Apparatus for investigating non-linear microwave interactions in magnetised plasma

In many plasma applications, electromagnetic (EM) waves are key to providing energy. Plasmas can demonstrate complex dynamics when exposed to multiple EM signals. Raman coupling (by Langmuir oscillation) in plasmas below one quarter critical density and Brillouin scattering (through ion-acoustic waves) for all plasmas below critical density are important in laser plasma interactions [1-4] and ionospheric situations. Microwave beams can be formed at normalised intensities comparable to those used for some laser plasma interactions, and can interact in tenuous, cool and accessible plasmas potentially enhancing insight into the non-linear plasma dynamics. Magnetic confinement fusion physics may directly benefit from developing the understanding of multifrequency microwave interaction in plasma. This is particularly relevant to future fusion experiments and reactors where it is expected to be more difficult to directly heat the ions with EM waves, whilst access to the lower cyclotron harmonics of the electrons is difficult in the dense plasmas seen in spherical aspect ratio tokamaks. Coupling of two higher frequency waves to cyclotron and hybrid resonances in dense plasma, either for heating or current drive may mitigate these issues [5,6]. Building on earlier research investigating geophysical cyclotron wave emissions [7,8], a new “linear plasma” experiment is under construction to test multifrequency microwave interactions in magnetised plasma.