Untersuchung der Prozesse in der aktiven Zone der Hohlkatodenbogenentladung. II. Die Bilanzgleichungen,Ergebnisse

In [1] we studied the electron distribution function and the processes of excitation and ionization inside the cathode of hollow cathode arc discharge. In this paper we solve the equations of energy and particle balances using the results of [1]. Adding the minimum principle of energy it is possible to calculate the concentration and the temperature of electrons, the cathode drop, the temperature of the cathode wall and the current density in the active zone. Some of calculated values will be compared with experimental ones. We found satisfactory agreement.     

Ionisations- und Rekombinationsprozesse in der Hohlkathodenentladung

If a plasma is not in local thermal equilibrium (LTG) it is necessary for the calculation of the ionisation rate to know the elementary processes of ionisation and recombination. Some calculations concerning these processes and the relevant probability coefficients under hollow cathode discharge conditions are given and an approximated equation for the ionisation rate is developed and discussed. The possibility for the appearance of two distinct groups of electrons in a hollow cathode discharge and their influence on the developed equation is also discussed.     

Zur Theorie der Rückstreuung

Electrons emitted from a cathode, are partially backscattered to the cathode surface by collisions with gas molecules. No equilibrium between electrons, gas and field is presumed for a theoretical treatment of this process, in contrary to the conception of Thomson [1]; instead of it the effect of single collisions is investigated assuming isotropy of scattering. The collision numbers, which may be calculated from successive integral transforms, are shown to form a monotone decreasing sequence. In the field-free case the collision numbers and the back diffusion rates for the first collisions may be explicitely stated; the convergence of this method is rather poor, however. A model for back diffusion in an electric field, whereby the effect of primary collisions only is considered, is completely treatable. The results depend on the angular and energy-distribution of the emitted electrons. A comparison with other formulas and with experimental results for back scattering shows a better agreement between the latter and our equations than in the case of the Thomson-Loeb relation. The consequences on the theory of cathode fall are briefly discussed.     

Structure and parameters of vacuum arc cathode spots

The effect of such parameters of cathode materials as the heat of atom evaporation, atomic weight, work function of electrons on the structure of cathode spots of a vacuum arc, conditions of charged particle generation, and, most important, the F-emission of electrons, is considered. Determining the interrelation of cathode parameters and processes in a vacuum arc cathode spot helps develop conditions for a vacuum arc to effectively modify the surfaces of materials.     

Motion of the cathode spot of a vacuum arc in an external magnetic field

The problem of the motion of the cathode spot of a vacuum arc electrical discharge in a magnetic field applied tangential to the cathode surface is considered. The treatment is based on concepts of the nonstationary, cyclical nature of processes occurring in the cathode spot and the key role of return electrons falling out of the near-cathode plasma back onto the cathode. Zh. Tekh. Fiz. 68, 60–64 (June 1998)     

The Role of High-Velocity Electrons in a Hollow-Cathode Discharge

In this paper, the features of a low-pressure discharge in a hollow cathode are considered. It has been shown that a free mode can be realized with a double electric layer at the cathode and high density of the current of high-velocity electrons in the discharge bulk, considerably exceeding the current density at the cathode. In this case, the rate of ionization by high-velocity electrons considerably exceeds the rate of ionization by plasma electrons.     

Zündspannung und normaler Katodenfall der Glimmentladung für Edelgase und reine Molybdänkatoden

Breakdown voltage near PASCHEN -minimum and normal cathode fall of the glow discharge were calculated for inert gases and molybdenum cathodes on the basis of a simple theory. The method used was similar to TAKEISHI 's one. The calculated breakdown voltages are in good agreement with measured values, if back scattering of the y_i -electrons and the distance which electrons travel from the cathode without ionization is taken into account. In the case of the normal cathode fall the values calculated with the same assumptions for inert gases and molybdenum cathodes are much higher (up to 50%) than the well known experimental values. It was concluded, that the y_i-process in the glow discharge ist not the only important one. Comparing the calculated and experimental values of the normal cathode fall we obtain the result, that photons and/or ions from the glow release about 40–60% of all electrons at the cathode.     

工业X光二极管重复频率实验研究

工业X光二极管型单焦点高重复频率闪光X光机在科学研究、工业检测等领域具有重要应用前景。基于光导开关脉冲驱动源开展了金属阴极工业X光二极管重复频率运行实验, 采用烘烤处理方法研究阴极表面吸附特性对重复频率发射特性的影响;以二极管阻抗模型为理论基础, 通过重复频率实验获得的二极管电压维持时间和阻抗特性分析等离子体扩散过程。研究表明:对于高阻抗结构工业X光二极管, 金属阴极为表面吸附杂质或气体解吸附形成等离子体发射机制, 一次放电后阴极表面对气体的再吸附过程限制了其在高重复频率条件下的电流发射能力, 同时由于阴极等离子体扩散过程变慢使得二极管电压脉宽变长。具有高重复频率电流发射能力的阴极是发展单焦点重复频率X光机的基础。     

Messungen von Anregungstemperaturen in der Hochstromhohlkathode

Measurements of excitation temperatures in the negative glow light of a high-current hollow cathode discharge lamp with a gas temperature of about 1,500 °K have shown values forT _a of approximately 5,000 °K, when the atomic spectral lines are used as indicator. However, from ionic lines a temperature of 30,000–100,000 °K is deduced depending on the nature of the discharge gas. This big difference indicates that there is no Maxwell distribution in the hollow cathode discharge. A possible explanation could be that two energetically distinct types of electrons take part in ionisation and recombination respectively.     

A physical model of the low-current-density vacuum arc

A one-dimensional (1-D) physical model of the low-current-density steady-state vacuum arc is proposed. The model is based on the continuity equations for ions and electrons and the energy balance for the discharge system; the electric potential distribution in the discharge gap is assumed to be nonmonotonic. It is supposed that the ion current at the cathode is generated within the cathode potential fall region due to the ionization of the evaporated atoms by the plasma thermal electrons having Boltzmann's energy distribution. The model offers a satisfactory explanation for the principal regularities of a hot-cathode vacuum arc with diffuse attachment of the current. The applicability of the model proposed to the explanation of some processes occurring in a vacuum arc, such as the flow of fast ions toward the anode, the current cutoffs and voltage bursts, and the backward motion of a cathode spot in a transverse magnetic field is discussed     

Decolorization of acid red B aqueous solution by positive and negative electrical discharge

We investigated the decolorization of acid red B in aqueous solution by atmospheric discharge. It was found that decolorization was significantly greater when the aqueous solution served as the cathode than when it served as the anode. Our investigation suggests that hydroxyl radicals could be a major factor for decolorization in the solution phase. An analysis of the energy transportation by charge carriers in the discharge processes revealed that the mean energy transported from positive ions to the aqueous cathode was considerably higher than that transported from electrons/negative ions to the aqueous anode, and this could probably have indirectly affected the decolorization.     

Full-dimensional Monte Carlo simulation of glow discharges with superposed magnetic fields

A Monte Carlo simulation code is described that is suitable for modelling low-pressure glow discharges that possess cylindrical symmetry, but are of otherwise completely variable geometry. In this single-particle simulation in 3 space and 3 velocity dimensions, an entire discharge including the cathode fall can be modelled with or without magnetic fields of arbitrary shape. Electric and magnetic fields are given externally and are not adjusted self-consistently. Collision processes are modelled in great detail, and cathode sputtering phenomena are also included in the simulation. This simulation code is applied to hollow cathode discharges with and without superimposed magnetic fields and to a Penning discharge. Exemplary results are shown that include density profiles of cathode-sputtered atoms, energy distribution functions of electrons and cathode sputtering effects for a Penning discharge. Comparisons to results from experiment and other simulations are given.     

Investigation of unstable motion characteristics of vacuum arc cathode spots between transverse magnetic field contacts

With the improvement of the current level of power grids, the requirements of the opening level of the vacuum switches are also increasing. Vacuum arc cathode spots provide steam and electrons and, to a certain extent, determine the opening capacity of the vacuum switch. In this paper, a vacuum arc cathode spot research platform based on the de-mountable vacuum chamber is constructed. The characteristics of the vacuum arc cathode spots under the transverse magnetic field (TMF) contacts are assessed by a high-speed charge coupled device. The experimental results show that the cathode spot diffusion process can be divided into three processes through cathode spot distribution, arc voltage and current: initial diffusion stage of cathode spots, unstable motion stage of cathode spots, and extinguishing stage. The motion mode of cathode spots during unstable motion stage can be divided into cathode spots group stagnation (CSGS) to multi-cathode jet (MCJ) switch mode, cathode spots group motion (CSGM) to MCJ switch mode, CSGM mode, and MCJ mode. The effects of peak current and contact diameter on unstable motion mode were analysed.     

Optimum conditions for pumping laser transitions of cadmium ions by various processes in a hollow-cathode discharge

The interaction of electrons of various energies with helium and cadmium atoms in a hollow-cathode discharge is analyzed. On the basis of the results of this analysis the conclusion is made that helium is ionized predominantly by electrons moving from the cathode wall to the cavity axis and having energies 70<ε<300 eV, whereas helium and cadmium are ionized predominantly by electrons with energies 9<ε<70 eV which move chaotically. For each of these energy ranges, the kinetic equation is solved and the electron energy distribution function (EDF) is determined, which is used for calculating pumping rates for laser transitions of cadmium ions. The conclusion is made that the rate of population of laser transitions through charge transfer is determined by electrons having a predominant direction of motion and an anisotropic EDF. The population rate associated with electron impact and the Penning ionization is determined by electrons moving chaotically and having an isotropic EDF. The analysis of the EDF made it possible to explain differences in discharge conditions (helium and cadmium pressures) providing optimum lasing for lines pumped by different processes. Radial profiles of pump rates obtained from the analysis made it possible to calculate and explain the dependence of the laser output power on the cathode diameter.     

槽型空心阴极放电中槽底阴极面的电子发射对放电的影响

运用粒子和流体组合模型理论研究了槽型空心阴极放电中槽底阴极面上二次电子发射对放电等离子体特性、电离特性及阴极溅射的影响.研究表明,从槽底阴极面发射的电子在进入负辉区后,可以形成振荡电子,因而具有增强电离的作用.根据各阴极面上的离子的空间分布可以推知槽底附近的阴极面上的溅射较强,这可以解释槽型空心阴极放电实验中观察到的因溅射导致槽底截面形状圆形化的现象     

具有空心阴极放电特征的射频放电的两电子组模型

 运用两电子组模型，考虑了射频放电中的α过程和γ过程两种电离机制，并结合流体模型，研究了中等气压下窄电极间隙容性耦合射频放电在运行模式转变区的等离子体密度以及电离速率分布等特性。理论研究表明，γ电离过程在高电流模式运行中起主要作用，并证实了此类放电中存在显著的电子摆钟效应，具有类似于空心阴极放电的特征。     

铁电介质阴极电子枪

 给出并分析了铁电介质阴极电子枪的初步数值模拟和实验结果。实验表明其发射电子密度可达110A/cm²。该种电子枪产生的电流密度大于阴极发射电子初始能量为零时的空间电荷限制电流,PIC数值模拟结果表明可以通过给发射电子赋予一定的初始能量来解释这一现象,理论分析认为铁电介质阴极发射电子具有初始能量是合理的。     

Eine Untersuchung der Elektronenkomponente von Elektronenlawinen im homogenen Feld II

Electron avalanches in uniform fields are studied by means of a short duration spark light source. Electron drift velocities ν_? are measured in hydrogen, nitrogen, oxygen, and some vapours. It is shown, that in hydrogen and nitrogen the number of electrons increases exponentially by gas amplification with a time constant 1/αν_?, in accordance with a conventional assumption and with previous measurements in methane, α is the first Townsend coefficient. In oxygen and air it is, however, demonstrated that the number of electrons increases considerably less than exp (αυ_?·t), and the multiplication process takes longer time. This is evidently due to time losses of the electrons on their paths across the gap. Thus the mean time interval for successors, started by photons at the cathode, is increased. — In addition, this paper gives details of some measurements of the first Townsend coefficient α, the electron diffusion coefficient, and ionic drift velocities for certain gases.     

Intensitätshysterese der Photoemission von Multialkalikathoden bei 77 °K

In a preceding paper it was reported on the photoemission of multialkali photocathodes with temperatures of about 77 °K, where nonlinearities, discontinuities and hystereses of the emission current were observed when the wave length and the intensity of the light was varied. In the following a detailed account is given on measurements of hystereses with alternating light intensities. Furtherly the absorption of the photocathodes was measured, while the emission current was at a discontinuity with a jump of the current by a factor of two and more. The absorption was independent of the jumps. From this and from a detailed discussion of the intensity hystereses it can be concluded an independence of the effect of: a) the primary interaction of the light with the cathode, b) the conduction mechanism of electrons through the cathode (for then otherwise a band gap of 7.05 eV should follow), c) the potentialstep at the cathode surface. Observed quantum yields of 100% are not due to electron multiplication by the initial energy of the excited photoelectrons but seem to indicate an exciton mechanism and/or field effect, the latter being quite different from the Malter effect. The intensity at which the upward jump occurs increases by a factor of ten when the cathode temperature rises by 0.36 °K. This temperature sensitivity is interesting in application as radiation detector.     

Importance of high local cathode spot pressure on the attachment ofthermal arcs on cold cathodes

The importance of having high local cathode spot pressures for the self-sustaining operation of a thermal arc plasma on a cold cathode is theoretically investigated. Applying a cathode sheath model to a Cu cathode, it is shown that cathode spot plasma pressures ranging 7.4-9.2 atm and 34.2-50 atm for electron temperatures of ~1 eV are needed to account for current densities of 10⁹ and 10¹⁰ A·m^-2, respectively. The study of the different contributions from the ions, the emission electrons, and the back-diffusing plasma electrons to the total current and heat transfer to the cathode spot has allowed us to show the following. 1) Due to the high metallic plasma densities, a strong heating of the cathode occurs and an important surface electric field is established at the cathode surface causing strong thermo-field emission of electrons. 2) Due to the presence of a high density of ions in the cathode vicinity, an important fraction of the total current is carried by the ions and the electron emission is enhanced. 3) The total current is only slightly reduced by the presence of back-diffusing plasma electrons in the cathode sheath. For a current density j_tot=10⁹ A·m^-2 , the current to the cathode surface is mainly transported by the ions (76-91% of j_tot while for a current density j_tot = 10¹⁰ A·m^-2, the thermo-field electrons become the main current carriers (61-72% of j_tot). It is shown that the cathode spot plasma parameters are those of a high pressure metallic gas where deviations from the ideal gas law and important lowering of the ionization potentials are observed