T. D. Akhmetov

Model of Neutral-Beam Propagation in a Duct With Scrapers

A model of propagation of a neutral beam with geometric focusing and angular divergence in a duct is described. An algorithm is presented for calculation of a 2-D current-density profile at an arbitrary distance from a flat circular emitter with the account of multiple plane scrapers in the beam duct, which limit cross section of the beam. Numerical code is applied to calculation of current-density profiles and power loads on circular scrapers due to neutral particles.

Production and Study of a High-Temperature Plasma in the Central Solenoid of the AMBAL-M Device

Results are presented from experiments on the production and study of a hot dense plasma in the central solenoid of the AMBAL-M fully axisymmetric ambipolar magnetic confinement system. The hot plasma in the solenoid and end cell is produced by filling the system with a thermally insulated current-carrying plasma stream with developed low-frequency turbulence. The plasma stream is generated by a gas-discharge plasma source placed upstream from the magnetic mirror of the solenoid. As a result, an MHD-stabilized plasma with a length of 6 m, a diameter of 40 cm, a density of 2×1013 cm−3, an ion energy of 250 eV, and an electron temperature of 60 eV is produced in the central solenoid. It is found that, in the quiescent decay phase, transverse plasma losses from the solenoid due to low-frequency oscillations and nonambipolar transport are rather small and comparable with the classical diffusion losses.

Auxiliary Electron Heating and Plasma Control in GDT Device with Electron Beam: The Results of Initial Experiments

The results of preliminary experiments with relatively low power electron beam interacting with plasma in GDT device are discussed. The beam was injected into the device through one of the end mirrors. In the experiments, the problems related to the beam transport through the magnetic mirror were addressed.

ICR heating in an axisymmetric solenoid

The density and diameter of plasma obtained In the central solenoid of the fully axisymmetric ambipolar mirror trap AMBAL-M are sufficient enough for ioncyclotron heating using fast waves, which provides plasma heating at the axis. At present the experiment on such ICR heating of the solenoid plasma is under preparation. The heating will be carried out two semiloop antennas installed in the end of the solenoid. For protection from the impact of the edge plasma, the antennas are equipped with Faraday shields and graphite limiters with slanted slits.

Gas Puffing into the AMBAL-M Solenoid Plasma

The central solenoid of AMBAL-M was filled with a turbulent plasma stream generated by a source located outside the entrance magnetic throat, the plasma ~0.4 m in diameter, with density ~1.5·1013 cm-3, electron temperature ~50 eV and ion energy ~200 eV was obtained. Additional hydrogen puffing allowed plasma density increase. The plasma with a cold component from ionized gas and charge exchange ions was heated by electrostatic oscillations produced by the working source. At optimized gas puffing the plasma density was increased to 5·1013 cm-3 without substantial reduction of the ion temperature. No big differences in plasma properties were found between gas puffing through a gas-box and a ceramic tube. The plasma density increment was shown to depend only on the total amount of the injected gas. The experimental optimization was made for different values of solenoid magnetic field taking the diamagnetism into account. Neutral hydrogen distribution in the solenoid vacuum chamber and recycling rate were estimated from data of fast inverse magnetron gauges constructed in BINP.

RF discharge-based plasma emitter

An injector of hydrogen atoms for plasma diagnostics in modern tokamaks has been developed at the Budker Institute of Nuclear Physics (Novosibirsk). The ion source of the injector produces a proton (helium ion) beam with a current of up to 2 A (1 A), an ion energy of up to 55 keV, a beam divergence of ∼0.6\deg, and a pulse duration of up to 10 s. An RF discharge-based plasma emitter, which is one of the main parts of the ion source, is described. The emitter diameter is 72 mm, the ion current density is 120 mA/cm2, and the inhomogeneity of the current density is ±6%. The beam is formed by a four-electrode ionoptical system with 163 round apertures. At a current of 2 A, the ion beam consists of 67% protons, 18% H2+ ions, and 15% H3+ ions, the total content of heavier ions in the beam being no higher than 2–3%.

Measurements of the electron distribution function in the AMBAL-M startup plasma by an electrostatic analyzer

The electron distribution function over longitudinal energies in the startup plasma of the end cell of the AMBAL-M device is measured with a small-size movable electrostatic analyzer. It is found that, in the region where a substantial longitudinal current flows, the electron distribution function over longitudinal energies has a plateau in the 150–350-eV energy range.

Behavior of the initial plasma in AMBAL-M

Recent experimental results on the initial plasma behavior in the AMBAL-M solenoid are reported. Attempts of forced destabilization and stabilization of the solenoid plasma by varying magnetic field structure in the solenoid to create a local mirror trap and divertor are described. Observations of unstable MHD plasma behavior after cut-off of the essentially stabilizing plasma gun are presented.

Experiments on the AMBAL-M Central Solenoid

Experimental studies of a high-β plasma in a long solenoid of the axisymmetric mirror trap AMBAL-M are being continued. In order to increase the density of the initial warm plasma generated by a plasma source, additional gas puffing was used. Optimization of gas puffing through a gas-box and reduction of magnetic field in the solenoid aimed at β enhancement were performed. Another way of increasing β consists in forming a small local mirror-trap in the solenoid where the plasma volume is much smaller than that of the whole solenoid plasma, and it is easier to achieve high β-values. A preliminary result on the local-mirror-trap experiment is presented. Further steps on β increase in the solenoid are proposed and discussed.