V. M. Antonov

A STUDY OF THE COLLISIONLESS INTERACTION OF INTERPENETRATING SUPER-ALFVEN PLASMA FLOWS

The authors attempt to obtain plasma parameters as required for effective magnetic laminar mechanism (MLM) interaction, while examining the collisionless interaction of an expanding laser-plasma cloud with a magnetized background for high mach numbers (M /sub A/ greater than or equal to 5) and the interaction parameter greater than 1. The experiments were preformed with the KI-1 apparatus for simulating astrophysical plasma processes. The main components were the 1-kJ CO/sub 2/ laser and a high vacuum chamber of diameter 1.2 m and length 5 m fitted with a pulsed background plasma source. Particular attention was given to eliminating the effects from ordinary Coulomb collisions, and various forms of collisional interaction were examined including Coulomb, screened nuclear repulsion, polarization-type attraction, and charge transfer.

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.

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.

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.

Experimental Investigation of the Behavior of Bubbles in Water under the Effect of Strong Electric Fields

Investigations are performed of the formation of long-lived microbubbles 20 to 100 μm in size in water with the aid of a pulse-heated wire electrode. The results of optical investigations of the behavior of bubbles in a strong pulsed electric field of up to 300 kV/cm demonstrate that the bubbles stretch out in the field direction, are compressed in the transverse direction, are divided, and separate from the electrode. Differences in the behavior of anode and cathode bubbles are registered.

Laboratory experiment on region-1 field-aligned current and its origin in the low-latitude boundary layer

In previous experiments by the authors on a magnetic dipole interacting with a laser-produced plasma the generation of an intense field-aligned current (FAC) system on terrella poles was observed. In this paper the question of the origin of these currents in a low-latitude boundary layer of magnetosphere is investigated. Experimental evidence of such a link was obtained by measurements of the magnetic field generated by tangential drag and sheared stress. This specific azimuthal field was found to have quadruple symmetry and local maxima inside the magnetosphere adjacent to the boundary layer. Cases of metallic and dielectric dipole covers modeling good conductive and non-conductive ionosphere revealed that the presence or absence of FACs results in different amplitudes and spatial structures of the sheared field. The current associated with the azimuthal field flows upward at the dawnside, and toward the equator plane at the duskside. It was found to coincide by direction and to correspond by amplitude to a total cross-polar current measured independently. The results suggest that compressional and Alfven waves are responsible for FAC generation. The study is most relevant to FAC generation in the magnetospheres of Earth and Mercury following pressure jumps in solar wind.

Simulation of astrophysical plasma dynamics in the laser experiments

The properties of laser‐produced plasma are similar in many features to the ones of various space plasma releases of explosive nature. It allows to investigate the processes of an interaction of those plasmas with background media by the means of laboratory simulation. In the given paper such simulation experiments with quasispherical plasma clouds at KI‐1 laser facility are presented. The experiments are related to dynamics of collisionless expansion of exploding space plasmas in the surrounding magnetized media at various Alfven‐Much numbers. A non‐uniform media as well has been simulated. The results on generation of shock and wistler waves in background, on formation of diamagnetic cavity and flute instability of plasma clouds are described. Data on a dynamics of laser‐produced plasma in a dipole magnetic field are presented also. Results are analyzed in connection with dynamics of Supernova remnants in interstellar medium, Barium releases in Earth magnetosphere and possible disturbances of the latter...

Laboratory model of magnetosphere created by strong plasma perturbation with frozen-in magnetic field

Transient interactions of a magnetic dipole with plasma flow carrying a southward magnetic field has been studied in laboratory experiments. Flow with a transverse frozen-in field was generated by means of laser-produced plasma cross-field expansion into background plasma, which filled a vacuum chamber, along with the external application of a magnetic field prior to interaction. Probe measurements showed that at the plasma parameters realized, effective collisionless Larmor coupling takes place resulting in the formation of strong compressive perturbations, which propagate in the background with super-Alfvenic velocity and generate a frame-transverse electric field comparable in value to the expected induction one in the laboratory. Compression pulses with a southward field interact with a dipole and create a well-defined magnetosphere after a short propagation. Comparison of the magnetospheres created by laser-produced plasma expanding in a vacuum field and in a magnetized background revealed fundamental differences in the structure and behaviour of the electric potential in plasma. In the presence of a frozen-in southward field direct «sub-solar» penetration of outside electric potential deep inside of the magnetosphere was observed to take place, with a velocity close to the upstream Alfven speed.