Peng SHA, 20180525 On behalf of CEPC SRF group CEPC SRF Cavity Peng SHA, 20180525 On behalf of CEPC SRF group IHEP, CAS
Introduction Outline Development of 650 MHz cavity N-doping/N-infusion research Test cryomodule of CEPC 650 MHz SRF Other work Next IHEP, CAS
SRF cavities for CEPC 650 MHz 2-cell cavity 240 19.7 1.5E10 22 2E10 Cavity amount Gradient (MV/m) Q for long period Gradient in horizontal test (MV/m) Q in horizontal test Gradient in vertical test (MV/m) Q in vertical test 650 MHz 2-cell cavity 240 19.7 1.5E10 22 2E10 4E10 1.3 GHz 9-cell cavity 96 19.8 1E10 24 3E10 1.3 GHz Cryomodule (8 cavities inside, as E-XFEL, LCLS-II, ILC, SCLF) 3 650 MHz Cryomodule (6 cavities inside, new!)
Progress of CEPC SRF cavity study Vertical test result of 650 MHz 2-cell cavity: Q0=4.0E10@19.2MV/m, which is close to the CEPC target (Q0=4.0E10@22.0MV/m). N-doping research has gained progress. Q0 increased obviously for 650 MHz 1-cell cavities after N-doping. Design of the test cryomodule is nearly finished, which consist of two 650 MHz 2-cell cavities and other components (main coupler, HOM coupler and absorber, tuner…). The fabrication of a new N-doping/N-infusion furnace has completed over 50%. Design of Nb3Sn coating equipment has been finished. Main components of electropolishing (EP) finished factory acceptance tests. IHEP, CAS 4
Development of 650MHz cavity Outline Introduction Development of 650MHz cavity N-doping/N-infusion research Test cryomodule of CEPC 650MHz SRF Other work Next IHEP, CAS
RF design of 650 MHz 2-cell cavity (1) Cavity type CEPC-V1 CEPC-V2 Parameters Mid & end half cell Mid half cell End half cell Riris (mm) 78 75 80 Alpha (deg) 3.22 8 15.3 A (mm) 94.4 93 B (mm) a (mm) 20.123 20 b (mm) 22.09 30 D (mm) 204.95 412.5 R/Q (Ω) 213 211 G (Ω) 284 279 Ep/Eacc 2.4 Bp/Eacc 4.2 IHEP, CAS 6
RF design of 650 MHz 2-cell cavity (2) Cavity type CEPC-V1 CEPC-V2 Design goals Ep/Eacc: 2~2.4 Bp/Eacc: 3.8~4.2 Same half cells design α：8~10° Trap modes: TM012 & TE121 Advantages Four same half cells, save dies, economic Different designs for mid half cell and end half cell, improve the trap modes Easy to extend to multi-cell cavity Large side wall angle is better for surface processing and cavity mechanics. Disadvantages Trap modes Hard to extend to multi-cell cavity Two different end half cell design is better for trap modes IHEP, CAS 7
Comparison IHEP, CAS f (MHz) R/Q (Ω) Ep/Eacc Bp/Eacc Ri/Rt (mm) CEPC-V2 (2-cell) 650 211 2.4 4.2 75/80 CEPC-V1 213 78/78 FCC (4-cell) 435 2.2 4.1 74/80.2 TESLA (9-cell) 1036 2.0 4.3 70/78 * All geometrical parameters are scaled to 650 MHz. IHEP, CAS 8
Vertical test (11 May, 2018) IHEP, CAS Vertical test result: Q0=4.0E10@19.2MV/m，which is close to the CEPC target (Q0=4.0E10@22.0MV/m). IHEP, CAS 9
N-doping/N-infusion research Outline Introduction Development of 650MHz cavity N-doping/N-infusion research Test cryomodule of CEPC 650MHz SRF Other work Next IHEP, CAS
Surface resistance (Rs) of SRF cavity Depend on smoothness, cleanliness and flux trapping, etc If T<TC/2, then Δ(T) ≈ Δ(0) A is a constant related with London penetration depth, coherent length, Fermi velocity, mean free path… Δ(T) is the energy gap. IHEP, CAS 11
N-doping and N-infusion: reduce RBCS, increase Q! High Q (LCLS-II, SCLF, CEPC) N-doping High Q and gradient (ILC) CEPC Goal N-doping N-infusion N-doping for PIP-II 650 MHz single-cell cavity A. Grassellino, ICFA seminar 2017 IHEP, CAS 12
N-doping at OTIC and KEK N-doping at KEK N-doping at Ningxia Orient Tantalum Industry Co., Ltd (OTIC) OTIC: The furnace heater is made by Tantalum, not molybdenum. N-infusion isn’t allowed, because N2 injection at 120C for 48 hours may harm the heater. KEK: The furnace can be used for N-doping and N-infusion. IHEP, CAS 13
SIMS Results of N-doping at OTIC and KEK No N, NbN N increase! NbN NbN H decrease H decrease N increase! Before N-doping N-doping at OTIC (~3 Pa, 800℃ for 2 minutes) N-doping at KEK (~3 Pa, 800℃ for 2 minutes) IHEP, CAS 14
Results of SEM, R-T SEM 9.05K: TC of pure Nb 9.86K: TC of Nb N-doped 846nm 9.86K is between Nb (9.23K) and NbN (16.2K), a mixture of Nb and NbN. After N-doping, clear formation of NbN precipitates in the surface. IHEP, CAS 15
SIMS Results of N-infusion at KEK (1) Nb sample with Buffered Chemical Polishing (BCP) SIMS Results of N-infusion at KEK (1) Nb sample with Electropolishing (EP) H decrease N, NbN H decrease N, NbN BCP sample before N-doping BCP sample after N-infusion （~3 Pa, 125℃ for 48 hours ） BCP sample after N-infusion （ ~3 Pa, 160℃ for 48 hours ） IHEP, CAS 16
SIMS Results of N-infusion at KEK (2) H decrease H decrease N, NbN N, NbN Intensity of N, NbN EP sample after N-infusion （~3 Pa, 125℃ for 48 hours ） EP sample after N-infusion （ ~3 Pa, 160℃ for 48 hours ） EP sample before N-doping There’re fewer N/NbN of N-infusion than N-doping. IHEP, CAS 17
N-doping process of 650 MHz 1-cell cavities 1st, the baseline vertical test of 650 MHz single-cell cavity before N-doping. 2nd , this cavity received light BCP and was N-doped. 3rd, the cavity received High Pressure Rinsing (HPR) , following with class -10 assembly for vertical test. 4th, the cavity received vertical test again. N-doping HPR Assembly Vertical test IHEP, CAS 18
Vacuum and temperature curve during N-doping ~3 Pa for 2 minutes IHEP, CAS 19
Vertical test results IHEP, CAS After N-doping, Q0 increased obviously at low field for both cavities. 650S1: Q0=7e10@Eacc=10MV/m. But Q0 decreased quickly at high field (>10 MV/m) because of no BCP/EP after N-doping. 650S2: Quench at Q0=6.9e10@Eacc=8.8MV/m. CEPC Target IHEP, CAS 20
Test cryomodule of CEPC 650MHz SRF Outline Introduction Development of 650MHz cavity N-doping/N-infusion research Test cryomodule of CEPC 650MHz SRF Other work Next IHEP, CAS
Test cryomodule IHEP, CAS Design of the test cryomodule is underway, which consist of two 650MHz 2-cell cavities and other components (main coupler, HOM coupler and absorber, tuner, Helium Vessel, etc). The assembly will be finished in the middle of 2019. IHEP, CAS 22
HOM Coupler for 650MHz 2-cell cavity Result measured is almost the same as simulated. Error is introduced during machining and assembly. IHEP, CAS 23
Helium vessel, main coupler, HOM absorber Helium vessel design is being optimized. HOM absorber is under fabrication. Main coupler finished design and began fabrication. IHEP, CAS 24
Other work Outline Introduction Development of 650MHz cavity N-doping/N-infusion research Test cryomodule of CEPC 650MHz SRF Other work Next IHEP, CAS
N-doping/N-infusion furnace、EP The fabrication has completed over 50%. The furnace will be transported to IHEP in middle of 2018. Factory acceptance test of mechanical part for EP. IHEP, CAS 26
Nb3Sn film Nb3Sn: high Tc, much higher Q than Nb at 4.2K, higher gradient (120MV/m in theory) than Nb (50 MV/m). Nb cavity coating with Nb3Sn film is promising in future. Vertical test results of 1.3GHz @ Cornell Martina Martinello, FCC week 2018. ~30 times! IHEP, CAS 27
Equipment for Nb3Sn coating Parameters Value Min vacuum 5.0E-5 Pa Max temperature 1400℃ Min vacuum@1400℃ 9.0E-4 Pa Uniform temperature area Φ300mm×500mm Nb chamber Main heater (molybdenum-lanthanum alloy) Inner vacuum Heater (tungsten) Sn Nb cavity Outer vacuum Design has been completed (bid opening on 30th May). It will be transported to IHEP in the end of 2018. IHEP, CAS
Frontier research of Fe-pnictides Fe-pnictides: high Tc, much higher gradient (200 MV/m in theory) than Nb (50 MV/m). Key: coating with curved surface. RS Measurement Dewar will be completed in June. Theoretical Model (by Alex Gurevich) First step (simplified) Nb（9.2K）+ FeSe（11K) FeSe LiF Nb IHEP, CAS 29
Next Outline Introduction Development of 650MHz cavity N-doping/N-infusion research Test cryomodule of CEPC 650MHz SRF Other work Next IHEP, CAS
Upcoming IHEP, CAS June ~ July，vertical tests of over 10 cavities. 1st week: 650 MHz 2-cell (baseline), 1.3 GHz 1-cell (baseline) 2nd week: 650 MHz 5-cell (baseline) 3rd week: 650 MHz 2-cell (baseline), 1.3 GHz 1-cell (baseline) 4th week: 650 MHz 1-cell (N-doping), 650 MHz 1-cell (N-doping) 5th week: 650 MHz 1-cell (baseline)，650 MHz 1-cell (Japan Nb + baseline) 6th week: 650 MHz 1-cell (Japan Nb + baseline), 650 MHz 1-cell (Japan Nb + N-doping) 7th week: 3.9 GHz 1-cell (baseline), 3.9 GHz 1-cell (N-doping), 3.9 GHz 1-cell (LG + N-doping) Higher frequency, better N-doping performance. Two 1.3 GHz 1-cell cavities would be transported to KEK for EP, N-doping and test in August. Martina Martinello, FCC week 2018. IHEP, CAS 31
Goal within 1 year Research on N-doping/N-infusion, increase the Q value (650 MHz, 1.3 GHz) by N-doping/N-infusion and EP further. Complete the development of test cryomodule and begin experiments. Complete eight 1.3 GHz 9-cell cavities for SCLF, target: 2.7E10@16MV/m. Besides, make 8 couplers for these cavities, target: 14kW (traveling wave). IHEP, CAS 32
3~5 years 2021: Exceed CEPC target (650MHz 2-cell: 4E10@22MV/m, 1.3GHz 9-cell: 3E10@24MV/m）；Transfer N-doping/N-infusion technology to HE-RACING TECHNOLOGY. Meanwhile: 600 cavities for SCLF start batch production. 2023: Master Nb3Sn coating technology. Complete coating with 1.3 GHz cavity. Goal: Q=1.01010@Eacc=5~10MV/m (at 4.2K). 2023: Preliminarily master key technology of Fe-pnictides coating with curved surface. IHEP, CAS 33
Acknowledgements: PKU and KEK. Thanks for your attention! IHEP, CAS