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

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

3/27 T18_VG2.4_Disk #2 T18_VG2.4_Disk #2 was installed and the processing has started in October last year.

4/27 Nextef: RF Monitors along waveguide

5/27 Nextef: Monitors along beam axis 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. RF

T18 trend 6/27

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

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

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

Dark Current F-N plot 10/27

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

12/27 Summary of 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.

13/27 TD18_VG2.4_Quad_#5 Quadrant

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

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

Meas. At 11416MHz, 20.3degC Average phase advance = deg/cell dF ~ (1.9/120)*11424*0.0138~ ( ) ~ MHz Average phase advance per cell degrees / cell /27

Summary of TD18_VG2.4_Quad_#5  The frequency of the present quad #5 at operation becomes MHz.  Freq. = MHz 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. v=c Drive freque ncy Actu al 17/27

18/27 Narrow waveguide Parts before bonding

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

CU004 Setup for High-Power Nextef  We are on going high power testing of coupper(CU004) at Klystron Test Stand. PPM GHz 50 MW, 50 pps, 400ns Narrow waveguide in 5mm lead shield High power Dummy Load (Load Tree)  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 ～ ) 20/27 PMT 1, 2, 3, 4 Acoustic sensors

Processing history (Accumulated No. breakdown events vs. power  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 21/27

22/ [MV/m] Breakdown rate as a function of pulse width of #SUS003 waveguide

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

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

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

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 test other 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

Thank you for your attention ! 27/27