1. 23 October 2005MICE Meeting at RAL1 MICE Tracker Magnets, 4 K Coolers, and Magnet Coupling during a Quench Michael A. Green Lawrence Berkeley Laboratory MICE Collaboration Meeting 23 October 2005

2. MICE Meeting at RAL2 Tracker Module 1 Tracker Module 2 AFC Module 1 AFC Module 3 AFC Module 2 RFCC Module 1 MICE Channel with the Trackers Drawing by S. Q. Yang

3. 23 October 2005MICE Meeting at RAL3 The New Tracker Magnet Design

4. 23 October 2005MICE Meeting at RAL4 Tracker Magnet Cryostat Iron Shield Iron Shield Brackets Cold Mass Support Coolers Vent Stack Lead Neck Radiation Shield Space Tracker Magnet Stand Cooler Neck Drawing by S. Q. Yang

5. 23 October 2005MICE Meeting at RAL5 Lead Neck Cold Mass Support Liquid He Tube Fill & Vent Neck Condenser 4 K Cooler He Gas Tube Tracker Magnet Cold Mass and Coolers The 50 K shields are not shown. Drawing by S. Q. Yang

6. 23 October 2005MICE Meeting at RAL6 Cold mass and the Superconducting coils Cold mass support system that can carry a 50 ton longitudinal force. A Cooling system based on three 1.5 W coolers. Superconductor specification. Temperature margin for all magnet coils. Magnet Components Studied

7. 23 October 2005MICE Meeting at RAL7 End Coil 2 Center Coil Match Coil 1 End Coil 1 Match Coil 2 Coil Cover Aluminum Mandrel Liquid Helium Space 490 mm 690 mm 2535 mm Tracker Magnet Cold Mass Cross-section Drawing by S. Q. Yang

8. 23 October 2005MICE Meeting at RAL8 50 K intercept Tracker Magnet Cold MassCold Link Warm Link 300 K End 4 K End Tracker Magnet Cold Mass Support System Drawing by S. Q. Yang

9. 23 October 2005MICE Meeting at RAL9 Tracker Magnet Parameters Uniform Field Magnet S * The uniform field magnet coils in series have a self inductance of 78 H. Separately Powered Coil package length = 2530 mm

10. 23 October 2005MICE Meeting at RAL10 Tracker Magnet Temperature Margin

11. 23 October 2005MICE Meeting at RAL11 Things that have not Changed The length of the cryostat from end plate to end plate is unchanged (~2634 mm), but cold mass length is shorter (2535 mm). The 400 mm magnet warm bore is unchanged. The 250 mm distance from the far end plate to the iron shield is unchanged. The longitudinal position of the coil current centers is unchanged. The radiation shield position at the AFC end is unchanged.

12. 23 October 2005MICE Meeting at RAL12 Tracker Magnet Changes The outer diameter of the vacuum vessel was increased from 1080 mm to 1407 mm. The new stand takes a 50 ton longitudinal force directly to the floor. Because the tracker magnet cryostat is the same diameter as the AFC and RFCC modules, one can carry the magnetic forces to an adjacent module. The iron support was changed to fit the new cryostat diameter. There are small changes in the coil position and coil thickness.

13. 23 October 2005MICE Meeting at RAL13 Tracker Magnet Progress to Date Basic module design is almost completed Coils are designed except for possible minor changes in a couple of coils. Superconductor specification and start the bid process. Cold mass supports are understood. Design of the cooling system is understood. Magnet assembly plan has been started. Magnet quench analysis has been started. Power supply specification started.

14. 23 October 2005MICE Meeting at RAL14 Tracker Magnet Tasks Remaining Place the order for the superconductor. Finish the quench calculations. Prepare a tracker solenoid specification. Qualify potential magnet vendors. Finish the magnet assembly plan and write quality control documents. Place the order for the tracker solenoids (probably more than one contract). Tracker magnet fabrication.

15. 23 October 2005MICE Meeting at RAL15 Issues with 4 K Coolers and their Connection to the Magnets

16. 23 October 2005MICE Meeting at RAL16 Cooler Issues for MICE The GM cooler cold heads do not work in a magnetic field above 0.02 to 0.08 T. This is a problem for the magnet coolers, the absorber coolers, and the RFCC vacuum pump coolers. The MICE fringe fields can be as high as 2 T. There is more data on the performance of a cooler at temperatures from 2.5 to 300 K. The connection of two or more coolers to a magnet can be done so that the magnet will remain cold (at a higher temperature) while one cooler is shut off.

17. 23 October 2005MICE Meeting at RAL17 Possible Solutions to the Cold Head Magnetic Field Sensitivity Issue Move the coolers away from the magnetic field. This may be a solution for the RFCC cryopump coolers but it is not a solution for the magnet and absorber coolers. Use iron to shield the cooler cold heads from the magnetic field. The effect of the iron on the field in MICE and on magnetic forces must be investigated. Use 4 K pulse tube coolers in place of the GM coolers for the magnets and absorbers.

18. 23 October 2005MICE Meeting at RAL18 Should 4 K Pulse Tube Coolers be used on MICE Pulse tube coolers have always been an option for MICE. The design was based on 1.5 W GM coolers, because 1.5 W pulse tube coolers were not available. In January 2006, a 1.5 W cooler will be available from Cryomech. Pulse tube cooler pros: cooler not sensitive to magnetic field, cooler maintenance while cold, and 50 percent more cooling at 50 K. Pulse tube cooler cons: the cooler input power is higher (11 kW versus 7.5 kW) and the cooler is sensitive to cold head orientation.

19. 23 October 2005MICE Meeting at RAL19 Where do we go from here on the cooler magnetic field question? We will look at the magnetic field at the location of all of the coolers. We will look at how to shield the cold heads to reduce the magnetic field to <0.05T at the cooler cold head locations. We will look at the effect of the shields on the field in the channel and we will look at forces. We will look at 1.5 W pulse tube coolers. We may be able to reduce the number of coolers on the trackers (3 to 2) and the AFCs (3 to 2).

20. 23 October 2005MICE Meeting at RAL20 Reduce  T with a Liquid Heat Pipe

21. 23 October 2005MICE Meeting at RAL21 The Advantages of a Liquid Interface The  T between the magnet surface and the 2nd stage cold head can be very low (as low as 0.03 K). The cooler can be located more optimally. The heat pipe will filter out the cyclical variations of the cold head temperature (about 0.3 K at 4.4 K). In a multiple cooler system, individual coolers can be connected to the magnet with their own heat pipes. The system will balance out optimally. If there is no conductive strap between the coolers and the magnet, the heat pipe will behave like a thermal diode. Heat flow from the cooler to the magnet is low, when the cooler cold head is warmer than the magnet.

22. 23 October 2005MICE Meeting at RAL22 Cooler #1 Cooler #2 Cooler #3 Cooler 1st Stage Cooler 2nd Stage Gas Return Pipe Flexible 304 SS Liquid He Supply Pipe Flexible 304 SS He Condenser Top Plate Three Coolers for the Tracker Magnet Drawing by S. Q. Yang

23. 23 October 2005MICE Meeting at RAL23 Magnet Coupling During a Quench

24. 23 October 2005MICE Meeting at RAL24 Comments on Inductive Coupling There is a lot of inductive coupling between the focusing magnet string F and the coupling magnet C1 or C2 (despite a horizontal distance of 1375 mm between current centers). The coupling coil is large and couples to everything. The coupling in largest for the non-flip operating mode. The inductive coupling between the focusing magnet circuit F and the first match coil circuit M1 is large enough to cause a problem, because the current centers are 861 mm apart. The coupling in largest for the non-flip operating mode. The tracker solenoid magnet circuits M1, M2, and S are well enough coupled to each other to cause problems. The coils share a common mandrel, which mean a quench in one tracker magnet circuit will quench the other two circuits.

25. 23 October 2005MICE Meeting at RAL25 MICE Inductance Network in the Flip Mode

26. 23 October 2005MICE Meeting at RAL26 MICE Inductance Network in the Non-flip Mode

27. 23 October 2005MICE Meeting at RAL27 Peak Circuit di/dt and Induced Voltage Circuitdi/dt Time Constant F~48 A s -2 ~5.2 s C1 or C2~35 A s -2 ~6.1 s M1~60 A s -1 ~4.5 s M2~70 A s -1 ~4.1 s S~50 A s -1 ~5.3 s The induced voltage in circuit 1 due to a current change in circuit 2;

28. 23 October 2005MICE Meeting at RAL28 Quenches due to Coupling Large mutual inductance between circuits will mean the the induced voltages can be large in other circuits. The time constants are short (from 4 to 6 seconds), so the total circuit current change will be relatively small. It is unlikely that a quench in one circuit will cause other circuits to quench directly by driving the current above the critical current. The large induced voltages may mean that currents flow in the magnet mandrels. If the temperature margin is low, a quench in one magnet circuit can drive another magnet circuit normal through quench back from its mandrel.

29. 23 October 2005MICE Meeting at RAL29 Coupling between Coils and Mandrels Coupling Coefficient from the coil to the mandrels

30. 23 October 2005MICE Meeting at RAL30 Comments on Quench Coupling The MICE magnet circuits quench passively because of quench back from the magnet mandrels. The MICE magnet circuits will be hooked in series with corresponding coils in MICE, except for the two coupling coils. Because the MICE solenoids have no magnetic shield, every coil in MICE is coupled with every other coil in MICE. The six MICE magnet circuits are coupled to each other inductively. When the temperature margins in the magnets are low, a quench in one magnet circuit can cause another magnet circuit to quench by quench back.

31. 23 October 2005MICE Meeting at RAL31 Concluding Comments The new tracker magnet will fit with the rest of the tracker module now being designed. Magnetic fields above 0.08 T are a problem for the motors in a GM cooler cold head. MICE should look at pulse tube coolers. Liquid interface heat pipes are a good way to connect the coolers to the load being cooled. A quench in one magnet can cause other MICE magnets to quench through inductive coupling between coils and mandrels.