic/utility
for this
iii) STS-2 seismometer measurements
iv) collimator wakefield box/measurements
v) EFD DAQ support
vi) additional correctors?
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