Cathode Cavity Research Articles

Electrical Characterization of Plasma-Assisted Electron Beam Source With Sub-mm Sheet Aperture

In this article, the electrical characterization of a plasma-assisted electron beam source with a sub-mm sheet aperture has been performed. The developed sheet electron beam source comprises a hollow cathode cavity, two floating anodes, and one ground potential anode with a sheet aperture of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\times0.3$ </tex-math></inline-formula> mm. The source has been characterized under varying applied gap potential range, i.e., 10–30 kV in self-breakdown operating mode. The breakdown parameters and resultant beam parameters, such as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} - {I}$ </tex-math></inline-formula> characteristics, electron beam current density, duration to reach the conductive phase, and the energy transformation efficiency of the developed source, have been analyzed. The successive breakdown phenomenon has also been presented in the profile of the developed electron beam source.

Simulation of the spatio-temporal evolution of the electron energy distribution function in a pulsed hollow-cathode discharge

This article presents the 2D simulation results of a nanosecond pulsed hollow cathode discharge obtained through a combination of fluid and kinetic models. The spatio-temporal evolution of the electron energy distribution function (EEDF) of the plasma column and electrical characteristics of the nanosecond pulsed hollow cathode discharge at a gas pressure of 5 Torr are studied. The results show that the discharge development starts with the formation of an ionization front at the anode surface. The ionization front splits into two parts in the cathode cavity while propagating along its lateral surfaces. The ionization front formation leads to an increase in the fast isotropic EEDF component at its front, as well as in the anisotropic EEDF component. The accelerated electrons enter the cathode cavity, which significantly contributes to the formation of the high-energy EEDF component and EEDF anisotropy.

Insights into the effect of hollow cathode with external injection of fast ions in a sputter-type negative ion source

In sputter-type negative ion sources, the negative ion currents and ionization efficiencies are very dependent upon the creation of a sputter crater and formation of an intense plasma glow. This effect has many similarities with the well-known phenomena of hollow cathode discharges (HCDs). This paper discusses the phenomenological model related to conventional HCDs, including modes with injection of external energetic particles. We propose that HCDs play a major role in sputter-type negative ion sources. In this study, we evaluate the phenomenology of a discharge with a hollow cathode and derive an analytical formula that defines the neutral particle density inside the cathode cavity and substantiates how the classic HCD occurs in sputter-type negative ion sources. The cathode pit geometry was revealed by optical microscopy. Volt–ampere characteristics were investigated in order to compare it to typical discharges with hollow cathodes. In sputter-type negative ion sources, known as SNICS, discharge characteristics and observed light glow inside the cathode pit after its formation were very similar to data published on HCDs. The HCD phenomenon explains how the cathode current increases by orders of magnitude after creation of the cathode pit. The HCD effect in SNICS and similar sputter sources compliments existing mechanisms of negative ion production, especially ion pair production close to the cathode surface due to low energy ionization based on the collision–radiation model. The wealth of information accumulated over the last century on HCDs can be used to describe and explain the phenomenology of physics and operation of sputter negative ion sources.

GLOW DISCHARGE WITH A HOLLOW CATHODE IN CARBON DIOXIDE

This paper is devoted to an experimental study of the dc discharge with a hollow cathode within the carbon dioxide pressure range of 0.06...2 Torr. The registered CVCs in the pressure range below 0.5 Torr possess a hysteretic pattern with transitions between glow and hollow modes. We have demonstrated that the value of the product of gas pressure and distance between cathode plates p·dh = 0.32 Torr·cm is optimum for the application of the discharge with hollow cathode for plasma conversion of the carbon dioxide when the maximum discharge current is observed. Then the cathode cavity is filled with a high density discharge. Treating the optical emission spectrum has revealed that in the negative glow there have to be present the electron flows with the energy above 18 eV, what must provide the high rate of the CO2 molecules conversion via direct electron impact. Slow electrons produced inside the negative glow itself have to supply an additional contribution to the conversion process and to make an efficient excitation of oscillatory levels of CO2 molecules.

ASYMMETRY OF THE OPTICAL TRANSMISSION SPECTRA OF A PULSED DISCHARGE WITH AN EXTENDED HOLLOW CATHODE DURING AT RESONANCE INTERACTION OF SHORT POLYCHROMATIC LASER PULSES WITH EXCITED NEON ATOMS

The processes of resonant interaction of short pulses of polychromatic radiation of a dye laser with plasma of a nanosecond discharge in neon with an extended hollow cathode are experimentally studied. During the propagation of laser radiation inside the cathode cavity near the spectral absorption line of Ne I with a wavelength of 650.6 nm, the formation of asymmetric optical transmission spectra of the plasma of the dispersion type are detected, while during the propagation of laser radiation in the region between the electrodes, symmetric transmission spectra of the classical kind are formed.

Operating modes in a low-pressure glow discharge with hollow cathode

The paper deals with investigations of the discharge in hydrogen in conditions close to those for the trigger units of pseudospark switches. The following modes of discharge sustaining are classified: the Townsend discharge, the suppressed glow discharge with hollow cathode, the intermediate mode of the gradual transition from the suppressed discharge to the ordinary glow discharge, and the ordinary discharge in which the negative glow plasma occupies the whole depth of the cathode cavity. As applied to the ordinary discharge, the theoretical model that offers a possibility to estimate the negative glow parameters is developed. In the current range 1.6–10 mA the electron densities in the negative glow region are 1.7–8.7 108 cm−3. The interpretation for the mechanism of the current passage to the anode is also proposed based on the model. In particular, the explanation is given for the fact that the region of the positive column plasma near the flat anode appears at a low discharge current.

Studying a microwave discharge cathode, both inside and out

Using an optical window, plasma behavior inside the microwave cavity of a discharge cathode was measured for the first time.

Simulation investigations on stepwise penetration of virtual anode in pseudospark discharge

Pseudospark discharge is a special low pressure discharge and has been widely used in the gas switch and electron beam sources. From experiments, when the work pressure is relatively low, the electron beam current or loop current generated by a pseudospark discharge usually has two or more peaks, which has not been fully explained. In this paper, a single-gap pseudospark discharge model is established using 2D kinetic plasma simulation code VSim to study this phenomenon. According to the simulation results, when the anode voltage is 20 kV and the helium pressure is 100 Pa, the current has two peaks, which is similar to the experimental results, accompanied by the stepwise penetration of the virtual anode. This is mainly related to the formation and disappearance of the potential barrier in the cathode hole region. The formation of the potential barrier is caused by the consumption of ions at the cathode hole, and the disappearance is caused by the increase in electrons in the cathode cavity. By classifying the electrons, it is found that the increased electrons are generated by secondary emission caused by ion bombardment on the wall of the cathode. The simulation results also show that the stepwise penetration of the virtual anode can be suppressed or eliminated by increasing the working gas pressure, the secondary electron yield of the cathode material, or the trigger intensity.

Функция распределения электронов по энергиям в высоковольтном импульсном разряде с протяженным полым катодом

The dynamics of a nanosecond discharge with an extended hollow cathode in argon is studied and the electron energy distribution function (EEDF) in a plasma column is calculated. The issues of the formation of the EEDF in the discharge column and inside the cathode cavity are considered. The conditions of the validity the two-term approximation of the EEDF in the plasma column are analyzed and the appropriate evaluations are given.

Electron energy distribution function in a high-voltage pulsed discharge with an extended hollow cathode

The dynamics of a nanosecond discharge with an extended hollow cathode in argon is studied and the electron energy distribution function (EEDF) in a plasma column is calculated. The issues of the formation of the EEDF in the discharge column and inside the cathode cavity are considered. The conditions of the validity the two-term approximation of the EEDF in the plasma column are analyzed and the appropriate evaluations are given. Keywords: hollow cathode, pulse discharge, argon, electron energy distribution function.

Spectroscopy of the Mirror Instability Growth Rate in Hollow Electrodes Discharge (HED) Plasma

In this work, an experimental study was conducted about the effect of gas pressure on the growth rate of the mirror instability produced in hollow electrodes discharge (HED) plasma in two regions: inter-electrodes gap and internal cathode cavity, by optical emission spectroscopy. Optical emission spectroscopy measurements, at different gas pressures in two regions under study, show that the electron number density (ne) increase with increasing gas pressure from 0.04 to 0.2 Torr. While the electron temperature (Te) decrease with increased gas pressure. In addition, the growth rate increase with increasing electron temperature anisotropy in both regions.

Axial Distribution of Plasma Properties in a Hollow Cathode Plasma Discharge

Hollow cathode plasma discharge technology has several engineering and industrial applications. To further enhance these applications, information on plasma characteristics (such as its axial distribution inside the hollow cathode cavity) is essential. This work determines the axial distributions of electron temperature and density inside said cavity by inserting a triple probe. The temperature and density inside the hollow cathode cavity were approximately 4 eV and −1017 m−3, respectively. It was also confirmed that the plasma existed over almost the inside the cathode cavity and the electron temperature increased and the electron density decreased rapidly in the region near the anode.

Method of nanosecond triggering for a sealed-off pseudospark switch

This paper describes a method of nanosecond triggering for the modified version of the commercially produced pseudospark switch TPI1-10k/50. The switch uses the trigger unit with the auxiliary glow discharge, and the proposed method is based on the principle of the current interception from the trigger unit to the grounded cathode cavity when the trigger pulse arrives. Different electric circuits for triggering have been investigated. In the circuit, where the so-called trigger resistor or the trigger inductance are available, in the whole range of hydrogen operating pressure, the range of the delay time of triggering corresponds to (80–100) ns with a jitter of (3–6) ns. In the electric circuit, where the trigger resistor is shortened, the delay time increases to about (110–140) ns. However, the jitter remains at approximately the same level.

Effect of a longitudinal magnetic field on the emission characteristics of a forevacuum plasma electron source based on a hollow cathode discharge

The effect of a longitudinal magnetic field on the emission characteristics of a forevacuum plasma electron source based on a discharge with a hollow cathode is studied. It is shown that, starting from a certain threshold value of the induction Bc, the magnetic field leads to a decrease in the plasma concentration on the axis of the cathode cavity. With a decrease in the diameter of the cathode cavity, the threshold value of Bc increases. On the other hand, the longitudinal magnetic field makes it possible to increase the diameter of the emission chan-nel, which contributes to a significant increase in the current of electron emission from the plasma. In this case, the degree of increase in the emission current is determined by the ge-ometry of the cathode cavity and the pressure of the working gas.

Characteristics of Low-Pressure Discharge in a Forevacuum Plasma Electron Source Using an Electrode System With Extended Hollow Cathode

The results of investigations of the processes of ignition and burning of a glow discharge with an extended hollow cathode at pressures of 3–50 Pa are presented. Such a discharge system is used in forevacuum plasma sources of ribbon electron beams. The effect of the discharge current, the geometry of the cathode cavity, pressure, and type of gas on the uniformity of the discharge plasma is studied. It is shown that at relatively low discharge currents in the cathode cavity, local regions with an increased plasma density are formed, leading to a sharp inhomogeneity of the current density of electrons extracted from the plasma.

A Sealed-Off Pseudospark Switch With Nanosecond Stability of Triggering

This article describes the modified version of the commercially produced pseudospark switch TPI1-10k/50 (pulsed current-10 kA and anode voltage-up to 50 kV) and the results of testing. The main idea of the modification was to use the high-voltage electrode system of this switch but to incorporate the novel trigger unit in the main cathode cavity. This unit uses the auxiliary glow discharge with hollow cathode and hollow anode. The modified switch is intentionally developed for parallel operation of a large number of the switches to a common load. In such conditions, the nanosecond triggering stability of the switches is required. The results of tests demonstrate that the minimum delay time of triggering (the time interval between the instant of arrival of the trigger pulse and the instant of starting the main discharge current) amounts to 80 ns with a jitter of 3 ns. At a decreased hydrogen pressure, the delay time is not increased essentially and amounts to 105 ns with a jitter of 6 ns.

Electrophysical Processes in the Cathode Cavity of Vacuum Plasma Generators

Electrophysical Processes in the Cathode Cavity of Vacuum Plasma Generators

Spectroscopic analysis of magnetized hollow cathode discharge plasma characteristics

The present work investigated the discharge characteristics in the magnetized hollow cathode system. Also, the gas pressure effect on the discharge characteristics has been examined with a gas pressure between (0.08 and 0.4) Torr. The voltage-current curve of magnetized hollow cathode discharges has the voltage become approximately constant with slight increases in current. The normal glow discharge was established with constant voltage and increasing current. When the current is increased even more, then, the discharge turns into a mode comparable to the normal glow discharge between the parallel electrodes. The increasing of the pressure causes compressing of the cathode falls inside the cathode cavity and the negative glow becomes thin and more luminous. The spectroscopic method used depends on analyzing the argon’s emission atomic spectra. The electron temperature has been evaluated with the use of Boltzmann plot approach. The influence of the pressure on electron temperature observed the reduction in electron temperature when the pressure is increased. The electron number density has been calculated with the use of the Stark broadening method. The density curve indicated that the increase in electron number density with increasing of pressure until 0.4 Torr and then reduced with pressure exceeds 0.4 Torr.

Implementation of Trigger Unit for Generation of High-Current-Density Electron Beam

In this article, a trigger unit has been implemented to generate a high-current-density electron beam from a pseudospark (PS) discharge-based electron gun. A trigger pulse power supply unit has been designed and developed to provide the seed electrons from the ferroelectric cathode (FEC). The FEC has been used inside the hollow cathode cavity of a single-gap PS discharge-based electron gun. The electron gun has been operated in the self-breakdown as well as the trigger-based breakdown mode. A comparative analysis has also been performed between self-breakdown and trigger breakdown modes with the developed trigger unit’s help for different applied gap voltages ranging between 0 and 16 kV. The designed trigger unit is based on a high-voltage-gain isolated dc–dc converter and a pulse-forming network. It is compact and capable of generating a negative pulse of ~–5 kV with a pulsewidth of ~500 ns. It provides better control over PS discharge to produce a high-current-density electron beam.

A Hollow-Cathode Ion Source in Glow Discharge Mass Spectrometry

The paper proposes a new glow discharge ion source based on a hollow cathode. The proposed source produces a denser plasma than the previously used glow discharge sources. It is shown experimentally that the maximum rate of cathode sputtering of a conducting solid sample in a hollow cathode ~25 mm in diameter is achieved when the sample has the shape of a rod with a diameter of 2–4 mm and a length of 10–15 mm and is placed along the axis of the cathode cavity. If a cover with a hole is placed on the cathode cavity, a plasma bunch is formed near the hole (a “plasma plug”), which resists the flow of argon from the hollow cathode. The pressure in the discharge chamber decreases, and the glow discharge is concentrated in the cathode cavity. This results in a decrease in the background level in the glow discharge source by approximately two orders of magnitude. The mechanism of formation and extraction of ions from a glow discharge ion source is considered. The ions formed in the glow discharge plasma form two oppositely directed ion flows in the source, one of them with an ion energy of 100 eV or higher. These ions, accelerating in the region of the cathode potential drop, are directed to the cathode, bombard the analyzed sample, and spray it. The second flow of low-energy ions is drawn from the same region of negative luminescence and is transported in the opposite direction, that is, to the surface of the discharge chamber-anode due to ambipolar diffusion. These ions are extracted from a hole in the anode chamber of a conventional ion source by an accelerating voltage and used for mass spectral analysis. The use of a hollow cathode with a plasma plug, the effect of ambipolar diffusion, and a modified Pierce lens makes it possible to increase the luminosity of the glow discharge source by more than one order of magnitude.