Recent high-gradient results, rf testing, places and plans Steffen Döbert, CLIC Workshop, Test facilities High gradient results Future testing program For more detailed high gradient results please see: The x-band structure design and testing workshop: June The High-Gradient workshop, October

Drive Beam Injector Drive Beam Accelerator X 2 Delay Loop X 4 Combiner Ring Probe Beam Injector 4 A  s 1.5 GHz, 150 MeV 30 A ns 12 GHz, 150 MeV 16 structures - 3 GHz - 7 MV/m High Power test fasilities at CERN Two Beam Test stand 12 GHz, GHz Test stand Rf power production with CTF3 70 MW, 100 ns 200 MW, 140 ns TBL, 16*160 MW, 140 ns Klystron Test stand 12 GHz, MW-150 MW, 500 ns

X-band test facilities at SLAC NLCTA: 3 Test Stations: 2x50 MW into SLEDII, 300 MW, ns, fully automated conditioning Klystron Lab: 2 single Klystron test stands 2x50 MW into SLED II ASTA bunker

X-band Test Facilities at KEK Single Klystron (50 MW) test stand up and running NEXTEF: Available from fall 2007, 2x50 MW, 400 ns, 24/7 operation

Reached nominal 30 GHz CLIC values : 150 MV/m 70 ns Overview of 30 GHz results Molybdenum shows higher gradient but different slope HDS performs worse than round brazed structure

New Materials for High-Gradient Copper has still the best performance at low break down rate

HDS4vg2.6_thick_150deg C40vg8_pi/2 Recent 30 GHz results

StructureP (MW) E (MV/m) PT 1/3 /C (wue) C30vg HDS60vg HDS60vg C40vg7.4_pi/ HDS4vg2.6_thick All data at 70 ns pulse length and breakdown rate Summary of 30 GHz results

Hybrid damped structures (HDX) at x-band Frequency scaling Scaled structures show very similar performance HDS-type structures show consistently limited performance

A reference structure for CLIC from NLC Length:53 cm Phase advance:120 deg Group velocity:3 % a/ :0.13 Es/Eacc:2.2 P in (65 MV/m):41 MW Coupler:mode luncher Preparation:H-brazing, diamond turning

Tests of old NLC structures at short pulses T53vg3MC can be used as a first reference for the new CLIC parameters CLIC goal

StructureP (MW) E (MV/m) PT 1/3 /C (wue) T53vg3MC (50ns) T53vg3MC (100ns) H75vg3 (150 ns) HDX11vg5 (70 ns)59609 All data around ~10 -6 breakdown rate Summary of 11 GHz results

Pulse Length Dependence

Conclusions on recent structure tests Current CLIC design within experimentally demonstrated region 27 wue have been measured (Design used 18) 120 MW input Power for 100 ns into first cell of T53 Hybrid Damped Structures show performance deficit (short phase advance, slots, quadrants and milling) Copper is still the best material to make accelerating structures (Molybdenum still has some potential, shallow slope seen in previous experiments could be due to iris clamping, slow processing as usual) Exactly scaled structures seem to perform independent of frequency (therefore 30 GHz test are still meaningful) Structure manufacturing technology seems to play an important role Damping has to be integrated and tested

Structure Program Philosophy 1.Gradient program (highest priority): Demonstrate a CLIC prototype structure: (100 MV/m,300ns, 12 GHz, damping) 2.General high gradient R&D (high priority): Find the universal breakdown theory, P/C, phase advance, materials Try to do that with simple and clear experiments (single cells) 3.Fabrication technology for potential cost savings (high priority): Disks, slots, quadrants, surface treatment, procedures Start with simple structures and experiments (single cells, DC-spark), eventually we need to go to full structures

30 GHz break down R&D program in CTF3 - HDS4_vg2.6_thick (iris thickness, phase advance, P/C) Finished ! - NDS4_vg2.5_thick (Effect of slots and quadrants) Installed ! - C30_vg4.7_quad (clear experiment for fab. Tech.) Decision point, see flow chart ! - HDS11_vg2 (clear P/C experiment without other changes) - HDS4_vg2.6_thick_clean (compares cleaning with previous) - NDS4_vg3.6_thin (iris thickness in comparison with NDS4_thick) - C30_vg2.6 (P/C) - C30_vg8.2 (P/C) - C30_vg4.7_sb (speed bump) - C30_vg2_TM02 (vg) - HDS 11 copper/molybdenum (for better statistics) New list of planned experiments ordered by priority and reality

30 GHz flow chart C30_vg2_TM02 HDS4_vg2.6_thick (negative test result) HDS11_vg2 HDS4_vg2.6_thick_clean NDS4_vg2.5_thick (under test) NDS4_vg3.6_thin Quads or slot are a problem Quads or slot are not a problem P/C ok C30_vg2.6 C30_vg8.2 C30_vg4.7_sb New ideas if needed Input for x-band C30_vg4.7_quad

11 GHz CLIC structure program 11.4 GHz: - TD18_vg2.4_quad (CERN, VDL, Japanese industry) [2x] (test of P/C, damping, quadrant technology) - T28_vg2.9 (done by SLAC) (conservative approach) - T18_vg2.4_disk (SLAC,KEK) [4x] {1 CERN, 2 SLAC/KEK (test 1 at SLAC and 1 at KEK), 1 KEK} (test of P/C in conservative technology, technology comparison) Decision point, see flow chart - T18_vg2.4_quad (CERN) (test of P/C, quadrant technology) - TD18_vg2.4_disk (CERN, KEK) [2x] (mainly test of damping) - TD28_vg2.9 (CERN) (back up test of damping if others are not successful) New list of planned experiments

11 GHz flow chart TD18_vg2.4 geometry OK 2008 TD18_vg2.4 geometry not OK Disks OK Quads OK +Damp 2009 CLIC prototype disks damped CLIC prototype TD28 like CLIC prototype quads damped Go towards more extreme structures 2010 Input from break down R&D TD18_vg2.4_quad T28_vg2.9 T18_vg2.4_disk TD28_vg2.9 (T18_vg2.4_quad) TD18_vg2.4_disk ? Damping Not OK TD24vg1.7

AugOctNovDec CTF3 30 GHz NLCTA Station GHz Pi/2HDS4_vg2.6_ thick heat treated NEXTEF 11.4 GHz SeptJul Current structure testing program HDX11 Cu large grains C30_vg4.7_quad NLCTA Station GHz 2007 NDS4_vg2.6_ thick T53vg3MC H60vg3S18 ? Old Clic vg1.1 ?

Apr-JunJul-SepOct-Dec CTF3 30 GHz NLCTA Station GHz C30_vg2.6 NEXTEF 11.4 GHz Jan-Mar Current structure testing program C30_vg8.2 C30_vg2_TM02 NLCTA Station GHz 2008 C10vg2.9 [2x] C10vg0.7 [2x] C10vg2.2_ thick [2x] T18_vg2.4_ disk [1] TD18_vg2.4 T18_vg2.4_ disk [2] TD18_vg2.4_quad PETS 11.4 GHz HDS11_vg2 TD18_vg2.4 _quad T28_vg2.9 C10vg1.3 [2x] CLEX 12GHz T18_vg2.4_diskPETS 12 GHz Shut down T18_vg2.4_ disk [4] T18_vg2.4_disk [3]

TD18_vg2.4 TD28vg3 Parameters along the structures TD18_vg2.4 is more extreme in maximum surface field, pulsed heating and lowest group velocity

Parameters of new structure TD24vg1.7 StructureTD24vg1.7 Frequency: f [GHz]12 Average iris radius/wavelength: /λ0.11 Input/Output iris radii: a 1, 2 [mm]3.15, 2.35 Input/Output iris thickness: d 1, 2 [mm]1.67, 1.00 N. of reg. cells, str. length: N c, l [mm]24, 229 Bunch separation: N s [rf cycles]6 Luminosity per bunch X-ing: L b× [m -2 ]1.22×10 34 Bunch population: N3.72×10 9 Number of bunches in a train: N b 312 Filling time, rise time: τ f, τ r [ns]62.9, 22.4 Pulse length: τ p [ns]240.8 Input power: P in [MW]63.8 P in /Ct P p 1/3 [MW/mm ns 1/3 ]18 Max. surface field: E surf max [MV/m]245 Max. temperature rise: ΔT max [K]53 Efficiency: η [%]27.7 Figure of merit: ηL b× /N [a.u.]9.1

Structure Nick-Names TypeNo of cellsvg (start)special feature HDS118.3thick C onstant Imp 302.4thin T apered 53.6quad TD amped clean Old namesNew names - CLIC vg3/1 quadrants damped TD18_vg2.4_quad - T26vg3MC T28_vg2.9 - CLIC vg3/1 disks undamped T18_vg2.4_disk - CLIC vg3/1 quadrants undamped T18_vg2.4_quad - CLIC vg3/1 disks damped TD18_vg2.4_disk - T26vg3MC disks damped TD28_vg2.9

Scattered Dark Spots Areas of Discoloration Patchy breakdown areas along sides of irises High Current Region Input Coupler Iris Post mortem inspection of HDX11cu

Comparison of 11.4 GHz results