1. Status and plan for X-band high field experiments at KEK US High Gradient Collaboration Workshop University of Maryland Jan. 23-24, 2008 KEK T. Higo

2. Contents KEK road map Plans of X-band activities Collaborations with SLAC and CERN Nextef commissioning NWG on-going test Surface creation for basic high-gradient studies Structure fabrications Conclusion

7. X-band strategy X-band activity is not explicitly written in the road map. However, We understand –the accelerator laboratory and KEK DG support the study for high gradient, at least spiritually, –but also hopefully with some budgetary support JFY08 KEK is progressing to engage –MoU between SLAC and KEK on advanced accelerator research including high gradient study, provably under US-Japan collaboration framework. –Agreement of collaboration between CERN and KEK including high gradient study.

8. Gross plan of X-band activity at KEK 2006 2007 2008 2009 2010 Trial fabrication Low power test Feasibility of CLIC scheme Narrow waveguid e SLAC short-cell stack High power / high field experiment at New XTFHigh power test GLC acc structu re CLIC equivalent, acc structure Basic structure ・・・ CLIC acc structure ・・・ Design electrical and mechanical Fabrication of actual acc structure Fabrication of CLIC equivalent. acc structure High power test at SLAC and CERN We are basically along the same plan as this, but probably taking a little more time, extending beyond 2010. (Taken from presentation by Matsumoto in the last workshop last June)

9. Nextef progress Establishing power generation and transport in 2007

10. Nextef inside shield room most basic components are now in line.

11. Nextef components in shield room SLAC 3dB 60cm KX03 structure Lounine Load (based on SLAC design) Ohtsuka Load Guard window TE01-type IP 30l/s WR90 DC made by BINP

12. Nextef commissioning in 2007 Independent Klystron operation in Sep. Two-klystron operation in Oct. Power feeding to structure in Nov.-Dec. Skip structure and establishing high power capability in Jan. ‘08 Now 24 hr/d running (during linac operation) at ~20MW, 50ns, 50Hz level.

13. Now increasing the system power after back to skipping structure RF Pulse shapes Automatic control by seeing VAC level Trend of RF power and VAC level The very basic features are now working. We need sophistication of the system and establishment of high power level.

14. Nextef near future plan

15. Various detection tools are to be integrated into Nextef control system System control PC Python, Linux TDS3034B (300MHz) TDS3054B (500MHz) DPO7104 (1GHz) VME Acoustic (SLAC) Mod. PLC Acc PLC CCG RF crystal Various signal CT FCAM Data storage KEKB Inj. control DL7480 (500MHz) History 4MW/ch Modulator Klystron LLRF FPGA (100MHz) S/H & DC Amp Discri Acoustic INTLKSafety X-ray Etc. X-ray Yet to be implemented

16. Future problem: Time / area sharing in Nextef among X + C + S? For a C-band RF unit preparation –Two acc. structures are tested at the same area as Nextef in 2009 spring-summer. –Though probably Super KEKB will not use C-band for energy exchange. S-band acc. structure processing –When needed for e+ area usage, we should do it. We may need to operate the C-band (and S- band in principle) setup in “Nextef” area for three months or so in 2009!? Best is to expand the area under management- level decision.

17. Basic high field study with narrow waveguide (NWG) Started study at GLCTA –Cu-002 (first copper) in 2006 Restarted at klystron assembly hall in 2007 –Cu-002 Baking troubles in a new setup Tested, cut and inspected, Cu-004 study copper again in an established setup –SUS-003 (first SUS) tested Troubles in baking again but studied up to the max available power level Tried BD rate evaluation, but found it difficult We want further to –Test the same sample in a different places to compare criteria of processing and breakdown –Refrain study one made in the same manner to get variations and statistics.

18. Surface field at 100MW power flow high magnetic field in addition to high electric field TypeWidthHeigh t vg/cEyHxEy / Hx mm %MV/mkA/m  WR90 (standard) 22.8610.12822861460 SLAC high magnetic field (low impedance) 22.861.38279171460 SLAC low magnetic field (high impedance) 13.3310.121880372137 KEK Narrow waveguide (actual HFSS) 14135 176 (150- 215) 163 (???) 1080 (???)

19. NWG test setup and some result Baking 2 nd one (out of three times) NWG setup with a klystron Effect of baking at 200 degC with leakage trouble!? Installation in April after Cu-002 Baking at 200 C vac leakage two times (at low temp) Processing moderately (!?) Suffered from Modulator inverter power supply Klystron pulse shortening TE01 guard window acivity But almost reached the system power limit ~ 50MW Now remove SUS-003 and start processing the system again toward higher power level.

20. Processing and identification of event Program controlled processing By seeing VAC level INTLK with increase of RF reflection, light from window, etc Oscilloscope view taken as a picture Analyze with RF shapes and X-rays. Klystron pulse shortening Breakdown at narrow waveguide triggered by NWG discharge? Power VAC Klystron Output RF reflectLight from GW Transmitted RF

21. Evaluation of high field performance Calibration of power and the method of evaluation of high field are under way. We want to compare this result to other experiments. Power level to be recalibrated. Rate evaluated during four hours.

22. Why limited at so low field level Due to large magnetic field? –108 degC rise at 400ns with 50MW –Comparing to copper with 30 times less rise Large power density? Material preparation? Processing criteria? –Slow ramping with keeping good vacuum ~10 -6 Pa  Do copper study again

23. Materials preparation for basic studies on E and H field Higashi has been collaborating with Dolgashev of SLAC –Test in SW and TW in a-cell or three-cell setup –Test of magnetic field in TE01 mode cavity –Materials and surface preparation Copper, Moly, OFC, 6N, single crystal, … Rinsing method Baking in a close volume until just before installation to high power setup We want to proceed this-type of study also at KEK. –Which shield room? Not yet determined.

24. SLAC chemical etching procedure Frontier Cleaner A02 + Megasonic (3 min x 3 time) Ultra-purer water + Megasonic (5 min) IP (50degC, 5min) Diffusion bonding + Brazing (Structure completed) Frontier Cleaner A02 + Megasonic (3 min x 3 time Ultra-purer water + Megasonic (5 min) IP (50degC, 5min) Baking (300-500 degC, 5days) Purged N 2 Shipping to SLAC and installation in high power test stand Semiconductor rinsing technologies

25. Pulse heating (TE01) test sample Designed by G. Bowden 76.0 +/- 0.05 67.46 6.0 +/- 0.05 7.2 4.32 4.24 Drill through 6 holes EQ spaced Defects (dislocation, hole, impurity): scattering of conduction-band electron makes non-vector field  Electrical conductivity? Stress due to dislocation: not continual body of elastical material. What happens with annealed 6N copper? What about HIP copper? What about single crystal 100-face copper (100)? Single crystal

26. Pulse Heating Test Samples 6N copper, Single crystal(100) Finished by Diamond Tuning Surface conditions As received 800 degC. 3days annealing HIP HIP + Chemical Etching

27. Fabrication of structures for high gradient study Target –Extend SLAC/KEK X-band legacy to recent CLIC approach. Framework –Electrical design by CERN –Mechanical design and fabrication by KEK and SLAC –Assembly and tuning at SLAC and/or KEK –High power rest at SLAC and KEK until CERN stand-alone system is established Three CLIC_VG1 in collaboration with CERN and SLAC –T18_VG2.4_Disk –Assembly and testing are being done by SLAC and KEK –These structures serve as a cross referencing. Quadrant-type CLIC structure –T18D_VG2.4_Quad –Pilot study was done with five vendors. –We plan to proceed a structure fabrication by next summer.

28. Disk based structure: fabrication in the same manner as previous SLAC/KE X-band collaboration for GLC Bead pull by KEK Chemical treatment and bonding by SLAC Parts fab. by KEK and ship to SLAC

29. Quadrant : fabrication of short test parts and measurement by ZEISS CMM at KEK

30. Obtained reasonable quality to proceed to full quadrant test fabrication Item / Present / Next program Local profile shape control: OK with deviation from design within specified 2.5 microns. Absolute profile shape : Positioning is to be studied in a full-size fabrication study. Roughness: Ra ~ 0.2 – 0.4 micron. improvement to Ra~0.1 micron within a reasonable cutting time is to be studied. Edge treatment: Burr within a few 10 microns level. 50- micron radius is to be studied. Other high field related issues?:

31. Local profile shape within +-2.5 microns from design (Case: U-corp)

32. Surface roughness (Case: U-corp) Present Ra ~ 0.2—0.4 micron  To be studied in actual full-size fabrication: whether to reach specified Ra~0.1 micron

33. Spurs with carbide tool (case of YADSA) 2 1 3

34. Conclusion Nextef hardwares are now ready. System high power operation is ongoing. Additional sophisticated measurement tools are to be established. A series of tests of CLIC-directed structures will be from coming March. We continue basic studies on high gradient with varying surface treatment and material. Formal collaboration frameworks are being established with CERN and SLAC. Through proceeding the above actions, high gradient X- band activities in KEK will be more formally acknowledged.