Simulations of constant poloidal beta experiments on ZT‐40M using a one‐dimensional multispecies transport model

Abstract

A one‐dimensional (1‐D) multispecies transport model for the reversed‐field pinch plasma, which includes neutral deuterium and a coronal nonequilibrium model for impurities, is used to simulate a set of ZT‐40M [Fusion Technol. 10, 307 (1986)] experiments. In these experiments, the radiation fraction is varied from 15% to 95% by use of krypton seeding, while the plasma operating parameters Iφ and ne are constrained to within a small variation from a fixed operating point. In effect, these experiments maintain an almost constant βθe on axis for the range of radiation fractions. The simulations match experimental estimates of particle, energy, and nonradiative confinement times, and of the electron poloidal beta. The results show that the anomalous thermal transport needed to reproduce the observed experimental behavior, i.e., constant βθe on axis, can be modeled by use of a small amount of parallel thermal conduction. Such a model phenomenologically accounts for anomalous heat transport due to fluctuations or stochastic field line diffusion. This model is also used for parametric studies on the design conditions of ZTH [Bull. Am. Phys. Soc. 31, 1546 (1984)]. To achieve the ZTH design values it is necessary for particle and thermal diffusivities to improve by a factor of 10–15 over ZT‐40M.