Table of contents

This issue of Journal of Physics: Conference Series includes 16 articles submitted by the participants of the XLVIII International Zvenigorod Conference on Plasma Physics and Controlled Fusion (March 15–19, 2021). The conference is named after the town of Zvenigorod, Moscow region, where it has been held annually for 48 years. More than 650 scientists took part in the conference this year, and among them, 11 participants were from foreign scientific institutions. The papers presented and discussed at the conference showcase a wide range of topical issues in the field of plasma physics.

Leading foreign scientists have participated in Zvenigorod conferences from the very first time they were organized. They were invited by the conference organizers to give talks on the challenging problems of plasma physics. By now, several dozen of foreign scientists from the USA, Europe and Japan take part in the conference annually. They represent the leading research centers working in different fields of plasma physics.

List of International Advisory Board, Programming Committee, Organizing Committee, Invited Speakers, Organizing Institutions, Sponsors are available in this pdf.

The XLVIII Zvenigorod International Conference on Plasma Physics and Controlled Fusion (ICPAF 2021) used the following peer review procedure:

• Type of peer review: Single-blind

• Describe criteria used by Reviewers when accepting/declining papers: the paper should have been presented and discussed during one of the sections of the ICPAF 2021 conference; the objective and the problems stated in the paper should be relevant, the obtained results should be new and valid, the conclusions should be justified, the citations of the previous research should be correct, and the paper should be formatted according the Guidelines of Authors of IOP Publishing.

The authors were given the opportunity to resubmit their paper after revision.

• Conference submission management system: the number of participants did not warrant the use of automatic management system, therefore, the papers (and, previously, abstracts) were managed manually.

• Number of submissions received: 17

• Number of submissions sent for review: 17

• Number of submissions accepted: 16 (two of those, after significant revision)

• Acceptance Rate (Number of Submissions Accepted / Number of Submissions Received × 100): (16 / 17) × 100% = 94%

• Average number of reviews per paper: 1

• Total number of reviewers involved: 3

• Any additional info on review process (e.g., plagiarism check system): none

• Contact person for queries:

Name: Ms. Elena V. Voronova

Affiliation: Prokhorov General Physics Institute of the Russian Academy of Sciences

Email: voronova@fpl.gpi.ru

The effect of the high-power ECRH on the quasi-coherent (QC) mode in the plasma of the T-10 tokamak with the magnetic field B_t = 2.2 T, plasma current I_pl = 230 kA and chord-averaged electron density <n_e> ≈ 1⋅10¹⁹ m^-3 is discussed. The most pronounced changes appear in the core plasma region with r < 0.5a. For the ECRH power P_ECRH = 2.2 MW causing the appearance of the positive radial electric field ${{\rm{E}}}_{{\rm{r}}}^{{\rm{EC}}}=+20{\rm{V}}/{\rm{cm}}$ (in the OH stage, the occurring field is ${{\rm{E}}}_{{\rm{r}}}^{{\rm{OH}}}=-75{\rm{V}}/{\rm{cm}}$), the mean frequency of the QC-mode gradually decreases from ${f}_{{\rm{QC}}}{}^{{\rm{OH}}}=80-100{\rm{kHz}}$ (in the OH stage) to ${f}_{{\rm{QC}}}{}^{{\rm{EC}}}=20{\rm{kHz}}$, and its frequency spread Δf_QC decreases from ${\rm{\Delta }}{f}_{{\rm{QC}}}{}^{{\rm{OH}}}=\pm 50{\rm{kHz}}$ to ${\rm{\Delta }}{f}_{{\rm{QC}}}{}^{{\rm{EC}}}=\pm 10{\rm{kHz}}$. For the ECRH power P_ECRH = 1.7 MW and weak negative radial electric field (${{\rm{F}}}_{{\rm{r}}}^{{\rm{EC}}}=-20{\rm{V}}/{\rm{cm}}$), the mean frequency decreases to ${f}_{{\rm{QC}}}{}^{{\rm{EC}}}=40{\rm{kHz}}$, and the frequency spread becomes ${\rm{\Delta }}{f}_{{\rm{QC}}}{}^{{\rm{EC}}}=\pm 30{\rm{kHz}}$. After the ECRH-induced drop, the QC-mode mean frequency increases with increasing line-averaged density.

Active charge exchange spectroscopy will be used for measuring the ion temperature, density and rotation velocity of the ITER plasma. Because of the halo effect, the measurement accuracy can get worse. In this paper, the active spectroscopy measurement errors caused by the halo effect are estimated for ITER. The estimates were performed using the Simulation of Spectra (SOS) code. According to the simulation results, the halo effect decreases the density measurement accuracies by less than 4% and 1% for the impurity and bulk ions, respectively, and the measurement errors for the temperature and velocity are less than 1%. It was also obtained, that the halo effect can decrease the active spectroscopy spatial resolution by 1.5 and 2.5 cm for impurities and bulk deuterium atoms, respectively. The measurement errors were also estimated for determining the deuterium-to-tritium concentration ratio.

The small university-scale tokamak GOLEM equipped with the electric and magnetic probes becomes a test bench for studying the plasma turbulence and Zonal Flows, which are the essential processes affecting the plasma confinement. The broadband (f_BB < 250 kHz) magnetic turbulence was detected for the first time using the Mirnov probes. The two-dimensional (frequency–wavelength) Fourier power spectra S(k, f) of the magnetic turbulence indicate the turbulence poloidal propagation. The long-range correlations (LRC) between the signals of magnetic and electric probes installed at different toroidal cross-sections were detected in the low-frequency range (f_LRC < 60 kHz), which is similar to the plasma potential LRC range observed in other devices.

Soft X-ray plasma emission spectra were measured at the L-2M stellarator in the OH regime with low plasma density (n_e ∽ 10¹⁹ m^-3) and temperature (∽200–400 eV). It is demonstrated that on the X-ray spectra, there is no dip in the energy range corresponding to several thermal energies of electrons or higher. This means that at the L-2M stellarator, the "X-ray dip" phenomenon is not observed, as it was at the T-11M tokamak. In the axial ECRH regime at the heating power P_ECRH = 250 kW, the soft X-ray spectra of plasma emission were also measured. In this case, the X-ray dip phenomenon was not observed too.

The experimental results are presented from the experiments on the high-power electron cyclotron resonance heating (ECRH) of the current-free plasma with the power 200–500 kW (the specific power was 0.8–2 MW/m³). The spontaneous transport transitions were observed that resulted in an increase in the plasma density and energy. At the ECRH powers exceeding 150 kW, the processes are observed accompanied by the abrupt changes in the plasma edge parameters, while the core plasma parameters change only slightly. At the ECRH powers exceeding 400 kW, a jump-like increase in the plasma density and energy is observed. At a power of approximately 500 kW, the regime was obtained, in which at time of transition, the plasma energy and lifetime increase by 20%, despite a decrease in the electron temperature. At the same time, at heating powers up to 700 kW, the energy lifetime corresponds on average to the L-2M single-machine stellarator scaling.

The system has been developed for initiating and quenching the arc discharges by means of moving apart the initially closed electrodes at a variable speed. The experimental studies of the extensive high-current electric arc discharges were performed in the atmospheric air. By means of optimizing the process of moving apart the electrodes and matching their sizes and shapes, it is possible to increase up to ten times the length of the stably burning high-current arc without using the external magnetic field for its stabilization.

Propagation of the low-pressure surface-wave-sustained microwave discharge becomes unstable in the final stage of the discharge development. The development of such instability is associated with the field perturbations in the region near the discharge front. The discharge development becomes stochastic that manifests itself in partial decays, jumps and stops of the front propagation. By means of setting the configuration of the field created by the discharge along its propagation path, it becomes possible to control the discharge development. The discharge propagation was studied in the standing wave field between two metal mirrors. It was found that between the mirrors, the discharge propagates irregularly in the form of successive plasma bunches with the λ/2 length.

The studies of neutron emission in Z-pinches are analyzed in this work. The available ideas concerning the nature of neutron emission are contradictory. The terms "fusion mechanism" and "acceleration mechanism" used in publications concerning neutron generation are unable to explain all characteristic properties of Z-pinches observed experimentally. The physical grounds for using these mechanisms are also not fully confirmed. The revision of the existing theoretical approaches makes it possible to reveal new methods for studying Z-pinches, such as the studies of considerable energy release in the Z-pinch plasmas due to the development of MHD instability, as well as the studies of the energy transport during which the most of the magnetic field energy is transported directly to ions, without the participation of the electron component.

Electron beam generators operating directly in gaseous medium are a promising means of solving several technological problems. In order to solve these problems, it is required to broaden the working pressure range of these generators. Investigations of the current-voltage characteristics of the generator, which was modified to supply the substitutional gas into the discharge gap, showed that by means of blowing helium at a pressure of 2.6 kPa into air medium at a pressure of 2.5 kPa, it is possible to reach a voltage of 5.5 kV at a current of 23 mA. The substitutional gas flows have been determined that ensure the stable generator operation at air pressures in the range from 1 to 2.5 kPa.

Helicon plasma source is being developed at the Budker Institute of Nuclear Physics SB RAS, Novosibirsk. The parameters are studied of the plasma confined in a mirror trap configuration of the magnetic field at an operating frequency of 13.56 MHz. For matching the antenna impedance and generator load, the Π-type matching box was designed and successfully tested at powers of 20–25 kW. The low reflected power (1–2%) was obtained, as compared to that for the L-type matching network used previously (the reflected power was more than 15% at the generator output power of 18 kW). The triple Langmuir probe is used to determine the plasma density. The plasma resistive characteristics were determined using the Rogowski coil measuring the RF antenna current. In the experiments, the plasma with a density of ∽5⋅10¹² cm^-3 and an electron temperature on axis of 10 eV was obtained, and the RF power transfer efficiency was ∽85% at the RF power of 25 kW.

Cold electric discharge plasma can be in direct contact with the water solution being treated. Active species are generated directly in the discharge and penetrate into the solution through the gas-liquid interface. Hot plasma of pulsed electric discharge can remotely affect an object without causing any thermal damage to it, e.g., by means of irradiating it. The effect of light penetrating into the solution is fundamentally different from the effect of cold plasma which is in contact with the solution: cold plasma already contains all active species, while radiation does not contain any of them. The species are generated in water solution when radiation passes through it. It is shown that the penetration depth of radiation into distilled water can be considerable. The method for activated water production based on the effect of plasma radiation can be more advantageous than that based on its treatment with cold plasma.

The results are presented from studies of the high-voltage pulse-periodic surface spark discharge propagating along the water-gas interface. In the case of CO₂ or CO₂:H₂ mixture used as gaseous medium, the plasma-chemical conversion of CO₂ to carbon monoxide CO was also studied. In the experiments, we used the generator with reservoir capacitor energy of 1.6 J, a voltage of 20 kV, and pulse duration of 2–3 μs. The average velocity was determined of the discharge propagation along the water surface in the CO₂, CH₄ and Ar atmospheres. It was shown that the leader velocities in the CO₂ and CH₄ atmospheres coincide, and they turned out to be 3–4 times lower than that in the Ar atmosphere. The integrated emission spectra are presented of the discharge in the CO₂ atmosphere, in which the lines corresponding to CO₂, CO, H_α, H_β, and OI are distinguished. The electron concentration in the discharge channel was N_e = 10¹⁷ cm^-1. The dynamics of conversion of CO₂ to CO was traced at different energies inputted into the discharge. For the discharges in the atmospheres of CO₂ and CO₂:3H₂ mixture, the degrees of conversion were 24 and 61%, respectively. And in the quasi-linear stage, the energy efficiencies of conversion were ∽13 and ∽6 eV per molecule for the CO₂ and CO₂:3H₂ atmospheres, respectively.

In this work, we investigated the energy input of high-power gyrotron microwave radiation into mixtures of Al₂O₃/Pd powders for various concentrations of the initial components. It was found that the absorption coefficient of microwave radiation as a result of the start of microdischarges (breakdowns) n the powder mixture depends on in the Pd concentration in the initial mixture with aluminium oxide (Al₂O₃) in a complex way. It is shown that the addition of a catalyst, carborane (C₂H₂B₈), with a concentration equal to 10% of the mass of the initial Al₂O₃/Pd mixture increases the number of breakdown in the experimental session.

Nonlinear waves are studied in the framework of the magnetic hydrodynamics with allowance for the Hall effect (HMHD). Along with the classical magnetic hydrodynamics (MHD), this model is one of the widely used models in the plasma theory. When solving the problem in the framework of HMHD, in addition to the usual MHD parameters, it is possible to obtain the electron velocities. In the problems considering the systems of electrodes, the Hall effect allows to distinguish one or another type of polarity. Also, the waves in HMHD (as opposed to MHD) have dispersion. One-dimensional waves are considered propagating in the finite-temperature plasma along the magnetic field. It is shown that there can be both solitary waves and periodic solutions, and their properties are investigated.

The mathematical model is proposed of the magnetic tornado in magnetohydrodynamic plasma. This model is based on the equations of mechanics of continua and the Maxwell electrodynamics. Two specific examples are considered to study the cross-effect of the plasma and magnetic field dynamics, which may result in the occurrence of the magnetic tornado. The plasma-magnetic field interaction is of particular interest in the case of the ideal plasma motion along the magnetic field lines. In this case, the studies of the magnetic tornado can be reduced to the purely hydrodynamic consideration of the tornado occurrence in atmospheric air. The relevant numerical results obtained theoretically confirm the existence of vortex formations identified with the magnetic super-tornados observed in the chromosphere of the solar plasma.

It is shown that in quantum optics of extended media, when constructing the Feynman graphs, a specific unitary transformation can be used to avoid the questionable procedure of transition to the thermodynamic limit. Thereby, the calculations can be made considerably more precise, and there occurs the possibility of discovering new optical phenomena.