Spectrometer Solenoid Fabrication & Testing Update

1. Spectrometer Solenoid Fabrication & Testing Update S. Virostek and M. Zisman Lawrence Berkeley National Laboratory MICE Funding Agency Committee Meeting—RAL April 23, 2010

2. Outline • Layout • Overview • Technical review • Magnet 2 modifications • Magnet 2 configuration • Cool-down • Training and test results • M2 coil connection • Implications for Magnet 1 • Possible improvements • Schedule • Effort level • Summary Spectrometer Solenoid Update (FAC) - SV/MZ

3. MICE Cooling Channel Layout Spectrometer Solenoid #1 (ready for reassembly) Spectrometer Solenoid #2 (testing in progress) Spectrometer Solenoid Update (FAC) - SV/MZ

4. Overview • Modifications to Magnet 2 including adding a single stage cryocooler were completed at the end of Feb. ’10 • Several delays in reassembly, caused by vacuum leaks in lead-test apparatus, vendor extended illness, redesign of warm leads, and leaks in magnet vacuum vessel • Seven coil training runs completed during March • Open-circuit found in internal connection of one lead of M2 coil during training process • Magnet kept cold for several more weeks to complete additional power supply and thermal tests • minimal disassembly to assess M2 issue now under way Spectrometer Solenoid Update (FAC) - SV/MZ

5. Technical Review • Review held November 18-19, 2009 at LBNL • members: Pasquale Fabbricatore (chair); Amalia Ballarino*; Elwyn Baynham*; Tom Bradshaw*; Mike Courthold; Chris White*; Alain Blondel and Andy Nichols (both ex officio) *participated via phone or e-mail • Committee recommendations: • add single-stage cryocooler for leads • continue thermal modeling • install further instrumentation • use Magnet 2 results to determine final configuration of Magnet 1 Spectrometer Solenoid Update (FAC) - SV/MZ

6. Magnet 2 Modifications • Added single-stage cryocooler for leads • did not require full disassembly of magnet, only turret area • provides ~170 W of heat removal at 55K • sufficed to maintain lead temperature and avoid any damage to HTS leads in subsequent tests • Based on tests, leads modified to reduce I2R heating into first stage of coolers • some increase in static load, but closer to optimal design • Added more voltage-tap instrumentation • provides information, but adds heat load Spectrometer Solenoid Update (FAC) - SV/MZ

7. Magnet 2 Configuration (1) Cold head 1st stage HTS leads Fill & vent lines Radiation shield Cold mass • Original version Spectrometer Solenoid Update (FAC) - SV/MZ

8. Magnet 2 Configuration (2) Single-stage cooler Thermal link • Outfitted with new single-stage cooler HTS leads Spectrometer Solenoid Update (FAC) - SV/MZ

9. Magnet 2 Configuration (3) Lead vacuum guard • HTS and RT leads tested prior to reuse • had to repair leak in ceramic feed-through • added guard-vacuum to avoid recurrence HTS leads partially installed Spectrometer Solenoid Update (FAC) - SV/MZ

10. Cool-down • Magnet cooled down without incident in 4 days • MICE staff present 24/7 during this operation • Results of adding single-stage cooler • HTS lead temperatures at upper end reduced by 30-35 K • shield temperatures 20-25 K lower than seen before  cooler is doing its job Spectrometer Solenoid Update (FAC) - SV/MZ

11. Training and Test Results (1) • Initial phase had five training quenches (all 5 coils in series) • 165, 219, 238, 253, 257 A • first quench believed due to power supply problem • desired current is 275 A • After last quench, M2 coil showed open circuit • voltage taps indicated open LTS section between cold-mass feed-through and bottom of HTS leads • Bypassed M1 and M2 coils to continue training • with E1-C-E2 in series, reached 270 A • one final quench later only reached 253 A in this configuration  Spectrometer Solenoid Update (FAC) - SV/MZ

12. Training and Test Results (2) • Tested power supplies while magnet cold • with E1-C-E2 at 150 A, trimmed E1 and E2 50 A with 60 A supplies • also demonstrated ramp-down circuit, so supplies operate properly in bipolar mode • Carried out thermal tests (no current) to quantify heat loads into stage 2 of coolers • looked at He boil-off rate determined from liquid-level monitors • measured temperatures of sealed system (constant volume) • measured He boil-off directly with a gas meter Preliminary Spectrometer Solenoid Update (FAC) - SV/MZ

13. Training and Test Results (3) • Also looked at heat load into stage 1 of coolers • it appears unusually high compared with corresponding measurements for magnet 1 taken in summer 2008 • (my) suspicion is that the LN reservoir is causing a problem • even when empty Preliminary Spectrometer Solenoid Update (FAC) - SV/MZ

14. M2 Connection • Magnet was warmed and opened for inspection on April 15 • no visual indication of a problem near the HTS lead • further disassembly being done to look nearer cold-mass feed-through • One theory is that heating was due to sudden conductor motion arising from I x B forces Spectrometer Solenoid Update (FAC) - SV/MZ

15. Implications for Magnet 1 • Magnet 1 already modified compared with Magnet 2 • improved shield thermal connections • including LN reservoir that is not yet attached • provision for 4th 2-stage cooler • If Magnet 1 heat load at 4 K is comparable to ~6 W for Magnet 2 • “5+0” option looks safer • and necessary unless we can improve things • There remain questions about Magnet 2 “plumbing” • different configuration than that tested in lead tests • straight vent pipe • nitrogen reservoir Spectrometer Solenoid Update (FAC) - SV/MZ

16. Possible Improvements • Some ways for reducing the heat load into the cold mass are being considered • extend copper plate and turret to cover vent-pipe region • vent and fill pipes should be well attached to copper plate • bend He vent tubes above shield to reduce direct radiation from 300 K to 4 K • eliminate potential sources of thermal acoustic oscillations • e.g., add low-temperature check valves to vent and fill lines • extend shield to better cover support bands • improve connection between shield and cooler stage 1 • already done for upgraded Magnet 1 • make direct connections between cooler recondensers and He tank • can do for 4 2-stage coolers, probably not for 5 • While all these would help, there is no obvious “smoking gun” Spectrometer Solenoid Update (FAC) - SV/MZ

17. Effort Level • Task is an LBNL responsibility • Virostek and MZ, plus consultation from M. A. Green • hiring new cryogenics engineer (Igor Sekachev) to help us • available June 1 • expect some help from S. Prestemon and possibly Al McInturff in the intervening period • hiring Li Wang (SINAP) as consultant • primarily for Coupling Coil, but she can help with FEA on spectrometers also, as needed • vendor effort also available for design and fabrication • LBNL has requested some assistance from Fermilab • hope for at least one cryogenics expert to review our design, analysis, and plans • Solenoid review committee has also been helpful in assessing results to date and providing advice Spectrometer Solenoid Update (FAC) - SV/MZ

18. Short-term Tasks • First steps (1-2 months) • examine thermal model in comparison with measurements to look for significant discrepancies • Li Wang and S. Prestemon, in consultation with Al McInturff • Sekachev will take over after June 1 • review magnet design and implementation • MZ, SV, and MAG with vendor assistance • anticipate that Fermilab will provide effort to help with this • evaluate possible changes/improvements in terms of risk/benefit • vendor involvement important here • Then • make recommendations on what changes to implement • finalize in consultation with review committee and MICE TB • Finally • go do it! Spectrometer Solenoid Update (FAC) - SV/MZ

19. Schedule • Schedule based on assumption that Magnet 1 fixes studied first, while Magnet 2 is being disassembled • the review stage is included Spectrometer Solenoid Update (FAC) - SV/MZ

20. Summary • We have reached 270 A (275 A needed) on E1-C-E2 coils • Opened up M2 coil connection; searching for problem now • Inferred heat load at 4 K looks marginal even for four 2-stage coolers • 5 coolers looks more realistic unless we can find and fix a ~1 W problem • Heat load at 60 K degraded badly in Magnet 2 • manageable but need to understand this • Goal is still to make magnets operational as soon as possible Spectrometer Solenoid Update (FAC) - SV/MZ