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 Magnetic Field Issue in CM Solenoid Fringe Field and Magnetic Shield design Materials in CM K. Saito, 5 November 2012 Page 2

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 0.085 QWR showed a remarkable Q-drop at very low Field. A. Facco, April 2012 Lehman Review - B08 K. Saito, 5 November 2012 Page 3

Similar Experience in IPN @ Orsay S.Bousson K. Saito, 5 November 2012 Page 4

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 Page5

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

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

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 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 Β=0.53, SC cavities A 9 T Solenoid 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 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 Page13