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.     

Anlagerungskoeffizienten und Driftgeschwindigkeiten von Elektronen in Luft

Electron drift velocities and attachment coefficients were measured in dry air (E/p=0.1–30 V/cm Torr) and in a 9∶1 nitrogen/oxygen mixture (E/p=0.2–3 V/cm Torr) in the pressure range from 50 to 200 Torr, using a modified spark chamber technique. The primary electrons were released by anα-particle. The temporal development of the electron density in the gap was determined from the amplitude of the current due to the avalanches, which were produced by applying high voltage pulses at different delay times. — It was found that in air the dissociative attachment sets in at higherE/p (～10–15 V/cm Torr) than in oxygen. At lowerE/p three body attachment is predominant. — When the high voltage pulses were applied after the transit time of the primary electrons, electron avalanches still appeared. It was concluded that they were started by electrons which were detached from negative ions. The estimated detachment rates indicate the formation of O ₂ ^? ions at lowE/p and of O^? ions at higherE/p.     

Radiative characteristics of nitrogen upon excitation by volume discharge initiated by runaway electron beam

The amplitude, time, spectral, and energetic characteristics of a volume (diffuse) discharge at an elevated pressure (up to 5 atm) in a gap with an inhomogeneous electric field without an additional preionization source are studied. The concentration and temperature of electrons in the discharge plasma are mea-sured by spectral methods. The effective lifetime of the C ³Π _u state of the nitrogen molecule at the trailing edge of the radiation pulse is shown to be determined by radiative and collisional quenchings. For transitions of the second positive system of nitrogen, a plasma discharge radiation power into the complete solid angle is obtained to be ～120 kW, with a specific radiation power of up to ～50 kW/cm³.     

Messung der Elektronendriftgeschwindigkeit in N2 imE/p-Bereich von 0,05 bis 40 Volt/cm Torr (Funkenkammerverfahren)

A special spark chamber technique was used to measure drift velocities of electrons for N₂ over anE/p-range from 0.05 to 40 volts/cm·Torr. The inaccuracy is smaller than 5% in the mediumE/p-range and increases to 10% at the ends of the region. This method uses a single α-particle traversing a parallel plate gap. The α-particle triggers by a photomultiplier a high voltage pulse which initiates an avalanche discharge. By varying the delay time after which the high voltage pulse is triggered one deduces from the height of the avalanche discharge the time necessary for the electrons to cross the gap and thus the drift velocity.     

Untersuchung über die gasionisierende Strahlung einer Entladung II

This paper gives a report on measurements of the coefficient of absorption and intensities of a gas-ionizing radiation, which is emitted by a gas discharge. Earlier measurements in oxygen with a discharge in a cylindrical electrical field had yielded components of radiation with values ofμ≈550,μ≈250, andμ= 38 cm^?1 according to 760 mm Hg. By new measurements using a spark discharge an additional component with a value ofμ=2,5 has been found, which already has been measured by other authors. Measurements with mixtures of oxygen and nitrogen are compared with results of measurements in air. From this it may be deduced that the gas-ionizing radiation effective in air is essentially emitted by nitrogen and ionizes oxygen, the coefficient of absorption being aboutμ≈5 cm^?1. The number of ionizing quantums emitted per ionizing collision of electrons in the discharge tube is about 10^?3 for oxygen, nitrogen, and air. In oxygen this figure proves to be essentially independent ofE/p. In air, however, this figure is reduced with increasing values ofE/p. The absorption of the ionizing radiation in air is increased by the addition of methane (μ=960 cm^?1 for 760 mm Hg of methane). In carbon dioxyde several components of ionizing radiation are found, with coefficients of absorption in the range 200<μ<800.     

Plasma-volume generation of H<Superscript>−</Superscript> ions in a low-voltage xenon-hydrogen discharge. II

A low-voltage xenon-hydrogen discharge is considered theoretically at an interelectrode distance of L = 1 cm and cathode emission current densities of j _s = 2–20 A/cm². Basic parameters of the discharge plasma, in particular, the total hydrogen and xenon densities, are optimized to attain the maximum possible density of negative hydrogen ions \(N_{H^ - } (L)\) at the plasma-anode boundary. The distributions of the plasma parameters over the discharge gap are calculated for optimized regimes. According to calculations, at intermediate cathode emission current densities (j _s ≈ 5–10 A/cm²) in optimized discharge regimes, the density of negative hydrogen ions in the anode region of the plasma is \(N_{H^ - } (L)\) ≈ (1.5–2.5) × 10¹² cm^?3 and the total plasma pressure is p ₀ = 0.5–0.6 Torr.     

Bestimmung der Driftgeschwindigkeit von Elektronen in Wasserstoff und Stickstoff bei hohem Druck

By means of a time of flight method the electron drift velocity in hydrogen and nitrogen was determined for high pressure, at which no measurements were as yet available. The values are obtained in the range fromE/p=12 toE/p=0,03 V/cm Torr with an accuracy from 1% to 1,5%. The pressure range available (up to 31000 Torr) enabled an examination of the similarity rule. The measurements show that for constantE/p, in the rangeE/p<1, the drift velocities decrease with increasing pressure.     

Mittlere Energien und Driftgeschwindigkeiten von Elektronen in Stickstoff,Argon und Xenon,ermittelt aus Bildverstärkeraufnahmen von Elektronenlawinen

Local and temporal development of electron avalanches in a pulsed discharge gap (d=3,00 cm) are investigated in N₂, Ar, Xe and mixtures of N₂ and CH₄ by simultaneously applying high gain image intensifier- and photomultiplier techniques. Electron drift velocities are obtained from time-of-flight and way-of-flight measurements in these gases. The mean energy of agitation of the electrons is derived both from electron mobility and avalanche image trace profile (diffusion broadening). The results obtained (for 20°C), being in fair agreement with one another, read N₂: (4·6...5·0) eV forE/p=50...200 V/cm Torr; Ar: (9·0...9·5) eV forE/p=24... 45 V/cm Torr; Xe: (4·8...5·0) eV forE/p= 40... 90 V/cm Torr; CH₄(10% N₂): 6·3 eV forE/p= 89 V/cm Torr. The mean energy of agitation does not change very much withE/p in the ranges investigated. Some results concerning the radiation properties of these gases are included such as lifetime of the excited states, quenching pressure etc.     

Anregung von UV-Strahlung in Stickstoff und Wasserstoff durch einen Elektronenschwarm

The radiation excited in nitrogen and hydrogen by an electron swarm moving in a uniform electric field is investigated. In nitrogen the bands of the 2 ^nd positive group in the region from 3400 to 3800 Å are the dominating part of the radiation. In hydrogen the main part of the radiation is lying in the far ultraviolet (1000 to 1200 Å) due to the excitation of the state 2¹ II _u . The coefficientδ describing the intensity of the radiation is measured with a photomultiplier device as a function of the electric fieldE and the pressurep in the range from about 10 to 100 Torr. Besides the dependence ofδ onE/p a pressure dependence is found which is explained as a quenching process of the excited molecules by collisions. The pressurep ₀ for equal probability of radiating and non-radiating decay of the states involved is 60 Torr in N₂ and 20 Torr in H₂. The theoretical interpretation of the dependence onE/p supports the excitation energy of the state C³ II _u of N₂ for electron impact to be equal to the spectroscopical value of 11·04 eV and yields 0·9·10^?16 cm² for the maximum of the excitation cross section. The results of the measurements in H₂ can be described assuming a cross section of 0·55·10^?16 cm² for the excitation of the state 2¹ II _u by electron impact.     

Drift−diffusion model of normal glow discharge in an axial magnetic field

A two-dimensional axisymmetrical computing model is formulated with using of which the mathematical modeling of the normal glow discharge in molecular hydrogen is fulfilled in an axial magnetic field with the induction B = 0.1 T in the pressure range p = 1.25?5 Torr and the current-source electromotive force E = 1?3 kV.     

Recombination population of excited states of the hydrogen atom in an He-H<Subscript>2</Subscript> plasma

The population of excited states of the hydrogen atom in an afterglow plasma produced by a pulsed discharge in helium (40 Torr) with a small admixture of hydrogen ([H₂] ≈ 10¹² cm^?3) has been studied spectroscopically. The contribution from electron-ion recombination Γ ₃ ^rec to the production rate of atoms H(n = 3) has been separated. On the basis of an experiment in which the response of the spectral line intensities to the perturbation of the electron temperature in the afterglow phase was observed, the dependence Γ ₃ ^rec (T _e ～ T _e ^?(0.9–1.0) has been obtained in the region kT _e = 0.026–0.064 eV.     

Messung der Elektronendriftgeschwindigkeit in N2 und in CH4

In a homogeneous electrical field a swarm of electrons was released at the cathode by means of a short light flash. The development of the electron avalanches and their transit time were measured by photomultiplier technique. The transit timesT _- and the gap distanced allows to calculate the electron drift velocitiesv _?=d/T _?. The drift velocities in N₂ were measured in theE/p-region between 34 and 49 V/cm·Torr, in CH₄ between 30 and 35 V/cm·Torr and in N₂+CH₄ between 33,5 and 42 V/cm·Torr.     

Studying the effect of biaxial anisotropy on nonlinear magnetization oscillations accompanying the 90° pulsed magnetization process in ferrite–garnet films with easy-plane anisotropy

Time dependences of the azimuthal component of the torque T _φ(t) acting on magnetization are calculated to understand the nature of the delayed magnetization acceleration effect observed during the 90° pulsed magnetization of real ferrite–garnet films, in which biaxial anisotropy exists alongside with in-plane anisotropy. A calculation technique based on analyzing an operating point trajectory is used. Calculations show that if the effective anisotropy field H _K2 is comparable to the magnetizing pulse amplitude H _ma, abruptly ascending regions at characteristic times t* in curves T _φ(t) arise, in the limit of which nonlinear magnetization oscillations formed. The shape of these regions depends weakly on the magnetizing pulse front duration τ_f. This explains the reason of the weak dependence of the nonlinear magnetization oscillations on duration of the magnetizing pulse front. Calculations also show that the main features of the delayed acceleration effect are less clear upon an increase of the pulse amplitude: the behavior of curves T _φ(t) becomes smoother near times t*, and an increase in the pulse front duration is accompanied by a stronger drop in the intensity of magnetization oscillations.     

Homogeneous nucleation in liquid nitrogen at negative pressures

The kinetics of spontaneous cavitation in liquid nitrogen at positive and negative pressures has been studied in a tension wave formed by a compression pulse reflected from the liquid–vapor interface on a thin platinum wire heated by a current pulse. The limiting tensile stresses (Δp = p_s–p, where p_s is the saturation pressure), the corresponding bubble nucleation frequencies J (10²⁰–10²² s^–1 m^–3), and temperature induced nucleation frequency growth rate G_T = dlnJ/dT have been experimentally determined. At T = 90 K, the limiting tensile stress was Δp = 8.3 MPa, which was 4.9 MPa lower than the value corresponding to the boundary of thermodynamic stability of the liquid phase (spinodal). The measurement results were compared to classical (homogeneous) nucleation theory (CNT) with and without neglect of the dependence of the surface tension of critical bubbles on their dimensions. In the latter case, the properties of new phase nuclei were described in terms of the Van der Waals theory of capillarity. The experimental data agree well with the CNT theory when it takes into account the “size effect.”     

Meson Effect in the Proto Neutron Star PSR J0348+0432

The effect of mesons f ₀(975) (named as f), ?(1020) (named as ?) and δ on the moment of inertia of the PNS PSR J0348+0432 is examined in the framework of the relativistic mean field theory considering the baryon octet. It is found that the energy density ε and pressure p will increase considering the mesons δ whereas will decrease as the mesons f and ? being considered. When the mesons f,? and δ are considered, the energy density and pressure will all decrease. It is also found that the contribution of mesons f, ? and δ to the central energy density is only the central energy density’s 0.06 ～0.6% whereas the contribution of mesons f, ? and δ to the central pressure is the central pressure’s 4 ～7%. For the radius, it will decrease when the contributions of mesons f, ? and δ are considered. The moment of inertia I will increase considering the mesons δ whereas will decrease as the mesons f and ? being considered. When the mesons f, ? and δ are all considered, the moment of inertia will decrease. It is found that the contribution of mesons f and ? to moment of inertia is 4 ～9 times larger than that of mesons δ. Our results show that the mesons f, ? and δ contribute to the moment of inertia’s 2 ～5%.     

The townsend coefficient and runaway of electrons in electronegative gas

We have studied the character of variation of the number of electrons formed in an electronegative gas (SF₆) under the action of an external electric field. At any value of the electric field strength E, the number of generated electrons exponentially increases with the distance from the cathode, while the average velocity and energy of electrons attain constant values. At small values of the reduced field strength, E/p<94 V/(cm Torr) (p is the gas pressure), the regime of electron attachment prevails that is characterized by negative values of the exponent (negative Townsend coefficients). For E/p>94 V/(cm Torr), the electron multiplication proceeds in the usual Townsend regime with positive exponents. In the intermediate region of E/p=40–160 V/(cm Torr), the electron multiplication coefficient exhibits a linear dependence on E/p. Numerical calculations based on a simple model show that the Townsend multiplication regime takes place even in very strong fields where the drag caused by ionization can be ignored. A universal function describing the electron runaway in SF₆ is obtained.     

On <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> pair production by colliding electromagnetic pulses

Electron-positron pair production from vacuum in an electromagnetic field created by two counterpropagating focused laser pulses interacting with each other is analyzed. The dependence of the number of produced pairs on the intensity of a laser pulse and the focusing parameter is studied with a realistic three-dimensional model of the electromagnetic field of the focused wave, which is an exact solution of the Maxwell equations. It has been shown that e⁺e^? pair production can be experimentally observed when the intensity of each beam is I～10²⁶ W/cm², which is two orders of magnitude lower than that for a single pulse.     

Das Eindringen der Glimmentladung in Spalte

The fractional area of the cathode covered by the negative glow in low pressure hydrogen discharges has been studied using a special co - planar anode - cathode configuration. The cathode was a steel bar of 2×2×64 cm, sectionalised into 32 insulated parts. An identical electrode mounted directly above the cathode at a variable separation facilitated the simulation of screening effects of insulating or conducting walls and of hollow cathode conditions. The depth of penetrationξ of the discharge into this gap was studied for various conditions. In general for the insulating wall condition,ξ is approximately proportional to the applied voltage and depends on the gap width and pressure. The electron current in the negative glow parallel to the cathode surface as well as the cathode current density at any distancex from the anode vary exponentially withη=ξ-?. The potential of the negative glow in the gap decreases slowly with? to the “normal” cathode fall at?=ξ. In the case of the conducting wall, the discharge can penetrate to any depth, provided the wall is maintained at a potential ≧ the “normal” cathode fall. For a hollow cathodeξ is small, but the current density near the anode reaches extremely high values.     

Die Elektronenlawine als Sonde zur Ausmessung von Raumladungsfeldern

The dependence of the carrier amplification of an electron avalanche on the electric field allows to observe space charge fields in the discharge gap by measurements of carrier amplifications using the oscilloscopic method. This procedure is demonstrated by investigations of discharge processes in atmospheric air in a homogeneous field atE/p=34 V/cm Torr with an electrode distanced=15 cm. A test-avalanche was started to run through a positive space charge cloud produced by previous ionisation processes. The increase of the electron number was observed by a photomultiplier (optical method). There was found a strong modification of the time constant 1/αv _?. From this modification there was deduced a field distribution along the gap. The observed space charge was found moving towards the cathode with a velocity, which is equal to the drift velocity of the positive ions.