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Beam Delivery System collimators for the International Linear Collider

The collimation system for the International Linear Collider (ILC) consists of a spoiler and an absorber. The collimator's mission is to clean the beam from unwanted particles and photons that could interfere with detector measurements. This article highlights the key tasks and achievements related to the design and testing of the ILC collimators.

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Beam Delivery System collimators for the International Linear Collider

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  1. Beam Delivery System collimators for the International Linear Collider J. L. Fernandez-Hernando STFC/ASTeC Daresbury Lab

  2. The ILC collimation system is composed of a spoiler and an absorber. The collimator mission is to clean the beam halo from e- or e+ off orbit which could damage the equipment, but mainly to clean the beam from photons generated during the bending of the beam towards the Interaction Point. These photons, if not removed, would generate a noise background that would not allow the detectors to work properly. Task 5.3 Programme Highlights • T480 data analysis/test beam • Mafia/GdfidL simulations of T480 Collimators • Beam damage simulations • Fluka/Geant4 • Ansys

  3. 0.6c0 a • Specification of requirements for LC spoilers - Complete • Eurotev Report 2006-015 and ILC RDR • Long, shallow tapers (~20mrad?), reduce short range transverse wakes • High conductivity surface coatings • Require spoilers survive at least 2 (1) bunches at 250 (500) GeV • Design external geometry for optimal wakefield performance, reduce longitudinal extent of spoiler if possible • Design internal structure using materials found most appropriate from survey of material properties.

  4. Report on spoiler damage estimates and comparison with test beam data – Partially achieved • Simulations carried out with Fluka, Geant4 (+EGS with Keller), see EPAC’06 and EUROTeV Reports 2006-015 and 2006-021 • FEA studies in ANSYS3D/Fluka of transient stress waves, see PAC’07, EPAC’06 • Beam test proposal (2007) approved for ATF and in preparation, see PAC’07

  5. beam beam collimator reflected shear waves heated zone beam compressive waves Reflected tensile waves UK a leading contributor on critical collimator issues: wakefields, survivability. Strong collaboration with SLAC and EUROTeV groups. Made most detailed Simulations of spoiler jaw damage to date. G. Ellwood, J. Greenhalt

  6. 10mm low mass mounting target area Cu Ti reference pin hole guide channels pin hole x y Material damage test beam at ATF • The purpose of the first test run at ATF is to: • Make simple measurements of the size of the damage region after individual beam impacts on the collimator test piece. This will permit a direct validation of FLUKA/ANSYS simulations of properties of the materials under test. • Allow us to commission the proposed test system of vacuum vessel, multi-axis mover, beam position and size monitoring. • Validate the mode of operation required for ATF in these tests. • Ensure that the radiation protection requirements can be satisfied before proceeding with a second phase proposal. • Assuming a successful first phase test, the test would be to measure the shock waves within the sample by studying the surface motion with a laser-based system, such as VISAR (or LDV), for single bunch and multiple bunches at approximate ILC bunch spacing. sample holder

  7. Report on wakefield beam tests - Achieved • Analysis of 2007 and 2006 T480 data for publication in progress, including: • BPM uncertainties/calibrations, bunch length monitoring • Original plan was to use SCP and established instrumentation See PAC’07, EPAC’06, EUROTeV Reports 2007-044, 2006-059, 2006-060 3D simulation of wakefields for various candidate spoiler prototypes - Achieved • For 16 ESA collimators, most recently using non-conformal moving mesh GdfidL • Additional mesh dependence studies ongoing, esp. for smallest sz • PAC’07, EPAC’06, EUROTeV-Reports 2006-055 (GdfidL) and 2006-103 (MAFIA) • Report on applicability of bench tests for ILC collimator design - Achieved • Initial report EPAC’06/EUROTeV Report 2006-056 • 2007 work  method not useful for quantitative tests (for collimator jaws), final report in preparation

  8. Variation of GdfidL predictions of transverse kick as a function of mesh resolution, for T480 collimator 3 (depth 1m), for σz = 1.0mm at an offset from electrical centre of 0.4mm. GdfidL calculated kick for collimator 3 (depth 1m) for z = 1.0mm: KF= 4.09 ± 0.80V/pC/mm J. Smith, C. Beard A. Bungau, R. Barlow 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

  9. Beam Parameters at SLAC ESA and ILC *possible, using undamped beam

  10. T480 “wakefield box” a = 166 mrad r = 1.4 mm Col. 12 ESA beamline T480 (prelim.) 2007 data E.M. predictions GdfidL vs. ECHO (ESA collims. 1- 8) Angular kick (V/pC) Kick factor (V/pC/mm) Collimator y (mm) Designed, modelled and tested collimators at SLAC ESA facility

  11. V/pC/mm V/pC/mm 1.2 ± 0.3 (1.7 ± 0.4) 1.7 ± 0.3 (2.4 ± 0.9) 1.2 ± 0.3 (3.1± 0.8) 2.2 ± 0.3 (2.7 ± 0.5) 3.7± 0.3 (7.1 ± 0.9) 0.9 ± 0.3 (2.4 ± 1.1) 0.5 ± 0.4 (0.8) 4.9 ± 0.2 (6.8) V/pC/mm V/pC/mm V/pC/mm 0.7 ± 0.2 (2.4 ± 1.1) 1.2 ± 0.3 (1.2 ± 0.3) 1.1 ± 0.2 2.3 ± 0.3 2.5 ± 0.3 1.1 ± 0.3 1.5 ± 0.2 1.2 ± 0.3

  12. a = 166 mrad r = 1.4 mm Col. 12 L=1000 mm a = 324 mrad r = 2 mm Col. 1 a = 166 r = 1.4 mm (r = ½ gap) Col. 6 Col. 3 a = 324 mrad r = 1.4 mm

  13. beam • Optimal spoiler design to achieve requirements (geometry, material, but not engineering) – Partially achieved • We have designs for material and geometry which can satisfy beam damage requirements • Outcome of ongoing wakefield optimisation likely to require further iteration on candidate designs

  14. Lead into LC-ABD2 (WP4) LC-ABD1 result • 3D wakefield simulations for collimator prototypes • Simulations validated by our test beam data are used to predict transverse wakes for more realistic prototype collimator designs. • Wakefield test results for collimator jaws • This is an ongoing programme to ensure modelling capability is reliable in regimes where calculations are known to be inadequate.. • Data-validated material response simulations for BDS components • Essential to test collimator materials/components under conditions which emulate instantaneous ILC bunch heating. • Prototype damage detection system for collimators • An unsolved problem ranked very highly, will become a major part of new project.  Closely linked with material response test above. • Full engineering designs for BDS absorbers, protection collimators, masks • Design of these various components, ~20 different types • Prototypes of critical subsystems of adjustable jaw collimators • Deliver demonstration hardware of critical components. GdfidL simulations T480 beam tests Damage simulation + ATF test Expertise in STFC

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