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Recent Fundamental RF Power Coupler developments at CERN

Recent Fundamental RF Power Coupler developments at CERN. First SLHiPP meeting CERN, Geneva, 8 & 9 December 2011. Acknowledgements. SPL coupler review committee :

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Recent Fundamental RF Power Coupler developments at CERN

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  1. Recent Fundamental RF Power Coupler developments at CERN First SLHiPP meeting CERN, Geneva, 8 & 9 December 2011

  2. Acknowledgements • SPL coupler review committee : • Ali Nassiri, Wolf Dietrich Moeller, Mark Champion, Sergey Kazakov, MirceaStirbet, Amos Dexter, Rama Calaga, Miguel Jimenez, Sergio Calatroni, Ofelia Capatina, Vittorio Parma • DESY : • Wolf-dietrich Moeller, Axel Matthaisen, Birte Van der Horst, and team • CEA : • Stephane Chel, Guillaume Devanz, Michel Desmond, and team • ESRF : • Jorn Jacob, Vincent Serriere, Jean-Maurice Mercier, Didier Boilot, and team • APS : • Ali Nassiri, Doug Horan, GianTenko, Dave Brubenker, and team • CERN : • Mechanical & Material Engineering group : • Ramon Folch, Francesco Bertinelli, Serge Mathot, AgostinoVacca, Thierry Tardy, Thierry Calamand, Thierry Renaglia, Ofelia Capatina, Marc Polini, Laurent Deparis, Philippe Frichot, Jean-Marie Geisser, Jean-Marc Malzacker, Pierre Moyret, Alain Stadler, and team • Vacuum, Surface & Coating group : • Miguel Jimenez, Sergio Calatroni, Wilhelmus Vollenberg, Marina Malabaila, Nicolas Zelko, and team • Magnets, Superconductors & Cryostats group: • Vittorio Parma, Arnaud Van de Craene, and team • RF group : • Sebastien Calvo, Antoine Boucherie, Nicolas Jurado, Charles Julie, all FSU-AB03 team members First SLHiPP meeting, 8 & 9 December 2011

  3. Contents • SPL couplers • ESRF/SOLEIL/APS couplers • Linac 4 window First SLHiPP meeting, 8 & 9 December 2011

  4. SPL coupler requirements First SLHiPP meeting, 8 & 9 December 2011

  5. Two proposed designs First SLHiPP meeting, 8 & 9 December 2011

  6. SPL coupler project • Four ‘vacuum lines’: • 4 cylindrical window couplers • 4 planar disk window couplers • 8 Double walled Tubes • 4 test boxes • DESY clean process assembly • (Jlab also proposed to help) • CERN LLRF measurements • CEA RF power tests • (BNL also proposed to help) First SLHiPP meeting, 8 & 9 December 2011

  7. Couplers construction • All components have been constructed by May 2011 • 4 cylindrical window couplers • 4 planar disk window couplers • 8 Double walled Tubes • 4 test boxes • All components have been individually vacuum leak free tested • Specific transport boxes with springs as per tetrodes have been designed to avoid any shocks First SLHiPP meeting, 8 & 9 December 2011

  8. Test box • Test box is made with only two parts with a helicoflex seal : • Upper cover with included machined vacuum knife flanges included • Two covers with inner copper plated • Advantages : • Easier (not easy) to copper plate • Easily cleanable regarding clean room requirements for high gradient field cavity • Can be used for several sets of couplers (if large series : SPL, …) • Drawbacks : • Helicoflex faces have to be very well prepared • Self-supporting structure : heavy weight • Holes for vacuum port : • without sharp edges • L = 5 x D to allow correct RF shielding (P peak max = 1’000 kW !), helped with additional vacuum tombac First SLHiPP meeting, 8 & 9 December 2011

  9. Waveguides • Six parts waveguide • Easy mounting • Easily exchangeable shims and allows post machining of internal step for matching if needed • Knife contacts all along to suppress any gap at intersections in order to avoid any arcing (DESY difficulties with brazed WG) • No mechanical stress given to the ceramic, fixed point onto the body only • Capacitor self centered around the ceramic and designed to symmetrically air cool the ceramic First SLHiPP meeting, 8 & 9 December 2011

  10. Planar disk inner line • As the coupler must be air cooled to avoid any water leak • Specific trick to ensure inner RF contact : • Inner line on top of the ceramic • Springs are compressed • Air cane inside the inner line • Screw to the inner ceramic • Release springs to ensure RF contacts • Absolutely no stress to the ceramic 1 MW RF contact First SLHiPP meeting, 8 & 9 December 2011

  11. Clean room assembly (DESY) • Test box assembly not easy because of specific surfaces roughness needed for helicoflex • Couplers assembly was also not easy because : • Couplers are heavy • Last connection has to be done manually • Ok for few prototypes, not for a large series • Two cavities were sent to CERN, but… First SLHiPP meeting, 8 & 9 December 2011

  12. Double walled Tube (DT) • Despite a previous long experience with LEP and LHC DT, a difficulty occurred in the construction process : • An additional machining has erased all the care put into the preparation of DT • Copper sputtering was removed with a simple water Ultra Sonic cleaning process • Decision to condition the two first vacuum lines with NOT copper coated DT First SLHiPP meeting, 8 & 9 December 2011

  13. Low Power measurements (CERN) • S11 with 2 x N/WG adaptors + 2 couplers + 2 DT + test box : • Cylindrical = -26.5 dB • Planar disk = -18 dB • Even with -16 dB, 1 MW corresponds to 25 kW reverse power • Ok for first tests First SLHiPP meeting, 8 & 9 December 2011

  14. RF tests (CEA premises) • Tests started with cylindrical window couplers • Not baked out, static vacuum ~ 2 x 10 -7 mbar • Wanted to check RF • Size of the test box 250 mm x 600 mm • Helicoflex • Pulse mode process • After 3 weeks, 50 kW 20 us / 20 Hz • We stopped the test First SLHiPP meeting, 8 & 9 December 2011

  15. RF tests • In the meantime, second test box with two planar disk window coupler has been baked out • No helicoflex leak • Very slow heating up and heating down ramps 10 C / hour • Maximum temperature was only 150 C during three days • Nitrogen onto copper rings to avoid any oxidization • Very good static vacuum after the process: • ~ 1 x 10 -9 mbar • Was 2 x 10-5 mbar before starting the bake out First SLHiPP meeting, 8 & 9 December 2011

  16. RF tests • Restarted the tests with the planar disk window couplers • Pulse mode process starting with 20 µs pulses / 8 Hz • After 10 days : 1000 kW 2 ms / 8 Hz First SLHiPP meeting, 8 & 9 December 2011

  17. RF tests • Still some out gazing around three power levels : • 20 kW • 140 kW • 300 kW • No more vacuum activity above 300 kW • Processing around these values is under way and vacuum decreases ramp after ramp • Tests ongoing to reach 1000 kW 2ms / 50 Hz (uncoated DT limitation) First SLHiPP meeting, 8 & 9 December 2011

  18. Next steps • While testing the planar disk window couplers, we baked out cylindrical couplers (already seen RF) : • Initial static vacuum ~ 1.0 x 10-6 mbar • After bake out, static vacuum ~ 1 x 10-10 mbar • Once planar disk window coupler tests finished, restart cylindrical window coupler tests • These tests are scheduled beginning 2012 • Corrected DT copper coating under way • Cryostat flanges to be added prior to new clean room assembly • Mounting of chosen design at DESY clean room: • Two tests cavities • Four copper coated DT with cryostat flanges • Four couplers • RF tests at Saclay premises of the four chosen couplers First SLHiPP meeting, 8 & 9 December 2011

  19. Key RF items • Ceramic and waveguide as a whole matching system • Waveguides: • ‘Plug and Play’ • No doorknob • Reduced height • Screwed waveguide • No mechanical stress to the ceramic • Test cavity in two parts, easier to copper plate and easy to clean • Inner line of planar disk window with RF contacts ensured by compression of springs • Only air cooled couplers First SLHiPP meeting, 8 & 9 December 2011

  20. ESRF/SOLEIL/APS coupler requirements First SLHiPP meeting, 8 & 9 December 2011

  21. Kovar vs copper window Ceramic • LEP Kovar® brazed window : • Kovar® rings on both ends • Body and Antenna with Stainless Steel rings brazed onto copper • TIG welding under mechanical pressure ensuring RF contact • Easy Kovar® brazing process • Weakness of the design : RF contact • High field between two Kovar® ‘antennas’, arcing • LHC copper brazed window : • Massive copper ring for high power • No RF contact, fully continuous RF path • Spherical ends of copper rings for no arcing • Very difficult brazing process (6 years to be finalized) • Advantage of the design: extremely powerful LEP kovarcollar RF contact via compression while TIG welding Ceramic LHC copper collars EB welded Metallic continuity First SLHiPP meeting, 8 & 9 December 2011

  22. Kovar vs copper window • APS coupler with kovar/copper misalignment : • RF contact lost • kovar has metalized ceramic (grey) • Thermal losses • Vacuum leak • CERN Kovar vs CERN copper with a LHC test : • kovar RF losses • Thermal overheating • Burnt kapton and peek (> 250 C) • Copper ceramic window is not only a simple upgrade, it is a very new design really stronger than kovar window ceramic First SLHiPP meeting, 8 & 9 December 2011

  23. ESRF coupler project • LEP I style coupler became ESRF trouble maker (five unexplained vacuum leaks in 2008) • Proposal of a new coupler to fit into existing premises with NO infrastructure modification • Coupling loop : • Water cool to be sure there will be no mechanical stress given to the ceramic • Three vacuum ports for conditioning process: • Vacuum gauge close to the ceramic • Glass window for arc detection • e- antenna • First prototype delivered September 2011 First SLHiPP meeting, 8 & 9 December 2011

  24. ESRF coupler tests • Bake out onto cavity process • CERN pulsed mode conditioning process under vacuum feedback • Off tune, 200 kW pulsed 5 ms / 50 Hz in 22 hours • On tune, 200 kW cw in 60 hours • Qualified for ESRF needs • Last week, on tune 300 kW cw First SLHiPP meeting, 8 & 9 December 2011

  25. ESRF/SOLEIL next steps • Further tests to higher power levels, up to maximum test bench capability, i.e. 350 kW cw • Two additional ESRF ‘series couplers’ • Two SOLEIL couplers: • Electrical antenna, air cooled • CERN LEP type test cavity • Outer coaxial line with corrected length • Tests at ESRF First SLHiPP meeting, 8 & 9 December 2011

  26. APS coupler project • Collaboration requested during CWRF workshop Barcelona in April 2010 • Present coupler also LEP I type limited to 100 kW cw • Design similar to ESRF: • Coupling loop differs • Inches vs mm • Waveguide air cooling as personal safety interlock • Individual bake out of the coupler, reduced exposition to air (not under mobile clean room) First SLHiPP meeting, 8 & 9 December 2011

  27. APS ‘picture horizontal flip’ • Loop angle does not allow any vacuum ports to be useful • Not needed because cavity is small enough, pumping perfect (1 x 10-9 Torr without RF) • If one additional coupler, it will be with no more vacuum ports: • Reduces the costs to its minimum • Reduces the risk of vacuum potential leaks • Cavity small enough to ensure a correct vacuum monitoring First SLHiPP meeting, 8 & 9 December 2011

  28. APS coupler tests and next steps • Tests started last week • Conditioning in cw mode with a very low pressure: • 1 x 10-8 Torr maximum • interlock at 5 x 10-8 Torr • 25 kW cw after two days • Further tests to higher power levels, up to maximum test bench capability, i.e. 200 kW cw • Implementation of CERN pulse mode conditioning system Vacuum Power First SLHiPP meeting, 8 & 9 December 2011

  29. Linac 4 window requirements First SLHiPP meeting, 8 & 9 December 2011

  30. Ceramic assembly • As simple as possible : • 1 : Ceramic Ø 400 mm x 25 mm • 2 : Inner copper ring Ø 400 mm x 1.25 mm • Outer copper ring • Stainless steel ring for Helicoflex • Two first individually brazed sub-assemblies: • Brazed ceramic = ceramic + inner copper ring • Outer ring for Vacuum seal = outer copper ring + stainless steel ring • Main ceramic = EB welding of two parts • Ti sputtering of the vacuum side First SLHiPP meeting, 8 & 9 December 2011

  31. LINAC 4 window project • As simple as possible • 1-2-3-4 : Ceramic assembly • 5 : spacer • 6 : Helicoflex seal • 7-8 : Stainless Steel flanges • Massive flanges, not copper plated • More difficult design than it look likes because of the two shapes : cylindrical and rectangular, with incorporated screws First SLHiPP meeting, 8 & 9 December 2011

  32. LINAC 4 window next step • First prototype with helicoflex • Low Power RF ok • Second prototype with no helicoflex but an Electron Beam Welding is under construction • Tests of two prototypes face to face onto a vacuum waveguide line in CEA premises : • 1.25 MW 2 ms 50 Hz • Define the best design (Helicoflex/EBW) • Series construction of 30 windows • Ceramics already ordered First SLHiPP meeting, 8 & 9 December 2011

  33. Future coupler developments • HIE-Isolde, under way • 100 MHz • 500 W (1 kW ?) • Operating at 2k • Inside vacuum vessel • LIU-SPS 200 MHz • New concept with coaxial plain disk and capacitive coupling • 900 kW pulsed 50 % (ms) • 450 kW cw power • SPS 800 MHz consolidation • Scaling of Linac 4 to 800 MHz • 150 kW cw • One for all Crab Cavities coupler • Same window for all cavities • Compatible with various coupling system • Whatever new coupler needed First SLHiPP meeting, 8 & 9 December 2011

  34. Thank you very muchfor your attention And many thanks again to all the persons involved in all these projects First SLHiPP meeting, 8 & 9 December 2011

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