Spectrometer Solenoid: Plans to
Fix Magnet 2
Spectrometer Solenoid Review
November 18, 2009
Steve Virostek
Lawrence Berkeley National Lab
Topics
•Proposed magnet fix
•Modified magnet geometry
•Other system improvements
•Fallback plans
•Schedule overview
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 2
Magnet 2 Added Cryocooler
Single-stage cooler
Thermal link
HTS leads
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 3
Added Single Stage Cooler
•A modification to Magnet 2 has been proposed which adds a
single stage cryocooler to provide additional cooling to the
HTS leads and won’t require full magnet disassembly
•The plan to add a single-stage Cryomech AL330 cooler
(arrived 11/13/09) provides 170 W at 55 K and requires
modifications only in the “turret” area
•The added cooling power should lower the upper HTS lead
temperature sufficiently to train to full current
•The new cooler could remove enough heat to permit the
other 3 two-stage coolers to maintain the cold mass LHe
level (i.e. closed system)
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 4
Cryomech AL330 Performance
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 5
Modification Details
Added turret
space
Access port
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 6
Modification Details
•Multilayer flexible Cu link
•Soldered ends
•Thermal grease in joints
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 7
Cooler Conduction Link
Note: link thickness has
been increased to ¾”
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 8
Thermal Calculations and Measurements
•The thermal model of the magnet is being used to better
understand the cooling mechanisms and heat loads
•Initial calculations indicate the upper HTS leads
temperature will be <70K during operation
•The temperature drop across the thermal link between the
single stage cooler and the 1st stage copper plate is
expected to be ~10 K
•An off line magnet lead test is being carried out by Wang
NMR to measure all relevant temperatures and voltages
during operation
•Additional sensors will directly measure cold head temps.
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 9
HTS Lead Protection
The HTS leads can be actively protected from burnout due to
quench as follows:
i)
Interlock the power supply with the temperature of the
top of the HTS leads/heat sink to cut power when the
temperature is too high
ii)
Active quench protection based on the voltage across the
HTS leads in case of resistive transition (~3 mV limit) – a set of
voltage taps will be added to the lower end of the leads
This type of system could possibly be implemented at RAL, but
Wang NMR does not currently have the capability to implement
an active control system
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 10
Other Issues
• Our modeling indicates the new cooler won’t
substantially affect the shield temperature
• It is uncertain whether the addition of the singlestage cooler will solve the LHe boil off issue
• Cannot address known deficiencies in Magnet
2(shield connection, copper plate thickness,
leads arrangement) without fully disassembling
magnet
• Additional cooler(s) will increase utility costs for
running the magnets (water and power)
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 11
Magnet 2 Fallback Scenario
•If the addition of a single-stage cooler to Magnet 2 does not
result in a closed system, there are two options:
i) Accept the thermal properties as is and top up the
magnet with external cryogens as needed
ii) Disassemble and modify the magnet to improve the
shield connections and to accommodate a fourth twostage cooler (in addition to the single-stage cooler)
•The 2nd option will add 3 to 6 months to the delivery of the
2nd magnet to RAL and will create additional risks of damage
or assembly errors in the repair process
•For these reasons, the first option is preferred
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 12
Power Supply Issues
•During magnet training, a problem with the power supply
controller was noted – the controller would allow the system
to ramp up in current but not down
•Modifications to the power supply circuit external to the
magnet have been developed and briefly tested
•The ramp down system is similar to the magnet discharge
circuit previous developed and implemented
•The vendor has been contracted to fabricate and install the
system in both sets of RAL racks
•Installation in the first rack is complete
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 13
Schedule Overview
* These step are only required if the initial modifications to Magnet 2 are unsuccessful
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
Page 14
Summary
• A fix to Magnet 2 has been devised which
does not require full magnet disassembly
• Addition of a single-stage cooler to the first
stage copper plate is expected to solve the
HTS leads temperature problem
• Temperature of the thermal shield may still
be an issue (cooler will have minimal impact)
• Operation without the need for cryogen top
off is probable but not guaranteed
Steve Virostek -- Lawrence Berkeley National Laboratory -- November 18, 2009
MICE Spectrometer Solenoid: Plans to Fix Magnet 2
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