Vol 50, No 1 (2024)

The physics of confinement of a rotating plasma in a magnetic field with linear helical symmetry is being studied at the Institute of Nuclear Physics SB RAS on the open SMOLA trap. An indicator of the quality of confinement is the plasma flow velocity in the system. The paper describes the applied diagnostics based on the Mach probe under conditions of non-magnetized plasma, which made it possible to determine the longitudinal flow velocity in experiments. The measured longitudinal flow velocity was (0.5–5) · 10⁶ cm/s in various operating modes of the installation. The dependence of the speed on the magnitude of the magnetic field corrugation is discussed. A reverse flow of trapped particles returning to the containment zone has been detected.

Using computer simulation, the sputtering coefficients of Be and W targets, promising materials for the first wall and divertor in the ITER tokamak, are calculated in a wide range of incident atom energies 10–100 000 eV. The following atoms were chosen as projectiles: H, D, T, He, Be, C, N, O, Ne, Ar, W. A strong influence of the surface profile on the results obtained is shown. The limiting cases of a planar potential barrier (smooth surface) and a spherical potential barrier (rough surface) are considered. Data on the average energy and angular distributions of sputtered atoms were obtained, which are necessary for calculating the influx of impurities into the tokamak plasma. The influx of wall material atoms into the ITER tokamak plasma is estimated when the wall is sputtered by flows of fast deuterium and tritium atoms leaving the plasma.

The effect of two-dimensional localization of an upper hybrid (UH) wave in a magnetic island is found. The influence of this effect on the threshold and saturation level of the absolute parametric decay instability of an extraordinary wave, which results in the excitation of two two-dimensional localized UH waves, is investigated.

At the S-300 generator (2 MA, 400 kV, 100 ns), the appearance of superhard X-ray radiation was observed during magnetic compression of cylindrical nested aluminum arrays with a linear mass of ~350 μg/cm, consisting of aluminum wires with a diameter of 15 μm. At the final compression phase of the arrays, a compact pinch is formed, consisting of a large number of hot spots located along the axis. This phase is accompanied by the emission of soft X-rays with a duration of ~10 ns. Simultaneously with the pulses of soft X-ray radiation, superhard X-ray radiation with an energy exceeding 450 keV was discovered. Superhard X-ray radiation was measured with shielded scintillation detectors with lead filters 20–70 mm thick. The main cause of overvoltage on the plasma column appears to be constriction instability.

A description is given of low-frequency nonlinear dust acoustic waves in Saturn’s dusty magnetosphere, which contains electrons of two types (hot and cold) obeying the kappa distribution, magnetospheric ions, and charged dust particles. For the corresponding conditions, the derivation of the Zakharov–Kuznetsov equation is given, which describes the nonlinear dynamics of dust acoustic waves in the case of low frequencies and a pancake-shaped wave packet along an external magnetic field. It is shown that under the conditions of Saturn’s magnetosphere there exist solutions of the Zakharov–Kuznetsov equation in the form of one-dimensional and three-dimensional solitons. Possible observations of the considered solitons in future space missions are discussed.

In this work, we carried out studies of the properties of an inductive RF discharge placed in a magnetic field with an induction of less than 70 G at frequencies of 2, 4 and 13.56 MHz. Experiments have shown that when operating at frequencies of 2 and 4 MHz at low powers of the RF generator, the range of existence of the discharge is limited by large magnetic fields. The efficiency of RF power input η non-monotonically depends on the magnitude of the magnetic field. The position of the main maximum η shifts to the region of higher B with increasing frequency, power of the RF generator and argon pressure, and at the same time the maximum broadens. An increase in frequency, power and argon pressure is accompanied by an increase in the absolute values of η. When operating at a frequency of 4 MHz, in addition to the main maximum η, a local maximum appears in the region B 35–70 G. With increasing pressure, a shift in the position of the local maximum and its smoothing is observed. Comparison of experimental data with calculated data allows us to conclude that the local maximum of plasma density observed at weak magnetic fields is associated with resonant excitation of waves in the plasma source. At a frequency of 2 MHz, the excited wave is close to a transverse helicon, and at a frequency of 13.56 MHz, its properties approach the Trivelpiece–Gold wave.

The concept of equipotential length of positive quasi-stationary streamers is introduced as a criterion for assessing their degree of isolation. The equipotential length of positive critical streamers (streamers moving in the minimum electric field sufficient for the unrestricted propagation of a positive streamer) in the normal atmosphere is defined, both for individual streamers and those forming a thin bundle of streamers. The dependence of the equipotential length of positive quasi-stationary streamers on external field, velocity, radius, and electron concentration in the streamer head is investigated. A criterion is proposed for analytical models of quasi-stationary streamers, providing an additional independent equation to the system of equations describing the dynamics of quasi-stationary streamers, valid only for critical streamers. The insignificance of the influence of electrodes located at a distance greater than its equipotential length from the streamer head on the quasi-stationary streamer is proven, confirming the adequacy of using the equipotential length to assess the isolation of positive streamers.

Numerical modeling of the dynamics of a discharge initiated by a high-power femtosecond laser pulse in air at atmospheric pressure in pre-breakdown fields was carried out. Calculations were conducted within the framework of a 1D-axisymmetric model that describes the evolution of the radial profiles of the main parameters of the discharge under study. The model includes a system of reaction that determine gas heating and a detailed description of the kinetic processes in a given discharge, as well as a system of gas-dynamic equations to describe the expansions of the heated channel. The results of calculations of the breakdown time of the discharge gap are conсistent with the measurement data over the entire studied range of electric field strengths, E = 9–17 kV/cm. It is shown that one of the key factors determining the evolution of the parameters of a given discharge is the rate of gas heating.

We determined critical values for the ignition voltage and magnetic induction for a self-sustained plasma discharge in crossed electric and magnetic fields, both at inert gases and in their mixtures. As parameters that enabled to visualize igniting an E×B discharge, we used the ion current and the induction current derivative, and provided the temporal characteristics for the process. We found a double structure of the ion current (discharge current) during the ignition. The working media initial state for the discharge current first jump is a neutral gas, whereas the working media initial state for the second jump is plasma. A peak of ions originated within the near-cathode area is detected on the energy distributions of the ions obtained during the ignition. Also detected is a wide ion energy spectrum related to the discharge gap. We show a various discharge ignition character for Penning pairs, when the gas changes its role (main or admixture) in the mixture. The character is determined by features of forming the electric potential distribution in the near-cathode layer.