Study of limiter damage in a magnetic-field error region of the ZT-40M experiment

A study has been initiated of material plasma interactions on the ZT-40M, Reversed Field Pinch (RFP) plasma physics confinement experiment at Los Alamos National Laboratory. Observations of the evaporation and cracking to TiC coatings, initially placed on an AXF-5Q Graphite mushroom limiter, installed in a high field error region (e.g. an experimental vacuum vessel/liner port) were investigated. A parametric study was performed of the thermal and stress behavior of the limiter and coating materials undergoing plasma material heat exchange processes, in order to infer the magnitude of heat flux necessary to explain the observed material damage. In addition the vacuum (liner) wall material behavior was studied parametrically using the same heat flux values as the limiter study. A one-dimensional conduction model was used with applied heat and radiation boundary conditions, for predicting temperature distributions in space and time, where the thermal stress was calculated using a restrained in bending only plate model. Wall loadings corresponding to first wall, limiter energy fluxes ranging between 1 x 102 W/cm2 and 1 x 105 W/cm2 were used as parameters with plasma material interaction times (tau/sub QO) between 0.5 ms and 10 ms. Short plasma energy deposition time (tau/sub QO/ > 10 ms) spacial and time histories of temperature and stress were calculated for SS-304, Inconel-625, TiC and AXF -5Q Graphite materials