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

Spectrometer Solenoid Update (FAC) - SV/MZ2 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

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ3 MICE Cooling Channel Layout Spectrometer Solenoid #1 (ready for reassembly) Spectrometer Solenoid #2 (testing in progress)

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ4 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

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ5 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 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

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ6 Magnet 2 Modifications Added single-stage cryocooler for leads —did not require full disassembly of magnet, only turret area o 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 I 2 R 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

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ7 Magnet 2 Configuration (1) Original version HTS leads Cold head 1 st stage Radiation shield Fill & vent lines Cold mass

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ8 Magnet 2 Configuration (2) Outfitted with new single-stage cooler HTS leads Single-stage cooler Thermal link

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ9 Magnet 2 Configuration (3) HTS and RT leads tested prior to reuse —had to repair leak in ceramic feed-through o added guard-vacuum to avoid recurrence Lead vacuum guard HTS leads partially installed

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ10 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 K —shield temperatures K lower than seen before  cooler is doing its job

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ11 Training and Test Results (1) Initial phase had five training quenches (all 5 coils in series) —165, 219, 238, 253, 257 A o 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 o one final quench later only reached 253 A in this configuration 

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ12 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

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ13 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 o (my) suspicion is that the LN reservoir is causing a problem –even when empty Preliminary

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ14 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

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ15 Implications for Magnet 1 Magnet 1 already modified compared with Magnet 2 —improved shield thermal connections o including LN reservoir that is not yet attached —provision for 4 th 2-stage cooler If Magnet 1 heat load at 4 K is comparable to ~6 W for Magnet 2 —“5+0” option looks safer o 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

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ16 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 o 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 o 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 o already done for upgraded Magnet 1 —make direct connections between cooler recondensers and He tank o can do for 4 2-stage coolers, probably not for 5 While all these would help, there is no obvious “smoking gun”

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ17 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 o available June 1 —expect some help from S. Prestemon and possibly Al McInturff in the intervening period —hiring Li Wang (SINAP) as consultant o 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

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ18 Short-term Tasks First steps (1-2 months) —examine thermal model in comparison with measurements to look for significant discrepancies o Li Wang and S. Prestemon, in consultation with Al McInturff o Sekachev will take over after June 1 —review magnet design and implementation o MZ, SV, and MAG with vendor assistance o anticipate that Fermilab will provide effort to help with this —evaluate possible changes/improvements in terms of risk/benefit o 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!

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ19 Schedule Schedule based on assumption that Magnet 1 fixes studied first, while Magnet 2 is being disassembled —the review stage is included

April 23, 2010Spectrometer Solenoid Update (FAC) - SV/MZ20 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