激光触发伪火花开关的研究

通过等离子体建模仿真及物理实验结合的方式验证了激光触发伪火花开关的可行性。分别使用波长266 nm和532 nm的激光,对激光触发伪火花开关的最低激光触发能量、阳极着火延迟时间和时间跳动三项参数进行测试。在非聚焦模式下,仅调整激光能量,测得开关在波长266 nm激光触发下,最低触发能量为15 mJ,该触发能量下,阳极着火延迟时间约为340 ns,时间跳动约为40 ns;在波长532 nm激光触发下,最低触发能量为83 mJ,该触发能量下,阳极着火延迟时间约为420 ns,时间跳动约为60 ns。在维持实验平台不变的情况下,仅对入射激光进行聚焦,测得波长266 nm激光触发下,最低触发能量为4 mJ,当触发能量8 mJ时,阳极着火延迟时间190 ns,开关时间跳动小于1 ns;波长532 nm激光触发下,最低触发能量为6 mJ,当激光触发能量为8 mJ时,阳极着火延迟时间240 ns,开关时间跳动小于1 ns。     

Silicon carbide as electrode material of a pseudospark switch

Through the last years, the pseudospark switch, a low-pressure gas discharge switch with hollow cathode geometry, became established as a promising element of pulsed power technology and a serious alternative to other high-power switches. The use of a novel electrode material silicon carbide yields performance improvements in two main areas. Quenching phenomena, a long-standing problem for several applications, are suppressed completely and the switch lifetime can be distinctly increased, approaching that of thyratrons for operation with high repetition rate. As a crow-bar switch, the lifetime is nearby unlimited due to cold electrode usage. Spatial and temporal resolved spectroscopy revealed new insight into the extraordinary discharge behavior of silicon carbide electrodes. The radial plasma expansion from the central bore hole to the outer electrode regions, forming vesicular shells of different ionization stages of Si and C, are described in detail. The remaining problem, a significant loss of deuterium gas during discharge, has been long-term tested and is assumed to be the outcome of absorption in the silicon carbide electrodes. An envisaged promising remedy is presented     

辉光放电触发赝火花开关的时延及抖动特性

 设计了一种辉光放电触发赝火花开关,对其时延和抖动特性进行系统研究。研究了开关时延、抖动与辉光放电电流、气压、触发电压及阳极电压的关系。当辉光放电电流小于0.30 mA时,开关无法触发导通;当电流为0.35~0.60 mA时,随辉光放电电流的增大,开关时延、抖动减小;当辉光放电电流为0.60 mA时,开关时延、抖动基本不变,出现饱和。当氦气气压低于6 Pa,开关难以触通,与理论计算值6.95 Pa吻合;当氦气气压为6~12 Pa时,开关的时延、抖动随气压的升高而减小;气压为12~30 Pa时,开关工作在比较稳定的状态。当触发电压小于3 kV,开关难以触通;随着触发电压的增大,开关时延、抖动减小;当触发电压大于5.3 kV,开关时延、抖动基本保持不变。开关在稳定工作条件下,阳极电压在8~25 kV范围内变化时;开关时延基本不变。     

辉光放电触发赝火花开关的时延及抖动特性

设计了一种辉光放电触发赝火花开关,对其时延和抖动特性进行系统研究。研究了开关时延、抖动与辉光放电电流、气压、触发电压及阳极电压的关系。当辉光放电电流小于0.30 mA时,开关无法触发导通;当电流为0.35~0.60 mA时,随辉光放电电流的增大,开关时延、抖动减小;当辉光放电电流为0.60 mA时,开关时延、抖动基本不变,出现饱和。当氦气气压低于6 Pa,开关难以触通,与理论计算值6.95 Pa吻合;当氦气气压为6~12 Pa时,开关的时延、抖动随气压的升高而减小;气压为12~30 Pa时,开关工作在比较稳定的状态。当触发电压小于3 kV,开关难以触通;随着触发电压的增大,开关时延、抖动减小;当触发电压大于5.3 kV,开关时延、抖动基本保持不变。开关在稳定工作条件下,阳极电压在8~25 kV范围内变化时;开关时延基本不变。     

伪火花放电开关电压跌落过程实验研究

 设计了典型参数下的伪火花放电开关，进行了空气介质下的电压特性实验，给出了伪火花开关放电电压与气压变化的关系曲线；测量了产生伪火花放电的气压范围（1~29Pa）和单间隙伪火花放电开关耐受电压的最大值(40kV)，测得了伪火花放电与辉光放电的转折点气压(29Pa)，并对实验结果进行了理论分析。研究了伪火花放电开关电压跌落时间与放电电压的关系，首次将开关电压跌落过程分为暂态阶段和稳态阶段，讨论了放电电路参数，气体压力，开关结构和放电电压对电压跌落时间的影响。实验表明，在气压和开关结构不变的条件下，暂态过程时间由放电电压决定，电压越高，则所需时间就越短；稳态过程时间由放电电路参数决定，不受放电电压影响。     

Development of a high current pseudospark switch and measurement ofelectron density

The pseudospark, a low-pressure gas discharge in a special geometry, is suitable for high-current switching. A single-channel prototype is tested with a 3.3-μF capacitor bank, voltages up to 30 kV, and peak currents up to 120 kA. The electrical circuit, not comprising any load resistor causes weakly damped sinusoidal pulses of 5-μs duration at 90% current reversal. For lifetime tests, a switch with an alumina insulator and copper seals is used. Hydrogen is the working gas. Several electrode materials like molybdenum, tungsten, graphite and chromium-copper are tested. Optical investigations of the discharge and of plasma parameters are done with an O-ring sealed pseudospark switch. The light of the discharge is observed spectrally integrated with a streak camera. Spectral resolution is obtained by using a high-speed shutter in combination with a monochromator. The radial electron density is determined by measuring the Stark broadening of the Balmer H_β-line. At 60 kA a maximum electron density of about 2×10¹⁷cm^-3 is calculated     

辉光放电触发赝火花开关实验研究

设计了一种辉光放电触发赝火花开关,进行了He气介质下的放电实验研究。测得了耐受电压和气压关系,结果表明：随着气压的升高,开关耐受电压减小;开关电极孔径为3 mm、电极间距为4 mm时的耐受电压约是电极孔径和电极间距均为3 mm时的85%。在电极孔径和电极间距均为3 mm时,研究了辉光放电电流、气压、触发电压等参数对开关时延、抖动的影响。结果显示：当辉光放电电流大于0.45 mA、气压为7～30 Pa、触发电压达到一定值,开关就能比较稳定地触发,时延短、抖动小。在辉光放电触发下,实现了开关耐受30.5 kV、时延223.2 ns的输出,并实现了开关抖动小于1 ns的稳定输出。     

辉光放电触发赝火花开关实验研究

设计了一种辉光放电触发赝火花开关,进行了He气介质下的放电实验研究。测得了耐受电压和气压关系,结果表明:随着气压的升高,开关耐受电压减小;开关电极孔径为3mm、电极间距为4mm时的耐受电压约是电极孔径和电极间距均为3mm时的85%。在电极孔径和电极间距均为3mm时,研究了辉光放电电流、气压、触发电压等参数对开关时延、抖动的影响。结果显示:当辉光放电电流大于0.45mA、气压为7～30Pa、触发电压达到一定值,开关就能比较稳定地触发,时延短、抖动小。在辉光放电触发下,实现了开关耐受30.5kV、时延223.2ns的输出,并实现了开关抖动小于1ns的稳定输出。     

赝火花开关放电的蒙特卡罗粒子模拟

采用粒子模拟和蒙特卡罗相结合的方法,应用静电求解模型,对赝火花开关初始放电过程进行了模拟。赝火花开关初始放电过程主要由汤森放电过程、等离子体形成、空心阴极效应和场致发射引发主放电组成;等离子体形成和空心阴极效应对赝火花开关的发展导通具有至关重要的作用。改变赝火花开关工作参数,如气压、电极孔径、阳极电压和阴极腔中初始粒子密度,研究其对赝火花开关电子峰值电流形成时间的影响。结果表明：随着气压、电极孔径、阳极电压和初始粒子密度的增大,赝火花开关电子峰值电流形成时间减小。     

赝火花开关放电的蒙特卡罗粒子模拟

采用粒子模拟和蒙特卡罗相结合的方法,应用静电求解模型,对赝火花开关初始放电过程进行了模拟。赝火花开关初始放电过程主要由汤森放电过程、等离子体形成、空心阴极效应和场致发射引发主放电组成;等离子体形成和空心阴极效应对赝火花开关的发展导通具有至关重要的作用。改变赝火花开关工作参数,如气压、电极孔径、阳极电压和阴极腔中初始粒子密度,研究其对赝火花开关电子峰值电流形成时间的影响。结果表明:随着气压、电极孔径、阳极电压和初始粒子密度的增大,赝火花开关电子峰值电流形成时间减小。     

Requirements for simultaneous ignition of all channels in ahigh-current radial multichannel pseudospark switch

In order to reduce erosion of electrodes and consequently achieve a long lifetime for high-power switches, a low-pressure switch, namely the pseudospark switch (PSS), is investigated as an alternative to the conventional high-power switches. The erosion can be reduced further along with an enhancement of the current and the rate of current rise, if more channels are introduced for the passage of current. An intense electron beam is known to be emitted by the hollow cathode during the starting phase in a pseudospark discharge. It has been reported that in a multichannel setup each installed channel can ignite only if it gets ionized by its respective beam. The results presented in this paper show how this multichannel operation can be accomplished. These results are based on a statistical study of a radial multichannel pseudospark switch and an observation of the discharge course by means of high-speed photography and show that a glow discharge trigger, with a high glow current (⩾1.2 mA) and slowly rising trigger pulses (⩾150 ns), allows a simultaneous ignition of up to 12 channels     

Study of the breakdown phase in a pseudospark switch. I. Basisexperiments and crude model

A transparent and compact pseudospark prototype was built to analyze the physical processes of pseudospark breakdown. It allows accurate measurements of the current and gap voltage during the collapse of the switch impedance. This led to a surprising result-the pseudospark impedance follows the same time-evolution law as the high pressure spark-gaps. However, electronic collision processes are of a different nature. A crude theoretical model based on plasma relations is proposed to solve this contradiction. This model shows how the current is controlled by the azimuthal magnetic field it induces. However, discrepancies still remain. A more sophisticated distribution of the field and current lines is assumed and investigated in a companion paper     

The plasma in high-current pseudospark switches

The discharge behavior and the erosion rate of pseudospark switches for high currents (50-150 kA) and pulse lengths of several microseconds were investigated for different electrode materials. A capacitor discharge (3.3 μF) without any load was used at a maximum voltage of 30 kV. Side-on optical investigations were performed either with a streak camera or a fast shutter camera. Using metal electrodes, the discharge ignites on axis, then widens up radially and burns homogeneously at the edge of the central apertures. After about 500 ns, a stable anode spot is observed on the plane electrode surface (at currents exceeding 45 kA), the location of which is statistical. The discharge is transformed to a metal vapor are discharge and the erosion rate increases by more than one order of magnitude. With semiconductor electrodes (i.e., silicon carbide), a different discharge behavior is observed, After ignition on axis, the discharge burns homogeneously on the whole carbide surface. No contraction to a small area occurs in comparison to metal electrodes. The reignition of later current half cycles starts at the triple point metal-carbide-gas. Then the discharge again spreads homogeneously over the total carbide surface. The erosion rate is about two magnitudes lower in comparison to metals. We assume that the current is conducted in a thin surface sheath which is heated to more than 2000 K     

初始空间有序分布下超冷等离子体的演化模拟

超冷等离子体是一种极低温的强耦合等离子体.无序诱导加热过程是制约其达到高耦合强度的主要因素.我们使用德拜势场单体系等离子体模型的分子动力学方法模拟超冷等离子体的演化过程,研究初始空间分布对无序诱导加热过程的影响.在周期性边界条件下,我们研究了不同初始空间下超冷等离子体的演化过程,证明了有序初始空间分布能够有效提高等离子体的最终耦合强度,其结果与近期的理论计算相符合.进一步我们在演化模拟中考虑了有限体积下超冷等离子的膨胀过程,发现其在有序初始分布下会引发无序过程显著加热超冷等离子体,导致了耦合强度的逐渐降低.     

Tomographic reconstruction of high-energy-density plasmas with picosecond temporal resolution

Three-dimensional reconstruction of the electron density in a plasma can be obtained by passing multiple beams at different field angles simultaneously through a plasma and performing a tomographic reconstruction of the measured field-dependent phase profiles. A relatively simple experimental setup is proposed and simulations are carried out to verify the technique. The plasma distribution is modeled as a discrete number of phase screens, and a Zernike polynomial representation of the phase screens is used to reconstruct the plasma profile.     

The temporal evolution of population densities of excited states in atomic oxygen thin plasmas

Population densities of transient oxygen plasmas have been calculated solving a system of differential equations, which describes the temporal evolution of the considered quantum levels. The results, which refer to a temperature of 1 eV and to electron number densities ranging from 10⁸ to 10¹⁴ cm^-3, show the strong importance of the metastable 3s⁵S state in determining the evolution of these plasmas. The present results are then applied to the calculation of relaxation times of selected quantum levels and to the definition of quasistationary conditions of plasmas having low lying excited states (i.e. states belonging to the same principal quantum number as the ground state).     

Nonmonotonic spatial decay and shield height effects in inductivelycoupled plasmas

Nonmonotonic spatial decay in electric field and space current distributions was recently observed in weakly collisional plasmas. The anomalous skin effect is found to be responsible for this phenomenon. Based on our proposed self-consistent analytic model, we successfully modeled the nonmonotonic spatial decay effect in inductively coupled plasma sources. The simulated spatial distribution of the induced E-field is compared to the measurements for different applied RF powers. Quantitative agreements for the electric field and qualitative agreement for the induced space current are achieved between the simulated and measured data. Also demonstrated is that the RF power and the reactor geometry such as the shield height has a direct impact upon the anomalous skin effect and its skin depth     

无碰撞等离子体中电子束流不稳定性的时空演化研究

应用二、三维相对论电磁粒子模拟程序研究双电子束流在无碰撞等离子体中传播引起的横向 电磁(Weibel类型)不稳定性和纵向静电不稳定性的发展演化过程.讨论了纯粹Weibel不稳定 性的发生和非线性饱和过程，观察到电流束合并、磁场重联等引起的电子横向加热现象.研 究了电流束传播方向激发的静电场对快电子束传播的影响，观察到其导致的束的横向调制、 磁场通道破坏现象.对这些过程的细致研究对更好的理解快点火物理中自生磁场的产生、快 电子输运等过程有重要意义.     

Klein paradox in spatial and temporal resolution

Based on spatially and temporally resolved numerical solutions to the relativistic quantum field equations, we provide a resolution to the controversial issue of how an incoming electron scatters off a supercritical potential step and how the electron-positron pair production is affected by this collision. The treatment of the problem as a correlated three-particle problem suggests revealing insight into the process.