This article describes the vacuum system of the KTM tokamak and also presents an algorithm for the technological mode of conditioning of the tokamak vacuum chamber (VC) performed before and during the experiment and its influence on production of glow discharges. The applied procedure of the vacuum chamber preparation, despite the atmospheric leakage in 2021, provided the possibility to develop conditions for conducting experiments at the KTM tokamak and to obtain discharges with the highest currents and discharge durations for this facility achievable at the time of writing of this article. As a result of the analysis of experimental data, the conditions have been established under which plasma discharges are not formed.

This article presents estimates of the operating region of the KTM tokamak in terms of plasma density and current for ohmic regimes on the basis of machine design parameters. The discharge parameters obtained in the experiments in 2021 are plotted on the diagram (n_e, I_p). The increase in operating values of plasma current and achievement of boundary values of stability factor q ~ 4 are mentioned. It has been demonstrated that progressing into the region of higher plasma currents in the implemented density range leads to achievement of the limit in development of beams of accelerated electrons. Accordingly, the increase in operating plasma density is one of the aims of the next experimental campaign at the KTM tokamak.

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.

In modern tokamaks, plasma with a vertically elongated cross section is created; however, this configuration is unstable with respect to the vertical position of the plasma, and control systems for the vertical position of the plasma are necessary for the operation of such tokamaks. An important parameter characterizing the capabilities for controlling the vertical position of the plasma is the controllability region. This article assesses the controllability region of the plasma in the KTM tokamak using an HFC coil, taking into account limitations from the power supply. To obtain this assessment, the plasma equilibrium was reconstructed from experimental signals of the tokamak, and a model of plasma motion was constructed on the basis of the reconstructed equilibria. Subsequently, a current control system was simulated for the HFC powered by a voltage inverter in a pulse-width modulation (PWM) mode. The calculated lower estimate of the plasma controllability region was 23 cm, which is sufficiently large for a tokamak with a small plasma radius of 45 cm, and demonstrates the potential for creating an effective plasma position control system using the HFC coil in the KTM tokamak.