平面二极管爆炸发射阴极特性实验研究

 在电压0.6~1.0 MV,脉冲重复频率为100 Hz条件下,实验研究了爆炸发射阴极的有效发射面积、平均发射电流密度、二极管阻抗、电子束能量损耗机制等特性。结果表明：阴极有效发射面积随时间呈方波变化,在脉冲开始后5 ns内有效发射面积基本达到稳定。在碳纤维、天鹅绒、石墨、不锈钢4种阴极材料中,碳纤维阴极有效发射面积最大且变化相对稳定,并且碳纤维阴极具有最大的平均发射电流密度。二极管阻抗随着阴阳极间隙的增加并非呈平方关系增加,而是呈线性增长,阻抗失配是降低电子束能量传输效率的主要机制。     

Approximate calculation of current in a diode with an explosive emission cathode

The approximation of electron motion along electric field force lines is used to calculate current in diodes with knife-edge and point emitters. The diode current is limited by space charge, with each current tube considered as a diode element with electrodes in the form of coaxial cylinders or concentric spheres. The effect of the cathode cavity in which the emitter is installed upon current magnitude is considered by limiting beam dimensions at the anode.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 3–6, February, 1992.     

Interaction of cathode plasma with the cathode surface in an electron source with explosive electron emission

The interaction of the plasma formed at emission centers of an electron source using explosive electron emission with the cathode surface is studied. It is found that the plasma flux does not flow around obstacles located in its path and is effectively deionized upon incidence on the wall.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 26–29, November, 1981.     

二极管爆炸发射阴极等离子体的膨胀扩展

分析了二极管中爆炸发射产生阴极等离子体的演化特征,在考虑了阴极等离子体朝阳极膨胀运动使二极管阴阳极间距缩短这一效应的同时,还计入了阴极等离子体沿发射表面径向扩展运动对二极管有效发射面积的影响。基于Child-Langmuir定律,利用在一个四脉冲强流电子束源装置上得到的电流、电压等实验数据,假定阴极等离子体轴向膨胀和径向扩展速度近似相等,研究了阴极等离子体的膨胀扩展动力学行为。计算结果表明,阴极等离子体朝阳极的膨胀和沿径向的扩展速度为0.9～2.8 cm/s。     

Perveance of a planar diode with a multipoint cathode

The I–V characteristics of a planar diode with a multipoint explosive emission cathode are studied under the conditions when the impedance of the diode is matched to the output resistance of the nanosecond generator. The experiments are carried out on the TÉU-500 (350–500 keV, 60 ns, 250 J per pulse) high-current electron accelerator. The perveances of the diodes with a spike (140 spikes) cathode, multipoint copper cathode, and cathode made of carbon felt are measured in the course of electron beam generation. Comparison is performed between the I–V characteristics of the diodes with multipoint and continuous cathodes made of the same material. It is found that the electron current of the diode is described well by Child’s law with regard to the shrinkage of the anode-cathode gap and an increase in the emissive surface due to the expanding plasma (formfactor). When the cathode is made of carbon felt or is multipoint, the space-charge-limited electron current mode sets in even 5–10 ns after the voltage is applied.     

Pulsed X-ray diode with a long-lifetime plasma cathode

6 shots, the X-ray dose, uniformity, and ionisation rate values guarantee an effective preionisation of excimer laser discharges. Owing to both the long lifetime and the substantial absence of maintenance, this X-ray diode seems suitable to preionise commercial gas lasers, such as excimer and TEA CO₂ lasers. Received: 28 August 1998 / Revised version: 16 November 1998 / Published online: 24 February 1999     

Specific features of explosive decomposition of pentaerythritol tetranitrate exposed to an electron beam with an explosive emission cathode

A comparative examination of the critical energy density of explosive decomposition of pentaerythritol tetranitrate exposed either to an electron beam of a GIN-600 accelerator (240 keV, 20 ns) with an explosive emission cathode or to this beam combined with metal low-temperature diode plasma has been performed. It has been demonstrated that the contribution of plasma to the development of explosive decomposition is appreciable at explosion probabilities P ≤ 0.2. At higher energy densities and explosion probabilities P ≥ 0.5, the contribution of plasma to the overall beam energy density did not exceed 10%.     

Generation of a submillisecond electron beam with a high-density current in a plasma-emitter diode under the conditions of open plasma boundary emission

The generation of a 250-μs-wide electron beam in a plasma-emitter diode is studied experimentally. A plasma was produced by a pulsed arc discharge in hydrogen. The electron beam is extracted from a circular emission hole 3.8 mm in diameter under open plasma boundary conditions. The beam accelerated in the diode gap enters into a drift space in the absence of an external magnetic field through a hole 4.1 mm in diameter made in the anode. The influence of electron current deposition at the edge of the anode hole on the beam’s maximum attainable current, above which the diode gap breaks down, is studied for different accelerating voltages and diode gaps. The role of processes occurring on the surface of the electrodes is shown. For an accelerating voltage of 32 kV, a mean emission current density of 130 A/cm² is achieved. The respective mean strength of the electric field in the acceleration gap is 140 kV/cm. Using the POISSON-2 software package, the numerical simulation of the diode performance is carried out and the shape of steady plasma emission boundaries in the cathode and anode holes is calculated. The influence of the density of the ion current from the anode plasma surface on the maximum attainable current of the electron beam is demonstrated.     

Near-cathode potential drop in a vacuum diode with explosive emission of electrons

The near-cathode potential drop u_K is studied in a high-voltage high-current (U=20–40 kV, i=100–500 A) vacuum diode with a cathode operating under explosive emission of electrons. The magnitude of U_K is estimated from oscillograms of the probe current under conditions of breakdown of the layer between the probe and the cathode-flare plasma. It is shown that u_K is the same order of magnitude as the near-cathode potential drop in vacuum arcs. U_K does not change greatly when there are sharp rises in diode current, indicating that oscillations in diode current are probably related to processes at the boundary for drawing of electrons from the flare plasma.     

Intense emission from a grid-stabilized plasma cathode

Intense emission from a grid-stabilized plasma cathode based on a glow discharge with an expanded anode area is studied. In the electrode system of the ion source, the potential difference between a large-mesh grid electrode (a hole diameter of 4–6 mm) and cathode and anode plasma reaches 200 V and the glow discharge current is up to 1 A. The current distribution over the electrodes of the plasma cathode is taken, and the dependences of the electron extraction efficiency and electron-emitting-plasma potential on the gas pressure and discharge parameters are obtained. A relationship between the geometric parameters of the grid, cathode plasma potential, and efficiency of electron extraction from the plasma is derived. It is shown that stable intense emission from the plasma cathode can be provided in wide ranges of gas pressure and discharge current by varying the geometry and mesh size of the plasma cathode grid. Discharge contraction in the grid plane at elevated gas pressures is explained. It is assumed that the emitting plasma becomes inhomogeneous due to variation in the thickness of near-electrode layers in the holes of the grid, which makes the distribution of the emission current from the plasma more nonuniform.     

On the self-consistent states of a planar vacuum diode with an electron beam

The self-consistent stationary solutions for a planar vacuum diode with a monoenergetic electron beam are fully classified. Formulas are presented to calculate potential distributions of all types and the maximum electric current that can pass through the diode under steady-state conditions at an arbitrary applied voltage. The stability of the solutions is studied.     

爆炸电子发射初期阴极表面电场的研究

为了研究二极管爆炸电子发射初始阶段阴极表面复杂的物理现象及规律, 建立了由场致电子发射阴极构成的一维平板真空二极管物理模型,通过自行编程数值求解泊松方程, 考虑了发射出的电子对阴极表面电场的非线性影响,自洽模拟得到了阴极表面电场随时间的变化情况. 模拟结果表明,爆炸电子发射初期,阴极表面电场随时间的增加而呈现出不断振荡的规律, 且振荡幅度越来越小,最终到达一个稳态的值,二极管两极板之间的外加电场越大, 阴极表面稳态电场的绝对值越大;电场增强系数越大,阴极表面稳态电场的绝对值越大. 在整个时间演变过程中,阴极表面的实际电场强度决定着阴极发射的电流密度大小, 反过来阴极发射的电流密度又会影响到阴极表面的电场.     

Capacitance of a planar diode

The capacitance of a planar diode is analyzed in the quasisteady-state approximation. The differential capacitance is derived for three operating modes of the diode: with a negative voltage on the anode, with a space-charge limited anode current, and at current saturation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 104–112, April, 1971.     

Development of a ferroelectric cathode diode

As a promising kind of high current cold cathode, the Ferroelectric Cathode （FEC） has several significant advantages, such as a controllable trigger time, lower vacuum requirement and large emitting area fabricability. The emitting current density of the FEC fabricated at Tsinghua University was more than 200 A/cm^2. In order to make the ferroelectric cathode into practical applications, a high current density diode using a ferroelectric cathode was designed, based on the PIC simulation. The performance of the FEC diode was investigated experimentally. When the applied diode voltage was 60 kV, a current density of more than 250 A/cm^2 was obtained, and the current density distribution was also measured.     

Simulations of plasma formation in the cathode sheath of an efficient excimer lamp

Based on the available experimental data and computer simulations, analytical approximations of the quantities characterizing electron multiplication in the cathode sheath are proposed. The critical electric field is found above which runaway electrons are observed. Using the approximations proposed, the dependences of the plasma parameters (the electron and ion densities and currents and the electric field strength) on the distance from the cathode are analyzed. Simple formulas for the total current, the cathode sheath thickness, and the cathode potential drop as functions of the electric field on the cathode surface are derived.