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Results of CLIC Prototype Accelerating Structure Testing in 2008: 30 GHz & X-band Results

This text describes the results of the CLIC prototype accelerating structure testing in 2008, including the results at 30 GHz and X-band, as well as the tentative schedule for 2009 and the conclusions drawn from the experiments. Thanks to the collaboration between SLAC, KEK, and CERN for their involvement in the CLIC structure collaboration.

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Results of CLIC Prototype Accelerating Structure Testing in 2008: 30 GHz & X-band Results

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  1. Results of CLIC prototype accelerating structure testing in 2008 • 30 GHz results • X-band results • Tentative schedule for 2009 • Conclusions in between Thanks to everybody involved in the CLIC structure collaborationat SLAC, KEK and CERN ! Steffen Döbert, CLIC-meeting 6.2.2009

  2. 30 GHz Structures tested in 2008 Only two… • HDS4_thick : re-test, bad results. Didn’t reach an accelerating gradient much higher than 60 MV.m-1. • C30 speed bump : same geometry as the older 3.5 mm structure except for a « speed bump » lowering the group velocity at the input. Two measurements : fed by the input and by output. 2 Mathias Gerbaux - CTF3 Collaboration Technical meeting - 27/01/2009

  3. HDS4_thick re-test: wholehistory In total : 1,244,800 pulses, mainlyat 1 Hz corresponding to 5.76 SLAC hoursat 60 Hz but crappy data 3 Mathias Gerbaux - CTF3 Collaboration Technical meeting - 27/01/2009

  4. C30-sb • In total : • 4,101,250 pulses, mainlyat 1 Hz corresponding to 18.99 SLAC hoursat 60 Hz • 2186 breakdowns Weird things due to calibration problems (now solved) 4 Mathias Gerbaux - CTF3 Collaboration Technical meeting - 27/01/2009

  5. 30 GHz speed bump results

  6. 30 GHz conclusions • HDS4_thick did not work as expected even so designed using ‘new’ theories Technology (quadrants) doubted rather then theory • Speed bump did not show an influence on breakdown rate vs gradient • 30 GHz experiments will end in 2009 to focus on 12 GHz One more structure (TM02) will be tested after start up • Nevertheless the 30 GHz test stand will not be dismantled in 2009

  7. X-band structures tested in 2008 • HDX11 repolished and heat treated at 1000 deg C • T18_vg2.6_disk [1], [2] and [5] (2009) • T28_vg2.9_disk • TD18_vg2.4_quad • PETS (will not be mentioned) TD18_vg2.4_quad T18_vg2.6_disk T28_vg2.9_disk Steffen Döbert, CLIC-meeting 6.2.2009

  8. Chris Adolphsen HDX11 retesting Electro-polishedBrazed at 1000 degBetter alignment

  9. Faya Wang

  10. Chris Adolphsen HDX11 retesting

  11. Structure parameters Rf parameters along the structure for T18 and T28 design TD28_vg3 TD18_vg2.4 75 35 Structure design aimed for low group velocity, small aperture and low input power

  12. T18_vg2.6_disk Collaboration between KEK, SLAC and CERNDesign by CERN, fabrication by KEK, surface prep., bonding and testing at SLAC Second structure with identical preparation currently under test at KEK

  13. Conditioning history of T18_disk Faya Wang

  14. Conditioning history of T18_disk Short pulse higher gradient condition Pulse shape dependence BKD study. BKD pulse width dependence study at 110MV/m. BKD gradient dependence study at 230ns pulse width

  15. T18_vg2.6_disk results CLIC goal: trip rate < 3 10-7/m

  16. Long term operation t-2 fit • ~ factor 50-100 improvement during conditioning(5-10 observed during NLC/GLC R&D)

  17. Break down distribution along the structure Bead pull  Structure seems to be ‘limited’ at the end where the fields are highest

  18. T18_vg2.6_disk backwards Conditioning history Structure was turned around and tested shortly again to see at which level the output cell would be limited

  19. T18_disk, backward vs forward • given the very different conditioning times and strategies a very consistent resultConfirms that T18_disk was ‘limited’ by its last cell

  20. T18_vg2.6_disk backwards Break down distribution  Almost all the breakdowns are in the first (former last) cellpost mortem endoscope inspection showed mainly damage between the last regular iris and the matching iris

  21. T18_vg2.6_disk [2] tested at KEK Identical preparation as T18_vg2.6_isk [1], only difference are the high power rf flanges T. Higo and S. Matsumoto

  22. Recent 253ns processing and 80MV/m run Processing to 90MV/m. Most of the trips are due to klystron related matter. We are off-line analysed. Stable run at 80MV/m. Processing to 110MV/m. 12/4/2008 X-band WS in UL 2008

  23. Processing summary till late Nov. ~ 2x10-6/m Rumors: ~ 2x10-5/m • Processing reached up to 253ns, 90MV/m • 1000 BD’s in 650 hours • Breakdown rate • <1BD/15hr ~ <2x10-6 BD/pulse/m 80MV/m, 213ns just after processing • Dark current • Toward upstream 5~10mA • Toward downstream 20 ~30mA • Field enhance factor around 40~60 • Our strategy • stay at 253ns, 80MVm for a month • then restart processing to 100 MV/m and higher T. Higo and S. Matsumoto 12/4/2008 X-band WS in UL 2008

  24. T18_vg2.6_disk [5] made by CERN, tested at SLAC CERN-made disk structure: manufacturing procedures and assembly strategy is different, Structure not leak tight therefore tested in a tank, Assembled at SLAC

  25. RF process history of T18Disk_CERN RF process history of T18Quad RF process history of T18Disk_SLAC

  26. TD18_vg2.4_quad Same rf parameter as T18_disk but HOM damping Structure made out of 4 milled bars

  27. Surface Preparation, brazing and assembly done at SLAC identical to disk structures

  28. TD18_vg2.4_quad, results ~ 9.2 10-4/m  1000 Breakdowns after 25 hours Structure shows poor performance at low gradient and short pulse length, strong outgasing

  29. TD18_vg2.4_quad, results  clear difference in breakdown location compared to disk structuretherefore likely different limitation mechanism compared to disk version

  30. T28_vg3.3_disk Juwen Wang Structure entirely made by SLAC using NLC T53 cells

  31. T28, conditioning history (a) The average unloaded gradient. (b) normalized breakdown rate.

  32. T28, breakdown position 0~250hrs 250~500hrs Similar to T18_disk behavior, breakdowns prefer the end of the structure

  33. T28, trip rate vs gradient Average gradient Peak gradient  factor 10 more breakdowns for same average gradient but in terms of peak gradient not very different performance

  34. Structure comparison Peak gradient  smaller apertures (group velocities) sustain higher surface fields

  35. Testing Conclusions • We basically reached our first milestone (100 MV/m unloaded with good break down rate and pulse length without damping and optimum efficiency) • Damping is the next important milestone • Disk technology gives clearly better performance, if done right (T18_quad might be limited by damping features) • It seems that the result is reproducible too • Very high temperature treatment and baking does not make the difference • T28 results unexpected (not ‘limited’ by first cell) but not inconsistent • Tapering (surface field, power flow ?), did we go to far in T18 What is really limiting this structure ? • New T24vg1.7_disk seems still to be the right structure for the next step towards a prototype CLIC structure

  36. Mile stones and decision points • 100 MV/m average gradient for CLIC pulse length with good breakdown rate and acceptable efficiency > 10 % • Similar performance with damping • Similar performance, damping, better efficiency ‘CLIC prototype structure T24vg1.7’ • Fully featured structure HOM loads and s-BPM’s integrated (ASSET test ?) CDR  • Review manufacturing technology, optimization strategy, baseline geometry, rf parameters • Review damping options and parameter optimization

  37. Tentative Structure testing program

  38. Testing Program Conclusions • We did less structures than originally planned • CERN has to sort out its manufacturing procedures (a task force is currently working out a strategy to do so) • If we have to wait for SLAC/KEK made T24’s we most likely get our ‘CLIC Prototype’ milestone only in 2010 • CLIC X-Band collaboration works great and is essential !

  39. The END

  40. Structure parameters

  41. Parameters of new structure TD24vg1.7

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