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Laboratory simulation at microwave frequencies of auroral kilometric radiation emission mechanisms

When a beam of electrons encounters an increasing magnetic field along its vector of motion, conservation of the magnetic moment results in the formation of a crescent or horseshoe shaped velocity distribution. A scenario analogous to this occurs in the terrestrial auroral zone where particles are accelerated into the polar regions of the Earth's magnetic dipole and expand adiabatically in velocity space. The resultant horseshoe shaped velocity distribution has been shown to be unstable with respect to a cyclotron-maser type instability (Bingham and Cairns, 2000, Vorgul et al., 2004 and Speirs et al., 2004). This instability has been postulated as the mechanism responsible for auroral kilometric radiation and also non-thermal radiation from other astrophysical bodies (Bingham et al., 2001). In this paper we describe a laboratory experiment to investigate the propagation of an electron beam subject to a magnetic compression of up to a factor of 35.