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

Acknowledgements SPL coupler review committee : ▫Ali Nassiri, Wolf Dietrich Moeller, Mark Champion, Sergey Kazakov, Mircea Stirbet, 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, Gian Tenko, Dave Brubenker, and team CERN : ▫Mechanical & Material Engineering group :  Ramon Folch, Francesco Bertinelli, Serge Mathot, Agostino Vacca, 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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

Contents SPL couplers ESRF/SOLEIL/APS couplers Linac 4 window Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

SPL coupler requirements Eric MontesinosFirst SLHiPP meeting, 8 & 9 December Technical Choices Single window coupler Fixed coupler With a Double Walled Tube Mounted in clean room with its double walled tube horizontally in only one operation Vertically below the cavity and will be a support for the cavity (first time worldwide) With a HV DC biasing capacitor Air cooled RF Characteristics f0f MHz Power levels 1000 kW pulsed = 2.0 ms 50 Hz (20 ms) 100 kW average Cavity design gradient19-25 MV/m Q ext of input coupler1.2 x 10 6 Input line Ø 100 / 43.5 mm = 50 Ω (from the cavity design) WaveguidesWR 1150

Two proposed designs Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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) Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December MW RF contact

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… Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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

RF tests (CEA premises) Tests started with cylindrical window couplers Not baked out, static vacuum ~ 2 x 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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 mbar ▫Was 2 x 10-5 mbar before starting the bake out Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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) Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

ESRF/SOLEIL/APS coupler requirements RF Characteristics f MHz Power levels200 kW cw Technical choicesSingle window, fixed coupler WaveguidesWR 2300 half height Mechanical constraints Must match with previous design without any infrastructure modification Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

Kovar vs copper window 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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December LEP kovar collar RF contact via compression while TIG welding LHC copper collars EB welded Metallic continuity Ceramic

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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) Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December VacuumPower

Linac 4 window requirements RF Characteristics f MHz Power levels1250 kW pulsed 2ms / 50 Hz (SPL cycle) WaveguidesWR 2300 Mechanical constraintsAs short as possible Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

LINAC 4 window project As simple as possible ▫ : 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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

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 Eric MontesinosFirst SLHiPP meeting, 8 & 9 December

And many thanks again to all the persons involved in all these projects Eric MontesinosFirst SLHiPP meeting, 8 & 9 December