1Matthias LiepeAugust 2, 2007 Future Options Matthias Liepe

2Matthias LiepeAugust 2, 2007 Outline Options for cost reduction SRF Cavities and higher Q 0 Microphonics, RF Power and Input Couplers HOM damping –Waveguide HOM damping –Beam-line absorber Cryomodule Simplifications

3Matthias LiepeAugust 2, 2007 Options for cost reduction Parameteroldnewchange [%] Q0Q0 2.0E+103.0E loaded Q6.5E+071.0E module cost100%80%-6.70 fill factor49%55%-0.80 total-14%-27% “Baseline layout” should work well, but operating costreduction in construction and operating cost is desirable Need to balance lower cost against increased risk ExamplesExamples of parameter tuning/optimization: Cost of cryo- plant  (power) 0.4

4Matthias LiepeAugust 2, 2007 SRF Cavities and higher Q 0 Cavities account for  30% of cryomodule cost! –keep end groups simple: “the end groups (beam pipe, input coupler port, HOM couplers, flanges, transition to LHe container) cost a much as the 9-cells alone.” (D. Proch, COST REDUCTION IN CAVITY FABRICATION) Q 0 =3· at T=1.8K: –9 n  surface resistance gives Q 0 =3· –At 1.8 K with 120C bake: R BCS =3 n   need <6 n  residual resistance –Very good magnetic shielding required (<15 mOe) –This has been achieved in vertical tests

5Matthias LiepeAugust 2, 2007 Q 0 =3· at T=1.8K Such Q-values have been demonstrated in vertical cavity tests, but not in linacs Issues: shielding, FE 16.2 MV/m  R&D program for high Q 0 –High Q R&D program –Daresbury / Cornell / LBNL Test Module –Main linac test module –Main linac module

6Matthias LiepeAugust 2, 2007 Q L =10 8 Microphonics and RF Power for Q L =10 8 <600 W at 12.3 MV/m <1 kW  <1 kW at 16.2 MV/m! peak detuning [Hz] gradient [MV/m] For peak detuning <10Hz: Q L,opt = 10 8 P < 2kW sufficient! We have demonstrated this at the JLAB FEL: time [sec] klystron power [kW] 5.5 mA 4 mA 2.5 mA 0 mA 7-cell cavity

7Matthias LiepeAugust 2, kW RF System (R&D required!) Solid state amplifiers become an alternative to IOTs –Simpler, require less space in tunnel R&D item –40% overall efficiency is feasible (R&D item!) –Similar cost at kW power level, further reduction in cost likely Power RF cables instead of waveguides –Require less space in tunnel –Much simpler input couplers –Much simpler input couplers (similar to the once used in vertical cavity tests) and coupler ports at vacuum vessels 7/16 DIN 7/8" Foam Heliax 2kW cw RF amp Coax input coupler

8Matthias LiepeAugust 2, 2007 HOM Damping Alternative I: Waveguide HOM Damping Scheme Similar to JLAB 1 A plans 6 HOM waveguides per cavity (with integrated fundamental mode input coupler) Design / optimization under progress… High Q 0 requires relative long superconducting niobium waveguide sections Mechanical / thermal design needs to be worked out

9Matthias LiepeAugust 2, 2007 Waveguide HOM Damping Simulations Cell shape optimized for high R/Q*G 85º wall angle Fill factor: 59% 85º Length of beam tubes and Nb section of waveguides adjusted for sufficient attenuation of fundamental mode (-40dB) Niobium section of waveguide

10Matthias LiepeAugust 2, 2007 First HOM Damping Simulation Results Level of damping very similar to damping with beam line HOM absorbers Brillouin diagram Valery Shemelin

11Matthias LiepeAugust 2, 2007 HOM Damping Alternative II: Simplified HOM Beam Line Absorber Fewer absorber tiles Fewer parts overall Reduced length  fill factor increases by  4% to 53% 2 instead of 3 types of materials?

12Matthias LiepeAugust 2, 2007 Simplified HOM Beam Line Absorber: ANSYS Results HOM load allows for 2mm longitudinal length change from cool-down and cavity tuning 1mm longitudinal from F=1kNThermalAtmospheric pressure

13Matthias LiepeAugust 2, 2007 Simplified HOM Beam Line Absorber: CLANS HOM Damping Results  Similar level of HOM damping

14Matthias LiepeAugust 2, 2007 Cryomodule Simplifications No coaxial coupler ports (only feed-thoughts for power RF cables) –No precise machining of ports required –Cavities are free to move longitudinal during cool down  Can use simple, fixed cavity support without breaking the HGRP into sections Simplified thermal shield and outer magnetic shield Tolerances on many parts can be relaxed More items: see Eric’s talk