RF/SRF Working Group Charge
Matthias Liepe ,Cornell
Takaaki Furuya, KEK
The overall charge to Working Group 3 on superconducting RF, RF, and RFcontrol is to identify critical RF and SRF related items for the construction ofERLs, evaluate the readiness of the related science and technology, and to lay
out an R&D path for solving remaining open issues. In particular the following
questions will be explored:• What parameter space is covered by ERLs presently under discussion? A
template/questionnaire will be distributed in advance to participants of the WG,
which should be submitted prior to the workshop.
• What cavity performance is currently achievable with good reproducibility? What
intrinsic cavity Q0 is achieved in current SRF linacs (CEBAF, FLASH…)? What isneeded to increase it further? What is the best cavity surface treatment forachieving lowest surface resistance at medium fields? What field emission levelshould be expected at operating gradients? Which component/step during thebeam line assembly has the highest risk of causing field-emitting particles? Whatdiagnostics is needed for the detection of field emission and optimization of theoperating gradients in a main linac?
• What loaded quality factor QL is currently achievable with stable cavity operation andgood field stability? What is needed to increase it further? What is the optimalloaded Q? What field stabilities have been demonstrated at high QL? Is an
adjustable input coupler essential? What LLRF systems have been developed
specifically for high loaded Q operation and what are the related challenges?
• What main linac cavity designs have been developed for ERLs? What design criteria
were used? A template/questionnaire on cavity design will be distributed inadvance to participants of the WG, which should be submitted prior to theworkshop.
• How can peak cavity microphonics be reduced in SRF main linacs by passive andactive means? What is the main source driving microphonics? What is a realistic
value for the peak detuning in SRF linacs over a period of a day? What is theideal frequency tuner in terms of microphonics and its compensation?
• What RF input couplers have been developed? A template/questionnaire on RF inputcouplers will be distributed in advance to participants of the WG, which should besubmitted prior to the workshop.

• What HOM damping schemes have been developed? What is their parameter space?

A template/questionnaire on HOM dampers will be distributed
in advance to participants of the WG, which should besubmitted prior to the workshop.
• What are the cryomodule challenges, and how can they be addressed? What method
gives the highest reliability for vacuum sealing at cryogenic temperatures? Whatprecision is needed for the cavity alignment, and how can it be achieved? Whatlevel of magnetic shielding is needed and how can it be achieved?
• What are the injector RF/SRF challenges, and how can they be addressed?
• What is the best RF power source for the main linac SRF cavities? What is currently
available, and what will be the future direction?
• How should the cryogenic plant for an ERL linac be designed/optimized? How can it
be adjusted for changes in the operating temperature and total heat load?