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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 1 Towards Improved Collimation for the ILC Jonathan Smith (Lancaster University/Cockcroft Institute)

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 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/

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 3 People ● “Spoiler Wakefield and Mechanical Design” task ● Details on project web: http://hepunx.rl.ac.uk/swmd/ 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

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 4 SLAC T-480 Experiment Vertical mover BPM 2 doublets ~40m BPM Two triplets ~16m 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…

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 5 Vertical mover BPM 2 doublets ~40m BPM Two triplets ~16m 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…

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 6 ESA beamline layout (2006 version) 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? Wakefield box Beam

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 7 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?

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 8 Slot 1 Slot 4 Slot 2 Slot 3 L=1000 mm = 324 mrad r = 2 mm = 324 mrad r = 1.4 mm = /2 r = 3.8 mm = 324 mrad r = 1.4 mm (r = ½ gap)

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 9 Collimator Measured 4 Kick Factor V/pc/mm ( 2 /dof) Linear fit Measured 4 Kick Factor V/pc/mm ( 2 /dof) Linear + Cubic Fit Analytic Prediction 1 Kick Factor V/pc/mm 3-D Modelling Prediction 2 Kick Factor V/pc/mm 1 1.4 ± 0.1 (1.0) 3 1.2 ± 0.3 (1.0) 1.11.7 2 1.4 ± 0.1 (1.3)1.2 ± 0.3 (1.4) 2.33.1 3 4.4 ± 0.1 (1.5)3.7 ± 0.3 (0.8) 6.67.1 4 0.9 ± 0.2 (0.8)0.5 ± 0.4 (0.8) 0.30.8 5 1.7 ± 0.3 (2.0)1.7 ± 0.3 (2.2) 2.32.4 6 1.7 ± 0.1 (0.7)2.2 ± 0.3 (0.5) 2.42.7 7 0.9 ± 0.1 (0.9)0.9 ± 0.3 (1.0) 2.32.4 83.7 ± 0.1 (7.9)4.9 ± 0.2 (2.6)2.36.8 1 Assumes 500-micron bunch length 2 Assumes 500-micron bunch length, includes analytic resistive wake; modelling in progress 3 Kick Factor measured for similar collimator described in SLAC-PUB-12086 was (1.3 ± 0.1) V/pc/mm 4 Still discussing use of linear and linear+cubic fits to extract kick factors and error bars → Goal is to measure kick factors to 10% Preliminary results: L=1000 mm 208mm 28mm 159mm

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 10 GdfidL EM simulations… beam

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 11 166mrad r=1.4mm 12 =166mrad r =1.4mm 11 =166mrad r =1.4mm 10 166mrad r=1.4mm (1/2 gap) 6 Revised 27-Nov-2006 Beam viewSide view Collim.# h=38 mm 38 mm Roughened surface, compare with 12 As 10, in Ti-6Al-4V, polished, cf. 12 As 10, in OFE Cu, polished, cf. collim. 6, 13 Runs 3, 2007 Exists, from 2006 runs. For reproducibility ~211mm 1.4mm =21mm beam

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 12 Collim.#Side view (“SLAC sandwich”)Beam view Revised 08-Nov-2006 13 1 = /2 rad 2 =168mrad r 1 =4.0mm r 2 =1.4mm 14 1 = /2 rad 2 =168mrad r 1 =4.0mm r 2 =1.4mm 15 1 = /2 rad 2 =50mrad r 1 =4.0mm r 2 =1.4mm 16 =exp., sin r=1.4mm h=38 mm 38 mm 21 mm 52 mm Ti6Al4V OFE Cu 21 mm 125 mm 21 mm = 0.6 Ti6Al4V

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 13 Data analysis from this run… ● Is ongoing, but here is a preview...

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 14 Longitudinally Asymmetric?

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 15 Damage Studies ● 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… ) Last time: 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.

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 16 Manchester University involved in wakefield simulations of the ILC collimators (R.Barlow, A.Bungau) Merlin code development (includes higher order modes) Simulation of bunch kicks for different modes at different offsets Alignment studies (Adina Toader) EPAC 2006 Paper: “Simulation of High Order Short Range Wakefields” A.Bungau and R. Barlow, The University of Manchester, EUROTeV-2006-051 Merlin Simulations

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 17 Including EM simulations into Merlin Fourier Deconvolution W bunch (s,m)=W delta (s,m) Gaussian 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

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 18 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

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 19 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

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 20 Cylindrical jobs... ● W modal decomposition ● Jobs still running ● w(s,r,r', θ, θ')→w(s,r,θ,m ) ● Useful for rectangular geometry?

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 21 Bench “wire method” 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 Plot from S.F.Hill and M.J.Pugh, paper at EPAC'94

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Jonathan Smith, LC-ABD, 12 th April 07, RHUL 22 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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MERLIN 3.0 only considers first order (dipole) modes. Kick is linearly proportional to offset. For offsets close to the axis this is a reasonable approximation.

MERLIN 3.0 only considers first order (dipole) modes. Kick is linearly proportional to offset. For offsets close to the axis this is a reasonable approximation.

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