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High Gradient tests at the KEK Nextef Facility

WE08 XB-10 . High Gradient tests at the KEK Nextef Facility . Shuji Matsumoto On behalf of Nextef Group Accelerator Laboratory, KEK. Contents. Three topics I will report today are as follows.

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High Gradient tests at the KEK Nextef Facility

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  1. WE08 XB-10 High Gradient tests at the KEK Nextef Facility Shuji Matsumoto On behalf of Nextef Group Accelerator Laboratory, KEK XB-10 Cockcroft Institute

  2. Contents Three topics I will report today are as follows 1) Review of two X-band high power stations in KEK; Nextef, the 100MW X-Band test station and KT-1, 50MW. 2) Recent high power test results of TD18_Disk#2 (a CLIC prototype structure with HOM damping slots). 3) A overview of our on-going programs such as the pulse compression system of Nextef as well as the future plans of X-band study. XB-10 Cockcroft Institute

  3. Nextef facility Nextef stands for NEw X-band TEst Facility. Mission • Nextef was proposed in 2006 and was constructed in 2007 as a reassembled facility of GLCTA to be a 100MW high power station for the X-band accelerating structure tests. • Since 2008, the facility runs for the development of CLIC prototype high gradient accelerator structures (of 100MV/m or beyond). The collaboration program is ongoing. KT-1 • A 50MW facility originally started as an X-band klystron test station in 2006. • Small experiments utilizing the klystron power are performed. XB-10 Cockcroft Institute

  4. Nextef facility Nextef100MW X-Band station in KEK • y/m • 2007/8 Start operation • 2007/12 Commissioning Power production went upto 100MW • 2008/1 Start Retest of KX03 • 2008/9 Start test of T18 • /7 Start TD18Quad#5 test. • 2009/12 Starts TD18Disk2 test. • 2010/11 T24Disk installed. Ready to start testing • Features • Combined power of klystrons to produce 11.424GHz RF of peak power above 100MW (maximum power available depends on the pulse width). • Use of PPM klystrons (originally developed for GLC project). • Associated with a concrete shield (Shield-A) which is fully equipped for the structure high power tests. • No beam available. XB-10 Cockcroft Institute

  5. Nextef facility Nextef station configuration A: Modulator B: Klystrons C: Low Loss Power Transfer Line D:Accelerating structure under test in Shield-A (5m W x 3m D x 2m H) • The modulator drives two 50MW PPM klystrons. • The combined power is transferred into Shield-A. • Local control room (not shown in this picture). XB-10 Cockcroft Institute

  6. Plan View inside Shield-A observables along beam axis Nextef facility ACC str:Structure under test FC: Faraday Cup, PM: Profile Monitor, AM: Analyzer magnet, GV: Gate Valve. Comment: Some of the details are incorrect. The drawing should be updated. XB-10 Cockcroft Institute

  7. Nextef facility Frequency 11.424GHz Max power production 100MW Max power for test * 75MW Pulse width 400ns Repetition rate 50pps Performance • 24Hr operation is possible due to the linkage with KEKB Linac operation. (The linac operation=6000Hr/year.) • Local control as well as a remote control through Linac control system. • Possible to store / handle the operation data as well as experimental data through Linac control system (LINUXand EPICS). Specifications * Measured Transmission Loss is 25%. XB-10 Cockcroft Institute

  8. Nextef facility What we have achieved : Nextef • Continuous run established (Total RFON time is more than 20000hrs from 2006) . • Maximum power 70MW, 250ns, 50pps for recent structure tests. • The maximum power production is about 100MW. It is practically determined by the performance of one of the klystrons: Frequent Klystron gun breakdowns occur in one of the klystrons at the cathode voltage above 460kV. Below this voltage klystrons are stable. XB-10 Cockcroft Institute

  9. Nextef facility KT-1 : 50MW X-band test station (y/m) 2006/ 5 Start operation (as an X-band klystron test stand) 2006/6 Klystron test (PPM6A) 2007/1 Started to run for “small experiments” 2008/5 Narrow waveguides (SUS003 followed by CU005) testing. 2009/9 Testing RF Loads • Features • Use of a single PPM klystron, 11.424GHz RF of peak power of 50MW, 400ns is available. This station runs for small-size experiments such as a narrow waveguide and RF component test (e.g. RF load). • The current klystron sitting at KT-1 is old (constructed in 2003, repaired 2004) but it has been healthy so far. • 24Hr operation is possible. • This station is rather crucial for Nextef, since sometimes we need to check the performance of the high power devices before their installation. XB-10 Cockcroft Institute

  10. Nextef facility Test done at KT-1, an example.Test of CERN Cinel load and KEK Waveguide valve Lead Box (It is opened at this moment) RF CERN CINEL High power RF Load KEK Waveguide valve 2009.10.28 XB-10 Cockcroft Institute

  11. Nextef facility KT-1 (50MW) Nextef (100MW) Modulator and twin ppm klystrons Klystron test, small experiments (in Lead shield box) or component tests Test area in the bunker(Sheild-A) We are operating two X-band high power stations XB-10 Cockcroft Institute

  12. Nextef facility Frequency 11.424GHz Peak Power 75MW Pulse width 1.6ms Repetition 150Hz Cathode Voltage 480kV Cathode Current 266A Perveance 0.8uK Efficiency >55% Main Focus PPM Max B / period 0.32T / 30mm Magnet Material NdFeB Klystrons We have two(at Nextef)+one(at KT-1) ppm klystrons in operation and one spare. (“ppm” stands for “periodic permanent magnets”.) Spec of Nextef klystron: originally designed as a 75MW klystron for GLC project. XB-10 Cockcroft Institute

  13. Nextef facility X-band klystrons Result of high power testing. PPM4 (2003). We usually operate it at 50MW 400ns 50pps maximum. One tube has frequent gun breakdowns when it is operated more than at ~460kV. The performance of our X-band ppm focus klystron has a limit in available peak power and pulse width by RF instability. So far the tubes are good enough for our purposes. XB-10 Cockcroft Institute

  14. TD18 Test Structure Test Procedure:How the research Collaboration works Design for CLIC (CERN) High power test (NLCTA-SLAC) High power test (Nextef-KEK) Fabrication of parts (KEK) CP (SLAC) VAC bake (SLAC) Bonding (SLAC) Two structures are made and treated as the twin for the evaluation. XB-10 Cockcroft Institute

  15. TD18 Test Test structures made as twins T18_Disk_#2 TD18_Disk_#2 XB-10 Cockcroft Institute

  16. TD18 Test Unloaded 100MV/mT18 TD18 T18 unloaded 100MV/m TD18 unloaded 100MV/m Es Sc Sc Es P (MW), Es (MV/m), Ea (MV/m), DT(C), Sc*50 (MW/mm2) P (MW), Es (MV/m), Ea (MV/m), DT(C), Sc*50 (MW/mm2) Ea Ea P P DT DT Iris number Iris number XB-10 Cockcroft Institute

  17. TD18 Test Processing of damped structures TD18_Disk_#3 tested at SLAC TD18_Disk_#2 tested at KEK Total # BD Pulse widrh (ns)/10 Eacc (MV/m) 3000 2000 1000 0 RF-ON period (hrs) Big difference in ramping speed. (may be partially due to the difference in processing procedure) Both reached 100MV/m 240ns. XB-10 Cockcroft Institute

  18. TD18 Test Breakdown rate Damped structure: High pulse temperature rise? Any other mechanism? Single-cell SW test also shows tight correlation of BDR to pulse temperature rise. Helps if reducing temperature rise? See the result of TD24 to be tested in several months. T18 vs TD18 Undamped vs Damped SLAC vs KEK Sensitive to Eacc (Es, Hs) ~ X10 / 5 (MV/m) BDR(damped) ~ 100 X BDR (undamped) XB-10 Cockcroft Institute

  19. TD18 Test TD18_#2 all BDR versus Eacc It seems difficult to get a smooth curve as function of Eacc by collecting all data points scattered in time and in operation parameter space. Usually we get a smooth curve by measuring intentionally with focusing to take data of BDR vs Eacc!? XB-10 Cockcroft Institute

  20. TD18 Test Breakdown rate versus width or DT TD18_Disk_#3 BDR versus DT (pulse temperature rise) T18_Disk_#2 BDR versus pulse width Damped Undamped Tight correlation with pulse temperature rise. Same at 100MV/m but pulse length  DT Same DT 83~84 degC but diff. Eacc Tight correlation with pulse width. XB-10 Cockcroft Institute

  21. TD18 Test TD18_#2 Evolution of breakdown rate XB-10 Cockcroft Institute

  22. TD18 Test TD18_#2 BDR versus widthat 100MV/m around 2800hrand at 90MV/m around 3500hr The power of the width depends on Eacc. XB-10 Cockcroft Institute

  23. Evolution of dark current till early April in TD18_Disk TD18 Test IPAC10 Dark current reduced by three order of magnitude. It followed roughly modified F-N formula. b reduced from 70 to 40. b * Esmax ~ 5~7 GV/m XB-10 Cockcroft Institute

  24. TD18 Test Presented to IPAC10 Comparison of dark current T18_Disk TD18_Disk TD18_Quad TD18_Quad Eacc for peak dark current of 10 mA 90MV/m 70MV/m 40MV/m XB-10 Cockcroft Institute

  25. TD18 Test Summaryof TD18_Disk#2 testing • Testing of TD18_Disk#2 structure isfinished successfully. • Breakdown rates were and is being measured. It is 10-4/pulse/m at 100MV/m at 252nsec. It is fair to conclude that BDR of TD18_Disk#2 is greater than that of T18 by about one-two order of magnitude (depends on Eacc). • The amount of dark current has been decreasing by a few order of magnitude during the test (over some 2000hrs) and became very similar to that of T18. • The field enhancement factor, beta, has decreased by factor of 2. The final value is some 40. • Dark current was initially reduced but recently has been saturated. XB-10 Cockcroft Institute

  26. TD18 Test • A few attempts to understand the properties of RF breakdowns in the structure were done: operation with RF double pulses, operation with additional eight pulses after an RF reflection interlock and operation with switching RF input power periodically. • I quickly show the latter two results. XB-10 Cockcroft Institute

  27. TD18 Test Run 98 switching in three power levelsfor 46.2 hours Histogram of pulses in terms of Eacc Input power (MW) Input power (MW) 90 – 95 – 100 MV/m RF pulse counts Nicely separated with each other. Pulse width=252ns Switching every second among three power levels, controlled by Ushimoto program. XB-10 Cockcroft Institute

  28. TD18 Test Run 98 43 Higher power pulse makes bigger BDR. We compare this result to the usual BDR plot… 8 1 3.3*10-6 / 2.6*10-5 / 1.4*10-4 [BD/pulse/m] XB-10 Cockcroft Institute

  29. TD18 Test Relevant data points of BDR vs Eacc Data points from jumping among three levels XB-10 Cockcroft Institute

  30. TD18 Test Run 100 at 100 MV/m level Behavior of eight pulses after BD More than 50% of breakdowns are not accompanied by any consecutive breakdowns. Some are followed by breakdowns. Correlation between number of consecutive breakdowns and the hardness of the initial breakdown should be evaluated. XB-10 Cockcroft Institute

  31. TD18 Test Vaccum issuesVacuum at low power level Acc Input power Pressure @IN-WG Outgassing is observed at the monitor located at left arm of Acc output port when the power comes down (about a few MW) . Exact location of the outgas has not been identified yet. We inserted a long waveguide (and put an additional pump) between the structure and the load to “separate” the vacuum. We expect better vacuum due to the added pump but … XB-10 Cockcroft Institute

  32. TD18 Test T18 opeartion started TD18 6.3E-5 T24 4.0E-6 1.0E-6 2.5E-7 It does not change so much now. We will watch the behaviour. XB-10 Cockcroft Institute

  33. Future plans Demands for system upgrade There are always demand to improve the performance of a facility. Of course this is true for us.. For example, we have a room to improve the peak power of Nextef by introducing a relevant pulse compressor system, which should be useful for accelerating structure studies. Also from a technical point of view, this should be somewhat important for us to actually handle extremely high power over one hundred MW. We have started this upgrade work within the same framework of collaboration between three labs. XB-10 Cockcroft Institute

  34. Future plans Nextef Pulse Compressor • A pulse compression system (PCS) will be installed in order to improve the peak power of Nextef 100→150MW. 100MW power available for structure tests. • A practical solution to getting higher peak power, necessary for the structure • tests in the future. • Use of single delay line (circular waveguide of phi 80mm). The line partially exists already as a C-band transmission line in Nextef experimental area. The circular polarized TE11 mode in X band is employed to store energy in this line. • The compression gain of 3 expected. Final power of 150MW 150ns pulse width is expected in Phase 1. • PCS INPUT :X-band PPM Klystrons: 25 MW each X2 X 750ns • PCSOUTPUT: Gain 3 → 150MW, 150ns. • In Phase 2 we utilize TE12 mode also to obtain 300ns output pulse while the peak power will be kept. XB-10 Cockcroft Institute

  35. Nextef Delay Line Pulse Compressor Future plans 22m - One Channel 25 MW×2 Klyston ×gain=3 → 150MW TE11L Klystron 750ns → 150ns Gain = 3.6 @ 3dB Phase1 Accelerator TE11R Tunable reflector TE11 Mode Converter Upgrade possible if we use a higher mode. TE11L Klystron 1500ns → 300ns Gain = 3.3 @ 3dB Phase2 TE12R TE12L Accelerator TE11R TE11-TE12 Reflector (Mode exchanger) XB-10 Cockcroft Institute

  36. Nextef pulse compressor Layout Future plans The reflector will be put. 22m Delay line Originally constructed as the C-band transmission line in 2009 and will be converted as the X-band delay line for pulse compressor. C-band RF Source (will be removed.) X-band RF Source A PCS header (3dBHybrid+Mode Launcher) XB-10 Cockcroft Institute

  37. Future plans Production of RF components:Kazakov Mode Converter (Rect TE10→Circ TE01) Noboru Kudoh XB-10 Cockcroft Institute

  38. Parameter choice / klystron stability Future plans 25MW,0.75us pulse compression pulse compression Phase 2 50MW,0.25us: current operation point The points reflect the limit of the RF instability XB-10 Cockcroft Institute

  39. Future plans Improvement Plan for KT-1 Demand: There has been some requests on the testing of the cavity structures such as single cell structures, short structures, so on. Those experiments do not require much power and it can be provided by our single klystron. Problem: However it is difficult to perform these programs at current KT-1 station where only a small lead box is there for small experiments. It is not practical to make a good shield nearby. Solution: A simple solution is to use Shield-B which locates in next door. This can be done by constructing a new power transfer line. XB-10 Cockcroft Institute

  40. Future plans Power delivery from KT-1 to Shield-B We are able to start basic studies with structures using this test setup, though it sacrifices the usual KT-1 klystron activities (=Klystron test) somehow. This experimental activities should complement the series of high gradient tests on CLIC prototype structures proceeded at Nextef. XB-10 Cockcroft Institute

  41. Future plans Nextef X-band Shield-B Lead Box (now working for small experiments) Delayline Reflector KT-1 X-band KT-2 XB-10 Cockcroft Institute

  42. Future plans Whole Configuration of the Proposed Power Line from KT-1 to Shield-B The power from the klystron is transmitted through the circular waveguides (40mm diameter) with TE01 Mode. Those circular pipes, bends and vacuum ports are common to those used in the pulse compressor. XB-10 Cockcroft Institute

  43. Future plans Status Components: More than 80% fabricated. A hole was made through a wall between KT1 and shield-B. Installation of KT1-B in early next year. Pulse compression setup will follow KT1-B setup. XB-10 Cockcroft Institute

  44. Future plans Nextef and KT-1 as of 2011 KT-1toB Nextef with PCS A B XB-10 Cockcroft Institute

  45. Future plans Summary: Future plans Most of the components of those lines for Nextef Pulse Compressor and KT-1to B are in the final stage of the fabrication. The whole parts will be ready for construction soon. The construction depends on the schedule of the testing in Shield-A and –B. The construction work will start in the end of this year. We expect the power of more than 100MW * with 150ns pulse width in Nextef as well as that of 35MW *, 400ns in Shield-B available. * Due to the transmission loss. XB-10 Cockcroft Institute

  46. Nextef near future plan revised as of IWLC10 2010 2011 2012 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 TD18_Disk #3 T24_Disk #3 A TD24_Disk_R05 ?? ?? TD24_Disk #3 Components fabrication ?? PC commissioning PC Construction C-band Structure Test Construction in shield-B B X-band basic studies KT1  B connection PPM6B, Component tests, NWG test or serving shield-B, ……. KT-1 XB-10 Cockcroft Institute

  47. Conlusions Nextef, a 100MW X-band power station in KEK, has been running for the test of high gradient structures in last three years. The facility is dedicated for CLIC prototype structure tests in the framework of an international collaboration. High power test of the structure TD18_Disk, the structure with damping slots has been over. The basic time trend of the BDR is and it is fair to say that its final value is from ten to hundred times higher (the factor depends on Eacc) than that of T18 structure. Works for the future plans are ongoing to establish the higher peak power at Nextef and to provide a new experimental area (Shield-B) for KT-1. XB-10 Cockcroft Institute

  48. 5th Collaboration Meeting on X-band Accelerator Structure Design and Test Program Date: May 16th to 18th , 2011 Place: Seminar hall of 4th building, KEK, Tsukuba, Japan (KEK Homepage: http://www.kek.jp/intra-e/) Chaired by K.Ueno (KEK). Organized by T.Higo(KEK) S.Tantawi(SLAC) W. Wuensch(CERN). XB-10 Cockcroft Institute

  49. Now we suppose those issues to be covered: • Structure design: electrical and mechanical • Manufacturing of parts; disks, couplers and loads • State-of-the-art precision machining • Fabrication of quadrant/half structure • Experimental study on high gradient performance • Breakdown physics and simulations • On-going and possible new collaborations • …. Others In this 5th collaboration meeting, we set one day dedicated for the effort to understand and suppress the vacuum breakdowns in addition to the usual collaboration meeting. Especially we try to introduce those activities ongoing in Japan for making perfect or special surface based on the state-of-the-art precision machining technology. Details and registration procedures will be posted at conference web site soon. See you in Tsukuba in next spring! XB-10 Cockcroft Institute

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