1. C100 Operation Enhancing gradient reach for the
12 GeV physics program via fault management

2. We are still learning and pressing forward
Overview
From commissioning to the present, C100 gradient maximization while maintaining an acceptable trip rate has been… challenging.
Many avenues for enhancing cryomodule performance have been discovered, explored and acted upon by many contributors from multiple divisions.
Intra-divisional collaboration has been key in investigating and resolving issues
And - while some mysteries remain in fully mastering C100 performance to realize true and sustainable 12 GeV operation –
To date…
The five C100 modules in each linac provide about 40% of the energy gain required
Highest gradients to date for cryomodules in a CW machine
Beam quality has been acceptable and most 12 GeV era milestones have been attained
We are still learning and pressing forward

3. Brief history of issues
Heaters
Went from 4 to 8
Individual cavity heater control installed in injector
V2 chassis now being tested for remaining zones
Tuner performance
Bolts installed in non-tensioned tuners
Went from EPICS to fiber input, faster updates – tighter tuning
Tightened dead bands
Waveforms give real-time detune information
SEL to GDR transition
Automated turn on and recovery
Implemented 27 degree shift for POFF
Service building temperature excursions
Caused the 56 MHz clock to lose lock
Crosstalk
Re-terminated many heliax cables
Still present as regulation degradation (across cavities and zones)

4. Brief history of issues, cont’d.
Microphonics
Stiffened tuner lever arms
Construction obstruction
Tom Powers, Ken Baggett, George Biallis and Bob Legg tackled this one – wiggly waveguide
Solution most apparent in 0L04
More hardening in the future
Helium pressure standardization
Helium vessel design for heat dissipation = 2.07K (0.037 Atm)
Had to research spec
C100 placement = higher return pressure than at “T”
Further testing (Freyberger, et al) suggests higher return pressure may be sufficient, which puts less stress on CHL

5. Present concerns Particulate contamination Field Emission
Dark current generation
Radiation damage
Quench at lower gradient than commissioning limits
“Anomalous” Quench – (field depletion due to non-classic quench)

6. Types of faults “Hard” RF is turned off due to fault detection
SEL quench
Arc
Vacuum
Quench
Others…
“Soft”
Cavity transitioned to SEL mode to reduce recovery time
GLDE
GDCL
DETA
PLDE
Every fault (hard or soft) pulls an FSD

7. GDCL “soft faults”

8. Quench Faults

9. So why are the C100 cavities quenching so often?
Focus on quench
As we know, there are multiple fault flavors to contend with. There may be some interaction between detuning and the “soft” faults, but “quench” is concerning since the cavities were commissioned with gradient constraints below the field potential where a quench was induced – and this was historically reliable as long as a new field emitter didn’t turn on…
So why are the C100 cavities quenching so often?

10. Quench Algorithm
E field collapses from cavity faster than the Qext decay rate
Derived from probe signal
Calculate gradient reduction in counts for 2 MV/m
Find time of gradient loss in msec
Monitor gradient loss slope based on these values

11. Classic quench event
600 usec
decay

12. Different “quench” event
50 usec
decay??

13. Multi – cavity response to quench event

14. Quench rate mitigation – 1L23

15. Cavity field depletion aka “quench” - Questions
Are there multiple mechanisms (besides classic “quench”) that induces cavity field depletion at a rate faster than the normal decay time of the cavity? (Arcs as Tom alludes to?)
End group heating? (1L23-8?)
Are the quenches being detected “real” or is another mechanism at play?
Is the algorithm for quench correctly applied?
Regardless of the cause for quench detection – it still counts as a trip, and the only defense we have is to reduce operating gradient….

16. Closing comments
Quench faults dominate the trip rate of the C100 cavities. There are other areas of concern that requires further investigation, however, if the quenches, arcs, or whatever mechanisms that cause rapid field depletion can be defined (or perhaps mitigated), that information could be used to develop a strategy towards maximizing gradients and minimizing trip rates in the C100 zones.
Thanks to all the people who provided information and assistance to help us understand unfamiliar concepts.

17. End

18. GDCL Soft Fault

19. GLDE Soft Fault

20. Day to day operation
Goal – provide desired energy at the lowest trip rate
For C100 zones - How do we get there?

21. Now for something completely different
Original Display

22. FSD Count – Is this acceptable?
24 hour period
of FSDs from
C100 cavities

23. Different, cont’d.

24. Still different