Cathode Aperture Research Articles

Optical emission from a ‘beam mode’ transparent cathode glow discharge

We investigate optical emission from a low-pressure ‘beam mode’ inertial electrostatic confinement glow discharge, created using cylindrical grid electrodes, having cathode inside a grounded, concentric anode. Spectral line distributions were measured in helium from this and a hollow cathode mode, with four lines emitted from singlet and triplet states with n = 3 and L = P and D compared against simple models for impact excitation by electrons and by ions and neutrals, suggesting much beam mode emission is caused by fast neutrals, and a significant component also caused by electrons. Beam mode emission occurs in a pattern of radial lines, that pass through aligned electrode apertures and extend across the chamber. Shadows cast by the electrode wires indicate electrically-neutral, beam-like sources of excitation, that cross the electrode assembly from bright radial lines in the opposing inter-electrode space, and calculated potential distributions show lensing surfaces around the anode grid apertures, focussing for inward-drifting ions. These indicate the emission pattern is caused by radially-convergent ion beams, and co-linear beams of fast neutrals produced in these. Emission was also observed with various alterations made to the electrode arrangement: with the anode removed, no beams were observed; with the cathode apertures rotated out of phase with those of the anode, bright radial beams between the electrodes followed the distribution of anode apertures; similar beams appeared with the grid cathode replaced by a solid version. In these experiments, progressive obstruction of pathways through the cathode caused increasing reduction in the beam pattern of emission beyond the anode radius, and in discharge perveance at similar pressure and voltage. Beam-like emission was also observed for a parallel-planar configuration, in which a cathode grid was held between two identical anode grids. The beam mode is shown to be a convergent, anode-focussed ion beam discharge, distinct to the star mode described elsewhere.

Study the effect of cathode electrode aperture shapes on ion beam properties using SIMION program

Abstract This work was concerned with a simulation study of different cathode electrode aperture shapes (pierce, reversed pierce, cone, reversed cone, triangle, reversed triangle, rectangle, circle, and sphere), which confirms that, pierce and cone shapes are the best extraction apertures. The minimum values of ion beam diameter and ion beam emittance, at collector plate which placed at 30 mm distance from cathode electrode were obtained using pierce and cone shapes. Also, the distance of the ion beam trajectories focal point was studied using different shapes for cathode aperture, which found to be decrease with increasing of the voltage applied to the cathode electrode. The main parameter in this study was the applied voltage to the cathode electrode. It was found that the observed changes on the ion beam parameters in the range 100 - 1500 V, but higher than these values the behavior of diameter, emittance and focal point of the ion beam were quasi-saturated. Also, it was found that the general behavior of ion beam diameter and its emittance nearly the same.

Analysis of Hollow Cathode Aperture Wall Profile on Pseudospark Discharge-Based Sheet Electron Beam Source

In this article, an investigation has been performed to analyze the role of hollow cathode aperture wall profile on pseudospark (PS) discharge-based single gap sheet electron beam source. A simulation study using COMSOL Multiphysics has been carried out for different hollow cathode aperture wall profile parameters, such as thickness and radius of curvature of aperture wall. The role of hollow cathode aperture wall thickness “ $t$ ” and the radius of curvature of aperture wall “ $R$ ” for different gas pressures, 16–20 Pa, and the corresponding applied gap voltage 16–20 kV have been studied. The hollow cathode aperture wall thickness has been analyzed for the range of ~1–3 mm, keeping the constant aspect ratio 12:1, while the radius of curvature of aperture wall has been analyzed for the range of 0–3 mm for different wall thicknesses. Experimental studies have also been performed to analyze the role of the thickness of the aperture wall on PS discharge. A good correlation has been obtained between the simulation and experimental studies.

Plasma simulation to analyze velocity distribution characteristics of pseudospark-sourced electron beam**Project supported by the Sichuan Science and Technology Program, China (Grant No. 2019YJ0188) and the National Natural Science Foundation of China (Grant Nos. 61671116 and 11905026).

Pseudospark-sourced electron beam is a promising candidate for driving vacuum electronic devices to generate millimeter wave and terahertz wave radiation as it has a very high combined beam current density. However, the inherent velocity spread of the beam, which is difficult to measure in experiment, has a great influence on the operating frequency and efficiency of the vacuum electronic device. In this paper, the velocity distribution characteristics of the electron beam produced by a single-gap hollow cathode electron gun are numerically studied and a three-dimensional kinetic plasma simulation model of a single-gap hollow cathode electron gun is built by using particle in cell and Monte Carlo collision methods in Vorpal. Based on the simulation model, the time-dependent evolution of the plasma formation inside the hollow cathode and electron beam generation process are observed. It is demonstrated that the pseudospark-sourced electron beam has a relatively large velocity spread. The time-dependent velocity distribution of the beam is analyzed, and the dependence of the beam velocity distribution under various operating conditions such as anode–cathode potential difference, gas pressure, and cathode aperture size are also studied.

Element sensor based on microplasma generators

PurposeThe purpose of this paper is to present a study on miniaturized instruments for analytical chemistry with a microplasma as the excitation source.Design/methodology/approachThe atmospheric pressure glow microdischarge could be ignited inside a ceramic structure between a solid anode and a liquid cathode. As a result of the cathode sputtering of the solution, it was possible to determine its chemical composition by analyzing the emission spectra of the discharge. Cathodes with microfluidic channels and two types of anodes were constructed. Both types were tested through experimentation. Impact of the electrodes geometry on the discharge was established. A cathode aperture of various sizes and anodes made from different materials were used.FindingsThe spectroscopic properties of the discharge and its usefulness in the analysis depended on the ceramic structure. The surface area of the cathode aperture and the flow rate of the solution influence on the detection limits (DLs) of Zn and Cd.Originality/valueConstructed ceramic structures were able to excite elements and their laboratory-size systems. During the experiments, Zn and Cd were detected with DLs 0.024 and 0.053 mg/L, respectively.

Simulation for the Characteristics of Plasma of the Multi-gap Pseudospark Discharge

A high-energy electron beam was produced by a multi-gap pseudospark device under high breakdown voltages. In this work, a simulation model was developed to ascertain the mechanism of the discharge process in the multi-gap pseudospark, which was verified by the triggered multi-gap pseudospark discharge experiment. The characteristics of the plasma were investigated for different anode voltages and pressures. Results suggest the formation of a virtual anode in the cathode aperture during the discharge process, followed by the release of an electron from the plasma in the triggered hollow cavity. The propagation velocity of the ionization wave stimulated by the electron beam is increased with pressure and applied voltage on the anode. The highest density of the particles was found in the region of the cathode aperture. The densities of the particles in the aperture of the intermediate electrodes are higher than at the right adjacent side gaps when the entire gap space is filled with the plasma. The peak of the electron distribution function is found to be situated at higher energies at the beginning of discharge, then the electron distribution function gets shifted to lower energies on the completion of discharge.

Investigation of Electron Beam Generation in Pseudospark Discharge-Based Plasma Cathode Electron Source

In this paper, an investigation has been carried out for the generation of electron beam in the pseudospark discharge-based plasma cathode electron (PD-PCE) source for a wide range of geometrical and operating parameters, such as cathode aperture, gas pressure, and seed electron energy, using 2-D kinetic plasma simulation code. It has been observed that the peak electron beam current’s time to appear at the anode surface decreases with an increase in the cathode aperture size, gas pressure, and injected seed electron energy. Investigation of the peak electron beam current and its time to appear at the anode is presented with reference to the variation of cathode aperture and gas pressure. It has been found that the generated electron beam current increases with increase in gas pressure while decreases with increase in the cathode aperture. The potential profile is also presented which is responsible for confinement of the plasma inside the hollow cathode (HC) cavity. The simulation has been performed for the required aperture size 2–10 mm, argon gas pressure 20–80 Pa, and seed electron energy 1–4 kV. The gas pressure, cathode aperture, and seed electron energy strongly influence the growth of plasma inside the HC cavity and also the generation of corresponding energetic electron beam. As a result, electron beams of different current amplitudes, sizes, and energies can be realized by proper control of the gas pressure, cathode aperture size, and seed electron energy of PD-PCE source for its use in extreme ultraviolet/X-ray and microwave applications.

PIC Simulation to Analyze Peak Electron Current Generation in a Triggered Pseudospark Discharge-Based Plasma Cathode Electron Source

In this paper, an investigation has been carried out for the analysis of peak electron current at the anode surface in pseudospark discharge-based plasma cathode electron (PCE) source using 2-D kinetic plasma simulation code OOPIC-PRO. It has been observed that peak electron current is a function of hollow cathode (HC) dimension, gas pressure, and seed electron energy. The investigation has also been carried out for temporal evolution of the plasma formation inside the HC and electron-beam generation processes. Trends in size of the generated electron beams have been presented as a function of the potential distribution at the cathode aperture and applied gas pressure. As a result, on increasing gas pressure for the constant aperture size of HC, electron beam of higher current is generated while on other hand, by increasing cathode aperture for constant gas pressure, electron beam of lower current is achieved. The spatial characteristics of cathode fall region have also been presented for the different gas pressures and cathode aperture sizes. The simulation has been carried out for the variation of cathode apertures 1–10 mm as well as argon gas pressures 1–80 Pa. The gas pressure, cathode aperture and seed electron energy strongly influence the potential distribution in PCE source, and therefore, the peak electron currents as well as electron beams of different amplitudes and sizes can be realized.

Dependence of pre-breakdown time on ionization processes in a pseudospark discharge

The formation and development of pseudospark discharge, especially the onset of the breakdown, are of great technological interests in multiple applications due to their influences on the limits of current rising and fast switching performances of the devices. In this work, the development of pseudospark discharge in the pre-discharge and hollow cathode phases in a single-gap device are investigated by a time-dependent model to calculate the temporal development of total ionization cross section in varying times and regions. The simulations in our work are performed using the two-dimensional kinetic plasma simulation code XOOPIC. The time-dependent evolutions of the ionization cross section in pre-discharge and hollow cathode phases are presented under varying electric fields and hollow cathode configurations. Thus the electron multiplications and plasma generation processes by ionizing collisions in varying phases are examined and their dependences on a variety of external parameters are determined in different regions in the pseudospark device. A sequence of physical events and their influences in different regions are also identified via the quantitative analysis of time-dependent ionization cross section. The discharge formation time shows highest dependences on the cathode aperture diameters and anode voltages. Additionally, a linear dependence of the pseudospark breakdown time on the time-averaged ionization cross section is illustrated under varying external parameters. It indicates that the influences of the external parameters on the discharge performances can be determined and estimated via the total and average ionization cross sections under varying external conditions. In this work, both a qualitative understanding of the pseudospark onset mechanism and a quantitative approach to estimate the formation time in a pseudospark device with varying parameters are developed via this model.

Study of the beam profile and position instability of a post-accelerated pseudospark-sourced electron beam

A pseudospark-sourced electron beam is a promising candidate for driving a THz millimeter wave radiation source. However, the physics governing the electron beam density profile and the beam center deviation from the axis of the structure, which may be caused by the randomness in the pseudospark discharge process, remains still unclear especially for the high energy component of the pseudospark-sourced electron beam, which is usually non-mono-energetic. It is essential to study the electron beam density profile and the beam center position distribution for optimizing the pseudospark discharge configuration. In this paper, images of some single-shot electron beam pulses have been captured using a 50 μm thickness stopping copper foil and a phosphor screen coated with a P47 scintillator to study the electron beam density profile and the beam center position distribution of the high energy component of the electron beam. The experiments have been carried out on two pseudospark discharge configurations with two different size hollow cathode cavities. The influence of the cathode aperture of each configuration has also been studied according to the beam images. Experimental results show that the beam profile of the high energy component has a Lorentzian distribution and is much smaller than the axial aperture size with the beam centers dispersing within a certain range around the axis of the discharge structure. The pseudospark-sourced electron beam with a larger hollow cathode cavity shows a smaller full width at half maximum radius and a more concentrated beam center distribution.

Study on the electron emission process of the pseudospark during the hollow cathode phase under nanosecond pulsed voltage

Pseudospark discharge, discovered in 1979, has remarkable parameters that may make it useful in various applications. This paper explores the influence of the cathode aperture on the breakdown characteristics of pseudospark discharge. In addition, the discharge process in both the main gap and the cathode aperture has been researched by a high-speed framing camera. Results revealed that the influence of the structure of the hollow cathode on the breakdown voltage characteristics lies in the structure of the cathode aperture. Besides, the delay of the electron emission process has been calculated based on the explosive electron emission model. In the end, a possible reason for the great discharge current and high increase rate of the discharge current has been discussed.

Angular dose variations from 320 kV rod pinch diode flash X-ray experiments on the modified Kali-1000 Pulsed Power System

This paper highlights the angular distribution of radiation dose emitted from a rod-pinch diode. The typical RP diode employed used a small diameter (1–2 mm) anode rod extended through a cathode aperture (5–8 mm). The diode chamber is maintained at 2 × 10–5 Torr vacuum by a rotary backed diffusion pump. Experiments performed on a modified Kali-1000 Pulsed Power System (300 kV, 30 kA, 100 ns) were aimed at optimizing the source by maximizing the figure of merit (dose at 1 m in rad/spot diameter2 in mm2) with minimizing of the diode impedance. The typical electron beam parameters used in the experiments are 240–320 kV, 6.5–27.5 kA, 100 ns, with a few hundreds of kA/cm2 current density. The radiation emitted from a rod-pinch diode is measured using thermoluminescence dosimeters at an angular interval of 15° on either side of the rod in horizontal and vertical plane with different aspects ratio ranging from 2.5 to 10.0. Experimentally found that the radiation dose produced from the rod pinch diode configuration is maximum in the axial direction and decreases with angular variation on either side of the axis in horizontal and vertical planes, which indicates the directivity of the source. Maximum radiation dose at 1 m distance on the axial line is ranging from 42 to 307 mR.

The hollow cathode effect in a radio-frequency driven microhollow cathode discharge in nitrogen

A two-dimensional particle-in-cell Monte-Carlo code has been developed to study the physical mechanism of the hollow cathode effect (HCE) in an rf microhollow cathode discharge (rf-MHCD). Under the simulated conditions, the HCE in the rf-MHCD is the result of sheath-superposition, and both α ionization and γ ionization play a role. However, α ionization mode is predominant. Electrons undergo a pendular motion during the negative portion of the rf cycle. When the rf hollow electrode has a positive voltage, the majority of the electrons move toward the rf electrode, and the mean electron energy near the rf electrode is higher than that in a dc hollow cathode discharge, resulting in a large number of energetic electrons bombarding the hollow cathode wall, an important characteristic of the rf-MHCD. When the hollow cathode aperture is sufficiently small, many electrons strike the hollow electrode and are removed from the discharge space, so that the plasma density decreases. The average energy of the ions in the quasi-neutral plasma region near the axis is greater than the thermal energy in a molecular gas. Therefore, high density, high energy, and high chemical activity are characteristic advantages of rf-MHCD plasma sources.

Hollow Cathode Electron Beam Formation and Effects on X-Ray Emission in Capillary Discharges

Electron beams produced by the hollow cathode effect are studied in a compact gas filled 24-kV, 5-kA capillary discharge. The characteristics and role of electron beams on X-ray production are studied in order to better understand their impact on X-ray production. X-ray plasma emission is analyzed with a spectrometer, while wideband diodes and Faraday cup probe both electron beams and X-rays. Electron beams of >5 keV are observed early on the discharge and two types of electron beams are identified: a first beam of high energy and low current (with a speed of $\sim 5 \times 10^{7}$ m/s and a current density of $\sim 4\times 10^{\mathrm {-2}}$ A/cm $^{2})$ enhanced by larger cathode apertures, and a second beam of low energy and high current enhanced by smaller cathode apertures. The use of a simple configuration of external magnets prevents X-ray fluorescence production, caused by electron beams, from reaching electronic detectors hence confusion when evaluating X-ray yield from the plasma source is avoided. This is particularly important in extreme ultraviolet lithography and soft X-ray production applications. Furthermore, the presence of the external magnets does not modify line emission, which is detected by means of spectrometry. Therefore, the use of external magnets provides a way to discriminate X-ray diode signals produced by source emitted X-rays and X-ray fluorescence from electron beams.

The Breakdown Characteristics of Single-Gap Pseudospark Discharge Under Nanosecond Pulsed Voltages

In this paper, an experimental investigation of pseudospark discharge behaviors was conducted under nanosecond pulsed voltages using a flexible discharge chamber. The breakdown voltages of the pseudospark discharge gap were measured for a wide range of gas pressures, anode-cathode gap distances, and cathode aperture diameters to find the match of gap distance and cathode aperture diameter at a certain gas pressure with the nanosecond pulsed voltage. According to the experimental results, an empirical relationship was obtained. The roles of the parameters in the empirical relationship during the discharge were analyzed. The breakdown characteristics were also consistent with the Paschen's law in the pseudospark under nanosecond pulsed voltages, when the gap distance was replaced by the effective gap distance. In the end, a possible reason was put forward to explain the difference between the empirical relationships obtained under dc voltages and nanosecond pulsed voltages.

Investigation of condition-induced bubble size and distribution in electroflotation using a high-speed camera

In the flotation process, bubble is a key factor in studying bubble-particle interaction and fine particle flotation. Knowledge on size distribution of bubbles in a flotation system is highly important. In this study, bubble distributions in different reagent concentrations, electrolyte concentrations, cathode apertures, and current densities in electroflotation are determined using a high-speed camera. Average bubble sizes under different conditions are calculated using Image-Pro® Plus (Media Cybernetics®, MD, USA) and SigmaScan® Pro (Systat Software, CA, USA) software. Results indicate that the average sizes of bubbles, which were generated through 38, 50, 74, 150, 250, 420, and 1000μm cathode apertures, are 20.2, 29.5, 44.6, 59.2, 68.7, 78.5, and 88.8μm, respectively. The optimal current density in electroflotation is 20A/m2. Reagent and electrolyte concentrations, current density, and cathode aperture are important factors in controlling bubble size and nucleation. These factors also contribute to the control of fine-particle flotation.

Study of the Discharge Mode in Micro-Hollow Cathode

In this study, micro-hollow cathode discharge (MHCD) is investigated by a fluid model with drift-diffusion approximation. The MHC device is a cathode/dielectric/anode sandwich structure with one hole of a diameter D=200 μm. The gas is a Ne/Xe mixture at a pressure p=50∼500 Torr. The evolutions of the discharge show that there are two different discharge modes. At larger pD the discharge plasma and high density excited species expand along the cathode surface and, a ringed discharge mode is formed. At smaller pD, the discharge plasma and the excited species expand along the axis of the cathode aperture to form a columnar discharge.

Hydrogen bubble flotation of fine minerals containing calcium

One characteristic of electro-flotation is the presence of micro bubbles that are well known for improving the flotation performance of fine particles. An electro-flotation method was studied with fine scheelite and fluorite particles sized into three different fractions. Experiments were performed in a modified Hallimond tube. We investigated the effects of gas holdup, particle size, and different mesh electrode apertures on mineral recovery. Flotation results show that two size fractions show increased flotation recovery as the gas holdup increases. For the sized scheelite and fluorite, the flotation effect is diverse for different sizes of the cathode aperture. Pictures of the bubbles taken by a high speed CCD were used to determine the hydrogen bubble size distribution generated as a function of collector, current density, and electrode size. The diameters of the hydrogen bubbles ranged from 12 to 117 μm in alkaline conditions.

Detailed Simulation of the CYGNUS Rod Pinch Radiographic Source

In this paper, we present the results from particle-in-cell simulations of the nominally 2-MV 40-kA CYGNUS radiographic machine using a standard rod pinch diode. The rod pinch electron-beam diode consists of a small-diameter high-atomic-number anode extending through a thin cathode aperture. A significant shot-to-shot variation of the photon spectrum emerging from the anode can introduce an error in interpreting the radiograph. We present the results from these integrated simulations of the electron and photon generation and quantify the sensitivities on the photon distribution.

Study of the parameters affecting ion beam emerging from cold conical cathode ion source

The aim of this work is study of the parameters affecting ion beam emerging from cold conical cathode ion source. The input discharge and output ion beam characteristics have been measured at different pressures using nitrogen and argon gases. The optimum distance between the ion exit aperture of the cathode and the movable copper ion collector plate has been determined using nitrogen and argon gases. The ion collector plate has been placed at different distances from the ion exit aperture of the cathode equal to 2, 3, 4, 4.5, 5, 5.5 and 6 cm respectively. It is found that the optimum distance between the ion exit aperture of the cathode and the ion collector plate equals 5 cm for high output ion beam current. At this optimum distance, the efficiency of the ion source reaches 28.3% and 21.3% using nitrogen and argon gases respectively. The divergence angle of the ion beam exit from the cathode aperture has been determined for each distance by measuring the ion beam diameter which obtained on the ion collector plate. It is found that at the optimum distance between the ion exit aperture of the cathode and the ion collector plate, a minimum divergence angle of the ion beam emerging from the ion source equal to 1.14º and 2.29º using nitrogen and argon gases respectively. Also the aspect ratio of the ion source, the ratio between the radius of the ion exit aperture of the cathode to the distance between the ion exit aperture of the cathode and ion collector plate, has been determined.