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

23 October 2005 MICE Meeting at RAL 1

MICE Tracker Magnets,4 K Coolers, and Magnet

Coupling during a Quench

Michael A. Green

Lawrence Berkeley Laboratory

MICE Collaboration Meeting

23 October 2005


Tracker Module 1

Tracker Module 2

AFC Module 1AFC Module 3

AFC Module 2

RFCC Module 1

RFCC Module 1

MICE Channel with the Trackers

Drawing by S. Q. Yang


The New Tracker Magnet Design

23 October 2005 MICE Meeting at RAL 4Tracker Magnet Cryostat

Iron Shield

Iron Shield Brackets

Cold Mass Support

Coolers

Vent Stack

Lead Neck

Radiation Shield Space

Tracker Magnet Stand

Cooler Neck



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.



• 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


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



50 K intercept

Tracker Magnet Cold Mass Cold Link

Warm Link

300 K End

4 K End

Tracker Magnet Cold Mass Support System



Tracker Magnet Parameters

Parameter Match 1 Match 2 End 1 Center End 2Coil length (mm) 198 197 110 1294 110Coil inner radius (mm) 258 258 258 258 258Coil thickness (mm) 46.2 28.6 61.6 22.0 68.2Number of layers 42 26 56 22 62Number of turns per layer 120 119 66 784 66Coil overall current density (A mm –2) 147.6 161.3 136.8 146.9 145.4Coil current I (A) 267.8 271.2 249.5 265.9 265.2Coil self inductance (H) 12.8 5.0 9.6* 41.6* 11.4*Coil Stored Energy at I (MJ) 0.47 0.20 0.30 1.49 0.40

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


Tracker Magnet Temperature Margin

1098765432100

50

100

150

200

250

300

350

400

450

500

T = 3.4 KT = 4.2 KT = 5.0 KTracker M1Tracker M2Tracker E1Tracker CTracker E2

Magnetic Induction at the Conductor (T)

Conductor Current (A)

Tracker M1 Margin = 2.0 KTracker M2 Margin = 2.5 KTracker E1 Margin = 1.9 KTracker C Margin = 2.3 KTracker E2 Margin = 1.7 K

Conductor Ic Versus B


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.


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.


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.


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.


Issues with 4 K Coolers and their Connection to the Magnets


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.


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.


Should 4 K Pulse Tube Coolersbe 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.


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).


Reduce T with a Liquid Heat Pipe

P

T3

T2

T1

T0

2nd Stage Cold Head

Condensor

Vacuum Vessel

Liquid Tube

Gas Tube

Liquid

Magnet

Relief Valve

Cryostat Neck


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.


Cooler #1

Cooler #2 Cooler #3

Cooler 1st Stage

Cooler 2nd Stage

Gas Return PipeFlexible 304 SS

Liquid He Supply Pipe Flexible 304 SS

He Condenser

Top Plate

Three Coolers for the Tracker Magnet



Magnet Coupling During a Quench


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.


MICE Inductance Networkin the Flip Mode

S M2 M1 F C1 C2S 155.8 1.283 0.711 0.190 0.549 0.549

M2 1.283 6.880 0.809 0.121 0.132 0.132M1 0.711 0.809 26.24 1.160 0.441 0.441F 0.190 0.121 1.160 304.4 5.569 5.569

C1 0.549 0.132 0.441 5.569 563.0 6.713C2 0.549 0.132 0.441 5.569 6.713 563.0


MICE Inductance Networkin the Non-flip Mode

S M2 M1 F C1 C2S 156.5 1.285 0.721 0.705 0.810 0.810

M1 1.285 6.886 0.809 0.278 0.161 0.161M2 0.721 0.809 26.46 1.963 0.631 0.631F 0.705 0.278 1.963 416.3 17.91 17.91C 0.810 0.161 0.631 17.91 563.0 6.713C 0.810 0.161 0.631 17.91 6.713 563.0


Peak Circuit di/dt and Induced Voltage

Circuit di/dtTime

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

€

V2 =M1−2

di2dt

The induced voltage in circuit 1 due to a current change in circuit 2;


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.


Coupling between Coils and Mandrels

Primary Secondary ε

Coupling Coupling Mandrel ~0.923 Focusing Focusing Mandrels ~0.821 Coupling Focusing Mandrels ~0.0041

3 Focusin gFlip Coupling Mandrel ~0.000183 Focusin gNon-flip Coupling Mandrel ~0.0014

€

ε =2M1−2

L1L2

Coupling Coefficient from the coil to the mandrels


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.


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.

Documents

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