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Collimation

Ongoing R&D at ESA/Eurotev. Collimation. EDR to specify and find optimal solutions for Damage survival, 2 (1) bunches at 250 (500) GeV Jaw construction (coatings, inhomogeneous bonding, shockwave damage) Wakefield mitigation 3d geometry, half-gaps Surface resistivity Surface finish

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Collimation

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  1. Ongoing R&D at ESA/Eurotev Collimation EDR to specify and find optimal solutions for • Damage survival, 2 (1) bunches at 250 (500) GeV • Jaw construction (coatings, inhomogeneous bonding, shockwave damage) • Wakefield mitigation • 3d geometry, half-gaps • Surface resistivity • Surface finish • Stabilisation • Damage detection/inspection after incident • Promising paths • Front load material on spoiler leading taper (maybe hollow interior), improve damage resistance and reduce/avoid need for Be in system • Simulations, beam test proposal in preparation • Reduced length of shallow tapers as much as possible using data-validated 3d wakefield modelling (cost) • R&D in progress at ESA

  2. 0.6c0 a Starting point for spoiler design • Long, shallow tapers (~20mrad?), reduce short range transverse wakes • High conductivity surface coatings • Robust material for actual beam spoiling • Long path length for errant beams striking spoilers • Large c0 materials (beryllium…, graphite, ...) • Require spoilers survive at least 2 (1) bunches at 250 (500) GeV • Design approach • Consider range of constructions, study relative resiliance to damage (melting, fracture, stress) • Particularly important for beam-facing surfaces (wakefields) • Also within bulk (structural integrity, heat flow) • Design external geometry for optimal wakefield performance, reduce longitudinal extent of spoiler if possible • Use material of suitable resivity for coating • Design internal structure using most promising results in damage simulations (improve on Be tapers + 0.6 c0Ti)

  3. Aims • Design of spoiler jaws (geometry and materials) to optimise performance for wakefields: • E.M. modelling (J.Smith) • T480 beam test of collimator profiles (Fernandez-Hernando) • Develop data-validated ability to predict (3D) short range transverse wakes to 10% in regimes ~ ILC • Realistic wakefield models implemented in tracking codes (Bungau, Latina) • “Simple”, direct experimental measurement at ESA • … and beam damage • Fluka, Geant4, EGS simulations (Fernandez-Hernando, Bungau, Keller) • ANSYS (Ellwood, Greenhalgh) • More difficult to quantify “significant” damage • Need to consider wakefield and damage mitigation designs together

  4. Spoilers considered include… 0.6c0 2.1010 e-, Ebeam=250 GeV, sxsy=1119mm2 also, Ebeam=500 GeV 2mm 335mrad 10mm Option 1: Ti/C, Ti/Be As per T480 Ti, Cu, Al Graphite regions Option 3: Ti/C Option 2: Ti/C, Cu/C, Al/C 0.6 Xo of metal taper (upstream), 1 mm thick layer of Ti alloy 0.3 Xo of Ti alloy upstream and downstream tapers [Details, see Eurotev Reports 2006-015, -021, -034]

  5. Summary of simulations Temperature increase from 1 bunch impact Exceeds fracture temp. Exceeds melting temp. [Simulations L.Fernandez, ASTeC]

  6. Manufacturing study Ti6Al4V profile • Ti “option 3”, spoiler can survive if profile not supported by C (rigidity, uniformity of surface, taper angle) • At 50mrad, 0.6c0(Ti6Al4V) in z is 1mm thick layer • Wire erosion process used, also characterise surface quality • Importance of outer geometry optimisation from wakefield study • Pillars are artefact of ESA vacuum vessel

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