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
Outline
 RF-Design in QWRs (similar experience at Orsay)
• b=0.085 QWR
• b=0.041 QWR
 Magnetic Field Issue in CM
• Solenoid Fringe Field and Magnetic Shield
design
• Materials in CM
, Slide
2 2
K. Saito, 5 November 2012 Page
Issue Faced in FRIB β=0.085 QWR
4.2K
(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)
FRIB QWR
(80.5MHz)
Original 0.085 QWR showed a remarkable
Q-drop at very low Field.
A. 2012
Facco, April 2012 Lehman Review - B08, Slide 3
K. Saito, 5 November
Page 3
Similar Experience in IPN @ Orsay
S.Bousson
K. Saito, 5 November 2012 Page 4
Potential Causes
Tuning plate overheating
LHe
Inner
conductor
or
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.
FRIB 5ASD,
19 June
2012Page5, Slide 5
K. Saito,
November
2012
Implemented cure for the β=0.085 QWR
ReA3 0.085 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, Slide 6
Low Cost Bottom Flange with 0.041 QWR
NbTi
Flange
 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.
RRR Nb
EBW
b=0.041 cavity ring
This idea looks
no work.
Why ?
A. Facco, June 2012 ASAC Review
A. Facco,
- 07 April 2012 Lehman Review - B08, Slide, Slide
7
7
Elongation/Copper tunig plate/ New matreial flange ??
Cavity
parameters
B-joint (G)
K (kHz/mm)
Orizinal Elongated
QWR041 QWR085
5.9
6.1
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 Page 8
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
Page 9
Field on the cavity
surface
A
B
Hc1 ~ 1250 G @ 4.2K
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
Page10
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
Page 11
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
Page 12
Cost Optimization of Magnetic Shield
Global Shielding
Concept #1,
room temp
global shielding
Local 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
Page13