Exploration of the CNT parameter space

The Columbia Non-neutral Torus (CNT) is perhaps the simplest possible stellarator, using only four circular coils: two interlinked coils and two poloidal-field coils. The configuration space is well-described by only three parameters: the distances between the linked coils, the angle between them, and their total current.

The small CNT parameter spaces can been fully mapped out with field-line tracing, and features stellarator configurations with a wide range of properties, from approximately quasisymmetric to piecewise-omnigenous configurations. The configurations may feature sharp ridges and islands.

A particularly interesting feature is that nested flux-surfaces exist in disconnected parts of the parameter space, and disappears for certain current ratios. Since current can be easily adjusted in an experiment, these configurations could be used to study the transition from nested to open field-lines, and be of potential interest for divertor studies.

We present a database of over 100000 different CNT configurations and investigate their physics properties. This database could serve as a starting point for anyone looking to build budget small-scale stellarators, and for optimizations of CNT-like configurations with less restricted coils (similar to the CSX experiment).