1. 1 Superconducting Magnets for the MICE Channel Michael A. Green Oxford University Physics Department Oxford OX1-3RH, UK

2. 2 The MICE channel is divided into seven modules. The MICE modules come in three types, the focusing and absorber module, the coupling and RF module, and the detector module. The focusing module contains two coils, which can create a either solenoid field or a gradient field. The coupling module contains one coil. Each detector module has two matching coils and three coils to create a uniform magnetic field. Location of the MICE Magnets

3. 3 A 3 Dimensional View of the MICE Superconducting Coils Detector Center Coil Matching Coils Detector End Coils Coupling Coils Focusing Coils Matching Coils Detector End Coils Detector Center Coil Figure from J. H Rochford RAL

4. 4 Separation of the Magnet Cryostat from the Rest of the Module The superconducting coils are vacuum insulated in their own vacuum vessel. This vessel is designed in accordance with the pressure vessel code. The magnet cryostat vacuum vessel is completely separated from any other vacuum vessel that is part of the module. The wall that separates the vacuum vessels must be leak tight to 10 -7 mbar liter s -1 in order to prevent gas migration between the vessels.

5. 5 October 2003 Coupling Magnet Vacuum Space for RF Cavity Cryostat Vacuum

6. 6 Focusing Module Magnet with a Hydrogen Absorber

7. 7 Focus Magnet Cross-section

8. 8 Focusing and Coupling Magnet Load Line

9. 9 Detector Magnet Module Cryostat Vacuum Detector Vacuum

10. 10 MICE Channel on Axis Field Profile Mice Channel Center Focus Coils Detector and Matching Coils Coupling Coil Baseline Case: 200 MeV/c, Beta = 43 cm in the flip mode

11. 11 Magnet Power Supplies Each of the focus coils has its own leads so that the magnet can be changed from a gradient magnet to a straight solenoid magnet. The focusing magnets will be powered by a single 300 A, 10 V power supply. Each coupling coil will have a 10 V, 300 A power supply. The detector end and center coils will be hooked is series and powered by a single 300 A, 10 V power supply. End coil #1 will have a separate 100 A, 5 V power supply to adjust its current for tuning. Each of the matching coils will be in series with its corresponding coil in the other module. They will have 300 A, 10 V power supplies.

12. 12 Magnet Quench Protection Each focus coil will be protected by a warm diode and resistor across its leads. The coupling coils will sub-divided into three parts. Each part will have a cold diode and resistor across that part. This quench protection scheme is commonly used in high field MRI magnets. The three detector coils in series will be protected by warm diodes and resistors across their leads. The matching coils will also be protected by a warm diodes and resistors. All of the magnets will be protected in part by heating due to currents flowing the magnet winding mandrel (quench back).

13. 13 MICE Magnet Refrigeration The MICE magnet coil will be cooled by conduction from the winding mandrel and support structure. Cooling is from by two-phase 4.4 K helium flowing in tubes attached to these parts. About 70 W of 4.4 K refrigeration are needed to cool the seven magnet modules for MICE. Cooling for the magnet shields and leads comes from a 14 K helium circuit from the refrigerator.

14. 14 Some MICE Magnet Safety Issues The coupling solenoid leads and the detector magnet leads are located outside of the hydrogen safety zone. Only the focusing magnet leads may be located within a hydrogen safety zone. Since the magnet are cooled by force helium in tubes, a magnet quench causes very little helium to be released and this release is outside of the MICE shielding. The cryostat vacuum vessels have relief devices that will open in the event of pressure buildup in the vacuum space. The handling of cryogenic fluids and cold transfer lines will be done by trained personnel using standard safety procedures for handling liquid helium prescribed by RAL.

15. 15 Focusing Magnet and Hydrogen Safety Issues If possible, the leads and cables for the focusing solenoids will be located outside of the hydrogen safety zone. If the focusing coil leads and cables are within a hydrogen safety zone, they will have to be shielded using a cover of an inert gas such as argon. Sparking must not occur in a region where hydrogen gas can accumulate. Instrumentation wires for the focusing solenoids must be located outside of the hydrogen safety zone, if possible. A focusing magnet quench does not cause hydrogen venting.

16. 16 Concluding Comments Each of the magnet modules has its own insulating vacuum vessel. The magnets do not share a common vacuum with any other components of MICE. The cryogenic system has a minimum amount of liquid helium within it. The magnet quench protection system will limit the voltages seen at the magnet leads to about 10 volts. Only the focusing magnets are in a hydrogen area. A quench of this magnet does not cause a general release of hydrogen. The major safety concern is the location of the magnet leads.