Numerical and laboratory investigation of astrophysical cyclotron emission processes

There are numerous types of astrophysical radio emission in association with non-uniform magnetic fields that have been the subject of particular interest and debate over the last thirty years [1]. Such sources, including planetary and stellar auroral radio emission are spectrally well defined with a high degree of extraordinary (X-mode) polarisation. In particular, for the terrestrial auroral case it is now widely accepted that such emissions are generated by an electron cyclotron-maser instability driven by a horseshoe shaped electron velocity distribution [2,3] formed through magnetic compression. Experiments have been conducted at the University of Strathclyde investigating the electrodynamics of an electron beam subject to significant magnetic compression within a bounding waveguide structure [4]. More recently, a background plasma of variable density has been introduced to the interaction region of the laboratory experiment through use of a Penning discharge geometry [5]. Corroboratory simulations have been conducted using the PiC code VORPAL to investigate the cyclotron emission process in the presence of a background plasma of variable density. The dynamics of the emission mechanism will be discussed for both bounded and unbounded interaction scenarios as a function of ωce / ωpe in line with recent laboratory experiments [5] and earlier numerical simulations of unconstrained electron-cyclotron emission [6].