Luminescence From Minerals Excited by Subnanosecond Pulses of Runaway Electrons Generated in an Atmospheric-Pressure High-Voltage Discharge in Air

The duration of the luminescence from minerals excited by low-current subnanosecond pulses of runaway electrons generated in an atmospheric-pressure high-voltage discharge in air at high overvoltages was used to characterize specific minerals. Advantages of using an atmospheric-pressure air discharge as the electron source versus the use of evacuated acceleration tubes are discussed. The luminescence-duration measurement is a simpler approach as compared to other methods that are conventionally employed in the elemental analysis of minerals. PACS: 52.80.-s; 52.80.Tn; 52.80.Yr; 78.60.Hf; 91.60.Mk.      

Air Breakdown in the Field of Traveling Tem-Wave Assisted by Runaway Electrons

Russian Physics Journal - The method of dynamic time-domain reflectometry is used to investigate a pulsed breakdown of an air-filled coaxial line assisted by the traveling voltage wave with...     

Physical Kinetics of Electrons in a High-Voltage Pulsed High-Pressure Discharge with Cylindrical Geometry

Russian Physics Journal - Results of theoretical modeling of the phenomenon of a high-voltage discharge in nitrogen at atmospheric pressure are presented, based on a consistent kinetic theory of...     

Runaway Electrons at the Formation of a Positive Ionization Wave in Nitrogen and Air

JETP Letters - The generation of runaway electrons (REs) at a subnanosecond breakdown of a “plane–needle” gap caused by the development of a positive ionization wave starting from...     

Thermal Runaway Prevention in Arc Spots

After recapitulation of the energy balance equation of cathode arc spots, the condition of thermal runaway is derived, i.e., of the unlimited increase of the temperature at a finite critical current density, because of temperature dependent resistive heat generation. It is shown that in arc spots such a thermal runaway is not possible for two reasons. First, the temperature dependent electron emission cooling forces a limitation of the stationarily achievable temperature (negative feedback). The current density remains limited, however. Second, the short time scale of arc spot development (crater formation time, ~10 ns) is not sufficient for thermal runaway that needs ~100 ns (order-of-magnitude values), besides the case of very small protrusions, where the time scale drops to less than 0.1 ns.     

Spark Discharge Action on a Cathode Surface in Air Atmosphere

New results obtained by electron microscopy investigations of cathode spot parameters are qualitatively and quantitatively analysed to the view of further understanding of the cathode processes in spark discharges.     

Scaling Properties of Runaway Electrons in HL-1M Tokamak

1 Introduction Runaway electrons in tokamaks have been widely studied theoretically and experimentally. Runaway electrons have received lately a great attention due to several reasons： a） the possibility to study electromagnetic turbulence by measuring the runaway flux fluctuations and its energy spectra, and b） the runaway electrons are powerful diagnostics capable of yielding valuable information on the actual distribution function of fusion experiments.     

Scaling Law of Runaway Electrons in HL-1M Tokamak

Runaway electrons in tokamaks have been widely studied theoretically and experimentally. The runaway confinement time τr in ohmic and additionally heated tokamak plasmas presents an anomalous behavior compared with theoretical predictions based on neoclassical models. A one-dimensional numerical model including generation, acceleration and loss effect of runaway electrons is used to deduce the runaway energy εr dependence on the runaway confinement time.     

空气中空心阴极不同放电模式下的发光特性

为了进一步揭示空心阴极放电中放电模式的转换机制,特别是空心阴极放电过程中自脉冲的形成机理,利用柱型空心阴极放电结构,在空气环境下研究了放电处于不同模式时的发光特性。测量得到了不同放电模式下的伏安特性曲线、放电发光图像、自脉冲阶段的脉冲波形等。实验结果表明随着放电电流的增加放电分为汤生放电模式、自脉冲放电模式、正常辉光放电模式和反常辉光放电模式。虽然所用电源为直流电源,但在自脉冲放电阶段电流和电压随时间呈周期性变化。实验结果表明在不同的放电模式下具有不同的发光特性。在由汤生放电转换为自脉冲放电模式和由自脉冲模式转换为正常辉光放电模式过程中,放电腔的径向中心处和轴向孔口附近均存在光强的突变。实验同时在200～700 nm范围内测量得到了不同电流时的发射光谱。结果表明发射光谱主要集中在330～450 nm,主要包括氮分子的第二正带系(C3Π_u→B3Π_g )和氮分子离子的第一负带系（B2Σ+_u→X2Σ+_g）。其中氮分子离子第一负带系具有较强的发射光谱。由于B2Σ+_u激发电位较高,因此该谱带较强发射光谱的存在表明空心阴极放电较其他放电形式更容易获得高激发态粒子和高能量电子。在650～700 nm附近存在一弱的发光谱带,主要为氮分子的第一正带发射谱（B3Π_g→A3Σ+_u）。在此基础上根据双原子光谱发射理论,结合氮分子第二正带系的三组顺序组带：Δν=-1,-2和-3,利用玻尔兹曼斜率法计算得到了不同放电模式下氮气的分子振动温度。结果表明在实验电流范围内分子振动温度在3 300 K左右,随着电流的增加而升高,并且在自脉冲消失时存在一突变迅速增强。由于电子能量、电子密度与分子振动温度密切相关,因此该结果也表明随着放电电流的增加电子平均能量和电子密度不断增加,当脉冲消失时,电子平均能量和电子密度出现跃变升高。最后,对空心阴极放电中自脉冲的形成机理进行了讨论,结果表明自脉冲放电源于放电模式的转换。     

Control of a Self-Sustained Discharge by Runaway Electron Beams

Russian Physics Journal -     

Erosion Craters and Arc Cathode Spots in Vacuum

The development of erosion craters on clean, smooth cathodes in UHV has been investigated with a time resolution of nanoseconds (current range 10–200 A). Furthermore, crater size erosion rate and velocity of spot displacement have been measured in dependence on current and surface conditions. The relevance of the results for different cathode spot models is discussed in detail. From the measurements the following conclusions are drawn. The craters are caused by the action of the discharge pressure on the molten metal within a spot. The spots move in a random manner in elementary steps of a crater radius with time constants of the order of 10^?8 s. The main reason for the movement is the formation of micropoints at crater boundaries. Droplets and contaminations induce jumps of more than a crater radius. The impact of droplets causes considerable deformations of the cathode surface. Nanosecond pulse breakdowns and quasi-stationary arcs result in values of crater size, spot velocity and erosion rate that are comparable within an order of magnitude. These results support a non-stationary spot model that describes the cathode spot as a sequence of surface explosions.     

Possible High Power Laser Construction Using a New Discharge Type-Heated Cathode Discharge in the Copper Vapours Continuously Evaporated from the Anode

The possibility to build a high power copper laser using a new type of discharge – heated cathode discharge in the copper vapours continuously evaporated from a melted spot on the anode surface is analysed. From the experimental data on this new discharge type, the equivalent pressure of the copper atoms in the discharge space has been obtained. This pressure can be as high as 1 torr. The density of the power in the discharge volume is evaluated to be more than 1 kW/cm³.     

Multicolor Laser Generation Resulting from a Chain Reaction of Atmospheric Nitrogen Oxidation Initiated by an Electric Discharge in Air

It was demonstrated that the luminous cloud arising during an explosion in air initiated by an electric discharge produces superluminescence and laser generation in the visible spectrum. Both these types of radiation presumably originate from the stimulated emission of NO* (blue light) and NO*₂ (orange and red) molecules and N₂O(¹S) exciplexes (green). In addition, if the process occurs inside an optical resonator, the mixture of nitrogen oxidation products with air autoignites.     

On Thermal Runaway Electrons and the Polarization of X-ray Emission in Solar Flares

Journal of Experimental and Theoretical Physics - A model for the thermal runaway of electrons in solar flares based on an approximate analytical solution of the kinetic equation with a linearized...