Transverse Thermal Conductivity in an Epoxy Impregnated ${\rm MgB}_{2}$ Coil

Abstract

Superconducting magnets operate at low temperatures, and therefore, even small heat pulses can ruin their stable operation. For example, resistive joints or changes in the operation current generate heat which must be extracted to prevent a quench. In impregnated magnets, the transverse thermal conductivity inside the coil has a vital influence on the heat extraction, and it dominates the 3D quench propagation. In this study, the transverse heat conductivity is measured from the cross-section of a small epoxy impregnated MgB2 coil at temperatures between 10 and 35 K. Finally, the results are analysed and compared with the results of a computational model based on heat conduction equation solved with the finite element method. The results show that effective thermal conductivity is over two orders of magnitude higher in the parallel direction with conductor axis compared to the perpendicular direction. The measured effective thermal conductivities at 20 K parallel to the broad tape face and perpendicular to the broad tape face were 1.55 W/mK and 0.31 W/mK, respectively. The fill factor of the measured coil was 60.5% for the whole conductor.

Numerical Analysis on the Quench Process and Protection of Conduction Cooled ${\rm MgB}_{2}$ Magnet

“…The thermal conductivities in axial and radial directions should be computed based on heat conduction equation solved with FEM [14], [15]. Fourier's law expresses the constitutive relation between the heat flux density and the temperature gradient: 1051-8223/$26.00 © 2010 IEEE (2)…”

“…(14): (15) where S is the cross-section area of the tape including the insulation. E is the stored energy of the magnet.…”

“…The thermal conductivities in axial and radial directions are computed based on heat conduction equation solved with the finite element method [14], [15]. The quench propagation velocities (QPV) along and between the tapes are computed by the parallel-tapes model in the selected conditions beforehand.…”