A. L. Solomakhin

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.

First results from the modular multi-channel dispersion interferometer at the TEXTOR tokamak

At the TEXTOR tokamak in Jülich, Germany, a modular dispersion interferometer was installed and operated for the first time. Equipped with four lines of sight, the line-integrated density could be measured in parallel at different major radii with a resolution of better than 3 × 10(17) m(-2). This paper will describe the setup and show the first measurement results. Among others, it was possible to detect the evolution of a disruption with a time resolution of 4 μs. The movement of the runaway beam following the disruption could be resolved spatially and temporarily.

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.

Electron cyclotron emission at the fundamental harmonic in GDT magnetic mirror

New electron cyclotron emission (ECE) diagnostics has been installed to facilitate the successful experiment of electron cyclotron plasma heating (ECRH) in a large open magnetic trap GDT at Budker Institute. The particularities of ECE in the vicinity of the ECRH frequency were studied experimentally for a broad range of discharge scenarios. The measured thermal emission has partly validated the existing physical conceptions about microwave plasma heating in the machine. Besides the expected emission of thermal electrons, a clearly resolved non-thermal ECE was observed which unambiguously confirmed the presence of suprathermal electrons driven by high-power microwave heating.

Dispersion interferometer based on CO2 laser

A dispersion interferometer based on CO2 laser for measurements of plasma line density in the gas dynamic trap (GDT) experiment has been developed with sensitivity min ~ 1·1013 cm-2, temporal resolution ~50 ns. The main advantages of the interferometer are compactness and low sensitivity to vibrations. The interferometer does not require specific vibration isolation structure and can be mounted directly on the working chamber of the plasma device. The above mentioned advantages have been successfully demonstrated in the Gas Dynamic Trap experiments.

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.

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.