Effects of impurity radiation on reversed-field pinch evolution

The effects of impurity radiation on the evolution of a reversed-field pinch plasma are studied by means of a one-dimensional MHD simulation code that includes both plasma transport and impurity effects, and follows the plasma through a series of equilibrium states. The equations are split into two sets, one that contains plasma transport and another that contains atomic physics effects. Two codes were developed and linked together to solve the full problem. Results are presented for the ZT-S, ZT-40, and RFX experiments with a fixed set of parameters, typical or envisioned, and various concentrations of impurities. Radiation barriers are encountered, and limits are found on the acceptable level of low Z impurities that may be present in these devices. It is shown that the temperatures currently observed in the ZT-S experiment are radiation limited. Next, a criterion for radiation barrier burn-through is derived in terms of appropriate nondimensional parameters and calibrated by comparison to the numerical simulations for the case of oxygen