W.Ootani

1
COBRA Magnet Status

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

2
First Excitation Test in June03

• 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 June03
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 ?T and ?V below the acceptable level.
7
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
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.1213, 2003.
• Placed in SLS hall for the initial test before
  the installation in pE5, 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 pE5 this April.