Generation and propagation of kilometric radiation in the auroral plasma cavity

Two‐dimensional particle simulations and three‐dimensional ray‐tracing calculations are used to investigate the generation and propagation of electromagnetic radiation produced by the electron cyclotron maser instability under conditions that prevail in the auroral plasma cavity. The simulations incorporate a continual flow of primary energetic electrons along the magnetic field. In such a driven system the maser instability leads to a quasi‐steady state in which as much as 7% of the incident flux of electron energy is converted into radiation. The maximum radiation intensity occurs within 20‐30 km from the injection point of the primary electrons, and the radiation consists of discrete wave packets with a spatial extent of 4‐6 km parallel to the field. The magnetic field gradient is shown to be unimportant for these quasi‐local properties of the maser instability. The ray path calculations are performed in a dipolar field geometry and retain the relativistic corrections to the wave dispersion. For the case where the energetic electrons are the dominant species, amplifications of the order of e 10 are achieved within path lengths of less than 100 km. This indicates that the maser instability can produce the observed amplification of auroral kilometric radiation above cosmic background levels within a distance smaller than the dimensions of the auroral cavity.