Electromagnetic radiation from double layers
  The background motivation, and some preliminary results, are reported for a recently begun investigation of a potentially important mechanism for electromagnetic radiation from space, Double Layer Radiation (DL-radiation). This type of radiation is proposed to come from DL-associated, spatially localized high frequency (hf) spikes that are driven by the electron beam on the high-potential side of the double layer. It is known, but only qualitatively, from laboratory experiments that double layers radiate in the electromagnetic spectrum. In our experiment the spectrum has high amplitude close to the plasma frequency, several hundred MHz. No clear theoretical model exists today. The quantitative evaluation is complicated because measurements are made in the near field of the radiating structure, and in the vicinity of conducting laboratory hardware that distorts the field. Because the localized electrostatic wavelengths (approximately 1 cm) can be relatively small compared to the emitted electromagnetic wavelengths, the situation is further complicated. We discuss the mutual influence between the ion density profile and hf-spike formation, and propose that some kind of self-organization of the density profile through the ponderomotive force of the hf spike might be operating. First results regarding the electromagnetic radiation are reported: the frequency, the time variation of the amplitude, and the spatial distribution in the discharge vessel. 
Nils Brenning, Mark Koepke, Ingvar Axnas, Michael A. Raadu