Comparative study of heat transfer from Nb-Ti andNb3Sncoils to He II

Abstract

In superconducting magnets, the energy deposited or generated in the coil must be evacuated to prevent temperature rise and consequent transition of the superconductor to the resistive state. The main barrier to heat extraction is represented by the electric insulation wrapped around superconducting cables. In the LHC, insulation improvement is a key point in the development of interaction region magnets and injector chain fast-pulsed magnets for luminosity upgrade; the high heat load of these magnets, in fact, is not compatible with the use of current insulation schemes. We review the standard insulation schemes for NbTi and Nb 3 Sn technology from the thermal point of view. We implement, in an analytical model, the strongly nonlinear thermal resistances of the different coil components including the permeability to superfluid helium of Nb-Ti insulations, measured during the LHC main dipole development. We use such a model to compare Nb-Ti and Nb 3 Sn technologies by taking into account their specific operating margin in different working conditions. Finally, we propose an insulation scheme to enhance the heat transfer capability of Nb-Ti coils.

Testing Results for Nb-Ti, 120-mm-Aperture, Low-B Quadrupole Models for the LHC High-Luminosity Insertion

“…It can be assumed that the amount of heat reaching the second cables away from the heater is negligible, as suggested from the dedicated thermal tests reported in [13]. In the above mentioned assumptions we can estimate that 50 mW/cm 3 can be removed without quenching the coil, at a bath temperature of 1.87 K. Such heat extraction is about 4 times larger than the 12 mW/cm 3 [14,15] estimated for the standard insulation, not far from what expected from simulations and measurements.…”

Accelerator Engineering and Technology: Accelerator Technology

“…With the exception of internally cooled cables, the temperature gradient is directly proportional to the thermal resistance of the coil. Low thermal resistance insulation schemes can be obtained by proper choice of insulation thickness and overlap, as demonstrated by recent work [32] devoted to the upgrade of the quadrupoles for the inner triplet of the LHC.…”

LHC IR Upgrade Nb–Ti, 120-mm Aperture Model Quadrupole Test Results at 1.8 K

“…A more detailed analysis of the results, where a numerical model is used to reproduce the coil thermal behavior, is reported in [15][16][17][18][19].…”