23 october 2005mice meeting at ral1 mice tracker magnets, 4 k coolers, and magnet coupling during a...
Post on 19-Dec-2015
214 views
TRANSCRIPT
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
23 October 2005 MICE Meeting at RAL 2
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
23 October 2005 MICE Meeting at RAL 3
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
Drawing by S. Q. Yang
23 October 2005 MICE Meeting at RAL 5
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
23 October 2005 MICE Meeting at RAL 6
• 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
23 October 2005 MICE Meeting at RAL 7
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
23 October 2005 MICE Meeting at RAL 8
50 K intercept
Tracker Magnet Cold Mass Cold Link
Warm Link
300 K End
4 K End
Tracker Magnet Cold Mass Support System
Drawing by S. Q. Yang
23 October 2005 MICE Meeting at RAL 9
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
23 October 2005 MICE Meeting at RAL 10
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
23 October 2005 MICE Meeting at RAL 11
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.
23 October 2005 MICE Meeting at RAL 12
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.
23 October 2005 MICE Meeting at RAL 13
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.
23 October 2005 MICE Meeting at RAL 14
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.
23 October 2005 MICE Meeting at RAL 15
Issues with 4 K Coolers and their Connection to the Magnets
23 October 2005 MICE Meeting at RAL 16
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.
23 October 2005 MICE Meeting at RAL 17
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.
23 October 2005 MICE Meeting at RAL 18
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.
23 October 2005 MICE Meeting at RAL 19
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).
23 October 2005 MICE Meeting at RAL 20
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
23 October 2005 MICE Meeting at RAL 21
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.
23 October 2005 MICE Meeting at RAL 22
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
Drawing by S. Q. Yang
23 October 2005 MICE Meeting at RAL 23
Magnet Coupling During a Quench
23 October 2005 MICE Meeting at RAL 24
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.
23 October 2005 MICE Meeting at RAL 25
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
23 October 2005 MICE Meeting at RAL 26
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
23 October 2005 MICE Meeting at RAL 27
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;
23 October 2005 MICE Meeting at RAL 28
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.
23 October 2005 MICE Meeting at RAL 29
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
23 October 2005 MICE Meeting at RAL 30
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.
23 October 2005 MICE Meeting at RAL 31
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.