G. I. Shulzhenko

Characterization of 1 MW, 40 keV, 1 s neutral beam for plasma heating

Neutral beam with geometrical focusing for plasma heating in moderate-size plasma devices has been developed in Budker Institute of Nuclear Physics, Novosibirsk. When operated with hydrogen, the neutral beam power is 1 MW, pulse duration is 1 s, beam energy is 40 keV, and angular divergence is 1.2 degrees. Initial ion beam is extracted and accelerated by triode multiapertures ion-optical system. To produce 1 MW neutral beam, about 40 A proton current is extracted with nominal current density of 320 mA/cm(2). Ion-optical system has 200 mm diameter grids with 44% transparency. The grids have inertia cooling and heat is removed between the pulses by water flowing in channels placed on periphery of the grids. A plasma emitter for ion extraction is produced by rf-plasma box. Ion species mix of rf plasma source amounts to 70%, 20%, and 10% of H(+), H(2)(+), and H(3)(+) ions, respectively, by current. Heavy impurities contribute less than 0.3%.

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.

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.

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.

Use of the focusing multi-slit ion optical system at RUssian Diagnostic Injector (RUDI).

The upgrade of the diagnostic neutral beam injector RUDI in 2010 was performed to increase the beam density at the focal plane in accordance with the requirements of charge-exchange recombination spectroscopy diagnostics. A new focusing ion-optical system (IOS) with slit beamlets and an enlarged aperture was optimized for 50% higher nominal beam current and reduced angular divergence with respect to the previous multi-aperture IOS version. The upgraded injector provides the beam current up to 3 A, the measured beam divergence in the direction along the slits is 0.35°. Additionally, the plasma generator was modified to extend the beam pulse to 8 s.

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.

Development of focused neutral beams with small angular divergence for plasma heating and diagnostics

Abstract A series of neutral beam injectors for plasma heating and diagnostics in modern magnetic fusion devices has been developed in the Budker Institute of Nuclear Physics. In ion sources of these injectors arc discharge or RF plasma boxes are used. Ion optical systems are optimized to produce ion beams with a low enough angular divergence. In order to provide beam focusing, the grids are formed as spherical segments. Such ballistically focused beams are further neutralized in a gas target and subsequently are used to heat or diagnose plasma. Obtained diagnostic neutral beams with precise focusing are widely used to measure plasma parameters by beam emission spectroscopy methods in tokamaks, stellarators, reversed field pinches and open traps. High power focused beams with small divergence are also necessary for heating of localized regions of plasma and in the devices with narrow access ports through which only small size, high power density beams can be transported. Transition to steady state operation regime of the injectors is discussed.

Multi: Seconds diagnostic neutral beam injector based on arc-discharge with LaB6 hollow cathode

The diagnostic neutral beam injector based on arc-discharge plasma source with LaB6 hollow cathode is described. The ion source of the diagnostic injector provides a proton beam with a current up to 2.5A, the particle energy up to 50 keV, the beam divergence is ~0.5°. The beam species at the 2 A ion current are: H+-83%, H2+-5%, H3+-12%. The injector was tested at pulse duration up to 2 seconds.

FIRST EXPERIMENTS ON ELECTRON BEAM INJECTION INTO THE GAS-DYNAMIC TRAP

Инжекция мощных электронных пучков вдоль магнитного поля является перспективным методом нагрева электронов плазмы и управления радиальным профилем потенциала в открытых ловушках. В работе представлены результаты первых экспериментов по инжекции электронного пучка в плазму установки Газодинамическая ловушка (ГДЛ) в ИЯФ СО РАН. Продемонстрирована возможность инжекции электронного пучка мощностью 400 кВт и энергией электронов 40 кэВ через магнитную пробку со степенью сжатия пучка до 120 в плазму. Особенность продольной инжекции пучка заключается в наличии встречного потока плазмы, который приводит к нестабильности работы электронной пушки. В работе определён диапазон параметров, в котором генератор пучка работал надёжно. Показано, что энергосодержание плазмы растёт линейно в течение всей длительности инжекции электронного пучка, не достигая стационарного уровня. При этом зафиксирован рост температуры электронов плазмы.

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.