SRF Cryomodule 2 Cavity Test Results Andy Hocker TD/SRF Dev Dept. All Experimenters Meeting, 10-OCT-2011

Context ILC “S1” goal: 31.5 MV/m in an 8-cavity cryomodule –DESY did it once with an XFEL prototype –Yet to be demonstrated in Asia/Americas regions Industry/labs are getting good at high-gradient (>35 MV/m) cavities (~50% yield) High-gradient cryomodules still challenging –Maintain high performance of cavities –Functionality of auxiliary components (tuners, couplers, etc.) bare dressed CM1 x 8

Recent History DESY sent us a “cryomodule kit” in 2007 and helped us assemble it --- CM1 –An educational tool… mainly mediocre cavities In parallel, New Muon Lab was re-habbed as a SRF cryomodule test facility –And eventually, a mini-ILC (e- beam, up to 6 cryomodules) –Infrastructure: cryo, RF power, shielding block caves, etc. CM1 was installed at NML and used to commission the facility –First cooldown in Dec 2010 –Mostly successful, lessons learned…. future talk from Elvin Harms CM2 now under assembly as first US-built ILC CM

Vertical Tests ILC S0 spec = CM2

CM2 Cavity VT Results Q 0 vs. E acc Field Emission (X-rays)

Horizontal Tests = CM2 ILC S1 spec

(some) CM2 Cavity HT Results For a dressed cavity, Q 0 must be measured from heat dissipated to cryo 1 W or less, DIFFICULT measurement Q vs E in general agrees with VT results to within a factor of 2 But usually a little lower Plan to re-visit the methodology, investigate alternate approaches

Those left behind 8/14 cavities tested were deemed CM2-worthy, what about the rest? –2 performed just as well as they did in VT, but were not 35 MV/m One went to KEK for the S1-Global project, one was a CM2 backup –1 quenched early (33 MV/m) due to heating from FE Has since been HPR’d, likely OK now –1 had extremely high FE that was NOT fixed by HPR –1 quenched early (29 MV/m) for reasons unknown (no FE) Very few quench diagnostics possible with a dressed cavity –1 had an input coupler breakdown that contaminated the cavity No FE before breakdown, extremely high FE after breakdown Breakdown happened at ~37 MV/m, led to administrative HT limit of 35 MV/m

Input Coupler Failure Void in Cu plating “vapor trail”

Tuners Slow blade tuner for static tuning of the cavity frequency Modifications to stepper motor linkage to address failure mode uncovered in horizontal testing Dynamic compensation for Lorentz force detuning using fast piezoelectric tuners Piezo OFFPiezo ON

Discussion and caveats One CM2 cavity had a miserable horizontal test –Extremely high heat loads, hard to even do a meaningful test –Upon disassembly of input coupler, glitter-like flakes of copper found stuck to antenna tip and elsewhere FNAL and SLAC working with vendor to understand plating process and improve QA –HPR and subsequent vertical test of cavity (dressed) showed very good performance, so used for CM2 One “good” cavity was removed from HTS, and then immediately reinstalled and re-tested –Result: FE observed where there had previously been none Changed cavity handling procedures to eliminate contamination risk State of previously “successful” cavities (four) called into question –HPR and subsequent horizontal test showed good performance again Re-HPR’d the four CM2-ready cavities, but no horizontal re-test

Conclusions Eight cavities have been certified in the HTS for CM2 assembly –7 reach at least 35 MV/m, one reaches 33 MV/m ILC S1 goal theoretically attainable –Cavities look good from a Q 0 and FE standpoint as well Most cavity tests were successful –Demonstrates that high performance can be maintained through the dressing process –The failed tests have helped point out areas of improvement for the CM production chain Coupler QA, handling, etc. Will good cavities make a good cryomodule? –I’m cautiously optimistic

Thanks CM2 under assembly at MP-9