LCLS-II 1.3 GHz CM Demagnetization & Active Cancellation Saravan K. Chandrasekaran Technical Review Meeting for BCR May 25, 2016
Outline • Introduction – Previous work – Residual magnetic fields and Q 0 • pCM test plan for demagnetization & active cancellation – Understanding till now, & what remains to be understood • Production demagnetization & active cancellation coil – Proposed design of coils and connectorization – Cost summaries for different options – Need-by schedule • Operational modes – Information for SLAC controls 2 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Outline • Introduction – Previous work – Residual magnetic fields and Q 0 • pCM test plan for demagnetization & active cancellation – Understanding till now, & what remains to be understood • Production demagnetization & active cancellation coil – Proposed design of coils and connectorization – Cost summaries for different options – Need-by schedule • Operational modes – Information for SLAC controls 3 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Magnetic scope, specifications & sources • First large CW project where magnetic shielding being analyzed stringently, especially longitudinal component of magnetic field – B avg ↓ → R s ↓ → Q 0 ↑ → P diss ↓ → $ oper ↓ • LCLS-II specification [1]: – B avg <5 mG to reach Q >2.7E10 at 2 K, 16 MV/m • Major magnetic field sources: vacuum vessel, components, earth – B vessel < 3 G [2] – B components ~ 1 G – B earth ≈ 483 mG at SLAC [3] – B //,beamline ≈ 150 mG • Most analyses done assuming SLAC tunnel magnetic fields [1] “1.3 GHz Superconducting RF Cryomodule ,” Functional Requirements Document, LCLSII -4.5-FR-0053. [2] A. Crawford, arXiv:1507.06582v1. [3] National Oceanic and Atmospheric Administration, 2014--2019 World Magnetic Model. 4 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Trapped Magnetic Flux & Q 0 ↓ B ↑ ↑ Q 0 S. Posen et al., arXiv 2016 M. Martinello et al., IPAC 2016 • Smaller ambient magnetic fields beneficial – For high Q & for low flux expelling material • Q 0 >3 x 10 10 may be realized for trapped B <3 mG 5 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Benefits of degaussing vessel [4,5] Expt. With B // ≈50 mG • Vessel must be degaussed after final handling – Fields in steel could be ~200 G when exposed to ~500 mG • Edge ~factor of 3 reduction • Central ~factor of 2 reduction 400 Bz Pipe Before DeMag 300 Bz Pipe After 600 A-Turns/m 200 B [milligauss] 100 0 -100 -200 -300 -400 0 1 2 3 4 5 6 7 8 9 10 11 Z [meters] [4] A. Crawford, arXiv:1409.0828v1. [5] A. Crawford, arXiv:1503.04736v1. 6 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
What Q to expect with & without demagnetization & compensation coils? • At 2 K, 16 MV/m • R BCS = 4.5 n Ω , R 0 = 1.5 n Ω • R s = R BCS + R 0 + (Flux trap. sens. x B avg ) Flux Oper. cost trapping Demag. (M$) sensitivity & Comp. B avg R s Q ($100/MW-h) ( nΩ /mG) (n Ω ) Scenario coil? (mG) (x10 10 ) [13] Realistic 0.5 No 15 13.5 2 4.6 [10,11] Yes 3 7.5 3.5 <3.4 Conservative 1.2 No 15 24 1.1 >>5.7 (100% trapping) [12] Yes 3 9.6 2.8 3.5 Q =3.5x10 10 higher gradient operation possible • Q =1.1x10 10 current cryoplant capacity insufficient • [10] D. Gonnella et al., J. Appl. Phys. 117, 023908, 2015. [11] A. Grassellino et al., SRF proceedings, MOP028, 2015. [12] M. Martinello et al., SRF proceedings, MOPB015, 2015. [13] J. Theilacker, personal communication with A. Grassellino, 2015. 7 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Outline • Introduction – Previous work – Residual magnetic fields and Q 0 • pCM test plan for demagnetization & active cancellation – Understanding till now, & what remains to be understood • Production demagnetization & active cancellation coil – Proposed design of coils and connectorization – Cost summaries for different options – Need-by schedule • Operational modes – Information for SLAC controls 8 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Overview • Overall goal: – Prove the importance of demagnetization & active cancellation systems to the performance of the cryomodules • Testing in three phases – Phase I: Vacuum vessel only • pCM assembly schedule must be unaffected – Phase II: Coldmass as it transitions into cryomodule • pCM assembly schedule must be unaffected – Phase III: Cryomodule at CMTS • Data for production readiness review is priority • Cooldowns for understanding other systems/overall pCM beyond the scope of this topic 9 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Phase I: Vacuum vessel (VV) only • Goal: Obtain data for the effects of physical movement & transport on the residual magnetic field of the VV Measure the remnant field inside VV 1. a. Beamline, top & bottom equator locations Wind coils to VV 2. Demagnetize VV 3. Measure the remnant field inside VV 4. 5. Pick up VV, move inside building using crane, rotate 360°, set down where it was before (If time permits) Transport VV on an air-ride 6. equipped flatbed truck for ~10 miles inside FNAL Measure the remnant field inside VV 7. 8. (If time permits) Test tune active cancellation coils 10 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
pCM Vacuum Vessel Demagnetization • Wires wound onto the outer surface of vessel • Used Powerpole connectors to test them for use in the ‘belt’ type system • FNAL electrical standards determined size of wire – NFPA-70 = AWG 6; FNAL = AWG 4 – Strand count not taken into consideration due to low duty factor – HI-POT testing of insulation required at FNAL after each move of vessel with coils, or installation of coils if removed 11 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Results: VV demagnetization ( B magnitude) B avg at cavities >500 mG ↓ <50 mG & uniform 12 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Results: VV demagnetization ( B longitudinal) B z at cavities >300 mG ↓ <50 mG & uniform 13 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Effect of crane handling • Handling – Lifted demagnetized VV using crane, moved within building while slung from crane, rotated 360 ° , set back down 14 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Effect of transport • Transport – Set demagnetized VV on air-ride equipped, lowboy, flatbed truck – Drove within Fermilab for 10 miles, max. speed 30 mph 15 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Results: Effect of crane handling & transport • No change in magnetic field distribution within VV after handling and transport experiments • Demagnetization may not be required after each move for each CM 16 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Phase II: Coldmass as it transitions into CM • Goal: Obtain data with and without vessel 1. Measure magnetic field at cavities when coldmass attached to Big Bertha, before VV is slid on Fluxgates in longitudinal direction outside cavities’ helium vessel, & a. azimuthal direction inside cavities’ helium vessels 2. Re-measure magnetic field at cavities after VV slid on, and CM is formed 17 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Phase III: Cryomodule at CMTS • Goal: Prove effectiveness & need for demagnetized VV (dVV) & active cancellation (AC) 1. Install CM at CMTS 2. Before cooldown, tune AC coils to obtain minimal longitudinal mag. field Compare fields without & with AC – prove effective a. 3. Demagnetize VV/CM if deemed necessary 4. Cooldown (#1) with dVV, AC ON, fast cooldown (FCD) a. Determine Q 0 of cavities at nominal gradient b. Provide data for production readiness review, best case scenario 5. Cooldown (#2) with dVV, AC ON, slow cooldown (SCD) a. Determine Q 0 of cavities at nominal gradient b. Baseline for SCD, with best case magnetic fields 18 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
Phase III: Cryomodule at CMTS 6. Warm-up, cooldown (#3) with dVV, AC OFF, FCD a. Determine Q 0 of cavities at nominal gradient b. Isolate contribution of un-cancelled longitudinal magnetic fields 7. Simulate non-ideal VV (non-dVV) 8. Warm-up, cooldown (#4) with non-dVV, AC OFF, FCD a. Determine Q 0 of cavities at nominal gradient b. Isolate contribution of VV demagnetization 9. Warm-up, cooldown (#5) with non-dVV, AC OFF, SCD a. Determine Q 0 of cavities at nominal gradient b. SCD with worst-case magnetic fields (at CMTS) 10. Warm-up, non-dVV, AC ON a. Determine if non-dVV longitudinal field can be cancelled b. Transverse field still remains 19 S.K. Chandrasekaran | LCLS-II CM Demag & Active Cancellation Tech. Review 5/25/2016
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