Transcript Component Implementation: Magnets

Superconducting Magnets
for the MICE Channel
Michael A. Green
Oxford University Physics Department
Oxford OX1-3RH, UK
1
Location of the MICE Magnets
• The MICE channel is divided into seven modules.
• The MICE modules come in three types, the
focusing and absorber module, the coupling and
RF module, and the detector module.
• The focusing module contains two coils, which can
create a either solenoid field or a gradient field.
The coupling module contains one coil. Each
detector module has two matching coils and three
coils to create a uniform magnetic field.
2
A 3 Dimensional View of the
MICE Superconducting Coils
Detector Center Coil
Matching Coils
Coupling Coils
Focusing Coils
Matching Coils
Detector Center Coil
Detector End Coils
Focusing Coils
Focusing Coils
Detector End Coils
Figure from J. H Rochford RAL
3
Separation of the Magnet Cryostat
from the Rest of the Module
• The superconducting coils are vacuum insulated in
their own vacuum vessel. This vessel is designed
in accordance with the pressure vessel code.
• The magnet cryostat vacuum vessel is completely
separated from any other vacuum vessel that is
part of the module.
• The wall that separates the vacuum vessels must be
leak tight to 10-7 mbar liter s-1 in order to prevent
gas migration between the vessels.
4
October 2003 Coupling Magnet
Cryostat Vacuum
Vacuum Space for RF Cavity
5
Focusing Module Magnet with a
Hydrogen Absorber
78 2 mm
Magnet Cryostat
Cold Mass Support
S/C Coil Vacuum
6061 Al Support
30 to 40 K Shield
~7 07 mm
Absorber Pipe Space
Absorber Radial Support
Absorber Vacuum
300 K Safety Window
260 mm
Liquid
Hydrogen
470 mm
320 mm
20 K Absorber Window
Absorber Longitudinal Support
S/C Coil
4.4 K He Cooling Tube
80 mm
RF or Detector
Vacuum
Absorber Vacuum Vessel End
Vacuum Vessel End Flange
Argon Cover Gas
18 0 mm
260 mm
6
Focus Magnet Cross-section
782 mm
9.5 mm Thick 304 St St Wall
6061 Al Cover Plate 13 mm
6.4 mm Thick 304 St St Vessel
Machined 6061-T6
Aluminum Forgeing
1 mm Thick Cu Shield
~707 mm
10 mm ID Helium Tube
1 mm G-10 Insulation
5 mm Thick 304 St St Tube
~450 mm
260 mm
80 mm
180 mm
1 mm G-10 Insulation
670 mm
725 mm
265 mm
249 mm
235 mm
7
Focusing and Coupling Magnet
Load Line
500
Current in the Conductor (A)
400
4.4 K
240 MeV/c Flip Case
300
T = 3.4 K
T = 4.2 K
T = 5.0 K
Focusing
Coupling
200 MeV/c Flip Case
200
100
0
0
1
2
3
4
5
6
Magnetic Indution (T)
7
8
9
10
8
Detector Magnet Module
Cryostat Vacuum
Detector Vacuum
9
MICE Channel on Axis Field Profile
Mice Channel Center
Detector and Matching Coils
Coupling Coil
Focus Coils
Focus Coils
Baseline Case: 200 MeV/c, Beta = 43 cm in the flip mode
10
Magnet Power Supplies
• Each of the focus coils has its own leads so that the magnet
can be changed from a gradient magnet to a straight solenoid
magnet. The focusing magnets will be powered by a single
300 A, 10 V power supply.
• Each coupling coil will have a 10 V, 300 A power supply.
• The detector end and center coils will be hooked is series and
powered by a single 300 A, 10 V power supply. End coil #1
will have a separate 100 A, 5 V power supply to adjust its
current for tuning. Each of the matching coils will be in
series with its corresponding coil in the other module. They
will have 300 A, 10 V power supplies.
11
Magnet Quench Protection
• Each focus coil will be protected by a warm diode and resistor
across its leads.
• The coupling coils will sub-divided into three parts. Each
part will have a cold diode and resistor across that part. This
quench protection scheme is commonly used in high field
MRI magnets.
• The three detector coils in series will be protected by warm
diodes and resistors across their leads. The matching coils
will also be protected by a warm diodes and resistors.
• All of the magnets will be protected in part by heating due to
currents flowing the magnet winding mandrel (quench back).
12
MICE Magnet Refrigeration
• The MICE magnet coil will be cooled by conduction
from the winding mandrel and support structure.
Cooling is from by two-phase 4.4 K helium flowing
in tubes attached to these parts.
• About 70 W of 4.4 K refrigeration are needed to cool
the seven magnet modules for MICE.
• Cooling for the magnet shields and leads comes from
a 14 K helium circuit from the refrigerator.
13
Some MICE Magnet Safety Issues
• The coupling solenoid leads and the detector magnet leads
are located outside of the hydrogen safety zone. Only the
focusing magnet leads may be located within a hydrogen
safety zone.
• Since the magnet are cooled by force helium in tubes, a
magnet quench causes very little helium to be released and
this release is outside of the MICE shielding.
• The cryostat vacuum vessels have relief devices that will
open in the event of pressure buildup in the vacuum space.
• The handling of cryogenic fluids and cold transfer lines
will be done by trained personnel using standard safety
procedures for handling liquid helium prescribed by RAL.
14
Focusing Magnet and Hydrogen
Safety Issues
• If possible, the leads and cables for the focusing solenoids
will be located outside of the hydrogen safety zone.
• If the focusing coil leads and cables are within a hydrogen
safety zone, they will have to be shielded using a cover of an
inert gas such as argon. Sparking must not occur in a region
where hydrogen gas can accumulate.
• Instrumentation wires for the focusing solenoids must be
located outside of the hydrogen safety zone, if possible.
• A focusing magnet quench does not cause hydrogen venting.
15
Concluding Comments
• Each of the magnet modules has its own insulating vacuum
vessel. The magnets do not share a common vacuum with
any other components of MICE.
• The cryogenic system has a minimum amount of liquid
helium within it.
• The magnet quench protection system will limit the voltages
seen at the magnet leads to about 10 volts.
• Only the focusing magnets are in a hydrogen area. A quench
of this magnet does not cause a general release of hydrogen.
The major safety concern is the location of the magnet leads.
16