Coherent MHD Behaviour in a Shallow Magnetic Well Configuration in Heliotron J

This article presents the first experimental results from a novel configuration in Heliotron J, which features a shallow magnetic well in the core of the plasma. A broadband coherent fluctuation of approximately 10 kHz is observed in a low-β electron cyclotron heated (ECH) plasma at rotational transform ι/2π = 0.55 in this configuration, while no mode appears in a deep magnetic well configuration. An electron cyclotron emission measurement shows the mode is excited in the core region where the magnetic well is shallow. This indicates Heliotron J is able to sustain viable plasmas with an edge-hill, although these can be destabilised even at low density and pressure.