Leader discharge over a water surface in a Lichtenberg figure geometry

A multichannel leader discharge over a water surface is investigated in a Lichtenberg figure geometry. It is established that the Ohmic conductivity of water causes nonlinearity of the R(t)C discharge circuit. A mutual one-to-one correspondence between the channel lengths and the currents flowing in them is established during the discharge, and the discharge has a selfconsistent character. A mechanism is proposed for the initiation of initial channels by maxima which arise in the charge structure of the planar double layer on the water surface during the development of Rayleigh-Bénard instability in the layer after the pulsed corona from the anode reaches the water. Zh. Tekh. Fiz. 68, 63–66 (November 1998)     

Characteristics of anodic glow pulsed plasma

Using the triple Langmuir probe, the characteristics of the glowing plasma adjacent to a constricted anode is obtained. The glow discharge is generated by applying a train of high voltage pulses between the constricted anode and cylindrical cathode with a pulse frequency of 2 kHz at 50% duty cycle. The axial plasma characteristics along the central line of the anode shows crest and trough resembling a double layer. The bulk plasma showed uniform electron density outside the glow. The visual images show an enhancement in the volume of the glow consistent with the discharge current. The mechanism behind the particular double layer characteristics around the anode is being explained in detail.     

Experimental investigation of the anode region of a free-burning atmospheric-pressure inert-gas arc I. General characteristics of the discharge. Low-current regime

This paper reports the experimental investigation of the anode region of a free-burning inert-gas arc at atmospheric pressure in the current range from a few amperes to hundreds of amperes. The tungsten thermionic-emission cathode and the large-diameter water-cooled copper anode that were used permitted the anode arc root to assume its natural form. The general characteristics of the discharge are given and results are presented from investigations of the anode region at low currents, where the anode arc root is single and constricted, but erosion-free. Measurements of the plasma parameters as well as the current density in the arc root are reported, and a comparison is made between the values obtained and those characteristic of the region of the cathode arc root. Zh. Tekh. Fiz. 67, 35–40 (January 1997)     

Emission properties of a plasma cathode based on a glow discharge for generating nanosecond electron beams

The emission properties of a plasma cathode based on a nanosecond pulsed glow discharge with currents of up to 200A at a pressure of 5×10⁻² Pa are studied experimentally. Stable ignition and burning of the discharge are ensured if the current in the auxiliary pulsed discharge is 25–30% of that in the main discharge and its pulse duration exceeds that of the main discharge by more than an order of magnitude. Emission current pulses from the cathode with amplitudes of up to 140A fully reproduce the discharge current and are determined by the transparency of the grid anode. Zh. Tekh. Fiz. 69, 62–65 (November 1999)     

Hollow Cathode Effect with Double Axial Electron Injection

The paper presents a new type of HCE glow discharge obtained with double plane-conical cathodes. The two identical cathodes are tronconical and screened with 1 mm² mailed wire net with a 3.5 mm diameter central washer each. The discharge is obtained between the two cathodes and a ring shaped anode equally distant from both. Optimum intercathodic span is 4 mm, allowing for maximum amplifications at the optimum pressure values for the two gases. Employed helium and argon are spectral pure. At the given distance and depending on voltage and gas pressure, a double axial electron self injection cathode effect is obtained between the electrodes, consisting of very large increase of current and radiations.     

Open discharges: Structure, development, and role of photoemission

The research reported in three preceding papers is summarized. The photoelectron mechanism for the formation of electron beams in an open discharge with a grid anode is revised. Revision of the discharge mechanism also requires revision of the optimal conditions for its excitation. A new method for pumping lasers by beams of fast atoms formed in an open discharge with an inverted voltage is proposed. Zh. Tekh. Fiz. 68, 33–38 (March 1998)     

Trapped and free electrons in the near-anode region of a striated discharge

Spatial potential profiles and electron energy distribution functions are measured in the near-anode region of a striated neon glow discharge. It is discovered that potential wells of small depth adjacent to the anode appear on the spatial potential profiles at certain moments in time. The distribution functions measured in the potential wells have a pronounced maximum of slow electrons, which sharply distinguishes them from the distribution functions in the striation phases where there are no wells. The mechanism which shapes the electron distribution function for electrons trapped in a potential well is analyzed. A perturbing effect of the anode on the electron distribution function as the anode is approached is discovered experimentally, and an interpretation of this effect is given. Zh. Tekh. Fiz. 68, 25–32 (March 1998)     

Analysis of the Near-Anode Processes Characters in Argon Arc Discharges of High Pressure

In this paper the anode layer model including two zones is considered. It is suggested that in the collisionalless zone (the sheath) the potential drop is negative. For the collisional part of the anode layer the equation system is considered. This system takes into account the ionization non-equilibrium in this layer. Here side by side with the electrical field the complementary diffusion mechanism of the current transfer is examined. This mechanism is stipulated by the existence of the electron gas pressure gradients in the anode layer. It is shown that the potential drop in the collisional part of the anode layer is also negative because of the action of the diffusion mechanism of the current transfer. In this way the full potential drop in the anode layer of the discharge burning in argon by atmospere pressure is turned out to be negative. The character of the change of the energy and impulse equations terms is discussed.     

Initiated subcritical microwave streamer discharge and the problem of global elimination of Freons from the Earth’s atmosphere

An analysis is made of an initiated streamer discharge in a microwave wave beam at subcritical field from the point of view of using this type of discharge for global elimination of Freons, which are damaging to the ozone layer, from the Earth’s atmosphere. The various stages of discharge evolution are illustrated with photographs and the physical factors determining its properties at these stages are indicated. Zh. Tekh. Fiz. 68, 15–24 (December 1998)     

Mechanism for the influence of the geometric parameters on the electrical characteristics of Penning ion sources

A steady-state Penning ion source is studied experimentally. Depending on the geometric parameter l _a (the anode length to diameter ratio) and pressure, maxima are observed in the discharge current and in the ion beam current extracted from an aperture at the center of the cathode. It is shown that at pressures of the order of 10⁻⁴ Torr, two maxima appear in these currents: one, for short discharge gaps with l _a =1–1.5, corresponds to a diverging ion beam, and the other, for longer anodes with l _a =4–5, to a collimated ion beam. At pressures of the order of 10⁻⁵ Torr, only one maximum appears in these currents, for short anodes l _a =2–3 with a diverging ion beam. A physical explanation is proposed for these findings. Zh. Tekh. Fiz. 68, 29–32 (September 1998)     

XPS study of the deposited Ti layer in a magnetron-type sputter ion pump

X-ray photoelectron spectroscopy (XPS) was used to study the surface chemical composition of the anode deposits in a miniature magnetron ion pump. The pump was mounted on an UHV system with the ultimate pressure of 1 × 10⁻⁹ mbar. A stable discharge was established in the nitrogen atmosphere with some traces of CO at about 10⁻⁷ mbar. The cathode was made of pure titanium. The sputtered titanium atoms deposited on the anode, where they reacted with gases to form a film of titanium compounds. The thickness of the deposited titanium layer on the anode was about 100 nm. The results from XPS investigations indicate that active gases such as O₂ and N₂ react with Ti forming TiO₂ and TiN. While carbon containing molecules just adsorb on the surface and do not form carbide. In the bulk of the deposited layer almost pure TiN was found with some traces of oxygen and carbon. The part of carbon was bonded to TiC, which can be caused by ion sputtering during the depth profiling.     

Ultrathin nickel oxide film as a hole buffer layer to enhance the optoelectronic performance of a polymer light-emitting diode

In order to promote a polymer LED (PLED), we fabricated and introduced an ultrathin nickel oxide (NiO) buffer layer (<10 nm) between the indium tin oxide (ITO) anode and the poly (3, 4-ethylenedioxythiophene) hole injection layer in the PLED. The NiO buffer layer was easily formed on the ITO anode by electron-beam deposition of a nickel (Ni) metal source and an oxygen plasma treatment process. As a result, the PLED device with the NiO buffer layer on its ITO anode had the same turn-on voltage as conventional PLED devices without the NiO buffer layer, and the luminance of the PLED device with the NiO buffer layer was doubled, compared with the conventional PLED devices without the NiO buffer layer. Improvement of the optoelectronic performance of the PLED can be attributed to the increase of the current driven into the diode, resulting from the NiO buffer layer, which can enhance the hole injection and balance the injection of the two types of carriers (holes and electrons). Thus it is an excellent choice to introduce the NiO buffer layer onto the ITO anode of the PLED devices in order to enhance the optoelectronic performance of PLED devices.     

Electromagnetic radiation of a nanosecond discharge in an open gas-filled diode

The properties of the discharge in and radiation from an open gas-filled diode to which high-voltage nanosecond pulses are applied from the RADAN-220 generator are studied. Electromagnetic radiation in the X-ray, UV, visible, and near-IR ranges of the spectrum, as well as high-power subnanosecond (0.5-to 0.7-ns-long) pulses of ultra-wide-band (UWB) electromagnetic radiation, are recorded when a diffuse discharge is initiated in atmospheric pressure air. For the coaxial cathode and anode, the open gas diode emits radially polarized UWB pulses, whereas for the cathode in the form of a segment, the UWB radiation is linearly polarized. The effective potential for both designs of the diode is ER = 6 kV. It is shown that the plasma in the discharge gap serves as a source of soft X rays and the metallic anode generates hard X rays.     

Conditions for the existence of a positively charged structure in a Penning discharge

An analytical model is developed for the high-current form of a low-pressure glow discharge in a magnetic field. Expressions are derived for the critical magnetic induction and critical pressure, below which it becomes impossible for this form of discharge to exist. It is shown that the transition from the high-voltage form to the high-current form of discharge with increasing pressure is not attributable to an increase in the ionization rate, but to an increase in the drift velocity of plasma electrons across the magnetic field. Estimates based on the expressions derived in the article agree in order of magnitude with the experimental data. It is shown that the region in which discharge exists can change considerably in the presence of electron emission. Zh. Tekh. Fiz. 68, 56–63 (July 1998)     

A Modified Version of the Grimm's Glow Discharge Lamp for Use as a Demountable Hollow Cathode Emission Source. III. Blackening as a Function of Discharge Parameters

Abstract

The influence of anode distance from hollow cathode on the blackening? of spectral lines excited by means of the modified Grimm's lamp was investigated for three representative cathodic materials, i.e. aluminium, copper and graphite using argon as the carrier gas. On the basis of the experimental results as well as voltage-current characteristic curves at distances of 7, 15, 20, 25 and 33 mm, it was possible to conclude that the optimal sets of discharge parameters for all the materials investigated are based on an electrode distance of 20-25 mm. In the case of copper a distance of 33 mm was also found to be highly suitable. An increase in the emission of copper lines at the largest anodic length with increasing pressure of the noble gas was also observed, in contrast with the behavior of the same element at shorter distances. A tentative interpretation of the phenomenon is given.     

Effect of gas pressure on amplitude and duration of electron beam current in a gas-filled diode

The parameters of an electron beam generated in helium in the pressure range p = 10⁻⁴−12 atm are studied. Nanosecond high-voltage pulses are applied to a gap between a tubular cathode and planar anode, which is made of 45-μm-thick AlBe foil. Behind the anode, an electron beam is detected at a helium pressure of 12 atm. The pressure dependence of the beam current amplitude shows three peaks at p ≈ 0.01, ≈ 0.07, and ≈ 3 atm. The beam-induced glow of a luminescent film placed behind the foil and the discharge glow at different helium pressures in the gas-filled diode are photographed.     

Effects of electron‐absorbing boundaries on the plasma parameters of a hot‐filament discharge

In this paper we investigate theoretically and experimentally the plasma parameters in a double‐plasma device in the presence of an additional electron‐absorbing boundary. The latter is formed by an electrode of variable size immersed in the plasma. It is found that, depending on its size and bias potential, such an anode can considerably influence the plasma parameters. Good qualitative and fair quantitative agreement between theoretical predictions and laboratory measurements of the plasma parameters is found for various discharge conditions. In addition we discuss the consequences of our results with respect to the existence conditions of anode‐type double layers in double‐plasma devices.     

Runaway of electrons in dense gases and mechanism of generation of high-power subnanosecond beams

New understanding of mechanism of the runaway electrons beam generation in gases is presented. It is shown that the Townsend mechanism of the avalanche electron multiplication is valid even for the strong electric fields when the electron ionization friction on gas may be neglected. A non-local criterion for a runaway electron generation is proposed. This criterion results in the universal two-valued dependence of critical voltage U _cr on pd for a certain gas (p is a pressure, d is an interelectrode distance). This dependence subdivides a plane (U _cr , pd) onto the area of the efficient electron multiplication and the 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 area of e-beam. The mechanism of the formation of the recently created atomospheric pressure subnanosecond e-beams is discussed. It is shown that the beam of the runaway electrons is formed at an instant when the plasma of the discharge gap approaches to the runaway electrons is formed at an instant when the plasma of the discharge gap approaches to the anode. In this case a basic pulse of the electron beam is formed according to the non-local criterion of the runaway electrons generation. The role of the discharge gap preionization by the fast electrons, emitted from the plasma non-uniformities on the cathode, as well as a propagation of an electron multiplication wave from cathode to anode in a dense gas are considered.     

气流对氮气介质阻挡放电气体温度及放电模式的影响

利用光谱测量和高速照相的方法,对大气压氮气介质阻挡放电进行了研究.在气流的帮助下,2mm气隙中的均匀放电可以长时间得以维持.根据放电电流波形和1μs曝光时间的放电图像,这种均匀放电被判定为汤森放电.用氦氖激光器对实验中所用的光谱仪带来的谱线轮廓展宽进行了标定,并将得到的仪器展宽数据输入Specair软件,计算了不同气体温度下氮分子二正系0—2谱带的谱线轮廓.通过用计算谱线轮廓去拟合实验谱线轮廓,确定了氮分子的转动温度并将其近似为气体温度.结果表明:大气压氮气介质阻挡汤森放电并不能使气体温度大幅上升(ΔTg≤50K),气体温度的小幅上升不会引起热不稳定性而导致放电发展成为细丝放电.气流确实可以降低放电气体温度,但这不是使汤森放电得以维持的原因.通过比较加入气流前后的放电光谱可知,气流降低了气隙中杂质氧的含量,使得更多的氮分子亚稳态N2(A3Σu+)的寿命延长到下一次放电的起始时刻,为汤森放电提供了必需的大量种子电子.     

Pulsed discharge in nitrogen and argon under an elevated pressure in a nonuniform electric field

The characteristics of a discharge and radiation in nitrogen and argon under pressures of 10–760 Torr and the discharge formation without pre-ionization of the gap from an auxiliary source are considered. A peak is detected on the pressure dependence of the radiation power of the second positive system of nitrogen for E ₀/p ～ 270 V/cm Torr and nitrogen pressure p ～ 70 Torr. In the pressure range 10–760 Torr and for a voltage pulse leading front duration of ～ 10 ns, an electron beam is formed behind the grid anode with various half-amplitude pulse durations. It is shown that, under the given conditions, the electron beam is formed at the voltage pulse front both in the case of a discharge gap breakdown and in the absence of a clearly manifested breakdown, as well as for a 10-ns delay of breakdown at the leading front of a discharge current pulse.