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Status of high gradient experiments at Nextef

Status of high gradient experiments at Nextef. Kazue Yokoyama, Toshiyasu Higo, Yasuo Higashi, Shuji Matsumoto, Shigeki Fukuda Accelerator Laboratory, KEK. T18_VG2.4_Disk #2 at Nextef TD18_VG2.4_Quad_#5 at KEK Narrow waveguide at KT-1. T18_VG2.4_Disk #2. Disk-damp cell. 2 /27.

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Status of high gradient experiments at Nextef

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  1. Status of high gradient experiments at Nextef Kazue Yokoyama, Toshiyasu Higo, Yasuo Higashi, Shuji Matsumoto, Shigeki Fukuda Accelerator Laboratory, KEK • T18_VG2.4_Disk #2 at Nextef • TD18_VG2.4_Quad_#5 at KEK • Narrow waveguide at KT-1

  2. T18_VG2.4_Disk #2 Disk-damp cell 2/27

  3. T18_VG2.4_Disk #2 • T18_VG2.4_Disk #2 was installed and the processing has started in October last year.

  4. Nextef: RF Monitors along waveguide

  5. Nextef: Monitors along beam axis RF • Steady state dark currents were evaluated at the Faraday cups (FC) at upstream and downstream of the beam line. • Downstream dark current can be energy analyzed.

  6. T18 trend 6/27

  7. T18_VG2.4_Disk_#2 in 2008 Power trend recorded by control program November 80MV/m (35MW) steady run December 7/27

  8. Power at BD’s and BDR during 27 days at 80MV/m (35MW) level Started at 10:00 on Nov. 28 Finished at 9:00 on Dec. 25 566 hrs run / 643 hrs = 88% ON ~10-5 ~10-6 BDR ~17 str. BD / 566 hr ~0.030 BD/hr/str ~0.75 x10-6 BD/Pulse/m 8/27

  9. Dark current trend during 35MW run FC-UP FC-Mid AM FC-DN 75cm 75cm 195cm 9/27

  10. Dark Current F-N plot 10/27

  11. Typical breakdown rate: on Feb. 17 65MW = 109MV/m run ACC BD ACC BD 2~3 BD? BD? BD? BD? Normal pulse Normal pulse Normal pulse Normal pulse Normal pulse Normal pulse Normal p Normal Need to analyze whether BD or not. Include ACC-BD + all BD?  8 BD / 14hr < 0.6BD/hr ~ 3x10-6/pulse ~ 1.5x10-5/pulse/m • Now on the way to evaluate the breakdown rate carefully. 11/27

  12. Summaryof T18_VG2.4_Disk #2 • Breakdown rates at steady-stare operation of 80 MV/m is approximately 0.75 x10-6 BD/Pulse/m . • We are going to do the high gradient experiments until the end of March. • The total run time will reach up to about 3000 h. • We are trying to estimate the BDR from the dark currant measurements.

  13. TD18_VG2.4_Quad_#5 Quadrant 13/27

  14. Measurement of TD18_VG2.4_Quad_#5 • Measurements at CERN for TD18_quad made in CERN give -2.23 dB. • Comparing to this, KEK quad gives 2.56dB measured in transmission mode. About 0.33dB more attenuation due to some reason. • -2.56dB = t=0.295  Q/Q~83% is all attributed to t~1/Q 14/27

  15. The result of the first measurement by Bead pull Input Output reflection amplitude Measurement N5230A F_IF=1kHz, 3pts Freq=11424MHz Tcavity=20.9C Pulse motor step ~ 0.2mm RF Input from input coupler side 15/27

  16. Meas. At 11416MHz, 20.3degC 19 16 1 2 4 3 17 18 20 Average phase advance per cell -118.086 degrees / cell Average phase advance = 118.1 deg/cell dF ~ (1.9/120)*11424*0.0138~ (11416 + 2.6) ~ 11418.6MHz 16/27

  17. Summary of TD18_VG2.4_Quad_#5 v=c Drive frequency • The frequency of the present quad #5 at operation becomes 11418.6 MHz. • Freq. = 11420.6MHz with120deg/cell at operation should be tuned up by 3.4MHz. • Test tuning has started last week. • We do tuning accurately at the operation frequency after EBW of cooling connection. • High-gradient experiments will start in April. Actual 17/27

  18. Narrow waveguide Parts before bonding 18/27

  19. Narrow Waveguide Design field gradient of 200 MV/m at an RF power of 100 MW group velocity of around 0.3c Rectangular Waveguide: WR90 Wavelength converter: Width 22.86(g 32.15 mm) → 14mm (g 76.59 mm) Cosine taper( 1 g) : Height 10.16 mm → 1 mm Calculated to get a low VSWR by an HFSS. 19/27

  20. CU004 Setup for High-Power processing @ Nextef PPM Klystron @11.424GHz 50 MW, 50 pps, 400ns • Cu002 • tested at XTF (06.11～07.01) • Moving to Nextef (～ 07.04) • Using for system checking (～ 07.05) • SUS003 • Tested at KT-1 (～ 08.10) • Cu004 • Testing at KT-1 (09.01～) • We are on going high power testing of coupper(CU004) at Klystron Test Stand. Narrow waveguide in 5mm lead shield PMT1,2,3,4 Acoustic sensors High power Dummy Load (Load Tree) 20/27

  21. Processing history (Accumulated No. breakdown events vs. power @XTF @Nextef • RF pulse ranged 50ns to 400ns with 50MW at repetition rate of 50pps. • SUS003 had less breakdown events than CU002. • SUS003 attained higher electric field than Cu002. 21/27

  22. Breakdown rate as a function of pulse width of #SUS003 waveguide 104 120 134 [MV/m] 22/27

  23. #CU002 and #SUS003 after high-gradient experiments Observation area • Many breakdown damages were seen on the E-plane surface. • The surface is intensively damaged, and it could also melt due to breakdown. 23/27

  24. #CU002 Surface observation by SEM RF Laser microscope 24/27

  25. #SUS003 Surface observation by SEM RF Laser microscope 25/27

  26. Summary of narrow waveguide • We’re conducting the high-gradient experiments of Cu004 to confirm the previous data of Cu002 and to measure BDR of copper type. - Prototype Cu002 and SUS003 had been tested under different system conditions (at XTF and Nextef). - Number of break down events for SUS003 is less than that for Cu002 which may be a result of different systems . • We’re planning to testother materials. • We’re trying to make a new narrow waveguide; one side is made of copper and the other side is made of stainless-steel. We might know the surface damage of different materials at the same RF power. 26/27

  27. Thank you for your attention ! 27/27

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