The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404.

Heat extraction through cable insulation

and quench limits

Pier Paolo Granieri, Rob van Weelderen, Lina Hincapié (CERN)

2nd Joint HiLumi LHC-LARP Annual MeetingINFN Frascati, 14-16 November 2012 (revised version 11/1/2013)

P.P. Granieri - Heat extraction and quench limits 2

Outline• Heat transfer through cable electrical

insulation: evolution• Experimental method• setup description• results

• Quench limits estimation• MQXF at 1.9 K bath temperature• vs. modeling results• vs. LHC magnets and MQXF at 4.2 K

P.P. Granieri - Heat extraction and quench limits 3

Heat transfer through cable electrical insulation: evolution

P.P. Granieri - Heat extraction and quench limits 4

Heat transfer through cable electrical insulation: evolution

P.P. Granieri - Heat extraction and quench limits 5

Heat transfer through cable electrical insulation: evolution

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Heat transfer through cable electrical insulation: evolution

*

*

*

* unpublished measurements from D. Richter (5 SC heated cables, actual MQX cables)

P.P. Granieri - Heat extraction and quench limits 7

Heat transfer through cable electrical insulation: evolution

* unpublished measurements from D. Richter (5 SC heated cables, actual MQX cables)

*

*

*

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Experimental method• Sample: - 150 mm long rectangular stack

made of 6 alternating cables

• Cable: - CuNi10

- LHC cables geometry, MB inner layer

• T sensors: - AuFe0.07at%/Chromel differential

thermocouples

- in grooves in the central cable

- installed before impregnation

• Heating: - Joule heating along resistive strands

- steady-state

- different configurations (heated cables)

P.P. Granieri - Heat extraction and quench limits

P.P. Granieri - Heat extraction and quench limits

Experimental method

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• Insulation: - fiber glass sleeve

- vacuum impregn. resin: CTD-101

- thickness: 150 µm

• Cooling (transversal): - He II, 1.9 K

- He I, 4.2 K

• Pressure: 0 MPa

1

2

3

4

5

6

QQ

Instrumented

cable

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Experimental results• Different position in the cable, Tbath, heating configuration

Tc (mid-plane, cable center)

Tc (mid-plane, cable edge)

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* 3 heated cables

Heat extraction from coil inner layer(cable center T)

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Heat extraction from coil inner layer(cable center T)

* 3 heated cables

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Quench limit estimation• Heat that must be (uniformly) deposited in the cable

until the cable center/edge reaches Tc:

P.P. Granieri - Heat extraction and quench limits

155 mW/cm3

198 mW/cm3 143 mW/cm3

247 mW/cm3

• MQXF

• 150 mm bore

(w/o µ-channels)

• 1.9 K constant bath T

• uniform heat deposit

88 mW/cm3

127 mW/cm3

39

188

80 mW/cm3

106

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Quench limit estimation

• Comparison tests vs. model *, independently carried outCoil position(inner layer)

ΔT from exp. tests (mK)

ΔT from model *(mK)

Difference(%)

mid-plane 230-420 390 8

cable adjacent to pole

16-58 68 17

* previous talk from H. Allain

2.13 K

2.32 K

• Mid-plane and pole cable temperature for heat deposit in nominal conditions (peak of 3.78 mW/cm3)

1.96 K1.92 K

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Quench limit estimation• Comparison at nominal conditions in mid-plane

Magnet Estimated quench limit(mW/cm3)

Expected peak heat deposit (mW/cm3)

MB 46 0.6

MQXA 65 3.5

MQXB 60 / 75 3.5

MQXC 104 4

MQXF at 1.9 K(140 T/m)

155 4

MQXF at 4.2 K(80% Bss)

129 4

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Conclusions

• Numerical model of the experimental tests

• Thermal measurement of a short model coil

Perspectives

• Heat extraction through Nb3Sn insulation was measured

• worse than through LHC Nb-Ti insulation below a ΔT of 1.8 K (in the cable center), since the He II contribution is missing

• better than through Enhanced Nb-Ti insulation above a ΔT of 5.7 K (in the cable center), because kNb3Sn > KNb-Ti

3.7 K 6.4 K

scaled to magnet geometry

to be confirmed by a

dedicated test

• Heat extraction from the cable allows a first estimate of the quench limit: • MQXF mid-plane cable is the most critical: 155 mW/cm3, vs. 4 mW/cm3 expected

• MQXF-MQXC will have a quench limit 2 to 3 times those of MB-MQXA-MQXB