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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

SUMMARY Thank you for your time Questions, Comments and Thoughts

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

C100 catastrophic failure Impact Loss of 400-500 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

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

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