Search

This paper describes the results of a laboratory experiment on the sub-Alfvén expansion of a quasi-spherical laser plasma cloud into a vacuum magnetic field in the regime of nonmagnetized ions. The role of Hall fields and currents in the anomalously fast dynamics of the magnetic field during the collapse phase of a diamagnetic cavity is considered. Detailed spatial measurements of the azimuthal Hall fields configuration are demonstrated and their relationship to diamagnetic cavity collapse is determined. As a result of the experiment, data were obtained confirming the hypothesis about the transfer of the main magnetic field by the movement of electrons associated with Hall currents. [ABSTRACT FROM AUTHOR]

Transit observations of exoplanets make it possible to measure temperature and relative abundance of various elements in their atmospheres. The infrared line of metastable helium HeI 10 830 Å is widely used to study the atmospheres of exoplanets by the transit absorption method. The emission spectra of stars have a significant impact on the physical and chemical parameters of the upper layers of the atmospheres. In this paper, we consider the features of absorption in the helium line for stars of different spectral classes by numerical simulation. The results show the key role of the star's emission spectrum in the formation of the upper atmosphere and in the amplitude of transit absorption of exoplanets in the HeI 10 830-Å line. [ABSTRACT FROM AUTHOR]

The laboratory experiment on modeling a sub-Alfvénic interaction of expanding plasma cloud with vacuum magnetic field is described. We produce spherically symmetric cloud by 4-beam laser irradiation of the pellet. The presented data reveal complex dynamic of cloud deceleration and formation of two field aligned jets, development of the flute instability and rapid collapse of the diamagnetic cavity. It is shown that cavity collapse can't be explained by plasma motion or anomalous diffusion and requires for explanation a new mechanism. [ABSTRACT FROM AUTHOR]

The results of modeling the Hα absorption spectrum of the atmosphere of the hot Jupiter WASP‑52b are presented. The atmosphere was modeled with a three-dimensional hydrodynamic code. Several different values of the XUV ionizing radiation were considered. The Lyα-photon transfer in the atmosphere was simulated by the Monte Carlo method. Spatial distributions of the volume density of hydrogen atoms excited to the second energy level H(2) were obtained, and absorption spectra in the Hα line were calculated. It was also shown that absorption takes place in a layer with a thickness of about 1.5 times the planetary radius, while the greatest influence on absorption is exerted by Lyα photons produced due to recombination of electrons and protons. [ABSTRACT FROM AUTHOR]

The paper presents the results of laboratory experiment modeling the interaction between Lunar magnetic anomalies and Solar wind. To model the LMA we use quadrupole magnetic field. The main dimensionless parameter of the problem, the ion inertia length relative to the mini-magnetosphere size, well corresponds between experiment and LMA conditions. The main result is measurement of the magnetically reflected proton fluxes, which show qualitative agreement to available satellite data. [ABSTRACT FROM AUTHOR]

Structural instabilities that develop during pulsed injection of dense plasma jets into vacuum in the presence of an external quasi-homogeneous magnetic field are studied by high-speed photography using ICCD cameras. The experiments are carried out in the chamber of the "Krot" stand, which has record-breaking dimensions in its class of installations (diameter—3 m, length of the working section—10 m), and makes it possible to study plasma dynamics by various diagnostic methods at scales of more than 1 m both along the magnetic field and in the direction transverse to the magnetic field. During injection along the magnetic field, a transverse collimation of the flow of ionized matter and the development of a flute instability of the plasma boundary are observed, which, at the late stages of expansion, leads to the plasma leaving the injection region in the form of several jets across the field. During transverse injection, the formation of a collimated flow, a "plasma sheet," is observed, in which, as the plasma moves across the field, inhomogeneous structures develop in the direction of injection. [ABSTRACT FROM AUTHOR]

An experiment to model a system of field-aligned currents in a dense inner magnetospheric plasma is performed under laboratory conditions for the first time. The magnitude and length of the flow of field-aligned currents were measured as a function of the magnetic field. [ABSTRACT FROM AUTHOR]

The studies of close-orbit gaseous exoplanets—hot Jupiters and warm Neptunes—are reviewed. Transit spectral observations of the Hubble Space Telescope stimulated the numerical modeling of these objects. The supersonic outflow of the upper atmosphere of hot exoplanets and its interaction with the stellar plasma flow is a newly-discovered phenomenon in plasma physics and astrophysics that pools photo- and plasma-chemistry, collision-induced gas-dynamics, and collisionless space plasma. Starting from 2003, the modeling of physical processes in this field has considerably developed from simple quasi-empiric analytical formulas to global three-dimensional magnetic hydrodynamic (3D MHD) codes. The attained level makes it possible to interpret the in-transit measurements in absorption lines of different elements and estimate the parameters of both the planetary atmospheres and the stellar plasma wind. [ABSTRACT FROM AUTHOR]

Simulation results are presented for the Lyα flux impact from the parent star on the Hα absorption spectrum in the atmospheres of the hot Jupiters HD189733b and HD 209458b. The atmosphere is simulated using a three-dimensional hydrodynamic code. Several options are considered for the upper atmospheric composition, including variations in the XUV parameter. The Lyα photon transfer in the atmosphere is simulated by the Monte Carlo method. Spatial distributions are obtained for the bulk density of hydrogen atoms excited to the second energy level; absorption spectra in the Hα line are calculated. It is shown that the transit absorption of the hot Jupiters in the Hα line can be described by a relatively simple model of the Lyα photon transfer in the upper atmosphere. [ABSTRACT FROM AUTHOR]

The discovery of thousands of highly irradiated, low-mass, exoplanets has led to the idea that atmospheric escape is an important process that can drive their evolution. Of particular interest is the inference from recent exoplanet detections that there is a large population of low mass planets possessing significant, hydrogen dominated atmospheres, even at masses as low as ∼ 2 M ⊕ . The size of these hydrogen dominated atmospheres indicates the envelopes must have been accreted from the natal protoplanetary disc. This inference is in contradiction with the Solar System terrestrial planets, that did not reach their final masses before disc dispersal, and only accreted thin hydrogen dominated atmospheres. In this review, we discuss the evidence for hydrogen dominated atmospheres on terrestrial mass (≲ 2 M ⊕ ) planets. We then discuss the possible origins and evolution of these atmospheres with a focus on the role played by hydrodynamic atmospheric escape driven by the stellar high-energy emission (X-ray and EUV; XUV). [ABSTRACT FROM AUTHOR]

As is known, the influence of the ionizing radiation and the gravity of a star on a hot Jupiter results in the outflow of its atmosphere. Due to the gravity of the planet, the outflowing matter acquires angular momentum, after which it is accumulated on a higher circular orbit around the star and forms a disk or a torus. The angular momentum interexchange between the torus and the planet induces the migration of the planet to the star. In this paper, we consider the effectiveness of this migration mechanism by the example of the HD 209458 system. It turns out that, after 4.5 × 109 years since the evaporation of the protoplanetary disk, the planet might migrate from an orbit at ≳0.67 AU to its current orbit at 0.045 AU. [ABSTRACT FROM AUTHOR]

The limiting mode of the generation of low-frequency torsional whistlers is obtained for the first time. Laser plasma clouds create only weak whistlers in a weakly magnetized laboratory plasma (argon), allowing the whistler magnetic field to reach record values of ~25% of the background magnetic field. [ABSTRACT FROM AUTHOR]

The results of a laboratory experiment on the simulation of the reflection of protons over regions of the local magnetization of the lunar crust have been reported. Quadrupole and dipole sources have been used to simulate a local magnetic field. The magnetic-field-induced reflection of protons near lunar magnetic anomalies reaches 50% of the incident flow. A significant difference between the quadrupole and dipole configurations has been detected both in the structure of the mini-magnetosphere and in the reflection of protons. The data obtained are in qualitative agreement with in situ measurements by spacecrafts over lunar magnetic anomalies. [ABSTRACT FROM AUTHOR]

Numerical modeling results of interactions of the planetary atmosphere of Gliese 436b with ionizing radiation and the plasma wind of an M star are presented. A self-consistent gas-dynamic 2D model characterizing the processes of radiation heating and ionization and hydrogen photochemistry reactions was used in the modeling. It is demonstrated that Gliese 436b should have an extended (several tens of planetary radii) exosphere, which is formed by partially ionized gas with added molecular components, with a supersonic outflow velocity. The influence of such factors as the XUV radiation intensity and the temperature of the lower atmosphere on the mass loss rate is examined. [ABSTRACT FROM AUTHOR]

Results of a study of the influence of solar-type host stars superflares on the gas dynamics of the extended envelopes of giant exoplanets are presented. During flare events, the radiation intensity of the host star in the extreme ultraviolet and soft X-ray can increase by several orders of magnitude for a short time, leading to strong local heating of the exoplanet atmosphere on the side facing the star, with the formation of shocks in the atmosphere. Computations of the gas-dynamical response of the atmosphere of the hot Jupiter HD 209458b to characteristic superflares of solar-like stars were carried out earlier in [1] using a one-dimensional aeronomical model correctly taking into account heating and chemical processes in the atmosphere. To investigate the outflow of atmospheric gas, the results obtained with this onedimensional model were used as simple boundary conditions for computations of the three-dimensional flow structure after a flare. The results of these three-dimensional gas-dynamical computations show that the mass ejection of the flare increases the size of the envelope over several hours, which could be detected with existing observing facilities. It is shown that the mass-loss rates for the most powerful superflare considered could be enhanced by an order of magnitude over several tens of hours after the flare. [ABSTRACT FROM AUTHOR]

A study is performed of the processes that occur during the interaction between the planetary atmosphere of Gliese 436 b and the incoming plasma wind and ionizing radiation of the parent star. The approximate values of the speed and density of the star's plasma wind are determined based on a comparison of the results from numerical modeling using a self-consistent 3D magnetohydrodynamic model with the results from observations using the Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS). [ABSTRACT FROM AUTHOR]

This paper presents the results of laboratory experiments with laser plasma flow around a magnetic dipole which model the extreme compression of the Earthś magnetosphere by the plasma generated by high-power coronal mass ejections. Data on the formation of an artificial magnetosphere, the boundary-layer structure, and the size of the magnetosphere as a function of the magnetic moment are given. It is shown that in the presence of a conducting dipole shell modeling the ionosphere, conditions are created for the flow of intense longitudinal currents in the polar regions. It is established that the longitudinal currents have little effect on the position of the plasma stagnation point and the transition layer but make a significant contribution to the disturbance of the magnetic field in the magnetosphere. [ABSTRACT FROM AUTHOR]

The ion composition of a plasma flow obtained by intense irradiation of a solid target is determined by methods of probing diagnostics and measuring the secondary emission rate. As the ions fly through a dense gas jet, C 5+ ions are found to recharge to C 4+ ions and then to C 3+ ions. The fraction of high-charge ions in the initial plasma flow and their concentration in the region of interaction with the jet are calculated. The concentration of atoms in the gas jet is estimated on the basis of the integral change in the charge value. Results necessary for analyzing the conditions of experiments on effective charge-transfer pumping and laser generation in the far ultraviolet spectral range are obtained. [ABSTRACT FROM AUTHOR]

Results of an experiment on the interaction of laser-produced plasma with a pulsed gas jet are reported. A resonant charge-exchange pumping of the n=3 level of the C3+ ion was observed. A spatial structure of the region of intensive interaction was obtained by a short time imaging of filtered plasma radiation. According to independent probe measurements, the interaction was realized at densities of ions and gas particles in excess of 1016 cm-3. The obtained data provide a prospect for future experiments on laser gain in the EUV spectral range based on charge-exchange pumping of the C5+ ion. [ABSTRACT FROM AUTHOR]

The paper deals with the physical and electrotechnical principles of the promising method of direct conversion of the kinetic energy of an expanding plasma cloud to electrical energy by inductive generation of currents in short–circuited load coils that enclose the plasma and are oriented across the external magnetic field. An analysis of plasma deceleration by a magnetic field and transfer of plasma energy to an inductive load gave a solution of the problem in general form and the dimensionless parameters of the problem that determine the deceleration radius, the coil current, and the theoretical conversion efficiency. The role of the basic physical effects, including parasitic ones (plasma instabilities and Joule heating), influencing the real efficiency is assessed. A comparison of the results with data of experiments with laser–produced plasma clouds on a KI–1 facility and with available numerical results shows that in the optimized version of the method for conversion of inertial confinement fusion energy, a 30% efficiency can be achieved. [ABSTRACT FROM AUTHOR]

Short pulse laser generated plasmas interacting with a pulsed gas jet are studied to aid the realization of novel XUV laser schemes based on recombination supported by charge exchange pumping. Interaction of C4+, O3+ and O4+ ions with hydrogen and nitrogen indicates strong charge exchange pumping of C3+(3p-2s, 3d-2p) lines at 31.2 and 38.4 nm, and O2+ (2p 3s-2p2) and O3+ (2s 3d-2s22p) lines at 37.4 and 23.8 nm. [ABSTRACT FROM AUTHOR]