An approach to implement a heat flux limit in a model for fusion relevant plasmas

Abstract

An approach to implement a heat flux limit (HFL) in a plasma model is proposed. The HFL arises if the mean free path length of the heat carrying electrons, λh, significantly exceeds the characteristic length of the temperature variation, LT. For [Formula: see text], the heat flux becomes nearly independent of the temperature gradient, in contrast to the case of [Formula: see text] where it is gradient dependent. As a result, by going from [Formula: see text] to [Formula: see text], the order of the heat balance equation changes and the method proposed allows a reliable integration of this equation in these limits, as well as for [Formula: see text]. By solving a set of one-dimensional fluid equations for particle, momentum, and heat balance numerically, the importance of the HFL for fusion relevant conditions is demonstrated for plasma parameter profiles at the edge of the heliotron Large Helical Device and detachment conditions in helium plasmas of the linear device NAGDIS-II.