Heat extraction through cable insulation and quench limits

Heat extraction through cable insulation and quench limits Pier Paolo Granieri, Rob van Weelderen, Lina Hincapié (CERN) 2 nd Joint Hi. Lumi LHC-LARP Annual Meeting INFN Frascati, 14 -16 November 2012 (revised version 11/1/2013) The Hi. Lumi 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.

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 2

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Heat transfer through cable electrical insulation: evolution * * unpublished measurements from D. Richter (5 SC heated cables, actual MQX cables) P. P. Granieri - Heat extraction and quench limits 6

Heat transfer through cable electrical insulation: evolution * * unpublished measurements from D. Richter (5 SC heated cables, actual MQX cables) P. P. Granieri - Heat extraction and quench limits 7

Experimental method • Sample: - 150 mm long rectangular stack made of 6 alternating cables • Cable: - Cu. Ni 10 - LHC cables geometry, MB inner layer • T sensors: - Au. Fe 0. 07 at%/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 8

Experimental method • 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 Q 1 Q 2 Instrumented 3 cable 4 5 6 P. P. Granieri - Heat extraction and quench limits 9

Experimental results • Different position in the cable, Tbath, heating configuration Tc (mid-plane, cable center) Tc (mid-plane, cable edge) P. P. Granieri - Heat extraction and quench limits 10

Heat extraction from coil inner layer (cable center T) * 3 heated cables P. P. Granieri - Heat extraction and quench limits 11

Heat extraction from coil inner layer (cable center T) * 3 heated cables P. P. Granieri - Heat extraction and quench limits 12

Quench limit estimation • Heat that must be (uniformly) deposited in the cable 80 m. W/cm until the cable center/edge reaches Tc: 3 106 • MQXF • 150 mm bore (w/o µ-channels) • 1. 9 K constant bath T • uniform heat deposit 127 m. W/cm 3 247 m. W/cm 3 155 m. W/cm 3 39 198 m. W/cm 3 143 m. W/cm 3 188 P. P. Granieri - Heat extraction and quench limits 13

Quench limit estimation • Mid-plane and pole cable temperature for heat deposit in nominal conditions (peak of 3. 78 m. W/cm 3) 1. 96 K 1. 92 K 2. 13 K 2. 32 K • Comparison tests vs. model *, independently carried out * previous talk from H. Allain Coil position (inner layer) ΔT from exp. tests (m. K) ΔT from model * (m. K) Difference (%) mid-plane 230 -420 390 8 cable adjacent to pole 16 -58 68 17 P. P. Granieri - Heat extraction and quench limits 14

Quench limit estimation • Comparison at nominal conditions in mid-plane Magnet Estimated quench limit (m. W/cm 3) Expected peak heat deposit (m. W/cm 3) 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 P. P. Granieri - Heat extraction and quench limits 15

Conclusions scaled to magnet geometry to be confirmed by a • Heat extraction through Nb 3 Sn insulation was measured dedicated test • 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 3. 7 K 6. 4 K • better than through Enhanced Nb-Ti insulation above a ΔT of 5. 7 K (in the cable center), because k. Nb 3 Sn > KNb-Ti • Heat extraction from the cable allows a first estimate of the quench limit: • MQXF mid-plane cable is the most critical: 155 m. W/cm 3, vs. 4 m. W/cm 3 expected • MQXF-MQXC will have a quench limit 2 to 3 times those of MB-MQXA-MQXB Perspectives • Numerical model of the experimental tests • Thermal measurement of a short model coil P. P. Granieri - Heat extraction and quench limits 16