Vol 49, No 2 (2023)

A simulator of the kinetics of hydrogen isotopes recycling in plasma for the H-alpha diagnostics of the fuel ratio in a tokamak-reactor is proposed. The simulator represents a generalization of the well-known SXB method developed for determining the density of impurity flux from the vacuum vessel first wall into plasma from intensity of the spectral line of an atom or ion integrated with respect to wavelength within the spectral line width, to the case of an isotope mixture. The simulator allows on to determine the parameters of the fuel ratio for a mixture of deuterium and tritium hydrogen isotopes in real time (e.g., within 100 ms, according to the requirements specified for controlling the parameters of hydrogen isotopes in the ITER demonstration tokamak-reactor). The developed approach allows one to determined the flux density of hydrogen isotopes from the first wall into the plasma based on the results obtained by means of the high-resolution spectroscopy of the Balmer series lines without using the molecular spectra of hydrogen that are difficult to interpret. Calculations carried out for typical conditions of the edge plasma in the tokamak-reactors revealed that the flux density and fuel ratio in a certain part of the operational space of the reactor can be reconstructed with an acceptable accuracy. The role of the simulator for more accurate but more time-consuming interpretation of the measurements using the H-alpha diagnostics is discussed.

The mechanisms are discussed for generation of frequency spectra of anomalous scattering in not-dense plasma during microwave heating using the extraordinary wave at the second resonance harmonic. The developed theory is used to interpret the results of experiments on electron cyclotron resonance heating (ECHR) of plasma in the Wendelstein 7-X stellarator, in which both the Stokes and anti-Stokes frequency bands were observed, shifted up and down with respect to the microwave frequency. The explanation is given for the paradoxical excess of the amplitude of the anti-Stokes spectral component over the Stokes component amplitude, which was observed in a number of experiments.

The paper presents a one-dimensional gas-dynamic model that gives an opportunity to establish the necessary conditions for the emergence and determine characteristics of a stationary flow of a compressible continuous medium with nonlinear thermal conductivity, an example of which is a fully or partially ionized plasma, in the presence of a localized heat source with a given power.

The quasistatic approximation (QSA) is an efficient method of simulating laser- and beam-driven plasma wakefield acceleration, but it becomes imprecise if some plasma particles make long longitudinal excursions in a strongly nonlinear wave, or if waves with non-zero group velocity are present in the plasma, or the plasma density gradients are sharp, or the beam shape changes rapidly. We present an extension to QSA that is free from many of its limitations and retains its main advantages of speed and reduced dimensionality. The new approach takes into account the exchange of information between adjacent plasma layers. We introduce the physical model, describe its numerical implementation, and compare the simulation results with available analytical solutions and other codes.

The features of the experimental operation of the Sinus 550-80 plasma relativistic microwave generator (PRG) at different plasma densities are considered. Two plasma density values are considered, at which the central frequencies of the PRG output microwave radiation are 5.1 and 11.5 GHz. Numerical simulation demonstrates a decrease in the plasma electron density as a result of the action of a relativistic electron beam (REB) charge during the Cherenkov interaction and the appearance of an “ion background” during the PRG pulse. At low plasma densities, this can lead to a change in microwave generation conditions accompanied by a change in the broadband radiation to the narrowband one and a decrease in the radiation power. At the same time, at high plasma densities, when the microwave radiation is generated at high frequencies, the average amplitude of the electric field of the wave almost does not change during the REB pulse, and the radiation remains broadband. The analysis of the experimental and numerical simulation results is supported by estimates of the linear theory, which proves that the PRG works more stably at higher plasma density values.

A system of one-dimensional multigroup equations for the first three moments of the electron distribution function in the range of intermediate and high energies is derived. The system includes equations for the balance of concentration, flux density and momentum flux density of electrons and it is intended for numerical simulations of processes involving fast electrons in weakly ionized cold plasma.

The characteristics are determined of three-dimensional dust structures created in three dust traps formed in glow discharges and compared to each other. The following dust traps turn out to be stable in the applied magnetic field with induction of up to 2 T: the standing stratum, the region of the current channel contraction (inside the special dielectric insert), and the discharge region located in highly inhomogeneous magnetic field. For each of these dust traps, the geometric characteristics of three-dimensional dust structures formed and distinctive features of their rotation dynamics are presented, such as the longitudinal and transverse sizes (with respect to the magnetic induction vector), angular velocities, and their longitudinal gradients. Differences are analyzed in the experimentally obtained characteristics of three-dimensional dust structures formed in glow and RF discharges in the strong magnetic field.

The results of the first experiments on studying the volume production of negative hydrogen ions using a dense gasdynamic plasma of an electron cyclotron resonance (ECR) discharge sustained by continuous wave (CW) microwave radiation from a gyrotron (28 GHz/5 kW) are described. The ECR hydrogen discharge is ignited in a vacuum chamber placed in a magnetic field created by a system of two consecutive magnetic traps. The system parameters are optimized to obtain the maximum average current density of negative ions at the level of j = 25 mA/cm2. The study involves the determination of the negative ion production area, me-asurement of the current density dependences on gas pressure and microwave radiation power, and demonstration of potential optimization opportunities for extraction voltage.