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IHEP 1.3GHz High Power Input Coupler R&D Progress

IHEP 1.3GHz High Power Input Coupler R&D Progress. Pan Weimin, Huang Tongming , Ma Qiang IHEP High Power Input Coupler Research Group. R&D Background. High power input coupler is one of the key components of IHEP 1.3GHz SCC program.

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IHEP 1.3GHz High Power Input Coupler R&D Progress

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  1. IHEP 1.3GHz High Power Input Coupler R&D Progress Pan Weimin, Huang Tongming, Ma Qiang IHEP High Power Input Coupler Research Group 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  2. R&D Background High power input coupler is one of the key components of IHEP 1.3GHz SCC program. Through carefully investigating and considering our fabrication experiences, we choose the STF baseline type coupler as IHEP 1.3GHz coupler design prototype. In phase I, we aim to fabricate a fixed coupling coupler; and in phase II, a variable coupling coupler will be designed and fabricated. STF baseline type coupler High power input coupler 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  3. Coupler specification 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  4. Outline 1. 1.3GHz coupler Design Have done To be done 2. 1.3GHz coupler Fabrication 3. 500MHz high power test stand 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  5. 1. 1.3GHz Coupler Design • Power transmission performance optimization • Resonant modes near window analysis • Window E-Field analysis • External Q calculation • Multipacting effect analysis • Thermal and stress analysis (static & dynamic heat losses) • Ceramic window position (at minimum E-Field) • Impedance matching: Coupler + Test stand • Other? Have done To be done 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  6. Cold part Warm part doorknob RF structures • Two Tristan type windows; • Cold coax: 50 Ohms, 60mm diameter; • Warm coax: 50 Ohms, 81mm diameter; • Flexibility: 4 bellows in the warm coax; • Doorknob: WR650 waveguide- coax with 104mm diameter transition; • Ceramics: 95%/99.5% Al2O3 with TiN coating on vacuum side • Copper plating (refer with TTF3, need calculated to decide): • 10/30 um on 1mm stainless steel warm outer/inner coax • 5um on 1mm stainless steel @ cold coax 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  7. Doorknob Two parameters belong to the doorknob( highlighted with yellow) have been modified to get the optimum power transmission performance. 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  8. Warm Part Warm window Bellow 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  9. Cold Part Cold window 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  10. RF simulation with HFSS E-field @Traveling wave,1MW H-field with Traveling wave,1MW 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  11. Power Transmission Performance The |S21| frequency sweep curve describes the power transmission performance: Mag(S21)=0.9974@1.3GHz shows a good RF structure design from the view of power transmission. Passband: 200MHz when VSWR<1.1; 250MHz when VSWR<1.2 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  12. Resonant Modes Near Window Analysis Both the warm window and cold window are Tristan type (coaxial, disk, with choke). The window structure should avoid resonant modes in operation frequency or its double/third/fourth…frequency, such as: 1.3GHz、2.6GHz、3.9GHz…… Cold window Warm window 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  13. E-Field near window • During the window design, we should try to reduce the E-field on ceramic surface, especially air side: keep the maximum E_feild far below air breakdown E_field : 30kV/cm • E_field alone the radius direction of the warm window (ie the radius E_feild on air side of warm window ): Maximum Mag_E: 8.23kV/cm, @ 1MW, TW, 325deg. 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  14. E_field around the inner circle of warm window (ie the inner ceramic-OFHC brazing area of warm window): Maximum Mag_E : 8.23kV/cm @1MW,TW,325deg 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  15. E_field around the inner circle of cold window (ie the inner ceramic-OFHC brazing area of cold window ): Maximum Mag_E: 5.62kV/cm @1MW,TW,250deg 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  16. E_field alone the radius direction of the cold window (ie the radius E_feild on air side of cold window ): Maximum Mag_E : 6.89138kV/cm@1MW,TW,200deg 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  17. Qe calculation It is very important to predict the coupling between the cavity and the high power input source in the coupler design. So Qe was calculated carefully, which discusses the positioning of the high power input coupler. 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  18. In order to faster solving, the model was reduced to 4.5-cell since Qe scales with the number of cells. The field flatness in every cell should be assured before the coupling analysis. Two parameters related with Qe were studied: 1) the coupler input port position; 2) the antenna penetration depth; E-field distribution on Z-Plane Model of 4.5-cell and simplified coupler field magnitude along the on axis curve Parameters related with Qe 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  19. Qext change VS antenna penetration depth To obtain the optimum 2×106，we can: Choose the distance from end cell to coupler port center D=55mm, adjust the antenna penetration near 4mm; Choose the distance from end cell to coupler port center D=60mm, adjust the antenna penetration near 8mm; • beam tube = 80mm • input port = 60 mm Distance from end-cell = ‘D’ The blend radius of antenna tip: R_tip=3mm Coaxial line = 50 W 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  20. Multipacting as a design criteria • Multipacting is a phenomenon of a large number of electrons avalanche. In high power input coupler, multipacting often hinders coupling RF power to beams, and results in ceramic crack in the worst case. • In order to avoid multipacting during conditioning and operating we have to: • choose the right coaxial line diameter (MP level moves up with the 4th power) • the right impedance (MP level moves up linear) • lower the secondary electron emission coefficient on the surfaces (especially the ceramic) 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  21. Multipacting effect analysis In three different conditions (TW, SW, MW) , Multipacting in the warm window, cold window and coaxial with bellows of the coupler are simulated carefully using MultiPac 2.1. Two basic tools were used for multipacting analysis: Counter functions: For those field levels where the enhanced counter function exceeds the number of initial electrons, multipacting occurs. Distance function: the minima of the distance function shows the initial points of those electron trajectories that survive N impacts and are able to multipact. Then the electron trajectories are recalculated by using these minima as initial points and the impact energy is computed. 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  22. Cold side of warm window @TW----Counter function Potential MP power levels: 500-1000kW if the surface of warm window contaminated. 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  23. Cold side of warm window @TW----Distance map Possible MP area: inside the gap between inner choke and inner conductor. 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  24. Cold side of warm window @TW----Trajectories Outer warm window Inner warm window MP: Two point One order RF power: 580kW 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  25. MP analysis conclusions If we choose low secondary electron yield materials, multipacting effects won’t be a serious problem. However, if the surface contaminated, potential multipacting may occur; For both warm window and cold window, possible multipacting may take place inside the gap between inner choke and inner conductor, on the choke tip where maximum electron field exists; and most possible mutipacting effects are two points one order, which is very stable and can not be neglected. So keep surface of the window clean is very important. For the coaxial with bellows, possible multipacting only occurs in traveling wave mode. Hardly any multipacting happen in standing wave and mixed wave mode. 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  26. Thermal and stress analysis Calculate static heat loss: thickness of copper plating for the stainless steel coaxial lines; Thermal anchor design Calculate dynamic heat loss: temperature distribution stress distribution Window Temperature of BEPCII 500MHz SCC Window Stress of BEPCII 500MHz SCC 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  27. Further RF simulation Ceramic window matching of the test stand Ceramic window position 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  28. 2. 1.3GHz Coupler Fabrication • Material • copper plating of stainless steel parts • TiN coating of ceramic window • Connecting: Welding, Brazing, Flanges, TIG • Leak test • Ultra-vacuum specifications for cleaning, rinsing and handling • Dimensional Control: tolerances • Manufacturing steps 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  29. Materials • Stainless steel: ur < 1.005 , H2 ougasing at 1000℃ 316L • OFHC: 99.99% content, oxygen free, electric conductivity 58 Sm/mm2; • Ceramic window: low tang δ, TiN coating 95%/ 99.5%Al2O3 • Cryogenic test of materials 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  30. Copper plating • 10 um on outer conductor of warm part coaxial; • 30um on inner conductor of warm part coaxial; • 5um on cold part coaxial; • low H2 content: H2 degasing; • uniform coating thickness; • free of bubbles and flaking up to high temperatures in high-vacuum; • After plating, heat treatment in vacuum (400 -800℃): Important • improvement of electrical conductance • Improvement and test of adhesiveness Find a plating company has knowledge of vacuum technology, brazing technology and analytical facilities 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  31. TiN coating • Normal DC Sputtering • Evacuate vacuum(4e-5Pa) • Fill into N2-Ar mixed gases (6.5Pa) • Pre-sputtering of Ti target • Ti sputtering: time depends on the thickness of TiN coating (10nm) • Fill into N2 for cooling 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  32. Connecting method Brazing in Vacuum Brazing in Vacuum after Cu coating on Inner /outer conductor TIG welding TIG welding before Cu coating on Inner/Outer conductor 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  33. Connecting method Brazing in Vacuum Brazing in Vacuum after Cu coating on Inner /outer conductor TIG welding before Cu coating on Inner/Outer conductor TIG welding 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  34. Connecting method Rubber seal flange for independent vacuum Indium seal flange Decided by Cavity design 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  35. Cleaning clean fabricating area: class 10000/100 clean room handling with no linty cotton (batiste) gloves only no scratches on RF surfaces no surface contamination with hydro carbons, grease, finger prints or dust intermediate storage in N2 containers intermediate packing only in non polymeric bags degreasing in dedicated bath only degreasing with steam e.g. perchlorethylene warm distilled water with detergent (parts clean) Ultra sonic cleaning rinsing with de-ionized water/ ultra pure water drying with high pure Nitrogen gas in clean atmosphere Stored in special container filled with Nitrogen gas 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  36. Others Leak test: leak checks of welds and subassemblies at RT in some specified cases leak checks after heating (specified at the drawing) final leak test after final assembly and cleaning He mass spectrum detector for leak test Leak rate: Dimensional and tolerance Control: Using fixture tight quality control shrink doe to weld has to be considered 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  37. Manufacturing steps 1. Machining the metal parts: Checking the dimensions, tolerances and surface roughness. Cleaning the parts 2. Brazing the cold window and warm window Brazing, leak testing 3. TiN coating on window 4. Welding the inner & outer conductor Welding the bellows, pipes. Leak testing 5. Cu coating on the inner & outer conductor Checking Cu coating quality 6. Brazing the window and coax conductor together Brazing, leak testing 7. Cleaning, evacuating, baking 8. Power testing 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  38. Cold part 3D model Warm part 3D model Doorknob 3D model 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  39. Ceramic list: 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  40. Technics investigation EBW facility Numerical control machine TiNO coating facility Vacuum furnace TIG welding facility Class100 clean room 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  41. 3. 500MHz high power test stand • In 2009.8, a 500MHz high power test stand was built in IHEP. • The test stand has been used to do high power test of the damper and input coupler for BEPCII 500MHz SCC : • The coupler passed 180kW CW RF power in the high power test (limited by the klystron) • About 4.4kW RF power absorbed by the damper in the high power test, and a 60% absorption efficiency is achieved. Coupler testing Damper testing 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

  42. Thank you! 2nd Workshop of the IHEP 1.3GHz SRF R&D Project

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