Plasma Physics Reports最新文献

The paper presents the results of experiments and radiation MHD calculations of the electric explosion of flat copper conductors in megagauss magnetic fields. The experiments were carried out on a te-rawatt-range MIG facility at a current of up to 2.5 MA and a rise time of 100 ns. The width of the conductors (along the x axis) was much greater than their thickness (along the y axis), and the current was directed along the z axis. It was shown experimentally and confirmed by RMHD calculations that the conductor expands in thickness along the y axis, while plasma expansion is suppressed in width along the x axis. This is due to the increase in the magnetic field at the conductor edges, which also causes an earlier explosion of the end faces. The substance from the end faces flies to the center of symmetry of the plate’s wide faces as a low-density plasma. As a result, on the conductor’s wide face (plane XZ), along its longitudinal z axis, a plasma channel is formed approximately 75 ns from the start of the current flow. X-ray images of the conductors were obtained from the X-ray radiation from the hot spot of the X-pinch. The detected expansion of the conductor along the y coordinate is in good agreement with the calculated data.

The work is devoted to the experimental simulation of processes that occur in high-altitude atmospheric discharges called red sprites. Miniature analogs of columnar red sprites are formed in low-pressure air, including those observed with single discharge current pulses. It is shown that the brightly luminous “glow” region of the primary “columns” is due to the transition from the plasma diffuse jet mode initiated by a positive streamer to the quasi-stationary glow discharge mode. The emission spectra from various regions of the discharge system along its longitudinal axis are presented, as well as data on the electron T_e, vibrational T_v, rotational T_r and gas T_g temperatures of the discharge plasma in these places. Photographs of the discharge glow are taken when its mode changes.

The influence of refined parameters of the upgraded system for 6-MW-power neutral beam injection into the T-15MD tokamak plasma was analyzed numerically. The efficiency of toroidal current drive in plasma has been determined, and the profiles of absorbed power of the injected neutral beam, the safety factor, and the bootstrap current have been calculated. The possibility of replacing the ohmic current in plasma with the current driven by the upgraded neutral beam injection system has been investigated. The results of calculations performed for neutral beams with monoenergetic distribution and more complicated three-component energy composition are compared. For the first time, for simulating future T-15MD shots with neutral beam injection, the NUBEAM code was used in combination with the ASTRA code. The calculations were performed with allowance for the real geometry of injectors and the parameters of ion sources. The calculation results obtained using the NUBEAM code are compared with the calculation results obtained using the new version of the ASTRA-NBI neutral beam injection module, as well as the BTR code, which optimizes the parameters of neutral beam injection. The calculations show that the fraction of current driven by the upgraded neutral beam injection system was approximately 30%.

The paper presents the results of measuring the spectral and dose characteristics of pulse-periodic X-ray radiation generated by a plasma accelerator. The device is based on the principle of electron autophasing in the oscillating electric field of a microwave cavity, implemented in the scenario of automatic maintenance of electron cyclotron resonance in a magnetic field that slowly increases in time in the interaction region (gyromagnetic autoresonance, GA). It was found that electrons of generated plasma bunches during acceleration reach energies of up to 0.5 MeV. Due to multiple acceleration and deceleration of electrons in the microwave field, hard X-ray radiation is generated, which is of interest for radiation technologies. It is shown that the bremsstrahlung of bunches has a pronounced anisotropy and spatial regions with its maximum output are experimentally determined. The measured average absorbed dose rate for biological tissue was 2 mGy/s. Conditions for increasing the accelerator’s bremsstrahlung power with an increase in the number of accelerated electrons and their energy are determined. The accompanying characteristic radiation of the plasma-forming gas and the accelerator’s structural elements facing the plasma is investigated.

The threshold of absolute parametric decay instability developing in inhomogeneous plasma in the presence of two decay points was studied as a function of the width of a pump beam of microwaves.

Previously, the gas temperature on the axis of the discharge with liquid non-metallic electrodes has been measured using the shadow background method. The discharge has been studied in the liquid cathode and metal anode configuration. Due to the features of the optical scheme, it has been impossible to obtain good spatial resolution, since the object under study is not in the focus of the photorecording device. As a result, the radial temperature variation is distorted by the instrument function of the lens. To restore the original distribution, it is necessary to solve the inverse problem. In this work, a method for restoring the radial temperature variation is proposed. First, two methods for solving the inverse convolution problem are compared on the basis of a model experiment. The method giving the best result is selected on the basis of the comparison results. The selected method is used to process the experimental data in order to restore the radial temperature variation.

Charging of micrometer-sized dust particles in multicomponent plasma of humid air and H₂O‒O₂–N₂ gas mixtures at different gas ionization rates by an outer ionization source has been considered. The charge of dust particles is determined based on the kinetic model of ion-molecular processes, which includes more than 600 reactions for electrons, negative and positive ions, including hydrated ions containing up to twelve water molecules. It was found that despite the negligible electron density far from a dust particle in an undisturbed plasma, the charge of dust particles in humid air when the gas ionization rate exceeds the critical value is determined precisely by the electron flux. This leads to sufficiently high dust particle charge comparable with the charge in electropositive gases. The influence of the gas ionization rate and its composition on the dust particle charge is studied. A comparative analysis of the obtained data with the results of the analytical theory of particle charging at elevated pressures is carried out. The issue of the influence of the particle charge polarization under the action of a point charge of an ion (electron) on the charge of dust particles is considered.

The problem of radiation amplification in a plasma microwave amplifier with a coaxial geometry in the presence of an absorber is considered. The absorber is used to suppress the parasitic feedback, which can lead to self-excitation of the system. At the same time, its presence leads to a modification of its electrodynamic properties. The spatial increments of the beam–plasma instability were calculated, and the parameter ranges where the self-excitation of the amplifier does not occur were determined. The effect of the absorber on the efficiency of the transformation of the kinetic energy of electrons into the energy of microwave oscillations was estimated.

The high-frequency wave propagation in homogeneous and inhomogeneous plasma at frequencies close to electron cyclotron resonance has been laboratory simulated. In the experiment, the electron cyclotron frequency is higher than the plasma frequency but lower than the radiation frequency, which corresponded to the conditions of the propagation of auroral kilometric radiation in the Earth’s magnetosphere recorded by high-orbit satellites at a large distance from the source region. The features of channeling of modes of magnetoplasma in an artificial magneto-oriented density duct with reduced density are studied. Experimental results show that plasma irregularities with transverse dimensions smaller than the wavelength in vacuum are effective channels for the transfer of fast waves along the magnetic field.