Density irregularities, currents, and magnetic fields generated by pulsed local rf heating of a magnetoplasma: Disturbances in rf antenna vicinity

Abstract

The dynamics of narrow, field-aligned magnetoplasma irregularities is studied, which develop under the action of a short rf pulse. The laboratory experiment is aimed at demonstrating the rapid, so-called “unipolar” plasma transport mode, which is accompanied by excitation of eddy currents, in the case of localized rf heating of plasma electrons. The experimental parameters are chosen in a special way. The size of the heating spot, determined by the diameter of the loop antenna, exceeds the electron gyroradius significantly but is smaller than the ion gyroradius. The rf pulse duration encompasses several electron collision times but is shorter than the gyroperiod of ions. As a result, the electrons, which are strongly magnetized, acquire energy in rf antenna vicinity and can escape the heating region only along the magnetic field B0. In turn, collisionless ions can travel across B0 under the action of space-charge electric fields. For these conditions, redistribution of the plasma occurs with “unipolar” transport coefficients and is accompanied by excitation of electric currents. Weak plasma density disturbances, which are less than 5% of the background, are measured precisely with a microwave resonator probe. Parallel electron currents are obtained from magnetic probe measurements; the ion current across B0 is restored from the density profile modifications in their dynamics. It is shown that the ions traveling across B0 with a velocity about one third of the ion-acoustic velocity can easily close the current loop, which is driven by the parallel motion of heated electrons. This regime of plasma irregularities evolution is discussed in application to previous laboratory measurements, as well as to active ionospheric experiments.

First SWARM Observations of the Artificial Ionospheric Plasma Disturbances and Field‐Aligned Currents Induced by the SURA Power HF Heating

“…Over time, the depth and the length of the density depletion around the heating region increase; the density enhancement travels away from the heating source (Aidakina et al, ). The proportionality between the magnitude of the T e and N e disturbances observed in space as well as the current densities (taken into account the geometrical scales) is good agreement with the quantitative estimates from the laboratory modeling presented by Aidakina et al ().…”

“…The possibility of the effects observed by SWARM was previously demonstrated in laboratory experiments. The laboratory modeling performed with KROT plasma facility under the experimental conditions similar to the conditions in the ionosphere, where the plasma irregularities develop under the impact of high‐power HF radio waves, has revealed redistribution of plasma accompanied by electric currents (Aidakina et al, , ; Kostrov et al, ; Starodubtsev et al, ). Because the heated electrons escape along the magnetic field lines, channels with reduced plasma density and enhanced N e above the depletion are formed.…”

In Situ Observations of Ionospheric Heating Effects: First Results from a Joint SURA and NorSat‐1 Experiment

“…Perhaps, this is due to the fact that the active experiment was carried out in the late morning (normally, the daytime ducts were weaker than those in the nighttime using the HAARP and SURA facilities Frolov et al., 2016; Vartanyan et al., 2012), there was a small pump wave power, and the pump wave frequency was almost equal to the critical frequency f 0 F 2 . Note that the effects of the interaction of the irregularities were studied near to and far from the heating source in laboratory experiments on modeling ionospheric heating (Aidakina et al., 2018, 2018a). It was shown that near the heating sources, the irregularities had the form of a set of channels with reduced plasma density and a transient process with a positive density perturbation was observed at a large distance from the heating sources.…”

“…laboratory experiments on modeling ionospheric heating (Aidakina et al, 2018(Aidakina et al, , 2018a. It was shown that near the heating sources, the irregularities had the form of a set of channels with reduced plasma density and a transient process with a positive density perturbation was observed at a large distance from the heating sources.…”