He II heat transfer through superconducting cables electrical insulation

Abstract

For the LHC upgrade projects, CERN will rely on the Nb 3 Sn technology to build high field dipole and quadrupole superconducting magnets. In the frame of this R&D program, cooling studies are carried out to determine the heat extraction from this new type of accelerator magnets and the relevant quench limits. In this paper we present and discuss experimental results of heat transfer through the electrical insulation of Nb 3 Sn cables. A cable-stack was prepared using fiberglass sleeves and CTD-101K impregnation resin. Two different measurement methods were compared, consisting of instrumenting the sample before or after the vacuum impregnation. The tests were performed both in 1.9 K superfluid and 4.2 K liquid helium baths, using different heating configurations. We also present results of the numerical model developed to reproduce the experimental results.  Index Terms-Electrical insulation, heat transfer, LHC upgrade, Nb 3 Sn, superconducting high field magnets.

Upscaling of the Superfluid Equations in the Landau Regime for Porous Media

“…The area (1) is the heated surface where a heat flux is applied. The temperature is imposed at the exit (2). Initially the fluid temperature is set at the temperature imposed at the exit (2) and the velocity fields are null.…”

“…It is then possible to obtain the momentum equation for the normal component by subtracting equation (3) from equation (2) .…”

“…In this study, we consider the steady state regime, inertial terms and terms corresponding to the Brinkman correction (such as those involving 2 ∇ n v ) are neglected. Then we obtain the following system of averaged equations Continuity equation…”

“…In their environment, these superconducting magnets will undergo much higher heat losses than in current particle accelerator. Since the thermal resistance due to the electrical insulation of the superconducting cables constitutes the main thermal resistance for cooling [1,2], new types of insulation, based on ceramic materials, are considered. These materials can be seen as a porous medium with a given porosity and average pore diameter.…”

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

“…Yet, the efficiency of spacing in the second layer can be reduced or canceled by other factors: for example, epoxy-impregnated fiberglass tape lets the epoxy flow out during heat treatment, filling up the channels of the second layer [23], contrarily to polyimide glue which does not flow. However, if polyimide glue is present on the internal side of the second layer (to bond first and second layer), it seals the outlets of the first layer channels and permeability is greatly reduced [24].…”