Demonstration of auroral radio emission mechanisms by laboratory experiment

Abstract

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Cyclotron maser radiation from inhomogeneous plasmas

“…2,7,13 A laboratory experiment and simulations in which this type of distribution was produced showed that it did indeed generate waves with many of the properties of AKR. [14][15][16][17][18][19] In the simulations and in the laboratory experiment an electron beam with initial finite pitch spread ␣ = v Ќ / v z was injected into an increasing axial magnetic field. Through conservation of magnetic moment, a progressive magnetic mirroring of the beam resulted in the conversion of axial momentum into perpendicular momentum yielding a horseshoe shaped velocity distribution.…”

Backward Wave Cyclotron-Maser Emission in the Auroral Magnetosphere

“…In all cases, the cyclotron-maser instability is presumed to be driven by an electron horseshoe or modified horseshoe-ring distribution. Scaled laboratory experiments have demonstrated the potential for such horseshoe distributions to generate narrowband cyclotron-maser emission at GHz frequencies over distances of a few meters [21][22][23][24][25].Although the generation mechanism is well established, there remain important questions with regard to how the radiation may propagate within the parent auroral density cavity and ultimately escape [26]. Cairns et al [27] have demonstrated how the radiation, generated just below the electron cyclotron frequency, may successfully couple onto the upper branch of the plasma dispersion relation and escape.…”

“…In all cases, the cyclotron-maser instability is presumed to be driven by an electron horseshoe or modified horseshoe-ring distribution. Scaled laboratory experiments have demonstrated the potential for such horseshoe distributions to generate narrowband cyclotron-maser emission at GHz frequencies over distances of a few meters [21][22][23][24][25].…”

Vlasov simulations of trapping and loss of auroral electrons

“…The emission mechanism they suggested is an electron cyclotron maser mechanism, where the electron distribution function is governed by the hole and may be different from the much studied horseshoe distribution (Ergun et al, 2000a). Similar systems have been seen to emit radio waves in laboratory plasmas (Lindberg, 1993;Volwerk, 1993;Brenning et al, 2006), although the electron beam energies were far below those used in dedicated cyclotron maser experiments (McConville et al, 2008) and simulations (Speirs et al, 2014). The simulations reported here are electrostatic and can therefore not be used to study radiation processes, which would require electromagnetic models.…”