Temperature Screening and Cross-Field Impurity Accumulation from a Thermodynamic Perspective

TL;DR

This paper uses non-equilibrium thermodynamics to explain how temperature gradients influence impurity accumulation in plasma systems, emphasizing the role of ambipolarity and temperature screening effects.

Contribution

It extends previous thermodynamic models by incorporating temperature gradients, demonstrating their impact on impurity behavior in plasma.

Findings

Ambipolarity remains crucial with temperature gradients.

Temperature screening effects are recovered in the thermodynamic framework.

Impurity accumulation tendencies are explained thermodynamically.

Abstract

In a variety of different systems, high-Z ion species show a marked tendency to accumulate in regions of high plasma density. It has previously been suggested that the apparent universality of this behavior could be explained thermodynamically, in terms of the maximum-entropy state attainable when the system must obey an ambipolarity condition. However, the previous treatment did not allow for the possibility of temperature gradients. Here, tools from non-equilibrium (Onsager) thermodynamics are used to show that ambipolarity continues to play a key role in producing this behavior in the presence of temperature gradients, and to recover well-known temperature screening effects that appear in these cases.