Laboratory experiment to investigate the impact of background plasma on cyclotron emission

The auroral density cavity (a region of partial plasma depletion situated at an altitude of around 3200km at the Earth´s pole) has been studied to have a background plasma density ~10⁶m^-3, and plasma frequency ~9kHz. Auroral Kilometric Radiation (AKR) is produced when particles descend through this region and are magnetically compressed as they approach the Earth´s magnetosphere and through conservation of the magnetic moment, a horseshoe shaped velocity distribution with a large spread in pitch factor is formed as the particles sacrifice axial for rotational momentum. Satellites have observed that the AKR is emitted and extends down to the local electron cyclotron frequency with peaks in frequency at ~300kHz, powers ~10⁹W and with emission efficiency ~1% of the total precipitated electron kinetic energy. Theory has shown this type of distribution to be unstable to cyclotron emissions in the X-mode [1].