E. A. Vinitskiy

An absolute error in measuring the plasma electric potential using the heavy ion beam probe (HIBP) is estimated for the T-15MD tokamak. The main sources of error are analyzed, including the instability of voltage and the inaccuracy of its setting in the high-voltage power supplies of the accelerator and the energy analyzer, the uncertainty in the entrance angle of the secondary ion beam into the analyzer, the noise in the measurement path and the shot noise. The error is calculated for various modes of tokamak operation with the toroidal magnetic field of B_Т = 1.2–2.0 T and the chord-averaged electron density of n_e = (3–5) × 10¹⁹ m^–3 for different profiles of electron temperature and density. The radial plasma regions accessible to reliable potential measurement are determined. Two-dimensional distributions of the absolute error for both the average potential and its fluctuations are obtained. It is demonstrated that optimizing the analyzer plate voltage, which reduces the normalized difference in partial currents at the detector, reduces the overall measurement error by approximately a factor of four and substantially expands the sample volume.

The design of the MEPhIST-0 tokamak microwave interferometer and its system of data acquisition and processing are described. Examples of the time evolution of the linear electron density in MEPhIST-0 discharges are presented. The use of a phasemeter based on AD8302 detectors and digital post-processing of interferometer signals is compared. The beam refraction in the MEPhIST-0 chamber has been calculated. The possibility of plasma probing with a microwave interferometer for single- and two-pass configurations has been evaluated. It is shown that the transition to single-pass plasma probing allows the upper limit of the measured density to be significantly expanded (up to n₀ = 3 × 10¹⁹ m⁻³).

Aim: to determine the operating parameters of the toroidal magnetic field system (operating temperature, number of CORC cables, transport current value) of the MEPhIST-1 superconducting tokamak Materials and Methods: numerical calculation of the toroidal magnetic field of a tokamak was performed in the COMSOL Multiphysics software Results: magnetic field distributions were obtained for various values of the transport current flowing through the tokamak coil. The proportionality coefficients between the maximum magnetic field on the coil and the transport current, the operating magnetic field and the operating transport current were determined. Conclusion: the number of CORC cables required to achieve an operating magnetic field induction of 1 T has been determined: 7 at a temperature of 37.6 K and 6 at a temperature of 33.6 K. It has been shown that it is possible to achieve an operating field value of about 1.5T with 7 CORC cables when the temperature is lowered to 21.1 K.

The potential of utilizing a multiple cell array detector (MCAD) [8] has been demonstrated as an additional tool for correlation studies of density and poloidal field fluctuations in a plasma as a part of the heavy ion beam probe on the T-15MD tokamak. The optimum position and size of the MCAD have been found, and its cell size has been determined. Trajectories of probing particles have been calculated and the plasma region for measurements has been estimated for the toroidal magnetic fields B_T = 1.2, 1.5, 1.7, and 2.0 T. It has been shown that simultaneous measurements with the MCAD and the energy analyzer as the main measurement tool are possible, which allows the study of radial and poloidal spatial correlations of medium scale comparable to the small plasma radius. The spatial resolution of measurements and attenuation of the beam current signal during its passage through the plasma have been estimated.

In the MEPhIST-0 tokamak, toroidal magnetic coil system is implemented as a single continuous toroidal solenoid. This design ensures synchronized operation of each segment of the solenoid and requires only one power supply line to operate. However, this configuration has the downside of introducing stray vertical and radial magnetic field components, which result from the inclination of the solenoid segments. Such stray fields can be measured using an electron beam, as previously demonstrated in experiments on T-15, TEXTOR, KSTAR, and SST-1. This paper describes the parameters of the experiment and presents the main results obtained from the MEPhIST-0 tokamak. Two experimental techniques for measuring the vertical magnetic field are discussed: one with a change in the current direction in the toroidal solenoid and one without. The ratio of the stray vertical field to the toroidal field was found to be approximately 0.5%. The conducted experiments highlight the necessity of compensating for the stray vertical field using additional poloidal coils.