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 Heat extraction through cable insulation and quench limits Pier Paolo Granieri, Rob van Weelderen, Lina Hincapié (CERN) 2 nd Joint HiLumi LHC-LARP Annual Meeting INFN Frascati, November 2012 (revised version 11/1/2013)

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 limits2

Heat transfer through cable electrical insulation: evolution 3

P.P. Granieri - Heat extraction and quench limits Heat transfer through cable electrical insulation: evolution 4

P.P. Granieri - Heat extraction and quench limits Heat transfer through cable electrical insulation: evolution 5

P.P. Granieri - Heat extraction and quench limits Heat transfer through cable electrical insulation: evolution 6 * * * * unpublished measurements from D. Richter (5 SC heated cables, actual MQX cables)

P.P. Granieri - Heat extraction and quench limits Heat transfer through cable electrical insulation: evolution 7 * unpublished measurements from D. Richter (5 SC heated cables, actual MQX cables) * * *

Experimental method Sample: mm long rectangular stack made of 6 alternating cables Cable: - CuNi10 - LHC cables geometry, MB inner layer T sensors: - AuFe 0.07at% /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 limits8

Experimental method P.P. Granieri - Heat extraction and quench limits9 Insulation: - fiber glass sleeve - vacuum impregn. resin: CTD thickness: 150 µm Cooling (transversal):- He II, 1.9 K - He I, 4.2 K Pressure: 0 MPa QQ Instrumented cable

Experimental results Different position in the cable, T bath, heating configuration P.P. Granieri - Heat extraction and quench limits10 Tc (mid-plane, cable center) Tc (mid-plane, cable edge)

P.P. Granieri - Heat extraction and quench limits11 * 3 heated cables Heat extraction from coil inner layer (cable center T)

P.P. Granieri - Heat extraction and quench limits12 Heat extraction from coil inner layer (cable center T) * 3 heated cables

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/cm mW/cm mW/cm mW/cm 3 MQXF 150 mm bore (w/o µ-channels) 1.9 K constant bath T uniform heat deposit mW/cm mW/cm 3 106

Quench limit estimation Comparison tests vs. model *, independently carried out P.P. Granieri - Heat extraction and quench limits Coil position (inner layer) ΔT from exp. tests (mK) ΔT from model * (mK) Difference (%) mid-plane cable adjacent to pole * 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/cm 3 ) K 1.92 K

Quench limit estimation Comparison at nominal conditions in mid-plane P.P. Granieri - Heat extraction and quench limits MagnetEstimated quench limit (mW/cm 3 ) Expected peak heat deposit (mW/cm 3 ) MB460.6 MQXA653.5 MQXB60 / MQXC1044 MQXF at 1.9 K (140 T/m) 1554 MQXF at 4.2 K (80% B ss )

Conclusions Numerical model of the experimental tests Thermal measurement of a short model coil P.P. Granieri - Heat extraction and quench limits16 Perspectives Heat extraction through Nb 3 Sn 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 k Nb3Sn > K Nb-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/cm 3, vs. 4 mW/cm 3 expected MQXF-MQXC will have a quench limit 2 to 3 times those of MB-MQXA-MQXB