CM-22 Magnet Issues, 6 June 2008 -1-

MICE Magnet Cool Downand Other Issues

Michael A. Green

Lawrence Berkeley Laboratory

Berkeley CA 94720

CM-22 Magnet Issues, 6 June 2008 -2-

Issue to be Covered in this Report

• The methods for cooling down of the three types of MICE coils at RAL

• Cool down using a helium compressor and a liquid nitrogen heat exchanger

• The proposed transfer line LBNL will provide to Fermilab and RAL for cooling the magnets

• The position of the tracker magnet feeds and vents and the proposed transfer line

• The location of the magnet power supplies and the length of the power cables

CM-22 Magnet Issues, 6 June 2008 -3-

Tracker Magnet Cold Mass w/o Cover

The space outside of the coils is filled with 200 liters of helium.

Space for LHe

Coil E2

Coil M1

Coil M2

Coil E1

Center Coil

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Tracker Magnet Cold Mass with Welded Cover

Magnet cooling is between the cover plate and the coils. Thespace inside is filled with liquid helium. The cool down gas flows in the same space. The cover plate gets colder faster than the magnet mandrel and the coils.

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Tracker Magnet Simplified Heat Flow Diagram

Cover PlateM = 500 kgRest of Magnet

M = 1350 kgHeat flow to Helium at Tby Forced ConvectionQQQTTMMCCMC0

€ QC=U1A1(TC−T0)QM=U2A2(TM−T0)QMC=U3A3(TM−TC)

€ RMC=1U3A3 €

RC0=1U1A1

€ RM0=1U2A2

Conduction Heat Flow

Cooling is supplied to the helium space between the cover plate and the mandrel.There is a 70 to 90 K T restriction between the cover plate and the coil mandrel.

V = ~1000 L of LN2

V = ~600 L of LHe

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Coupling Magnet Cold Mass

• There is no space for cooling tube on the inside RFCC magnet or at its ends.

• The coupling magnet is cooled using tubes attached to the cover plate.

• The magnet is cooled down using the same tubes that keep the magnet cold.

• This poses problems because the cover plate is thin compared to the magnet.

CM-22 Magnet Issues, 6 June 2008 -7-

Cover PlateM = 140 kgRest of Magnet

M = 1080 kgHeat flow to Helium at T

by Forced ConvectionQQTTMCCMC0

€ RMC=1U3A3€ RC0=1U1A1

Conduction Heat Flow

€ QC=U1A1(TC−T0)QMC=U3A3(TM−TC)

Coupling Magnet Simplified Heat Flow Diagram

Coupling coil cool down tubes are assumed to be attached to the magnet cover plate.There is a 50 to 60 K T restriction between the cover plate and the coil mandrel.

V = ~600 L of LN2

V = ~450 L of LHe

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Focusing (AFC) Magnet Cold Mass

It is proposed that the coupling magnet becooled from the outside of the coils. The cool-down tubes could be on the mandrel.

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Focusing (AFC) Magnet Simplified Heat Flow Diagram

Cover PlateM = 35 kgRest of Magnet

M = 730 kgHeat flow to Helium at Tby Forced ConvectionQQTTMCCMC0

€ RMC=1U3A3 €

RC0=1U1A1Conduction

Heat Flow Cover Plate

= 35 M kgTC

€ RMC=1U3A3

Conduction Heat Flow

€ QC=U1A1(TC−T0)QMC=U3A3(TM−TC)

The cool down tubes are assumed to be attached to the mandrel. This would makeany coil cool down restrictions totally unnecessary.

V = ~450 L of LN2

V = ~320 L of LHe

CM-22 Magnet Issues, 6 June 2008 -10-

Cool Down with Dewars or an LN2

to Helium Heat Exchanger• Magnet weld stress is an issue when the cover plate

temperature is colder than the mandrel.

• When the tracker magnet is at room temperature (TM = 293 K) the T between the cover plate and the mandrel must be <60 K. When TM is < 180 K, the T can be >100 K. The T between the RFCC magnet cover plate and its mandrel must also be controlled.

• If the AFC magnet is cooled down with cooling tubes on the mandrel section between the coils, the T is not a problem at all.

CM-22 Magnet Issues, 6 June 2008 -11-

Helium CompressorRest of Magnet

M = 730 kgLiquid NitrogenTM0T = 293 KT = ~85 KT = ~T - 50 KMT = ~T MT = 77 KT > 273 KFlow ValveT Control ValveSimplified He Temperature Control

using a Compressor and LN2

The use of a LN2 to helium gas heat exchanger is the most efficient way of controlling the cooling from 293 K to 85 K using liquid nitrogen as a coolant for the cool down.

TMT = TM - 60 K

Magnet Massup to 1900 kg

CM-22 Magnet Issues, 6 June 2008 -12-

Finished Tracker Magnet on PumpPT-415 Cooler Hoses from Compressor

Magnet Xmas Tree

Warm Bore

Cold Mass Support

Magnet Stand

CM-22 Magnet Issues, 6 June 2008 -13-

Tracker Magnet He Feed and Vent

PT-415 Cooler

Ball Valves for Cool Down

Relief Valves

Rupture Disc

PT-415 Cooler Valve

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Proposed LBNL Transfer Line

• LBNL must provide a cryogenic transfer line to Fermilab so that the tracker magnet magnetic field measurements can be done there.

• It is proposed that LBNL provide two cryogenic transfer lines. One is to be used at Fermilab while the other is to be used at RAL.

• The dimensions of the proposed line is shown on the next page. Are these dimensions acceptable for the MICE hall at RAL?

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Proposed Helium Transfer Line

2438 mm

2032 mm

851 mm

The drawing dimensions are inches.

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Power Supply Location and Cable Lengths

• A proposed location for the two tracker magnet power supply racks at MICE has be selected.

• It is believed that that the power supplies and rapid discharge diodes for all of the MICE magnets can be housed in a total of three racks.

• Power for the power supplies and their controllers is needed at the rack location. City water and drain piping for the cooling of the rapid discharge diodes (only when they are on) must also be provided at the rack location.

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MICE Plan View Showing Channel

Power Supply Racks

MICE Cooling Channel

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Tracker Magnet Power Supply Racks

60 A Power Supply

Rapid Discharge Diodes

300 A Power Supply controller

300 A Power Supply

CM-22 Magnet Issues, 6 June 2008 -19-

Magnet Cable Numbers and Lengths

• Cables made for one lab may not be transported to another lab. The lengths and Safety regulations are different for each laboratory.

• For the MICE the following cable lengths apply:

• The cable length given above are not exact, the trench location and size are important factors.

• For both trackers, a total of fifteen 300 A cables are needed. This includes (three 1-m, three 2-m, three 6-m, and six 17-m). A total of eight 60 A cables are needed. This includes (two 2-m, two 6-m, and four 17-m).

• For both coupling magnets, a total of six 300 A cables are needed. This includes (two 2-m, two 10-m, and two 13-m).

• For the three focusing magnets, a total of eleven 300 A cables are needed. This includes (four 1-m, three 2-m, one 6-m, two 9-m, and one 16-m).

CM-22 Magnet Issues, 6 June 2008 -20-

Concluding Comments

• A method for cooling down the tracker magnets has been developed. This method can be applied to the other magnets in MICE.

• A common vertical location for the magnet feeds should be developed so that one transfer line design can be used to cool down all of the MICE magnets.

• The magnet power supplies and rapid discharge resistors can be located in three racks. These racks can all be in the same location. Power and non-interruptible cooling water should be available at the power supply racks.