FNAL recent coupler troubles General coupler handling: TTF3-type couplers purchased from CPI Quality control, cleaning, room temperature conditioning at SLAC Sent to FNAL in clean room bag / Pairs of cold-end parts arrive mounted on coupling waveguide used for conditioning at SLAC Blown with dry nitrogen in FNAL clean room, using particulate counter, before assembly to cavity Additional room temperature and cold conditioning in FNAL Horizontal Test Stand before full cavity test Coupler photos and related information from Tug Arkan, Andy Hocker, Andrei Lunin, and many others from the FNAL/ANL cavity team

Ginsburg TTC Meeting - Milano TB9ACC013 Vertical qualification test 41 MV/m at JLab (1st EP, 1st test, 8.Dec.2008), retested without processing at FNAL for statistically consistent 38 MV/m Preparation for horizontal test: Titanium transition ring welding at Sciaky Helium vessel welding at MP9 HPR at FNAL/ANL horizontal test assembly at MP9 including coupler, magnetic shielding, tuner, etc. In horizontal test, initially achieved 37 MV/m, then heavy FE after an arc event finally reaching max 35 MV/m, with FE onset 20 MV/m (Feb.2010) Disassembly, HPR, re-assembly for horizontal test Defect seen on copper coating of inner rim of input coupler flange [see photo] Optically inspected cavity coupler region with Questar system, saw nothing unusual Reassembled for second horizontal test with different coupler after HPR Second horizontal test: FE onset 5 MV/m, 20 MV/m max. (Jul.2010) Lots of field emission seen already during cold coupler conditioning Since cavity performance during 2nd test was even worse than at the end of the 1st test, perhaps an additional failure mechanism was present Both couplers were blown clean and returned to SLAC for analysis 1.Mar.2011 Ginsburg TTC Meeting - Milano

Ginsburg TTC Meeting - Milano TB9ACC013 Coupler Photo shows feature in copper coating 1.Mar.2011 Ginsburg TTC Meeting - Milano

Ginsburg TTC Meeting - Milano TB9ACC016 Vertical qualification test 39 MV/m at JLab (2nd EP, 3rd test, 10.Feb.2010), shipped clean and sealed to FNAL Preparation for horizontal test: Titanium transition ring welding at Sciaky Helium vessel welding at MP9 HPR at FNAL/ANL Horizontal test assembly at MP9 including coupler, magnetic shielding, tuner, … In horizontal test, heavy FE was seen: FE onset 18 MV/m, 27 MV/m max. (Oct.2010) Disassembly after horizontal test: Flakes were found on input coupler antenna tip [see photo] , size 0.1~0.2 mm Standard optical inspection of cavity equators and irises with KEK/Kyoto system; no obvious problem observed EDX measurement of flakes confirmed flakes were copper Coupler was blown clean and returned to SLAC for analysis 1.Mar.2011 Ginsburg TTC Meeting - Milano

Ginsburg TTC Meeting - Milano TB9ACC016 Coupler Photo shows flakes on a glove, after flakes were wiped off coupler antenna 1.Mar.2011 Ginsburg TTC Meeting - Milano