COBRA Magnet Status

1
COBRA Magnet Status

• W.Ootani
• MEG Experiment Review Meeting, Jul. 2004

2
COBRA Excitation at pE5

• Apr.13 COBRA installation
• Apr.13-15 Cryostat evacuation
• Apr.16-19 Cooling
• Apr.21-26 Excitation
• Excitation test (Superconducting Magnet(SC) and
  Compensation Coils(NC))
• Fringing field measurements and test of active
  shielding in pM3
• PMT test for Timing counter inside COBRA
• PMT test for LXe calorimeter near COBRA
• Apr.29 Beam is back

3
COBRA Installation in pE5

• COBRA placed at almost right place on beam line
  without platform.

4
Excitation at pE5

• Only 4days for cooling thanks to LN2 pre-cooling.
• Both SC and NC successfully tested at full
  operating current. (The first time to fully test
  NC.)
• COBRA provided perfectly stabilized field
  (?B/Blt0.05) for PMT tests.

5
Fringing Field Measurements
Fringing field measured at pE5
Gauss
4.2
6.8
9.1
6.7
18.5
83.8
50.5
9.0
33.5
433.7
440.3
31.2
7.5
73.3
20.4
56.3
69.7
19.8
7.8
11.6
11.3
6
Fringing Field Measurements
Fringing field measured outside area
Gauss
0.5
1.6
1.6
1.6
8.4
6.1
4.0
pE5
2.1
3.3
4.8
7
Fringing Field Measurements
Requirement
Measured
µE1 lt 20mG
Neighboring area
0.5G
pE3 µLan lt 1G µCap lt 1G
2-4G
ECRIT lt ?G
1-2G
pE5
pM32 GPS lt 20mG
1.8G
pM33 LTF lt 20mG
0.3G
pM3 beam line Kicker lt ?G Septum lt ?G
3.3G
4.8G
8
Fringing Field Measurements

• Fringing field was measured as predicted
  (unfortunately).
• The problems are being fixed for most places.
• Fringing field was successfully compensated in
  µSR facilities at pM3 using compensating coils.
  Control system has to be implemented.
• Fringing field at pE3 seems possible to be
  reduced lt 1G by passive shielding.
• Detector at ECRIT did not work when COBRA was ON.
• Effect on kicker and septum in pM3 beam line has
  to be checked.

9
Possible Solution in pE3

• Installation of active shielding in the detector
  (µLAN, µCAP) is difficult because of limited
  space and cost(?).
• Passive shielding
• Shielding box built with 5mm-thick soft iron
  plates (5m-D, 4m-W, 3m-H)
• No front wall for minimizing influence on beam
  optics
• Roof might not be necessary. (For good
  accessibility)

Without roof
With roof
Beam
Beam
10
Summary

• COBRA magnet was installed in pE5 and totally
  tested.
• PMT tests were carried out by using COBRA field.
• ?B/Blt0.05
• Stray field around LXe detector region is
  successfully canceled.
• Fringing field was measured in the neighboring
  beam line and problems are being fixed.
• It was found that active shielding is able to
  compensate COBRA field very well.
• Calibration of field mapping machine will be made
  this year.
• System alignment
• Calibration of Hall sensors
• Investigate possibility to use NMR
• Field map reconstruction
• Final field measurement is supposed to be carried
  out during shutdown period in 2006 after beam
  line commissioning is finished.

11
Schedule
Feb. 2004
Jul. 2004