1. Spectrometer Solenoid: Plans to Fix Magnet 2 Steve Virostek Lawrence Berkeley National Lab Spectrometer Solenoid Review November 18, 2009

2. MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 2 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 Proposed magnet fix Modified magnet geometry Other system improvements Fallback plans Schedule overview Topics

3. MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 3 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 Magnet 2 Added Cryocooler Single-stage cooler Thermal link HTS leads

4. MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 4 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 Added Single Stage Cooler A modification to Magnet 2 has been proposed which adds a single stage cryocooler to provide additional cooling to the HTS leads and won’t require full magnet disassembly The plan to add a single-stage Cryomech AL330 cooler (arrived 11/13/09) provides 170 W at 55 K and requires modifications only in the “turret” area The added cooling power should lower the upper HTS lead temperature sufficiently to train to full current The new cooler could remove enough heat to permit the other 3 two-stage coolers to maintain the cold mass LHe level (i.e. closed system)

5. MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 5 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 Cryomech AL330 Performance

6. MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 6 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 Modification Details Added turret space Access port

7. MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 7 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 Modification Details Multilayer flexible Cu link Soldered ends Thermal grease in joints

8. MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 8 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 Cooler Conduction Link Note: link thickness has been increased to ¾”

9. The thermal model of the magnet is being used to better understand the cooling mechanisms and heat loads Initial calculations indicate the upper HTS leads temperature will be <70K during operation The temperature drop across the thermal link between the single stage cooler and the 1 st stage copper plate is expected to be ~10 K An off line magnet lead test is being carried out by Wang NMR to measure all relevant temperatures and voltages during operation Additional sensors will directly measure cold head temps. MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 9 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 Thermal Calculations and Measurements

10. MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 10 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 HTS Lead Protection The HTS leads can be actively protected from burnout due to quench as follows: i)Interlock the power supply with the temperature of the top of the HTS leads/heat sink to cut power when the temperature is too high ii)Active quench protection based on the voltage across the HTS leads in case of resistive transition (~3 mV limit) – a set of voltage taps will be added to the lower end of the leads This type of system could possibly be implemented at RAL, but Wang NMR does not currently have the capability to implement an active control system

11. Our modeling indicates the new cooler won’t substantially affect the shield temperature It is uncertain whether the addition of the single- stage cooler will solve the LHe boil off issue Cannot address known deficiencies in Magnet 2(shield connection, copper plate thickness, leads arrangement) without fully disassembling magnet Additional cooler(s) will increase utility costs for running the magnets (water and power) Other Issues MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 11 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009

12. If the addition of a single-stage cooler to Magnet 2 does not result in a closed system, there are two options: i) Accept the thermal properties as is and top up the magnet with external cryogens as needed ii) Disassemble and modify the magnet to improve the shield connections and to accommodate a fourth two- stage cooler (in addition to the single-stage cooler) The 2 nd option will add 3 to 6 months to the delivery of the 2 nd magnet to RAL and will create additional risks of damage or assembly errors in the repair process For these reasons, the first option is preferred Magnet 2 Fallback Scenario MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 12 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009

13. During magnet training, a problem with the power supply controller was noted – the controller would allow the system to ramp up in current but not down Modifications to the power supply circuit external to the magnet have been developed and briefly tested The ramp down system is similar to the magnet discharge circuit previous developed and implemented The vendor has been contracted to fabricate and install the system in both sets of RAL racks Installation in the first rack is complete MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 13 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009 Power Supply Issues

14. * These step are only required if the initial modifications to Magnet 2 are unsuccessful Schedule Overview MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 14 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009

15. A fix to Magnet 2 has been devised which does not require full magnet disassembly Addition of a single-stage cooler to the first stage copper plate is expected to solve the HTS leads temperature problem Temperature of the thermal shield may still be an issue (cooler will have minimal impact) Operation without the need for cryogen top off is probable but not guaranteed Summary MICE Spectrometer Solenoid: Plans to Fix Magnet 2Page 15 Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009