325 MHz RF Cave and SC Spoke Cavity Tests Robyn Madrak – Accelerator Physics Center (APC) for the HINS/Project X Group

Single Spoke Resonator (SSR) Cavities SSR1: 325 MHz,  = 0.22 superconducting cavities Init design for the proton driver/HINS pulsed linac (3ms, 1% DF), 4K Now being incorporated into design for the Project X CW linac, 2K Two SSR1 cavities have been fully fabricated (1 – Zanon, 2 – Roark) HINS design gradient 10 MV/m Bpeak/Eacc3.87mT/(MV/m) Q 0 at design gradient 0.5 x 10 9 R/Q 242  Effective L0.136 m 2/28/20112Robyn Madrak - APC

Dressed SSR1 Cutaway of cavity, He vessel 2/28/20113Robyn Madrak - APC

Cryostat in SCTF Test Cave 80 K shield He line Coils for B field test vacuum line Nitrogen line 2/28/20114Robyn Madrak - APC Cryostat has B field shield X-ray detectors  Diodes inside of cryostat  FOXES and Chipmunks outside 1.44 m OD Coupler port

SSR1-01 Test History Tested first in VTS at 4K and 2K, bare, CW. Tested CW at SCTF, dressed (these results) – Measured cavity Q 0 vs. E, max E acc, Xray activity vs E – Q disease test (dependence of Q on cooldown time) – Cavity df/dP (frequency sensitivity to pressure fluctuations) – Lorentz Force detuning coefficient – Sensitivity to external magnetic fields (Q degradation) – Fast Tuner tests (microphonics compensation, etc.) Tested Pulsed – Test of cavity along with design coupler – Max E acc – Tuner compensation for LFD during pulse Future upgrade planned: 2K operation 2/28/20115Robyn Madrak - APC

SCTF, Q 0 vs E, CW tests, high Q ext 2/28/20116Robyn Madrak - APC Quench limited, ~ 27 MV/m T = 4.7 K Measured by chipmunks, outside of cryostat, ~1m from cavity Design: Q 0 at 10 MV/m = 5e8

Tuner Tests/Pressure Sensitivity Measured df/dP = -145 ± 15 Hz/torr (sim predicted 210 Hz/torr) Lorentz force detuning coefficient : 1.5 ± 0.5 Hz/(MV/m) 2 (sim predicted 3.8 Hz/(MV/m) 2 ) ProjX Cavity BW Hz ; HINS initially ~400 Hz; here ~2Hz 7 Fast Tuner Pressure Compensation ~ 300 Hz variation w/o lock Yuriy Pischalnikov, Warren Schappert Good results with fast tuners for pressure fluct. compensation: 8 Hz variation w/lock compared to 300 Hz w/o lock ~ 8 Hz variation w/ lock 2/28/2011

Q Disease Is a drop in Q due to the formation of hydrides during cooldown Effects can be minimized by a fast cooldown ‘Sensitive’ temperature region is 150 – 70 K Typically does not appear during the ‘first’ cooldown after chemical processing Can possibly be ‘cured’ (or minimized) by hydrogen degassing (baking at 600C) followed by flash BCP Was observed on SSR1-01 in the VTS: saw x 8 drop in Q at 4.4 K with 7 hour hold at 100 K 2/28/20118Robyn Madrak - APC

Q Disease in the VTS VTS ~ factor of 8 drop in Q after 7 hour K From Ristori et. al, ‘Development of 325 MHz Single Spoke Resonators for HINS at Fermilab: Recent Results PAC ‘09 2/28/20119

Q Disease at SCTF After VTS, SSR1-01 Hydrogen degassed (600 C bake) at Jlab Q drops but drop is small (~20% drop)  minimal Q disease; baking was a success Will be more sensitive at 2K – awaiting upgrade to test this 2/28/201110Robyn Madrak - APC 3 hours in sensitive region 11 hours in sensitive region Note: Q in second cooldown same as in 1 st cooldown

Magnetic Field Sensitivity Tests Project X – will likely have solenoids for beam focusing near the cavities  test sensitivity of cavities to B field (look for Q drop) Installed two coils on each end of the cavity Quench cavity 5000X in 8-10 G Bfield Measured Q at high and low field – no degradation 11 I I

High Power Pulsed Tests w/Design Coupler 2/28/ st pulsed test, 1 st test with power coupler: Q L ~1e6 – Reached 36.5 MV/m with ~2ms flattop – ~40 MV/m quench limit for short pulse Fast tuner tests - piezos: (Pischalnikov, Schappert) – Lorentz Force detuning ~3kHz peak to peak w/no compensation – Piezo compensation reduces f drift to ~50 Hz during pulse f drift during pulse f (Hz)

Summary 1 st CW – dressed tests were a success for the facility and for SSR1 Cavity Q vs E and max E acc exceed design requirements 600 deg C bake (thanks to Jlab) good results at 4K, need studies at 2K Fast tuners compensate well for microphonics, LFD Magnetic field sensitivity results are encouraging. No effect due to quenching with field >50X expected fringe field Pulsed tests of coupler/cavity satisfactory, high max E acc during pulsed testing 2 K tests in the not-so-distant future 2/28/201113Robyn Madrak - APC