Cryomodule Maintenance Workshop Maintenance, Repair Strategies, and Fault Scenarios. J. Ozelis Senior SRF Coordinator

Transcription

1 Cryomodule Maintenance Workshop Maintenance, Repair Strategies, and Fault Scenarios J. Ozelis Senior SRF Coordinator

2 Outline for Discussions Maintenance - routine/preventative maintenance Schedules Specific systems/devices Equipment needed Maintenance - repair/performance restoration Examples of failures (types, rates) Restoration techniques Equipment needed Let s hear about experience with the above What do other labs/institutes do What works What doesn t What were surprises What were well predicted J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 2

3 Maintenance - Routine/Preventative Maintenance [1] Vacuum systems CM Insulating» If not actively pumped is there a scheduled regeneration period or specification that triggers (re-)pumping? Beamline» Ditto or should we rely solely on cryo-pumping when CM is not warmed up Cryo distribution lines insulating vacuum» Probably not actively pumped monitor pressure actively? Pump down periodically? Pumps maintenance plans/schedules for active pumping stations Instrumentation Sensor calibrations (external)» How often, if performed at all? Rolling schedule? Readout calibrations (in svc bldg. - PLCs, instr. modules, etc.)» Ditto J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 3

4 Maintenance - Routine/Preventative Maintenance [2] Cavities/Solenoids De-Gaussing cycles and cavity T c cycle» How often? What triggers cycle (assuming can t measure Q 0 degradation directly)» How far above T c to raise cavities? (Q-disease danger zone )» What do the solenoid current ramp cycles look like? Bipolar? Current steps?» How to handle multiple solenoids/coil components? Solenoid/Magnet Leads» Examine/tighten connections? Evidence of increase in voltage drop (contact resistance )? RF/HV Systems Transmission lines integrity of connections» Regularly checked or look for anomalous behavior (VSWR or power dissipation changes? How to differentiate a bad connection from Q 0 degradation?)» Visual check? S 21 Msmts? TDRs? HV cables (ion pumps, etc.)» Check insulation for rad damage? Replacement schedule? Run until failure (20+ yrs)? J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 4

5 Maintenance - Routine/Preventative Maintenance [3] Controllers (valve, flow) Cryogenic valve controllers limit switch positions/functionality, readback functionality» Routine check of operation and position setting? Solenoid lead flow controllers» Calibration Cryomodule/Cold Mass components alignment Shifts over time» Monitoring/detection (beam/optics settings, target measurement)» Mitigation re-position during scheduled downtimes Anything else? J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 5

6 Unexpected Failures - need to be addressed to recover/restore performance, can t wait until scheduled maintenance or accelerator down (not catastrophic failures (e.g., loss of vacuum accidents)) Examples : Maintenance - Repair/Performance Restoration [1] Vacuum CM insulating vacuum leak (to outside)» At bottom seal» At fittings/flanges Beamline vacuum leak to insulating vacuum» CF flanges at RF ports, beamline connections (cav/bellows/solenoid) Helium circuit leak to insulating or BL vacuum» Cracks in welds, leaking internal valves, leak in flanges in He ckt Shield circuit leak to insulating vacuum Leak in connectors, welds/braze joints J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 6

7 Restoration [2] Cavity Increased FE» Higher dynamic loss or» Can t achieve operating gradient for same loss» Cavity fratricide Recurrence of MP» Can t achieve operating gradient Q 0 degradation (trapped flux (quench or environmental), FE loading, surface contamination)» Same effect as increased FE Tuner Motor failure Mechanism failure (binding) Increased hysteresis (part wear) Decreased resolution J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 7

8 Restoration [3] Coupler Recurrence of MP Thermal instability Vacuum degradation/loss Diagnostic loss (vacuum sensor, E-probe, IR sensor) Solenoid Quenching below B op Lead flow restriction» Increase in lead voltage drop, lead heating, coil heating (loss of temp margin) He/Cryogenic circuits Control valve failures Liquid level probe failure Header heater (thermal load control/balancing) failure J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 8

9 Restoration [4] Instrumentation Thermometry failures» Control of cavity thermal cycles above T c 2 K header pressure transducer(s) failure» Cavity LHe bath temperature control Valve controller failures» Cryo operations or vacuum isolation (BL, IV) compromised J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 9

10 Restoration Proposed Mitigations [1] Vacuum CM insulating vacuum leak (to outside)» Active pumping to keep up with leak rate - pump cart (RP & TMP) in tunnel Beamline vacuum leak to insulating vacuum» Monitor BL vacuum (vac-vac leak), pump on ins vac? Helium circuit leak to insulating vacuum» Active pumping to keep up with leak rate - pump cart (RP & TMP) in tunnel Helium circuit leak to beamline vacuum» Close BL valves if pressure exceeds trip point. Need to warmup (eliminate LHe inventory) and isolate module from cry ckts.; may then be able to pump out BL space, cavities off. Eventually remove for repair. Shield circuit leak to insulating vacuum» Active pumping to keep up with leak rate - pump cart (RP & TMP) in tunnel J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 10

11 Restoration Proposed Mitigations [2] Cavity Increased FE» He processing need pump cart w/ He supply connected to BL vacuum (use portable cleanroom)» Plasma cleaning? When appropriate?» Run at lower gradient (below FE onset)» Thermal cycle (adsorbed gases removal) cavity & He ckt heaters, perhaps need pump cart w/rga attached to BL vacuum (use portable cleanroom), mass flow controller Recurrence of MP» CW RF or HPP processing use existing RF systems/amplifiers» Thermal cycle (adsorbed gases removal) cavity & He ckt heaters, perhaps need pump cart w/rga attached to BL vacuum (use portable cleanroom), mass flow controller J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 11

12 Restoration Proposed Mitigations [3] Cavity (cont d) Q 0 degradation (trapped flux (quench or environmental), FE loading, surface contamination)» De-Gaussing and thermal cycle if trapped flux bi-polar PSs for solenoids (& steerers), cavity, solenoid, & LHe header heaters» Reduce FE (see above)» Thermal cycle/pumping perhaps removes surface gases - need pump cart w/rga attached to BL vacuum (use portable cleanroom), mass flow controller Tuner Motor failure» External replace during tunnel access Mechanism failure (binding, internal)» Detune cavity if possible, turn off RF Increased hysteresis (part wear)» Modify tuning algorithm, incorporate directionality or dead zone» Replace worn external components (harm drive) during tunnel access Decreased resolution» Increase RF power as long as within BW spec J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 12

13 Restoration Proposed Mitigations [4] Coupler Recurrence of MP» Coupler processing off-resonance; need additional amplifier power» Add coil (solenoid) to shift MP orbit (ala TDCM) Thermal instability» Supplemental cooling (increase flowrate) Vacuum degradation/loss (80.5MHz only)» Active pumping of insulating vac - pump cart (RP & TMP) in tunnel Diagnostic loss (vacuum sensor, E-probe, arc detector - 322MHz only)» Can not replace CCG unless BL vacuum vented; others accessible during tunnel access Solenoid Quenching below B op» Run below quench threshold» Re-train Lead flow restriction» Thermal cycle to remove contamination J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 13

14 Restoration Proposed Mitigations [5] He/Cryogenic circuits Control valve failures» Replace controller during tunnel access; if valve itself fails (mechanically), may need to warm-up and isolate/remove CM Liquid level probe failure» Switch to installed redundant probe Header heater (thermal load control/balancing) failure» Switch to installed redundant heater; if none, warm-up CM, install new heater via relief lines Instrumentation Thermometry failures» Switch to redundant thermometer or use neighboring (e.g. cavity, mag shield) sensors 2K header pressure transducer(s) failure» Warm up to 4K (if sub-atm) and replace transducer while at positive pressure; use second transducer (loss of range or resolution) J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 14

15 Restoration Proposed Mitigations [6] Cavity heater failure» All cavities warmed up together; neighboring cavity heaters will provide necessary heat, but less efficiently J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 15

16 Maintenance/Repair/Operation General Observations Minimize # of thermal cycles (seal integrity, uncontrolled contamination (gas) migration) - or limit to < 50K Consider cold traps for intra-cm beamline sections Pump/purge carts should have mass flow controllers to ensure slow pumpdown/purge Eliminate Indium seals where possible (less an issue for similar surfaces, but still an added complication when disassembling cavities) Variable couplers significantly help in MP processing but practical ($$) for larger installations? All feedthroughs will eventually leak keep them out of the He circuits when possible Q 0 (and hence E acc for finite cryo capacity) will end up degrading over time, mostly due to increase in FE loading design in appropriate margins for continued operation (qualify cavities at higher E/Q 0 (this is $$), or balance CM cavity populations wrt performance e.g. don t put all low performers in one CM) Start off w/fe-free cavities!! J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 16

17 Example of He Processing in CEBAF (May 2001) South Linac CM #3, cavity #8 South Linac CM #2, cavity #3 J. Ozelis, March 2014 Workshop on Cryomodule Maintenance - 20, Slide 17