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The Russian program for development of low aspect ratio tokamaks (spherical tokamaks) is presented. The urgency of the theme is conditioned by the results of theoretical research and experimental data obtained from small-scale installations where the direction has proved to be greatly promising. The present work describes a number of spherical tokamak projects governed by certain logic. The intended research is supposed to solve the issues of maintaining the advantages of such tokamaks for mega-ampere range installations, overcoming the current difficulties typical for such tokamaks, and, finally, considering the possibility of building an inexpensive compact thermonuclear reactor.

In the present paper, the results of the research into the behaviour of protective dielectric elements of the T-11M tokamak RF-antenna after four years of operation in working conditions are presented. In a modernized RF antenna, all its structural plasma facing metal elements are changed by graphite ones with a 40 µm thick boron carbide coating deposited from the gas phase, the lateral metal surfaces are protected by shields, 2 mm thick flat plates made from pyrolytic boron nitride [1]. For boronization of the vacuum chamber walls, a new manner based on the decomposition of deuterated carborane (C2B10D12) in helium glow discharge was used. After completion of work, the RF-antenna and all dielectric elements were investigated with a standard set of surface diagnostics (scanning electron microscopy, Auger electron spectroscopy, X-ray and neutron diagnostics, profilometer etc.). The analysis has shown that all protective elements after four years of work have kept the coating integrity as well as chemical a...

The Kazakhstan Tokamak for Material testing (KTM) is proposed as a test bench for plasma-facing components investigation. Special attention is devoted to divertor plates testing under powerful particle and heat flux deposition. There are two important pecularities of KTM, which make it a unique installation: - single null (SN) plasma configuration with moderate-to-low aspect ratio A=2, high elongation k 95 , 1.7 and megaampere level of plasma current IP ; creation of database for elongated plasma with A=2 can be an important "bridge" between databases on traditional tokamaks with A >2.5-3 and spherical tokamaks with A h 1.5-1.6; - special equipment is designed for manipulation with divertor plates (vacuum sluices, a divertor "table" inside the vacuum vessel, which can be shifted both in vertical and azimuth directions).

The TSP tokamak—Russian fusion project based on very powerful adiabatic heating by compression (900 MJ power supply per pulse)—was entered into exploitation in 1987. The study program with circular cross-section plasma was carried out on the machine from 1988 to 1992. The TSP tokamak program object lost urgency for today. So, modernization of TSP tokamak is planned as creation of new version of machine, which will allow from one hand to use the basic infrastructure of existing machine and unique systems of the pulse power supplies and on another hand to execute greatest possible amount of researches on the fusion basic problems. This modernization was named TSP-AST tokamak (TSP in the mode of advanced or adiabatical spherical tokamak). In the paper the purposes and tasks of the machine, basic parameters of operations regimes and plasma discharge scenarios are submitted. The design version of the basic units of machine (magnet, vacuum vessel) are shown. The calculations results of tensile strength of the machine basic units are given.

Results are presented from numerical calculations of the near fields of ICRH antennas in the quasisteady current approximation in two-dimensional geometry. The distributions of the vacuum electric and magnetic fields as well as of the surface current density in the antenna elements and inside the tokamak chamber are obtained. The electrotechnical characteristics of the antennas are analyzed numerically as functions of their geometric parameters.

Conceptual design and construction of the “TMA” tokamak is presented. TMA is a Tokamak of Minor Aspect ratio (A = 2) and elongated cross section k ≤ 2. It is planned to be created on the basis of existing TSP tokamak-complex at TRINITI, Troitsk, on a short time. Main parameters of installation are: toroidal field Bto≤2T, major plasma radius R = 0.7 m, minor plasma radius a = 0.35 m, plasma current Ip ≤ IMA, plasma elongation k ≤ 2, triangularity δ ≤ 0.7. Inductor flux of a value Δφ = ±0.5 V.s, plasma RF heating power PRF ≤ 9 MW. Duration of plateau of toroidal field is expected to be Δt = 2 s. Main goals of TMA are: study of moderate aspect ratio of elongated shaped plasma with divertor, achievement of a high bootstrap current, study of active controllable SOL plasma.

The paper deals with the main features of RF systems (P ≤ 5 MW, f ≤ 30 MHz) for ioncyclotron heating of plasma on the TSP tokamak. The systems are based on the principle of self-excitation of oscillations in a complex distributed circuit, including resonant antennas and feeders, with a powerful RF triode as the only nonlinear element. Two circuit configurations are discussed: 2 MW/I (2) antenna and 5 MW/4 antennas. The concept and design of a compact modul ar resonant antenna with high density of radiated power (P/S ≤ 5 KW/cm2) are examined. Results of computer simulation of RF oscillatory circuit parameters are presented.

The paper examines the possibility of the current drive (CD) and electron heating in the Volumetric Neutron Source (VNS) (tokamak with high neutron flux) by means of Lower Hybrid Waves (LHW), Ion B...

With the aid of a magnetic and an electric probe, turbulent fields (noise) in a magnetized plasma prepared according to the method of magneto-acoustic ionization have been measured. Presence of magnetic noise with a frequency maximum in the region of 12 MHz (?i??e) and low-frequency electric noise with a broad frequency spectrum increasing toward low frequencies and followed down to 80 kHz has been established. The magnetic noise can, by the nature of the frequency spectrum, be identified as free magneto-acoustic vibrations of a plasma column that are excited by non-linear interaction between the plasma and the power wave of the ionizing generator.The electric noise has both an azimuthal component characteristic of drift waves and an axial component with a phase velocity like ionic sound. Drift-wave excitation is associated with universal inhomogeneous-plasma instability, and ionic-sound excitation can be explained by both non-linear interactions of drift waves and non-stationary phenomena in the ionization process itself.

Magneto-sonic oscillations have been induced by a high power r.f. generator serving simultaneously for ionization and heating of a plasma. With the quasi-static magnetic field approaching 15 kOe magneto-sonic resonance was observed. The amplitude of the alternating magnetic field in the plasma attained a value of 150 Oe compared with an initial amplitude of 10–12 Oe in the absence of the plasma. The Q of the circuit dropped by more than an order of magnitude because of the presence of the plasma, but this gives no direct indication of true energy dissipation inside the plasma since experimental conditions did not exclude energy loss through open ends of the cylinder.