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W.OotaniICEPP, University of Tokyo

MEG experiment review meeting Feb.11 2004, PSI

W.OotaniICEPP, University of Tokyo

MEG experiment review meeting Feb.11 2004, PSI

COBRA Magnet Status

COBRA Magnet Status

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First Excitation Test in June’03 First Excitation Test in June’03

SummaryFirst excitation test was carried out 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.

SummaryFirst excitation test was carried out 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.

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First Excitation Test in June’03 First Excitation Test in June’03

Design fieldDesign field Measured fieldMeasured field

Graded field profile measured at 200AGraded field profile measured at 200A

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Problems in First Test 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 wallToo thick super Insulation layers in narrow gap of the cryostat.Radiation shield cylinder was slightly displaced.

Protection heaters were burned.All heaters were replaced with larger heaters and back-up heaters were added.

Cold spots on the cryostat wallToo 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.

The problems were quickly fixed and the second excitation test was carried out last

August.

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Second Excitation TestSecond Excitation TestThe 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 spotNo protection heater was broken.

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 spotNo protection heater was broken.

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Quench TestsQuench TestsQuench 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 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.

Quench was propagated in the magnet fast enough to keep ΔT and ΔV below the acceptable level.

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SQD Reaction in Quench TestSQD Reaction in Quench Test

Time[msec]

-130 Heater at central coil is fired0 SQD reacted at central coil

+54 Protection heaters ON+74 DC OFF

+(150-200)

SQDs reacted at the other coils

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Voltage Change in Quench TestVoltage Change in Quench Test

Maximum voltage across the central coil of 1200V was observed ~500msec after the quench in the central coil.

Maximum voltage across the central coil of 1200V was observed ~500msec after the quench in the central coil.

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Temperature Rise in Quench TestTemperature Rise in Quench Test

Temperature was peaked at 110K in the central coil 16sec after the quench occurred.

Temperature was peaked at 110K in the central coil 16sec after the quench occurred.

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Mechanical StrengthMechanical StrengthStrains in the central coil and support cylinder measured up to coil current of 380A.Fairly linear relation between strain and I2

Strains in the central coil and support cylinder measured up to coil current of 380A.Fairly linear relation between strain and I2

360A360A 380A380A

Sufficient mechanical strength Sufficient mechanical strength

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COBRA arrived at PSICOBRA arrived at PSICOBRA 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.

Main bodyMain body Power supply, compressor, mapping machine, etc

Power supply, compressor, mapping machine, etc

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Excitation Test at PSIExcitation Test at PSICOBRA 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 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 hallCOBRA in SLS hall MEG magnet teamMEG magnet team

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Excitation Test at PSIExcitation Test at PSI

COBRA seems to survive long journey from Japan.

COBRA seems to survive long journey from Japan.

5.6% over excitation was successfully done at PSI.

5.6% over excitation was successfully done at PSI.

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Excitation Test at PSIExcitation Test at PSIMechanical strengthMechanical strength

TemperatureTemperatureVoltageVoltage

Good performance was confirmed in quench test up to 360A.

Good performance was confirmed in quench test up to 360A.

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Influence of Fringing Field

Influence of Fringing Field

Position Brequirement

BCOBRA

GPS(πM32) < 20mG 2~3GLTF(πM32) < 20mG ~1GμLAN(πE3) < 1-2G 4~5GπM3 beam

line? 5~10G

COBRA

COBRA fringing field would affect neighboring facilities.

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What Can We Do?What Can We Do?COBRA is placed inside shielding box

Strong EM interaction bw/ shield and COBRADestroy field suppression around photon detector

Beam time sharing

The beam lines are supposed to be used all the time.

Iron walls between πE5 and neighboring beam line (passive shielding).Active shielding for each device in neighboring beam line

COBRA is placed inside shielding box

Strong EM interaction bw/ shield and COBRADestroy field suppression around photon detector

Beam time sharing

The beam lines are supposed to be used all the time.

Iron walls between πE5 and neighboring beam line (passive shielding).Active shielding for each device in neighboring beam line

Not possible

Not possible

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Effect of Iron WallEffect of Iron Wall3cm-thick and 5m height soft iron wallFinite element calculation with 3D model

3cm-thick and 5m height soft iron wallFinite element calculation with 3D model

Iron wall

πM3

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Effect of Iron WallEffect of Iron Wall

Some effect (25-45% reduction),Not sufficient especially for GPS and LTF

B field at this level can be distorted easily by surrounding materials not only in direction but also in strength Difficult to predict what actually happens.

Some effect (25-45% reduction),Not sufficient especially for GPS and LTF

B field at this level can be distorted easily by surrounding materials not only in direction but also in strength Difficult to predict what actually happens.

PositionWithout

wallWith wall

GPS(πM32) 1.9 Gauss 1.1 GaussLTF(πM32) 0.8 Gauss 0.6 GaussμLAN(πE3) 4.8 Gauss 2.6 Gauss

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Active ShieldingActive ShieldingCube shape active shielding composed of six compensating coils.

B field in any direction can be canceled.

Two settings of coil current are necessary corresponding to two states of COBRA magnet (ON & OFF).

More efficient and much lighter.

This type of active shielding is already working in GPS and LTF in πM3 to compensate earth field.

Details of effect are being investigated.

Cube shape active shielding composed of six compensating coils.

B field in any direction can be canceled.

Two settings of coil current are necessary corresponding to two states of COBRA magnet (ON & OFF).

More efficient and much lighter.

This type of active shielding is already working in GPS and LTF in πM3 to compensate earth field.

Details of effect are being investigated.Active shielding in LTF of πM3

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Possible SolutionPossible SolutionCOBRA Magnet has only two states (ON and OFF).

COBRA field will be highly stabilized within 0.1%.

Active shielding is already working in GPS and LTF of πM3 to compensate earth field.

What is reasonable solution?Active shielding with two settings of compensating coil current corresponding to COBRA ON and OFF. Passive shielding can be added if necessary.

Possibility that existing compensating coils in πM3 can cancel COBRA fringing field. It has to be tested after the installation of COBRA in πE5.

We plan to measure the fringing field around πE5 after the installation.

COBRA Magnet has only two states (ON and OFF).

COBRA field will be highly stabilized within 0.1%.

Active shielding is already working in GPS and LTF of πM3 to compensate earth field.

What is reasonable solution?Active shielding with two settings of compensating coil current corresponding to COBRA ON and OFF. Passive shielding can be added if necessary.

Possibility that existing compensating coils in πM3 can cancel COBRA fringing field. It has to be tested after the installation of COBRA in πE5.

We plan to measure the fringing field around πE5 after the installation.

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SummarySummaryThe 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.

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 in SLS hall and COBRA is planned to move to πE5 this April.

COBRA is going to be used in various tests (LXe, timing counter,...) this year and final field measurement will be done after arrival of BTS around at the end of this year.

Reasonable solution to fringing field problem might be a combination of active and passive shielding. Further investigation needed.

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.

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 in SLS hall and COBRA is planned to move to πE5 this April.

COBRA is going to be used in various tests (LXe, timing counter,...) this year and final field measurement will be done after arrival of BTS around at the end of this year.

Reasonable solution to fringing field problem might be a combination of active and passive shielding. Further investigation needed.