Improvement of the efficiency of a glow discharge-based ion emitter with oscillating electrons

Ion emission from the plasma of a low-pressure (≈5×10⁻² Pa) glow discharge with electrons oscillating in a weak (≈1 mT) magnetic field is studied in relation to the cold hollow cathode geometry. A hollow conic cathode used in the electrode system of a cylindrical inverted magnetron not only improves the extraction of plasma ions to ≈20% of the discharge current but also provides the near-uniform spatial distribution of the ion emission current density. The reason is the specific oscillations of electrons accelerated in the cathode sheath. They drift in the azimuth direction along a closed orbit and simultaneously move along the magnetic field toward the emitting surface of the plasma. A plasma emitter with a current density of ≈1 mA/cm² over an area of ≈100 cm² designed for an ion source with an operating voltage of several tens of kilovolts is described.     

Intense emission from a grid-stabilized plasma cathode

Intense emission from a grid-stabilized plasma cathode based on a glow discharge with an expanded anode area is studied. In the electrode system of the ion source, the potential difference between a large-mesh grid electrode (a hole diameter of 4–6 mm) and cathode and anode plasma reaches 200 V and the glow discharge current is up to 1 A. The current distribution over the electrodes of the plasma cathode is taken, and the dependences of the electron extraction efficiency and electron-emitting-plasma potential on the gas pressure and discharge parameters are obtained. A relationship between the geometric parameters of the grid, cathode plasma potential, and efficiency of electron extraction from the plasma is derived. It is shown that stable intense emission from the plasma cathode can be provided in wide ranges of gas pressure and discharge current by varying the geometry and mesh size of the plasma cathode grid. Discharge contraction in the grid plane at elevated gas pressures is explained. It is assumed that the emitting plasma becomes inhomogeneous due to variation in the thickness of near-electrode layers in the holes of the grid, which makes the distribution of the emission current from the plasma more nonuniform.     

Thermal regime of self-heated hollow cathode in a low-pressure high-current pulsed-periodic discharge

Technical Physics - We have studied the thermal regime of a self-heated hollow cathode in combined low-current (1–5 A) dc discharge and high-current (up to 100 A) pulsed-periodic discharge...     

Discharge System with a Self-Heated Hollow Cathode and an Evaporating Anode in a Cusp Magnetic Field for Oxide Coatings Deposition

Technical Physics - The properties of a discharge with a self-heated hollow cathode and an evaporating anode placed in a cusp magnetic field created by two oppositely connected coils installed near...     

Studying the fine structure of a nanosecond breakdown channel in potassium chloride

The fine structure of a breakdown channel from a positive electrode in KCl single crystal is studied in the multipulse exposure at a voltage of 140 kV. The dimensions and the shapes of breakdown structures are established as the functions of the applied voltage. The velocity of propagation of a crack vertex forming the breakdown structure, as well as the pressure in the breakdown channel, are estimated. It is shown that under certain conditions the mechanical destruction structure near the breakdown channel is retained even after several dozen pulses are applied.     

Study of breakdown in yttrium aluminum garnet at subnanosecond times of increasing voltage

Crystallographically oriented channels with bottlenecks in the regions of reflection of the pulses have been obtained in aluminum yttrium garnet during multipulsed nanosecond breakdown from the anode under voltages of 100–140 kV, and the propagation rate of the fronts of the phase transition in this voltage range has been determined. It has been shown that the character of the observed pattern of the sequential formation of separate chains of the complete breakdown structure indicates that the channel is formed only locally and immediately at the point of time of passing the breakdown front since the maximal field strength, the magnitude of which determines the diameter of the breakdown channel, is observed in the vicinity of the breakdown front.     

Measurement of the high-voltage breakdown channel propagation velocity in crystalline and amorphous quartz on a subnanosecond time scale

The formation time of a breakdown channel in 0.5- to 1.6-mm-thick crystalline and amorphous quartz samples is measured at a pulse voltage of 240 kV, and the effective velocity and direction of breakdown front propagation are determined. In the crystal, the velocity is more than 2.5 times higher than in amorphous SiO₂. This may be associated with a higher mobility of free carriers and, consequently, with a quicker motion of the avalanche breakdown front owing to a higher effective velocity of nonequilibrium carriers responsible for the high-energy tail of the distribution function.     

Resistance of a pulsed electrical breakdown channel in ionic crystals

A technique for estimating the resistance of the electrical breakdown channel in ionic crystals is proposed. This technique is based on measuring the channel velocity in a sample when a ballast resistor is connected to the circuit of a needle anode and on using the theoretical dependence of the channel velocity on the channel conductivity. The breakdown channel resistance at a voltage of 140 kV is about 6.5 kΩ in KCl and about 6.1 kΩ in KBr. These resistances are shown to characterize a gas phase. The gas-phase resistance is found to be nonuniform along the breakdown channel. The head part ～1 mm long has the maximum resistance. This head region is concluded to contain dielectric substance clusters, which then decompose into metal and halogen ions. The cluster lifetime is ～10^?9 s.     

Anisotropy of electrical breakdown in crystalline quartz

Partial breakdown of crystalline silicon dioxide in a pulsed nonuniform electric field is considered. Breakdown channels lie in planes of silicon ions that are parallel to the c axis of the crystal (up to six equivalent directions of the channels are observed). The formation of breakdown channels is satisfactorily described in terms of cascade Auger transitions with regard to the crystallochemical symmetry of the quartz lattice.