Simulating auroral kilometric radiation emission mechanisms through a 3D PiC code

Auroral kilometric radiation (AKR) generation occurs naturally in the auroral zone above the Earth´s atmosphere, within a large area of plasma depletion in which particles are accelerated into the polar regions of the Earth´s magnetic dipole. Satellite missions revealed that the peak power emitted in AKR is around 10⁹ W centred at a frequency of ~ 300 kHz. The radiation emissions are observed at frequencies close to the electron cyclotron frequency and are polarised in the X mode. The electron beam in the auroral region is subject to magnetic compression as it descends towards the atmosphere, resulting in a horseshoe-shaped velocity distribution in the auroral electron flux through conservation of the magnetic moment. It is now thought that the transverse momentum in this distribution can give rise to a cyclotron maser instability. KARAT 3D particle in cell (PiC) code simulations were carried out to further investigate results from a laboratory experiment built to reproduce the mechanisms of AKR generation and also previous 2D PiC code simulations. The 3D results proved to be consistent with results from the laboratory experiment. Coupling with other modes with azimuthal structure was found that could not be accounted for in 2D simulations. Investigation is ongoing to study an up-shifted interaction regime, to investigate the viability of injecting a seed signal into the laboratory experiment to study the spatial growth rate of the instability to compare with theoretical predictions. Predicted spectra are consistent with the expectations of dispersion plots and indicate high pitch electrons are dominating the interaction. Simulations show the backward wave instability to be more resilient to Doppler broadening than the forward wave coupling. Resilience of the backward wave instability to Doppler broadening has important implications where there is a cold tenuous plasma in the resonant region.