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Narrow waveguide experiments

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

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Narrow waveguide experiments

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

  2. Introduction • 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 (Cu002) and stainless-steel (SUS003)waveguides. • The measurement system for the breakdown rate is set up now.

  3. Contents 1. Design and Fabrication of Narrow Waveguide 2. Experimental Setup • CU002 at XTF (old X-band Test Facility at KEK) • SUS003 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

  4. 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.

  5. Fabrication • Annealing in a hydrogen furnace • Processing by milling and and wire electrical discharge machining (WEDM) • E-plane finished by milling. • 10 m chemical polishing by acid • 4 pieces for a narrow waveguide • braze bonding in hydrogen furnace

  6. Cu002 Setup for High-Power processing @XTF RF Narrow waveguide Acoustic sensors PMT5 PMT1, 2, 3, 4 High power Dummy Load • The first high-power test of copper(Cu002) was done at XTF (previous X-band Test Facility at KEK).

  7. SUS003 Setup for High-Power processing @ Nextef PPM Klystron • We are on going high power testing of stainless-steel(SUS003) at Klystron Test Stand. Narrow waveguide in 5mm lead shield • Cu002 • tested at XTF (06.11～07.01) • Moving to Nextef (～ 07.04) • Using for system checking (～ 07.05) • SUS003 • Tested at Nextef (～ now) PMT 5, 6 Acoustic sensors PMT1,2,3,4 High power Dummy Load

  8. Processing Scheme @XTF Power ~25 MW Time (~8h) • 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

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

  10. Processing history (Accumulated No. breakdown events vs. power @XTF @Nextef • RF pulse ranged 50ns to 400ns with 50MW at repetition rate of 50pps. • Cu002 had more breakdown events than SUS003.

  11. Accumulated number of breakdown events vs. P*T^0.5 during processing @Nextef @XTF • The temperature related parameter, P*T1/2, attained approximately 400 MWns1/2 of Cu002 and 900 MWns1/2 of SUS003. P*T^0.5 – the product of RF power and the square root of the pulse width

  12. Results of Cu-002 and SUS-003 • SUS003 attained higher electric field than Cu002.

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

  14. BD Measurement System 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.

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

  16. Cu002 After high-power processing top body 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.

  17. Observation of Breakdown surface (top) by SEM and Laser Microscope 27.70 m

  18. Conclusion • RF breakdown studies on different material has just begun. • Prototype Cu002 and SUS003 had been tested under different system conditions. • Number of break down events for SUS003 is less than that for Cu002 which may be a result of different systems . • We’re testing a processing scheme. • We’re going to observe the surface of SUS003 after measuring BDR. • We’re going to test Cu004, other stainless-steel waveguides and other materials.

  19. Thank you for your attention. !

  20. Summary

  21. Breakdown location PMT6 PMT5 Area of frequent breakdowns Cu-002 Acoustic sensors ?

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