Minutes of 13 Oct Sept 2006 SWMD Telephone Meeting

Brief reports on:

1. Collimator designs and manufacturing
   Q: What do we want to use next beam time for? What aspect of design or calculation are we trying to test?
   • wire eroded collimators
     George summarised status of manufacturing study using electrical discharge machining process of new collimators (by outside manufacturing company), where "hollowed out" versions of two taper collimator 8 from 2006 ESA run had been produced. Versions had been made in OFE copper and Ti-alloy. Small bowing of the longest surface - which would be screwed to the wakefield box sandwich - had been seen after the central portion of the collimator had been removed. This could probably have been avoided by heat treating prior to manufacture. It may be adequate for the ESA tests as the distortion may be reduced during installation at SLAC. Characterisation of surface quality of one and two passes of EDM were compared, approx. 30% improvement in average roughness (R_a) gained by second pass. [R_a is the average (absolute value) deviation from the mean; R_max is the sum of the absolute values of the most positive deviation above mean with corresponding most negative deviation in a particular sampling length; and R_z is the average R_max over several sampling lengths (one evaluation length), therefore always less than R_max].
     Quality significantly less good than that obtained for 2006 collimators, but R_a thought to be acceptable for 2007 SLAC tests, as impact would be relative to vertical beam size at ESA (~100microns). NKW to discuss results at next ESA phone meeting (NKW version of George's slides for 16-Oct-2006 ESA meeting).

   • Coupled field analysis, and movie files for talk: vM stress and stress in y direction
     George had returned to coupled field analysis within ANSYS, using 2D slice (longitudinal section) of a tapered collimator. Extending earlier study to use real FLUKA energy deposition from Ti-alloy + graphite spoiler from Luis. Maximum stress observed in the region where reflected stress wave meets heated zone (beam trajectory)... To be continued using alternative energy depositions from Ti-alloy/hollow structures.

2. T-480 Data analysis et al
   • Luis plots
     Luis studied alterntive method of assigning resolutions to individual BPMs by using 9 BPMs to determine a reference value against which the measurement of the remaining BPM could be compared. This can be used for reference runs only and values for resolution are obtained which are comparable to those obtained using information within a doublet or triplet along, from which a single resolution is determined and attributed to all members of a given doublet/triplet.
     Will continue with this method and produce results for deflections for all runs, to summarise results in spreadsheet.
   • NKW had briefly looked into use of MINUIT for fitting within Matlab, to cross-check results obtained using "noplot_polyfit.m". This is in context of trying to reformulate fits which directly extract deflection per pulse from modified paramatrisation.

3. Wire Tests
   Luis and Carl had been in the RF lab., wire stretched in reference vessel, some tests with old TDR equipment but resolution obtained not too promising, also some difficulty obtaining data for offline analysis due to lack of GPI card. Agreed to investigate using the faster network analyser recently obtained in RF lab..

4. Wakefield Simulations (update from Jonny)
   New version of moving mesh GdfidL (12-Oct): corrects for bug when charge was traveling on a magnetic wall and napoly integration was needed (ie a scraper/collimator). The transverse wakepotential calculated was incorrect, often showing a large offset.

5. Merlin Simulations - Rectangular vs. circular apertures
   Adriana and Roger had been following up using both higher order mode wakefields in whole ILC BDS using circular apertures, and using lower order modes only but with geometryfor wakefields that matches physical apertures. More news soon.
   Query to Frank about how critical the z location of the collimator material is, in context of distributing the material together with a shallow taper - not thought to be a critical problem.

6. Review timescales on critical path
   
   • Lead time to manufacture collimators by EDM ~3 weeks
   • "Physicist" designs by 13 Nov., latest
   • Drawings generated/approved at RAL, 17 Nov
   • Fabrication start, 20 Nov
   • Ship to SLAC by early Jan for installation and run start end Jan.

7. Next meeting: Wed. 25 Oct. 1530 - 1700 (UK)

   NKW After meeting notes:

   • EDM OK for ESA tests, what would be suitable for final ILC beam with sigma_y ~ 10microns?
   • Hollowed out collimators: if needed single taper angle of ~20mrad, 0.6rad. length of Ti6Al4V = 2.1cm, thickness of taper material would be 0.4mm...