1. 1 Quench Protection and the Power Supplies for the MICE Focusing and Coupling Magnets Michael A Green Lawrence Berkley Laboratory 10 February 2005

2. 2 Focusing and Coupling Magnet Quench Protection The focusing and coupling magnets have a shorted secondary (the mandrel) to induce quench back in the coil for passive quench protection. Quench back will quench all magnets when more than one magnet is hooked up in series. Resistors and diodes across the coil will provide additional quench protection by shunting some current from the coil. The resistors and diodes limit the voltage within the coils during a magnet Quench.

3. 3 Unprotected Quenches of a Single Focusing Magnet and Three Focusing Magnets in the Flip Mode L 1 = 98.6 H E 1 = 3.10 MJ L 3 = 295.2 H E 3 = 9.30 MJ

4. 4 Unprotected Quenches of a Single Focus Magnet in the Flip Mode and the Non-flip Mode L flip = 98.6 H E flip = 3.10 MJ L non-flip = 134.8 H E non-flip = 4.65 MJ The non-flip current is the worst case.

5. 5 Lab G Solenoid Power Supply and Quench Protection

6. 6 Three MICE Focusing Coils in Series with Quench Protection

7. 7 An Unprotected Quenches of a Single Coupling Magnet L 1 = 563 H E = 12.8 MJ

8. 8 Should the coupling coils be in series? One can argue this question either way, but the argument favor powering the coils separately. The inductance of a single coil is 563 H. It will take 3.4 hours to charge one coil at 10 V. The inductance of all other magnet circuits is less than the inductance of a single coupling coil. A single coupling coil produces force that are smaller than the maximum force with the coils hooked in series. A quench of the coupling magnet will probably quench the focusing magnets.

9. 9 The MICE Coupling Coil Power Supply with Quench Protection Note: The coil is shown split into two parts. The coil may be split into three or four parts instead of two parts.

10. 10 Detector Magnet Quenches The INFN magnet design is different from the focusing and coupling magnet design from a quench standpoint. Active quench protection is proposed. Quench back is not a factor in the quench. The current densities are lower so quenches are safe even without quench back from a mandrel. The detector should have separate 300 A leads on the match coils. The other three coils are in series with added 50 A power supplies across the end coils. Like detector coils can be put in series. The circuit inductances are less than 200 H.

11. 11 Detector Magnet Power Supplies Match 1 Match 2End 1CenterEnd 2

12. 12 Concluding Comments on Quenches The focusing and coupling magnets will have passive quench protection. The detector magnet will likely have an active quench protection system. The three focusing magnets should be in series. Each coupling magnet should have its own power supply to reduce the charge time. Like detector magnet coils can be put in series. A coupling coil quench will quench the rest of MICE. A focus coil quench will not quench a coupling coil.