Scaling law for a low-pressure gas breakdown in a homogeneous DC electric field

Gas breakdown in nitrogen, air, and oxygen in a dc electric field at various interelectrode distances L is studied experimentally. A scaling law for a low-pressure gas breakdown U _dc =f(pL, L/R) is deduced. According to this scaling law, the breakdown voltage U _dc is a function not only of the product of the gas pressure p and the gap length L, but also of the ratio of the gap length L to the chamber radius R. It is shown that, for any dimensions of the cylindrical discharge chamber (in the range of L/R under investigation), the ratio of the breakdown electric field to the gas pressure p at the minimum of the ignition curve remains constant: (E _dc /p)_min≈const. A method for calculating the ignition curve in a cylindrical discharge chamber with arbitrary values of L and R is proposed.     

A modified Paschen law for the initiation of a dc glow discharge in inert gases

Breakdown of inert gases in a homogeneous dc electric field is studied experimentally and theoretically at various distances L between the electrodes and radii R of the discharge tubes. It is shown that, for arbitrary geometric dimensions of the discharge chamber and cathode materials, the ratio of the breakdown electric field strength to the gas pressure holds constant at the breakdown curve minimum. A modified Paschen law is obtained, according to which the breakdown voltage is a function of both the product of the gas pressure by the distance L and the ratio L/R.     

Decrease in the static electric gas breakdown voltage in the presence of free electrons in a discharge gap

The dependence of the gas breakdown voltage U _B on the anode-cathode spacing d, pressure p, and other gas characteristics in the presence of a steady external ionizer in the discharge gap was determined within the avalanche discharge theory. The case was considered where the spatial charge created by the external ionizer did not distort the electric field in the discharge gap. In the absence of external ionizer the obtained dependence comes down to the well-known expression for the gas breakdown voltage (the Paschen law).     

Optimal length of capacitive-discharge and glow-discharge excilamps

The optimal tube length of capacitive-discharge and glow-discharge excimer lamps with ring and circular electrodes of equal radii is considered. It is demonstrated that, at the same potential difference between electrodes and their radii, the ratio of the optimal lengths of the tubes with circular and ring electrodes depends on width L of the ring electrodes. The ratio of the lengths decreases with decreasing L. A relationship between the tube length and radius, the width of ring electrodes, and the minimum voltage at the tube that provide for an approximately uniform glow of the discharge column in the presence of voltage pulses with opposite polarities at the electrodes is derived.     

Hall breakdown in a modulation-doped GaAs/AlAs heterostructure

The effect of dc current I _dc on the electron transport in a GaAs quantum well with AlAs/GaAs superlattice barriers is studied experimentally at a temperature of 4.2 K in magnetic fields up to 2 T. A sharp increase in resistance R _xx is observed in magnetic fields higher than the critical field B _c. The value of B _c is found to decrease with increasing the current I _dc. The phenomenon observed in the experiment is qualitatively explained by the electric breakdown of superlattice barriers under the action of the Hall field.     

Effect of the microwave signal power on the controllability of a ferroelectric phase shifter

We consider a microwave phase shifter based on thin-film ferroelectric parallel-plate capacitors operating as a part of a phased array at an elevated microwave power level and for a limited power in the control circuits. To eliminate capacitance modulation in parallel-plate capacitors by an ac field, we propose the separation of the effects of the dc control voltage and the ac voltage based on the symmetry of the capacitance-voltage characteristic of the unit including two capacitors parallel-connected in the ac voltage U _ac and series-connected in dc voltage U _dc. The experiment shows that for U _dc > U _ac, the phase of the wave passing through the phase shifter weakly depends on the microwave signal power. The reflection phase shifter is tested for a pulsed power of the microwave signal up to 6 W and a power in the control circuit on the order of 10 μW.     

Validity of diffusion theory in radio frequency breakdown in molecular gases in longitudinal magnetic field

The breakdown of a gas excited by a radio frequency voltage of frequency 5.6 MHz has been studied in a cylindrical discharge tube 7.2 cm long and 2.9 cm in dia and fitted with two internal electrodes at a distance of 2.5 cm in hydrogen, oxygen and air within the pressure range of a few microns to 2 torr in the presence of a longitudinal magnetic field varying from zero to 800 G. Experimental results indicate that the breakdown is diffusion controlled and the values of (a/P) at differentE/P values calculations obtained by Brown as well as by Kihara’s theory have been compared with (a/P) values obtained in the literature. It is concluded that the diffusion theory is also valid when the frequency of the exciting voltage is scaled down to radio frequency provided the collision frequency is much higher than the exciting frequency. The change of diffusion length in the presence of longitudinal magnetic field has been obtained from measuredE/P values and comparison with theoretical values indicates that there is quantitative agreement for small (H/P) values whereH is the magnetic field. The calculated values of pressure at which the breakdown voltage shows a minimum in the presence of magnetic field is in very good agreement with experimental values. It is concluded that in the presence of magnetic field also the loss of electrons takes place predominantly by the process of diffusion.     

High-temperature proton conductors: hydrogen injection and pumping

The electrochemical injection of hydrogen into inert gases was demonstrated using tubes of the high-temperature proton conductors BaZr_0.9Y_0.1O_3−x and CaZr_0.9In_0.1O_3−x. By applying a voltage with the right polarity protons can be driven to the inner electrodes. Recombination of the protons at the cathode leads to high-purity hydrogen which is injected into the gas stream. Since most inert gas streams contain a small amount of oxygen, hydrogen evolving at the cathode can react with that O₂ effectively lowering the p_o2. Thus, by increasing the proton current gas titration curves are obtained in analogy to strong acid — strong base titrations. Modelling of such curves is presented. This method of reducing the effective p_o2 by adding hydrogen in a controlled manner is discussed and compared with the classic technique of pumping oxygen electrochemically out of a gas stream using Y-stabilized zirconia tubes. Steam electrolysis was also demonstrated as well as the proton pick-up of the tubes by exposure of one side of the tubes to ethanol or acetone vapors. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Symmetries and the mass ratio of the electron and muon

A model of symmetries and gauge interactions relating the electron and muon is considered. The model is based on the U_L(1)?U_R(1)?R_L?R_R group where U_L(1)?U_R(1) denotes the chiral e-μ rotation and R_L?R_R the chiral reflection of the electron field. The invariance under this group is spontaneously broken by the vacuum expectation values of scalar fields. A zeroth-order vacuum is found for which the zeroth-order electron mass vanishes, while one-loop corrections lead to a finite $\text{m}{}_{\mathrm{<mtext>e</mtext>}}\text{mμ}$ ratio. The decay process μ → e + γ is strictly forbidden in this model.     

The effect of external visible light on the breakdown voltage of a long discharge tube

The breakdown characteristics of a discharge tube with a configuration typical of gas-discharge light sources and electric-discharge lasers (a so-called “long discharge tube”) filled with argon or helium at a pressure of 1 Torr have been investigated. A breakdown has been implemented using positive and negative voltage pulses with a linear leading edge having a slope dU/dt ~ 10–10⁷ V/s. Visible light from an external source (halogen incandescent lamp) is found to affect the breakdown characteristics. The dependences of the dynamic breakdown voltage of the tube on dU/dt and on the incident light intensity are measured. The breakdown voltage is found to decrease under irradiation of the high-voltage anode of the tube in a wide range of dU/dt. A dependence of the effect magnitude on the light intensity and spectrum is obtained. Possible physical mechanisms of this phenomenon are discussed.     

Quantum oscillations of rectified dc voltage as a function of magnetic field in an “almost” symmetric superconducting ring

Periodic oscillations in the dependence V _dc(B) of rectified dc voltage on the perpendicular magnetic field have been experimentally observed near the critical temperature in a single superconducting aluminum ring with slight geometric inhomogeneities (without specially formed circular asymmetry), biased by an external ac current (without a dc component). With a change in the external current and temperature, the voltage V _dc(B) behaves like the corresponding voltage on a circularly asymmetric ring but has a much smaller amplitude. The Fourier spectrum of the function V _dc(B) contains the fundamental frequency, corresponding to the ring area, and its highest harmonics. “Satellite” frequencies, dependent on the structure geometry and external parameters, were unexpectedly found in the spectrum.     

Necessity of intermediate mass scales in grand unified theories with spontaneously brokenCP invariance

It is demonstrated that the spontaneous breakdown ofCP invariance in grand unified theories requires the presence of intermediate mass scales. The simplest realization is provided by weakly broken left-right symmetry in the context ofSU(2)_L×SU(2)_R×U(1) _B?L model embedded in grand unified theories.     

Impulse breakdown characteristics of the plane-to-plane electrode system with a needle-shaped protrusion in SF6

This paper presents the impulse pre-breakdown and breakdown characteristics of the plane-to-plane electrode system with a needle-shaped protrusion in SF₆ gas. The breakdown voltage–time (V–t) characteristics and the breakdown voltage–gas pressure (V–p) characteristics of a highly non-uniform SF₆ gas gap under positive and negative lightning impulse voltages are investigated in the pressure range between 0.1 and 0.5 MPa. The pre-breakdown developments are examined by the corona current and light emission measurements with high time resolution. As a result, the dielectric strengths versus time-to-breakdown of SF₆ gas gap under positive lightning impulse voltages were nearly independent of the gas pressure. The first streamer corona was initiated at the tip of the needle electrode, and the streamer corona pulses developed with a stepwise propagation. The discharge paths were zigzag, and the branches of the discharge channel for positive polarity were created. On the other hand, the leader channel in the negative polarity was thicker and brighter than that in the positive polarity.     

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

This 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)     

Asymmetry with respect to the magnetic field direction in the interaction between the quantum states of two coupled superconducting rings

The interaction between the quantum states of two circularly asymmetric superconducting aluminum rings forming figure eight, threaded by a magnetic flux and biased by an external sinusoidal ac current with zero dc component, has been investigated. Quantum oscillations in the dependence V _dc(B) of the rectified dc voltage on magnetic field for these structures have been measured at different external currents and temperatures close to critical. Fourier and wavelet analyses of the function V _dc(B) have revealed, along with the two fundamental ring frequencies, various combination frequencies; this fact is indicative of interaction in the structure. Deviation of the function V _dc(B) from oddness with respect to the magnetic field direction has been found for the first time.     

Vortex oscillations in TFA-grown YBCO thin-films with BZO nanoparticles

An ac susceptibility methodology has been applied to investigate the vortex dynamics of YBa₂Cu₃O_7−x–BaZrO₃ nanocomposites grown by the chemical solution deposition TFA route, close to the irreversibility line. By analysing the linear, non-dissipative Campbell regime at low ac fields, we determined the temperature and field dependence of the restoring pinning constant, α_L(H_dc, T), characterising the harmonic oscillation of vortices inside their potential wells. Different than standard TFA–YBCO films, BZO nanocomposites displayed increasing α_L(H_dc) curves in the whole studied (H_dc, T) phase diagram, a behavior not predicted by the standard collective theory. We suggest results may be explained by the softening of the vortex-lattice, owed to the microstrain induced by the nanoparticles in the YBCO matrix.     

A new critical point in the non-linear conductivity due to variable range hopping in Si

A critical point in the non-linear conductivity has been observed in epitaxial silicon in the variable range hopping regime, due to a negative differential resistance with a dc bias currentI _dc. This gives thermal breakdown via the electron-phonon coupling and circuit-limited oscillations with a frequencyf∝I _dc, below a critical temperatureT _c. This critical behaviour is intrinsic, and forR(T)=R ₀ exp(T ₀ /T)^1/2 we show thatT _c=0.00512T ₀.     

The universal dependence of the relative voltage of static breakdown in gases on a generalized variable

In terms of the Townsend model of a static electrical gas discharge, the ratio of breakdown voltage U _B to its minimal value U _min is expressed as a function of generalized variable Ξ _B ? f(Ξ _b ), such that the function depends on neither the gas type nor the cathode material.     

On the mechanism of the runaway of electrons in a gas: The upper branch of the self-sustained discharge ignition curve

Based on the results of simulation by the method of particles, it is shown that the Townsend mechanism of electron multiplication in a gas at a sufficiently large electrode spacing is valid at least up to such large values of E/p at which relativistic electrons are generated. On the other hand, the phenomenon of electron runaway in a gas is determined by the electrode spacing, which must be either comparable with or smaller than the characteristic electron multiplication length, rather than the local criteria accepted presently. It is shown that, for a particular gas, the critical voltage across the electrodes at which the runaway electrons comprise a significant fraction is a universal function of the product of the electrode spacing by the gas pressure. This function also determines the condition of self-sustained discharge ignition. It not only incorporates the known Paschen curve but also additionally contains the upper branch, which describes the absence of a self-sustained discharge at a high voltage sufficiently rapidly supplied across the electrodes.     

Self-consistent theory for the built-in voltage in metal–organic semiconductor–metal structures

A self-consistent theory for calculation of built-in voltage (U_bi) of metal–organic semiconductor–metal (MOSM) structures is developed based on Gaussian energy distribution of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). It is shown that the built-in voltage depends not only on the work function difference of the two electrodes, but also on the mean energy level of HOMO and LUMO, as well as the Gaussian width of the energy distribution. The theory predicts that the spreading of HOMO and LUMO levels will results in an increase of U_bi, and that U_bi decreases with increasing temperature.