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Review of rf structure test results

Review of rf structure test results. High gradient results 30 GHz 11.4 GHz. For more detailed high gradient results please see: The first ACE, June 2007 http://indico.cern.ch/conferenceDisplay.py?confId=15452 The x-band structure design and testing workshop: June 2007

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Review of rf structure test results

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  1. Review of rf structure test results • High gradient results • 30 GHz • 11.4 GHz For more detailed high gradient results please see: The first ACE, June 2007 http://indico.cern.ch/conferenceDisplay.py?confId=15452 The x-band structure design and testing workshop: June 2007 http://indico.cern.ch/conferenceDisplay.py?confId=15112 The High-Gradient workshop, October 2006 http://hg2006.web.cern.ch/HG2006 Steffen Döbert, ACE, 16.01.2008

  2. Damage in high field areas Copper Tungsten

  3. Clamped-Iris Structure Tests in CTF II

  4. Accelerating Structure Tests in CTF II Short, 16 ns rf pulses New Record for classical accelerating structures !

  5. Reached nominal 30 GHz CLIC values : 150 MV/m70 ns Overview of 30 GHz results Molybdenum shows higher gradient but different slope HDS performs worse than round brazed structure

  6. Hybrid Damped Structure (HDS) CLIC damped and detuned accelerating structure:30 GHz, 150 MV/m, 70 ns, < 10-6 trip probability

  7. Accelerating Structures made out of milled quadrants HDS60

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

  9. Damage vs aperture or group velocity HDS60 Large HDS60 Small Evidence for correlation between damage and power flow (a,vg,P): Criteria for optimizing rf designs (P/C): Px(t1/3)/p/2a < threshold

  10. Parameters for 30 GHz test strcutures

  11. Recent 30 GHz results C40vg8_pi/2 HDS4vg2.6_thick_150deg

  12. NDS4_vg2.5_thick result

  13. Summary of 30 GHz results in 2007 Probing phase advance and P/C theory

  14. Summary of 30 GHz results All measured data at 70 ns pulse length and 10-3 breakdown rate

  15. First CLIC x-band structure One tested at KEK and one tested at SLAC 150 MV/m peak, 125 MV/m avg 150 ns pulse length No breakdown monitoring

  16. Typical NLC/GLC prototype structures Length: 60 cm Phase advance: 120 deg Group velocity: 4 % a/l: 0.17 Es/Eacc: 2.2 Pin (65 MV/m): 59 MW Coupler: mode luncher Preparation: H-brazing, diamond turning

  17. FXC3 0 FXB-006 10 FXB-007 H60vg4R17 H60vg4S17-1 H60vg4S17-3 FXD1 FXC5 Average trip rate goal -1 Breakdown rate per hour 10 -2 10 58 60 62 64 66 68 70 72 Average gradient Performance of NLC/GLC structures

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

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

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

  21. Pulse Length Dependence

  22. Summary of 11 GHz results All data around ~10-6 breakdown rate First result on power ramping during filling: 100 ns ramp (50%-100%) + 100 ns flat top: 97 MV/m at 10-6 BDR

  23. Test results Tapered Damped Structure Test in ASSET Successful experimental verification of strong cell damping and benchmarking of codes

  24. SLAC/KEK results on short SW accelerating structures 3D model of single cell SW structure Assembly of a three cell SW structure made by KEK David Martin Yasuo Higashi, KEK

  25. Breakdown rate vs. accelerating gradient, all breakdowns, flat pulse, a/l~0.21 Time of flat pulse after filling time Time of flat pulse after filling time Single Cell SW1 Single Cell SW2 V. Dolgashev, S. Tantawi

  26. Conclusions on recent structure tests(some of them preliminary) • 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 (the structures showing a promising gradient are not damped) • 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) • Some doubts on P/C theory used to optimize this years structures • Quadrant technology appears not mature • Short phase advance seems not beneficial

  27. The end, reserve slides following

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

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