Stepan Krat

I. Plasma-wall interaction is currently considered one of the most significant groups of processes affecting performance of fusion devices with magnetic plasma confinement, such as tokamaks. The ch...

Experimental studies were performed on the use of HF waves in the ion cyclotron resonance (ICR) frequency range for plasma preionization in the MEPhIST-0 small spherical tokamak. The conditions of the resonant interaction of the ICR wave with plasma particles were described, and the main mechanisms of plasma formation using ICR waves were outlined. The results of preionization experiments were presented, in which the generator frequency, the level of the toroidal magnetic field, and the composition of the working gas were varied. It was shown that stable low-temperature plasma can be obtained in the MEPhIST-0 tokamak using ICR ionization.

Intrinsic and mutual inductances of the central inductor, the MEPhIST-0 tokamak electromagnetic system coils PF1–PF6, and the tokamak discharge chamber are determined in the frequency range from 50 to 15 000 Hz. It has been found that, in the low-frequency range up to ~200 Hz, in order to determine the mutual interference of the most strongly coupled coils, it is possible to represent the discharge chamber as one short-circuited turn inductively coupled with the coils of a poloidal system.

The effect of UV radiation on deuterium retention in codeposited lithium-deuterium layers has been investigated. The samples were obtained by sputtering a liquid lithium cathode with a deuterium plasma of a magnetron discharge. The deuterium content in the films was analyzed by in-vacuo thermal desorption spectroscopy. After deposition, the deuterium content in the films averaged D/Li = 15 at %. Irradiation with ultraviolet radiation led to the formation of additional low-temperature desorption peaks (T ~ 500 K), as well as to the disappearance of high-temperature peaks (T > 700 K) or to their shift to a lower-temperature region. In the future, the results obtained may form the basis for methods for detecting the places of predominant accumulation of lithium hydride in tokamaks, as well as facilitating the process of removing tritium from the internal elements of thermonuclear installations.

A diagnostic method for material transport (erosion and deposition) in the KTM tokamak vessel has been developed and tested for durations comparable to an experimental campaign. It is based on witness samples mounted in the tiles of the first wall of the tokamak vacuum vessel. It was found that the regions of greatest wall erosion are located near the equatorial plane and on the inner side of the upper dome. Deposition zones were identified on the outer periphery on the lower side of the chamber. Possible effects of conditioning and operational discharges on wall sputtering were considered.

The paper reviews the main mechanisms of hydrogen isotope accumulation in fusion devices: the implantation of particles from plasma into plasma-facing components (PFCs), followed by diffusion into the bulk of material, and capture into growing redeposited layers in areas of preferential deposition (co-deposition). The specific features of hydrogen isotope accumulation, depending on the selection of plasma facing material, are considered during the regular application of auxiliary coatings and the utilization of wall components based on liquid metals.

The parameters of the convective filamentary transport in the edge region of the small spherical tokamak MEPhIST-0 are estimated. To describe dynamics of the installation scrape-off-layer plasma, an electromagnetic two-fluid MHD model was employed. The operational parameters of the tokamak and their impact on the characteristics of turbulent plasma transport are discussed. Using the BOUT++ code, dynamics of isolated filaments were simulated under conditions corresponding to the edge region of the tokamak in various discharge scenarios. It is shown that, despite the compactness of the machine, it may be possible to create and study both electrostatic and electromagnetic regimes of anomalous edge plasma transport in the installation.