V. Ya. Savkin

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.

Operation and upgrade of diagnostic neutral beam injector RUDI at TEXTOR tokamak.

The status and the executing modernization of RUssian Diagnostic Injector (RUDI) are described. The ion source consists of arc plasma emitter and multiaperture four-electrode ion optical system. The present ion optical system with round beamlets is to be replaced by new slit apertures system for the reducing beam angular divergence in one direction. Due to enlarged dimensions and transparency of new ion optical system the extracted ion beam current will be by 50% increased. For the extension of beam pulse duration from 4 s to 8-10 s an optimized metal-ceramic arc-discharge channel is introduced. In the paper, the optical measurements results of beam parameters, including the profile of species distribution, scanned by custom-built multichannel spectroscope, are also 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.

Note: Arc discharge plasma source with plane segmented LaB6 cathode.

A plane cathode composed of close-packed hexagonal LaB6 (lanthanum hexaboride) segments is described. The 6 cm diameter circular cathode is heated by radiation from a graphite foil flat spiral. The cathode along with a hollow copper anode is used for the arc discharge plasma production in a newly developed linear plasma device. A separately powered coil located around the anode is used to change the magnetic field strength and geometry in the anode region. Different discharge regimes were realized using this coil.

Measurements of the radial profile of magnetic field in the Gas-Dynamic Trap using a motional Stark effect diagnostic

We have implemented a spectral motional Stark effect diagnostic for spatially localized measurements of magnetic field on the Gas-Dynamic Trap (GDT) magnetic mirror device. A 7 A, 40 keV diagnostic neutral hydrogen beam was focused to a current density of 0.25 A/cm2 in the measurement volume, allowing achievement of a radial resolution of 4.5 cm by viewing the beam at 45° with a well-defined light collection chord. The entire Stark spectrum was recorded by a spectrometer with a charge-coupled device detector. Analysis of the splitting of the components of the Stark spectrum directly results in a measurement of local |B|. When operated with deuterium heating neutral beam injection into a hydrogen target plasma, the GDT axial magnetic field is strongly perturbed by plasma diamagnetic effects. Thus, measurement of the radial profile of the perturbed magnetic field, combined with equilibrium modeling, will yield an estimate of the plasma beta.

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.

Computer System for Unattended Control of Negative Ion Source

The computer system for control of cw surface‐plasma source of negative ions is described. The system provides an automatic handling of source parameters by the specified scenario. It includes the automatic source start and long‐term operation with switching and control of the power supplies blocks, setting and reading of source parameters like hydrogen feed, cesium seed, electrodes’ temperature, checking of the protection and blockings elements like vacuum degradation, absence of cooling water, etc. The semi‐automatic mode of control is also available, where the order of steps and magnitude of parameters, included to scenario, is corrected in situ by the operator. Control system includes the main controller and a set of peripheral local controllers. Commands execution is carried out by the main controller. Each peripheral controller is driven by the stand‐alone program, stored in its ROM. Control system is handled from PC via Ethernet. The PC and controllers are connected by fiber optic lines, which prov...