Pseudospark Device Research Articles

Simulation of pulsed electron-beam emission from a triggered multi-gap pseudospark device

Results simulating time-resolved pulsed electron-beam emission from a triggered four-gap pseudospark device are presented. It is important for many applications to explore the mechanisms of the pulsed electron-beam current generated in the multi-gap pseudospark discharge devices. From experiments, it is known that the pulsed emitted electron pulse is principally at the beginning, characterized by a rather short part of high energetic electrons followed by a broad pulse of electrons with an average energy of half of applied voltage. These characteristics of the electron-beam current have been simulated for a four-gap pseudospark discharge device with anode voltages from 20 to 50 kV, and with Ar as working gas in a pressure range from 20 to 60 Pa. According to the results, when the pressure becomes higher than a specific threshold, the two peaks are found to merge together. When the anode voltage is 20 kV, the pressure threshold is about 30 Pa. When the anode voltage is above 30 kV, the pressure threshold is about 40 Pa. It is observed that the energy spectrum of the high-energetic part of pulsed electron-beam contains a large peak corresponding to several keVs in the initial stage, and then it shifts toward lower energies. From the simulation, this specific characteristic is verified that the time duration of the high-energetic part of the pulsed electron-beam current grows with increasing anode voltage and decreasing pressure.

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.

Influence of Electrode Geometry and Gas on the Breakdown Voltage of Hollow Cathode Discharge With Spark Geometry Under Nanosecond Pulses

Pseudospark-sourced electron beam with high energy can be produced by the pseudospark device. In this paper, the breakdown voltages of the hollow cathode discharge with the pseudospark geometry influenced by electrode geometry and the gas have been studied and analyzed. In the wide range of pressure and gap, the breakdown voltage increases with the increase in the pressure and the gap distance. There is a pressure threshold and a gap distance threshold, below which the discharge mode will change. The product of the pressure threshold and the gap distance threshold is about 65 Pa · mm. The breakdown voltage is affected by the aperture diameter and the gap distance together. When the ratio of the gap distance to the aperture diameter is greater than 4, the electric field inside the small hole is almost zero and the discharge is converted to the plate electrode discharge. When the ratio is in the range of 0.67-4, the breakdown voltage decreases with the increase in the aperture diameter. When the ratio is less than 0.67, the breakdown voltage hardly changes with the aperture diameter.

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.

Experimental investigation of time-resolved electron beam energy distributions generated in a transient hollow cathode discharge

In this paper, a retarding potential energy analyzer (RPEA) specific for pulsed electron beams within the pressure range of tens of mTorr is developed and used to investigate the energy of transient hollow cathode discharge produced electron beams. This RPEA has been applied in a pseudospark-based electron beam source at applied potential up to 20 kV. Experimental investigations under applied potential of 5 kV, 10 kV, 15 kV, and 20 kV were carried out and the time-resolved electron energy distributions are constructed. The numbers of electrons within various energy groups are calculated from the time-resolved electron energy spectra. Results show that the maximum number of electrons is emitted within the energy range of 40%–60% of the full applied potential on the pseudospark device, and varies from 22.5 ± 2.0% to 38.9±2.0% of the total number of emitted electrons. Additionally, the energy transformation efficiency of stored electrical energy to electron beam energy is calculated from presented data. The energy transformation efficiency increases from 11.4 ± 0.5% at 5 kV breakdown voltage to 23.2 ± 3.5% at 20 kV breakdown voltage.

Pseudospark electron beam as an excitation source for extreme ultraviolet generation

A xenon pseudospark device is used to generate energetic and intense electron beams (e-beams) that induce extreme ultraviolet (EUV) emission in the range of 11–17 nm. This e-beam-based EUV source is compact, and the device is of interest because it has potentially attractive EUV conversion efficiency and pulse energy requirement, with potential for long lifetime and high repetition-rate operation. The role of e-beam-induced inelastic electronic collisions is considered.

Characterization of a Pulse-Charge-Mode Multigap Pseudospark Device as an Enhanced Electron Beam Source

Multigap pseudospark devices can be used to produce intense pulsed electron beams. Pseudospark discharge is generally initiated by self-breakdown or an external trigger in which DC high voltage is used. In this work, we investigated a pulse charge mode to generate an enhanced pulsed electron beam from a 10-gap pseudospark device. In the pulse charge mode, pulsed high voltage is applied to the device. Using the pulse charge mode, we could obtain enhanced electron beams in wider ranges of voltage and pressure than in the self-discharge or the trigger mode. We achived a maximum efficiency of enhanced electron beams at 3×10-1 mbar of Ar gas. Under this best pressure condition, we also observed well-focused electron beams with a diameter of down to 0.1 mm, peak current of up to 130 A, and full width at half maximum (FWHM) of 10 ns. The peak power density was 1010 W/cm2.

Recent results from the low inductance Z-discharge metal vapor ion source

The low inductance Z-discharge metal vapor (LIZ-MeV) ion source, which uses a magnetized Z-pinch, is a pseudo-spark device capable of producing intense currents (several kA) of highly charged gold or other ions. Typical operations produce an extracted charge-state distribution with a range in gold ion charge state from 4 to 19. Time-of-flight (TOF) spectra (excluding contributions from impurities) indicate that charge states at least as high as Au+12 were generated. Various TOF spectra are presented here to support this conclusion. Although the results are preliminary, LIZ-MeV shows great potential. Existing heavy-ion sources can produce either high beam currents, but low charge states (e.g., the metal-vapor vacuum arc) or high charge states, but low beam currents (e.g., the electron beam ion source). For ion beam injection our goal has been to develop an ion source that produces both high charge states and high beam currents. The existing LIZ-MeV has sufficiently large electron impact energies and electron current densities, but performance is limited by charge exchange with ambient gas and short confinement times. Plans are underway to add another Z-pinch stage to both lengthen confinement times and to minimize charge-state reducing processes. Such an enhanced LIZ-MeV should eventually produce even larger currents of more highly ionized heavy metal ions for accelerator applications.

Properties of a differential pressure pseudospark device

A differential pressure pseudospark device is developed to produce a discharge at a pressure of 10−4 mbar near the anode. This pressure range is two orders in magnitude lower than conventional pseudospark devices. In this device a pressure gradient is maintained between the cathode and the anode by providing a gas flow through the discharge column. The pressure gradient helps in shifting the Paschen curve more towards the left in comparison to the conventional case. The empirical relationship V∝(p2dD)−2, valid without a gas flow, is not applicable when the pressure difference between the cathode and the anode is over two orders in magnitude. Self-biasing collector technique reveals the presence of energetic electrons (0.4–1.2 keV) present in the plasma downstream of the anode. The nature of this plasma at two distinct pressure ranges of operation of the device shows marked difference in properties. A qualitative discussion is presented that explains the possible discharge mechanism in this device.

Numerical description and development of plasma stripper targets for heavy-ion beams

A Monte-Carlo simulation was developed to describe the stopping power of ions in ionized matter or cold non-ionized gases. The simulation confirmed that the enhanced energy loss in a plasma is mainly due to the higher mean charge state of the projectile ions in a plasma. The energy loss of copper ions and the mean charge states of argon and xenon ions were calculated. The numerical results showed good agreement with experimental data. Founded on the predictions of the simulation a new plasma stripper target was developed with a possible application in future heavy-ion driven ICF facilities. The new stripper target is based on the design of a pseudo-spark device. The stripping properties have been tested on an oxygen ion beam with an initial charge state of 4+ at 0.9 MeV/u. With the new device the yield of completely stripped oxygen ions increased almost four times compared with a corresponding cold gas stripper target.

Emittance and brightness measurement of a high voltage pseudospark electron beam

This is a report of the emittance and brightness measurement of an electron beam produced in a pseudospark discharge device driven by a pulse line accelerator. A ten-gap pseudospark device was operated at 200 kV, in a nitrogen gas fill pressure of 15 Pa. The typical value of emittance was measured to be 47 mn mrad about 5 cm downstream of the anode plane. The dependence of the beam current, HWHM emittance, the normalized emittance, and the normalized brightness on the axial distance from the anode were obtained. The highest brightness is about 2.7 × 1012A/(mrad)2 near the anode, and is still higher than 1010A/(mrad)2, 160 mm downstream of the anode. Such a high quality electron beam can be used for Raman free electron laser, X ray laser producing, and high power microwave.

Effect of magnetic field on breakdown voltage characteristics of a multigap pseudospark

An experimental investigation of the effect of magnetic field on the breakdown voltage characteristics of a multigap pseudospark device, with hydrogen gas, in a hollow anode–cathode, as well as a hollow cathode–anode configuration, is presented. The breakdown pressure at a particular discharge voltage increases with the increase in the applied axial magnetic field, and the magnitude of the increase is more pronounced at lower discharge voltages causing a right shift to the characteristic discharge curve in both the configurations. Application of a transverse magnetic field also resulted in a shift of the characteristic discharge curve towards the right. The observed results are compared and discussed with that found for parallel electrode geometry.

Repetitive high current density pseudospark-produced ion beams

A multigap pseudospark device filled with hydrogen or argon gas is operated up to 20 kV and ejected ion beam characteristics are experimentally investigated. The ion beam of peak current density in excess of ∼500 A/cm2 and pulse duration ∼50 ns is extracted at repetitive frequency of several tens of Hz. Results of the scaling study for the ion beam current with breakdown voltage, external capacitance, and number of insulator gaps are presented.

Investigation of the Transient Glow Discharge in Nitrogen

With the development of the pseudospark device, glow discharge with high power has recently become of interest. In this study, the voltage across a gap, the discharge current and the glow duration have been measured during transient glow discharge in the pressure range of 40-130 Torr in nitrogen. The results show that there exists a large difference between a previous investigation by Chalmers (1971) and the present study in the quantity of energy dissipated in the gap during the transient glow. However, in regard to the volume density of energy dissipated in the cathode fall, the values obtained by Chalmers and the present authors almost agree. From this result it is considered that the energy density is more essential than the energy quantity with respect to the transition of discharge from a transient glow to an arc.

Breakdown voltage characteristic of a pseudospark device

The breakdown voltage of a pseudospark device is measured for a wide range of gas pressure and anode–cathode gap distance. The data are analyzed by least-squares-fit methods, and the breakdown voltage is expressed by an empirical function of the gas pressure and the anode–cathode gap distance. It is found that the breakdown voltage is a function of p2d, the product of the pressure squared and anode–cathode gap distance. This is in contrast to that of a parallel-plate system that is described by Paschen’s curve, where the breakdown voltage is a function of pd.