Largegrain cavities in a CEBAF cryomodule TTC Meeting

Large-grain cavities in a CEBAF cryomodule TTC Meeting Milan, 6 -9 Feb. 2018 G. Ciovati Sunday, November 22, 2020 CEBAF tunnel

Outline • “C 75” project • C 75 large-grain cavities: fabrication, processing and testing • Installation of C 75 cavities in the cryomodule • C 75 cavity performance in the cryomodule Large-grain cavities in a CEBAF cryomodule 2

Cavities and Cryomodules in CEBAF • Cryomodules labeled “Cxx” (xx = design energy gain) －“C 20” = original cavities installed in 1990 s －“C 50” = refurbished original cavities (EP, 600°C anneal, HPR) －“C 100” = new cavities for 12 Ge. V upgrade －Proposed “C 75” = new cells for CEBAF energy maintenance Large-grain cavities in a CEBAF cryomodule 3

Cavity parameters and specifications Parameter Number of cells R/Q·G ( 2) Epk/Eacc Bpk/Eacc [m. T/(MV/m)] Kcc (%) Specifications Eacc (MV/m) Q 0(2. 07 K) Qext_FPC Rtr ( /m) C 100 cavity 7 243553 2. 17 3. 74 1. 49 C 100 cavity 19. 2 8× 109 3. 2× 107 (± 20%) ≤ 2× 1010 C 50 cavity 5 132205 2. 56 4. 56 3. 15 C 50 cavity 12. 5 6. 8× 109 8× 106 (± 25%) ≤ 2× 1010 C 75 cavity 5 144805 2. 45 4. 18 3. 12 C 75 cavity 19. 07 8× 109 2× 107 (± 15%) ≤ 2× 1010 C 75 cavity: • ~10% more efficient that C 50 cavity by design • Same stiffness as C 50 cavity • Similar performance than C 100 cavity • Same cryomodule as C 20/C 50 cavities Large-grain cavities in a CEBAF cryomodule 4

Prototype C 75 cavities • Three prototype cavities built, processed and tested “in house” (Sep. 2016 – Jan. 2017) • Two cavities (5 C 75 -001 and 5 C 75 -002) made from large-grain Nb discs multi-wire sliced from CBMM ingot (RRR~120, Ta = 6701350 wt. ppm) • One cavity (5 C 75 -003) made from large-grain Nb discs from Tokyo-Denkai (RRR = 496, Ta = 29 wt. ppm) 5 C 75 -001 Large-grain cavities in a CEBAF cryomodule 5 C 75 -002 5 5 C 75 -003

Cavity fabrication and processing • 4 inside/outside equator welds, 1 full penetration outside weld • Processing and testing: 5 C 75 -001 70 mm CBP 30 mm EP 5 C 75 -002 70 mm CBP 35 mm EP 800 °C/ 3 h vacuum anneal 30 mm EP HPR RF Test 800 °C/ 3 h vacuum anneal 20 mm EP HPR RF Test 5 C 75 -003 95 mm BCP 1: 1: 2 600 °C/ 3 h vacuum anneal 30 mm EP HPR RF Test Local grinding 30 mm BCP 1: 1: 2 HPR RF Test 20 mm EP • Limit: quench at equator weld defects • There were issues with EBW machine during cavity fabrication Large-grain cavities in a CEBAF cryomodule 6

C 75 large-grain cavity pair • Installed FPC “dog-leg” with ceramic window, HOM “elbows” and HOM loads T = 2. 07 K Large-grain cavities in a CEBAF cryomodule 7

Installation in Cryounit • Installation of cold tuner and magnetic shield • Installation into Helium vessel • Installation of secondary magnetic shield, MLI, thermal shield • Installation into Cryounit vacuum vessel • 3 flux-gate magnetometers attached to center cells of 5 C 75 -001 1546 1544 1545 Large-grain cavities in a CEBAF cryomodule 8

Residual field during CM assembly • Increased residual field at the cavity after welding operations Large-grain cavities in a CEBAF cryomodule 9

Cryomodule cool-down 5 C 75 -001 (cav 1) 5 C 75 -003 (cav 2) The remaining 6 cavities in the cryomodule are standard C 50 cavities • Installed in slot “ 1 L 13” in CEBAF • Cavity 1 cool-down across Tc at a rate of 0. 44 K/min (“slow”) • Cryomodule commissioned in Oct. -Nov. 2017 Large-grain cavities in a CEBAF cryomodule 10

Cavity performance in cryomodule (1) • Cav 1 quenched at 19. 1 MV/m after RF processing of field emission • C 75 large-grain cavities have higher Q 0 than the other C 50 finegrain cavities: better flux expulsion? Large-grain cavities in a CEBAF cryomodule 11

Cavity performance in cryomodule (2) • The additional following parameters of C 75 cavities met specifications and were equivalent to those of C 50 cavities: －Tuner operation －Microphonics (peak detuning ~10 -17 Hz) －HOM • The two large-grain C 75 prototype cavities have been operating in CEBAF since Nov. 2017 Large-grain cavities in a CEBAF cryomodule 12

Future plan • Fabricate two additional prototype cavities “in-house” • Evaluate schedule for contracting the fabrication of 8 additional cavities to a cavity vendor • Evaluate “in-situ” cryomodule degaussing Large-grain cavities in a CEBAF cryomodule 13

Acknowledgments • SRF R&D R. Rimmer, F. Marhauser, J. Guo • Engineering G. Cheng, E. Daly, F. Fors, C. Hovater • SRF Cavity Fab. Group L. Turlington, B. Clemens, J. Henry, S. Williams • Machine Shop D. Combs, R. Martin, J. Dail • SRF Cavity Prod. Group A. Anderson, K. Davis, C. Dreyfuss, J. Follkie, D. Forehand, T. Harris, C. Johnson, R. Overton, T. Sessoms, A. Wildeson • SRF Test and Meas. Group N. Brock, C. Wilson, M. Drury • SRF CM Assembly Group J. Fischer, R. Legg, M. Mc. Crea • Accel. Div. Management A. Freyberger, A. Hutton, A. Mc. Ewen, G. Myneni Large-grain cavities in a CEBAF cryomodule 14