status of cobra magnet wataru ootani meg review meeting july 11 th, 2003 psi switzerland

Status of COBRA MagnetStatus of COBRA Magnet

Wataru OOTANIWataru OOTANI

MEG review meetingMEG review meetingJuly 11July 11thth, 2003 PSI Switzerland, 2003 PSI Switzerland

Wataru OOTANI, July 11Wataru OOTANI, July 11thth 2003, MEG review meeting, PSI 2003, MEG review meeting, PSI

Construction finished!Construction finished!• Construction was finished!Construction was finished!• Excitation test was done between Jun.21th and Jul.7th.Excitation test was done between Jun.21th and Jul.7th.

Compensation coilsCompensation coilsSuperconducting coil in cryostatSuperconducting coil in cryostat

PotentiometerPotentiometer

Support frameSupport frame


Construction finished!, Construction finished!, cont’dcont’d

RefrigeratorRefrigeratorInstrument panelInstrument panelPower supply for SCPower supply for SC

Power supply for NCPower supply for NCNC current adjustorNC current adjustor


Excitation testExcitation test PurposesPurposes• Excitations with up to 5% and 10% higher coil current for the SC Excitations with up to 5% and 10% higher coil current for the SC and NC, respectively.and NC, respectively.• Intentional quench tests.Intentional quench tests.

• Quench propagation in the SC.Quench propagation in the SC.• Temperature rise.Temperature rise.• Voltage rise.Voltage rise.• Optimization of the protection heater parameters.Optimization of the protection heater parameters.

• Stress distribution in the superconducting magnet.Stress distribution in the superconducting magnet.• Interaction between SC and NC.Interaction between SC and NC.• Safety circuit of the magnet control system.Safety circuit of the magnet control system.• Stability and accuracy of power supply.Stability and accuracy of power supply.• Test of the device for the magnetic field measurement.Test of the device for the magnetic field measurement.

• Installation procedure.Installation procedure.• Driving system of Hall probe.Driving system of Hall probe.• Test measurement of the magnetic field.Test measurement of the magnetic field.

• Fringe field in the photon detector region.Fringe field in the photon detector region.


Two Troubles in Excitation Two Troubles in Excitation TestTest

• Cold spots on the inner wall of the cryostat.Cold spots on the inner wall of the cryostat.– Dew condensation around the spots.Dew condensation around the spots.– Radiation shield is touching the cryostat wall.Radiation shield is touching the cryostat wall.– No problem in the magnet operation.No problem in the magnet operation.– But, it might be problem for the detectors installed into the But, it might be problem for the detectors installed into the

magnet or filed measurement (Hall probe stability).magnet or filed measurement (Hall probe stability).

• Protection heaters in the downstream end-coil were broken.Protection heaters in the downstream end-coil were broken.– Protection heater: When a quench occurs somewhere in the Protection heater: When a quench occurs somewhere in the

magnet, all coils are intentionally quenched using protection magnet, all coils are intentionally quenched using protection heaters to avoid local energy dump.heaters to avoid local energy dump.

– Quench without the protection heater might damage the coil due Quench without the protection heater might damage the coil due to voltage and temperature rise in the coil.to voltage and temperature rise in the coil.


Cold SpotsCold Spots• Radiation shield is thermally connected to the cryostat wall dRadiation shield is thermally connected to the cryostat wall due to too much superinsulation layers in narrow gap.ue to too much superinsulation layers in narrow gap.• Dew condensation was observed around the cold spots.Dew condensation was observed around the cold spots.• The magnet will be disassembled to fix this problem.The magnet will be disassembled to fix this problem.


Quench Test ResultsQuench Test Results• Voltage rise in the quench triggered by the protection heaters in Voltage rise in the quench triggered by the protection heaters in all the coils except the end coil with broken heater.all the coils except the end coil with broken heater.• Coil current: 300ACoil current: 300A

Voltage across the end coil with broken heater rose up to –900V.Voltage across the end coil with broken heater rose up to –900V.

Coil current

V (central coil)

V (end coil w/o heater)


Quench Test Results, cont’dQuench Test Results, cont’d• Temperature rise in the quench triggered by the protection Temperature rise in the quench triggered by the protection heaters in all the coils except the end coil with broken heater.heaters in all the coils except the end coil with broken heater.• Coil current: 300ACoil current: 300A

Temperature of the central coil rose up to 110K.Temperature of the central coil rose up to 110K.

T (central coil)


Excitation w/o protection Excitation w/o protection heaterheater

• We were increasing coil current step by step and carefully We were increasing coil current step by step and carefully checking the temperature and voltage rise in the checking the temperature and voltage rise in the intentional quench tests, but we had to give up the intentional quench tests, but we had to give up the excitation with full operating current (360A) for the SC excitation with full operating current (360A) for the SC only only for safety reasonfor safety reason..

• We reached 300A (83% of normal operating current) for the We reached 300A (83% of normal operating current) for the SC and successfully done the quench test at the coil SC and successfully done the quench test at the coil current. current.

• We found the SC magnet worked well under much more We found the SC magnet worked well under much more severe conditions. (severe conditions. (V=-900V, V=-900V, T=110K)T=110K)

• For the NC, I=400A(111% of normal operating current) For the NC, I=400A(111% of normal operating current) reached.reached.


StrainStrain

• No strange behavior up to coil current of 300A.No strange behavior up to coil current of 300A.• Mechanical strength was already confirmed in Mechanical strength was already confirmed in the previous excitation test of the central part of the previous excitation test of the central part of the magnet last November.the magnet last November.


External Control System of External Control System of MagnetMagnet

• External operation of the magnet using MIDAS slow control system External operation of the magnet using MIDAS slow control system (MSCB) was tested in this excitation test.(MSCB) was tested in this excitation test.• Control software based on LabVIEW.Control software based on LabVIEW.

MSCB modulesMSCB modules


Field Measurement DeviceField Measurement Device• Point-by-point precision of the field map ~ 10GaussPoint-by-point precision of the field map ~ 10Gauss• 3-axis Hall probe.3-axis Hall probe.• Position accuracy ~ a few hundred Position accuracy ~ a few hundred mm• Ultrasonic motor with a rotary encoder (4000pulses/rotation) Ultrasonic motor with a rotary encoder (4000pulses/rotation) for R- and Z-motion and high-torque AC servo-motor for for R- and Z-motion and high-torque AC servo-motor for -motion -motion • Timing belt will be used for the motion in all directionsTiming belt will be used for the motion in all directions• Probe position is measured by optical scale sensorsProbe position is measured by optical scale sensors


Field Measurement Device, Field Measurement Device, cont’dcont’d

• Construction completed.Construction completed.

• Installed into the COBRA cryostat and tested during the excitation Installed into the COBRA cryostat and tested during the excitation test.test.

• Test measurement of the COBRA field was done with the Hall Test measurement of the COBRA field was done with the Hall probe used in the Belle magnet.probe used in the Belle magnet.

Hall probeHall probe


Test measurement of the magnetic field was done in the Test measurement of the magnetic field was done in the excitation test.excitation test.– SC Coil only.SC Coil only.– Coil current: 200A (Normal operating current 360A).Coil current: 200A (Normal operating current 360A).– No calibration of Hall probe.No calibration of Hall probe.– Hall probe and driving system were roughly aligned to the magnet Hall probe and driving system were roughly aligned to the magnet

cryostat.cryostat.

Field Measurement Device, Field Measurement Device, cont’dcont’d

On the axis

Good agreement with calculation!Good agreement with calculation!

Radial direction at z=0


Fringe FieldFringe Field• Fringe field around the photon detector region was roughly Fringe field around the photon detector region was roughly measured.measured.• IISCSC=180A, I=180A, INCNC=180A (50% of full excitation)=180A (50% of full excitation)• The fringe field in the full excitation can be estimated by The fringe field in the full excitation can be estimated by simply scaling.simply scaling.

• The compensation of the fringe field works very well!The compensation of the fringe field works very well!• Fringe field is suppressed below ~ 50 Gauss all over the pFringe field is suppressed below ~ 50 Gauss all over the photon detector region as designed.hoton detector region as designed.


SummarySummary• Construction of the COBRA magnet was finished.Construction of the COBRA magnet was finished.• Excitation test was done between Jun.21th and Jul.7th.Excitation test was done between Jun.21th and Jul.7th.

– Two problems. Two problems. • Cold spots in the inner wall of the cryostat.Cold spots in the inner wall of the cryostat.• Protection heaters in the downstream end-coil are broken.Protection heaters in the downstream end-coil are broken.

– I=300A (83% of normal operating current) reached for the SC, but full I=300A (83% of normal operating current) reached for the SC, but full excitation had to be given up because the full excitation w/o protection excitation had to be given up because the full excitation w/o protection heater is dangerous.heater is dangerous.

– I=400A (111% of normal operating current) reached for the NC. I=400A (111% of normal operating current) reached for the NC.

• Field measurement device was completed.Field measurement device was completed.– Test measurement was done in the excitation test.Test measurement was done in the excitation test.– Measured magnetic field shows good agreement with calculation.Measured magnetic field shows good agreement with calculation.– Precise field measurement will be done at PSI.Precise field measurement will be done at PSI.

• Fringe field around the photon detector region was measured.Fringe field around the photon detector region was measured.– Good suppression of the fringe field.Good suppression of the fringe field.


Summary, cont’dSummary, cont’d

• We are now strongly confident in the performance of the COBRA magWe are now strongly confident in the performance of the COBRA magnet.net.– Graded magnetic field and small fringe field as designed.Graded magnetic field and small fringe field as designed.– Survived under much more severe conditions (Survived under much more severe conditions (V=-900V, V=-900V, T=110K).T=110K).– Good mechanical performance up to 300A (no strange behavior in strain Good mechanical performance up to 300A (no strange behavior in strain

plots).plots).– Two problems can be easily fixed after the test.Two problems can be easily fixed after the test.

• More reliable and powerful protection heaterMore reliable and powerful protection heater• Reduce the superinsulation layers.Reduce the superinsulation layers.


ScheduleSchedule

status of cobra magnet wataru ootani meg review meeting july 11 th, 2003 psi switzerland

Documents

end coil

coil current step

higher coil current

protection heaters

downstream endcoil

sc magnet

test measurement

protection heater parameters