The particle in cell (PiC) code KARAT has been used to investigate electron cyclotron radio-emissions that are known to originate in the X-mode from regions of locally depleted plasma in the terrestrial polar magnetosphere. These emissions are commonly known as Auroral Kilometric Radiation (AKR). A laboratory experiment was constructed to study the emission mechanism of AKR scaled to microwave frequencies . Initial investigations were conducted numerically in the form of 2D PiC code simulations , with subsequent 3D PiC
simulations conducted to study resonant energy transfer with non-azimuthally symmetric modes of the bounding interaction structure .
These 3D simulations show a backward-wave instability to be more resilient to Doppler broadening of the beam-wave resonance than forward-wave coupling. This resilience has important implications when there is a cold, tenuous plasma in the resonant region. It would suggest that the auroral process may emit with backward-wave coupling giving a spectral downshift and thus avoiding the upper hybrid stop-band . Simulations show how various factors such as electron beam current and cyclotron-wave detuning influence mode excitation within the interaction region and the saturated rf output power. The results also emonstrate that cyclotron-wave coupling becomes weaker as the resonant wave moves away from near transverse propagation (|kz| > 0) and provide for a detailed analysis of the output radiation mode content and impact of injecting an RF seed signal into the apparatus for convective growth.
Comparisons will be presented with the latest experimental studies testing the numerical predictions. Recent experimental results have shown a clear backward wave interaction verifying simulations.
|Title of host publication||11th International Workshop on the Interrelationship between Plasma Experiments in the Laboratory and in Space (IPELS)|
|Publication status||Published - 2011|