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Pier Paolo Granieri, Rob van Weelderen CERN, Cryogenics group

International Conference on Magnet Technology July 14 – 19, 2013 The Westin Copley Place Boston, MA USA . Pier Paolo Granieri, Rob van Weelderen CERN, Cryogenics group.

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Pier Paolo Granieri, Rob van Weelderen CERN, Cryogenics group

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  1. International Conference on Magnet Technology July 14 – 19, 2013 The Westin Copley Place Boston, MA USA Pier Paolo Granieri, Rob van Weelderen CERN, Cryogenics group Deduction of steady-state cable quench limits for various electrical insulation schemes with application to LHC and HL-LHC magnets P.P. Granieri - Steady-state quench limits

  2. Introduction P.P. Granieri - Steady-state quench limits • Preventingbeaminducedquenchesrequires an accurateknowledge of the quenchlimits • Especially important for future LHC exploitation at 6.5 – 7 TeV • Comprehension of quenchlimitsisalso important for design of future SC magnets, as those for High Luminosity and High Energy LHC • The mechanismsdeterminingmagtnetsstabilitystronglydepend on the beamloss time scale • Wedescribe how to deducequenchlimitsfromheattransfermeasurements of stack of cables • canbeused to set thresholds for the BeamLoss Monitors • Outline • Experimental technique • Heattransferthroughcableelectricalinsulation • Deduction of quenchlimits: method • Quenchlimits of LHC main dipole and HL-LHC interaction regionsquadrupole

  3. Experimental technique P Cable center Cableedge P.P. Granieri - Steady-state quench limits • The mostwidespreadmethod to thermallycharacterize SC coilsis the so-calledstackmethod • It allows to measure the heattransferthrough the cable’selectricalinsulation • mostseverebarrier for heat extraction from the magnet • Measureheatextracted as a function of the cabletemperature • Under a controlled pressure

  4. Heattransferthroughcableelectricalinsulation • SSC: C. Meuris, B. Baudouy et al. • LHC MB and EI4: D. Richter, P.P. Granieri et al. • NB3Sn: P.P. Granieri et al. P.P. Granieri - Steady-state quench limits

  5. Heattransferthroughcableelectricalinsulation • SSC: C. Meuris, B. Baudouy et al. • LHC MB and EI4: D. Richter, P.P. Granieri et al. • NB3Sn: P.P. Granieri et al. P.P. Granieri - Steady-state quench limits

  6. Deduction of cablesteady-state quenchlimits mid-plane 11.8 kA, 5.4 T ΔTcs ΔTλ P.P. Granieri - Steady-state quench limits • For steady-state beamlosses, a quenchoccurs if TcableexceedsTcs(~ 4 K for Nb-Ti, ~ 7 K for Nb3Sn in a 1.9 K bath) • not Tλ, whichis a design limit for Nb-Ti coils • The cablequenchlimitsdepend on : • Heat extraction: • Cablecoolingwithin the magnet • Mechanical pressure, if Nb-Ti coil • Stackheating configuration • Operating conditions: • Transport current • Magneticfield, thuscable and strandconsidered

  7. Deduction of cablesteady-state quenchlimits: the method P.P. Granieri - Steady-state quench limits • 1) experimentallycorrelateheat extraction and strandstemperature • Heating configuration of the cables: typicallyheating all the cables • As a function of the mechanical pressure (for He II porous Nb-Ti coils) • In different positions of the cable (center vs. edge) • 2) scale the heat extraction to the coilgeometry • Only the innermostcables’ small face is in direct contact with the He II bath • The outermostsmall face canbe, depending on the magnet design, in contact with He • 3) computeTcs (Iop, B) • Cable location within the coil cross-section • Strand location within the cable cross-section • 4) compute the heatextractedatTcs (Iop, B) • At the pressure corresponding to the cable location within the coil cross-section • LHC dipole (MB): pressure varyingbtw 50 MPa (mid-plane) to 5 MPa (pole) • HL-LHC IR quad (MQXC): pressure varyingbtw120 MPa (mid-plane) to 25 MPa (pole) • HL-LHC IR quad (MQXF): no pressure

  8. Results MQXF P.P. Granieri - Steady-state quench limits Tbath = 1.9 K, held constant duringheatremoval The deducedquenchlimitsrefer to an averageheatdeposit over the cable Quench limit along the azimuthal direction:

  9. Results MQXF Heatdeposit data provided by L.S. Esposito, L. Skordis, F. Cerutti P.P. Granieri - Steady-state quench limits • Quench limit / heat deposit along the azimuthal direction • to determine the mostcriticalcables • for bothmagnets the mostheatedcables have unluckily the smallestquenchlimit

  10. Results LHC quench test data provided by S. Redaelli, L. Skordis et al. LHC collimation Review 2013: http://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=251588 P.P. Granieri - Steady-state quench limits • Quench limit as a function of the transport current • in the mostcriticalregions, i.e. mid-plane for MB and close to the pole for MQXF

  11. Conclusion P.P. Granieri - Steady-state quench limits By measuringheattransfer on cablestacks, whiletakingintoaccount the cablecoolingwithin the magnet, one candetermine the quenchlimits Wepresented a generalmethod to determinesteady-state cablequenchlimits, basedupon the coolinggeometry, the coilmechanical and operating conditions The method has been successfullyapplied to LHC magnets and to magnetsforeseen for the High Luminosity upgrade

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