Parameters of the beam plasma formed by a forevacuum plasma source of a ribbon beam in zero-field transportation system

We have studied the generation of the beam plasma formed by a forevacuum plasma source of a ribbon electron beam in the conditions of its transportation without an accompanying magnetic field. The ignition conditions in the beam transportation region of the beam–plasma discharge producing a plasma formation of the plasma sheet type with a plasma concentration of ~10¹⁶ m^–3 and an electron temperature of 1–2.5 eV have been determined. The attained values of parameters and the sizes of the plasma formation make it possible to use it in technologies of the surface modification of planar extended articles.     

Formation of narrow-focused electron beams generated by a source with a plasma cathode in the forevacuum pressure range

Results are presented from experimental studies of the formation of focused electron beams produced by extracting electrons from the plasma of a steady-state discharge with a hollow cathode in the forevacuum pressure range. Based on the measurements of the energy spectrum and diameter of the electron beam, as well as of the emission parameters of the plasma produced in the course of beam-gas interaction, a conclusion is drawn about the excitation of a beam-plasma discharge that deteriorates the beam focusing conditions. The threshold beam current density for the excitation of a beam-plasma discharge is found to increase with accelerating voltage and gas pressure.     

Inhomogeneous extended hollow cathode discharge for raising the current density in a forevacuum plasma source of a ribbon electron beam

The plasma parameters and the emissivity of a ribbon electron beam source based on a discharge with an inhomogeneous extended hollow cathode are measured. A constriction in the cathode cavity increases the plasma density near the emitting area boundary, which adds to the electron current density in the beam. The reason for the above effect is the formation of the plasma density distribution nonuniform across the cavity with a maximum in the middle. This maximum is caused primarily by a plasma electron flow from the constriction, which is generated by the electric field and is directed toward a slit emission-extracting aperture.     

Charge compensation in an insulated target bombarded by a pulsed electron beam in the forevacuum pressure range

We report on the results of computation of the time dependence of the ion flux and the dielectric target potential at the initial stage of bombardment by an electron beam in forevacuum. It is shown that a satisfactory agreement with experimental data is attained with allowance for the possibility of the discharge between the target and the earthed walls of the vacuum chamber.     

Potential of a dielectric target during its irradiation by a pulsed electron beam in the forevacuum pressure range

The potential induced on the surface of a nonconducting ceramic during irradiation by an electron beam in the forevacuum pressure range (5?C15 Pa) remains negative, but its absolute value is much smaller than the energy of accelerated electrons. The factors affecting the negative potential of a nonconducting ceramic target are determined. The evolution of the charge injected in the ceramic is analyzed by a numerical simulation.     

Initiation of a low-pressure glow discharge in a plasma electron source with a ribbon beam

Results are presented from an experimental investigation of a low-pressure glow discharge with a wedge-shaped hollow cathode in a plasma electron source, where this discharge is initiated by reflex and magnetron discharges. Zh. Tekh. Fiz. 69, 135–137 (July 1999)     

Influence of the longitudinal magnetic field in the accelerating gap on the limiting parameters of a plasma electron source operating in the forevacuum pressure range

Results are presented from experimental studies of the influence of the longitudinal magnetic field in the accelerating gap on the emission current, accelerating voltage, and maximum gas pressure in a plasma electron source generating a continuous electron beam in the forevacuum pressure range. It is shown that the magnetic field in the beam-formation region stabilizes the emitting boundary of the plasma in the accelerating gap, thereby considerably improving the source parameters.     

Plasma localization in an extended hollow cathode of the plasma source of a ribbon electron beam

The plasma density distributions in the slit aperture of the extended rectangular hollow cathode of the source of a ribbon electron beam are investigated experimentally. It is found that a local maximum whose parameters are determined by the discharge current appears in the density distribution when the slot width is less than a certain threshold value. This maximum results in an inhomogeneous current density distribution in the beam. It is shown that the appearance of the local maximum in the plasma density is related to the overlapping of the ion sheaths in the slit aperture of the hollow cathode.     

Specific features of the excitation spectrum of helium II in a plasma initiated by an electron beam

The emission of a low-pressure helium plasma (P≤2 Torr) initiated by a monochromatic electron beam is investigated. It is found that an increase in the current leads to a drastic increase in the rate of charge exchange of doubly charged helium ions. The assumption is made that inelastic collisions of He⁺⁺ ions with metastable helium atoms provide the main channel of charge exchange of these ions due to the reaction He⁺⁺+Hem→ He⁺*+He ₀ ⁺ .     

Expansion of the working range of forevacuum plasma electron sources toward higher pressures

It is shown that the pressure in forevacuum plasma electron sources is limited from above by a current component that arises in the accelerating gap from a high-voltage glow discharge and dominates in the electron beam. The working pressure range of such electron sources can be expanded toward higher pressures by limiting the current of the high-voltage glow discharge in the accelerating gap.     

Formation of a pulsed electron beam in a plasmacathode system under forevacuum pressures

Results of an experimental study of the features of the production of pulsed beams by a plasma electron source operating in the forevacuum pressure range (5–15 Pa) are presented. For this pressure range, the emission properties of the plasma are substantially affected by the backward ion flow generated in the regions of formation and transport of the electron beam. It has been shown that in experimental conditions the ratio of the current of backward ions to the current of the electron beam can reach 10%, which is an order of magnitude greater than the same parameter for electron sources operating in the pressure range that is conventional for devices of this type (0.01–0.1 Pa). The principal factors that impose an upper limit on the beam current in a plasma-cathode source are analyzed.     

Localization of plasma in the extended hollow cathode of a ribbon-electron-beam plasma source at forevacuum pressures

The results of a study of the plasma density distribution in the slit aperture of a right-angled extended hollow cathode used in a ribbon-electron-beam plasma source operating at forevacuum pressures (1–10 Pa) are presented. It is shown that a local peak of plasma density appears in some region of the slit aperture as the slit width is decreased. This results in the appearance of a region of increased current density when the ribbon beam forms. The uniformity of the beam current density distribution is additionally disturbed by the reverse ion flow whose effect on the emission properties of the plasma is significant in the region of elevated pressure. A model which describes the development of plasma density nonuniformity in a hollow cathode is proposed which is based on the idea that the electron current flows predominantly through the slit aperture regions that are associated with local openings of the cathode layer ion sheaths. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 3–9, June, 2007.     

Parametric excitation of electromagnetic and surface plasma waves of a ribbon electron beam in a periodic magnetic field

Rostov State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 4, pp. 488–496, April, 1990.     

Dynamics of a ribbon electron beam in the plane-symmetric reverse of a magnetic field

The dynamics of a charged particle in the model of a ribbon beam is studied in a plane-symmetric reversing magnetic field by means of numerical simulation. It is shown that the efficiency of converting the particle’s cyclotron rotation into the energy of its longitudinal motion depends on the initial phase of the particle’s entry. Increasing the length of the reverse field reduces the effect of the initial entry conditions.     

Self-oscillating mode of electron beam generation in a source with a grid plasma emitter

Plasma processes and electron beam generation in an electron source with a grid plasma cathode are investigated. Experiments are conducted under the conditions of efficient electron extraction and an intense counter ion flux, which break grid stabilization. It is shown that a rise in the gas pressure and in the emitting plasma potential leads to the plasma potential modulation in the frequency range 10⁴–10⁵ Hz. Under the self-oscillation conditions, an electron beam is obtained with a constant current of up to 16 A and an electron energy modulated up to 100% of the accelerating voltage level (100–300 V). An explanation is given for relaxation self-oscillations arising when the plasma potential grows and for the system’s inertial non-linearity arising when the plasma potential induced by the space charge of the counter ion flux lags behind the current of electron-beam-generated ions.     

A reflex electron beam discharge as a plasma source for electronbeam generation

A reflex electron beam glow discharge has been used as a plasma source for the generation of broad-area electron beams. An electron current of 120 A (12 A/cm²) was extracted from the plasma in 10 μs pulses and accelerated to energies greater than 1 keV in the gap between two grids. The scaling of the scheme for the generation of multikiloamp high-energy electron beams is discussed     

Generation of a pulsed high-current low-energy beam in a plasma electron source with a self-heated cathode

The transition of a low-current discharge with a self-heated hollow cathode to a high-current discharge is studied, and stability conditions for the latter in the pulsed–periodic mode with a current of 0.1–1.0 kA, pulse width of 0.1–1.0 ms, and a pulse repetition rate of 0.1–1.0 kHz are determined. The thermal conditions of the hollow cathode are analyzed, and the conclusion is drawn that the emission current high density is due to pulsed self-heating of the cathode’s surface layer. Conditions for stable emission from a plasma cathode with a grid acting as a plasma boundary using such a discharge are found at low accelerating voltage (100–200 eV) and a gas pressure of 0.1–0.4 Pa. The density of the ion current from a plasma generated by a pulsed beam with a current of 100 A is found to reach 0.1 A/cm². Probe diagnostics data for the emitting and beam plasmas in the electron source are presented, and a mechanism behind the instability of electron emission from the plasma is suggested on their basis.     

Wide-aperture high-current electron beam in a discharge with cathode plasma at elevated pressure

This work pursues investigations into the discharge with a cathode plasma in a cavity one wall of which is an insulating plate with a hole D in diameter (the cavity is 0.5 or 1.5 mm wide). This discharge is thoroughly analyzed in comparison with the high-voltage hollow-cathode discharge. Owing to the reduced emission of electrons from the cathode plasma, the discharge becomes more stable against transition to the low-voltage form, as a result of which an electron beam can be generated under higher gas pressures. Such a beam formed at the entrance to the cavity is used as an auxiliary one that propagates over the remaining (flat) surface of the cathode and adds to the gas ionization. Accordingly, the beam current from the main discharge to the anode rises (high-current regime). Wide-aperture (D = 22 mm) ≈1-μs-long pulsed beams with a current an order of magnitude higher than the total current of the equivalent anomalous discharge are obtained. Experiments are carried out at a helium pressure to 20 Torr and a voltage from 1 to 20 kV.     

Specific features of the population kinetics of levels of noble gases in experiments with a pulsed electron beam

The population kinetics of the energy levels of atoms excited in a tube with an electron beam is studied. A method of separating the contributions made by direct electron impact and by secondary processes to the population of the levels considered is proposed.     

Parametric instabilities produced by a relativistic electron beam in a plasma

The parametric instability driven by the primary spectrum of the hydrodynamic two-stream instability produced by a relativistic electron beam in a plasma is investigated. The saturated level of the primary wave electric field is determined by electron trapping in the potential well of the wave or by the quasilinear beam relaxation process. After saturation, the primary wave collapses by way of the oscillating two-stream instability. The cases of the strong and weak primary electric field in comparison with the thermal energy of a plasma are considered. For a strong field the growth rates of the parametric instability and plasma heating due to the latter are found. Ion heating is not significant in comparison with electron heating (approximately as the cube root of the mass ratio). In a weak field the parametric oscillating two-stream spectrum of saturation is found. In the one-dimensional case this spectrum of electric field energy fluctuations varies as k⁻² if the fluctuation field exceeds the threshold pump electric field for the oscillating two-stream instability. For the weak field plasma heating rate is found. Since the energy transfer is via Landau damping, the particle heating is characterized by the formation of high-energy tails on the distribution function.