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Thermal Stability of a Superconductor Cooled by a Turbulent Flow of Supercritical Helium

M. C. M. Cornelissen
Applied Physics Department, Delft University of Technology, 2628 CJ Delft, The Netherlands

Charles J. Hoogendoorn
Faculty of Applied Physics, Delft University of Technology, The Netherlands.

W. M. P. Franken
Netherlands Energy Research Foundation, Petten, The Netherlands

Abstrakt

The thermal stability of large superconductors as used in magnets for fusion research depends strongly on dynamic effects on the heat transport to the cooling medium. For large magnets in general supercritical helium is used for cooling. It flows through long narrow channels adjacent to the superconductor material. If a thermal transient occurs locally in the cable the heat transport through the copper/superconductor matrix itself and the transport to the turbulent helium flow should stabilize the conductor to prevent a large local energy release.
The stability of superconducting magnets has extensively been studied by Stekly [1] , Maddock [2] , Keilin [3] , Iwasa [4] and Cornelissen and Hoogendoorn [5] using static criteria. The latter authors also studied dynamic criteria [6] and in a further paper [7] considered the propagation velocity of a thermal disturbance during a transient.
The use of static criteria is insufficient. A full study of thermal stability requires a dynamic simulation in which both transient heat conduction in the copper /superconductor matrix and transient thermal and flow effects in the helium are considered. In this paper we will shortly discuss the full model and then give particular attention to the transient effects in the helium flow. The model has been applied to study the stability of a specific conductor as used in the superconductor test facility SULTAN. In cooperation with several European countries a high current superconductor is tested in a high magnetic field. The conductor is cooled by a turbulent flow of supercritical helium.

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