1 Matthias Liepe August 2, 2007 Future Options Future Options Matthias Liepe
Jan 21, 2016
1Matthias Liepe August 2, 2007
Future Options Future Options
Matthias Liepe
2Matthias Liepe August 2, 2007
Outline
• Options for cost reduction
• SRF Cavities and higher Q0
• Microphonics, RF Power and Input Couplers
• HOM damping– Waveguide HOM damping
– Beam-line absorber
• Cryomodule Simplifications
3Matthias Liepe August 2, 2007
Options for cost reduction
Parameter old new change [%] change [%]
Q0 2.0E+10 3.0E+10 -4.1 -13.8
loaded Q 6.5E+07 1.0E+08 -2.5 -13.4
module cost 100% 80% -6.7 0
fill factor 49% 55% -0.8 0
total -14% -27%
• “Baseline layout” should work well, but
• reduction in construction and operating costoperating cost is desirable
• Need to balance lower cost against increased risk
• ExamplesExamples of parameter tuning/optimization:
Cost of cryo-plant
(power)0.4
4Matthias Liepe August 2, 2007
SRF Cavities and higher Q0• 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)
• Q0=3· 1010 at T=1.8K:– 9 n surface resistance gives Q0=3· 1010
– At 1.8 K with 120C bake: RBCS=3 n need <6 n residual resistance
– Very good magnetic shielding required (<15 mOe)
– This has been achieved in vertical tests
5Matthias Liepe August 2, 2007
Q0=3· 10 10 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 Q0
– High Q R&D program– Daresbury / Cornell /
LBNL Test Module– Main linac test module– Main linac module
6Matthias Liepe August 2, 2007
Microphonics and RF Power for QQLL=10=10
88
<600 W at 12.3 MV/m
<1 kW<1 kW at 16.2 MV/m!
11
1
2
2
22
3
3
33
4
pe
ak d
etu
nin
g [
Hz]
gradient [MV/m]10 15 20 250
10
20
30
40
50
60 For peak detuning <10Hz:•QL,opt = 108
•P < 2kW sufficient!
•We have demonstrated this at the JLAB FEL:
0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
time [sec]klys
tron
pow
er [
kW]
5.5 mA4 mA2.5 mA0 mA
7-cell cavity
7Matthias Liepe August 2, 2007
2kW RF System (R&D required!)
• Solid state amplifiers become an alternative to IOTs– Simpler, require less space in tunnel– 40% overall efficiency is feasible (R&D itemR&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 couplersMuch 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 Liepe August 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 Q0 requires relative long superconducting niobium waveguide sections
• Mechanical / thermal design needs to be worked out
9Matthias Liepe August 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 Liepe August 2, 2007
First HOM Damping Simulation Results
• Level of damping very similar to damping with beam line HOM absorbers
Brillouin diagram
Valery Shemelin
11Matthias Liepe August 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 Liepe August 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=1kN Thermal Atmospheric pressure
13Matthias Liepe August 2, 2007
Simplified HOM Beam Line Absorber: CLANS HOM
Damping Results
Similar level of HOM damping
2000 2500 3000 3500 4000 4500 500010
1
102
103
104
frequency [MHz]
Q
box HOM loadflat load
Monopoles
14Matthias Liepe August 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