On the Shafranov shift in stellarators

TL;DR

This paper introduces an average measure of the Shafranov shift in stellarators, analyzing its properties across different configurations and highlighting its minimal size in certain optimized stellarators, indicating robustness to pressure changes.

Contribution

It provides a new measure of the Shafranov shift and analyzes its behavior in various stellarator configurations, emphasizing the robustness of quasi-helical and quasi-isodynamic designs.

Findings

Shafranov shift is small in quasi-helical stellarators with many field periods.

The measure helps understand plasma stability in different stellarator types.

Optimized stellarators show reduced sensitivity to pressure variations.

Abstract

As first shown by Shafranov, toroidal plasmas in magnetohydrodynamic equilibrium tend to expand in major radius when the pressure is increased. Here, an average measure of the resulting Shafranov shift is introduced, and its properties are discussed for various classes of optimised stellarator configurations. It is shown to be particularly small in quasi-helical and quasi-isodynamic stellarators with a large number of field periods, which are thus particularly robust to variations in the plasma pressure.