Thermohydraulic behavior of the WENDELSTEIN 7-X magnet system

A quench of the superconducting magnet system of the stellarator fusion experiment WENDELSTEIN 7-X, as well as eddy current heating of the coil housings caused by the subsequent emergency discharge, leads to helium expulsion from the conductor and housing cooling circuits. A simplified numerical analysis of the helium mass flow from the coils to the storage tanks is carried out on the basis of a given worst case quench propagation velocity. For the design of the quench gas relief system a simultaneous quench of all coils is assumed. The quench origins are presupposed to be evenly distributed throughout the coil conductor lengths. The quench gas is collected inside the cryostat by the circular coolant supply manifolds which are scaled up for this purpose. Five expulsion lines around the torus lead from each manifold via safety valves to a warm circular quench gas collector outside the cryostat. From there the helium is transferred to the gas storage tanks. Only a moderate decrease of the tank wall temperature, without cold spots, is achieved.