Linear plasma experiment for non-linear microwave interaction experiments

As a non-linear medium, plasma can exhibit diverse dynamics when excited bymultiple EM waves. Electromagnetic waves are vital to the introduction of energyin laser plasma interactions and the heating of magnetically confined fusion reactors.In laser plasma applications Raman coupling via a Langmuir oscillation or Brillouinscattering mediated by ion-acoustic waves are of interest. Signals with normalisedintensities approaching those used in some recent laser plasma interactions can begenerated using powerful and flexible microwave amplifiers, interacting in relativelytenuous, cool and accessible plasma. Other multi-wave interactions are interesting formagnetic confinement fusion plasmas, for example beat-wave interactions betweentwo microwave signals coupling to cyclotron motion of the ions and electrons or thelower hybrid oscillations may be useful in heating the plasmas or for driving currents.A linear plasma experiment is being built to test such multifrequency microwaveinteraction in plasma, based on prior research on geophysical cyclotron wave emissionand propagation [1,2]. The main section of the plasma will be magnetised at up to0.05T, with the plasma created by an RF helicon source to generate a dense, large,cool plasma with a high ionisation fraction. A range of frequency-flexible sources willprovide microwave beams to enable multi-wave coupling experiments. The paper willpresent progress on this apparatus and experiments.The authors gratefully acknowledge support from the EPSRC, MBDA UK Ltd andTMD Technologies Ltd.[1] Ronald K., Speirs D.C., McConville S.L., Phelps A.D.R., Robertson C.W., WhyteC.G., He W., Gillespie K.M., Cross A.W., Bingham R., 2008, Phys. Plasmas, 15,art.056503[2] Speirs, D.C., Bingham, R., Cairns, R.A., Vorgul, I., Kellett, B.J., Phelps, A.D.R.,Ronald, K, 2014, Phys. Rev. Lett., 113, art 15500