An Analytical Theory for Spontaneous Emission of Electromagnetic Radiation on Curved Plasma-Vacuum Interfaces*

Spontaneous emission of electromagnetic (EM) waves from bodies of plasma is a subject of interest for many applications, particularly for areas relevant to the space environment. These include, but are not limited to, emission from meteors, radiofrequency (RF) emission from hypersonic reentry vehicles, and RF emission from hypervelocity-impact plasmas. Of notable interest is emission in relatively low frequency regimes (i.e., less than 30 MHz) due to their unknown generation mechanism. In this work, we develop a theoretical 2D model to show the possible existence of EM waves at curved plasma-vacuum interfaces which then propagate throughout vacuum. We suggest these waves are formed due to spontaneous electrostatic (ES) perturbations at the curved plasma-vacuum interface (i.e., thermal ES surface waves) as they propagate along the interface. The EM radiation is characterized by emission frequency lower than the plasma frequency, and amplitude attenuation inversely proportional to the square root of the distance away from the plasma for the case of a 2D wave. We derive dispersion relations for these waves and provide a simplified approximation of these dispersion relations for practical use in experimental and computational analyses.