SRF Cryomodule 2 Cavity Test Results

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.) CM1 dressed bare 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 = CM2 ILC S0 spec

CM2 Cavity VT Results Q0 vs. Eacc Field Emission (X-rays)

Horizontal Tests = CM2 ILC S1 spec

(some) CM2 Cavity HT Results • For a dressed cavity, Q0 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 Piezo OFF Piezo ON Dynamic compensation for Lorentz force detuning using fast piezoelectric tuners

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 Q0 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

SRF Cryomodule 2 Cavity Test Results