Paschen Curve Research Articles

On the mechanism of electric breakdown under low-pressure discharge in helium

It us shown that the left branch of the Paschen curve is determined by the gas phase breakdown, which is caused by the electron avalanche at pD ≥ (pD)e and by the gas ionization by fast positive ions at pD < (pD)e. The (pD)e threshold value is evaluated, and it is established that the E/p ratio is the main parameter determining the gas breakdown.

α , γ, and normal, abnormal glow discharge modes in radio-frequency capacitively coupled discharges at atmospheric pressure

Discharge modes, α and γ, of a radio-frequency helium capacitively coupled discharge at atmospheric pressure were investigated with the discharge gap distance between electrodes varied from 1 to 5mm. As similarly observed in other experiments, the α and γ mode and the α–γ mode transition were observed with large drops in the voltage (310–179V) and the phase angle between the voltage and current (54°–18°), and a contraction of the plasma volume (8.5–0.17cm3, at 3mm gap distance). The discharge voltage where the α–γ mode transition occurred versus the gap distance showed a similar behavior with the Paschen curve for a gas breakdown. Depending on the gap distance, normal and abnormal glow regimes were observed in the αmode. At 1 and 2mm, the α mode remained in the abnormal glow discharge until the α–γ mode transition occurred as the discharge current increases. At 3mm, however, the α mode was excited as a normal glow discharge with a constant current density (17mA∕cm2) but it became an abnormal glow discharge as the current increased. At 4mm, the α mode was sustained as a normal glow discharge, then the transition to the γ mode occurred. Using a simple resistor-capacitor circuit model and a α sheath breakdown model, the discharge modes and the mode transition properties were studied.

Ignition and dynamics of high-voltage glow discharge plasma implantation

The self-ignition and dynamics of glow discharge plasma in the pulsed high-voltage plasma immersion ion implantation mode have been investigated. After ignition during the pulse-on period, the glow discharge continues to be sustained for a long period of time after the high-voltage pulse has been turned off as monitored by a Langmuir probe. The glow discharge and ignition lie on the left side of the Paschen curve when pd (gas pressure times electrode separation) is adjusted by using different anode to cathode distances utilizing a conducting grounded grid. The increased or constant implantation current Ia reveals that the ion sheath is stable and conforms to the cathode structure as the plasma density increases by one to two orders of magnitude towards the anode. In addition, the duration of the post-pulse-off plasma can be as long as several times of the pulse duration. The ignition time and duration of the plasma depend on the working pressure, applied voltage and pulse duration.

Production of Plasma Jet Based on High-Current Pseudo-Spark Discharge

A plasma jet based on a high-current pseudo-spark discharge has been developed. A pseudo-spark discharge (PSD) is a high-current glow-like discharge, which is formed on the left side of the minimum of the Paschen curve. Although the discharge current exceeds several tens of kiloamperes, the discharge retains the glow mode because of the hollow cathode effect. The PSD is formed with a large number of arc channels, which are usually narrow. Consequently, the PSD has a large cross section. In this study, the PSD anode has a hole with a larger diameter than that of the cathode in order to generate a plasma jet. The plasma is effectively accelerated by the electromagnetic force due to the modified shape of electrodes. The electron temperature and density of the plasma jet were measured by a double probe technique. At the discharge current of 10 kA, the temperature of the plasma jet reached approximately 1.9 eV and the density was of the order of 1014 cm-3 at the distance of 72 mm from the anode.

Measurements of Temperature Dependence of Partial Discharge in Air Gaps Between Insulated Bi-Sr-Ca-Cu-O Tapes

Partial discharge (PD) in trapped air-filled gaps between two adjacent insulated high temperature superconducting (HTS) tapes made of Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ (BSCCO) was investigated experimentally. PD measurements were performed at several temperatures ranging from 295 K to 41 K. At each temperature a series of AC voltages of equal duration and increasing magnitude was applied to the inter-turn insulation until PD was initiated and observed on the insulation condition monitor ICM digital PD system. The PD data are presented in the form of phase and amplitude resolved PD (PRPD) patterns. The voltage at which PD initiation (PDIV) and extinction (PVEV) is observed at a particular temperature was measured on an oscilloscope. Experimentally obtained PDIV and PDEV values are compared with the Paschen curve values for air and the effect of temperature on PDIV is discussed. The data show that relatively low PD onsets can occur even when the insulation is cooled to the 40 to 50 K range which may be due to the presence of ice layers on the surface of the voids.

Current spots in an obstructed planar glow discharge

Pattern formation in a gas discharge operating on the left-hand branch of the Paschen curve (obstructed discharge) is investigated. Such a discharge (in contrast to that operated on the right-hand branch) has a monotonic current–voltage characteristic and is believed to occupy the whole electrode area and to evolve continuously with current increase. This theoretical picture sharply contradicts a recent experiment (Nasuno S 2003 Chaos 13 1010–13) where both current constriction and current patterns have been observed for an obstructed dc discharge. We demonstrate experimentally in this paper that such a behaviour is indeed possible, but is always accompanied by current pulsation. We also suggest that the current pulsation, constriction and pattern formation are caused by local current-heating of the gas. This process explains the observed time-scales, occurrence and multiplicity of current spots.

Particle-in-cell simulation of gas breakdown in microgaps

Gas breakdown in large scale systems has been widely studied and is reasonably well understood. Deviations from the well-known Paschen law, however, have been reported in microgaps. One possible mechanism responsible for these deviations is the increase of the secondary electron emission yield due to the quantum tunnelling of electrons from the metal electrodes to the gas phase. The high electric fields obtained in small gaps combined with the lowering of the potential barrier seen by the electrons in the cathode as an ion approaches lead to the onset of ion-enhanced field emissions. Particle-in-cell/Monte Carlo simulations including ion-enhanced field emission have been performed to evaluate the importance of these mechanisms in the discharge breakdown. Deviations from the Paschen curve in gaps smaller than 5 µm can be explained based on this mechanism.

High-Power Subnanosecond Beams of Runaway Electrons Generated in Dense Gases

New understanding of the mechanism of runaway electrons beam generation in gases is presented. It is shown that the Townsend mechanism of avalanche electron multiplication is valid even for strong electric fields when the electron ionization friction on the gas may be neglected. A non-local criterion for runaway electron generation is proposed. This criterion results in the universal two-valued dependence of critical voltage Ucr on pd for a certain gas (p is pressure, d is interelectrode distance). This dependence subdivides a plane (U, pd) onto an area of efficient electron multiplication and an area where the electrons leave the gas gap without multiplication. On the basis of this dependence analogs of Paschen's curves are constructed, which contain an additional new upper branch. This brunch demarcates the area of discharge and the e-beam area.Electron beams of subnanosecond pulse duration and amplitudes of hundreds of amperes have been created at atmospheric pressure in various gases. It is shown that the beam of the runaway electrons is formed at an instant when the plasma of the discharge gap approaches the anode. In this case a basic pulse of the electron beam is formed according to the non-local criterion of runaway electron generation.A volume nanosecond discharge with high specific excitation power in the absence of gap preionization by an additional external source has been realized. The role of discharge gap preionization by the fast electrons, emitted from the plasma non-uniformities on the cathode, as well as propagation of an electron multiplication wave from cathode to anode in a dense gas are considered.

Discharge Properties and Emitted Electromagnetic Wave Spectrum in Low Vacuum Region of Vacuum Interrupter

Study on reliability of vacuum interrupter (VI) such as detection method of the slow leak has been extensively carried out, while study on discharge properties in low vacuum of VI is still insufficient. In this report, we experimentally investigated discharge properties inside VI under closed contact and open contact conditions of main contactors in low vacuum of VI to simulate vacuum leakage. We also measured current waveforms and spectrum of electromagnetic wave (EMW) emitted by discharges in VI. Furthermore, we discussed the relationship between partial discharge against the product of pressure and gap spacing, and compared the results with the Paschen's curve of air. We also discussed flowing path of the discharge current in an experimental circuit including VI.

Basic Phenomena in Low-Pressure Noble Gas Discharges: the Role of Heavy Particle Induced Processes

We have studied in detail the role of heavy particle processes in the gas phase (fast atom-atom and ion-atom collisions) and at the electrode surfaces (impact of fast atoms and ions on the metal surface) in low pressure He and Ar d.c. discharges by means of computer simulation and experiments. Our numerical studies have been based on Monte Carlo and hybrid (Monte Carlo + fluid) simulations. We have quantified the contributions of these processes to the characteristic breakdown behavior (Paschen curve) of He discharges, the complex self-sustainment mechanism of a low pressure, 4000 Volt helium discharge and the characteristic light emission profiles of Ar discharges.

Longitudinal magnetic field effect on the electrical breakdown in low pressure gases

The electrical breakdown has been investigated for low-pressure argon and nitrogen discharges under the influence of an external longitudinal magnetic field. Plane-parallel aluminum electrodes (5 cm diameter) separated by a variable distance d (4.0 cm < d < 11.0 cm) were sustained with a dc voltage (0 < V < 1 kV). A Helmholtz coil was used to produce an uniform magnetic field(B) parallel to the discharge axis. Paschen curves were obtained and the secondary electron emission coefficient (g), the first Townsend ionization coefficient (a) and the ionization efficiency(h), were plotted with respect to the variation of the reduced field (E/P). To observe the effect of the magnetic field these curves were plotted for fixed values of B=0 and B=350 Gauss. As consequence of the longitudinal magnetic field, the free paths of the electrons in the Townsend discharge are lengthened and their lateral diffusion is reduced, thus reducing electron losses to the walls. The data presented in this paper give a quantitative description of the B-field effect on the Townsend's coefficients and overall it is concluded that the DC electrical breakdown of the gases is facilitated if a longitudinal magnetic field is applied along the discharge axis.

Light emission in a laser-initiated transient glow discharge in argon and air with butane

By observing light emissions from flares, we systematically investigated transient phenomena from glow to arc discharges under designated durations. To describe properly the discharge flare behavior, we introduced a parameter νa defined as (electrode gap)/(flare traveling time). The main findings are as follows. The parameter νa is proportional to the initial electrode voltage. The maximum value of νa is obtained at a certain gas pressure and it falls on the Paschen curve. The flare behavior follows Townsend’s theory at each instant, therefore, it is governed by the state of the electrolytic dissociation of the gas.

Low-thermal expansion electrostatic chuck materials and clamp mechanisms in vacuum and air

Low-thermal expansion electrostatic chuck materials have been evaluated for use in the EUVL α-tool of ASML because of the requirements for overlay and critical dimensions. The material investigated showed clear capacitive Coulomb clamping behavior, giving a maximum pressure of 1.04 bar. In vacuum, the limitation to the maximum pressure is the spontaneous field emission of electrons across the gap between wafer and dielectric material. In dry air, the actual voltage over the air-filled gap limits the maximum pressure because of electrical breakdown (Paschen curve minimum). The humidity in normal air further decreases the pressures obtained. Model clamps and test set-ups were designed and manufactured by TNO TPD.

The Townsend coefficient and electron runaway characteristics in nitrogen

The results of analytical description and numerical simulation show that the Townsend ionization mechanism (characterized by a constant mean electron drift velocity and energy and by exponential growth in the number of electrons) is operative even in rather strong electric fields, for which the ionization drag of electrons can be ignored. The universal function Ucr(pd) calculated for nitrogen establishes the relationship between the critical interelectrode voltage (separating the regions of effective multiplication and significant runaway of electrons) and the product pd of the gas pressure and interelectrode gap width. The Ucr(pd) curve has two branches—the upper, characterizing the runaway of electrons, and the lower, describing their loss by drift. A minimum pd value on the Ucr(pd) curve corresponds to the maximum Townsend coefficient as a function of E/p. Using the Ucr(pd) function, an analog of the well-known Paschen curve characterizing self-sustained discharge in nitrogen has been constructed.

Determination of electric field-dependent effective secondary emission coefficients for He/Xe ions on brass

Effective secondary emission coefficients, γeff, for He+ and Xe+ ions are determined from the experimental Paschen curves of Postel and Cappelli [Appl. Phys. Lett. 76, 544 (2000)] through Townsend’s condition for a self-sustained discharge. The γeff dependence on the reduced electric field E/p, where p is the gas pressure, is obtained using the calculated dependence of the reduced Townsend’s ionization coefficient α(E/p)/p on the reduced electric field. Average values of the secondary emission coefficients are also estimated for brass and atomic and molecular ions as well as excited atoms and molecules of He and Xe, through a best fit of the simulated Paschen curves to the experimental ones. The found average values of the secondary emission coefficients are 0.1 for He and 0.0016 for Xe. Comparison is made with the limited available experimental results.

Low-thermal expansion electrostatic chuck materials and clamp mechanisms in vacuum and air

Low-thermal expansion electrostatic chuck materials have been evaluated for use in the EUVL α-tool of ASML because of the requirements for overlay and critical dimensions. The material investigated showed clear capacitive Coulomb clamping behavior, giving a maximum pressure of 1.04 bar. In vacuum, the limitation to the maximum pressure is the spontaneous field emission of electrons across the gap between wafer and dielectric material. In dry air, the actual voltage over the air-filled gap limits the maximum pressure because of electrical breakdown (Paschen curve minimum). The humidity in normal air further decreases the pressures obtained. Model clamps and test set-ups were designed and manufactured by TNO TPD.

On the mechanism of the runaway of electrons in a gas: The upper branch of the paschen curve

Abstract Basing on the simulation results, it is shown that the Townsend mechanism of electron multiplication in a gas at sufficiently large interelectrode distances is valid at least up to such large values of E/p at which relativistic electrons are generated. Correspondingly, the runaway electron producing in a gas is determined not by the local criteria accepted presently, but by the ratio of interelectrode distance and the characteristic electron multiplication length. It is shown that the critical discharge voltage U, at which the runaway electrons appear in a given gas, is a function of the product of the interelectrode distance by the gas pressure. This function (U-pd dependence) defines not only well-known Paschen curve but also an additional branch, which describes the absence of a self-sustained discharge at a high voltages sufficiently rapidly supplied across the electrodes. Critical discharge voltage dependence for helium and xenon are presented.

Frequency scaling in a hollow-cathode-triggered pinch plasma as radiation source in the extreme ultraviolet

The hollow-cathode triggered discharge extreme ultraviolet source is based on the same principle as pseudospark switches. The electrode geometry consists of a planar anode and cathode with central opposing holes, the one on the cathode side being connected to the hollow cathode. Radiation is generated by magnetic compression of the working gas under high-current operation. Essential for the operation is that the pressure and voltage are chosen to be on the left side of the Paschen curve to insure insulation of the gap between the electrodes. However, this insulation of the electrode system needs to be reinstalled after breakdown. Typical recovery times of a xenon-based system are down to 100 /spl mu/s, depending on the electrode geometry. It will be shown that the decay of the electron density in the hollow cathode is the limiting process. Investigation of the recovery mechanism has led to a design that allows operation above 4 kHz which is close to the required frequency for extreme ultraviolet lithography.

Minimization of Impedance Fluctuations in Cold-Cathode Pseudospark Switches (PSS)

The pseudospark discharge is characterized as a low-pressure gas discharge located on the left branch of the Paschen curve. Based on this discharge, a family of fast gas discharge closing switches for pulsed-power applications have been developed at Erlangen for more than 10 years. Due to the similarity to thyratrons, however, without having a hot cathode, the pseudospark devices are often described in literature as cold-cathode thyratron. The main features of a pseudospark switch are a high current rise closed to 10/sup 12/ A/s, the ability to carry reverse currents up to 100% and a high lifetime. The cold cathode also reduces the required standby power one magnitude lower than in thyratrons. On the other hand, especially at low-peak currents, undesired phenomena appear by the physics of the cold cathode. Current quenching, chopping, and impedance fluctuations are problems which occur at currents in the range of a few kiloamperes. Especially, the impedance fluctuations cause pulse-to-pulse fluctuations of the energy transferred to the load which could influence, i.e., the output energy of a laser system. For reducing this described problem of impedance fluctuations the dependencies of the geometry and material are investigated. With use of tungsten compound electrodes, this behavior of a cold cathode could be reduced significantly. This material shows also an improved reignition behavior after current zero.

High-voltage constraints for vacuum packaged microstructures

In order to understand the details of high-field breakdown in microstructures that are vacuum packaged, a series of experiments are used to determine characteristics of microdischarges. The results support a reinterpretation of conventional assumptions based upon large scale discharges. When planar microelectrodes are used, Paschen's curve is not applicable in the traditional sense: the breakdown voltage is relatively insensitive to pressure in the 1-20 torr range, and remains at /spl sim/400 V for air ambient. However, the spatial distribution of discharge current does vary with the pressure and the power. Large voltage gradients are supported in the glow region which is confined to a few millimeters directly above the cathode, and within a few hundred microns of its lateral edge. Their magnitudes range from 100,000-500,000 V/m for operating pressures ranging from 1.2-6 torr. Based on these results, guidelines are provided for the design of high-voltage microsystems.