V. V. Mishagin

Radio frequency ion source for plasma diagnostics in magnetic fusion experiments

Low-divergent quasistationary neutral beams are often applied in modern magnetic fusion devices as a diagnostic tool providing unique information about plasma parameters. The most important requirements of these beams are sufficiently large current and energy of the particles, so that the beam can penetrate to the plasma core. Also the duration of the beams must be long enough, i.e., close to that of a plasma discharge, amounting to at least a few seconds for large fusion devices. We developed a neutral beam injector for plasma diagnostics in the tokamak TEXTOR-94 which is capable of meeting these requirements. The maximum beam energy is 50 keV and the source operated in hydrogen delivers an ion current of up to 2 A with a pulse duration of up to 4 s. The low divergent beam (∼0.5°– 0.6°) is geometrically focused 4 m downstream from the source having a 1/e width of ∼ 70 mm at the focal point. The beam can be modulated with a frequency variable up to 500 Hz. The ion source plasma is produced by a radio freq...

Low energy, high power hydrogen neutral beam for plasma heating

A high power, relatively low energy neutral beam injector was developed to upgrade of the neutral beam system of the gas dynamic trap device and C2-U experiment. The ion source of the injector produces a proton beam with the particle energy of 15 keV, current of up to 175 A, and pulse duration of a few milliseconds. The plasma emitter of the ion source is produced by superimposing highly ionized plasma jets from an array of four arc-discharge plasma generators. A multipole magnetic field produced with permanent magnets at the periphery of the plasma box is used to increase the efficiency and improve the uniformity of the plasma emitter. Multi-slit grids with 48% transparency are fabricated from bronze plates, which are spherically shaped to provide geometrical beam focusing. The focal length of the Ion Optical System (IOS) is 3.5 m and the initial beam diameter is 34 cm. The IOS geometry and grid potentials were optimized numerically to ensure accurate beam formation. The measured angular divergences of the beam are ±0.01 rad parallel to the slits and ±0.03 rad in the transverse direction.

Neutral beam injector for active plasma spectroscopy

A diagnostic beam system has been developed for the RFX reversed field pinch, Padova, Italy. Currently the system is loaned to Alcator C-mod, MIT, Boston. The system is primarily used for measurement of the ion temperature by charge-exchange recombination spectroscopy and for magnetic field measurements via motional Stark effect. The system comprises an ion source, beam duct equipped with vacuum pumps and various diagnostics of the beam. The ion source provides 50 keV, 5 A hydrogen beam. Ions are extracted from a plasma created by an arc-discharge source and, after accelerating and focusing, are neutralized in a gas target. A plasma emitter, which is formed by collisionless expansion of a plasma jet on to the grids, has low perpendicular ion temperature. These results are in rather low (0.01 rad) angular divergence of the extracted ion beam. The grids of ion optical system are spherically curved providing geometric focusing of the beam at a distance 4 m. Current density at the focal plane reaches 100 mA/c...

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.

Multi-slit triode ion optical system with ballistic beam focusing.

Multi-slit triode ion-optical systems with spherical electrodes are of interest for formation of intense focused neutral beams for plasma heating. At present, two versions of focusing multi-slit triode ion optical system are developed. The first ion optical system forms the proton beam with 15 keV energy, 140 A current, and 30 ms duration. The second ion optical system is intended for heating neutral beam injector of Tokamak Configuration Variable (TCV). The injector produces focused deuterium neutral beam with 35 keV energy, 1 MW power, and 2 s duration. In the later case, the angular beam divergence of the neutral beam is 20-22 mrad in the direction across the slits of the ion optical system and 12 mrad in the direction along the slits.

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.

Ion source with LaB6 hollow cathode for a diagnostic neutral beam injector

In this article ion source capable of providing 8 A, 54 keV proton beam in maximum 3 s pulses is described. A general description of the diagnostic injector based on this ion source is also given. The ion beam is extracted and accelerated by a four-electrode multiaperture ion-optical system. In the ion source, hydrogen (deuterium) plasma is generated by an arc discharge plasma box with a hot LaB6 cathode. The plasma jet diverging from a small anode orifice enters the plasma expansion volume with a peripheral multipole magnetic field and after partial reflection from this field forms a uniform plasma emitter of 160 mm in diameter in the plasma grid plane. The plasma box operates with an arc current of 350–700 A, providing more than 75% of full energy specie in the extracted ion beam. The ion beam is subsequently neutralized in a hydrogen target with ∼50% efficiency and is focused 4 m downstream from the ion source that is provided by a spherical shape of the grids. The beam angular divergence is 0.6°. The ...

Advanced Neutral Particle Analyzer for Fusion Plasma Diagnostics

Abstract An advanced neutral particle analyzer for the diagnostics of hot plasma has been designed and fabricated in the Budker Institute of Nuclear Physics. The analyzer measures the ion energy distributions of both bulk plasma ions as well of fast ions created by neutral beam injection. The main feature of the analyzer is the ability to simultaneously measure hydrogen and deuterium atoms. The design of the analyzer, calculation of registration efficiency, and possible applications for plasma diagnostics on GOL-3 and GDT facilities are presented.

Commissioning of heating neutral beams for COMPASS-D tokamak.

Two neutral beam injectors have been developed for plasma heating on COMPASS-D tokamak (Institute of Plasma Physics, Prague). The 4-electrodes multihole ion-optical system with beam focusing was chosen to provide the low divergence 300 kW power in both deuterium and hydrogen atoms. The accelerating voltage is 40 kV at extracted ion current up to 15 A. The power supply system provides the continuous and modulated mode of the beam injection at a maximal pulse length 300 ms. The optimal arrangement of the cryopanels and the beam duct elements provides sufficiently short-length beamline which reduces the beam losses. The evolution of the impurities and molecular fraction content is studied in the process of the high voltage conditioning of the newly made ion sources. Two injectors of the same type have been successfully tested and are ready for operation at tokamak in IPP, Prague.

High power hydrogen neutral beam injector with focusing for plasma heating

High power neutral beam injector has been developed with particle energy of 25 keV, a current of 60 A, and several milliseconds pulse duration. Six of these injectors are planned to be used for the upgrade of the neutral beam system of a gas dynamic trap device. The injector ion source is based on an arc-discharge plasma box. The plasma emitter is produced by a 1 kA arc discharge in hydrogen. A multipole magnetic field produced with permanent magnets at the periphery of the plasma box is used to increase its efficiency and improve homogeneity of the plasma emitter. The ion beam is extracted by a four-electrode ion optical system (IOS). Initial beam diameter is 200 mm. The grids of the IOS have a curvature for geometrical focusing of the beam. The optimal IOS geometry and grid potentials were calculated to provide precise beam formation. The measured angular divergence of the beam is 0.02 rad, which corresponds to the measured width of the beam profile at a focal point of 2.5 cm.