H-1NF

The H-1 flexible Heliac is a three field-period helical axis stellarator with major radius $R=1\,m$ and average minor radius $\langle r\rangle =0.2\,m$. Optimisation of the H-1 power supplies for low current ripple allows precise control of the ratio of secondary (helical, vertical) coil to primary (poloidal, toroidal) coil currents, resulting in a finely tunable magnetic geometry. Slight variation in the current ratio between shots (plasma discharges) in a sequence corresponds to a high resolution parameter scan through magnetic configurations (ie: rotational transform profile, magnetic well). The programmable control system allows for repetition rates of around 30 shots per hour, limited by data acquisition time and magnet cooling time.