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Towards Improved Collimation for the ILC

Jonathan Smith (Lancaster University/Cockcroft Institute). Towards Improved Collimation for the ILC. Outline. Damage Studies Merlin Simulations Bench Tests T480@ESA EM Simulation activity Plans. LC-ABD WP5.3 /EUROTeV WP2 (BDS)

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Towards Improved Collimation for the ILC

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  1. Jonathan Smith (Lancaster University/Cockcroft Institute) Towards Improved Collimation for the ILC

  2. Outline • Damage Studies • Merlin Simulations • Bench Tests • T480@ESA • EM Simulation activity • Plans • LC-ABD WP5.3 /EUROTeV WP2 (BDS) • Collimation is crucial for beam delivery and detector protection/performance http://hepunx.rl.ac.uk/swmd/talks/

  3. People • “Spoiler Wakefield and Mechanical Design” task • Details on project web: http://hepunx.rl.ac.uk/swmd/ • Birmingham: N.Watson • CCLRC: C.Beard,G.Ellwood,J.Greenhalgh,J.O'Dell,L.Fernandez • CERN: F.Zimmermann,G.Rumolo,D.Schulte • [DESY: I.Zagorodnov] • Lancaster: D.Burton,R.Carter,N.Shales,J.Smith,A.Sopczak,R.Tucker • Manchester: R.Barlow,A.Bungau,R.Jones • TEMF, Darmstadt: vice-M.Kärkkäinen,W.Müller,T.Weiland • For ESA tests, working closely with • CCLRC on optics for wakefield and beam damage studies • SLAC Steve Molloy et al. for all aspects

  4. 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…

  5. 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…

  6. ESA beamline layout (2006 version) Wakefield box Beam • Measure kick factor using incoming/outgoing beam trajectory, scanning collimator gap through beam • 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 • Physics runs, Mar 2007, Jul 2006, May 2006 + Jul’07?

  7. Slot Slot Side view Side view Beam view Beam view Slot Slot Side view Side view Beam view Beam view a a p p = = /2rad /2rad a a =335mrad =335mrad a r=2 mm r=1.4mm r=1.4mm r=1.9mm r=1.9mm 38 mm 38 mm 38 mm 38 mm 38 mm 1 1 1 1 r=1/2 gate 7 mm h=38 mm h=38 mm h=38 mm h=38 mm h=38 mm a= a= 335mrad 335mrad a= a= 168mrad 168mrad r=1.4mm r=1.4mm r=1.4mm r=1.4mm 2 2 2 2 208mm a a p p = = /2 /2 rad rad a= a= 335mrad 335mrad 1 1 a a =168mrad =168mrad r=1.4mm r=1.4mm 2 2 3 3 3 3 L=1000 mm L=1000 mm L=1000 mm r r =3.8mm =3.8mm 1 1 28mm r r =1.4mm =1.4mm 2 2 a a a a p p = = /2rad /2rad =298mrad =298mrad 1 1 159mm a a r=3.8mm r=3.8mm =168mrad =168mrad 2 2 4 4 4 4 7mm r r =3.8mm =3.8mm 1 1 r r =1.4mm =1.4mm 2 2 Collimator 1 is similar to collimator described in SLAC-PUB-12086 Collimator 2 is like 1 but with a narrower gap Collimator 3 has the same taper angle and gap as 2. We hope to measure the difference due to resistive wakefield. Collimator 2, 3 and 4 have same taper angle, but 3 and 4 just in the top. The aim is to measure the difference between each geometry, if there is any. A small taper angle is better to reduce wakefields but it also need longer (more space) collimators. Can be model it?

  8. 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

  9. 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%

  10. GdfidL EM simulations… beam

  11. 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 beam 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

  12. 38 mm 21 mm h=38 mm 52 mm 21 mm 125 mm 21 mm OFE Cu Ti6Al4V = 0.6c0 Ti6Al4V 21 mm

  13. Data analysis from this run… • Is ongoing, but here is a preview...

  14. Longitudinally Asymmetric?

  15. Damage Studies Last time: • EGS/Geant4/FLUKA in agreement • ANSYS modelling of temperature flow done. • Shockwave studies underway • Focus now on manufacturability – e.g. wire erosion • Search for a site to conduct damage tests (CERN? Discussions at EPAC… ) Now: • Wire erosion method tested in manufacture on non-linear profile collimator. • Proposal for damage tests at ATF in preparation, awaiting discussion at next ATF users meeting.

  16. Including EM simulations into MerlinFourier Deconvolution Take FT of ECHO result (here mode=1) and FT of Gaussian (red and blue are sine and cosine parts) Divide to obtain FT of delta wake Back-transform.Horrible! (Look at y axis scale) But mathematically correct: combined with Gaussian reproduces original Due to noise in spectra at high frequency. Well known problem Wbunch(s,m)=Wdelta(s,m)Gaussian

  17. Delta wakes: Consistency check Give the same delta wakes Use FT to extract delta wakes from the different bunch wakes Agreement reasonable: method validated Green oscillation artefact of ECHO2D, not of Fourier extraction

  18. Merlin studies: emittance dilution due to wakefield Looked at emittance dilution due to higher order mode wakefields -> get an increase in the beam size and consequently a decrease in luminosity Beam excursions due to small offsets are under study. A.Bungau - Manchester University

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

  20. Plot from S.F.Hill and M.J.Pugh, paper at EPAC'94 Bench “wire method” setup Proof of principle using Crab team setup. • Calculate impedence of structure • Simulate mode structure • Use where wire is not interfering with the mode, or use simulation results to subtract wire induced effects Parts on Order!

  21. Summary • Run 3 at ESA successful, data analysis well advanced • Collimator damage simulations in 2006… • ATF proposal in preparation, submission 2 May 2007 • EM simulations • Being used to design optimal spoiler geometries • Wire tests • devices in production, test utility of method at DL • Merlin/Placet simulations with wakefields • Quantify effect of higher order modes

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