Status of COBRA Magnet Wataru OOTANI MEG review meeting July 11 th, 2003 PSI Switzerland

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI 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 coils Superconducting coil in cryostat Potentiometer Support frame

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Construction finished!, cont ’ d Refrigerator Instrument panel Power supply for SC Power supply for NC NC current adjustor

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Excitation test Purposes Purposes Excitations with up to 5% and 10% higher coil current for the SC and NC, respectively. Excitations with up to 5% and 10% higher coil current for the SC 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.

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Two Troubles in Excitation Test Cold spots on the inner wall of the cryostat. Cold spots on the inner wall of the cryostat. –Dew condensation around the spots. –Radiation shield is touching the cryostat wall. –No problem in the magnet operation. –But, it might be problem for the detectors installed into the 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 magnet, all coils are intentionally quenched using protection heaters to avoid local energy dump. –Quench without the protection heater might damage the coil due to voltage and temperature rise in the coil.

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Cold Spots Radiation shield is thermally connected to the cryostat wall due to too much superinsulation layers in narrow gap. Radiation shield is thermally connected to the cryostat wall due 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.

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Quench Test Results Voltage rise in the quench triggered by the protection heaters in all the coils except the end coil with broken heater. Voltage rise in the quench triggered by the protection heaters in all the coils except the end coil with broken heater. Coil current: 300A Coil current: 300A Voltage across the end coil with broken heater rose up to – 900V. Coil current  V (central coil)  V (end coil w/o heater)

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Quench Test Results, cont ’ d Temperature rise in the quench triggered by the protection heaters in all the coils except the end coil with broken heater. Temperature rise in the quench triggered by the protection heaters in all the coils except the end coil with broken heater. Coil current: 300A Coil current: 300A Temperature of the central coil rose up to 110K.  T (central coil)

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Excitation w/o protection heater We were increasing coil current step by step and carefully checking the temperature and voltage rise in the intentional quench tests, but we had to give up the excitation with full operating current (360A) for the SC only for safety reason. We were increasing coil current step by step and carefully checking the temperature and voltage rise in the intentional quench tests, but we had to give up the excitation with full operating current (360A) for the SC only for safety reason. We reached 300A (83% of normal operating current) for the SC and successfully done the quench test at the coil current. We reached 300A (83% of normal operating current) for the SC and successfully done the quench test at the coil current. We found the SC magnet worked well under much more severe conditions. (  V=-900V,  T=110K) We found the SC magnet worked well under much more severe conditions. (  V=-900V,  T=110K) For the NC, I=400A(111% of normal operating current) reached. For the NC, I=400A(111% of normal operating current) reached.

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Strain No strange behavior up to coil current of 300A. No strange behavior up to coil current of 300A. Mechanical strength was already confirmed in the previous excitation test of the central part of the magnet last November. Mechanical strength was already confirmed in the previous excitation test of the central part of the magnet last November.

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI External Control System of Magnet External operation of the magnet using MIDAS slow control system (MSCB) was tested in this excitation test. External operation of the magnet using MIDAS slow control system (MSCB) was tested in this excitation test. Control software based on LabVIEW. Control software based on LabVIEW. MSCB modules

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Field Measurement Device Point-by-point precision of the field map ~ 10Gauss Point-by-point precision of the field map ~ 10Gauss 3-axis Hall probe. 3-axis Hall probe. Position accuracy ~ a few hundred  m Position accuracy ~ a few hundred  m 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  -motion for R- and Z-motion and high-torque AC servo-motor for  -motion Timing belt will be used for the motion in all directions Timing belt will be used for the motion in all directions Probe position is measured by optical scale sensors Probe position is measured by optical scale sensors

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Field Measurement Device, cont ’ d Construction completed. Construction completed. Installed into the COBRA cryostat and tested during the excitation test. Installed into the COBRA cryostat and tested during the excitation test. Test measurement of the COBRA field was done with the Hall probe used in the Belle magnet. Test measurement of the COBRA field was done with the Hall probe used in the Belle magnet. Hall probe

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Test measurement of the magnetic field was done in the excitation test. –SC Coil only. –Coil current: 200A (Normal operating current 360A). –No calibration of Hall probe. –Hall probe and driving system were roughly aligned to the magnet cryostat. Field Measurement Device, cont ’ d On the axis Good agreement with calculation! Radial direction at z=0

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Fringe Field Fringe field around the photon detector region was roughly measured. Fringe field around the photon detector region was roughly measured. I SC =180A, I NC =180A (50% of full excitation) I SC =180A, I NC =180A (50% of full excitation) The fringe field in the full excitation can be estimated by simply scaling. The fringe field in the full excitation can be estimated by 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 photon detector region as designed. Fringe field is suppressed below ~ 50 Gauss all over the photon detector region as designed.

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Summary 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. 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 excitation had to be given up because the full excitation w/o protection heater is dangerous. –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. –Measured magnetic field shows good agreement with calculation. –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.

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Summary, cont ’ d We are now strongly confident in the performance of the COBRA magnet. We are now strongly confident in the performance of the COBRA magnet. –Graded magnetic field and small fringe field as designed. –Survived under much more severe conditions (  V=-900V,  T=110K). –Good mechanical performance up to 300A (no strange behavior in strain plots). –Two problems can be easily fixed after the test. More reliable and powerful protection heater More reliable and powerful protection heater Reduce the superinsulation layers. Reduce the superinsulation layers.

Wataru OOTANI, July 11 th 2003, MEG review meeting, PSI Schedule