Minutes from September 27, 2004 Phone Meeting

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
     - 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
           - also I put some background refs at
           - 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?