Characteristics Of Hollow Cathode Discharge Research Articles

A study of pulsed high voltage driven hollow-cathode electron beam sources through synchronous optical trigger

In this study, a pulsed, high voltage driven hollow-cathode electron beam sources through an optical trigger is designed with characteristics of simple structure, low cost, and easy triggering. To validate the new design, the characteristics of hollow-cathode discharge and electron beam characterization under pulsed high voltage drive are studied experimentally and discussed by discharge characteristics and analyses of waveform details, respectively. The validation experiments indicate that the pulsed high voltage supply significantly improves the frequency and stability of the discharge, which provides a new solution for the realization of a high-frequency, high-energy electron beam source. The peak current amplitude in the high-energy electron beam increases from 6.2 A to 79.6 A, which indicates the pulsed power mode significantly improves the electron beam performance. Besides, increasing the capacitance significantly affects the high-current, lower-energy electron beam more than the high-energy electron beam.

Analysis of anode surface roughness influence on heaterless hollow cathode discharge

This research delves into the influence of cylindrical and planar anode surface roughness on heaterless hollow cathode discharge characteristics. Three surface roughness levels, Ra 1.6 μm, Ra 3.2 μm, and Ra 6.4 μm, along the cylindrical anode’s azimuthal direction and the planar anode’s radial direction, have been selected and modified by the machining process. A central finding is the correlation between the discharge voltage and anode surface roughness. As the roughness increases, cylindrical and planar anodes require less discharge voltage to sustain the primary discharge. This reduction is likely due to the enhanced surface area from the roughness, which aids in electron current collection. The discharge voltage oscillations appear inversely related to the surface roughness of planar anodes, which may be associated with changes in the neutral gas density gradient between the planar anode and the cathode. In contrast, cylindrical anodes show fewer effects from their surface roughness, likely due to the distinct neutral gas flow dynamics. These findings offer insights into standardizing hollow cathode testing and allow future research to explore these interactions more deeply.

Surface state change influence’s theoretical approach of pressed iron on hollow cathode discharge characteristics: first results of plasma heating reproducibility for sintering purposes

In this work first results of the plasma heating process reproducibility for sintering purposes of pressed iron powder sample was investigated analyzing changes on the current-voltage characteristics of pulsed direct current (dc) Ar + H2 hollow cathode discharges sequentially carried out. For this purpose, the temperature of a sample acting as central cathode was varied by changing the switched-on time (duty cycle) of the pulse, via plasma species bombardment (ions and fast neutrals), which typically occurs in both cathode cylindrical surfaces that constitute the annular (hollow cathode) glow discharge, and measured by a thermocouple inserted in the central cathode sample holder. After two sequential plasma heating experiments, the third one practically reproduced the measured plasma parameters evidenced in the second heating, and the respective heating curves as a function of the time have led to similar current-voltage characteristics suggesting the iron sample sintering in non-isothermal way. Principles comprising plasma-surface interface and metallurgical-physical-chemical reactions, powder surface aspects, thermodynamic properties, metallurgical transformation of the pressed sample, and hollow cathode discharge properties are presented and discussed. The main points considered in the present approach are related to plasma (oxygen-affected plasma ionization, high ionization and excitation rate, and the intense light radiation of the annular glow discharge), thermodynamics (oxidation-reduction reactions, electron work function, sintering driving force, and surface energy), and powder (particle size distribution, morphology, specific surface, and iron recrystallization). To the best of the author’s knowledge, it is the first time that it is brought to the light the changes on hollow cathode discharge characteristics while an iron sample acting as the central cathode of an annular glow discharge is subjected to distinct heating steps on the temperature range of 20 to ∼1250 °C, leading it to have its sintering initiated.

Dynamics of hollow cathode discharge using fluid models with and without metastable atom involvement in helium

The characteristics of hollow cathode discharge are simulated by two types of fluid models in helium, one with metastable atom involvement and another without. Discharge current, particle density, and ionization rate are simulated. Results show that metastable atoms exert an important influence on the steady state discharge and the temporal characteristics of this discharge. Discharge is maintained at a lower sustain voltage in the model with metastable atoms than in that without metastable atoms. At the same low sustain voltage, marked differences in quantitative and qualitative characteristics are observed between the two models. With increasing sustain voltage, the discharge parameters simulated by the two models become qualitatively similar, but their quantitative differences increase. The discharge current and electron density in the model with metastable atoms are significantly higher than that in the model without metastable atom involvement at the same sustain voltage. Furthermore, the discharge current and electron density gap simulated by the two models increase as the sustain voltage increases. The difference in characteristics between the two models originate from variation of the contribution of different ionization types to the generation of new electrons at different sustain voltages. With increasing sustain voltage, stepwise ionization originating from metastable atoms becomes increasingly crucial to the discharge. Results further show that the temporal characteristics of the two models are similar when the metastable atom density is low. However, in the model with metastable atoms, discharge current and particle density continue to rise until a steady discharge is obtained after a quasi-steady stage. The different temporal characteristics observed between the models appear to originate from the influence of metastable atoms. The percentage of stepwise ionization relative to the total ionization increases with time.

The Effect of Gas Flow Rate on Radio-Frequency Hollow Cathode Discharge Characteristics

It is known that gas flow rate is a key factor in controlling industrial plasma processing. In this paper, a 2D PIC/MCC model is developed for an rf hollow cathode discharge with an axial nitrogen gas flow. The effects of the gas flow rate on the plasma parameters are calculated and the results show that: with an increasing flow rate, the total ion (N+2, N+) density decreases, the mean sheath thickness becomes wider, the radial electric field in the sheath and the axial electric field show an increase, and the energies of both kinds of nitrogen ions increase; and, as the axial ion current density that is moving toward the ground electrode increases, the ion current density near the ground electrode increases. The simulation results will provide a useful reference for plasma jet technology involving rf hollow cathode discharges in N2.

Influence of metastable atoms in the simulation of hollow cathode discharge

The characteristics of hollow cathode discharge are investigated by using two-dimensional fluid model combined with a transport model for metastable atoms (F-M model) in argon. It shows that the stepwise ionization is one of main important mechanism for electrons production. The distribution of electric potential, density of electrons, ions, and metastable atoms are calculated with a pressure of 10 Torr and a voltage of 250 V. The peak density of electron and ion is 1.2×1013 cm−3, and the peak density of metastable atoms is 3.5×1013 cm−3. The results obtained in F-M model are compared with that in fluid model (without metastable atoms involved). Metastable atoms are found to play an important role in the discharge. In addition, with the increase of pressure and voltage, the percentage of stepwise ionization in the total ionization increase, and the difference of discharge characteristics simulated by these two kinds of models rises.

Transition of Discharge Mode of a Local Hollow Cathode Discharge

The discharge characteristics of hollow cathode discharge in argon in a cylindrical cavity are investigated experimentally. The voltage-current (V – I) characteristics and the light emission are measured. It is found that the discharge plasma is localized inside the hollow cavity, with an extensive Faraday dark space between the cathode and the anode. The discharge develops from predischarge to abnormal glow discharge, the hollow cathode effect (HCE) and a hybrid mode as the discharge current increases. The onset of the HCE is found for the first time by the transition from abnormal glow discharge together with a significant decrease in the slope of the V – I curve which shows a positive differential resistivity. The voltage increases proportionally with the current when the HCE is reached.

Formation of CN in N2 + He discharges in graphite hollow cathodes

Carbonaceous vapour created by nitrogen and helium discharges in graphite hollow cathodes has been investigated to identify the mechanisms for CN formation. The characteristics of hollow cathode discharge have been exploited to provide the two-energy-regime electrons that initiate a complex process for the production of ions and metastable atoms and molecules of He and N2. These introduce the sputtered carbon species Cx (x ≥ 1) from the graphite cathode. Dominant among the Cx species are C1 and C2 that are excited and participate in inter- and intra-species collisions. CN, therefore, is the direct by-product of reactions between sputtered C and N2. From the optical emission spectra the level densities of nitrogen and helium were recorded during the cycling of discharge current idis of the graphite hollow cathode. The emission spectra are dominated by strong emission bands of CN (violet system Δν = −1, 0, +1) and N2 (2nd positive system), along with the atomic lines of He and C. We have identified and suggested a mechanism for the formation of CN in nitrogen plasmas in graphite hollow cathodes.

Influence of the phase transformation of a metal on hollow cathode discharge characteristics

The influence of properties of metals (copper, tantalum, titanium, TiAl and nickel) constituting the cathode on the characteristics of a hollow cathode discharge has been investigated for different pressures and currents. We point out that the phase transformations of the cathode material induce a modification in the current-voltage characteristics of the discharge. This phase transformation effect of the cathode material combines with the geometrical effect induced by the typical hollow cathode discharge which seems to be independent of the material properties. The evolution of the electron density and the evolution of the intensities of emission lines in the plasma are also affected by the phase transition. This effect is related to a work function change of the metal at the phase transition. It can be used as a test of work function variation of materials or for optimization of plasma processes.

Material effects of titanium and titanium alloys on hollow cathode discharge characteristics

The influence of material properties on the hollow cathode discharge has been investigated at different pressures and currents. It was found that the crystallographic phase transformations of titanium and titanium alloys modify the evolution of the current-voltage characteristics of the discharge, these different variations being mainly explained by a modification of the cathode material work function at the phase transitions. The evolutions of electron density and the intensity of plasma emission lines are also perturbed at these phase transitions. On the other hand, hollow cathode geometry effects only manifest in discharge characteristics in the cathode material has no phase transformation (such as copper and tantalum). These modifications of hollow cathode discharge characteristics can be used to build up a diagnostic on the existence of variation of material properties occurring at phase transitions and to optimize plasma processes.

Hollow-cathode discharge characteristics of glow-modulator tubes

The hollow-cathode glow-modulator tube has a cylindrical molybdenum cathode cavity and ring anode. An abnormal glow discharge is formed between these electrodes in a low pressure neon-argon gas mixture to create a high intensity source of light which passes out through the anode. The tube is used mainly in scanning and facsimile equipment.Impedance-frequency measurements have been made over the range 200 Hz to 6 MHz which at low frequencies have been related to the static voltage-current curves of the discharge. The effects of sputtering over periods up to 200 h have been observed and the cathode cavity has been sectioned and photographed. The results for various depth/diameter ratios are shown, each of which forms a spherical hollow after many hours of operation. The noise characteristics in a 6 kHz bandwidth have been measured over the range 5 kHz to 6 MHz and are explained with reference to the basic gas processes and the impedance characteristics. Identification has been made of the spectral lines from the discharge which are linearly proportional to current for the gas atoms and proportional to current cubed for cathodic atoms.