Narrow waveguide experiments Kazue Yokoyama Toshiyasu Higo Yasuo

Narrow waveguide experiments Kazue Yokoyama, Toshiyasu Higo, Yasuo Higashi, Noboru Kudo, Shuji Matsumoto, Shigeki Fukuda, Mitsuo Akemoto, Mitsuhiro Yoshida, Tetsuo Shidara, Hiromitsu Nakajima Accelerator Laboratory, KEK

Introduction n n The study of characteristics of different materials on high-gradient RF breakdown at Nextef (New X-band Test Facility at KEK). Experiments performed using a narrow waveguide with field of approximately 200 MV/m at RF power of 100 MW. Status report on prototype copper (Cu 002) and stainless-steel (SUS 003) waveguides. The measurement system for the breakdown rate is set up now. 2

Contents 1. Design and Fabrication of Narrow Waveguide 2. Experimental Setup Ø Ø Ø CU 002 at XTF (old X-band Test Facility at KEK) SUS 003 at Nextef (New X-band Test Facility at KEK) Scheme of RF Processing 3. Results of High-Power Testing 4. Measurement system of BDR 5. Conclusion and Summary 3

Narrow Waveguide Design field gradient of 200 MV/m at an RF power of 100 MW group velocity of around 0. 3 c Rectangular Waveguide: WR 90 Wavelength converter: Width 22. 86( g 32. 15 mm) → 14 mm ( g 76. 59 mm) Cosine taper ( 1 g) : Height 10. 16 mm → 1 mm Calculated to get a low VSWR by an HFSS. 4

Fabrication Cu-002 SUS-003 Cu-004 material OFC SUS 316 L OFC anneal 500 C 1020 C 500 C processing milling, WEDM milling cleaning CP SUSpika CP bonding Cu/Au/Ni, hydrogen furnace Cu/Au hydrogen furnace VSWR @11. 424 GHz 1. 4 1. 12 1. 02 status Prototype Tested at XTF Under Testing at Nextef plan to be tested on June. ØAnnealing in a hydrogen furnace ØProcessing by milling and wire electrical discharge machining (WEDM) Ø 4 pieces for a narrow waveguide ØE-plane finished by milling. Øbraze bonding in hydrogen furnace Ø 10 m chemical polishing by acid 5

Cu 002 Setup for High-Power processing @XTF RF Narrow waveguide PMT 5 Acoustic sensors PMT 1, 2, 3, 4 High power Dummy Load ØThe first high-power test of copper(Cu 002) was done at XTF (previous Xband Test Facility at KEK). 6

SUS 003 Setup for High-Power processing @ Nextef PPM Klystron Narrow waveguide in 5 mm lead shield PMT 5, 6 Acoustic sensors PMT 1, 2, 3, 4 High power Dummy Load Ø Cu 002 n tested at XTF (06. 11～ 07. 01) n Moving to Nextef (～ 07. 04) n Using for system checking (～ 07. 05) Ø SUS 003 n Tested at Nextef (～ now) Ø We are on going high power testing of stainless-steel(SUS 003) at Klystron 7 Test Stand.

Processing Scheme @XTF Power ~25 MW Time (~8 h) n Ø n n n Interlock system -> a reflect power is large (vswr>1. 4) and vacuum degrades for RF component protection. Options: Controlled fixed time and power step RF breakdowns caused deterioration of vacuum Daytime processing 8

Processing Scheme @Nextef Ø Ø Power~30 MW Ø Control time step (flexible) Control power step by limiting Vac. (flexible) Processing time is almost 24 H. Pulse width 200 ns -> 400 ns Vac. < 1 E-6 Pa Power step Time (4 h) Ø We’re seeking for ways of processing. Vac. 9

Processing history (Accumulated No. breakdown events vs. power @XTF @Nextef Ø RF pulse ranged 50 ns to 400 ns with 50 MW at repetition rate of 50 pps. Ø Cu 002 had more breakdown events than SUS 003. 10

Accumulated number of breakdown events vs. P*T^0. 5 during processing @Nextef @XTF Ø The temperature related parameter, P*T 1/2, attained approximately 400 MW ns 1/2 of Cu 002 and 900 MW ns 1/2 of SUS 003. P*T^0. 5 – the product of RF power and the square root of the pulse width 11

Results of Cu-002 and SUS-003 n SUS 003 attained higher electric field than Cu 002. 12

RF Power vs. number of BD events @XTF n Many breakdown events at pulse width > 100 ns and power 20 MW. @Nextef n n Few RF break down events at 50 ns and 100 ns. We had a guard window problem around 200 ns. 13

BD Measurement System n n oscilloscope A rf pulse is detected with a crystal diode and a OSC that calculates a power, vswr and power loss. After processing, we’ve measured the rate of breakdown events at a constant power for one day at 50 pps. 14

Data taking from OSC n n n 10 pulses at a System down (HV, Reflected trigger and rf off). Changed pulses with Forward 5 % form a normal pulse (area and peak). Transmitted Estimated power, vswr and power loss We are testing this Reflected upper stream system now. Problem is pulse shape is unstable from pulse to pulse n Typical rf pulses at a breakdown events. (rf jitter, rf power and noise). 15

Cu 002 After high-power processing top body Observation area ØMany breakdown damages were seen on the E-plane surface. ØThe surface is intensively damaged, and it could also melt due to breakdown. 16

Observation of Breakdown surface (top) by SEM and Laser Microscope 27. 70 m 17

Conclusion n n n RF breakdown studies on different material has just begun. Prototype Cu 002 and SUS 003 had been tested under different system conditions. Number of break down events for SUS 003 is less than that for Cu 002 which may be a result of different systems. We’re testing a processing scheme. We’re going to observe the surface of SUS 003 after measuring BDR. We’re going to test Cu 004, other stainless-steel waveguides and other materials. 18

Thank you for your attention. ! 19

Summary Cu-002 SUS-003 Cu-004 material OFC SUS 316 L OFC anneal 500 C 1020 C 500 C processing milling, WEDM milling cleaning CP SUSpika CP bonding Cu/Au/Ni, hydrogen furnace Cu/Au hydrogen furnace VSWR @11. 424 GHz 1. 4 1. 12 1. 02 status Prototype Tested at XTF Under Testing at Nextef next month Power @ 50 - 400 ns [MW] 40 - 20 < 55? – 45 Field @ 50 -400 ns [MV/m] 140 - 100 < 140? - 120 P*T 1/2 [MW ns 1/2] 400 900 BDR × measured now Observation of surface SEM, Laser Microscope next month? 20

Breakdown location PMT 6 PMT 5 Area of frequent breakdowns Cu-002 Acoustic sensors ? 21