1. Technical Issues Facing in the FRIB Cryomodule
NSCL Professor, SRF Department Manager
Kenji Saito
TTC Meeting WG-1, 6 November 2012
K. Saito, 5 November 2012
Page 1

2. Outline RF-Design in QWRs (similar experience at Orsay) b=0.085 QWR
Magnetic Field Issue in CM
Solenoid Fringe Field and Magnetic Shield design
Materials in CM
K. Saito, 5 November 2012
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3. Issue Faced in FRIB β=0.085 QWR
(a) Before elongation, regular plate
(b) After elongation, regular plat
(c) After degassing, regular plate
(d) Directly Cooled 14 mm plate
(e) Thin plate + titanium bottom flange
(f) ReA6 Goal (4K)
(g) ReA3 Goal (4K)
4.2K
FRIB QWR (80.5MHz)
Original QWR showed a remarkable Q-drop at very low Field.
A. Facco, April 2012 Lehman Review - B08
K. Saito, 5 November 2012
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4. Similar Experience in IPN @ Orsay
S.Bousson
K. Saito, 5 November 2012
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5. Potential Causes Tuning plate overheating LHe Inner or conductor
Poor RF Contact
Outer conductor
NbTi Bottom Flange
Tuning Plate(Nb) In
sealing
Thermal simulation result suggests the overheating at tuning plate.
Bottom flange is outside of the liquid helium.
NbTi material has very poor thermal conductivity, 10 times lower than Nb.
Tuning plate is cooled by very inefficient conduction cooling.
K. Saito, 5 November 2012
FRIB ASD, 19 June 2012
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6. Implemented cure for the β=0.085 QWR
ReA QWR 4.2K
Elongated Bottom tube and reduced the magnetic field ( < 0.5mT = 5G).
Material of the bottom flange changed
NbTi to Nb.
This looks to work expect for one case (SC248).
Nb Flange is expensive way.
A. Facco, April 2012 Lehman Review - B08

7. Low Cost Bottom Flange with 0.041 QWR
Not elongated the bottom pipe.
EBW thinner Nb ring on NbTi flange with channel.
Cooling improved more sufficiently through LHe in the channel and thinner Nb flange.
=0.041 cavity ring
NbTi
Flange
RRR Nb
EBW
This idea looks no work.
Why ?
A. Facco, April 2012 Lehman Review - B08
A. Facco, June 2012 ASAC Review - 07
, Slide 7

8. Elongation/Copper tunig plate/ New matreial flange ??
Cavity parameters
Orizinal
QWR041
Elongated
QWR085
B-joint (G)
5.9
6.1
K (kHz/mm)
12.6
2.8
NC50 flange ?: Better cooling + better RF contact + low cost
Low H-field on the tuning plate
? Sufficient cooling for the tuning
plate
? RF contact
Copper Tuner Plate ?
K. Saito, 5 November 2012
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9. Solenoid coil in cryomodule
INP (Orsay) LINAC
FRIB CM design: Contain 9T SC solenoids in the cryomodule to make short the LINAC
SC 9T solenoid
ISAC (TRIUMF)
K. Saito, 5 November 2012
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10. Field on the cavity surface
Β=0.53, SC cavities A
9 T Solenoid B
Hc1 ~ K
16 G at the closest cavity surface to the solenoid(9T).
When cavity quenched, flux trapping happens in the global shielding.
Magnetization happens if use SS.
K. Saito, 5 November 2012
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11. Magnetization and Demagnetaization Process
Magnetized SS316L Bellows after switch on SC solenoid
SS 316L: even welded, none magnetized material.
The welded area gets magnetization after exposed magnetic field.
~2G
Solenoid
Need demagnetization process
Cooling process is complicate
More concern to the magnetization of the material.
Need to use reliable none magnetization
material
K. Saito, 5 November 2012
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12. Field on Global Shield Surface with one dipole correction coils
M-metal will saturate under the 9T solenoid + dipole correction coil (0.12T)
K. Saito, 5 November 2012
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13. Cost Optimization of Magnetic Shield
Global Shielding
Local Shielding
Concept #1, room temp global shielding
Concept #2, cryogenic local shielding
Both shielding options require < 15 mG when resonator makes superconducting transition ~9K.
Once resonator is superconducting magnetic field can be > 15mG
K. Saito, 5 October 2012
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