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Quench Protection and the Power Supplies for the MICE

Focusing and Coupling Magnets

Michael A Green

Lawrence Berkley Laboratory

10 February 2005

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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.

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Current 1Hot Spot T 1Current 2Hot Spot T 2

Time from the Start of the Quench (s)

Current in the Coil (A) and Hot Spot T (K)

Single Magnet

Three Magnets in Series

Unprotected Quenches of a Single Focusing Magnet and Three Focusing Magnets in the Flip Mode

L1 = 98.6 HE1 = 3.10 MJL3 = 295.2 HE3 = 9.30 MJ

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Current 1Hot Spot T 1Current 3Hot Spot T 3

Time

Current in the Coil (A) and Hot Spot T (K)

Single Magnet Flip Mode

Single Magnet Non-flip Mode

Unprotected Quenches of a Single Focus Magnetin the Flip Mode and the Non-flip Mode

Lflip = 98.6 HEflip= 3.10 MJLnon-flip = 134.8 HEnon-flip = 4.65 MJ

The non-flip currentis the worst case.

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Lab G Solenoid Power Supplyand Quench Protection

PSMandrelMagnetWarm ResistorWarm DiodePower Supply10 V, 300 A

Cryostat

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Three MICE Focusing Coils in Serieswith Quench Protection

PSPower Supply10 V, 300 A

Total Inductance from 295 H to 410 H

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Current 1Hot Spot T 1

Time after the Quench has Started (s)

Magnet Current (A) and Hot Spot Temperature (K)

An Unprotected Quenches of a Single Coupling Magnet

L1 = 563 HE = 12.8 MJ

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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.

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The MICE Coupling Coil Power Supplywith Quench Protection

PSPower Supply10 V, 300 A

Coupling MagnetMandrelCold DiodeCold ResistorInductance = 563 H

Note: The coil is shown split into two parts. The coil may besplit into three or four parts instead of two parts.

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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.

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Detector Magnet Power Supplies

PSPower Supply10 V, 300 A

PSPSPSPSPower Supply10 V, 50 A

Match 1 Match 2 End 1 Center End 2

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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.