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Recent Developments with ILC Collimator Wakefield Calculations

Jonathan Smith (Lancaster University/Cockcroft Institute). Recent Developments with ILC Collimator Wakefield Calculations. Introduction/Project Objectives. LC-ABD WP5.3 (Nigel Watson)/EUROTeV WP2 (BDS)

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Recent Developments with ILC Collimator Wakefield Calculations

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  1. Jonathan Smith (Lancaster University/Cockcroft Institute) Recent Developments with ILC Collimator Wakefield Calculations

  2. Introduction/Project Objectives • LC-ABD WP5.3 (Nigel Watson)/EUROTeV WP2 (BDS) • Collimation is crucial for beam delivery and detector protection/performance of a particle accelerator • Quantification of longitudinal and transverse wakefield effects of collimators on the beam • Optimization of collimator design • Use and understanding of simulation tools, potential improvements and support of other projects • Verification by test beam measurement

  3. 2 doublets Two triplets BPM BPM BPM BPM ~40m ~16m SLAC T-480 Experiment Vertical mover • Wakefields measured in running machines: move beam towards fixed collimators • Problem • Beam movement  oscillations • Hard to separate wakefield effect • Solution • Beam fixed, move collimators around beam • Measure deflection from wakefields vs. beam-collimator separation • Many ideas for collimator design to test…

  4. 2 doublets Two triplets BPM BPM BPM BPM ~40m ~16m Vertical mover • Wakefields measured in running machines: move beam towards fixed collimators • Problem • Beam movement  oscillations • Hard to separate wakefield effect • Solution • Beam fixed, move collimators around beam • Measure deflection from wakefields vs. beam-collimator separation • Many ideas for collimator design to test…

  5. ESA beamline layout (plan) Wakefield box Beam • Measure kick factor using incoming/outgoing beam trajectory, scanning collimator gap through beam • Stage 1, 5 rf cavity BPMs, 1 stripline BPM, 2 wire scanners • Downstream BPMs themselves R&D project …layout has changed over course of runs. • Wakefield box, proposal for 2 sets of four pairs of spoiler jaws • Each set mounted in separate “sandwich” to swap into WF box • (Relatively) rapid change over, in situ – ½ shift for access • Commissioning run, Jan 4-9, 2006 • Physics run, May06, July06, Mar07, July07

  6. 1500mm Wakefield box Slide reproduced from talk by Nigel Watson Ebeam=28.5GeV ESA z ~ 300m – ILC nominal y ~ 100m (Frank/Deepa design) Magnet mover, y range = mm, precision = 1m

  7. Collim. #, slot Side view (“DESY sandwich”) Beam view Revised 4-May-2006 1, 1 =324mrad r=2.0mm 38 mm h=38 mm 2, 2 324mrad r=1.4mm 3, 3 324mrad r=1.4mm L=1000 mm 4, 4 =/2rad r=4.0mm  r=1/2 gap As per last set in Sector 2, commissioning Extend last set, smaller r, resistive WF in Cu 7mm cf. same r, tapered Slide reproduced from talk by Nigel Watson

  8. Collim.#, slot Side view (“SLAC sandwich”) Beam view Revised 4-May-2006 8, 1 r1 =4.0mm r2 =1.4mm =289mrad =166mrad 133mm 38 mm cf. collim. 7, and same step in/out earlier data h=38 mm 7, 2 1=/2 rad 2=166mrad r1=4.0mm r2=1.4mm 31mm cf. collims. 4 and 6 6, 3 166mrad r=1.4mm cf. collim. 2, same r 211mm 5, 4 =/2rad r=1.4mm 7 mm cf. collim. 4 smaller r Slide reproduced from talk by Nigel Watson

  9. a = 324 mrad r = 1.4 mm Slot 2 a = 324 mrad r = 2 mm Slot 1 (r = ½ gap) Slot 3 L=1000 mm a = 324 mrad r = 1.4 mm a = p/2 r = 3.8 mm Slot 4

  10. Run 1206 (ref. 1207) Multiplying each bunch by its ebpm_x ADC value Small improvement on the Chisq/n

  11. 208mm L=1000 mm 28mm 159mm Preliminary results: 1Assumes 500-micron bunch length 2Assumes 500-micron bunch length, includes analytic resistive wake; modelling in progress 3Kick Factor measured for similar collimator described in SLAC-PUB-12086 was (1.3 ± 0.1) V/pc/mm 4Still discussing use of linear and linear+cubic fits to extract kick factors and error bars → Goal is to measure kick factors to 10%

  12. Analytical estimate • Stupakov says: • Stupakov says: • Stupakov says: • Stupakov says: • Stupakov asserts that the h»b is met, but is this really valid?

  13. For SLAC collimators...

  14. Assessment/Familiarization of Simulation Tools • MAGIC (easy to use tool for first comparison with new calculations) • ECHO/ECHO3D • Thomas Weiland, Mikko Karkkainen(TEMF, Darmstadt) Igor Zagorodnov (DESY). Code development as part of EUROTeV project • MAFIA • CDB and JS working on comparison with Cho Ng’s results (PAC 2001) • GdfidL • Overlapping interest with David Miller and Alexei Liapine (UCL) as part of EUROTeV WP5 (Spectrometry) • Additional software for research if required: • BCI/TBCI/ABCI (old CERN tools), XWAKE, XOOPIC • Tau3P, Omega, T3P (next generation SLAC codes) • Boundary Element (BEM) codes (Sapporo, Japan)

  15. EM Simulations with GdfidL 4 5 2 7 1 6 8 3

  16. Mesh stability: Collimators 1&2 • Only 3 decent points at 300µm for most collimators • More at 500µm • 1mm ~ OK – can use spline fit on data to get an estimate – not done so far – further analysis to see if this takes us closer to ECHO/PBCI.

  17. What do we do about it? (1)

  18. What do we do about it?(2)

  19. Effect of mesh filtering…

  20. Misallignment

  21. Further collimator designs semi-circle, with[9]/without[10] flat, opposing demi-circles[10], 8 with flat[11].

  22. More possible collimators 7 with flat [13], half exponential[14], 13 with shallower angle[15] exponential profile[16], 13 with ellipse connecting 4mm and 1.4mm aperture[17] 13 with ellipse connecting beam pipe radius and 1.4mm aperture (also see 9)[18] half cosine taper [19], raised cosine taper [20], tanh tapers [21] (set typically to the length of collimator 6)

  23. Wakefields @300µm (6 cells/sigma)

  24. Wakefields @500µm (12 cells/sigma)

  25. Collim.# Side view Beam view Revised 27-Nov-2006 6 166mrad r=1.4mm (1/2 gap) ~211mm  38 mm 1.4mm h=38 mm 10  =166mrad r =1.4mm =21mm 11 =166mrad r =1.4mm  =21mm 12 166mrad r=1.4mm  =21mm Exists, from 2006 runs. For reproducibility Runs 3, 2007 Roughened surface, compare with 12 As 10, in Ti-6Al-4V, polished, cf. 12 As 10, in OFE Cu, polished, cf. collim. 6, 13

  26. Collim.# Side view Beam view Revised 27-Nov-2006 13 1=/2 rad 2=166mrad r1=4.0mm r2=1.4mm =21 mm  38 mm ~52 mm h=38 mm 14 1=/2 rad 2=166mrad r1=4.0mm r2=1.4mm =21 mm  ~52 mm 15 1=/2 rad 2=50mrad r1=4.0mm r2=1.4mm  =21 mm ~125 mm 16? non-linear taper r=1.4mm =21 mm OFE Cu Polished, cf. collim. 7, 12, 13 Ti6Al4V = 0.6 Ti6Al4V Runs 3, 2007 Polished, cf. collims. 7, 11, 13 Polished, cf. collim. 13 OFE Cu Form t.b.d. cf. ?

  27. Run 3 kicks

  28. WB's suggestion: Chop this bit off as beam will never see wake that has travelled this far from the bunch

  29. s_max s_max s_max s_max s_max s_max s_max s_max s_max s_max s_max s_max s_max s_max s_max s_max s_max s_max Two possibilities: “colimator 22” “colimator 23”

  30. Longitudinally Asymmetric?

  31. Results...

  32. Cylindrical jobs... • W modal decomposition • See Adriana's talk... • Jobs still running • w(s,r,r',θ,θ')→w(s,r,θ,m) • Useful for rectangular geometry?

  33. GdfidL & PBCI • TEMF working on ECHO/PBCI – 3D, moving mesh, conformal, non-dispersive solver GdfidL σ/Δz=6 PBCI W║(s)/(V/pC) With thanks to Mikko Kärkkäinen s/σ

  34. Alternatives: Code development

  35. Summary • Experimental programme to measure collimator wakefields at SLAC-ESA. • Numerical simulations to provide direction to the collimator design programme. • Alternative numerical/analytical techniques under development, which will provide useful comparison.

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