Roger started the meeting while waiting for Uli.
Collimators are sitting in SLAC and STFC has agreed for us to use them.
From previous experience significant discrepancies exist between model and
measured collimator wakefield deflections. Largest uncertainty was bunch length.
The key new input could be the electrooptic bunch length measurements.
Experimental options at SLAC.
ASSET 2 GeV, 1.5mm bunch length (too long for CLIC purposes), tentative plan to test CLIC cavities here (end 2012).
FACET 23 GeV, bunch length 15-40mum. Installation is complete, to turn on next week. FACET line is very
crowded, would it be possible to dismantle partially? Yes, but this is a big deal. There is a maximum of 7m,
getting up to 27m would need dismantling. Beam size in the area 1.25 inch. Plasma wakefield program will
be on and off for most of the lifetime of FACET. Few stripline BPMs are available.
The option would be to switch off the quads after the IP and place the high resolution BPMs downstream.
Javier asks about MAD file. Andrea has one and it will be posted in this page.
Always less than 10m space between BPM and rack. Amount of cables will be quite expensive since
there are ~50m to go.
ESTB bunch length is 100mu but upgradable to 44 mum (Mauro's talk)
Mauro Pivi.
ESA building is 60m long. This will host the ESTB beam so there is enough space to install devices.
Bunch length is 280 mum! The collimator box is already there.
The bunch is so long due to a large bend with 6m dispersion, R56=0.46. It might be possible
to reduce the dp/p to 0.02%, reducing the bunch length to 100mum. For smaller bunch length
installing new 4 quadrupoles would reduce dispersion and achieve R56<0.1 -> Sigma_z < 44mum
(in simulations 40mum).
The quads would be 2m long, aperture of 8cm. Cost ~1M$
ESTB to start in December.
Most reasonable is to do simulations of the wakefields for 100mum and 44mum and evaluate
the gain between the two different options. Lattice will also be made available.
Javier Resta, "Valencia plans"
Currently fracture of CLIC spoiler is possible. New simulations will be done to reasses the status
of the survivability of the collimator. Alternative materials to Be will be considered. Non-linear collimation
will be rescued and optimized to compete with the current collimation system.
Valencia is also interested in participating in the wakefields measurements. They could contribute to analytical calculations and simulations, and even new collimator prototypes (with funding). Data processing the experimental shifts are of interest too. Significant man power. One PhD student expected to start this year.
Javier could start evaluating the wakefields in the different facilities and scenarios.
Luis proposes to join forces for data analysis Manchester-Valencia.
Steven Jamison, "EO bunch length measurement"
Commissioning time after everything is installed is 1 week with accelerator access.
Spectral upconversion by measuring the Fourier spectrum could be simpler, requiring
only a few days for commissioning. This is the prefered option but valid only for bunches
above 150mum, maybe still works for 100mum. The more precise option that can also
do shorter bunches is more complex...
SLAC involvement would be required.
Uli asks whether these techniques work for 15mum (FACET), the answer is no.
Maybe this could be used to push the performance of the technique.
Uli also mentions that there are no laser installations in the FACET area. There is interest though
and they will start looking into that, as a laser room, etc. Uli will investigate how far this can be pursued
as this will make a big difference for Steven. For ESTB it should be easier.
We should ask Mauro about laser possibilities in ESTB.
Tom suggests to start in ESTB and move to FACET as an upgrade.
Next workshop will be in August, hopefully Andrea Latina will be able to join.
Funding and manpower are a very limited for electro-optic set-up.
Alexey Lyapin, "BPMs"
6 BPMs required in a triplet-like fashion. 2 Movers are required for calibration.
Available BPMs from ESA exps, reslution 250 nm.Posibly 3 ATF2 C-band ~30nm.
What are the specifications? This should be determined by the simulations from Valencia-Manchester.
From previous experience, completely separated groups was not a good idea, also there was
no on-line data analysis, plus the mechanical installation was not great.
Proposed improvements: ATF2 developments (30nm BPM, on-line analysis, calibration tone),
removal of orbit jitter and scale changes.
Cost quite high ~50k/BPM.
Synergies with the quad stabilisation studies (CLIC, Hermann) could make it cheaper and more efficient.
We should contact Hermann and try to combine these two studies.
ESTB rep rate max 10Hz, FACET 30Hz. During dedicated periods ESTB has 120Hz rep rate.
Luis Fernandez
Analysis was complicated in ESA. Also orbit and energy jitter was limitting the measurements.
The bunch length is critical for the future tests, plus energy variations. The main conclusion
is that tapering angle was not critical, so taper angle could be increased.
To avoid fracture maybe new materials as SiC foam coated with Be could help.
Will small deformation matter?
0.05 X0 is enough to spoil the beam but might fracture absorber (study is pessimistic).
It is required to continue this study.
Possibility to build SiC coll in Valencia.
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