Auroral cyclotron emission mechanisms demonstrated in the laboratory

In the auroral regions of the Earth´s magnetosphere, electric fields accelerate electrons downwards towards the Earth´s surface into an increasing magnetic field. Due to conservation of the magnetic moment, magnetic compression of the particles leads to the formation of a horseshoe distribution in velocity phase space. Kilometric radiation is observed in association with this process, polarised in the X-mode, occurring at > 3200 km above the Earth´s surface. The RF output power has been observed by various satellites at 10⁷-10⁹ W, corresponding to a beam-wave conversion efficiency of 1-2%. It has been postulated that a cyclotron maser instability driven by the horseshoe distribution is the source of this Auroral Kilometric Radiation (AKR). An experiment was created, scaled to laboratory dimensions, to simulate this naturally occurring phenomenon. Frequencies were altered from 100´s kHz to GHz by increasing the magnetic field intensity, with coupling to the TE₀₁ mode taking place at a resonant frequency of ~4.42GHz. Beam transport experiments allowed the horseshoe distribution to be mapped and further analysis of the 1D number density allowed deeper understanding of the results to be obtained. Measurements of the radiation conversion efficiency, mode and spectral content were obtained and seen to be in close agreement with numerical and theoretical predictions and also with satellite observations in the magnetosphere. The experiment is currently undergoing modifications to allow the introduction of a background plasma to give a better representation of the natural environment. The latest results of this alteration will be presented in this paper.