Progress on Characterisation of a Large Helicon Device for Non-Linear Microwave Interactions

Parametric instabilities [1] play an important role in understanding how electromagnetic power is absorbed by a plasma and are encountered across a wide range of environments: magnetic confinement fusion [2], inertial confinement fusion [3] and in the ionosphere [4]. The traditional tokamak has enjoyed success with electron cyclotron current drive; spherical tokamaks present a challenge since they are over-dense at low harmonics of the cyclotron frequency, impeding efficiency or limiting potential fusion performance. This forces the heating system to access the plasma using higher harmonics, reducing the efficiency. An alternate heating scheme could involve beat-wave type couplings like those found in parametric scattering processes; these could be used to resonantly couple the energy from injected electromagnetic waves to a plasma oscillation.