"Resistive Interchange Mode destabilized by Helically Trapped Energetic Ions and its stabilisation by the on-axis Electron-Cyclotron-Heating in a Helical Plasma"

 

 

 

A new bursting m=1/n=1 instability (m, n: poloidal and toroidal mode numbers) with rapid frequency chirping down has been observed for the first time in a helical plasma with intense perpendicular neutral beam injection. This is destabilized in the plasma peripheral region by resonant interaction between helically trapped energetic ions and the resistive interchange mode. A large radial electric field is induced near the edge due to enhanced radial transport of the trapped energetic ions by the mode, and leads to clear change in toroidal plasma flow, suppression of microturbulence, and triggering an improvement of bulk plasma confinement. This bursting instability is mitigated when the electron-cyclotron-heating (ECH) near the magnetic axis is superimposed and the complete stabilisation is observed when the power of the ECH exceeds a certain threshold. The finite Larmor radius effect is considered to be important on the observed stabilising effect in LHD.