ERL Director’s Review Main Linac Outline of Presentations H. Padamsee (10 min)

Distinguishing Features for ERL Main Linac CW operation Low beam loading due to energy recovery High reliability operation desired as a light source

Some High Level Consequences CW operation: dynamic heat load is dominant Refrigeration is a major part of the facility Influences optimal gradient choice, Design for highest reasonable Q0 T = 1.8 K is a serious possibility Reliability Choose modest gradient (16 MV/m) for higher reliability if cost optimum vs gradient is broad Radiation dose from cavity is CW Favors modest gradient (field emission grows exponentially) RF architecture : One RF source/cavity Loss of one RF source means loss of one cavity Optimize for the best performance of each cavity, as needed Low beam power Low peak and low CW RF power High Qext, low microphonics and excellent LLRF control desired

Outline of ERL Main Linac Presentations

Part I: Overall Parameters, Cavity and HOM Issues (Matthias Liepe, 30 min) Optimization of capital, operating and total costs Parameter Choices Gradient, Q0… Cavity and HOM issues (coupled) cell shape, number of cells, multipactor… QHOM, HOM power, HOM frequency range String layout, filling factor

Overall Parameters Energy 5 GeV Beam current 2 x 100 mA Bunch charge 77 pC, Bunch length 2 ps (0.6 mm) Main Linac Tunnel length: 319 m 2 linacs, 4 sections, 639 m total, 64 modules, 384 cavities Cryo-module: 6 SRF cavities + 1 magnet package (9.8 m total) 7 cells per cavity Average gradient = 16.2 MV/m Q0 = 2 x1010, Top = 1.8 K Total Refrigeration including 50% margin: 6.3 kW @ 1.8 K, 8.1 kW @ 5 K, 98 kW @ 80K Qext = 6.5x107 HOM power (average) 150 watt/cavity Peak & average RF power/cavity = 5 kW & 2 kW

Part II: Cryomodule Design Aspects (Eric Chojnacki, 20 min) Number of cavities per module Use basic TTF module design concepts Variations improve alignment and allow re-positioning in linac (with CM under vacuum and cold)

Part III: RF Choices Sergey Belomestnykh, 20 min IOT vs Klystrons RF architecture, one IOT/cavity Optimize each cavity for its gradient potential Higher reliability lose only one cavity per IOT lost, instead of many cavities Save space on RF distribution system Coupler choices

Part IV: LLRF (Matthias Liepe, 20 min) Low beam loading Amplitude and phase stability requirements from beam quality Qext, microphonics tolerance, tuner, LLRF

Each Talk Will Cover Baseline design choices Options still to be explored R&D program to address open issues Prototyping plan after fixing design choices

Final Talk : New Ideas (Mathias Liepe, 20 min ) To reduce capital and operating costs Push for highest Q0 Highest Qext, Low RF power Alternate cavity/HOM designs Simplify HOM coupler Input coupler Cryomodule