Paschen Curve Research Articles

Intersection of Paschen's curves for argon

The intersection of Paschen's curves for argon with a same gap length but a different electrode radius was observed. While the breakdown voltage increases with the increase of the nonuniformity in the electric field of the gap at lower pressures, it decreases at higher pressures. The reason for the intersection of Paschen's curves was given based on the mean free path length of the electrons inversely proportional to the gas pressure and the electron impact ionization coefficient exponentially increasing with the electric field. The intersection of the Paschen's curves was qualitatively reproduced by a numerical simulation.

The position effect on electrical field intensity for metal deposition process

Material characteristics, such as electric potential, distance between target material and substrate, and so on, are important parameters for vacuum metal films deposition (sputtering) system. Properly controlling these parameters during the sputtering process can reduce the residual stress after deposition and can effectively improve the deformation of substrate and density of metal thin film. This study aims at simulating a vacuum metal film deposition system for substrate application with normal metal material. Both the copper foil, as a target material, and the substrate that is placed on a carrier platform are included in a vacuum chamber. The argon ion gas is excited by a radio frequency power generator to form the plasma source in the sputtering system. “Glow Discharge” of the “Paschen Curve” during plasma generation process is employed to excite the argon ion gas to bombard the target material. The ejected atoms of target material are deposited on the substrate surface to form the desired thin films. Several different parameters, such as radio frequency power, electric field intensity, distance between the target materials and the substrate, and so on, are discussed in this article. Numerical analysis results indicate that the distance between the substrate and target materials may affect the density of metal film significantly. The MATLAB simulation results can provide the technique of finding better workpiece height and high coating quality for the semi-conduction industrial adopting sputtering system for metal thin film production.

Experimental Investigations on the Pulsed Power Switch of a HIRA based UWB System

The ultrawideband (UWB) system has been a subject of research in the last few decades due to its utility in various high-power electromagnetic applications. Effectiveness of the UWB system, for the targeted performance, is expressed mainly in terms of the intensity and the frequency spectrum of the radiated field. If the system is simultaneously meant for high-energy output with good pulse repetition rate and jitter then the performance of the source of the UWB system, i.e., the pulsed power system, and in particular, the switch becomes extremely important. This paper presents the work carried out on such a UWB system with focus on the experimental investigations performed on a 50 kV pulsed power system. The switch of the pulsed power system is designed to use various dielectric gases, such as dry Air, N 2, SF6, and a mixture of these gases as the switching media at varying pressures which are above and below atmospheric pressure levels. For gas pressures above the atmospheric pressure level, the relationship between the switch breakdown voltage and the gas pressure as well as between the rise time and the gas pressure have been studied. Rise time performances of the switch for various pure gaseous media have been estimated. Jitter and shot life performance of the switch for N2 and SF6 as the switching media have also been studied. Effect of shot life on the switch jitter has been evaluated for N2 filled switch for a shot life of 10.8 × 106 shots. In case of switch filled with subatmospheric pressure SF6 gas, the rise time as a function of pressure has been characterized up to a voltage level of 45 kV. The Paschen's curve for the subatmospheric pressure levels is also derived from the results.

Non-Maxwellian to Maxwellian transitions of atmospheric microplasmas at microwave frequencies

Particle-in-cell/Monte Carlo simulations and numerical analysis of a single particle motion are performed for atmospheric He microplasmas at microwave frequencies to determine the characteristics of non-Maxwellian to Maxwellian transition. The left and the right regimes of Paschen curve, divided by this transition, reveal that the transition frequencies depend on the gap of electrodes and the neutral gas pressure to follow scaling laws for a new extended Paschen law. The fluid models are reasonable at the right-side regime of Paschen breakdown areas, but not on the left side, which is highly kinetic for electrons. The plasmas driven by weaker electric fields of high enough frequencies at the right-side Paschen regime breed more energetic electrons.

The role of magnetic energy on plasma localization during the glow discharge under reduced pressure

Abstract In this work, we present the first results of our research on the synergy of fields, electric and magnetic, in the initiation and development of glow discharge under reduced pressure. In the two-electrode system under reduced pressure, the breakdown voltage characterizes a minimum energy input of the electric field to initiate and sustain the glow discharge. The glow discharge enhanced by the magnetic field applied just above the surface of the cathode influences the breakdown voltage decreasing its value. The idea of the experiment was to verify whether the contribution of potential energy of the magnetic field applied around the cathode is sufficiently effective to locate the plasma of glow discharge to the grounded cathode, which, in fact, is the part of a vacuum chamber wall (the anode is positively biased in this case). In our studies, we used the grounded magnetron unit with positively biased anode in order to achieve favorable conditions for the deposition of thin films on fibrous substrates such as fabrics for metallization, assuming that locally applied magnetic field can effectively locate plasma. The results of our studies (Paschen curve with the participation of the magnetic field) seem to confirm the validity of the research assumption. What is the most spectacular - the glow discharge was initiated between introduced into the chamber anode and the grounded cathode of magnetron ‘assisted’ by the magnetic field (discharge did not include the area of the anode, which is a part of the magnetron construction).

Plasma generation by dielectric resonator arrays

Arrays of dielectric resonators—illuminated by an antenna—are used to ignite and sustain multiple microwave plasmas in parallel. Calcium titanate cylindrical resonators were arranged in a linear array with separation distances between 0.5 and 5 mm. The operating frequency was near the HEM111 resonance of 1.1 GHz. Paschen curves of the breakdown field and voltage in argon atmosphere are consistent with parallel plate microwave breakdown except within discharge gaps of 1 mm or less. Sustaining of argon plasma between 0.5 Torr and 1 atm within the array is found to alter the electromagnetic scattering from the dielectric resonators, suggesting applications in plasma-reconfigurable metamaterials and photonic crystals.

The radiofrequency magnetic dipole discharge

This paper describes a novel and simple concept of plasma source, which is able to produce a radiofrequency magnetized discharge with minimal power requirements. The source is based on the magnetron concept and uses a permanent magnet as an active electrode. The dipolar field produced by the magnet confines the electrons, which cause further ionization, thus producing a toroidally shaped plasma in the equatorial region around the electrode. A plasma can be ignited with such scheme with power levels as low as 5 W. Paschen curves have been built for four different working gases, showing that in Helium or Neon, plasma breakdown is easily obtained also at atmospheric pressure. The plasma properties have been measured using a balanced Langmuir probe, showing that the electron temperature is around 3–4 eV and higher in the cathode proximity. Plasma densities of the order of 1016 m−3 have been obtained, with a good positive scaling with applied power. Overall, the electron pressure appears to be strongly correlated with the magnetic field magnitude in the measurement point.

Field emission driven direct current argon discharges and electrical breakdown mechanism across micron scale gaps

In this paper results of the experimental and theoretical studies of the field emission driven direct current argon microdischarges for the gaps between 1 μm and 100 μm are presented and discussed. The breakdown voltage curves and Volt-Ampere characteristics proved to be a fertile basis providing better understanding of the breakdown phenomena in microgaps. Based on the measured breakdown voltage curves, the effective yields have been estimated confirming that the secondary electron emission due to high electric field generated in microgaps depends primarily on the electric field leading directly to the violation of the Paschen’s law. Experimental data are supported by the theoretical predictions that suggest departure from the scaling law and a flattening of the Paschen curves at higher pressures confirming that Townsend phenomenology breaks down when field emission becomes the key mechanism leading to the breakdown. Field emission of electrons from the cathode, the space charge effects in the breakdown and distinction between the Fowler-Nordheim field emission and the space charge limited current density are also analyzed. Images and Volt-Ampere characteristics recorded at the electrode gap size of 20 μm indicate the existence of a discharge region similar to arc at the pressure of around 200 Torr has been observed.

Decay Modes of Anode Surface Temperature After Current Zero in Vacuum Arcs—Part II: Theoretical Study of Dielectric Recovery Strength

Anode surface temperature after current zero has a great impact on the interruption capacity of a vacuum interrupter. The objective of this paper is to theoretically investigate the relation between breakdown voltages and anode surface temperature after current zero. A heat conduction model was adopted to describe the temperature development of the anode, taking account of phase transition and evaporation. The breakdown voltages in certain metal vapor densities were obtained by the Particle-in-Cell/Monte Carlo collision (PIC-MCC) method. Finally, the Paschen curve for copper vapor was obtained using the PIC–MCC method and verified by the theoretical model. Moreover, the minimum breakdown voltage, 30 V, was obtained at a density of $1.3\times 10^{22}/\text{m}^{3}$ with a gap of 10 mm, which corresponded to a surface temperature of 1983 K. In order to ensure a successful interruption, anode surface temperature should not be higher than 1983 K at current zero, and the melting time should be kept as short as possible.

Breakdown and dc discharge in low-pressure water vapour

In this paper we report studies of basic properties of breakdown, low-current Townsend discharge and high-current discharge regimes in water vapour. Paschen curves and the corresponding distributions of emission intensities at low current were recorded in the range of pd (pressure x electrode gap) from 0.1 to 10 Torrcm covering the region of Paschen minimum. From the experimental profiles we obtained effective ionization coefficient of water vapour for the E/N range 650 Td–7 kTd and fitted the results by using the extended Townsend analytical formula. Using the obtained ionization coefficient, we calculated the effective yield of secondary electrons from the copper cathode. Results of the measurements of Volt-Ampere characteristics in water vapour were presented together with the images of the axial structure of the discharge in a wide range of discharge currents for two pd values. Recorded profiles showed development of the spatial structure of the discharge in different operating regimes. We were able to identify conditions where processes induced by heavy particles, probably fast hydrogen atoms, are dominant in inducing emission from the discharge. Finally, standard scaling laws were tested for low current and glow discharges in water vapour.

Electric field vector measurements in a surface ionization wave discharge

This work presents the results of time-resolved electric field vector measurements in a short pulse duration (60 ns full width at half maximum), surface ionization wave discharge in hydrogen using a picosecond four-wave mixing technique. Electric field vector components are measured separately, using pump and Stokes beams linearly polarized in the horizontal and vertical planes, and a polarizer placed in front of the infrared detector. The time-resolved electric field vector is measured at three different locations across the discharge gap, and for three different heights above the alumina ceramic dielectric surface, ~100, 600, and 1100 μm (total of nine different locations). The results show that after breakdown, the discharge develops as an ionization wave propagating along the dielectric surface at an average speed of 1 mm ns−1. The surface ionization wave forms near the high voltage electrode, close to the dielectric surface (~100 μm). The wave front is characterized by significant overshoot of both vertical and horizontal electric field vector components. Behind the wave front, the vertical field component is rapidly reduced. As the wave propagates along the dielectric surface, it also extends further away from the dielectric surface, up to ~1 mm near the grounded electrode. The horizontal field component behind the wave front remains quite significant, to sustain the electron current toward the high voltage electrode. After the wave reaches the grounded electrode, the horizontal field component experiences a secondary rise in the quasi-dc discharge, where it sustains the current along the near-surface plasma sheet. The measurement results indicate presence of a cathode layer formed near the grounded electrode with significant cathode voltage fall, ≈3 kV, due to high current density in the discharge. The peak reduced electric field in the surface ionization wave is 85–95 Td, consistent with dc breakdown field estimated from the Paschen curve for hydrogen. The present set of data on electric field distribution in a surface ionization wave discharge provides an experimental reference for validation of kinetic models and assessing their predictive capability.

Breakdown in hydrogen and deuterium gases in static and radio-frequency fields

We report the results of a combined experimental and modeling study of the electrical breakdown of hydrogen and deuterium in static (DC) and radio-frequency (RF) (13.56 MHz) electric fields. For the simulations of the breakdown events, simplified models are used and only electrons are traced by Monte Carlo simulation. The experimental DC Paschen curve of hydrogen is used for the determination of the effective secondary electron emission coefficient. A very good agreement between the experimental and the calculated RF breakdown characteristics for hydrogen is found. For deuterium, on the other hand, presently available cross section sets do not allow a reproduction of RF breakdown characteristics.

Effect of the Mesh Transparency on the Electrical Characteristics of DC Pseudo Discharge

A DC pseudo discharge for air has been studied. Air pressure is used in the range between 0.7 Torr and 12 Torr. The breakdown occurs between a plane cathode and a mesh anode at transparencies of 19%, 46%, and 65%. The current-voltage characteristic curves of the discharge, which are measured at different pressures, distances, and mesh transparences, take effect in the region of abnormal glow. The discharge voltage decreases as the air pressure increases, while more voltage is needed to maintain the discharge when either the mesh transparency or the inter-electrode distance is increased. An increment of mesh transparency causes high negative potential behind the mesh due to the high concentration of electrons, which accumulate and collide with neutral atoms. Paschen curves deviate from the expected regular one. The left side of Paschen curves appears at inter-electrode distance of 1 mm, whereas the right side appears at inter-electrode distance of 5 mm. The intermediate region is observed only at 3 mm distance between the two electrodes. For the transparency range used in this work, it is found that the decrement of the breakdown voltage, on the right side, depends on the mesh transparency. For different electrode separations, the measured Paschen curves are coincident and deviate from the standard ones of Paschen's law.

The diffusion-ionization mechanism of the transverse propagation of Townsend and glow discharges and its influence on the stability and nature of a normal current density

The diffusion-ionization mechanism of the transverse propagation of a short Townsend discharge has been investigated theoretically and experimentally near the minimum of the Paschen curve. It has been found that the longitudinal electron diffusion causes significant enhancement of the transverse discharge propagation. The effective coefficient of diffusion-ionization discharge propagation in neon has been measured in different electric fields (E/p ≈ 100–220 V cm−1 Torr−1); its value may be several times larger than the ambipolar diffusion coefficient. The transverse-instability boundary of a Townsend discharge in neon has been determined theoretically and experimentally. The diffusion contribution to the boundary condition determining the normal current density is estimated.

Micrometer-scale electrical breakdown in high-density fluids with large density fluctuations: Numerical model and experimental assessment.

Experimentally observed electrical breakdown voltages (U(B)) in high-pressure gases and supercritical fluids deviate from classical theories for low-pressure gas discharges, and the underlying breakdown mechanisms for the high-density fluids making the U(B) differ from those in the classical discharges are not yet well understood. In this study, we developed an electrical breakdown model for the high-density fluids taking into account the effects of density fluctuations and ion-enhanced field emission (IEFE). The model is based on the concept that a critical anomaly of the U(B) (local minimum near the critical point) is caused by long mean free electron path leading to a large first Townsend coefficient in locally low-density spatial domains generated by the density fluctuations. Also, a modified Paschen's curve considering the effect of the IEFE on the second Townsend coefficient was used to reproduce the U(B) curve in the high-density fluids. Calculations based on the novel model showed good agreements with the experimentally measured U(B) even near the critical point and it also suggested that the critical anomaly of the U(B) depends on the gap distance. These results indicate that both the density fluctuations and the IEFE have to be considered to comprehend the plasmas in high-density and density-fluctuating fluids.

Self-organized patterns in successive bifurcations in planar semiconductor-gas-discharge device.

The formation of dissipative structures is investigated in a planar semiconductor-gas-discharge device at room temperature. The width of the discharge gap is about 1 mm. The gap is filled with nitrogen at a pressure that corresponds to the discharge operation at the right branch of the Paschen curve. Wafers of semi-insulating GaAs that exhibit linear transport in the whole range of voltage and current studied are used as semiconductor electrodes. In addition to the earlier investigated Andronov-Hopf bifurcation, a different mode of self-organization of the device is observed, where the transport of charge proceeds through an ensemble of pulsating current filaments. The corresponding critical current for the present bifurcation does not depend on the polarity of the bias voltage, while the spatiotemporal dynamics of a pattern differs substantially for a change in the polarity. Pulsating filaments can form a spatially ordered pattern when the GaAs electrode is under the positive potential. We also observe self-organization modes, where pulsating filaments form an irregular spatiotemporal dynamics of a pattern. The data obtained are briefly discussed in the frame of corresponding theoretical results in the field.

Physical Modeling of Secondary Arcing at Environmental Pressures in the Range from Atmospheric to Vacuum

An electrical breakdown in the onboard equipment of orbital space vehicles is a consequence of multifactor physical process related to vacuum electronics, low-temperature plasma physics, and gas discharge. The problem becomes especially urgent in connection with the application of an onboard electrical network voltage of 100 V and higher that exceeds the arcing threshold. The given problem is being actively investigated for more than 10 years; as a result, a number of standards regulating measures on prevention of secondary arcing as a consequence of electrostatic breakdown are currently in force in the world. However, arcing caused by internal processes in onboard equipment without high-voltage initiation has not yet practically been studied, despite the existence of such problem that makes these investigations urgent. The present work contains results of experiments on registration of the threshold parameters, first of all, the pressure that determines the risk of secondary arcing in the presence of the plasma imitating the primary discharge plasma and caused by wire evaporation. Results of experiments confirm the expected decrease of the threshold breakdown voltage below the minima of the Paschen curve. Experimental approaches used in this work are of methodological interest for imitation of arcing conditions and testing of stability of the equipment against arcing in orbital space.

On the difference between breakdown and quench voltages of argon plasma and its relation to 4p–4s atomic state transitions

Using a relaxation oscillator circuit, breakdown (VBD) and quench (VQ) voltages of a DC discharge microplasma between two needle probes are measured. High resolution modified Paschen curves are obtained for argon microplasmas including a quench voltage curve representing the voltage at which the plasma turns off. It is shown that for a point to point microgap (e.g., the microgap between two needle probes) which describes many realistic microdevices, neither Paschen's law applies nor field emission is noticeable. Although normally VBD > VQ, it is observed that depending on environmental parameters of argon, such as pressure and the driving circuitry, plasma can exist in a different state with equal VBD and VQ. Using emission line spectroscopy, it is shown that VBD and VQ are equal if the atomic excitation by the electric field dipole moment dominantly leads to one of the argon's metastable states (4P5 in our study).

The Applicability of Fluid Model to Electrical Breakdown and Glow Discharge Modeling in Argon

The simple fluid model, an extended fluid model, and the fluid model with nonlocal ionization are applied for the calculations of static breakdown voltages, Paschen curves and current-voltage characteristics. The best agreement with the experimental data for the Paschen curve modeling is achieved by using the model with variable secondary electron yield. The modeling of current-voltage characteristics is performed for different inter-electrode distances and the results are compared with the experimental data. The fluid model with nonlocal ionization shows an excellent agreement for all inter-electrode distances, while the extended fluid model with variable electron transport coefficients agrees well with measurements at short inter-electrode distances when ionization by fast electrons can be neglected.

Reduction of breakdown threshold by metal nanoparticle seeding in a DC microdischarge.

Significant reduction of the breakdown threshold in a DC microdischarge via seeding metal nanoparticles has been demonstrated. Compared to standard Paschen curves in dry air, reductions in the breakdown voltage of 5% to 25% were obtained for PD values (the product of pressure and electrode gap distance) ranging from 20 to 40 Torr-cm by seeding aluminum and iron nanoparticles with mean sizes of 75 nm and 80 nm, respectively. No secondary energy source was required to achieve this breakdown threshold reduction. From high-speed chemiluminescence imaging of the discharge evolution, breakdown was shown to be initiated at reduced voltages. Following breakdown, the increase in temperature ignited some of the nanoparticles near the cathode. Results suggest that possible charging of the nanoparticles within the gap may reduce the effective transient distance, leading to the threshold reduction.