Proto-CIRCUS tilted-coil tokamak-stellarator hybrid

We present the design, construction and field line modeling of a prototype circular coil tokamak-stellarator hybrid (Proto-CIRCUS) of major radius R = 11 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 [1]. The device can be operated 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 expected to be 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.