Proto-CIRCUS Tilted-Coil Tokamak-Torsatron Hybrid: Design and Construction

TL;DR

This paper details the design and construction of Proto-CIRCUS, a hybrid device combining features of tokamaks and torsatrons, with tilted coils to generate rotational transform and potentially improve plasma stability and operation.

Contribution

It introduces a novel hybrid coil configuration with tilted planar coils for tokamak-torsatron hybrid, enabling adjustable magnetic properties and lower plasma current operation.

Findings

Tilted coils generate rotational transform as predicted.

Device operates at lower plasma current than comparable tokamaks.

Reduced magnetic ripple compared to non-tilted coil configurations.

Abstract

We present the field-line modeling, design and construction of a prototype circular-coil tokamak-torsatron hybrid called Proto-CIRCUS. The device has a major radius R = 16 cm and minor radius a < 5 cm. The six "toroidal field" coils are planar as in a tokamak, but they are tilted. This, combined with induced or driven plasma current, is expected to generate rotational transform, as seen in field-line tracing and equilibrium calculations. The device is expected to operate at lower plasma current than a tokamak of comparable size and magnetic field, which might have interesting implications for disruptions and steady-state operation. Additionally, the toroidal magnetic ripple is less pronounced than in an equivalent tokamak in which the coils are not tilted. The tilted coils are interlocked, resulting in a relatively low aspect ratio, and can be moved, both radially and in tilt angle, between discharges. This capability will be exploited for detailed comparisons between calculations and field-line mapping measurements. Such comparisons will reveal whether this relatively simple concept can generate the expected rotational transform.