A. V. Melekhov

Breakdown Initiation in Water with the Aid of Bubbles

The breakdown initiation in water is investigated using artificially produced long-lived microbubbles 40–100 μm in size obtained with the aid of a pulse-heated wire electrode. In all cases, the discharge is initiated in a bubble, with the prebreakdown time in the presence of a bubble being much shorter than in its absence. In the case of a discharge from the anode, three series of shock waves are observed in the electrode region, associated with the ignition of the discharge, the propagation of a supersonic streamer, and the release of energy when the streamer closes the interelectrode gap. In the case of cathode breakdown initiation, disturbances develop on the bubble surface in the form of a “bush” propagating at a subsonic speed in the direction of the opposite electrode. The possibilities of streamer and multiavalanche mechanisms of the breakdown of microbubbles are discussed.

Experimental study of a mini-magnetosphere

Magnetospheres at ion kinetic scales, or mini-magnetospheres, possess unusual features as predicted by numerical simulations. However, there are practically no data on the subject from space observations and the data which are available are far too incomplete. In this paper we describe the results of a laboratory experiment on the interaction of plasma flow with a magnetic dipole with parameters such that the ion inertial length is larger than the size of an observed magnetosphere. A detailed structure of the non-coplanar or out-of-plane component of the magnetic field has been obtained in the meridian plane. The independence of this component on dipole moment reversal, as was reported in a previous work, has been verified. In the tail distinct lobes and a central current sheet have been observed. It was found that lobe regions adjacent to boundary layer are dominated by a non-coplanar component of magnetic field. Tail-ward oriented electric current in the plasma associated with that component appears to be equal to the ion current in the upstream part of magnetosphere and in the tail current sheet implying that electrons are stationary in those regions while the ions flow by. The data obtained strongly support the proposed model of mini-magnetosphere based on two-fluid effects as described by the Hall term.

Nonelectrode Streamers in Deionized Water

In this paper, the study results of nonelectrode streamers initiated by microparticles of sizes less than 50 μm are presented. The used method is anode screening with the help of a preliminarily prepared conductive layer close to an electrode surface. A microparticle initiates multiple simultaneous streamers, both fast cathode and slow anode directed.

Electrooptical measurements of the electric field strength in water with near-electrode conductive layers

The problem of increasing the pulsed electrical strength of water is topical for the development of capacitive energy storage systems [1]. Increased values of the breakdown strength of water were previously attained by a decrease in the electric field intensity near the electrodes [2]. This was realized by different ways, namely, via injection of the charges by electrode materials, via introduction of bipolar ions of amino

Laboratory simulation of field aligned currents in an experiment on laser-produced plasma interacting with a magnetic dipole

In an experiment on a magnetic dipole interacting with a laser-produced plasma the generation of an intense field aligned current (FAC) system was observed for the first time in a laboratory. The detailed measurements of the total value and local current density, of the magnetic field at the poles and in the equatorial magnetopause, and particular features of electron motion in the current channels revealed its similarity to the Region-1 current system in the Earth magnetosphere. Such currents were found to exist only if they can close via conductive cover of the dipole. Comparison of conductive and dielectric cases revealed specific magnetic features produced by FAC and their connection with electric potential generated in the equatorial part of the magnetopause. To interpret the data we consider a model of electric potential generation in the boundary layer which agrees with experiment and with measurements of the Earths transpolar potential in the absence of an interplanetary magnetic field as well. The results could be of importance for the investigation of Mercury as a magnetic disturbance due to FAC could be especially large because of the small size of the Hermean magnetosphere.

Laser Plasma Experiments to Simulate Coronal Mass Ejections During Giant Solar Flare and Their Strong Impact on Magnetospheres

Giant solar flares are the most powerful phenomenon in the solar system, which can strongly affect various geospheres and technical systems in the near Earths space or its surface. During the space era, only few events with a total energy of more than 1034 erg happened, and probably, only one of these ldquowas directedrdquo to the Earth (August 4, 1972). In this paper, we report on the first attempts to simulate in a laboratory both the initial (at the Sun) and final (near the Earth) stages of relevant interaction processes between the plasma flows and magnetic fields. By using laser-produced plasmas and intense magnetic dipole, we performed two types of simulation experiments: 1) on the interaction of ejected solar plasma flows with/in dipole magnetic field and 2) on the extreme (three fold) compression of the Earths magnetopause by giant coronal mass ejections from the Sun. General physical conditions of these phenomena are briefly described, and the developed methods of laboratory simulation and numerical modeling of various explosive processes in collisionless space plasmas are discussed on the basis of relevant dimensionless criteria of the problems.

Experimental study of collisionless super-Alfvénic interaction of interpenetrating plasma flows

An experiment on the interaction between an expanding super-Alfvénic laser-produced plasma flow and a magnetized background plasma under conditions in which the ion gyroradius is comparable with the characteristic scale length of magnetic field displacement is described. The depletion of the background plasma in a substantial volume and the formation of a large-amplitude compression pulse propagating with a super-Alfvénic velocity are revealed. The efficiency of energy conversion into perturbations of the background plasma was found to be 25%. Combined data from magnetic, electric, and plasma measurements indicate that the interaction occurs via the magnetic laminar mechanism.

INFLATION OF A DIPOLE FIELD IN LABORATORY EXPERIMENTS: TOWARD AN UNDERSTANDING OF MAGNETODISK FORMATION IN THE MAGNETOSPHERE OF A HOT JUPITER

Giant exoplanets at close orbits, or so-called hot Jupiters, are supposed to have an intensive escape of upper atmospheric material heated and ionized by the radiation of a host star. An interaction between outflowing atmospheric plasma and the intrinsic planetary magnetic dipole field leads to the formation of a crucial feature of a hot Jupiters magnetosphere—an equatorial current-carrying magnetodisk. The presence of a magnetodisk has been shown to influence the topology of a hot Jupiters magnetosphere and to change a standoff distance of the magnetopause. In this paper, the basic features of the formation of a hot Jupiters magnetodisk are studied by means of a laboratory experiment. A localized central source produces plasma that expands outward from the surface of the dipole and inflates the magnetic field. The observed structure of magnetic fields, electric currents, and plasma density indicates the formation of a relatively thin current disk extending beyond the Alfvenic point. At the edge of the current disk, an induced magnetic field was found to be several times larger than the field of the initial dipole.

Charge-exchange pumping of laser-produced plasma colliding with vapour cloud for lasing in XUV

A charge-exchange pumping of laser-produced ions on a compact gas cloud is experimentally investigated. An interaction at density of neutrals has been achieved for the first time. A record efficiency of charge-transfer pumping 10% has been measured which is close to maximum 25% predicted by developed analytical model. The intensity of VUV-emission from the region amounted to 1 MW with duration ns. The results obtained are promising for future laser gain experiments.

Estimations of the electric field strength of nonelectrode streamers in water

The electric field strength of a nonelectrode streamer in water has been estimated using data of electro-optical measurements. The microscopic field strength on the tips of the anode-directed and cathode-directed streamers is approximately 10 MV/cm, while the macroscopic field strength of cathode-directed and anode-directed streamers near the streamer zone is approximately 300 kV/cm and 2 MV/cm, respectively.