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

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

3. 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

4. Outline of ERL Main Linac Presentations

5. 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

6. 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:
K, K, 98 80K
Qext = 6.5x107
HOM power (average) 150 watt/cavity
Peak & average RF power/cavity = 5 kW & 2 kW

7. 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)

8. 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

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

10. 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

11. 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