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Breakdown Study on the CLIC Designed T18 X-band Structure

Breakdown Study on the CLIC Designed T18 X-band Structure. Faya Wang Jul.-31-2008. Topics. T18 RF Conditioning History Breakdown Study on T18 Summary. Cumulated Phase Change. T18 Structure Profile. Field Amplitude.

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Breakdown Study on the CLIC Designed T18 X-band Structure

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  1. Breakdown Study on the CLIC Designed T18 X-band Structure Faya Wang Jul.-31-2008

  2. Topics • T18 RF Conditioning History • Breakdown Study on T18 • Summary

  3. Cumulated Phase Change T18 Structure Profile Field Amplitude The structure is designed by CERN, built at KEK, assembled and bonded in SLAC and tested at SLAC (NLCTA). 120°

  4. RF Conditioning Statistics Max average Unloaded Gradient at different pulse width: 120MV/m at 70ns for 6hrs (*152MV/m) 120MV/m at 100ns for 76hrs (*152MV/m) 120MV/m at 140ns for 47hrs (*152MV/m) 110MV/m at 190ns for 41hrs (*140MV/m) 120MV/m at 200ns for 21hrs (*152MV/m) 120MV/m at 210ns for 24hrs (*152MV/m) 110MV/m at 230ns for 78hrs (*140MV/m) ~1400 hours total conditioning from 14 Apr. 2008 to 3-Jul-2008 ~2148 breakdowns (average 119 per cell) *:Max accelerator gradient in the structure RF Conditioning Time: hrs 1400 600

  5. T18VG2.4_Disk structure RF process history begin at Apr.14 2008 The gradient is the average unloaded gradient for the full structure. The beginning 500hrs, maximum unloaded gradient is 110MV/m The BKD Rate is normalized to the structure length(29cm).

  6. The following 900hrs, maximum unloaded gradient is 120MV/m 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

  7. Field Decay Time of Breakdown Field Decay Time for All Recorded 1100 Events Field Decay time: the time for field collapsed to 5% of normal field level

  8. BKD Rate Characteristics at Different Conditioning Time RF BKD Rate Gradient Dependence for 230ns Pulse at Different Conditioning Time RF BKD Rate Pulse Width Dependence at Different Conditioning Time After 900hrs RF condition BKD rate has a gradient dependence ~ and pulse width dependence ~

  9. Unloaded Gradient at Different Conditioning Time For Constant Breakdown Rate

  10. The following test after 1200hrs at 110MV/m@230ns shows BKD rate is very high up to 1.9e-5/pulse/m. Red cross—cell position Blue dot - breakdown position Then, set at 105MV/m@230ns for 140hrs ( 7 BKD Events )

  11. BKD Distribution along Structure at Different Stage Based on the Time of RF Signal

  12. Breakdown Distribution along the Structure in Cell Cluster

  13. Pulse heating related to breakdown study during the conditioning stage of 600~700hrs

  14. Pulse Heating BKD Study Main pulse No hot cells during this test Pre pulse After pulse Main pulse is fixed to 119MV/m of 100ns pulse width SLED output pulse

  15. P2 P1 0 0 t1 t2 Number of pulse to damage the surface at certain pulse heating Pulse Heating for a square pulse P(t) U is a constant, T0 surface temperature without pulse heating For step pulse case Bad Fit Red line: power level Blue line: pulse heating *V.F.Kovalenko, "Termophysical Processes and Electrovacuum Devices", Moscow, SOVETSKOE RADIO (1975), pp. 160-193.

  16. For a constant breakdown rate, we have: From T18 experiment result: *From pulse heating related damage caused breakdown: *V.F.Kovalenko, "Termophysical Processes and ElectrovacuumDevices", Moscow, SOVETSKOE RADIO (1975), pp. 160-193. #From pulse heating on thermal fatigue: Probability to break the link among atoms in a lattice Stresses caused by temperature gradient #S. V. Kuzikov & M. E. Plotkin,” Theory of Thermal Fatigue Caused by RF Pulsed Heating”, Int J Infrared Milli Waves (2008) 29:298–311

  17. RF Conditioning history in pulse heating scale Based on the experience on the NLC/GLC structure H60VG3, which has a pulse heating temperature of 43K at 65MV/m with 400ns pulse[1], it will not damage the surface on the scale of pulse heating of T18. [1] C. Adolphsen, ‘Normal-Conducting RF Structure Test Facilities and Results’, SLAC–PUB–9906, September 2003.

  18. Summary T18 has preformed very well during test, with a quiet low breakdown rate of less than 1e-6/pulse/m at 106 MV/m with 230 ns pulses at the end of conditioning, which maybe good enough for a collider at of 100MV/m, however, it doesn’t yet have all necessary features such as higher efficiency and wake field damping.

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