Yu. V. Kovalenko

Confinement of Hot Ion Plasma with β = 0.6 in the Gas Dynamic Trap

Abstract A so called vortex confinement of plasma in axially symmetric mirror device was studied. This recently developed approach enables to significantly reduce transverse particle and heat losses typically caused by MHD instabilities which can be excited in this case. Vortex confinement regime was established by application of different potentials to the radial plasma limiters and end-plates. As a result, the sheared plasma flow at periphery appears which wraps the plasma core. Experiments were carried out on the gas dynamic trap device, where hot ions with a mean energy of Eh ≈ 9 keV and the maximum density of energetic ions nh ≈ 5·1019m-3 were produced by oblique injection of deuterium or hydrogen neutral beams into a collisional warm plasma with the electron temperature up to 250 eV and density nw ≈ 2·1019m-3. Local plasma β approaching 0.6 was measured. The measured transverse heat losses were considerably smaller than the axial ones. The measured axial losses were found to be in a good agreement with the results of numerical simulations. Recent experimental results support the concept of the neutron source based on the gas dynamic trap.

Development of a multichannel dispersion interferometer at TEXTOR

The design and main characteristics of 14-channel dispersion interferometer for plasma profile measurement and control in TEXTOR tokamak are presented. The diagnostic is engineered on the basis of modular concept, the 10.6 microm CO(2) laser source and all optical and mechanical elements of each module are arranged in a compact housing. A set of mirrors and retroreflectors inside the TEXTOR vacuum vessel provides full coverage of the torus cross section with 12 vertical and two diagonal lines of sight, no rigid frame for vibration isolation is required. Results of testing of the single-channel prototype diagnostic and the pilot module of the multichannel dispersion interferometer are presented.

Electron Cyclotron Resonance Heating Experiment in the GDT Magnetic Mirror: Recent Experiments and Future Plans

Abstract A system for electron cyclotron resonance plasma heating (ECRH) has been recently installed at the GDT (Gas Dynamic Trap) facility at Budker Institute. The system is based on two 5.5-mm gyrotrons and is designed to deliver two microwave beams with total power of 700 kW and X-mode polarization that are absorbed at the fundamental cyclotron harmonic. A significant increase of basic plasma parameters (energy content, electron temperature, neutron flux) during the injection of microwave radiation has been registered. In particular, the on-axis electron temperature was increased from 200 eV to 600 eV in several shots with ECRH, which establishes a new record for this class of magnetic installation.

The GDT Experiment: Status and Recent Progress in Plasma Parameters

Abstract This paper presents a brief review of experimental results obtained on the Gas Dynamic Trap (GDT) device during the last few years. Special attention is paid to the problems of longitudinal plasma confinement and suppression of transverse transport caused by magnetohydrodynamic instabilities in mirror traps with an axisymmetric magnetic field configuration. We also consider problems of auxiliary electron cyclotron resonance heating in the GDT plasma. Electromagnetic fluctuations driven by anisotropic high pressure plasma in GDT will be discussed as well as influence of these fluctuations on plasma confinement.

ECR Heating System for the Gas Dynamic Trap

Physics and engineering aspects of a system for electron cyclotron resonance heating (ECRH) at the magnetic mirror device Gas Dynamic Trap (GDT, Budker Institute, Novosibirsk) are presented. This system based on two 450 kW/54.5 GHz gyrotrons is aimed at increasing the electron temperature up to the range 250-350 eV for improved energy confinement of hot ions. The basic physical issue of the GDT magnetic field topology is that conventional ECRH geometries are not accessible. The proposed solution is based on a peculiar effect of radiation trapping in inhomogeneous magnetized plasma. Under specific conditions, oblique launch of gyrotron radiation results in generation of right-hand-polarized (R) electromagnetic waves propagating with high N∥ in the vicinity of the cyclotron resonance layer, which leads to effective single-pass absorption of the injected microwave power. In the present paper, we investigate numerically an optimized ECRH scenario based on the proposed mechanism of wave propagation and discuss the design of the ECRH system, which is currently under construction at the Budker Institute.

Recent progress of plasma confinement and heating studies in the gas dynamic trap

The paper includes a brief overview of previous researches on the stabilization of MHD instabilities, study of micro-instabilities, and demonstration a tangible increase of the electron temperature with application of auxiliary ECR heating. A review of the results of recent researches related to application of microwave radiation for plasma generation, and plasma heating in the GDT device is presented. The paper summarizes also recent results of researches that oriented on study of expander physics.

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.

Magnetic Measurements at the GDT Facility

Plasma generated electromagnetic oscillations at the frequency an order ion-cyclotron have been investigated in the high energy content regimes of GDT operation. That waves are found to be an Alfvén ion-cyclotron instability. The microinstability threshold scaling law has been defined: with increase of the plasma column radius to Larmor radius ratio the threshold value of the diamagnetism in the midplane decreases. It qualitatively matches the theoretical calculations.

Measurement of Plasma Density in Modern Fusion Devices by Dispersion Interferometer

Abstract We propose to use dispersion interferometer for measurement of plasma density and control of plasma position on present and future fusion devices. Distinguishing feature of this scheme is probing of plasma on two wavelengths. Short-wave radiation is formed by method of frequency fundamental radiation doubling. Probing first and second harmonics rays are combined spatially at the same time. It allows to create interferometer which is sensitive only to dispersion of studied medium and weakly sensitive to vibration of optical elements. Designs of the optical system dispersion interferometer and results of plasma density measurements on GDT mirror and TEXTOR tokamak are presented.

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.