Biofouling prevention with pulsed electric fields

Temporary immobilization of aquatic nuisance species through application of short electric pulses has been explored as a method to prevent biofouling in cooling water systems where untreated lake, river, or sea water is used. In laboratory experiments, electrical pulses with amplitudes on the order of kilovolts/centimeter and submicrosecond duration were found to be most effective in stunning hydrazoans, a common aquatic nuisance species. Varying pulse amplitude and repetition rate allows us to control the stunning time in a temporal range from minutes to hours. The temporary immobilization is assumed to be caused by reversible membrane breakdown. This assumption is supported by results of measurements of the energy required for stunning. Based on the data obtained in laboratory experiments, field experiments in a tidal mater environment have been performed. The flow velocity was such that the residence time of the aquatic nuisance species in the system was approximately half a minute. The results showed that the pulsed electric field method provides full protection against biofouling when pulses of 0.77 μs width and 6 kV/cm amplitude are applied to the water at the inlet of such a cooling water system. Even at amplitudes of 1 kV/cm, the protection is still in the 90% range, at an energy expenditure of 1 kWh for the treatment of 60 000 gallons of water     

脉冲电场防治水生生物附着

为探究脉冲电场对防治水生生物附着效果的影响因素,确定有效防治附着生物所需的最低电场条件,搭建了脉冲电场试验平台,通过人工脉冲形成线产生近似方波的脉冲,统计不同条件下大型溞死亡率和形态结构发生的变化,通过函数拟合得到了脉冲电场诱导死亡率与电场强度、总等效处理时间、脉冲注入能量密度之间的函数关系,并以某干渠工程为例介绍了脉冲电场防治大型溞的参数选取原则和平台搭建方法。结果表明,脉冲电场对大型溞的处理效果与电场强度、总等效处理时间和脉冲注入能量密度都呈正相关关系。电场强度介于0.5～1.5 kV/cm之间时,电场强度每增加0.5 kV/cm,诱导死亡率增加35%左右。电场强度高于2.0 kV/cm、总等效处理时间大于900μs或脉冲注入能量密度高于80 J/L时,脉冲电场都可以产生80%以上的诱导死亡率。     

Evolution of pulse shortening research in narrow band, high powermicrowave sources

The achievements resulting from the application of advanced pulsed power to the generation of high power microwaves (HPM) have included the generation of multi-gigawatt pulses of RF energy. The power achievable is orders of magnitude greater than conventional microwave sources can generate. However, the introduction of the HPM technology into logical applications has been limited to date due to the phenomenon of pulse shortening in which the RF pulse terminates before the pulse power source used to produce it. Conventional microwave tubes can generate a few to 10 MW of power with pulsewidths of many microseconds when required. High power microwave sources can produce gigawatts of power, but only for relatively short pulsewidths, typically tens to hundreds of nanoseconds. An international effort during the past few years has generated important new discoveries toward the elimination of pulse shortening. Some of the new techniques have the potential for helping the conventional tube industry as well as being practical for high power microwave sources. This paper reviews the pulse shortening problem, its causes, and the worldwide scope and direction of research conducted to date to resolve it. The paper also discusses the potential remedies for the problem and recommends a course of research to further progress on the issue     

PZT 95/5陶瓷电致失效机理研究

对PZT 95/5陶瓷在直流电场、脉冲方波电场以及半正弦波电场作用下的失效机理进行了理论和实验分析.结果表明:在直流作用下,其失效机理以热-电耦合失效为主;而在脉冲电场作用下,考虑振动冲击效应以及相关的力谱分布,脉宽越短,能量向高频偏移,越可能发生力-电耦合失效;当脉宽增加,PZT 95/5陶瓷失效机理将从力-电耦合失效逐步转变成直流失效模式. 关键词： PZT 95/5 失效机理 直流电场 脉冲电场     

高压径向均压绝缘堆设计

以形成线储能结合脉冲压缩方式产生数MV高压输出,是脉冲功率系统中常见的技术途径,其中绝缘堆是该类装置工程成败的关键。分析了几种径向均压绝缘堆的均压机制,基于静电场分析程序对径向均压绝缘堆结构进行了优化设计,给出了径向电阻的设计方法。研究表明:采用均压环且均压环与径向电阻电气接触的绝缘堆结构可以获得较均匀的径向电场分布,而径向电阻是绝缘堆设计的关键。在有效作用时间100ns的4.5MV加载电压下,优化设计的绝缘堆阴极三相点电场控制在25kV/cm,Martin电场约120kV/cm,低于理论击穿值。     

天线阻抗特性对开关振荡器输出脉冲的影响

以单锥天线和螺旋天线作为开关振荡器辐射天线为例,采用等效电路模型和商业电磁仿真软件,分别对天线末端电压振荡信号和辐射电场脉冲进行了研究。研究结果表明:采用行波天线或者电长度与振荡器一致的振子天线作为辐射天线,都能够产生中心频率与振荡器本征频率一致的电磁脉冲信号;但采用振子天线时,振荡信号持续时间较短(Q值较低),频谱上能量较分散,带宽较宽,而采用行波天线则脉冲持续时间较长(Q值较高),频谱上能量较集中,带宽较窄。     

A fast pulsed power source applied to treatment of conductingliquids and air

Two pilot pulsed power sources were developed for fundamental investigations and industrial demonstrations of treatment of conducting liquids. The developed heavy-duty power sources have an output voltage of 100 kV (rise time 10 ns, pulse duration 150 ns, pulse repetition rate maximum 1000 pps). A pulse energy of 0.5-3 J/pulse and an average pulse power of 1.5 kW have been achieved with an efficiency of about 80%. In addition, adequate electromagnetic compatibility is achieved between the high-voltage pulse sources and the surrounding equipment. Various applications, such as the use of pulsed electric fields (PEFs) or pulsed corona discharges for inactivation of microorganisms in liquids or air, have been tested in the laboratory. For PEF treatment, homogeneous electric fields in the liquid of up to 70 kV/cm at a pulse repetition rate of 10-400 pps could be achieved. The inactivation is found to be 85 kJ/L per log reduction for Pseudomonas fluorescens and 500 kJ/L per log reduction for spores of Bacillus cereus. Corona directly applied to the liquid is found to be more efficient than PEF. With direct corona we achieve 25 kJ/L per log reduction for both Gram positive and Gram negative bacteria. For air disinfection using our corona pulse source, the measured efficiencies are excellent: 2 J/L per log reduction     

脉冲激光控制高超声速进气道来流捕获

针对高超声速进气道在非设计工况下来流捕获量减少的问题,进行了激光能量沉积控制来流捕获的物理建模和数值模拟,在连续激光能量沉积和脉冲激光能量沉积两种方式下获得了进气道的性能参数。激光功率为15kW时,脉冲重复频率越高,与连续能量注入情况下的进气道性能越接近。脉冲重复频率为100kHz时,计算了脉冲方波占空比为0.1,0.2,0.3和0.4时的进气道流场,结果表明:占空比对进气道性能的影响不大;激光脉宽为500ns时,保持激光平均功率不变,当频率为200kHz和100kHz时,流场结构与连续能量注入时类似,而当频率为500kHz和25kHz时的进气捕获量都有所降低,因此,提高激光脉冲重复频率的同时,降低平均功率,不仅可以有效增大来流捕获,还可降低能耗。     

短脉冲激光刻蚀加工铜材料的机制

 利用数值模拟方法,研究波长1 064 nm、脉冲宽度介于1~20 ps的激光在刻蚀铜靶时,单次脉冲作用下非平衡场刻蚀和热平衡刻蚀两种机制的竞争过程。结果表明：随着脉冲宽度的增加,刻蚀过程由非平衡电荷分离场刻蚀占主导地位转变为热平衡刻蚀起主要作用,且脉冲宽度和激光峰值功率密度增大到一定程度后,各种电子加速机制在不同时刻开始突显,电子能量分布出现多峰结构。在能量密度为15 J/cm2的激光作用下,1和5 ps脉宽对应的非平衡场刻蚀深度分别为110和101 nm,10和20 ps脉宽分别为25和18 nm。     

A compact high-voltage pulse generator using a rotary airhole sparkgap

A pulsed-corona-discharge nonthermal plasma technique offers the advantages of energy efficiency and capability for the simultaneous removal of coexisting pollutants. The key to success in a nonthermal plasma approach is to produce a corona discharge in which the bulk of the electrical energy goes into the production of energetic electrons, rather than into gas molecules heating. By driving the nonthermal plasma reactor with very short pulses of high-voltage, short-lived corona discharge plasmas are created that consist of energetic electrons, which in turn produce the radicals and ozone responsible for the decomposition of the toxic molecules. Because of the short lifetime of the pulsed corona discharge, little electrical power is dissipated in movement of heavy molecule ions in the processing region, thus avoiding heating the gas and providing good electrical energy efficiency.A high-voltage pulse generator with a rotary airhole sparkgap, instead of a conventional rotary ball sparkgap, has been proposed. Its rise and fall time characteristics to be used as a smart pulse generator for pulsed corona discharge-type nonthermal plasma reactor were investigated. Parametric studies showed that the proposed airhole sparkgap had a very fast rise time, very short fall time, very low-and-stable breakdown voltage, and reliable pulse repetition characteristics, compared with the conventional rotary ball sparkgap.     

Influence of spatiotemporal coupling on the capture-and-acceleration-scenario vacuum electron acceleration by ultrashort pulsed laser beam

This paper investigates the properties of the ultrashort pulsed beam aimed to the capture-and-acceleration-scenario (CAS) vacuum electron acceleration. The result shows that the spatiotemporal distribution of the phase velocity, the longitudinal component of the electric field and the acceleration quality factor are qualitatively similar to that of the continuous-wave Gaussian beam, and are slightly influenced by the spatiotemporal coupling of the ultrashort pulsed beam. When the pulse is compressed to an ultrashort one in which the pulse duration T_FWHM <5T₀, the variation of the maximum net energy gain due to the carrier-envelope phase is a crucial disadvantage in the CAS acceleration process.     

1kHz窄脉宽高峰值功率MgO∶LN电光腔倒空Nd∶YAG激光器

报道了一种1kHz窄脉冲宽度、高峰值功率的电光腔倒空1 064nm全固态激光器.该激光器采用808nm脉冲LD侧面泵浦Nd:YAG晶体棒的双凹型折叠谐振腔结构和同步延迟MgO∶LN晶体横向加压式电光腔倒空技术,通过优化设计谐振腔结构,在脉冲重复频率200Hz时,获得了最大单脉冲能量46.7mJ、脉冲宽度4.06ns、峰值功率11.50MW的1 064nm脉冲激光稳定输出,脉冲宽度和能量的峰峰值不稳定度分别为±1.52%和±2.02%;在1kHz时,最大单脉冲能量达到18.3mJ,脉冲宽度5.02ns,峰值功率3.69MW,脉冲宽度和能量的峰峰值不稳定度分别为±2.75%和±3.52%,激光束因子为3.849和3.868,远场发散角为3.46mrad和3.55mrad,束腰直径为1 508.84μm和1 477.30μm.     

On the feasibility of the coulomb explosion of a metal

The mechanism of the Coulomb explosion of a metal in an external pulsed electric field is discussed. In the case of a low-frequency field, when its frequency is lower than the frequency of electron collisions, it is impossible to reach the conditions of the Coulomb explosion of a metal if the field pulse duration is shorter than the time of electron energy relaxation upon elastic collisions, and the electron temperature is well above the Fermi energy and the work function. In the case of a high-frequency field, e.g., in a powerful pulse of ultraviolet laser radiation, the Coulomb explosion can occur if the field strength is well above the intraatomic field strength (i.e., when the laser power density is ≥10¹⁹ W/cm²).     

基于光导半导体的MHz高重频可调谐脉冲产生技术研究

随着微波光子学的发展,新型光导微波技术利用高重频脉冲簇激光,入射到线性光导半导体器件中产生可调谐高功率电磁脉冲的方式受到广泛关注。SiC光导半导体开关（PCSS）具有高击穿场强,高饱和载流子速率,高抗辐射能力,高热传导率和高温工作稳定性等优点,是产生高重频、高功率、超短脉冲的重要固态电子器件。介绍了一种基于钒补偿半绝缘4H-SiC PCSS的MHz重复频率亚纳秒脉冲发生器。该发生器采用1 MHz,1030 nm可调谐光脉冲宽度的激光簇驱动源,4H-SiC PCSS的厚度为0.8 mm。整系统可得到最大输出电功率176 kW、最小半高宽约为365 ps的MHz重频短脉冲。     

Application of femtosecond‐pulsed lasers for direct optical manipulation of biological functions

Absorption of photon energy by cells or tissue can evoke photothermal, photomechanical, and photochemical effects, depending on the density of the deposited energy. Photochemical effects require a low energy density and can be used for reversible modulation of biological functions. Ultrashort‐pulsed lasers have a high intensity due to the short pulse duration, despite its low average energy. Through nonlinear absorption, these lasers can deliver very high peak energy into the submicrometer focus area without causing collateral damage. Absorbed energy delivered by ultrashort‐pulsed laser irradiation induces free electrons, which can be readily converted to reactive oxygen species (ROS) and related free radicals in the localized region. Free radicals are best known to induce irreversible biological effects via oxidative modification; however, they have also been proposed to modulate biological functions by releasing calcium ions from intracellular organelles. Calcium can evoke variable biological effects in both excitable and nonexcitable cell types. Controlled stimulation by ultrashort laser pulses generate intracellular calcium waves that can modulate many biological functions, such as cardiomyocyte beat rate, muscle contractility, and blood–brain barrier (BBB) permeability. This article presents optical methods that are useful therapeutic and research tools in the biomedical field and discuss the possible mechanisms responsible for biological modulation by ultrashort‐pulsed lasers, especially femtosecond‐pulsed lasers.     

Design of correction electrodes for high-voltage vacuum-dielectricinterfaces

High-voltage vacuum insulators often set the limits on energy transfer in pulsed power systems. The ideal vacuum interface has a uniform electric field distribution on the insulator well below breakdown levels and an impedance matched to the pulse generator. This paper describes a procedure to design correction electrodes for the dielectric region of a cylindrical interface using a numerical field solution code. The approach has application to both pulsed and steady-state systems. The method is illustrated with a design for a 10 TW, 6.5 MV pulsed power generator using six correction electrodes. The design minimizes the interface impedance and gives less than 10% field variation along the insulator surface     

60 fs长脉宽双色场作用下孤立阿秒脉冲的产生

通过数值求解一维含时Schrödinger方程,研究了具有较长脉宽双色激光脉冲与氢原子相互作用产生的高次谐波和阿秒(as)脉冲.这里的双色激光脉冲由一束基频钛宝石主脉冲与另一束红外附加脉冲构成.研究发现,当合成脉冲的脉宽选为12 fs时, 选取合适的附加脉冲波长,合成电场的振幅在始末端时间段能被大幅抑制, 仅中间部分的电场对谐波谱平台区和截止位置起主要贡献. 通过分析合成脉冲电场始末端时间段抑制的机理,进一步扩展了合成脉冲脉宽到60 as, 并得到160 as的孤立短脉冲.这是迄今为止在孤立阿秒脉冲产生研究中所采用的最长脉宽. 该方案中的合成脉冲等效于单一5 fs短脉冲的作用, 却克服了5 fs脉冲低输出能量导致的阿秒脉冲能量低的困难.     

啁啾参数对光束远场分布的影响

啁啾脉冲光束的远场特性对其具体应用具有重要意义。利用夫琅禾费衍射积分公式导出了啁啾脉冲高斯光束远场光强分布的解析式,并通过数值计算分析了啁啾参数对远场分布的影响。结果表明,脉冲光束的远场中心光强随着脉宽的减小而增大,其远场轴上功率谱随着脉宽的增大而减小,与普通脉冲高斯光束相比,脉宽的变化对于啁啾脉冲光束的影响更大。脉冲光束的中心光强也随着谱宽的增大而增大,但啁啾参数的变化不会对其产生影响。     

放电引发的非链式高功率重复频率HF/DF激光器

高功率重频HF/DF激光因其具有的波长和功率优势成为当前中红外激光技术发展的热点之一。介绍了利用紫外预电离横向放电结构和工作气体循环系统建立的放电引发高功率重频HF/DF激光装置。在对激光工作介质SF6/C2H6混合气体放电特性和激光输出特性研究的基础上,开展了强电负性气体的重频均匀体放电技术和气体快速循环置换技术研究,解决了泵浦源重频放电能量在气体介质中的有效沉积和提取问题,实现了激光器50Hz的重频稳定运行和能量稳定输出,HF激光的平均功率达到28W,脉宽100ns,峰值功率5.6 MW。     

Optical levitation and manipulation of stuck particles with pulsed optical tweezers

We report on optical levitation and manipulation of microscopic particles that are stuck on a glass surface with pulsed optical tweezers. An infrared pulse laser at 1.06 microm was used to generate a large gradient force (up to 10(-9) N) within a short duration (approximately 45 micros) that overcomes the adhesive interaction between the particles and the glass surface. Then a low-power continuous-wave diode laser at 785 nm was used to capture and manipulate the levitated particle. We have demonstrated that both stuck dielectric and biological micrometer-sized particles, including polystyrene beads, yeast cells, and Bacillus cereus bacteria, can be levitated and manipulated with this technique. We measured the single-pulse levitation efficiency for 2.0 microm polystyrene beads as a function of the pulse energy and of the axial displacement from the stuck particle to the pulsed laser focus, which was as high as 88%.