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