Coherent Radiation from Electrostatic Double Layers

Abstract

The radiation properties of electrostatic double layers (DLs) are of potential significance for cosmic magnetic explosions. If the emission is sufficiently intense it can serve as a diagnostic tool for particle acceleration by localized strong potential drops in current-carrying plasmas. Moreover such intense emission may form the explanation of some of the observed intense and narrow-band bursts of radiation from stellar and planetary magnetospheres. Here we study the efficiency of two coherent radiation processes: antenna radiation and a maser process. It is found that both processes can operate in the DL to produce intense and narrow-band emission. Antenna radiation occurs if the dimensions of the double layer are smaller than the wavelength of the emitted radiation. This process is therefore relevant to laboratory rather than to astrophysical plasmas. The maser on the other hand requires an amplification length inside the double layer much larger than the emitted wavelength, and can lead to observable emission in astrophysical circumstances. The growth is exponential and the rate depends only on the electric field energy density of the DL. Since the latter is externally controlled by the electric circuit it is a constant for the emission process so as to constitute a true maser. The maximum brightness temperature is of order 1025K. Masing radiation from electrostatic DLs is therefore a candidate for some of the observed intense narrow-band cosmic radio emission.