COBRA Magnet Status

1. COBRA Magnet Status • W.Ootani • ICEPP, University of Tokyo • MEG experiment review meeting • Feb.11 2004, PSI

2. First Excitation Test in June’03 • Summary • First excitation test was done in Japan last June. • The test was not completed because of some problems. • Some of the quench protection heaters were burned. • Cold spots on the cryostat inner wall. • Superconducting magnet was tested up to 83% excitation. • Compensation coils were successfully tested up to 110% excitation. • Field measurement device was tested. • Field profile in the bore and fringing field around photon detector region were roughly measured.

3. First Excitation Test in June’03 Graded field profile measured at 200A Design field Measured field

4. Problems in First Test • Protection heaters were burned. • All heaters were replaced with larger heaters and back-up heaters were added. • Cold spots on the cryostat wall • Too thick super Insulation layers in narrow gap of the cryostat. • Radiation shield cylinder was slightly displaced. The problems were quickly fixed and the second excitation test was carried out last August.

5. Second Excitation Test • The second test was done in Japan last August. • The magnet was successfully tested up to 380A • (5.6% higher than the operating current, 360A) • No cold spot • No protection heater was broken.

6. Quench Tests • Quench propagation observed by voltage taps, temperature sensors and superconducting quench detectors (SQDs). • Severest test: heater quench test at central coil at 360A. • Quench induced by firing a heater in the central coil, which is the farthest coil from the refrigerator. • DC OFF and quench protection heater ON after the quench is detected. Quench was propagated in the magnet fast enough to keep ΔT and ΔV below the acceptable level.

7. Time[msec] -130 Heater at central coil is fired 0 SQD reacted at central coil +54 Protection heaters ON +74 DC OFF +(150-200) SQDs reacted at the other coils SQD Reaction in Quench Test

8. Voltage Change in Quench Test • Maximum voltage across the central coil of 1200V was observed ~500msec after the quench in the central coil.

9. Temperature Rise in Quench Test • Temperature was peaked at 110K in the central coil 16sec after the quench occurred.

10. 360A 380A Mechanical Strength • Strains in the central coil and support cylinder measured up to coil current of 380A. • Fairly linear relation between strain and I2 Sufficient mechanical strength

11. COBRA arrived at PSI • COBRA arrived at PSI Nov.12&13, 2003. • Placed in SLS hall for the initial test before the installation in πE5, which is planned this April. • System check after the transportation was carried out last December and no serious problem was found. Power supply, compressor, mapping machine, etc Main body

12. Excitation Test at PSI • COBRA is placed at Axis34-36 in SLS. • Excitation test was done between Jan.17-27,2004. • Full excitation for SC and 8% excitation for NC because of limited utility at SLS. COBRA in SLS hall MEG magnet team

13. Excitation Test at PSI 5.6% over excitation was successfully done. COBRA seems to survive long journey from Japan.

14. Excitation Test at PSI Good performance was confirmed in quench test up to 360A. Mechanical strength Voltage Temperature

15. Summary • The second excitation test of the COBRA magnet was successfully performed last August in Japan after fixing the problems in the first test. • The magnet was tested up to 380A(5.6% higher than normal operating current). • Good quench propagation and mechanical performance were observed. • The magnet was transported to the PSI and placed in SLS hall to be tested. • The excitation test was carried out in SLS hall between Jan.17 and 27 and the magnet was successfully tested up to 380A. • Field mapping study is starting at SLS hall and COBRA is planned to move to πE5 this April.