High Current Operation of a Semi-insulating Gallium Arsenide Photoconductive Semiconductor Switch Triggering a Spark Gap

A transient peak current as high as 5.6 kA is obtained by a GaAs photoconductive semiconductor switch （PCSS） in series with a spark gap. Based on the characteristics of the GaAs PCSS, mechanisms of discharge between the PCSS and the spark gap are discussed. It is implied that a hybrid operation mode of photo-activated charge domain occurs due to the superposition of the bias voltage and the instantaneous radio frequency voltage.     

Erosion of Spark Gap Electrodes

The erosion characteristics of spark gap electrodes operating with 10- and 20-?s square current pulses for various materials is presented. Cathode spot size and criteria for anode spot formation are estimated. Also, the effect of the acoustic properties on electrode erosion is described.     

An Electron-Beam Triggered Spark Gap

The triggering of a high-voltage gas-insulated spark gap by an electron (e) beam has been investigated. Rise times of approximately 2.5 ns with subnanosecond jitter (~0.2 ns) have been obtained for 3-cm gaps charged at voltages as low as 50 percent of the self-breakdown voltage (varied up to 0.5 MV). The switch delay (including the e-beam diode) was 52 ns. The triggering e-beam pulse has a duration of 15 ns and a 0-50 percent rise time of 1.5 ns. The e-beam current is 0.5 kA, and the electron energy can be varied in the range from 80 to 145 keV. The working media were N2, mixtures of N2 and A, and N2 and SF6 at pressures of 1-3 atm. Voltage, current, and jitter measurements have been made for a wide range of gap conditions and e-beam parameters. Variations in the character of the discharge have been inferred using streak and open shutter photography. The photographs show that the discharge has a broad cross section and that its character varies for differing polarites and voltages. The effects of varying the e-beam width and the beam energy are discussed.     

Long-Life High-Repetition-Rate Triggered Spark Gap

A forced-air-blown triggered spark gap (TSG) switch system capable of high-repetition rates on a continuous basis as well as a TSG comparative study is described. The system consists of two TSG's, each discharging its own 30-? pulse cable into a common load. The system was operated at 30 kV, 1 kHz, for 39 × 106 shots with erosion rates of approximately 60 mg/Ah. Each TSG discharged 0.423 J in 60 ns (full width at half maximum) (FWHM) per pulse. The switching losses were about 28 percent of the stored cable energy. Calculations indicate this can reduce to 14 percent by optimizing the TSG design and surrounding air channel insulation for a more uniform E-field. Test results indicate a multielement assembly capable of switching 50 kA or more, 40- to 100-ns pulses at 1 kHz from 50 kV for 500 × 106 shots without gap adjustnent is feasible with this concept.     

Space-Charge Effects in a Laser Fiber-Optics Triggered Multichannel Spark Gap

The dual channel triggering of a spark gap switch by fiberoptic transported ruby laser radiation is discussed. The spark gap is the output switch of a 20-ns water dielectric Blumlein generator. The Blumlein generator is pulse charged in approximately 250 ns by a three-stage Marx bank to 150 kV. The spark gap is operated at a pressure of 2540 torr with a mixture of Ar and N2 gas and an electrode separation of 2 cm. Two 1-mm diameter quartz optical fibers are used to transport 2 2-MW laser beams into the spark gap onto points 6 cm apart on the target electrode. The two beams are obtained by optical splitting of the output of a single laser. Under appropriate conditions, two arc channels are initiated by the laser beams along their paths. A small improvement in current rise time for dual channel events over single channel events is observed. Moreover, the number of successful dual channel events is observed to depend on the time of laser entry with reference to the beginning of the charging pulse, and not the gap polarity. The correlation of this behavior with the space charge build up in the slightly over-volted gap is discussed.     

EHF–Resonance Studies of Energy Gap in Reentrant Magnets

An EHF-resonance technique of millimeter wavelength band was used for the study of reentrant magnetic systems (Fe _p Ni _1–p ) ₇₇ B ₁₃ Si ₁₀ (p=0.09; 0.10) at low temperatures (down to 0.3K) and high applied magnetic fields. The linear dependence of magnetization on the temperature that characterizes the spin-glass state in such reentrant systems in strong magnetic field was discovered. The energy of localized excitations characterizing spin-glass state was estimated.     

Breakdown and Recovery of a 250-kV Low-Pressure Spark Gap

Tests of an experimental low-pressure spark gap Blumlein switch are presented. Gas flows from a pulsed valve into the gap at a steady rate through holes in the cathode and results in a steady pressure of about 0.1 torr. The pressure outside the gap over the Blumlein insulator is much lower. Trigger electrodes are mounted in the grounded cathode. Initially the current rises exponentially with time with rate constant proportional to gas density. Measurements of rise time, jitter, and voltage holding recovery time are presented for charge voltages up to 250 kV for variations of charge time, gas density, gas type, and triggering method.     

Laser Triggering through Fiber Optics of a Low Jitter Spark Gap

An optical filter is employed to transport a 15-ns light pulse from a high power ruby laser for precise triggering of a gas filed high voltage spark gap. The maximum power density that can be transmitted by the fiber is limited to 6 × 1012 W/m2 above which laser induced damage occurs on the fiber entrance face. The overall throughput efficiency of the optical system was measured as 62 percent. Results are presented for the switching delay time and associated jitter for various mixtures of A and N2 gas, and as a function of the voltage across a pulse-charged Blumlein generator gap. Pulse charging of the Blumlein generator was accomplished by a three-stage Marx generator, resulting in output voltages up to 250 kV. It was conclusively demonstrated that an optical fiber will transport a sufficiently intense laser pulse to evince subnanosecond jitter in the triggering of a pressurized gas switch under the conditions studied.     

高能量高峰值功率激光系统的稳定性问题研究

针对高能量高峰值功率激光系统建立了相应的理论分析模型和计算程序,并针对放大系统的稳定性进行了分析,同时还对放大链路中的B积分、频谱漂移、泵浦光和信号光之间的时间同步抖动进行了模拟分析.分析结果表明：采用两级放大结构,有利于提高系统的稳定性;同时需要严格控制全系统B积分累积,建议全系统B积分的累积值小于2,超过2的B积分累积意味着更多的注入能量,如果泵浦光和信号光之间的同步时间抖动控制在±0.2 ns之内,输出稳定性可控制在rms2％之内.     

Energy Balance of Low-Voltage Spark Discharges

In this work we are presenting an experimental and theoretical analysis of the energy balance of low-voltage spark discharges. It is pointed out that the greatest part of the energy from the central hot plasma region is lost in the form of radiation, but the radiation from electrode particles (here aluminium) can be important, too.     

Energy Gap and Electron Effective Mass in Chlorine Halide Superconductor at High Pressure

Dependences of the order parameter （ A ） and the electron effective mass （me^＊） on the temperature for the chlorine halide superconductor are determined in the present work. The high values of the pressure （p1 = 320 GPa andp2 = 360 GPa）, for which the critical temperature is equal to [Tc]m = 30.6 K and [Tc]p2 = 41.5 K, are taken into consideration. It is found that the dependence of the order parameter on the temperature deviates from the predictions of the classical Bardeen-Cooper-Schrieffer theory, due to the existence of the significant strong- coupling and retardation effects. The values of the order parameter, for the temperature close to zero Kelvin, are equal to [A（0）]p1 = 4.89 meV and [A（0）]p2 = 6.82 meV. The obtained results allowed next to calculate the dimensionless ratio R△ = 2A（O）/kBTc, which is equal to 3.71 and 3.81 in respect to pl and p2. In the last step, it is proven that the electron effective mass is weakly dependent on the temperature in the area of the existence of the superconducting state and reaches its maximum at the critical temperature. For the considered values of the max ＊ max pressure, we obtain [me^＊]pl^max = 1.69me and [me^＊]p2^max =1.78me, where the symbol me denotes the electron band mass.     

KrF Laser-Triggered SF6 Spark Gap for Low Jitter Timing

KrF laser-triggered spark gaps exploit the high dc-dielectric strength and low ultraviolet (UV) breakdown threshold of SF6 gas. Detailed measurements using a dc-charged pulser demonstrate subnanosecond jitter for switching a 0.5-cm gap operated at 80 kV with 7 mJ in 20 ns of 248-nm KrF radiation. A 200-kV pulse-charged 0.7-cm gap gives similar performance.     

激光制冷中能级间距的选择

激光制冷问题的核心是材料的选择。荧光中心能级的间距是其中的一个关键指标。确定合理的能级间距有助于选择合适的激光制冷材料。能级间距决定了对激光制冷至关重要的两个因素:量子效率和无辐射跃迁速率。如果单纯地从制冷功率的角度来看,能级间距越大量子效率越高,也越有利于荧光制冷。但当能级间距宽到某一值后,制冷功率基本上保持不变。如果从热一光转换效率的观点来考察激光制冷的效率问题,能级间距宽度的合理取值就应该小得多。如果在选择激光制冷材料时,确定制冷功率具有第一位的重要性,那么,能级间距选择在5000cm^-1左右的宽度是比较合适的、这不仅可以确定较大的热－光转换效率,同时也基本上保证了很高的制冷功率。     

Study on a New Ignition Method of the Spark Gap Based on Plasma Ejection in Air

A new ignition method of the spark gap based on plasma ejection is proposed in this paper, as the conventional trigatron spark gap performs poorly under the low working coefficient (the ratio of the charging voltage to the self‐breakdown voltage) in air. The plasma is generated by the capillary discharge, which has high pressure, high temperature and high velocity. The capillary discharge device is placed inside the low voltage electrode. As long as the triggering signal is sent to the device, a column of the plasma flow is ejected in axial direction and develops rapidly towards the high voltage electrode. Subsequently, the gap is broken down and a high resistive channel is formed, where the thermal ionization takes place and the arc across the whole gap is generated and develops into a well conductive channel. The process of the thermal ionization of the high resistive channel varies with the change of the spark gap distance. The breakdown delay and the delay jitter of the spark gap increase with the spark gap distance, as both parameters are mainly determined by the developing process of the plasma ejection. The characteristics of the plasma flow determine the possibility of the breakdown of the spark gap under the low working coefficient. The ignition method based on capillary plasma ejection has been proved by the preliminary experiments, which indicate that under the gap length of 8 cm and the working coefficient of less than 3%, the effective ignition is still achievable.     

Spark Temperature Enhancement by Adding a Parallel Capacitor in High Voltage Circuit

Temperature of sparks produced by automotive ignition systems have been measured spectro-scopically. It is shown that by adding a capacitor of the order of 10 to 100 pF, temperature of the arc phase of a spark can be considerably increased.     

一维自旋轨道模型中自旋-轨道能隙产生机理分析

讨论考虑洪特耦合的两带赫伯德模型得到的一维自旋轨道模型中自旋-轨道能隙的产生.运用SU(4)赝费米子表象下的平均场理论,计算求得价键序参数、准粒子激发谱能隙和自旋、轨道密度-密度关联函数随系统耦合参数变化的结果.随洪特耦合相互作用由零开始增强,系统激发谱能隙逐渐打开,并且系统在参数取值为J₁/J₂=1/3处由具有阻错的无序状态相变到自旋铁磁有序和轨道反铁磁有序的状态.     

核物质对称能的高密行为研究

同位旋物理的主要任务之一是通过放射性核束引起的核反应来探索介质中有效核子-核子相互作用的同位旋依赖性,尤其是同位旋相关的核物质状态方程, 即密度依赖的核物质对称能。由于对称能,尤其是其高密行为,对核物理学和天体物理学具有重要意义,密度依赖的对称能在过去10年一直是中能重离子物理研究领域的主要焦点之一。近年来,低密对称能的研究已经取得了重要进展, 而对称能的高密行为仍然很不确定。在理论方面,人们提出了许多对高密对称能敏感的观测量。 实验方面, 关于对称能高密行为研究的实验计划已经展开,世界各地正在建造的放射性核束装置为对称能的高密行为研究提供了新的机遇。基于IBUU输运模型综述了研究对称能高密行为的一些敏感观测量及其最新进展, 以及所面临的挑战与机遇。One of the major tasks of studying isospin physics via heavy ion collisions with neutron rich nuclei, is to explore the isospin dependence of in medium nuclear effective interactions and the equation of state of neutron rich nuclear matter, i.e., the density dependence of nuclear symmetry energy. Because of its great importance for understanding many phenomena in both nuclear physics and astrophysics, the study of the density dependence of nuclear symmetry energy has been the main focus of the intermediate energy heavy ion physics community during the last decade. Nowadays significant progress has been achieved in studying the low density behavior of nuclear symmetry energy, but the high density behavior of nuclear symmetry energy is still very uncertain. Theoretically, a number of observables have been proposed as sensitive probes to the high density behavior of nuclear symmetry energy. With new opportunities provided by the various radioactive beam facilities being constructed around the world, studies of the high density behavior of nuclear symmetry energy is expected to be one of the main forefront research areas in nuclear physics in the near future. In this report, based on the transport model IBUU we have reviewed the major progress achieved in studying the high density behavior of nuclear symmetry energy and discussed future challenges in this field.     

High Repetition Rate Miniature Triggered Spark Switch

A miniature triggered spark switch designed to operate at high repetition rates has been constructed. The device, along with associated triggered circuitry, has been incorporated into a simple LC generator which produces an oscillatory discharge at a frequency of 150 MHz. The switch is operated in the pressure range 760 torr-2.6 × 103 torr using commercial dry nitrogen as the working gas. Both brass (70/30) and aluminum (99.95 percent) electrodes were investigated for repetition frequencies as high as 20 kHz and for gas flow rates as high as 8 cm3/s. The effect of repetition rate on switch jitter and switch breakdown voltage is presented and discussed in terms of gas pressure and flow rate.     

An Energy Gap for Yang-Mills Connections

Consider a Yang-Mills connection over a Riemann manifold M = M ⁿ , n ≥ 3, where M may be compact or complete. Then its energy must be bounded from below by some positive constant, if M satisfies certain conditions, unless the connection is flat.