托卡马克装置的击穿条件

在CT-6B托卡马克实验装置上研究了充气气压、环向磁场、杂散磁场、环电压等放电条件对击穿的影响。发现垂直方向和水平方向的杂散磁场对击穿影响不同。指出实验结果与汤生放电模型的偏离。用Monte-Carlo方法解出击穿阶段电子分布函数,对汤生模型公式作出修正。 关键词：     

HL-2A装置气体击穿延迟时间

气体击穿延迟时间实验数据表明,HL-2A装置的气体击穿过程可以用修改了的有电极放电汤森德电离公式,并考虑电子的几何损失来进行描述。     

Electrical Breakdown of Gases: The Prebreakdown Stage

In this paper, a review of the theories and experiments devoted to the understanding of the development of the electrical breakdown of a gas insulated gap, i. e., the switching delay, is presented. The presentation is chronological. The classical Townsend and streamer models for breakdown are discussed; followed by a brief account of the continuous acceleration and avalanche-chain models. These last two models have been proposed primarily to describe breakdown at large electric fields. Then, the two-group model for breakdown at voltages above approximately 20-percent self-breakdown is presented. Finally, a brief analysis is given of the present state of the field and the direction it is takdng.     

Enhancement of the electric field threshold for microwave breakdown by crossed magnetic field

The enhancement of breakdown threshold is of benefit to the high power microwave transmission. We propose a magnetic field in the transverse direction to the electric field to enhance the breakdown threshold. A theory of electric field threshold with crossed magnetic field for short pulse is developed, and verified by particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. The result shows that the crossed magnetic field can enhance the breakdown threshold significantly.     

Townsend coefficient,escape curve,and fraction of runaway electrons in copper vapor

Ionization and drift characteristics of electrons in copper vapor in the presence of an external electric field are analyzed. In contrast to normal gases, in copper vapor, the excitation energy of lower states is significantly lower than the ionization potential and the excitation cross section is several times greater than the ionization cross section at the incident-electron energy on the order of the ionization energy. This can affect the characteristics of electron bunching in gas. It is demonstrated that, as in previously studied gases, the notion of the Townsend coefficient remains meaningful even in the presence of strong fields at which the electric force exceeds the electron drag force acting in gas. The dependences of the main ionization and drift characteristics on the reduced field strength, the escape curve (which separates the region of effective electron multiplication and the region where electrons leave the discharge gap without multiplication), and the curves of equal efficiency for the formation of runaway electrons are obtained. It is demonstrated that a relatively high excitation cross section of copper levels leads to a sharper peak on the dependence of the Townsend coefficient on the field strength and a narrower region of the effective electron multiplication in comparison with previously studied gases.     

高频H型放电离子源的场特性

 从Maxwell方程组出发，推导了高频H型放电离子源放电空间的场分布, 并采用Mafia软件进行了三维实体建模，计算了高频离子源放电击穿前和稳定工作后的电磁场分布，得到了高频离子源放电空间电磁场分布的直观图像。通过比较击穿前高频电场的轴向和环向分量，得出了轴向电场在高频离子源击穿中起主要作用的结论，并进而推导出了高频离子源的击穿判据，得出了气体击穿时离子源击穿电压和放电管内气压的关系，与实验结果符合较好。     

Kinetic parameters,collision rates,energy exchanges and transport coefficients of non-thermal electrons in premixed flames at sub-breakdown electric field strengths

The effects of an electric field on the collision rates, energy exchanges and transport properties of electrons in premixed flames are investigated via solutions to the Boltzmann kinetic equation. The case of high electric field strength, which results in high-energy, non-thermal electrons, is analysed in detail at sub-breakdown conditions. The rates of inelastic collisions and the energy exchange between electrons and neutrals in the reaction zone of the flame are characterised quantitatively. The analysis includes attachment, ionisation, impact dissociation, and vibrational and electronic excitation processes. Our results suggest that Townsend breakdown occurs for E/N = 140 Td. Vibrational excitation is the dominant process up to breakdown, despite important rates of electronic excitation of CO, CO₂ and N₂ as well as impact dissociation of O₂ being apparent from 50 Td onwards. Ohmic heating in the reaction zone is found to be negligible (less than 2% of peak heat release rate) up to breakdown field strengths for realistic electron densities equal to 10¹⁰ cm^?3. The observed trends are largely independent of equivalence ratio. In the non-thermal regime, electron transport coefficients are insensitive to mixture composition and approximately constant across the flame, but are highly dependent on the electric field strength. In the thermal limit, kinetic parameters and transport coefficients vary substantially across the flame due to the spatially inhomogeneous concentration of water vapour. A practical approach for identifying the plasma regime (thermal versus non-thermal) in studies of electric field effects on flames is proposed.     

Free‐Electron Gas Spectrum Uniqueness in the Mixture of Noble Gases

Gas mixtures can reach the Maxwell's specter shape in case of low‐ionized mono‐atomic mixtures in the weak electric field. The parameters pertaining to the Maxwell spectrum of free electrons' gas straightforwardly settle on the insulating characteristics of the examined gas mixture at the fundamental level. In this paper, a condition for breakdown has been accomplished taking as a starting point the ionization coefficients derived accordingly, as well as the conditions for breakdown in keeping with the Townsend mechanism. The dc breakdown voltage value of noble gases mixture has been measured in the experimental part of the paper. The hypothesis that the free‐electron gas spectrum is unique in the noble gas mixture and is of Maxwell's type has been verified. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Breakdown magnetic field in an inductively coupled plasma

The Paschen curve shows that the breakdown voltage over a gap is a non-linear function of the product of the gas pressure and the gap distance for plasmas which are generated inside an electric field driven source. The Paschen breakdown relationship does not depend on the applied frequency and covers secondary emission at the electrodes of the discharge. Adapting the Paschen curve, a breakdown curve for a time-dependent magnetic field, typical for inductively coupled plasmas which sources are without electrodes, is examined here. It is shown that in this case the magnetic field breakdown curve does depend on the applied frequency.     

Simulation of secondary processes in breakdown in air

The simulation of the buildup of a breakdown in air is made in a gap with an applied uniform electric field. The computer program is based on the classic determinist model of Townsend with account to secondary effects on the cathode and space charge effects in the gap. Nevertheless, this model takes into account the different ionic and electronic creative processes in the discharge. To the direct ionization must be added attachment, detachment and charge exchange processes. The continuity equation gouverning the densities is written for each charge carriers kind. The resolution of this system represents accurately the spatio-temporel evolution of the discharge. The results are in good agreement with the experimental results found in literature.     

Stoletov constant and the maximum of townsend coefficient as a function of the field strength

The relation between the Stoletov constant defined as a point corresponding to the maximum of the Townsend coefficient in pressure for a given field strength and the recently introduced constant corresponding to the maximum of the Townsend coefficient as a function of the field strength for a given pressure is investigated. We propose the use of a non-self-maintained discharge for an experimental study of the recently introduced runaway curves which, as distinct from the well-known Paschen curves, characterize the electron multiplication in a gas-discharge gap rather than the discharge ignition.     

Breakdown in the transverse magnetic field

The breakdown between coaxial cylindrical electrodes in the homogeneous axial magnetic field in the pressure range around the Paschen minimum is studied. On the right of this minimum the breakdown voltage is not practically influenced by a weak magnetic field. On the left of this minimum the breakdown U-B curves can be divided into two branches: the upper ones can be approximated by the magnetron cut-off parabola, the lower ones correspond qualitatively in some cases to the second solution of the equation for breakdown in the inhomogeneous electric field corrected with respect to the losses of electrons caused by recapturing on the cathode.     

波导型高功率微波输能窗的研究进展

波导型高功率微波输能窗是高功率速调管和高能粒子加速器的关键部件,输出窗高频击穿是引起高功率速调管失效的一个重要因素。综述了国内外电真空领域波导型输能窗的研究进展,介绍了传统盒型窗的研究现状、工艺要求和击穿机理;介绍了锥型窗、行波窗、复合模窗以及过模窗等新型输能窗的设计特点,给出了改变窗片材料属性、改变窗片表面形态、窗片边缘倒角、外置直流电场/直流磁场、改变信号波形等击穿抑制技术的研究进展。     

Influence of layer-to-layer electric and magnetic interactions on a magnetoelectric coefficient at high frequencies

We analyze the influence of electric and magnetic interconnection between the components of a magnetoelectric on its magnetoelectric coefficient at high frequency of the external electric and magnetic field. We interpret the obtained results on the basis of the existence in such structures of probing electromagnetic fields. It is shown that allowing for electric and magnetic field capture through the mechanical subsystem leads to a decrease in the magnetoelectric coefficient.     

非晶态磁性合金的磁阻和磁击穿现象

在室温下磁场在0—15kOe范围内测量了非晶态磁性合金(Fe_1-xCo_x)₈₂Cu_0.4Si_4.4B_13.2的横向磁阻△ρ/ρ。发现在高磁场下,磁阻与磁场强度有三种函数关系:(1)磁阻趋于饱和;(2)磁阻随磁场平方正比地增加;(3)对x=0.15的合金,在特殊的电流、磁场方向和确定的磁场强度下,有磁阻尖峰出现。情况(3)是一种磁击穿现象。磁击穿发生在自旋向上和向下的两片Fer 关键词：     

Electronic structure of paramagnetic In<Subscript>1-x</Subscript>Mn<Subscript>x</Subscript> As nanowires

The electronic structure, spin splitting energies, and g factors of paramagnetic In_1-xMn_xAs nanowires under magnetic and electric fields are investigated theoretically including the sp-d exchange interaction between the carriers and the magnetic ion. We find that the effective g factor changes dramatically with the magnetic field. The spin splitting due to the sp-d exchange interaction counteracts the Zeeman spin splitting. The effective g factor can be tuned to zero by the external magnetic field. There is also spin splitting under an electric field due to the Rashba spin-orbit coupling which is a relativistic effect. The spin-degenerated bands split at nonzero k_z (k_z is the wave vector in the wire direction), and the spin-splitting bands cross at k_z = 0, whose k_z-positive part and negative part are symmetrical. A proper magnetic field makes the k_z-positive part and negative part of the bands asymmetrical, and the bands cross at nonzero k_z. In the absence of magnetic field, the electron Rashba coefficient increases almost linearly with the electric field, while the hole Rashba coefficient increases at first and then decreases as the electric field increases. The hole Rashba coefficient can be tuned to zero by the electric field.     

强直流场介质表面次级电子倍增效应的数值模拟研究

通过粒子模拟方法,实现了强直流场下介质表面击穿过程中次级电子倍增效应的数值模拟.具体研究了强直流场场强、介质表面光滑度和次级电子产生率等对次级电子倍增的影响,以及倾斜直流场和外加磁场对次级电子倍增的抑制.结果表明,选择次级电子产生率较低的介质材料和倾斜强直流场可以有效降低次级电子倍增效应的强度,而外加磁场必须超过一定值时才可以有效降低次级电子倍增强度. 关键词： 次级电子倍增 强直流场 介质表面击穿 数值模拟     

Avalanche breakdown in narrow gap semiconductors in crossed fields

The paper presents the results of experimental and theoretical investigations of interband breakdown in narrow gap Bi_1?xSb_x and Hg_1?xCd_xTe semiconductors in crossed electric and magnetic fields. Both these alloys show an increase of breakdown electric field in sufficiently strong magnetic field. In the case of Hg_1?xCd_xTe the breakdown field changes nonmonotonically with H. This is interpreted as being due to the transverse breakdown.     

横磁模下介质表面二次电子倍增的抑制

在介质加载加速器结构(DLA)内, 提出采用刻槽结构结合外加磁场的方法用于在电磁场横磁(TM)模式下抑制介质表面的电子倍增. 通过理论分析和数值模拟, 比较了刻槽结构和纵向磁场对斜面上电子碰撞能量和渡越时间的影响, 得到了在介质表面同时存在法向RF电场及切向RF电场时, 采用刻槽结构并施加一定的纵向磁场强度, 可有效抑制二次电子倍增的发展, 提高介质面的击穿阈值.     

百kV/cm场强下SF6气体开关纳秒脉冲击穿场强和时延经验公式

百kV/cm高场强纳秒脉冲条件下,采用J. C. Martin经验公式估算SF₆气体击穿场强时,估算值与实验结果差异显著。为了进一步指导高场强脉冲气体开关设计,为开关工作状态调节提供依据,借鉴经典击穿场强经验公式形式建立了百kV/cm场强下SF₆气体开关纳秒脉冲击穿场强和时延与实验参数之间的关系,基于实验数据拟合形成了修正系数的击穿场强和时延经验公式。研究表明,百kV/cm场强和纳秒脉冲条件下脉冲电压斜率对开关击穿特性有重要影响,击穿场强与击穿时延相互关联。百ns至μs脉冲与几十ns脉冲气体放电机理的区别引起放电过程中击穿时延组成发生变化,导致了经典击穿场强经验公式估算值与实验结果的显著差异。修正系数的击穿经验公式可为电磁脉冲模拟器输出开关提供更为精确的工程设计依据。