1. C75 Risk Assessment Geoff Krafft
Also Contributing: Jay Benesch, Jonathan Creel, Curt Hovater, Arne Freyberger, Tony Reilly, Bob Rimmer
2/15/2018

2. Outline Specific Technical Risk Schedule Risk Organizational Risk
Cavity Performance
LLRF
Schedule Risk
Cryomodules
Cryoplant related
Organizational Risk
Resource Commitments
Summary/Questions/Comments
C100 Based Risk
C100 cavity degradation rate
Cavity/cryomodule catastrophic failure

3. Specific Technical Risks
As documented in the rest of the review, many of the risks associated with the cavity design and performance in operations have been addressed by the fact that 2 C75 cavities have been installed and operated in NL13. These cavities provide early prototypes for the project
RF power requirements
QL and microphonics
Tuner redesign
LLRF requirements
As discussed in Arne’s introduction, a recently adopted plan to reuse the LERF’s F100 and SL21 cryomodules has the benefit of reducing schedule and gradient risk in the current CEBAF Performance Plan (CPP)
In this talk, I will concentrate on many items, as compiled by Arne, Bob, Tony, and Curt, that we feel remain uncertain and that have significant potential impacts on the project

4. C75 field emission comparable to C100
Impact
Increased radiation fields near installed C75s
Potentially increased hardware degradation
Need to operate at reduced gradients
Risk Level
Moderate
Mitigation
Early prototyping
Improved pair assembly process incorporating lessons learned from LCLS-II production
Clean warm girder assembly procedures
Pair qualification goal: field emission free to spec gradient (time permitting)
Impact with Mitigation
Absence of field emission from C75 cavities
Risk Level with Mitigation
Low

5. Cavity tuning system issues
Impact
Cavity stiffness, tuner, stepper motor controls do not result in a tunable cavity
Risk Level
Moderate
Mitigation
Cavities designed to have the same stiffness as C50
Prototyping and analysis of prototype performance
Impact with Mitigation
Installed prototypes seem to tune as well as other C50 cavities
Risk Level with Mitigation
Low

6. Microphonics Impact Risk Level Mitigation Impact with Mitigation
Cavity microphonic detuning exceeds predicted levels
Risk Level
Moderate
Mitigation
Design includes stiffening supports for HOM loads
Prototyping and analysis of prototype performance
Impact with Mitigation
Installed prototypes seem to have small enough rms detuning and 6 sigma detuning to support QL choice
Installed cavities adequately controlled
Risk Level with Mitigation
Low

7. BBU Impact Risk Level Mitigation Impact with Mitigation
Multipass BBU reduces operating current of CEBAF
Risk Level
Moderate
Mitigation
Calculations and analysis of HOM performance
Measurement of HOM performance in all C75 cavities
Impact with Mitigation
Cavity deflecting HOMs damped to the correct Q levels
No BBU
Risk Level with Mitigation
Low

8. Schedule Risks First cryomodule delayed Impact Risk Level Mitigation
LLRF installed but cannot take advantage of full gradient
Module remains a C20 or C50
Progress on energy reach increase delayed
Risk Level
Moderate
Mitigation
Regular reporting on cryomodule progress
Impact with Mitigation
Schedule is maintained
Risk Level with Mitigation
Low

9. LLRF design and/or implementation delay
Impact
LLRF late delivery
Cannot take full advantage of first C75 cryomodule; becomes a C60
Risk Level
Moderate
Mitigation
Max gradient test on NL13-1 by November 2018
Develop and test prototype LLRF on installed C75 cavity pair in NL13 by February 2019
Impact with Mitigation
No delay
Risk Level with Mitigation
Low
In either case, will install cryomodule and LLRF during downs when ready

10. C75 “operational” performance similar to C100 (20% below expectations)
Impact
Effectively, have a C60
Delay achieving CPP goals
Plan goes on longer
Risk Level
Moderate
Mitigation
Early prototyping and analysis of prototype performance
Improved clean girder installation procedures
Impact with Mitigation
We have already achieved close to desired performance in one installed cavity (NL13-1)
Increased per module gradient
Achieving CPP goals
Risk Level with Mitigation
Low

11. Insufficient accelerator downtime for installation and commissioning
Impact
Cryomodule(s) not ready for beam operations
Possible need to commission cryomodule in parallel with beam operations
Delayed beam operations and 12 GeV running
Risk Level
Low with the expected funding profile for the next few years
Mitigation
Build up spare warm girders and commissioning infrastructure to reduce installation and commissioning time
Impact with Mitigation
Ability to support installation and commissioning of two C75 cryomodules during a two month down
Risk Level with Mitigation
Low

12. Insufficient end group availability
Impact
Delayed cavity assembly and C75 cryomodule assembly
Risk Level
Moderate
Mitigation
End groups from module replaced by SL21 will provide initial deposit in bank
Identify and/or procure another 8 usable end groups for a full C75 complement of cavities (third LERF cryomodule?)
Impact with Mitigation
Risk retired
Risk Level with Mitigation
Low

13. Major Power Outage
Hurricane Isabel (.75 MV/m/cavity), 2017 (verdict out)
Impact
Delayed implementation of CPP
Degraded energy reach for the user program
Failure to reach design energy
Need to reprocess cavities
Risk Level
Moderate
Mitigation
More/faster reworks required
Regain installed 100 MeV margin in each linac
Impact with Mitigation
Maintain energy reach
Have a buffer against step loss from a major event
Risk Level with Mitigation
Low

14. Cryogenics plants failures
Impact
Delayed cooldown and commissioning of newly installed C75s
2K He not available for full 12 GeV running
Uncontrolled warmup of the linacs and gradient loss, delaying progress from the CPP
Risk Level
Moderate
Mitigation
Redundancy in CHL design
New 2K coldbox up by December 2020
Work on cold compressor 4
Increased spending on special spares (long lead/expensive)
Upgrade of power distribution systems within CHL
Impact with Mitigation
Reduced risk of major outage
Increased flexibility in operation
Risk Level with Mitigation
Low

15. Organizational Risks
Insufficient institutional commitment to the C75 Program in CPP
Impact
Delayed implementation
Degraded energy reach for the user program
Failure to reach design energy
Risk Level
High
Mitigation
Internal reviews
Improve communication with stakeholders
Impact with Mitigation
Greater institutional “buy in” for C75 project
Risk Level with Mitigation
Moderate

16. Insufficient resources (people and procurements) devoted to achieving the CPP schedule
Impact
Delayed implementation
Degraded energy reach for the user program
Failure to reach design energy
Risk Level
Moderate
Mitigation
Regular Reports to Lab Planning and Coordination meeting
Project Tracking
Risk Level with Mitigation
Low

17. SUMMARY
Thank you for your time
Questions, Comments and Thoughts

18. C100 Based Risk C100 degradation beyond the present day level Impact
Depending on eventual rate, delayed or impossible 12 GeV operations
Need to adjust CPP up to produce more cryomodules
Risk Level
High
R&D Activity
Scientific understanding of the causes of degradation
Continued study of field emission causes and field emitter migration
Mitigation
Elimination of field emitter sources (warm girders, pumps, etc.)
Impact with Mitigation
Robust performance and reduced performance losses in all CEBAF cavities
Risk Level with Mitigation
Low

19. C100 catastrophic failure
Impact
Loss of MeV (5 passes) of beam energy
Lost beam operations time
Risk Level
Low
Mitigation
Install high-gradient F100 now in a C100 slot: provides C100 for early refurbishment and eventual spare
Rework SL21 into a true C100 style module (eliminate riser limitation)
Accelerate CPP to build in 100 MeV margin in each linac as quickly as possible
Impact with Mitigation
Able to recover much more quickly from failure
Risk Level with Mitigation

20. CEBAF Actual Cryomodule Energy Reach
CEBAF RF dashboard status: 2/6/2018
Cryomodule
Type
Energy Gain
(MEV)
Avg. ± STD % of
nominal
C20
27.5 ± 3.6
137
C50
41.9 ± 7.3 84
C100
79.9 ± 3.7 80
Red Interior Page Design 1

21. CEBAF Actual Cryomodule Energy Reach
CEBAF RF dashboard status: 2/6/2018
Cryomodule
Type
Energy Gain
(MEV)
Avg. ± STD % of
nominal
C20
27.5 ± 3.6
137
C50
41.9 ± 7.3 84
C100
79.9 ± 3.7 80
C75
~60 ?
~80 ?
Red Interior Page Design 1