COMSOL Modeling of Plasma Disruption Induced Effects on the DIII-D Tokamak Systems*

The DIII-D tokamak can produce plasma currents of 2.5 MA with magnetic fields up to 2.1 T for up to 10 seconds. The collapse of this current (‘disruption’) in a few milliseconds induces a current on the vessel walls which interacts with the toroidal magnetic field producing forces and torques on attached metallic structures. 

COMSOL Multiphysics, a commercial finite element analysis software package, was used to calculate the plasma current varying magnetic flux and its interaction with the vessel and attached 3D structures. The magnitude and direction of these calculated magnetic fields are compared with measurements of the tokamak magnetic probes. 

The induced current distribution is plotted on the vessel wall and attached structures to better understand its paths. In addition, the effect of the structure’s shape as well as different materials are studied in order to understand their role on the induced forces and torques and how to minimize them.

This analysis is presented for a number of recent DIII-D projects and hardware additions, including the Helicon Antenna, TZM Molybdenum plates for protecting Neutral Beam injection ports and Cross Polarization System diagnostic.