Paschen's Law Research Articles

On Correction Factor in Scaling Law for Low Pressure DC Gas Breakdown

The low pressure gas breakdown described by Paschen's law in Townsend theory, i.e. the breakdown voltage as a function of gas pressure p and the electrode distance d, provides an accurate description of breakdown in DC discharges when the ratio between inter-electrode gap distance d and electrode radii R tends to zero. On increasing of the ratio d/R, the Paschen's curves are shifted to the region of higher breakdown voltage and higher pd values. A modified Paschen's law recently proposed is well satisfied in our measurements. However, the value of constant b changes not only due to gas type but also according to electrode gap distance; furthermore, gas breakdown voltages are considerably modified by plasma-wall interactions due to glass tube proximity in the discharge.

Surface dielectric barrier discharges exhibiting field emission at high pressures

Surface dielectric barrier discharges (DBDs) are investigated experimentally in CO2 from atmospheric pressure up to supercritical conditions. Two discharge regimes are generated using 10 kHz ac excitation. The ‘standard’ regime is similar to previously studied surface DBDs in terms of onset voltage as a function of pressure, as well as electrical and optical emission characteristics. However, a ‘field-emitting’ regime emerges starting from 0.7 MPa that exhibits constant onset voltage up to 7.9 MPa, purely continuum emission spectra in the visible/near-infrared range and current waveforms similar to an atmospheric-pressure Townsend discharge with ionization instabilities. The maximum amount of negative charge deposited as a function of the applied voltage amplitude is consistent with the Fowler–Nordheim equation, which demonstrates the presence of field emission. Furthermore, this behavior cannot be attributed to the Townsend or streamer ionization mechanisms, secondary electron emission or non-discharge processes. No field-emitting structures are specially added to the electrodes. The onset voltage of the field-emitting regime does not follow the modified Paschen's law for field emission-assisted breakdown.

Differential Ion Mobility Separations in up to 100 % Helium Using Microchips

The performance of differential IMS (FAIMS) analyzers is much enhanced by gases comprising He, especially He/N2 mixtures. However, electrical breakdown has limited the He fraction to ~50%-75%, depending on the field strength. By the Paschen law, the threshold field for breakdown increases at shorter distances. This allows FAIMS using chips with microscopic channels to utilize much stronger field intensities (E) than "full-size" analyzers with wider gaps. Here we show that those chips can employ higher He fractions up to 100%. Use of He-rich gases improves the resolution and resolution/sensitivity balance substantially, although less than for full-size analyzers. The optimum He fraction is ~80%, in line with first-principles theory. Hence, one can now measure the dependences of ion mobility on E in pure He, where ion-molecule cross section calculations are much more tractable than in other gases that form deeper and more complex interaction potentials. This capability may facilitate quantitative modeling of high-field ion mobility behavior and, thus, FAIMS separation properties, which would enable a priori extraction of structural information about the ions.

Ultra-Low Breakdown Voltage of Field Ionization in Atmospheric Air Based on Silicon Nanowires

Classic field ionization requires extremely high positive electric fields, of the order of a few million volts per centimeter. Here we show that field ionization can occur at dramatically lower fields on the electrode of silicon nanowires (SiNWs) with dense surface states and large field enhancement factor. A field ionization structure using SiNWs as the anode has been investigated, in which the SiNWs were fabricated by improved chemical etching process. At room temperature and atmospheric pressure, breakdown of the air is reproducible with a fixed anode-to-cathode distance of 0.5 μm. The breakdown voltage is ∼38 V, low enough to be achieved by a battery-powered unit. Two reasons can be given for the low breakdown voltage. First, the gas discharge departs from the Paschen's law and the breakdown voltage decreases sharply as the gap distance falls in μm range. The other reason is the large electric field enhancement factor (β) and the high density of surface defects, which cause a highly non-uniform electric field for field emission to occur.

The Role of the Field Emission Effect in the Breakdown Mechanism of Direct‐Current Helium Discharges in Micrometer Gaps

AbstractThis paper contains results of experimental studies of the direct current breakdown voltage curves and volt‐ampere characteristics of discharges generated in a system consisting of two plane‐parallel tungsten and molybdenum electrodes at separations from 100 µ m to 1 µ m. The measurements were performed in the pressure range from 22.5 Torr to 738 Torr. The results are presented in the form of Paschen curves. Based on the measured breakdown voltage curves, the effective yields have been estimated in the case of different cathode materials. Differences between them are attributed to the influence of the work function of the cathode material on the current‐voltage characteristics due to field emission effect in small gaps and high pressures. At low‐pressures, however, vaporation of impurities from the electrodes material becomes significant. The present paper delivers new data on DC breakdown under these experimental conditions and conditions on the validity of the Paschen law in helium and provides better insight into the role of the field emission and the electrode materials on the breakdown voltage. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

대기압 플라즈마 제트의 기체 유량에 대한 방전 특성

대기압 플라즈마 제트 장치의 유량 변화에 대한 플라즈마 방전 특성을 실험적으로 조사하고 이를 유체역학적으로 해석하였다. 유리관에 주입되는 아르곤 기체의 유량 변화에 대한 레이놀즈 수(Re)로 결정되는 기체 흐름의 형태 변화와 베르누이 정리에 의한 압력 변화가 플라즈마 발생에 영향을 준다. 유리관 내부에 발생하는 플라즈마의 길이 변화의 실험을 통하여, 아르곤 기체에 대한 레이놀즈 수가 Re<2,000이면 층류이고, Re>4,000이면 난류가 형성된다. 이는 일반 유체에서 알려진 결과와 일치한다. 층류에서 유량의 증가로 플라즈마의 길이가 증가한다. 층류와 난류의 전환 영역에서 플라즈마의 길이는 줄어든다. 난류 영역에서는 방전 기체의 흐름이 불규칙함으로서 방전 경로가 흐트러져 플라즈마 칼럼의 길이가 매우 짧아지고 급기야 플라즈마가 소멸된다. 층류에서 주입 유량의 증가로 유리관 내의 유속이 증가하면, 베르누이 정리에 의하여 유리관 내부의 압력이 낮아진다. 관내의 압력이 낮아지면, 파센 법칙에 의하여 관내의 전기장의 세기가 증가하여 방전 전압이 낮아진다. 따라서 주입 유량이 증가하면, 동일한 구동 전압에서 유리관에 발생하는 플라즈마의 길이는 길어진다. 층류의 방전은 유리관 밖에서도 층류의 흐름이 일정 길이로 유지되므로 시료 표면에 조사되는 플라즈마 빔의 직경은 유리관의 직경 이하로 유지된다. The influence of gas flow on the plasma generation in the atmospheric plasma jet is described with the theory of hydrodynamics. The plasma discharge is affected by the gas-flow streams with Reynolds number (Re) as well as the gas pressure with Bernoulli's theorem according to the gas flow rate inserted into the glass tube. The length of plasma column is varied with the flow types such as the laminar flow of Re<2,000 and the turbulent flow of Re>4,000 as it has been known in a general fluid experiments. In the laminar flow, the plasma column length is increased as the increase of flow rate. Since the pressure in the glass tube becomes low as the increase of flow velocity by the Bernoulli's theorem, the breakdown voltage of plasma discharge is reduced by the Paschen's law. Therefore, the plasma length is increased as the increasing flow rate with the fixed operation voltage. In the transition of laminar and turbulent flows, the plasma length is decreased. When the flow becomes turbulent as the flow rate is increasing, the plasma length becomes short and the discharge is shut down ultimately. In the discharge of laminar flow, the diameter of plasma beam exposed on the substrate surface is kept less than the glass diameter, since the gas flow is kept to the distinct distance from the nozzle of glass tube.

Experimental Study on Paschen Tests of ITER Current Lead Insulation

An experimental Paschen test setup has been established to analyze the quality of ITER current lead (CL) insulation and extend the research on Paschen's law under various conditions. Insulation problems can destroy a machine if a Paschen discharge is triggered by an insulation defect that is caused by faulty manufacturing, electromagnetic force, and thermal stress load with a certain degree of vacuum helium or pipe leakage. The results show that the CL insulation mock-up worked well under normal temperature and pressure. Besides, the mock-up also worked well in helium conditions and at 80 K temperature at different pressures. One area of CL insulation was severely destroyed when the 80 K test was conducted after 5 thermal cycles, resulting in Paschen discharge phenomenon. The breakdown voltage is maintained at a relatively low level under different pressure conditions; the change of breakdown voltage was mainly due to the change of pressure, and such change was in line with the Paschen law.

Optimization of intrinsic hydrogenated amorphous silicon deposited by very high-frequency plasma-enhanced chemical vapor deposition using the relationship between Urbach energy and silane depletion fraction for solar cell application

Intrinsic hydrogenated amorphous silicon (i-a-Si:H) films were deposited by very high frequency (VHF) plasma enhanced chemical vapor deposition (PECVD) technique. It was found that there were three distinct deposition rate regions, when the deposition pressure and power were varied according to Paschen's law. The silane depletion fraction (SDF) is related to the reaction rates and the sticking probability of the radicals, which is smaller in the 1st region, where the SiH3 radical is the dominant deposition precursor giving rise to higher film density and a low Urbach energy (~68meV). The third region has higher SDF, where more SiH2 radicals are generated resulting in a reduction in film density and increased structural disorder due to polyhydride formation. The good quality films obtained with the condition of the 1st region, showed low SDF at lower pressure and power, following Paschen's law. Some of these i-a-Si:H films were used to fabricate p–i–n type solar cells. The measured photo voltaic parameters of one of the cells are as follows, open circuit voltage (Voc)=800mV, short circuit current density (Jsc) of 16.3mA/cm2, fill-factor (FF) of 72%, and photovoltaic conversion efficiency (η) of 9.4%, which may be due to improved intrinsic layer. Jsc, FF and Voc of the cell can be improved further with optimized cell structure and with i-a-Si:H having a lower number of defects.

Scaling law for direct current field emission-driven microscale gas breakdown

The effects of field emission on direct current breakdown in microscale gaps filled with an ambient neutral gas are studied numerically and analytically. Fundamental numerical experiments using the particle-in-cell/Monte Carlo collisions method are used to systematically quantify microscale ionization and space-charge enhancement of field emission. The numerical experiments are then used to validate a scaling law for the modified Paschen curve that bridges field emission-driven breakdown with the macroscale Paschen law. Analytical expressions are derived for the increase in cathode electric field, total steady state current density, and the ion-enhancement coefficient including a new breakdown criterion. It also includes the effect of all key parameters such as pressure, operating gas, and field-enhancement factor providing a better predictive capability than existing microscale breakdown models. The field-enhancement factor is shown to be the most sensitive parameter with its increase leading to a significant drop in the threshold breakdown electric field and also to a gradual merging with the Paschen law. The proposed scaling law is also shown to agree well with two independent sets of experimental data for microscale breakdown in air. The ability to accurately describe not just the breakdown voltage but the entire pre-breakdown process for given operating conditions makes the proposed model a suitable candidate for the design and analysis of electrostatic microscale devices.

The role of the field emission effect in direct-current argon discharges for the gaps ranging from 1 to 100 µm

This paper contains results of experimental and simulation studies of the direct-current breakdown voltage curves in argon discharges with parallel-plane electrodes separated from 1 to 100 µm. The negative slope of the Fowler–Nordheim plot indicates that the current flow is due to field-emitted electrons. Based on the breakdown voltage curves, the effective yield has been estimated. The secondary electron emission in microgaps depends primarily on the electric field E rather than reduced electric field E/N, leading directly to the violation of Paschen's law. The obtained results provide better insight into the role of the enhancement of the secondary electron emission due to high electric field generated in microgaps. Due to the lack of experimental data in microgaps, there are only a few values for the effective yield and no value for argon. By fitting presented experimental data, realistic values of the effective yield in microgaps are obtained and used for the calculations of the breakdown voltages representing basic design data of high-voltage equipment.

Fundamental properties of field emission-driven direct current microdischarges

For half a century, it has been known that the onset of field emission in direct current microdischarges with gap sizes less than 10 μm can lead to breakdown at applied voltages far less than predicted by Paschen's law. It is still unclear how field emission affects other fundamental plasma properties at this scale. In this work, a one-dimensional fluid model is used to predict basic scaling laws for fundamental properties including ion density, electric field due to space charge, and current-voltage relations in the pre-breakdown regime. Computational results are compared with approximate analytic solutions. It is shown that field emission provides an abundance of cathode electrons, which in turn create large ion concentrations through ionizing collisions well before Paschen's criterion for breakdown is met. Breakdown due to ion-enhanced field emission occurs when the electric field due to space charge becomes comparable to the applied electric field. Simple scaling analysis of the 1D Poisson equation demonstrates that an ion density of n+ ≈ 0.1VAε0/qd2 is necessary to significantly distort the electric field. Defining breakdown in terms of this critical ion density leads analytically to a simple, effective secondary emission coefficient γ′ of the same mathematical form initially suggested by Boyle and Kisliuk [Phys. Rev. 97, 255 (1955)].

Simulation analysis of triboplasma generation using the particle-in-cell/Monte Carlo collision (PIC/MCC) method

Previously, a microplasma was discovered in the rear gap of a sliding contact. This plasma is called a ‘triboplasma’, the behaviour of which obeys the Paschen law in a gas discharge. The generation of the triboplasma has been explained to be generated by discharging of ambient air due to the intense electric field caused by tribocharging, based on the experimental findings.In this report, the mechanism of triboplasma generation is theoretically analysed using the particle-in-cell/Monte Carlo collision (PIC/MCC) simulation method for the triboplasma generated in the tribosystem, where a diamond pin slides against a sapphire disc in ambient air. Two-dimensional sideward density distributions of the electrons, ions and ions in the rear gap of the sliding contact are obtained theoretically by the PIC/MCC method. These calculated particle distributions coincided well with the triboplasma distributions experimentally observed. The previously proposed triboplasma generation due to gas discharging is verified theoretically using the PIC/MCC simulation method.

A Method to Monitor Vacuum Degree Using Capacitive Partial Discharge Coupler

Internal pressure of vacuum interrupter (VI) is one of the most important parameters in VI operation and may increase due to the outgassing from the materials inside VI or gas permeation through metal flange or ceramic vessel. The increase of the pressure above a certain level leads to the failures of switching or insulation. Therefore, an effective pressure check of VI is essential and an analysis of partial discharge (PD) characteristics is an effective monitoring method to identify the degree of the internal pressure of VI. This paper introduces a research work on monitoring the internal pressure of VI by analyzing PDs which were measured using a capacitive PD coupler. The authors have developed cost effective capacitive coupler based on the ceramic material that has an excellent insulation properties and the main component of the capacitive coupler is made by SrTiO3. Detectable internal pressure range and distinguishability of the internal pressure of VI were investigated. From the PD tests results, the internal pressure range, from <TEX>$10^{-2}$</TEX> torr to 500 torr, can be monitored by PD measurements using the capacitive coupler and PD inception voltage (PDIV) follows the Paschen's law. In addition, rise time of PD pulse at 13.2kV decreases with the increase of the internal pressure of VI.

Breakdown Characteristics of SF6and Liquefied SF6at Decreased Temperature

<TEX>$SF_6$</TEX> gas has been used as arc quenching and insulating medium for high and extra high voltage switching devices due to its high dielectric strength, its excellent arc-quenching capabilities, its high chemical stability and non toxicity. Despite of its significant contributions, the gas was classified as one of the greenhouse gas in the Kyoto Protocol. Thus, many researches are conducted to find out the replacement materials and to develop the <TEX>$SF_6$</TEX> gas useless electrical equipment. This paper describes experiments on the temperature change-related breakdown characteristics of <TEX>$SF_6$</TEX> gas (<TEX>$SF_6$</TEX>) and <TEX>$SF_6$</TEX> liquid (<TEX>$LSF_6$</TEX>) in a model GIS(Gas-Insulated Switchgear) chamber in order to show the possibility of more stable and safe usages of <TEX>$SF_6$</TEX> gas. The breakdown characteristics are classified into three stages, namely the gas stage of <TEX>$SF_6$</TEX> according to Paschen's law, the coexisting stage of <TEX>$SF_6$</TEX> gas with liquid in considerable deviation at lower temperature, and the stage of <TEX>$LSF_6$</TEX> and remaining air. The result shows that the ability of the <TEX>$LSF_6$</TEX> insulation is higher than the high-pressurized <TEX>$SF_6$</TEX>. Moreover, it reveals that the breakdown characteristics of <TEX>$LSF_6$</TEX> are produced by bubble-formed <TEX>$LSF_6$</TEX> evaporation and bubbles caused by high electric emission and the corona. In addition, the property of dielectric breakdown of <TEX>$LSF_6$</TEX> is determined by electrode form, electrode arrangement, bubble formation and movement, arc extinguishing capacity of the media, difficulty in corona formation, and the distance between electrodes. The bubble formation and flow separation phenomena were identified for <TEX>$LSF_6$</TEX>. It provides fundamental data not only for <TEX>$SF_6$</TEX> gas useless equipment but also for electric insulation design of high-temperature superconductor and cryogenic equipment machinery, which will be developed in future studies.

Paschen law for argon glow discharge

Electric discharge between two electrically charged surfaces occurs at a well-defined, gas-dependent combination of atmospheric pressure and the distance between those surfaces, as described by Paschen's law. The understanding of when the discharge will occur in an Ar discharge is essential basic knowledge. A glow discharge apparatus was used in this experiment of Ar discharge at a pressure range between 2.0 Torr and 12 Torr, a power of 20 W and 40 l/min flow rate of gases. The optical emission spectroscopy was carried out in the wavelength range of 200 to 1100 nm. Here, we present experimentally measured plasma Paschen curves for Ar gas and compare our results of breakdown voltages with the literature. The minimum voltage measured for a discharge in Ar atmosphere was 215 ± 2.2 at 0.7 Torr-cm, which agree with previous measurements.

Numerical and theoretical calculation of breakdown voltage in the electrical discharge for rare gases

This work has been devoted to a numerical and analytical calculus of the voltage breakdown in electrical discharge for several rare gases such as argon, krypton, neon, xenon and helium. It was performed using a fluid model 2D, which is based on the numerical solution of the two Boltzmann equations (equation of continuity and momentum), coupled to Poisson's equation to measure the breakdown voltage according to the product of the electrode spacing and the pressure. This study allowed a better comprehension of the physical phenomena occurring in the discharges. We, thus, developed a calculation, based on the empirically Paschen's law, allowing the determination of the breakdown voltage, which describes the transition from insulating gas to the conductive state. Paschen's curves of the different gases are plotted and a comparison between numerical and experimental as well as analytical results is also presented and analyzed.

Paschen tests in superconducting coils: why and how

The Paschen breakdown is the outcome of an avalanche effect related with the ionization of a gas under electric stress. Paschen's law defines the voltage breakdown of rarefied (low pressure) gases as a function of the product of pressure and distance between electrodes showing a minimum value (typically of the order of hundreds V) below which the breakdown cannot take place. The actual field level depends on the gas, on the shape, material and surface conditions (roughness, cleanness and presence of oxide layers) of the electrodes; hence there is a big dispersion in the results available due to the referred number of parameters influencing the voltage breakdown. The design of the electrical insulation of superconducting magnets targets a safety factor of ×10 on dielectric strength over specified voltages using the intrinsic dielectric strength of the materials. A crack in the insulation or a flaw not detected by visual inspection would not necessarily lead to an electrical break during the acceptance tests in air given the high dielectric strength of air (typically values over 1 kV/mm). However, it would lead to an electrical failure during operation if Paschen conditions take place. Since the Paschen minimum occurs under vacuum, it is irrelevant for conventional High Voltage (HV) engineering. The application of superconducting technology for plasma fusion devices with a growing size and complexity of magnets has shown Paschen testing as an essential tool. During magnet operation inside the cryostat conditions, if a He leak takes place, critical pressures can be reached locally and Paschen breakdown might occur at voltages significantly lower than the designed ones. The present paper covers an existing gap in International Standards and scientific literature addressing Paschen testing of superconducting magnets and explains why it is needed and how the tests should be done in the most efficient way.

Inter‐Electrode Distance and Breakdown Voltage in Low Pressure Argon Discharges

AbstractThis work deals with the Paschen law in electrical breakdown of gases at pd values around the Paschen minimum. From the Townsend model, it is possible to deduce theoretical forms of the coefficients in Paschen's law, of which our calculated values are in the range of the tabulated values from the literature. These formulae show that the breakdown voltage must be influenced by the inter‐electrode distance, while the product pd remains a key parameter. This is confirmed by the Paschen curves measured in an argon discharge for inter‐electrode distances varying from 2 to 9 cm (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Breakdown voltage curves in direct current discharges in molecular gases at microgaps

This Letter reports on experimental studies of the direct current breakdown voltage curves in oxygen, dry air, nitrogen and hydrogen discharges with parallel-plane electrodes separated from 1 to 100 µm. For the gap sizes greater than 5 µm, the obtained breakdown voltage curves exhibit U-shaped form and follows the Paschen law. For the gaps less than 5 µm, however, in the left-hand side the curves show departure from the standard scaling law. To the author&apos;s knowledge, there is no data for the breakdown voltage in microgaps for some of the considered molecular gases. Owing to the lack of experimental data in microgaps, measured data represent basic design data of high voltage equipment.

Modelling of an Electromagnetic Space Propulsion System for Pulse Mode Operation

The chemical rocket propulsion has limitations while applied to space application, with respect to specific impulse, delta-v, volume and stored energy, which can be overcome by electric propulsion system. Among various type of Electric propulsion system, the electromagnetic propulsion has added advantages for many space applications. In this paper an electromagnetic propulsion system is considered known as Magnetoplasmadynamic thrusters (MPD). The MPD thrust works based on principle of Lorentz force.The thruster is modeled based on Paschen's Law and snow plow model to operate it in pulsed mode to generate instantaneous peak thrust. This model includes the designing of high-current power supply, ignition circuit, and electrodes. Simulations have been performed by considering all the parameters involved in the model. The design parameters are analyzed for optimum value to get maximum thrust force.