Minutes for 08 Feb 2006 SWMD Telephone Meeting

1. ESA test beam dates: 24-Apr-2006 - 08-May-2006 (proposed)
   To decide today who attends/when - further details. (From previous discussions by email, suggest several people for run period itself, and Carl+Luis for ~2 weeks prior to 25 Apr.)
   Expect we need ~5 people from UK specifically for T-480, dates to be agreed to ensure coverage, will follow up by email.

2. Material damage
   • Luis - Comparison of various spoiler properties - Supporting plots: 1 - 2
     Comparison of performance (max. temperature increase, longitudinal distribution along beam trajectory) for five different spoiler combinations at two depths in y (2mm, 10mm). Of the solid Ti, solid Al, and three variations on Ti+graphite geometries, best performance (lowest temperature increase except for Al, most stable with differing depths) was for Ti+graphite option 2 - note summary table of results has options one and two interchanged. Al looks interesting, but fracture temperature of material not known - perhaps available from Matweb web?
     Next steps include study of solid Cu collimator for comparison, composite spoiler "option 2" with Al/Cu, and simulation of the thin Cu coupons in the paper Single pulse damage in copper, to see whether Fluka would predict melting where it was observed in earlier tests at FFTB at SLAC.
   • Compilation/comparison of Geant4/Fluka/EGS results Adriana
     Step size / mesh size problems now fixed, and very good agreement obtained with Fluka/EGS results. Also implemented box (Ti) + graphite wedge spoiler, now also implemented coating of thin layer on the spoiler surface, essential to ensure high conductivity e.g. when using graphite bulk volume.
     General discussion about how to most reliably estimate peak temperature rise, taking a single mesh cell with peak rise will be sensitive to statistical fluctuations, may be more reliable to study distribution of temperature within the spoiler, and fit to a parametrisation such that can estimate the high end of this.
     Also, discussed implementation of wakefields and realistic collimator, tapered spoiler shapes in BDSIM, as Adriana had been on contact with Ilya Agapov at RHUL.
   • George - stress animation
     Refined study of the effect of two bunches on collimator, peak stress etimated at 200MPa, next step is to try using Luis' more recent input files and extending simulation to few x 0.1s, to correspond to timescale of ESA bunch spacing.
   • TTF possibility from discussion with Mike Seidel/Nick Walker - Roger J.
     3mm is the thickness of the sample they have been using at TTF, the transverse (exact) dimensions will be sent by a DESY engineer. The goal (from a TTF perspective) is to distort the beam not too much by the target in order to keep rad. safety people happy; the energy deposition is roughly constant as function of depth as long as the thickness stays below ~0.4 rad lengths. Above that a shower is developed and the energy loss rises strongly. My understanding is that a common concept for the collimation system is to use thin spoilers in combination with absorbers that can take the blown up beam. Therefore at TTF the hope is to make an experiment that concentrates on thin targets. Is this OK for us? The samples that you showed me looked larger. Perhaps we can still gain useful info from the exp nonetheless? What do you think? Also, the energy is 450MeV, the bunch charge 1nC (max 3nC) after installation of another module next year up to 1GeV is expected. The jig is moved remotely as well as the separation valve; exchange of the jig/samples has to be done manually.
   • Planning for experimental tests - discussion and plans to make proposal - see also Single pulse damage in copper, Marc Ross et al, paper at LC'00
   
   
3. Wire/bench test preparations
   Carl has been setting up the rig with Luis, trying to align the bench such that it is stable and flat with respect to the launch cones themselves. All launch cones (round and rectangular) necessary for the tests are now available. Missing some springy finger RF contacts, and have therefore put in order for these to be made at the lab - need to be chased up as consistently 1 week away. Old scope is set up and ready to go now. Trying to get dimensions of cavity under tests - already have simulation results for 1.3 GHz cavity, can be scaled up to high freq. (500 GHz?). Currently, rig is in magnet test area and ok to remain there as long as necessary. Plan is eventually to move to new building? Location of the jaws relative to the wire has to be varied, to be looked into. New jaws, could make mock up rather than full solid engineering design.

4. Higher order wakefields in Merlin

5. Wakefield simulations
   1. Comparisons with e.g. ABCI? - plots
      Jonny encouraginly already has ABCI working, ran some very simple models, needs to understand results and reconcile with GdfidL.
   
   
6. Progress for ESA tests
   1. Progress on collimator jaws 5-8
   2. Event reconstruction code
      Mark Slater et al will prepare files from Jan run in Matlab/root format for us to study and familiarise ourselves with within next two weeks.
   
   
7. Future plans
   • Further runs at ESA in (US)FY07? Need simulation results.