Two phase helium cooling characteristics in Cable-in-Conduit Conductors

Abstract

Cable-in-Conduit Conductors (CICCs) are used in the fabrication of superconducting fusion grade magnets. It acts as a narrow cryostat to provide cryo-stability with direct contact of coolant fluid to conductor. The superconducting magnets are cooled using forced flow (FF), supercritical helium or two phase (TP) cooling through void space in the CICC. Thermo-hydraulics using supercritical helium single phase flow is well-known and established. Research topic of behavior of forced flow, two phase (TP) helium cooling in CICC involves perceived risks of the CICC running into flow chocking and possible thermo-acoustic oscillations leading to flow instabilities. This research work involves study of forced flow two phase helium cooling in CICC wound superconducting magnets. The TP flow provides cryo-stability by the latent heat of helium not by enthalpy as in case of CICC being cooled with supercritical helium. Study reveals some attractive regimes in the case of TP cooling, at a given mass flow rate of single phase helium at the inlet and a heat flux acting on the CICC. Analysis carried out predicts significant gains with TP cooling on a prototype CICC, which is circular in cross section and appropriate for fusion devices for high magnetic field applications. These general formalisms may be extended to specific magnets wound with CICC. This paper describes analysis of TP cooling of a CICC.