Extrusion of a nanosecond surface discharge plasma near a dielectric ledge

The presence of a dielectric ledge along the pulse discharge propagation led to a redistribution of the pulsed surface (plasma sheets) discharge glow. Discharge glow on the surface without the ledge, was uniform and lasted no more than 200 ns. Two plasma channels with increased glow intensity were observed near the rectangular ledge placed in the discharge area. The duration of these longitudinal plasma channels increased and lasted for about 0.9 μs (at a voltage of 25 kV and a density of 0.03 – 0.18 kg/m3 ). A nine-frame nanosecond camera recorded the evolution of the plasma glow. The dynamics of the flow induced by the pulse surface discharge was recorded using a high-speed shadow imaging during 40-50 μs after the ignition of the discharge.

Scintillation Arcs Shed Light on Scattering from Planar Plasma Sheets

Scintillation arcs provide an unprecedented degree of detail into the scattering of radio waves from pulsars. We review evidence that has emerged over the last fifteen years that: a) the scattering of many nearby pulsars is dominated by one or several relatively thin “screens” of material, b) the resulting image on the sky is highly linear, with axial ratios at least as high as 10:1, and c) this arrangement is persistent for at least one source (B1133+16) for at least 25 years. We expand on the idea of Pen and Levin (2014) and previous authors that such scattering may be caused by linear sheets of plasma seen nearly edge-on. Further analysis of such scintillation arcs, including new work on multi-frequency, multi-epoch observations, should help elucidate the astrophysical nature of these ubiquitous scattering entities, which are currently not convincingly linked with any known structures.