Parallel transmission RF pulse design for eddy current correction at ultra high field.

PubMed

Zheng, Hai; Zhao, Tiejun; Qian, Yongxian; Ibrahim, Tamer; Boada, Fernando

2012-08-01

Multidimensional spatially selective RF pulses have been used in MRI applications such as B₁ and B₀ inhomogeneities mitigation. However, the long pulse duration has limited their practical applications. Recently, theoretical and experimental studies have shown that parallel transmission can effectively shorten pulse duration without sacrificing the quality of the excitation pattern. Nonetheless, parallel transmission with accelerated pulses can be severely impeded by hardware and/or system imperfections. One of such imperfections is the effect of the eddy current field. In this paper, we first show the effects of the eddy current field on the excitation pattern and then report an RF pulse the design method to correct eddy current fields caused by the RF coil and the gradient system. Experimental results on a 7 T human eight-channel parallel transmit system show substantial improvements on excitation patterns with the use of eddy current correction. Moreover, the proposed model-based correction method not only demonstrates comparable excitation patterns as the trajectory measurement method, but also significantly improves time efficiency. Copyright © 2012. Published by Elsevier Inc.

Terahertz spin current pulses controlled by magnetic heterostructures

NASA Astrophysics Data System (ADS)

Kampfrath, T.; Battiato, M.; Maldonado, P.; Eilers, G.; Nötzold, J.; Mährlein, S.; Zbarsky, V.; Freimuth, F.; Mokrousov, Y.; Blügel, S.; Wolf, M.; Radu, I.; Oppeneer, P. M.; Münzenberg, M.

2013-04-01

In spin-based electronics, information is encoded by the spin state of electron bunches. Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz regime. Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is used to drive spins from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter based on the inverse spin Hall effect, which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states. Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters.

Current Pulses Momentarily Enhance Thermoelectric Cooling

NASA Technical Reports Server (NTRS)

Snyder, G. Jeffrey; Fleurial, Jean-Pierre; Caillat, Thierry; Chen, Gang; Yang, Rong Gui

2004-01-01

The rates of cooling afforded by thermoelectric (Peltier) devices can be increased for short times by applying pulses of electric current greater than the currents that yield maximum steady-state cooling. It has been proposed to utilize such momentary enhancements of cooling in applications in which diode lasers and other semiconductor devices are required to operate for times of the order of milliseconds at temperatures too low to be easily obtainable in the steady state. In a typical contemplated application, a semiconductor device would be in contact with the final (coldest) somewhat taller stage of a multistage thermoelectric cooler. Steady current would be applied to the stages to produce steady cooling. Pulsed current would then be applied, enhancing the cooling of the top stage momentarily. The principles of operation are straightforward: In a thermoelectric device, the cooling occurs only at a junction at one end of the thermoelectric legs, at a rate proportional to the applied current. However, Joule heating occurs throughout the device at a rate proportional to the current squared. Hence, in the steady state, the steady temperature difference that the device can sustain increases with current only to the point beyond which the Joule heating dominates. If a pulse of current greater than the optimum current (the current for maximum steady cooling) is applied, then the junction becomes momentarily cooled below its lowest steady temperature until thermal conduction brings the resulting pulse of Joule heat to the junction and thereby heats the junction above its lowest steady temperature. A theoretical and experimental study of such transient thermoelectric cooling followed by transient Joule heating in response to current pulses has been performed. The figure presents results from one of the experiments. The study established the essential parameters that characterize the pulse cooling effect, including the minimum temperature achieved, the maximum

The structure and properties of boron carbide ceramics modified by high-current pulsed electron-beam

NASA Astrophysics Data System (ADS)

Ivanov, Yuri; Tolkachev, Oleg; Petyukevich, Maria; Teresov, Anton; Ivanova, Olga; Ikonnikova, Irina; Polisadova, Valentina

2016-01-01

The present work is devoted to numerical simulation of temperature fields and the analysis of structural and strength properties of the samples surface layer of boron carbide ceramics treated by the high-current pulsed electron-beam of the submillisecond duration. The samples made of sintered boron carbide ceramics are used in these investigations. The problem of calculating the temperature field is reduced to solving the thermal conductivity equation. The electron beam density ranges between 8…30 J/cm2, while the pulse durations are 100…200 μs in numerical modelling. The results of modelling the temperature field allowed ascertaining the threshold parameters of the electron beam, such as energy density and pulse duration. The electron beam irradiation is accompanied by the structural modification of the surface layer of boron carbide ceramics either in the single-phase (liquid or solid) or two-phase (solid-liquid) states. The sample surface of boron carbide ceramics is treated under the two-phase state (solid-liquid) conditions of the structural modification. The surface layer is modified by the high-current pulsed electron-beam produced by SOLO installation at the Institute of High Current Electronics of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia. The elemental composition and the defect structure of the modified surface layer are analyzed by the optical instrument, scanning electron and transmission electron microscopes. Mechanical properties of the modified layer are determined measuring its hardness and crack resistance. Research results show that the melting and subsequent rapid solidification of the surface layer lead to such phenomena as fragmentation due to a crack network, grain size reduction, formation of the sub-grained structure due to mechanical twinning, and increase of hardness and crack resistance.

Surface modification of steels and magnesium alloy by high current pulsed electron beam

NASA Astrophysics Data System (ADS)

Hao, Shengzhi; Gao, Bo; Wu, Aimin; Zou, Jianxin; Qin, Ying; Dong, Chuang; An, Jian; Guan, Qingfeng

2005-11-01

High current pulsed electron beam (HCPEB) is now developing as a useful tool for surface modification of materials. When concentrated electron flux transferring its energy into a very thin surface layer within a short pulse time, superfast processes such as heating, melting, evaporation and consequent solidification, as well as dynamic stress induced may impart the surface layer with improved physico-chemical and mechanical properties. This paper presents our research work on surface modification of steels and magnesium alloy with HCPEB of working parameters as electron energy 27 keV, pulse duration ∼1 μs and energy density ∼2.2 J/cm2 per pulse. Investigations performed on carbon steel T8, mold steel D2 and magnesium alloy AZ91HP have shown that the most pronounced changes of phase-structure state and properties occurring in the near-surface layers, while the thickness of the modified layer with improved microhardness (several hundreds of micrometers) is significantly greater than that of the heat-affected zone. The formation mechanisms of surface cratering and non-stationary hardening effect in depth are discussed based on the elucidation of non-equilibrium temperature filed and different kinds of stresses formed during pulsed electron beam melting treatment. After the pulsed electron beam treatments, samples show significant improvements in measurements of wear and corrosion resistance.

Multiple current peaks in room-temperature atmospheric pressure homogenous dielectric barrier discharge plasma excited by high-voltage tunable nanosecond pulse in air

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, De-Zheng; Wang, Wen-Chun; Zhang, Shuai

2013-05-13

Room temperature homogenous dielectric barrier discharge plasma with high instantaneous energy efficiency is acquired by using nanosecond pulse voltage with 20-200 ns tunable pulse width. Increasing the voltage pulse width can lead to the generation of regular and stable multiple current peaks in each discharge sequence. When the voltage pulse width is 200 ns, more than 5 organized current peaks can be observed under 26 kV peak voltage. Investigation also shows that the organized multiple current peaks only appear in homogenous discharge mode. When the discharge is filament mode, organized multiple current peaks are replaced by chaotic filament current peaks.

Effects of Pulse Parameters on Weld Microstructure and Mechanical Properties of Extra Pulse Current Aided Laser Welded 2219 Aluminum Alloy Joints.

PubMed

Zhang, Xinge; Li, Liqun; Chen, Yanbin; Yang, Zhaojun; Chen, Yanli; Guo, Xinjian

2017-09-15

In order to expand the application range of laser welding and improve weld quality, an extra pulse current was used to aid laser-welded 2219 aluminum alloy, and the effects of pulse current parameters on the weld microstructure and mechanical properties were investigated. The effect mechanisms of the pulse current interactions with the weld pool were evaluated. The results indicated that the coarse dendritic structure in the weld zone changed to a fine equiaxed structure using an extra pulse current, and the pulse parameters, including medium peak current, relatively high pulse frequency, and low pulse duty ratio benefited to improving the weld structure. The effect mechanisms of the pulse current were mainly ascribed to the magnetic pinch effect, thermal effect, and electromigration effect caused by the pulse current. The effect of the pulse parameters on the mechanical properties of welded joints were consistent with that of the weld microstructure. The tensile strength and elongation of the optimal pulse current-aided laser-welded joint increased by 16.4% and 105%, respectively, compared with autogenous laser welding.

Effects of Pulse Parameters on Weld Microstructure and Mechanical Properties of Extra Pulse Current Aided Laser Welded 2219 Aluminum Alloy Joints

PubMed Central

Zhang, Xinge; Li, Liqun; Chen, Yanbin; Yang, Zhaojun; Chen, Yanli; Guo, Xinjian

2017-01-01

In order to expand the application range of laser welding and improve weld quality, an extra pulse current was used to aid laser-welded 2219 aluminum alloy, and the effects of pulse current parameters on the weld microstructure and mechanical properties were investigated. The effect mechanisms of the pulse current interactions with the weld pool were evaluated. The results indicated that the coarse dendritic structure in the weld zone changed to a fine equiaxed structure using an extra pulse current, and the pulse parameters, including medium peak current, relatively high pulse frequency, and low pulse duty ratio benefited to improving the weld structure. The effect mechanisms of the pulse current were mainly ascribed to the magnetic pinch effect, thermal effect, and electromigration effect caused by the pulse current. The effect of the pulse parameters on the mechanical properties of welded joints were consistent with that of the weld microstructure. The tensile strength and elongation of the optimal pulse current-aided laser-welded joint increased by 16.4% and 105%, respectively, compared with autogenous laser welding. PMID:28914825

High-temperature performance of MoS2 thin-film transistors: Direct current and pulse current-voltage characteristics

NASA Astrophysics Data System (ADS)

Jiang, C.; Rumyantsev, S. L.; Samnakay, R.; Shur, M. S.; Balandin, A. A.

2015-02-01

We report on fabrication of MoS2 thin-film transistors (TFTs) and experimental investigations of their high-temperature current-voltage characteristics. The measurements show that MoS2 devices remain functional to temperatures of at least as high as 500 K. The temperature increase results in decreased threshold voltage and mobility. The comparison of the direct current (DC) and pulse measurements shows that the direct current sub-linear and super-linear output characteristics of MoS2 thin-films devices result from the Joule heating and the interplay of the threshold voltage and mobility temperature dependences. At temperatures above 450 K, a kink in the drain current occurs at zero gate voltage irrespective of the threshold voltage value. This intriguing phenomenon, referred to as a "memory step," was attributed to the slow relaxation processes in thin films similar to those in graphene and electron glasses. The fabricated MoS2 thin-film transistors demonstrated stable operation after two months of aging. The obtained results suggest new applications for MoS2 thin-film transistors in extreme-temperature electronics and sensors.

High-current-density electrodeposition using pulsed and constant currents to produce thick CoPt magnetic films on silicon substrates

NASA Astrophysics Data System (ADS)

Ewing, Jacob; Wang, Yuzheng; Arnold, David P.

2018-05-01

This paper investigates methods for electroplating thick (>20 μm), high-coercivity CoPt films using high current densities (up to 1 A/cm2) and elevated bath temperatures (70 °C). Correlations are made tying current-density and temperature process parameters with plating rate, elemental ratio and magnetic properties of the deposited CoPt films. It also investigates how pulsed currents can increase the plating rate and film to substrate adhesion. Using 500 mA/cm2 and constant current, high-quality, dense CoPt films were successfully electroplated up to 20 μm thick in 1 hr on silicon substrates (0.35 μm/min plating rate). After standard thermal treatment (675°C, 30 min) to achieve the ordered L10 crystalline phase, strong magnetic properties were measured: coercivities up 850 kA/m, remanences >0.5 T, and maximum energy products up to 46 kJ/m3.

Design of a New Acceleration System for High-Current Pulsed Proton Beams from an ECR Source

NASA Astrophysics Data System (ADS)

Cooper, Andrew L.; Pogrebnyak, Ivan; Surbrook, Jason T.; Kelly, Keegan J.; Carlin, Bret P.; Champagne, Arthur E.; Clegg, Thomas B.

2014-03-01

A primary objective for accelerators at TUNL's Laboratory for Experimental Nuclear Astrophysics (LENA) is to maximize target beam intensity to ensure a high rate of nuclear events during each experiment. Average proton target currents of several mA are needed from LENA's electron cyclotron resonance (ECR) ion source because nuclear cross sections decrease substantially at energies of interest <200 keV. We seek to suppress undesired continuous environmental background by pulsing the beam and detecting events only during beam pulses. To improve beam intensity and transport, we installed a more powerful, stable microwave system for the ECR plasma, and will install a new acceleration system. This system will: reduce defocusing effects of the beam's internal space charge; provide better vacuum with a high gas conductance accelerating column; suppress bremsstrahlung X-rays produced when backstreaming electrons strike internal acceleration tube structures; and provide better heat dissipation by using deionized water to provide the current drain needed to establish the accelerating tube's voltage gradient. Details of beam optical modeling calculations, proposed accelerating tube design, and initial beam pulsing tests will be described. Work supported in part by USDOE Office of HE and Nuclear Physics.

Current density imaging sequence for monitoring current distribution during delivery of electric pulses in irreversible electroporation.

PubMed

Serša, Igor; Kranjc, Matej; Miklavčič, Damijan

2015-01-01

Electroporation is gaining its importance in everyday clinical practice of cancer treatment. For its success it is extremely important that coverage of the target tissue, i.e. treated tumor, with electric field is within the specified range. Therefore, an efficient tool for the electric field monitoring in the tumor during delivery of electroporation pulses is needed. The electric field can be reconstructed by the magnetic resonance electric impedance tomography method from current density distribution data. In this study, the use of current density imaging with MRI for monitoring current density distribution during delivery of irreversible electroporation pulses was demonstrated. Using a modified single-shot RARE sequence, where four 3000 V and 100 μs long pulses were included at the start, current distribution between a pair of electrodes inserted in a liver tissue sample was imaged. Two repetitions of the sequence with phases of refocusing radiofrequency pulses 90° apart were needed to acquire one current density image. For each sample in total 45 current density images were acquired to follow a standard protocol for irreversible electroporation where 90 electric pulses are delivered at 1 Hz. Acquired current density images showed that the current density in the middle of the sample increased from first to last electric pulses by 60%, i.e. from 8 kA/m2 to 13 kA/m2 and that direction of the current path did not change with repeated electric pulses significantly. The presented single-shot RARE-based current density imaging sequence was used successfully to image current distribution during delivery of short high-voltage electric pulses. The method has a potential to enable monitoring of tumor coverage by electric field during irreversible electroporation tissue ablation.

Effect of a superconducting coil as a fault current limiter on current density distribution in BSCCO tape after an over-current pulse

NASA Astrophysics Data System (ADS)

Tallouli, M.; Shyshkin, O.; Yamaguchi, S.

2017-07-01

The development of power transmission lines based on long-length high temperature superconducting (HTS) tapes is complicated and technically challenging task. A serious problem for transmission line operation could become HTS power cable damage due to over-current pulse conditions. To avoid the cable damage in any urgent case the superconducting coil technology, i.e. superconductor fault current limiter (SFCL) is required. Comprehensive understanding of the current density characteristics of HTS tapes in both cases, either after pure over-current pulse or after over-current pulse limited by SFCL, is needed to restart or to continue the operation of the power transmission line. Moreover, current density distribution along and across the HTS tape provides us with the sufficient information about the quality of the tape performance in different current feeding regimes. In present paper we examine BSCCO HTS tape under two current feeding regimes. The first one is 100A feeding preceded by 900A over-current pulse. In this case none of tape protection was used. The second scenario is similar to the fist one but SFCL is used to limit an over-current value. For both scenarios after the pulse is gone and the current feeding is set up at 100A we scan magnetic field above the tape by means of Hall probe sensor. Then the feeding is turned of and the magnetic field scanning is repeated. Using the inverse problem numerical solver we calculate the corresponding direct and permanent current density distributions during the feeding and after switch off. It is demonstrated that in the absence of SFCL the current distribution is highly peaked at the tape center. At the same time the current distribution in the experiment with SFCL is similar to that observed under normal current feeding condition. The current peaking in the first case is explained by the effect of an opposite electric field induced at the tape edges during the overcurrent pulse decay, and by degradation of

Self-pulsing in a low-current hollow cathode discharge: From Townsend to glow discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Yu; School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081; Xie, Kan, E-mail: xiekan@bit.edu.cn

We investigate the self-pulsing phenomenon of a low current cavity discharge in a cylindrical hollow cathode in pure argon. The waveforms of pulsed current and voltage are measured, and the time-averaged and time-resolved images of hollow cathode discharge are recorded by using high-speed intensified charge coupled device camera. The results show that the self-pulsing is a mode transition between low-current stage of Townsend discharge and high-current stage of glow discharge. During the self-pulsing, the current rising time relates to the dissipation of space charges, and the decay time relates to the reconstruction of the virtual anode by the accumulation ofmore » positive ions. Whether or not space charges can form and keep the virtual anode is responsible for the discharge mode and hence plays an important role in the self-pulsing phenomenon in low current hollow cathode discharge.« less

Development of a low-energy and high-current pulsed neutral beam injector with a washer-gun plasma source for high-beta plasma experiments.

PubMed

Ii, Toru; Gi, Keii; Umezawa, Toshiyuki; Asai, Tomohiko; Inomoto, Michiaki; Ono, Yasushi

2012-08-01

We have developed a novel and economical neutral-beam injection system by employing a washer-gun plasma source. It provides a low-cost and maintenance-free ion beam, thus eliminating the need for the filaments and water-cooling systems employed conventionally. In our primary experiments, the washer gun produced a source plasma with an electron temperature of approximately 5 eV and an electron density of 5 × 10(17) m(-3), i.e., conditions suitable for ion-beam extraction. The dependence of the extracted beam current on the acceleration voltage is consistent with space-charge current limitation, because the observed current density is almost proportional to the 3/2 power of the acceleration voltage below approximately 8 kV. By optimizing plasma formation, we successfully achieved beam extraction of up to 40 A at 15 kV and a pulse length in excess of 0.25 ms. Its low-voltage and high-current pulsed-beam properties enable us to apply this high-power neutral beam injection into a high-beta compact torus plasma characterized by a low magnetic field.

Development and application of network virtual instrument for emission spectrum of pulsed high-voltage direct current discharge

NASA Astrophysics Data System (ADS)

Gong, X.; Wu, Q.

2017-12-01

Network virtual instrument (VI) is a new development direction in current automated test. Based on LabVIEW, the software and hardware system of VI used for emission spectrum of pulsed high-voltage direct current (DC) discharge is developed and applied to investigate pulsed high-voltage DC discharge of nitrogen. By doing so, various functions are realized including real time collection of emission spectrum of nitrogen, monitoring operation state of instruments and real time analysis and processing of data. By using shared variables and DataSocket technology in LabVIEW, the network VI system based on field VI is established. The system can acquire the emission spectrum of nitrogen in the test site, monitor operation states of field instruments, realize real time face-to-face interchange of two sites, and analyze data in the far-end from the network terminal. By employing the network VI system, the staff in the two sites acquired the same emission spectrum of nitrogen and conducted the real time communication. By comparing with the previous results, it can be seen that the experimental data obtained by using the system are highly precise. This implies that the system shows reliable network stability and safety and satisfies the requirements for studying the emission spectrum of pulsed high-voltage discharge in high-precision fields or network terminals. The proposed architecture system is described and the target group gets the useful enlightenment in many fields including engineering remote users, specifically in control- and automation-related tasks.

Oscillatory dependence of current driven domain wall motion on current pulse length

NASA Astrophysics Data System (ADS)

Thomas, Luc

2007-03-01

The motion of domain walls (DW) in magnetic nanowires driven by spin torque from spin-polarized current is of considerable interest. Most previous work has considered the effect of dc or ˜microsecond long current pulses. Here, we show that the dynamics of DWs driven by nanosecond-long current pulses is unexpectedly complex. In particular, we show that the current driven motion of a DW, confined to a pinning site in a permalloy nanowire, exhibits an oscillatory dependence on the current pulse length with a period of just a few nanoseconds [1]. This behavior can be understood within a surprisingly straightforward one dimensional analytical model of the DW's motion. When a current pulse is applied, the DW's position oscillates within the pinning potential out of phase with the DW's out-of-plane magnetization, where the latter acts like the DW's momentum. Thus, the current driven motion of the DW is akin to a harmonic oscillator, whose frequency is determined by the ``mass'' of the DW and where the restoring force is related to the slope of the pinning potential. Remarkably, when the current pulse is turned off during phases of the DW motion when it has enough momentum, the amplitude of the oscillations can be amplified such that the DW exits the pinning potential well after the pulse is turned off. This oscillatory depinning occurs for currents smaller than the dc threshold current, and, moreover, the DW moves against the electron flow, opposite to the propagation direction above the dc threshold. These effects can be further amplified by using trains of current pulses whose lengths and separations are matched to the DW's oscillation period. In this way, we have demonstrated a five fold reduction in the threshold current required to move a DW out of a pinning site, making this effect potentially important for technological applications. [1] L. Thomas, M. Hayashi, X. Jiang, R. Moriya, C. Rettner and S.S.P. Parkin, Nature 443, 197 (2006).

Progress of long pulse operation with high performance plasma in KSTAR

NASA Astrophysics Data System (ADS)

Bae, Young; Kstar Team

2015-11-01

Recent KSTAR experiments showed the sustained H-mode operation up to the pulse duration of 46 s at the plasma current of 600 kA. The long-pulse H-mode operation has been supported by long-pulse capable neutral beam injection (NBI) system with high NB current drive efficiency attributed by highly tangential injections of three beam sources. In next phase, aiming to demonstrate the long pulse stationary high performance plasma operation, we are attempting the long pulse inductive operation at the higher performance (MA plasma current, high normalized beta, and low q95) for the final goal of demonstration of ITER-like baseline scenario in KSTAR with progressive improvement of the plasma shape control and higher neutral beam injection power. This paper presents the progress of long pulse operation and the analysis of energy confinement time and non-inductive current drive in KSTAR.

High current plasma electron emitter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fiksel, G.; Almagri, A.F.; Craig, D.

1995-07-01

A high current plasma electron emitter based on a miniature plasma source has been developed. The emitting plasma is created by a pulsed high current gas discharge. The electron emission current is 1 kA at 300 V at the pulse duration of 10 ms. The prototype injector described in this paper will be used for a 20 kA electrostatic current injection experiment in the Madison Symmetric Torus (MST) reversed-field pinch. The source will be replicated in order to attain this total current requirement. The source has a simple design and has proven very reliable in operation. A high emission current,more » small size (3.7 cm in diameter), and low impurity generation make the source suitable for a variety of fusion and technological applications.« less

Fast and efficient STT switching in MTJ using additional transient pulse current

NASA Astrophysics Data System (ADS)

Pathak, Sachin; Cha, Jongin; Jo, Kangwook; Yoon, Hongil; Hong, Jongill

2017-06-01

We propose a profile of write pulse current-density to switch magnetization in a perpendicular magnetic tunnel junction to reduce switching time and write energy as well. Our simulated results show that an overshoot transient pulse current-density (current spike) imposed to conventional rectangular-shaped pulse current-density (main pulse) significantly improves switching speed that yields the reduction in write energy accordingly. For example, we could dramatically reduce the switching time by 80% and thereby reduce the write energy over 9% in comparison to the switching without current spike. The current spike affects the spin dynamics of the free layer and reduces the switching time mainly due to spin torque induced. On the other hand, the large Oersted field induced causes changes in spin texture. We believe our proposed write scheme can make a breakthrough in magnetic random access memory technology seeking both high speed operation and low energy consumption.

Transformer miniaturization for transcutaneous current/voltage pulse applications.

PubMed

Kolen, P T

1999-05-01

A general procedure for the design of a miniaturized step up transformer to be used in the context of surface electrode based current/voltage pulse generation is presented. It has been shown that the optimum secondary current pulse width is 4.5 tau, where tau is the time constant associated with the pulse forming network associated with the transformer/electrode interaction. This criteria has been shown to produce the highest peak to average current ratio for the secondary current pulse. The design procedure allows for the calculation of the optimum turns ratio, primary turns, and secondary turns for a given electrode load/tissue and magnetic core parameters. Two design examples for transformer optimization are presented.

High-voltage, high-current, solid-state closing switch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Focia, Ronald Jeffrey

2017-08-22

A high-voltage, high-current, solid-state closing switch uses a field-effect transistor (e.g., a MOSFET) to trigger a high-voltage stack of thyristors. The switch can have a high hold-off voltage, high current carrying capacity, and high time-rate-of-change of current, di/dt. The fast closing switch can be used in pulsed power applications.

High-speed pulse-shape generator, pulse multiplexer

DOEpatents

Burkhart, Scott C.

2002-01-01

The invention combines arbitrary amplitude high-speed pulses for precision pulse shaping for the National Ignition Facility (NIF). The circuitry combines arbitrary height pulses which are generated by replicating scaled versions of a trigger pulse and summing them delayed in time on a pulse line. The combined electrical pulses are connected to an electro-optic modulator which modulates a laser beam. The circuit can also be adapted to combine multiple channels of high speed data into a single train of electrical pulses which generates the optical pulses for very high speed optical communication. The invention has application in laser pulse shaping for inertial confinement fusion, in optical data links for computers, telecommunications, and in laser pulse shaping for atomic excitation studies. The invention can be used to effect at least a 10.times. increase in all fiber communication lines. It allows a greatly increased data transfer rate between high-performance computers. The invention is inexpensive enough to bring high-speed video and data services to homes through a super modem.

WC/Co composite surface structure and nano graphite precipitate induced by high current pulsed electron beam irradiation

NASA Astrophysics Data System (ADS)

Hao, S. Z.; Zhang, Y.; Xu, Y.; Gey, N.; Grosdidier, T.; Dong, C.

2013-11-01

High current pulsed electron beam (HCPEB) irradiation was conducted on a WC-6% Co hard alloy with accelerating voltage of 27 kV and pulse duration of 2.5 μs. The surface phase structure was examined by using glancing-angle X-ray diffraction (GAXRD), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM) methods. The surface tribological properties were measured. It was found that after 20 pulses of HCPEB irradiation, the surface structure of WC/Co hard alloy was modified dramatically and composed of a mixture of nano-grained WC1-x, Co3W9C4, Co3W3C phases and graphite precipitate domains ˜50 nm. The friction coefficient of modified surface decreased to ˜0.38 from 0.6 of the initial state, and the wear rate reduced from 8.4 × 10-5 mm3/min to 6.3 × 10-6 mm3/min, showing a significant self-lubricating effect.

Contribution for Iron Vapor and Radiation Distribution Affected by Current Frequency of Pulsed Arc

NASA Astrophysics Data System (ADS)

Shimokura, Takuya; Mori, Yusuke; Iwao, Toru; Yumoto, Motoshige

Pulsed GTA welding has been used for improvement of stability, weld speed, and heat input control. However, the temperature and radiation power of the pulsed arc have not been elucidated. Furthermore, arc contamination by metal vapor changes the arc characteristics, e.g. by increasing radiation power. In this case, the metal vapor in pulsed GTA welding changes the distribution of temperature and radiation power as a function of time. This paper presents the relation between metal vapor and radiation power at different pulse frequencies. We calculate the Fe vapor distribution of the pulsed current. Results show that the Fe vapor is transported at fast arc velocity during the peak current period. During the base current period, the Fe vapor concentration is low and distribution is diffuse. The transition of Fe vapor distribution does not follow the pulsed current; the radiation power density distribution differs for high frequencies and low frequencies. In addition, the Fe vapor and radiation distribution are affected by the pulsed arc current frequency.

Low-jitter high-power thyristor array pulse driver and generator

DOEpatents

Hanks, Roy L.

2002-01-01

A method and apparatus for generating low-jitter, high-voltage and high-current pulses for driving low impedance loads such as detonator fuses uses a MOSFET driver which, when triggered, discharges a high-voltage pre-charged capacitor into the primary of a toroidal current-multiplying transformer with multiple isolated secondary windings. The secondary outputs are suitable for driving an array of thyristors that discharge a precharged high-voltage capacitor and thus generating the required high-voltage and high-current pulse.

High-Energy Two-Stage Pulsed Plasma Thruster

NASA Technical Reports Server (NTRS)

Markusic, Tom

2003-01-01

A high-energy (28 kJ per pulse) two-stage pulsed plasma thruster (MSFC PPT-1) has been constructed and tested. The motivation of this project is to develop a high power (approximately 500 kW), high specific impulse (approximately 10000 s), highly efficient (greater than 50%) thruster for use as primary propulsion in a high power nuclear electric propulsion system. PPT-1 was designed to overcome four negative characteristics which have detracted from the utility of pulsed plasma thrusters: poor electrical efficiency, poor propellant utilization efficiency, electrode erosion, and reliability issues associated with the use of high speed gas valves and high current switches. Traditional PPTs have been plagued with poor efficiency because they have not been operated in a plasma regime that fully exploits the potential benefits of pulsed plasma acceleration by electromagnetic forces. PPTs have generally been used to accelerate low-density plasmas with long current pulses. Operation of thrusters in this plasma regime allows for the development of certain undesirable particle-kinetic effects, such as Hall effect-induced current sheet canting. PPT-1 was designed to propel a highly collisional, dense plasma that has more fluid-like properties and, hence, is more effectively pushed by a magnetic field. The high-density plasma loading into the second stage of the accelerator is achieved through the use of a dense plasma injector (first stage). The injector produces a thermal plasma, derived from a molten lithium propellant feed system, which is subsequently accelerated by the second stage using mega-amp level currents, which eject the plasma at a speed on the order of 100 kilometers per second. Traditional PPTs also suffer from dynamic efficiency losses associated with snowplow loading of distributed neutral propellant. The twostage scheme used in PPT-I allows the propellant to be loaded in a manner which more closely approximates the optimal slug loading. Lithium propellant

Long-pulse production of high current negative ion beam by using actively temperature controlled plasma grid for JT-60SA negative ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kojima, A.; Hanada, M.; Yoshida, M.

2015-04-08

The temperature control system of the large-size plasma grid has been developed to realize the long pulse production of high-current negative ions for JT-60SA. By using this prototype system for the JT-60SA ion source, 15 A negative ions has been sustained for 100 s for the first time, which is three times longer than that obtained in JT-60U. In this system, a high-temperature fluorinated fluid with a high boiling point of 270 degree Celsius is circulated in the cooling channels of the plasma grids (PG) where a cesium (Cs) coverage is formed to enhance the negative ion production. Because themore » PG temperature control had been applied to only 10% of the extraction area previously, the prototype PG with the full extraction area (110 cm × 45 cm) was developed to increase the negative ion current in this time. In the preliminary results of long pulse productions of high-current negative ions at a Cs conditioning phase, the negative ion production was gradually degraded in the last half of 100 s pulse where the temperature of an arc chamber wall was not saturated. From the spectroscopic measurements, it was found that the Cs flux released from the wall might affect to the negative ion production, which implied the wall temperature should be kept low to control the Cs flux to the PG for the long-pulse high-current production. The obtained results of long-pulse production and the PG temperature control method contributes the design of the ITER ion source.« less

Adjustable direct current and pulsed circuit fault current limiter

DOEpatents

Boenig, Heinrich J.; Schillig, Josef B.

2003-09-23

A fault current limiting system for direct current circuits and for pulsed power circuit. In the circuits, a current source biases a diode that is in series with the circuits' transmission line. If fault current in a circuit exceeds current from the current source biasing the diode open, the diode will cease conducting and route the fault current through the current source and an inductor. This limits the rate of rise and the peak value of the fault current.

Generation of High-Power High-Intensity Short X-Ray Free-Electron-Laser Pulses

DOE PAGES

Guetg, Marc W.; Lutman, Alberto A.; Ding, Yuantao; ...

2018-01-03

X-ray free-electron lasers combine a high pulse power, short pulse length, narrow bandwidth, and high degree of transverse coherence. Any increase in the photon pulse power, while shortening the pulse length, will further push the frontier on several key x-ray free-electron laser applications including single-molecule imaging and novel nonlinear x-ray methods. This Letter shows experimental results at the Linac Coherent Light Source raising its maximum power to more than 300% of the current limit while reducing the photon pulse length to 10 fs. As a result, this was achieved by minimizing residual transverse-longitudinal centroid beam offsets and beam yaw andmore » by correcting the dispersion when operating over 6 kA peak current with a longitudinally shaped beam.« less

Generation of High-Power High-Intensity Short X-Ray Free-Electron-Laser Pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guetg, Marc W.; Lutman, Alberto A.; Ding, Yuantao

X-ray free-electron lasers combine a high pulse power, short pulse length, narrow bandwidth, and high degree of transverse coherence. Any increase in the photon pulse power, while shortening the pulse length, will further push the frontier on several key x-ray free-electron laser applications including single-molecule imaging and novel nonlinear x-ray methods. This Letter shows experimental results at the Linac Coherent Light Source raising its maximum power to more than 300% of the current limit while reducing the photon pulse length to 10 fs. As a result, this was achieved by minimizing residual transverse-longitudinal centroid beam offsets and beam yaw andmore » by correcting the dispersion when operating over 6 kA peak current with a longitudinally shaped beam.« less

A new high current laboratory and pulsed homopolar generator power supply at the University of Texas

NASA Astrophysics Data System (ADS)

Floyd, J. E.; Aanstoos, T. A.

1984-03-01

The University of Texas at Austin is constructing a facility for research in pulse power technology for the Center for Electromechanics at the Balcones Research Center. The facility, designed to support high-current experiments, will be powered by six homopolar generators, each rated at 10 MJ and arranged to allow matching the requirements of resistive and inductive loads at various voltage and current combinations. Topics covered include the high bay, the power supply configuration and parameters, the speed and field control, and the magnetic circuit. Also considered are the removable air-cooled brushes, the water-cooled field coils, the hydraulic motor sizing and direct coupling, the low-impedance removable field coils, and the hydrostatic bearing design.

Using a small hybrid pulse power transformer unit as component of a high-current opening switch for a railgun

NASA Astrophysics Data System (ADS)

Leung, E. M. W.; Bailey, R. E.; Michels, P. H.

1989-03-01

The hybrid pulse power transformer (HPPT) is a unique concept utilizing the ultrafast superconducting-to-normal transition process of a superconductor. When used in the form of a hybrid transformer current-zero switch (HTCS), this creates an approach in which the large, high-power, high-current opening switch in a conventional railgun system can be eliminated. This represents an innovative application of superconductivity to pulsed power conditioning required for the Strategic Defense Initiative (SDI). The authors explain the working principles of a 100-KJ unit capable of switching up to 500 kA at a frequency of 0.5 Hz and with a system efficiency of greater than 90 percent. Circuit analysis using a computer code called SPICE PLUS was used to verify the HTCS concept. This concept can be scaled up to applications in the several mega-ampere levels.

Gas metal arc welding fume generation using pulsed current

DOE Office of Scientific and Technical Information (OSTI.GOV)

Castner, H.R.

1994-12-31

This paper describes a study of the effects of pulsed welding current on the amount of welding fume and ozone produced during gas metal arc welding (GMAW) using a range of welding procedures and pulse parameters. The results reported in this paper show that pulsed current can reduce GMAW fumes compared to steady current. This research also shows that welding parameters need to be properly controlled if pulsed current is to be used to reduce welding fumes. Fume and ozone generation rates were measured during this study for GMAW of mild steel using copper-coated ER70S-3 electrode wire and 95%Ar-5%CO{sub 2}more » and 85%Ar-15%CO{sub 2} shielding gases. Welds were made with both steady current and pulsed current over a wide range of welding parameters. Fume generation rates for steady current were found to be typically between 0.2 g/min and 0.8 g/min which agrees with other researchers. No significant difference was found in the chemical composition of welding fumes from pulsed current compared to the composition of fumes generated by steady current. New technology that can reduce arc welding fumes is of significant interest to a wide range of companies that use arc welding processes and this research should assist these users in evaluating the potential for the application of this technology to their own operations.« less

Surface alloying of aluminum with molybdenum by high-current pulsed electron beam

NASA Astrophysics Data System (ADS)

Xia, Han; Zhang, Conglin; Lv, Peng; Cai, Jie; Jin, Yunxue; Guan, Qingfeng

2018-02-01

The surface alloying of pre-coated molybdenum (Mo) film on aluminum (Al) substrate by high-current pulsed electron beam (HCPEB) was investigated. The microstructure and phase analysis were conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that Mo particles were dissolved into Al matrix to form alloying layer, which was composed of Mo, Al and acicular or equiaxed Al5Mo phases after surface alloying. Meanwhile, various structure defects such as dislocation loops, high-density dislocations and dislocation walls were observed in the alloying surface. The corrosion resistance was tested by using potentiodynamic polarization curves and electrochemical impedance spectra (EIS). Electrochemical results indicate that all the alloying samples had better corrosion resistance in 3.5 wt% NaCl solution compared to initial sample. The excellent corrosion resistance is mainly attributed to the combined effect of the structure defects and the addition of Mo element to form a more stable passive film.

Mechanism of formation of subnanosecond current front in high-voltage pulse open discharge

NASA Astrophysics Data System (ADS)

Schweigert, I. V.; Alexandrov, A. L.; Zakrevsky, Dm. E.; Bokhan, P. A.

2014-11-01

The mechanism of subnanosecond current front rise observed previously in the experiment in high-voltage pulse open discharge in helium is studied in kinetic particle-in-cell simulations. The Boltzmann equations for electrons, ions, and fast atoms are solved self-consistently with the Poisson equations for the electrical potential. The partial contributions to the secondary electron emission from the ions, fast atoms, photons, and electrons, bombarding the electrode, are calculated. In simulations, as in the experiment, the discharge glows between two symmetrical cathodes and the anode grid in the midplane at P =6 Torr and the applied voltage of 20 kV. The electron avalanche development is considered for two experimental situations during the last stage of breakdown: (i) with constant voltage and (ii) with decreasing voltage. For case (i), the subnanosecond current front rise is set by photons from the collisional excitation transfer reactions. For the case (ii), the energetic electrons swamp the cathode during voltage drop and provide the secondary electron emission for the subnanosecond current rise, observed in the experiment.

Electronic constant current and current pulse signal generator for nuclear instrumentation testing

DOEpatents

Brown, Roger A.

1994-01-01

Circuitry for testing the ability of an intermediate range nuclear instrut to detect and measure a constant current and a periodic current pulse. The invention simulates the resistance and capacitance of the signal connection of a nuclear instrument ion chamber detector and interconnecting cable. An LED flasher/oscillator illuminates an LED at a periodic rate established by a timing capacitor and circuitry internal to the flasher/oscillator. When the LED is on, a periodic current pulse is applied to the instrument. When the LED is off, a constant current is applied. An inductor opposes battery current flow when the LED is on.

Novel high-frequency energy-efficient pulsed-dc generator for capacitively coupled plasma discharge

NASA Astrophysics Data System (ADS)

Mamun, Md Abdullah Al; Furuta, Hiroshi; Hatta, Akimitsu

2018-03-01

The circuit design, assembly, and operating tests of a high-frequency and high-voltage (HV) pulsed dc generator (PDG) for capacitively coupled plasma (CCP) discharge inside a vacuum chamber are reported. For capacitive loads, it is challenging to obtain sharp rectangular pulses with fast rising and falling edges, requiring intense current for quick charging and discharging. The requirement of intense current generally limits the pulse operation frequency. In this study, we present a new type of PDG consisting of a pair of half-resonant converters and a constant current-controller circuit connected with HV solid-state power switches that can deliver almost rectangular high voltage pulses with fast rising and falling edges for CCP discharge. A prototype of the PDG is assembled to modulate from a high-voltage direct current (HVdc) input into a pulsed HVdc output, while following an input pulse signal and a set current level. The pulse rise time and fall time are less than 500 ns and 800 ns, respectively, and the minimum pulse width is 1 µs. The maximum voltage for a negative pulse is 1000 V, and the maximum repetition frequency is 500 kHz. During the pulse on time, the plasma discharge current is controlled steadily at the set value. The half-resonant converters in the PDG perform recovery of the remaining energy from the capacitive load at every termination of pulse discharge. The PDG performed with a high energy efficiency of 85% from the HVdc input to the pulsed dc output at a repetition rate of 1 kHz and with stable plasma operation in various discharge conditions. The results suggest that the developed PDG can be considered to be more efficient for plasma processing by CCP.

Novel high-frequency energy-efficient pulsed-dc generator for capacitively coupled plasma discharge.

PubMed

Mamun, Md Abdullah Al; Furuta, Hiroshi; Hatta, Akimitsu

2018-03-01

The circuit design, assembly, and operating tests of a high-frequency and high-voltage (HV) pulsed dc generator (PDG) for capacitively coupled plasma (CCP) discharge inside a vacuum chamber are reported. For capacitive loads, it is challenging to obtain sharp rectangular pulses with fast rising and falling edges, requiring intense current for quick charging and discharging. The requirement of intense current generally limits the pulse operation frequency. In this study, we present a new type of PDG consisting of a pair of half-resonant converters and a constant current-controller circuit connected with HV solid-state power switches that can deliver almost rectangular high voltage pulses with fast rising and falling edges for CCP discharge. A prototype of the PDG is assembled to modulate from a high-voltage direct current (HVdc) input into a pulsed HVdc output, while following an input pulse signal and a set current level. The pulse rise time and fall time are less than 500 ns and 800 ns, respectively, and the minimum pulse width is 1 µs. The maximum voltage for a negative pulse is 1000 V, and the maximum repetition frequency is 500 kHz. During the pulse on time, the plasma discharge current is controlled steadily at the set value. The half-resonant converters in the PDG perform recovery of the remaining energy from the capacitive load at every termination of pulse discharge. The PDG performed with a high energy efficiency of 85% from the HVdc input to the pulsed dc output at a repetition rate of 1 kHz and with stable plasma operation in various discharge conditions. The results suggest that the developed PDG can be considered to be more efficient for plasma processing by CCP.

A pulse-compression-ring circuit for high-efficiency electric propulsion.

PubMed

Owens, Thomas L

2008-03-01

A highly efficient, highly reliable pulsed-power system has been developed for use in high power, repetitively pulsed inductive plasma thrusters. The pulsed inductive thruster ejects plasma propellant at a high velocity using a Lorentz force developed through inductive coupling to the plasma. Having greatly increased propellant-utilization efficiency compared to chemical rockets, this type of electric propulsion system may one day propel spacecraft on long-duration deep-space missions. High system reliability and electrical efficiency are extremely important for these extended missions. In the prototype pulsed-power system described here, exceptional reliability is achieved using a pulse-compression circuit driven by both active solid-state switching and passive magnetic switching. High efficiency is achieved using a novel ring architecture that recovers unused energy in a pulse-compression system with minimal circuit loss after each impulse. As an added benefit, voltage reversal is eliminated in the ring topology, resulting in long lifetimes for energy-storage capacitors. System tests were performed using an adjustable inductive load at a voltage level of 3.3 kV, a peak current of 20 kA, and a current switching rate of 15 kA/micros.

Electronic constant current and current pulse signal generator for nuclear instrumentation testing

DOEpatents

Brown, R.A.

1994-04-19

Circuitry is described for testing the ability of an intermediate range nuclear instrument to detect and measure a constant current and a periodic current pulse. The invention simulates the resistance and capacitance of the signal connection of a nuclear instrument ion chamber detector and interconnecting cable. An LED flasher/oscillator illuminates an LED at a periodic rate established by a timing capacitor and circuitry internal to the flasher/oscillator. When the LED is on, a periodic current pulse is applied to the instrument. When the LED is off, a constant current is applied. An inductor opposes battery current flow when the LED is on. 1 figures.

High current, high bandwidth laser diode current driver

NASA Technical Reports Server (NTRS)

Copeland, David J.; Zimmerman, Robert K., Jr.

1991-01-01

A laser diode current driver has been developed for free space laser communications. The driver provides 300 mA peak modulation current and exhibits an optical risetime of less than 400 ps. The current and optical pulses are well behaved and show minimal ringing. The driver is well suited for QPPM modulation at data rates up to 440 Mbit/s. Much previous work has championed current steering circuits; in contrast, the present driver is a single-ended on/off switch. This results in twice the power efficiency as a current steering driver. The driver electrical efficiency for QPPM data is 34 percent. The high speed switch is realized with a Ku-band GaAsFET transistor, with a suitable pre-drive circuit, on a hybrid microcircuit adjacent to the laser diode.

Understanding the molecular mechanism of pulse current charging for stable lithium-metal batteries

PubMed Central

Li, Qi; Tan, Shen; Li, Linlin; Lu, Yingying; He, Yi

2017-01-01

High energy and safe electrochemical storage are critical components in multiple emerging fields of technologies. Rechargeable lithium-metal batteries are considered to be promising alternatives for current lithium-ion batteries, leading to as much as a 10-fold improvement in anode storage capacity (from 372 to 3860 mAh g−1). One of the major challenges for commercializing lithium-metal batteries is the reliability and safety issue, which is often associated with uneven lithium electrodeposition (lithium dendrites) during the charging stage of the battery cycling process. We report that stable lithium-metal batteries can be achieved by simply charging cells with square-wave pulse current. We investigated the effects of charging period and frequency as well as the mechanisms that govern this process at the molecular level. Molecular simulations were performed to study the diffusion and the solvation structure of lithium cations (Li+) in bulk electrolyte. The model predicts that loose association between cations and anions can enhance the transport of Li+ and eventually stabilize the lithium electrodeposition. We also performed galvanostatic measurements to evaluate the cycling behavior and cell lifetime under pulsed electric field and found that the cell lifetime can be more than doubled using certain pulse current waveforms. Both experimental and simulation results demonstrate that the effectiveness of pulse current charging on dendrite suppression can be optimized by choosing proper time- and frequency-dependent pulses. This work provides a molecular basis for understanding the mechanisms of pulse current charging to mitigating lithium dendrites and designing pulse current waveforms for stable lithium-metal batteries. PMID:28776039

Versatile Stimulation Back-End With Programmable Exponential Current Pulse Shapes for a Retinal Visual Prosthesis.

PubMed

Maghami, Mohammad Hossein; Sodagar, Amir M; Sawan, Mohamad

2016-11-01

This paper reports on the design, implementation, and test of a stimulation back-end, for an implantable retinal prosthesis. In addition to traditional rectangular pulse shapes, the circuit features biphasic stimulation pulses with both rising and falling exponential shapes, whose time constants are digitally programmable. A class-B second generation current conveyor is used as a wide-swing, high-output-resistance stimulation current driver, delivering stimulation current pulses of up to ±96 μA to the target tissue. Duration of the generated current pulses is programmable within the range of 100 μs to 3 ms. Current-mode digital-to-analog converters (DACs) are used to program the amplitudes of the stimulation pulses. Fabricated using the IBM 130 nm process, the circuit consumes 1.5×1.5 mm 2 of silicon area. According to the measurements, the DACs exhibit DNL and INL of 0.23 LSB and 0.364 LSB, respectively. Experimental results indicate that the stimuli generator meets expected requirements when connected to electrode-tissue impedance of as high as 25 k Ω. Maximum power consumption of the proposed design is 3.4 mW when delivering biphasic rectangular pulses to the target load. A charge pump block is in charge of the upconversion of the standard 1.2-V supply voltage to ±3.3V.

Novel design of high voltage pulse source for efficient dielectric barrier discharge generation by using silicon diodes for alternating current.

PubMed

Truong, Hoa Thi; Hayashi, Misaki; Uesugi, Yoshihiko; Tanaka, Yasunori; Ishijima, Tatsuo

2017-06-01

This work focuses on design, construction, and optimization of configuration of a novel high voltage pulse power source for large-scale dielectric barrier discharge (DBD) generation. The pulses were generated by using the high-speed switching characteristic of an inexpensive device called silicon diodes for alternating current and the self-terminated characteristic of DBD. The operation started to be powered by a primary DC low voltage power supply flexibly equipped with a commercial DC power supply, or a battery, or DC output of an independent photovoltaic system without transformer employment. This flexible connection to different types of primary power supply could provide a promising solution for the application of DBD, especially in the area without power grid connection. The simple modular structure, non-control requirement, transformer elimination, and a minimum number of levels in voltage conversion could lead to a reduction in size, weight, simple maintenance, low cost of installation, and high scalability of a DBD generator. The performance of this pulse source has been validated by a load of resistor. A good agreement between theoretically estimated and experimentally measured responses has been achieved. The pulse source has also been successfully applied for an efficient DBD plasma generation.

Novel design of high voltage pulse source for efficient dielectric barrier discharge generation by using silicon diodes for alternating current

NASA Astrophysics Data System (ADS)

Truong, Hoa Thi; Hayashi, Misaki; Uesugi, Yoshihiko; Tanaka, Yasunori; Ishijima, Tatsuo

2017-06-01

This work focuses on design, construction, and optimization of configuration of a novel high voltage pulse power source for large-scale dielectric barrier discharge (DBD) generation. The pulses were generated by using the high-speed switching characteristic of an inexpensive device called silicon diodes for alternating current and the self-terminated characteristic of DBD. The operation started to be powered by a primary DC low voltage power supply flexibly equipped with a commercial DC power supply, or a battery, or DC output of an independent photovoltaic system without transformer employment. This flexible connection to different types of primary power supply could provide a promising solution for the application of DBD, especially in the area without power grid connection. The simple modular structure, non-control requirement, transformer elimination, and a minimum number of levels in voltage conversion could lead to a reduction in size, weight, simple maintenance, low cost of installation, and high scalability of a DBD generator. The performance of this pulse source has been validated by a load of resistor. A good agreement between theoretically estimated and experimentally measured responses has been achieved. The pulse source has also been successfully applied for an efficient DBD plasma generation.

Capacitively-coupled inductive sensors for measurements of pulsed currents and pulsed magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ekdahl, C.A.

In experiments involving pulsed high magnetic fields the appearance of the full induced voltage at the output terminals of large-area inductive sensors such as diamagnetic loops and Rogowski belts imposes severe requirements on the insulation near the output. Capacitive detection of the inductive-sensor output voltage provides an ideal geometry for high-voltage insulation, and also accomplishes the necessary voltage division. An inductive-shunt current monitor was designed to utilize the capacitive-detection principle. The contruction of this device and its performance are described in this paper.

Preparation of scanning tunneling microscopy tips using pulsed alternating current etching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valencia, Victor A.; Thaker, Avesh A.; Derouin, Jonathan

An electrochemical method using pulsed alternating current etching (PACE) to produce atomically sharp scanning tunneling microscopy (STM) tips is presented. An Arduino Uno microcontroller was used to control the number and duration of the alternating current (AC) pulses, allowing for ready optimization of the procedures for both Pt:Ir and W tips using a single apparatus. W tips prepared using constant and pulsed AC power were compared. Tips fashioned using PACE were sharper than those etched with continuous AC power alone. Pt:Ir tips were prepared with an initial coarse etching stage using continuous AC power followed by fine etching using PACE.more » The number and potential of the finishing AC pulses was varied and scanning electron microscope imaging was used to compare the results. Finally, tip quality using the optimized procedures was verified by UHV-STM imaging. With PACE, at least 70% of the W tips and 80% of the Pt:Ir tips were of sufficiently high quality to obtain atomically resolved images of HOPG or Ni(111)« less

Design of a High-Energy, Two-Stage Pulsed Plasma Thruster

NASA Technical Reports Server (NTRS)

Markusic, T. E.; Thio, Y. C. F.; Cassibry, J. T.; Rodgers, Stephen L. (Technical Monitor)

2002-01-01

Design details of a proposed high-energy (approx. 50 kJ/pulse), two-stage pulsed plasma thruster are presented. The long-term goal of this project is to develop a high-power (approx. 500 kW), high specific impulse (approx. 7500 s), highly efficient (approx. 50%),and mechanically simple thruster for use as primary propulsion in a high-power nuclear electric propulsion system. The proposed thruster (PRC-PPT1) utilizes a valveless, liquid lithium-fed thermal plasma injector (first stage) followed by a high-energy pulsed electromagnetic accelerator (second stage). A numerical circuit model coupled with one-dimensional current sheet dynamics, as well as a numerical MHD simulation, are used to qualitatively predict the thermal plasma injection and current sheet dynamics, as well as to estimate the projected performance of the thruster. A set of further modelling efforts, and the experimental testing of a prototype thruster, is suggested to determine the feasibility of demonstrating a full scale high-power thruster.

Emittance of short-pulsed high-current ion beams formed from the plasma of the electron cyclotron resonance discharge sustained by high-power millimeter-wave gyrotron radiation.

PubMed

Razin, S; Zorin, V; Izotov, I; Sidorov, A; Skalyga, V

2014-02-01

We present experimental results on measuring the emittance of short-pulsed (≤100 μs) high-current (80-100 mA) ion beams of heavy gases (Nitrogen, Argon) formed from a dense plasma of an ECR source of multiply charged ions (MCI) with quasi-gas-dynamic mode of plasma confinement in a magnetic trap of simple mirror configuration. The discharge was created by a high-power (90 kW) pulsed radiation of a 37.5-GHz gyrotron. The normalized emittance of generated ion beams of 100 mA current was (1.2-1.3) π mm mrad (70% of ions in the beams). Comparing these results with those obtained using a cusp magnetic trap, it was concluded that the structure of the trap magnetic field lines does not exert a decisive influence on the emittance of ion beams in the gas-dynamic ECR source of MCI.

High current table-top setup for femtosecond gas electron diffraction.

PubMed

Zandi, Omid; Wilkin, Kyle J; Xiong, Yanwei; Centurion, Martin

2017-07-01

We have constructed an experimental setup for gas phase electron diffraction with femtosecond resolution and a high average beam current. While gas electron diffraction has been successful at determining molecular structures, it has been a challenge to reach femtosecond resolution while maintaining sufficient beam current to retrieve structures with high spatial resolution. The main challenges are the Coulomb force that leads to broadening of the electron pulses and the temporal blurring that results from the velocity mismatch between the laser and electron pulses as they traverse the sample. We present here a device that uses pulse compression to overcome the Coulomb broadening and deliver femtosecond electron pulses on a gas target. The velocity mismatch can be compensated using laser pulses with a tilted intensity front to excite the sample. The temporal resolution of the setup was determined with a streak camera to be better than 400 fs for pulses with up to half a million electrons and a kinetic energy of 90 keV. The high charge per pulse, combined with a repetition rate of 5 kHz, results in an average beam current that is between one and two orders of magnitude higher than previously demonstrated.

Phenomenological Model of Current Sheet Canting in Pulsed Electromagnetic Accelerators

NASA Technical Reports Server (NTRS)

Markusic, Thomas; Choueiri, E. Y.

2003-01-01

The phenomenon of current sheet canting in pulsed electromagnetic accelerators is the departure of the plasma sheet (that carries the current) from a plane that is perpendicular to the electrodes to one that is skewed, or tipped. Review of pulsed electromagnetic accelerator literature reveals that current sheet canting is a ubiquitous phenomenon - occurring in all of the standard accelerator geometries. Developing an understanding of current sheet canting is important because it can detract from the propellant sweeping capabilities of current sheets and, hence, negatively impact the overall efficiency of pulsed electromagnetic accelerators. In the present study, it is postulated that depletion of plasma near the anode, which results from axial density gradient induced diamagnetic drift, occurs during the early stages of the discharge, creating a density gradient normal to the anode, with a characteristic length on the order of the ion skin depth. Rapid penetration of the magnetic field through this region ensues, due to the Hall effect, leading to a canted current front ahead of the initial current conduction channel. In this model, once the current sheet reaches appreciable speeds, entrainment of stationary propellant replenishes plasma in the anode region, inhibiting further Hall-convective transport of the magnetic field; however, the previously established tilted current sheet remains at a fairly constant canting angle for the remainder of the discharge cycle, exerting a transverse J x B force which drives plasma toward the cathode and accumulates it there. This proposed sequence of events has been incorporated into a phenomenological model. The model predicts that canting can be reduced by using low atomic mass propellants with high propellant loading number density; the model results are shown to give qualitative agreement with experimentally measured canting angle mass dependence trends.

Xenon excimer emission from pulsed high-pressure capillary microdischarges

NASA Astrophysics Data System (ADS)

Lee, Byung-Joon; Rahaman, Hasibur; Petzenhauser, Isfried; Frank, Klaus; Giapis, Konstantinos P.

2007-06-01

Intense xenon vacuum ultraviolet (VUV) emission is observed from a high-pressure capillary cathode microdischarge in direct current operation, by superimposing a high-voltage pulse of 50ns duration. Under stagnant gas conditions, the total VUV light intensity increases linearly with pressure from 400 to 1013mbar for a fixed voltage pulse. At fixed pressure, however, the VUV light intensity increases superlinearly with voltage pulse height ranging from 08to2.8kV. Gains in emission intensity are obtained by inducing gas flow through the capillary cathode, presumably because of excimer dimer survival due to gas cooling.

Emittance of short-pulsed high-current ion beams formed from the plasma of the electron cyclotron resonance discharge sustained by high-power millimeter-wave gyrotron radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Razin, S., E-mail: sevraz@appl.sci-nnov.ru; Zorin, V.; Izotov, I.

2014-02-15

We present experimental results on measuring the emittance of short-pulsed (≤100 μs) high-current (80–100 mA) ion beams of heavy gases (Nitrogen, Argon) formed from a dense plasma of an ECR source of multiply charged ions (MCI) with quasi-gas-dynamic mode of plasma confinement in a magnetic trap of simple mirror configuration. The discharge was created by a high-power (90 kW) pulsed radiation of a 37.5-GHz gyrotron. The normalized emittance of generated ion beams of 100 mA current was (1.2–1.3) π mm mrad (70% of ions in the beams). Comparing these results with those obtained using a cusp magnetic trap, it was concluded thatmore » the structure of the trap magnetic field lines does not exert a decisive influence on the emittance of ion beams in the gas-dynamic ECR source of MCI.« less

MOSFET-based high voltage short pulse generator for ultrasonic transducer excitation

NASA Astrophysics Data System (ADS)

Hidayat, Darmawan; Setianto, Syafei, Nendi Suhendi; Wibawa, Bambang Mukti

2018-02-01

This paper presents the generation of a high-voltage short pulse for the excitation of high frequency ultrasonic transducers. This is highly required in the purpose of various ultrasonic-based evaluations, particularly when high resolution measurement is necessary. A high voltage (+760 V) DC voltage source was pulsated by an ultrafast switching MOSFET which was driven by a pulse generator circuit consisting of an astable multivibrator, a one-shot multivibrator with Schmitt trigger input and a high current MOSFET driver. The generated pulses excited a 200-kHz and a 1-MHz ultrasonic transducers and tested in the transmission mode propagation to evaluate the performances of the generated pulse. The test results showed the generator were able to produce negative spike pulses up to -760 V voltage with the shortest time-width of 107.1 nanosecond. The transmission-received ultrasonic waves show frequency oscillation at 200 and 961 kHz and their amplitudes varied with the voltage of excitation pulse. These results conclude that the developed pulse generator is applicable to excite transducer for the generation of high frequency ultrasonic waves.

High field terahertz pulse generation from plasma wakefield driven by tailored laser pulses

NASA Astrophysics Data System (ADS)

Chen, Zi-Yu

2013-06-01

A scheme to generate high field terahertz (THz) pulses by using tailored laser pulses interaction with a gas target is proposed. The laser wakefield based THz source is emitted from the asymmetric laser shape induced plasma transverse transient net currents. Particle-in-cell simulations show that THz emission with electric filed strength over 1 GV/cm can be obtained with incident laser at 1×1019 W/cm2 level, and the corresponding energy conversion efficiency is more than 10-4. The intensity scaling holds up to high field strengths. Such a source also has a broad tunability range in amplitude, frequency spectra, and temporal shape.

High current table-top setup for femtosecond gas electron diffraction

DOE PAGES

Zandi, Omid; Wilkin, Kyle J.; Xiong, Yanwei; ...

2017-05-08

Here, we have constructed an experimental setup for gas phase electron diffraction with femtosecond resolution and a high average beam current. While gas electron diffraction has been successful at determining molecular structures, it has been a challenge to reach femtosecond resolution while maintaining sufficient beam current to retrieve structures with high spatial resolution. The main challenges are the Coulomb force that leads to broadening of the electron pulses and the temporal blurring that results from the velocity mismatch between the laser and electron pulses as they traverse the sample. We also present here a device that uses pulse compression tomore » overcome the Coulomb broadening and deliver femtosecond electron pulses on a gas target. The velocity mismatch can be compensated using laser pulses with a tilted intensity front to excite the sample. The temporal resolution of the setup was determined with a streak camera to be better than 400 fs for pulses with up to half a million electrons and a kinetic energy of 90 keV. Finally, the high charge per pulse, combined with a repetition rate of 5 kHz, results in an average beam current that is between one and two orders of magnitude higher than previously demonstrated.« less

Saturation of subjective reward magnitude as a function of current and pulse frequency.

PubMed

Simmons, J M; Gallistel, C R

1994-02-01

In rats with electrodes in the medial forebrain bundle, the upper portion of the function relating the experienced magnitude of the reward to pulse frequency was determined at currents ranging from 100 to 1,000 microA. The pulse frequency required to produce an asymptotic level of reward was inversely proportional to current except at the lowest currents and highest pulse frequencies. At a given current, the subjective reward magnitude functions decelerated to an asymptote over an interval in which the pulse frequency doubled or tripled. The asymptotic level of reward was approximately constant for currents between 200 and 1,000 microA but declined substantially at currents at or below 100 microA and pulse frequencies at or above 250 to 400 pulses per second. The results are consistent with the hypothesis that the magnitude of the experienced reward depends only on the number of action potentials generated by the train of pulses in the bundle of reward-relevant axons.

Forward voltage short-pulse technique for measuring high power laser array junction temperature

NASA Technical Reports Server (NTRS)

Meadows, Byron L. (Inventor); Amzajerdian, Frazin (Inventor); Barnes, Bruce W. (Inventor); Baker, Nathaniel R. (Inventor)

2012-01-01

The present invention relates to a method of measuring the temperature of the P-N junction within the light-emitting region of a quasi-continuous-wave or pulsed semiconductor laser diode device. A series of relatively short and low current monitor pulses are applied to the laser diode in the period between the main drive current pulses necessary to cause the semiconductor to lase. At the sufficiently low current level of the monitor pulses, the laser diode device does not lase and behaves similar to an electronic diode. The voltage across the laser diode resulting from each of these low current monitor pulses is measured with a high degree of precision. The junction temperature is then determined from the measured junction voltage using their known linear relationship.

High voltage pulse generator

DOEpatents

Fasching, George E.

1977-03-08

An improved high-voltage pulse generator has been provided which is especially useful in ultrasonic testing of rock core samples. An N number of capacitors are charged in parallel to V volts and at the proper instance are coupled in series to produce a high-voltage pulse of N times V volts. Rapid switching of the capacitors from the paralleled charging configuration to the series discharging configuration is accomplished by using silicon-controlled rectifiers which are chain self-triggered following the initial triggering of a first one of the rectifiers connected between the first and second of the plurality of charging capacitors. A timing and triggering circuit is provided to properly synchronize triggering pulses to the first SCR at a time when the charging voltage is not being applied to the parallel-connected charging capacitors. Alternate circuits are provided for controlling the application of the charging voltage from a charging circuit to be applied to the parallel capacitors which provides a selection of at least two different intervals in which the charging voltage is turned "off" to allow the SCR's connecting the capacitors in series to turn "off" before recharging begins. The high-voltage pulse-generating circuit including the N capacitors and corresponding SCR's which connect the capacitors in series when triggered "on" further includes diodes and series-connected inductors between the parallel-connected charging capacitors which allow sufficiently fast charging of the capacitors for a high pulse repetition rate and yet allow considerable control of the decay time of the high-voltage pulses from the pulse-generating circuit.

Electromagnetic pulse-driven spin-dependent currents in semiconductor quantum rings.

PubMed

Zhu, Zhen-Gang; Berakdar, Jamal

2009-04-08

We investigate the non-equilibrium charge and spin-dependent currents in a quantum ring with a Rashba spin-orbit interaction (SOI) driven by two asymmetric picosecond electromagnetic pulses. The equilibrium persistent charge and persistent spin-dependent currents are investigated as well. It is shown that the dynamical charge and the dynamical spin-dependent currents vary smoothly with a static external magnetic flux and the SOI provides a SU(2) effective flux that changes the phases of the dynamic charge and the dynamic spin-dependent currents. The period of the oscillation of the total charge current with the delay time between the pulses is larger in a quantum ring with a larger radius. The parameters of the pulse fields control to a certain extent the total charge and the total spin-dependent currents. The calculations are applicable to nanometre rings fabricated in heterojunctions of III-V and II-VI semiconductors containing several hundreds of electrons.

High-intensity pulsed beam source with tunable operation mode

NASA Astrophysics Data System (ADS)

Nashilevskiy, A. V.; Kanaev, G. G.; Ezhov, V. V.; Shamanin, V. I.

2017-05-01

The report presents the design of an electron and an ion pulsed accelerator. The powerful high-voltage pulse generator of the accelerator and the vacuum bushing insulator is able to change the polarity of the output voltage. The low-inductance matching transformer provides an increase in the DFL output impedance by 4 times. The generator based on a high voltage pulse transformer and a pseudo spark switch is applied for DFL charging. The high-impedance magnetically insulated focusing diode with Br magnetic field and the “passive” anode was used to realize the ion beam generation mode. The plasma is formed on the surface of the anode caused by an electrical breakdown at the voltage edge pulse; as a result, the carbon ion and proton beam is generated. This beam has the following parameters: the current density is about 400 A/cm2 (in focus): the applied voltage is up to 450 kV. The accelerator is designed for the research on the interaction of the charged particle pulsed beams with materials and for the development of technological processes of a material modification.

A Double-Pole High Voltage High Current Switch

DTIC Science & Technology

2005-12-01

NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS Approved for public release; distribution is unlimited A DOUBLE- POLE HIGH...December 2005 3. REPORT TYPE AND DATES COVERED Master’s Thesis 4. TITLE AND SUBTITLE: A Double- Pole High Voltage High Current Switch 6. AUTHOR(S...to divert heavy charged particles, e.g. Cu+. 15. NUMBER OF PAGES 68 14. SUBJECT TERMS Double- Pole , Pulse Forming Inductive Network, PFIN

Adjustable, High Voltage Pulse Generator with Isolated Output for Plasma Processing

NASA Astrophysics Data System (ADS)

Ziemba, Timothy; Miller, Kenneth E.; Prager, James; Slobodov, Ilia

2015-09-01

Eagle Harbor Technologies (EHT), Inc. has developed a high voltage pulse generator with isolated output for etch, sputtering, and ion implantation applications within the materials science and semiconductor processing communities. The output parameters are independently user adjustable: output voltage (0 - 2.5 kV), pulse repetition frequency (0 - 100 kHz), and duty cycle (0 - 100%). The pulser can drive loads down to 200 Ω. Higher voltage pulsers have also been tested. The isolated output allows the pulse generator to be connected to loads that need to be biased. These pulser generators take advantage modern silicon carbide (SiC) MOSFETs. These new solid-state switches decrease the switching and conduction losses while allowing for higher switching frequency capabilities. This pulse generator has applications for RF plasma heating; inductive and arc plasma sources; magnetron driving; and generation of arbitrary pulses at high voltage, high current, and high pulse repetition frequency. This work was supported in part by a DOE SBIR.

Control of Analyte Electrolysis in Electrospray Ionization Mass Spectrometry Using Repetitively Pulsed High Voltage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kertesz, Vilmos; Van Berkel, Gary J

2011-01-01

Analyte electrolysis using a repetitively pulsed high voltage ion source was investigated and compared to that using a regular, continuously operating direct current high voltage ion source in electrospray ionization mass spectrometry. The extent of analyte electrolysis was explored as a function of the length and frequency of the high voltage pulse using the model compound reserpine in positive ion mode. Using +5 kV as the maximum high voltage amplitude, reserpine was oxidized to its 2, 4, 6 and 8-electron oxidation products when direct current high voltage was employed. In contrast, when using a pulsed high voltage, oxidation of reserpinemore » was eliminated by employing the appropriate high voltage pulse length and frequency. This effect was caused by inefficient mass transport of the analyte to the electrode surface during the duration of the high voltage pulse and the subsequent relaxation of the emitter electrode/ electrolyte interface during the time period when the high voltage was turned off. This mode of ESI source operation allows for analyte electrolysis to be quickly and simply switched on or off electronically via a change in voltage pulse variables.« less

Effects of high-level pulse train stimulation on retinal function.

PubMed

Cohen, Ethan D

2009-06-01

We examined how stimulation of the local retina by high-level current pulse trains affected the light-evoked responses of the retinal ganglion cells. The spikes of retinal ganglion cell axons were recorded extracellularly using an in vitro eyecup preparation of the rabbit retina. Epiretinal electrical stimulation was delivered via a 500 microm inner diameter saline-filled, transparent tube positioned over the retinal surface forming the receptive field center. Spot stimuli were presented periodically to the receptive field center during the experiment. Trains of biphasic 1 ms current pulses were delivered to the retina at 50 Hz for 1 min. Pulse train charge densities of 1.3-442 microC/cm(2)/phase were examined. After pulse train stimulation with currents >or=300 microA (133 microC/cm(2)/phase), the ganglion cell's ability to respond to light was depressed and a significant time was required for recovery of the light-evoked response. During train stimulation, the ganglion cell's ability to spike following each current pulse fatigued. The current levels evoking train-evoked depression were suprathreshold to those evoking action potentials. Train-evoked depression was stronger touching the retinal surface, and in some cases impaired ganglion cell function for up to 30 min. This overstimulation could cause a transient refractory period for electrically stimulated perception in the retinal region below the electrode.

Alternating current circuit theory and pulsed NMR (Nuclear Magnetic Resonance)

NASA Astrophysics Data System (ADS)

Gerstein, B. C.

1987-06-01

Pulsed NMR, by definition, deals with time varying excitations. These excitations, supplied by resonant circuits which provide a pulse of radiofrequency (frequencies in the megahertz region) power to a resonant circuit containing, among other things, a coil of wire, or inductor, in which a sample under investigation is placed for purposes of the nuclear magnetic resonance experiment. There are therefore two features of the pulse NMR experiment. First is the fact that we have available a source of continuous wave (CW) alternating current at some angular frequency, omega, measured in radians per second. This source is generally supplied by an ultrastable device called a frequency synthesizer. The second feature of the pulsed NMR experiment is that the sample is not continuously irradiated, but a pulse of radiofrequency oscillation is applied to the sample. This report discusses alternating current theory, resonant circuits and the equipment used in this experiment.

Interface demarcation in GaAs by current pulsing

NASA Technical Reports Server (NTRS)

Matthiesen, D. H.; Kafalas, J. A.; Duchene, G. A.; Bellows, A. H.

1990-01-01

GTE Laboratories is currently conducting a program to investigate the effect of convection in the melt on the properties of bulk grown gallium arsenide (GaAs). In addition to extensive ground based experimentation, a Get Away Special growth system has been developed to grow two GaAs crystals aboard the Space Shuttle, each with a one inch diameter. In order to perform a complete segregation analysis of the crystals grown in space, it is necessary to measure the interface shape and growth rate as well as the spatial distribution of the selenium dopant. The techniques for interface demarcation in selenium doped GaAs by current pulsing have been developed at GTE Laboratories and successful interface demarcation has been achieved for current pulses ranging from 20 to 90 amps, in both single crystal and polycrystalline regions.

HIGH POWER PULSED OSCILLATOR

DOEpatents

Singer, S.; Neher, L.K.

1957-09-24

A high powered, radio frequency pulse oscillator is described for generating trains of oscillations at the instant an input direct voltage is impressed, or immediately upon application of a light pulse. In one embodiment, the pulse oscillator comprises a photo-multiplier tube with the cathode connected to the first dynode by means of a resistor, and adjacent dynodes are connected to each other through adjustable resistors. The ohmage of the resistors progressively increases from a very low value for resistors adjacent the cathode to a high value adjacent the plate, the last dynode. Oscillation occurs with this circuit when a high negative voltage pulse is applied to the cathode and the photo cathode is bombarded. Another embodiment adds capacitors at the resistor connection points of the above circuit to increase the duration of the oscillator train.

Pulsed-High Field/High-Frequency EPR Spectroscopy

NASA Astrophysics Data System (ADS)

Fuhs, Michael; Moebius, Klaus

Pulsed high-field/high-frequency electron paramagnetic resonance (EPR) spectroscopy is used to disentangle many kinds of different effects often obscured in continuous wave (cw) EPR spectra at lower magnetic fields/microwave frequencies. While the high magnetic field increases the resolution of G tensors and of nuclear Larmor frequencies, the high frequencies allow for higher time resolution for molecular dynamics as well as for transient paramagnetic intermediates studied with time-resolved EPR. Pulsed EPR methods are used for example for relaxation-time studies, and pulsed Electron Nuclear DOuble Resonance (ENDOR) is used to resolve unresolved hyperfine structure hidden in inhomogeneous linewidths. In the present article we introduce the basic concepts and selected applications to structure and mobility studies on electron transfer systems, reaction centers of photosynthesis as well as biomimetic models. The article concludes with an introduction to stochastic EPR which makes use of an other concept for investigating resonance systems in order to increase the excitation bandwidth of pulsed EPR. The limited excitation bandwidth of pulses at high frequency is one of the main limitations which, so far, made Fourier transform methods hardly feasible.

Broad-spectrum neodymium-doped laser glasses for high-energy chirped-pulse amplification.

PubMed

Hays, Greg R; Gaul, Erhard W; Martinez, Mikael D; Ditmire, Todd

2007-07-20

We have investigated two novel laser glasses in an effort to generate high-energy, broad-spectrum pulses from a chirped-pulse amplification Nd:glass laser. Both glasses have significantly broader spectra (>38 nm FWHM) than currently available Nd:phosphate and Nd:silicate glasses. We present calculations for small signal pulse amplification to simulate spectral gain narrowing. The technique of spectral shaping using mixed-glass architecture with an optical parametric chirped-pulse amplification front end is evaluated. Our modeling shows that amplified pulses with energies exceeding 10 kJ with sufficient bandwidth to achieve 120 fs pulsewidths are achievable with the use of the new laser glasses. With further development of current technologies, a laser system could be scaled to generate one exawatt in peak power.

Detailed characteristics of intermittent current pulses due to positive corona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yang, E-mail: liuyangwuh520@sina.com; Cui, Xiang; Lu, Tiebing

In order to get detailed characteristics of intermittent current pulses due to positive corona such as the repetition rate of burst-pulse trains, the peak value ratio of the primary pulse to the secondary pulse, the number of pulses per burst, and the interval of the secondary pulses, a systematic study was carried out in a coaxial conductor-cylinder electrode system with the conductor electrode being set with a discharge point. Empirical formulae for the number of pulses per burst and the interval of the secondary pulses are first presented. A theoretical model based on the motion of the space-charge clouds ismore » proposed. Analysis with the model gives explanations to the experimental results and reveals some new insights into the physical mechanism of positive intermittent corona.« less

Plasma heating and current drive using intense, pulsed microwaves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cohen, B.I.; Cohen, R.H.; Nevins, W.M.

1988-01-01

The use of powerful new microwave sources, e.g., free-electron lasers and relativistic gyrotrons, provide unique opportunities for novel heating and current-drive schemes in the electron-cyclotron and lower-hybrid ranges of frequencies. These high-power, pulsed sources have a number of technical advantages over conventional, low-intensity sources; and their use can lead to improved current-drive efficiencies and better penetration into a reactor-grade plasma in specific cases. The Microwave Tokamak Experiment at Lawrence Livermore National Laboratory will provide a test for some of these new heating and current-drive schemes. This paper reports theoretical progress both in modeling absorption and current drive for intense pulsesmore » and in analyzing some of the possible complications that may arise, e.g., parametric instabilities and nonlinear self-focusing. 22 refs., 9 figs., 1 tab.« less

Enabling cost-effective high-current burst-mode operation in superconducting accelerators

DOE PAGES

Sheffield, Richard L.

2015-06-01

Superconducting (SC) accelerators are very efficient for CW or long-pulse operation, and normal conducting (NC) accelerators are cost effective for short-pulse operation. The addition of a short NC linac section to a SC linac can correct for the energy droop that occurs when pulsed high-current operation is required that exceeds the capability of the klystrons to replenish the cavity RF fields due to the long field fill-times of SC structures, or a requirement to support a broad range of beam currents results in variable beam loading. This paper describes the implementation of this technique to enable microseconds of high beam-current,more » 90 mA or more, in a 12 GeV SC long-pulse accelerator designed for the MaRIE 42-keV XFEL proposed for Los Alamos National Laboratory.« less

Apparatus for producing voltage and current pulses

DOEpatents

Kirbie, Hugh; Dale, Gregory E.

2010-12-21

An apparatus having one or more modular stages for producing voltage and current pulses. Each module includes a diode charging means to charge a capacitive means that stores energy. One or more charging impedance means are connected to the diode charging means to provide a return current pathway. A solid-state switch discharge means, with current interruption capability, is connected to the capacitive means to discharge stored energy. Finally, a control means is provided to command the switching action of the solid-state switch discharge means.

Cranial electrotherapy stimulation and transcranial pulsed current stimulation: a computer based high-resolution modeling study.

PubMed

Datta, Abhishek; Dmochowski, Jacek P; Guleyupoglu, Berkan; Bikson, Marom; Fregni, Felipe

2013-01-15

The field of non-invasive brain stimulation has developed significantly over the last two decades. Though two techniques of noninvasive brain stimulation--transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS)--are becoming established tools for research in neuroscience and for some clinical applications, related techniques that also show some promising clinical results have not been developed at the same pace. One of these related techniques is cranial electrotherapy stimulation (CES), a class of transcranial pulsed current stimulation (tPCS). In order to understand further the mechanisms of CES, we aimed to model CES using a magnetic resonance imaging (MRI)-derived finite element head model including cortical and also subcortical structures. Cortical electric field (current density) peak intensities and distributions were analyzed. We evaluated different electrode configurations of CES including in-ear and over-ear montages. Our results confirm that significant amounts of current pass the skull and reach cortical and subcortical structures. In addition, depending on the montage, induced currents at subcortical areas, such as midbrain, pons, thalamus and hypothalamus are of similar magnitude than that of cortical areas. Incremental variations of electrode position on the head surface also influence which cortical regions are modulated. The high-resolution modeling predictions suggest that details of electrode montage influence current flow through superficial and deep structures. Finally we present laptop based methods for tPCS dose design using dominant frequency and spherical models. These modeling predictions and tools are the first step to advance rational and optimized use of tPCS and CES. Copyright © 2012 Elsevier Inc. All rights reserved.

Surface microstructure and high temperature corrosion resistance of arc-sprayed FeCrAl coating irradiated by high current pulsed electron beam

NASA Astrophysics Data System (ADS)

Hao, Shengzhi; Zhao, Limin; He, Dongyun

2013-10-01

The surface microstructure of arc-sprayed FeCrAl coating irradiated by high current pulsed electron beam (HCPEB) with long pulse duration of 200 μs was characterized by using optical microscopy, scanning electron microscopy and X-ray diffractometry. The distribution of chemical composition in modified surface layer was measured with electron probe micro-analyzer. The high temperature corrosion resistance of FeCrAl coating was tested in a saturated Na2SO4 and K2SO4 solution at 650 °C. After HCPEB irradiation, the coarse surface of arc-sprayed coating was changed as discrete bulged nodules with smooth and compact appearance. When using low energy density of 20 J/cm2, the surface modified layer was continuous entirely with an average melting depth of ˜30 μm. In the surface remelted layer, Fe and Cr elements gave a uniform distribution, while Al and O elements agglomerated particularly at the concave part between nodule structures to form α-Al2O3 phase. After high temperature corrosion tests, the FeCrAl coating treated with HCPEB of 20 J/cm2 remained a glossy surface with weight increment of ˜51 mg/cm2, decreased by 20% as compared to the initial sample. With the increasing energy density of HCPEB irradiation, the integrity of surface modified layer got segmented due to the formation of larger bulged nodules and cracks at the concave parts. For the HCPEB irradiation of 40 J/cm2, the high temperature corrosion resistance of FeCrAl coating was deteriorated drastically.

Analysis of Current Pulses in HeLa-Cell Permeabilization Due to High Voltage DC Corona Discharge.

PubMed

Chetty, Nevendra K; Chonco, Louis; Ijumba, Nelson M; Chetty, Leon; Govender, Thavendran; Parboosing, Raveen; Davidson, Innocent E

2016-09-01

Corona discharges are commonly utilized for numerous practical applications, including bio-technological ones. The corona induced transfer of normally impermeant molecules into the interior of biological cells has recently been successfully demonstrated. The exact nature of the interaction of the corona discharge with a cell membrane is still unknown, however, previous studies have suggested that it is either the electric fields produced by ions or the chemical interaction of the reactive species that result in the disruption of the cell membrane. This disruption of the cell membrane allows molecules to permeate into the cell. Corona discharge current constitutes a series of pulses, and it is during these pulses that the ions and reactive species are produced. It stands to reason, therefore, that the nature of these corona pulses would have an influence on the level of cell permeabilization and cell destruction. In this investigation, an analysis of the width, rise-time, characteristic frequencies, magnitude, and repetition rate of the nanosecond pulses was carried out in order to establish the relationship between these factors and the levels of cell membrane permeabilization and cell destruction. Results obtained are presented and discussed.

Laminar iridium coating produced by pulse current electrodeposition from chloride molten salt

NASA Astrophysics Data System (ADS)

Zhu, Li'an; Bai, Shuxin; Zhang, Hong; Ye, Yicong

2013-10-01

Due to the unique physical and chemical properties, Iridium (Ir) is one of the most promising oxidation-resistant coatings for refractory materials above 1800 °C in aerospace field. However, the Ir coatings prepared by traditional methods are composed of columnar grains throughout the coating thickness. The columnar structure of the coating is considered to do harm to its oxidation resistance. The laminar Ir coating is expected to have a better high-temperature oxidation resistance than the columnar Ir coating does. The pulse current electrodeposition, with three independent parameters: average current density (Jm), duty cycle (R) and pulse frequency (f), is considered to be a promising method to fabricate layered Ir coating. In this study, laminar Ir coatings were prepared by pulse current electrodeposition in chloride molten salt. The morphology, roughness and texture of the coatings were determined by scanning electron microscope (SEM), profilometer and X-ray diffraction (XRD), respectively. The results showed that the laminar Ir coatings were composed of a nucleation layer with columnar structure and a growth layer with laminar structure. The top surfaces of the laminar Ir coatings consisted of cauliflower-like aggregates containing many fine grains, which were separated by deep grooves. The laminar Ir coating produced at the deposition condition of 20 mA/cm2 (Jm), 10% (R) and 6 Hz (f) was quite smooth (Ra 1.01 ± 0.09 μm) with extremely high degree of preferred orientation of <1 1 1>, and its laminar structure was well developed with clear boundaries and uniform thickness of sub-layers.

High frequency pulsed electromigration

NASA Astrophysics Data System (ADS)

Malone, David Wayne

Electromigration life tests were performed on copper-alloyed aluminum test structures that were representative of modern CMOS metallization schemes, complete with Ti/TiN cladding layers and a tungsten-plug contact at the cathode. A total of 18 electrical stress treatments were applied. One was a DC current of 15 mA. The other 17 were pulsed currents, varied according to duty cycle and frequency. The pulse amplitude was 15 mA (˜2.7 × 10sp6 A/cmsp2) for all treatments. Duty cycles ranged from 33.3% to 80%, and frequencies fell into three rough ranges-100 KHz, 1 MHz, and 100 MHz. The ambient test temperature was 200sp°C in all experiments. Six to 9 samples were subjected to each treatment. Experimental data were gathered in the form of test stripe resistance versus time, R(t). For purposes of lifetime analysis, "failure" was defined by the criterion R(t)/R(0) = 1.10, and the median time to failure, tsb{50}, was used as the primary basis of comparison between test groups. It was found that the dependence of tsb{50} on pulse duty cycle conformed rather well to the so-called "average current density model" for duty cycles of 50% and higher. Lifetimes were less enhanced for a duty cycle of 33.3%, but they were still considerably longer than an "on-time" model would predict. No specific dependence of tsb{50} on pulse frequency was revealed by the data, that is, reasonably good predictions of tsb{50} could be made by recognizing the dominant influence of duty cycle. These findings confirm that IC miniaturization can be more aggressively pursued than an on-time prediction would allow. It is significant that this was found to be true for frequencies on the order of 100 MHz, where many present day digital applications operate. Post-test optical micrographs were obtained for each test subject in order to determine the location of electromigration damage. The pulse duty cycle was found to influence the location. Most damage occurred at the cathode contact, regardless of

Featuring of transient tunneling current by voltage pulse and application to an electrochemical biosensor

NASA Astrophysics Data System (ADS)

Yun, Jun Yeon; Lee, Won Cheol; Choi, Seong Wook; Park, Young June

2018-03-01

We suggest a voltage pulse method for detecting the transient tunneling current component (faradaic current component) in a metal/redox-active monolayer/electrolyte system. After applying the pulse to the metal electrode, the capacitive current prevails; therefore, it is difficult to extract the tunneling current, which carries information on the biochemical reactions occurring between the biomarkers in the electrolyte and the self-assembled monolayer (SAM) as the probe peptide system. Instead of waiting until the capacitive current diminishes, and thereby, the tunneling current also decreases, we try to extract the tunneling current in an early stage of the pulse. The method is based on the observation that the capacitive current becomes symmetrized in the positive and negative pulses after introducing the SAM on the metal electrode. When the energy level of the redox molecule is higher than the Fermi level of the metal under zero-bias condition, the tunneling current in the negative pulse can be extracted by subtracting the capacitive current obtained from the positive pulse, where the tunneling current is neglected. The experiment conducted for detecting trypsin as a biomarker shows that the method enhances the sensitivity and the specific-to-nonspecific ratio of the sensor device in the case of the nonspecific protein-abundant electrolyte solution, as evinced by cyclic voltammetry measurements in comparison.

Wavelength stabilized high pulse power laser diodes for automotive LiDAR

NASA Astrophysics Data System (ADS)

Knigge, A.; Klehr, A.; Wenzel, H.; Zeghuzi, A.; Fricke, J.; Maaßdorf, A.; Liero, A.; Tränkle, G.

2018-03-01

Diode lasers generating optical pulses with high peak power and lengths in the nanosecond range are key components of systems for free-space communication, metrology, material processing, spectroscopy, and light detection and ranging (LiDAR) as needed for object detection and autonomous driving. Automotive LiDAR systems demand additionally a good beam quality and low wavelength shift with temperature due to the wide operating temperature span. We present here internally wavelength stabilized lasers emitting ns optical pulses from an emission aperture between 30 μm and 100 μm with peak powers of tens of Watts at wavelengths around 905 nm. The vertical structure based on AlGaAs (confinement and cladding layers) and InGaAs (active quantum well) is especially optimized for pulsed operation with respect to the implementation of a surface Bragg grating with a high reflectivity. The fabricated 6 mm long distributed Bragg reflector (DBR) broad area (BA) lasers are electrically driven by an in-house developed high-speed unit generating 3 to 10 ns long nearly rectangular shaped current pulses with amplitudes of up to 250 A. Such lasers emit optical pulses with a peak power of more than 30 W at 95 A pulse current up to a temperature of 85°C with a wavelength shift as low as 65 pm/K and a lateral beam propagation factor less than 10. The influence of the lateral aperture width and the pulse length on the beam quality will be shown. A monolithic integration of 3 DBR BA lasers on a single chip whose emission can be combined into a single beam raises the output power to more than 100 W.

High voltage pulse conditioning

DOEpatents

Springfield, Ray M.; Wheat, Jr., Robert M.

1990-01-01

Apparatus for conditioning high voltage pulses from particle accelerators in order to shorten the rise times of the pulses. Flashover switches in the cathode stalk of the transmission line hold off conduction for a determinable period of time, reflecting the early portion of the pulses. Diodes upstream of the switches divert energy into the magnetic and electrostatic storage of the capacitance and inductance inherent to the transmission line until the switches close.

Comparison between Trichel pulse in negative corona and self-pulsing in other configurations

NASA Astrophysics Data System (ADS)

Xia, Qing; Zhang, Yu; He, Feng; Qin, Yu; Jiang, Zhaorui; Ouyang, Jiting

2018-02-01

We present here a comparison study on self-pulsing phenomena in negative corona, hollow cathode discharges (HCD) and parallel-plate discharge in air. The voltage-current (V-I) curve, the waveforms of self-pulsed currents, and the time-resolved images of the pulsed discharge are measured under various operating conditions. It is experimentally evidenced that the Trichel pulse in a negative corona and the self-pulsing in HCD and/or parallel-plate discharge have similar features as well as spatial-temporal developing process. It is suggested that they should have a similar mechanism that the pulsing reflects the mode transition of discharge between the low-current Townsend and the high-current normal glow. The pulse rising corresponds to the breakdown and formation of temporal glow discharge in a background of low-current Townsend discharge, while the decay edge relates to the transition back to Townsend discharge. The pulse interval is the re-building process of the space charge layer of high density to ensure the glow breakdown.

A new model for volume recombination in plane-parallel chambers in pulsed fields of high dose-per-pulse

NASA Astrophysics Data System (ADS)

Gotz, M.; Karsch, L.; Pawelke, J.

2017-11-01

In order to describe the volume recombination in a pulsed radiation field of high dose-per-pulse this study presents a numerical solution of a 1D transport model of the liberated charges in a plane-parallel ionization chamber. In addition, measurements were performed on an Advanced Markus ionization chamber in a pulsed electron beam to obtain suitable data to test the calculation. The experiment used radiation pulses of 4 μs duration and variable dose-per-pulse values up to about 1 Gy, as well as pulses of variable duration up to 308 μs at constant dose-per-pulse values between 85 mGy and 400 mGy. Those experimental data were compared to the developed numerical model and existing descriptions of volume recombination. At low collection voltages the observed dose-per-pulse dependence of volume recombination can be approximated by the existing theory using effective parameters. However, at high collection voltages large discrepancies are observed. The developed numerical model shows much better agreement with the observations and is able to replicate the observed behavior over the entire range of dose-per-pulse values and collection voltages. Using the developed numerical model, the differences between observation and existing theory are shown to be the result of a large fraction of the charge being collected as free electrons and the resultant distortion of the electric field inside the chamber. Furthermore, the numerical solution is able to calculate recombination losses for arbitrary pulse durations in good agreement with the experimental data, an aspect not covered by current theory. Overall, the presented numerical solution of the charge transport model should provide a more flexible tool to describe volume recombination for high dose-per-pulse values as well as for arbitrary pulse durations and repetition rates.

A new model for volume recombination in plane-parallel chambers in pulsed fields of high dose-per-pulse.

PubMed

Gotz, M; Karsch, L; Pawelke, J

2017-11-01

In order to describe the volume recombination in a pulsed radiation field of high dose-per-pulse this study presents a numerical solution of a 1D transport model of the liberated charges in a plane-parallel ionization chamber. In addition, measurements were performed on an Advanced Markus ionization chamber in a pulsed electron beam to obtain suitable data to test the calculation. The experiment used radiation pulses of 4 μs duration and variable dose-per-pulse values up to about 1 Gy, as well as pulses of variable duration up to 308 [Formula: see text] at constant dose-per-pulse values between 85 mGy and 400 mGy. Those experimental data were compared to the developed numerical model and existing descriptions of volume recombination. At low collection voltages the observed dose-per-pulse dependence of volume recombination can be approximated by the existing theory using effective parameters. However, at high collection voltages large discrepancies are observed. The developed numerical model shows much better agreement with the observations and is able to replicate the observed behavior over the entire range of dose-per-pulse values and collection voltages. Using the developed numerical model, the differences between observation and existing theory are shown to be the result of a large fraction of the charge being collected as free electrons and the resultant distortion of the electric field inside the chamber. Furthermore, the numerical solution is able to calculate recombination losses for arbitrary pulse durations in good agreement with the experimental data, an aspect not covered by current theory. Overall, the presented numerical solution of the charge transport model should provide a more flexible tool to describe volume recombination for high dose-per-pulse values as well as for arbitrary pulse durations and repetition rates.

Conversion of continuous-direct-current TIG welder to pulse-arc operation

NASA Technical Reports Server (NTRS)

Lien, D. R.

1969-01-01

Electronics package converts a continuous-dc tungsten-inert gas welder for pulse-arc operation. Package allows presetting of the pulse rate, duty cycle, and current value, and enables welding of various alloys and thicknesses of materials.

Transmission line pulse system for avalanche characterization of high power semiconductor devices

NASA Astrophysics Data System (ADS)

Riccio, Michele; Ascione, Giovanni; De Falco, Giuseppe; Maresca, Luca; De Laurentis, Martina; Irace, Andrea; Breglio, Giovanni

2013-05-01

Because of the increasing in power density of electronic devices for medium and high power application, reliabilty of these devices is of great interest. Understanding the avalanche behaviour of a power device has become very important in these last years because it gives an indication of the maximum energy ratings which can be seen as an index of the device ruggedness. A good description of this behaviour is given by the static IV blocking characteristc. In order to avoid self heating, very relevant in high power devices, very short pulses of current have to be used, whose value can change from few milliamps up to tens of amps. The most used method to generate short pulses is the TLP (Transmission Line Pulse) test, which is based on charging the equivalent capacitance of a transmission line to high value of voltage and subsequently discharging it onto a load. This circuit let to obtain very short square pulses but it is mostly used for evaluate the ESD capability of semiconductor and, in this environment, it generates pulses of low amplitude which are not high enough to characterize the avalanche behaviour of high power devices . Advanced TLP circuit able to generate high current are usually very expensive and often suffer of distorption of the output pulse. In this article is proposed a simple, low cost circuit, based on a boosted-TLP configuration, which is capable to produce very square pulses of about one hundreds of nanosecond with amplitude up to some tens of amps. A prototype is implemented which can produce pulses up to 20A of amplitude with 200 ns of duration which can characterize power devices up to 1600V of breakdown voltage. Usage of microcontroller based logic make the circuit very flexible. Results of SPICE simulation are provided, together with experimental results. To prove the effectiveness of the circuit, the I-V blocking characteristics of two commercial devices, namely a 600V PowerMOS and a 1200V Trench-IGBT, are measured at different

Active cooling of pulse compression diffraction gratings for high energy, high average power ultrafast lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alessi, David A.; Rosso, Paul A.; Nguyen, Hoang T.

Laser energy absorption and subsequent heat removal from diffraction gratings in chirped pulse compressors poses a significant challenge in high repetition rate, high peak power laser development. In order to understand the average power limitations, we have modeled the time-resolved thermo-mechanical properties of current and advanced diffraction gratings. We have also developed and demonstrated a technique of actively cooling Petawatt scale, gold compressor gratings to operate at 600W of average power - a 15x increase over the highest average power petawatt laser currently in operation. As a result, combining this technique with low absorption multilayer dielectric gratings developed in ourmore » group would enable pulse compressors for petawatt peak power lasers operating at average powers well above 40kW.« less

Active cooling of pulse compression diffraction gratings for high energy, high average power ultrafast lasers

DOE PAGES

Alessi, David A.; Rosso, Paul A.; Nguyen, Hoang T.; ...

2016-12-26

Laser energy absorption and subsequent heat removal from diffraction gratings in chirped pulse compressors poses a significant challenge in high repetition rate, high peak power laser development. In order to understand the average power limitations, we have modeled the time-resolved thermo-mechanical properties of current and advanced diffraction gratings. We have also developed and demonstrated a technique of actively cooling Petawatt scale, gold compressor gratings to operate at 600W of average power - a 15x increase over the highest average power petawatt laser currently in operation. As a result, combining this technique with low absorption multilayer dielectric gratings developed in ourmore » group would enable pulse compressors for petawatt peak power lasers operating at average powers well above 40kW.« less

Extremely High Peak Power Obtained at 29 GHZ Microwave Pulse Generation

NASA Astrophysics Data System (ADS)

Rostov, V. V.; Gunin, A. V.; Romanchenko, I. V.; Pedos, M. S.; Rukin, S. N.; Sharypov, K. A.; Shunailov, S. A.; Ul'maskulov, M. R.; Yalandin, M. I.

2017-12-01

The paper presents research results on enhancing the peak power of microwave pulses with sub- and nanosecond length using a backward-wave oscillator (BWO) operating at 29 GHz frequency and possessing a reproducible phase structure. Experiments are conducted in two modes on a high-current electron accelerator with the required electron beam power. In the first (superradiation) mode, which utilizes the elongated slow-wave structure, the BWO peak power is 3 GW at 180 ns pulse duration (full width at halfmaximum, FWHM). In the second (quasi-stationary) mode, the BWO peak power reaches 600 MW at 2 ns pulse duration (FWHM). The phase spread from pulse to pulse can vary from units to several tens of percent in a nanosecond pulse mode. The experiments do not show any influence of microwave breakdown on the BWO power generation and radiation pulse duration.

Very Fast Current Diagnostic for Linear Pulsed Beams

NASA Astrophysics Data System (ADS)

Nassisi, Vincenzo; Delle Side, Domenico; Turco, Vito

2018-01-01

Fast current pulses manage lasers and particle accelerators and require sophisticate systems to be detected. At today Rogowski coils are well known. They are designed and built with a toroidal structure. In recently application, flat transmission lines are imploded and for this reason we develop a linear Rogowski coil to detect current pulses inside flat conductors. To get deep information from the system, it was approached by means of the theory of the transmission lines. The coil we build presents a resistance but it doesn't influence the rise time of the response, instead the integrating time. We also studied the influence of the magnetic properties of coil support. The new device was able to record pulses of more hundred nanoseconds depending on the inductance, load impedance and resistance of the coil. Furthermore, its response was characterized by a sub-nanosecond rise time ( 100 ps), The attenuation coefficient depends mainly on the turn number of the coil, while the quality of the response depends both on the manufacture quality of the coil and on the magnetic core characteristics. In biophysical applications often, a double line is employed in order to have a sample as control and a sample stressed by a light source. So, in this case we build two equal plane lines by 100 Ω characteristic resistance connected in parallel. We diagnosed the current present in a line. The attenuation factor resulted to be 11,5 A/V.

[Atomic/ionic fluorescence in microwave plasma torch discharge with excitation of high current and microsecond pulsed hollow cathode lamp: Ca atomic/ionic fluorescence spectrometry].

PubMed

Gong, Zhen-bin; Liang, Feng; Yang, Peng-yuan; Jin, Qin-han; Huang, Ben-li

2002-02-01

A system of atomic and ionic fluorescence spectrometry in microwave plasma torch (MPT) discharge excited by high current microsecond pulsed hollow cathode lamp (HCMP HCL) has been developed. The operation conditions for Ca atomic and ionic fluorescence spectrometry have been optimized. Compared with atomic fluorescence spectrometry (AFS) in argon microwave induced plasma (MIP) and MPT with the excitation of direct current and conventional pulsed HCL, the system with HCMP HCL excitation can improve AFS and ionic fluorescence spectrometry (IFS) detection limits in MPT atomizer and ionizer. Detection limits (3 sigma) with HCMP HCL-MPT-AFS/IFS are 10.1 ng.mL-1 for Ca I 422.7 nm, 14.6 ng.mL-1 for Ca II 393.4 nm, and 37.4 ng.mL-1 for Ca II 396.8 nm, respectively.

Considerations for human exposure standards for fast-rise-time high-peak-power electromagnetic pulses.

PubMed

Merritt, J H; Kiel, J L; Hurt, W D

1995-06-01

Development of new emitter systems capable of producing high-peak-power electromagnetic pulses with very fast rise times and narrow pulse widths is continuing. Such directed energy weapons systems will be used in the future to defeat electronically vulnerable targets. Human exposures to these pulses can be expected during testing and operations. Development of these technologies for radar and communications purposes has the potential for wider environmental exposure, as well. Current IEEE C95.1-1991 human exposure guidelines do not specifically address these types of pulses, though limits are stated for pulsed emissions. The process for developing standards includes an evaluation of the relevant bioeffects data base. A recommendation has been made that human exposure to ultrashort electromagnetic pulses that engender electromagnetic transients, called precursor waves, should be avoided. Studies that purport to show the potential for tissue damage induced by such pulses were described. The studies cited in support of the recommendation were not relevant to the issues of tissue damage by propagated pulses. A number of investigations are cited in this review that directly address the biological effects of electromagnetic pulses. These studies have not shown evidence of tissue damage as a result of exposure to high-peak-power pulsed microwaves. It is our opinion that the current guidelines are sufficiently protective for human exposure to these pulses.

Retarding field energy analyzer for high energy pulsed electron beam measurements.

PubMed

Hu, Jing; Rovey, Joshua L; Zhao, Wansheng

2017-01-01

A retarding field energy analyzer (RFEA) designed specifically for high energy pulsed electron beam measurements is described in this work. By proper design of the entrance grid, attenuation grid, and beam collector, this RFEA is capable of determining the time-resolved energy distribution of high energy pulsed electron beams normally generated under "soft vacuum" environment. The performance of the RFEA is validated by multiple tests of the leakage current, attenuation coefficient, and response time. The test results show that the retarding potential in the RFEA can go up to the same voltage as the electron beam source, which is 20 kV for the maximum in this work. Additionally, an attenuation coefficient of 4.2 is obtained in the RFEA while the percent difference of the rise time of the electron beam pulse before and after attenuation is lower than 10%. When compared with a reference source, the percent difference of the RFEA response time is less than 10% for fall times greater than 35 ns. Finally, the test results of the 10 kV pseudospark-based pulsed electron beam currents collected under varying retarding potentials are presented in this paper.

Fast Rise Time and High Voltage Nanosecond Pulses at High Pulse Repetition Frequency

NASA Astrophysics Data System (ADS)

Miller, Kenneth E.; Ziemba, Timothy; Prager, James; Picard, Julian; Hashim, Akel

2015-09-01

Eagle Harbor Technologies (EHT), Inc. is conducting research to decrease the rise time and increase the output voltage of the EHT Nanosecond Pulser product line, which allows for independently, user-adjustable output voltage (0 - 20 kV), pulse width (20 - 500 ns), and pulse repetition frequency (0 - 100 kHz). The goals are to develop higher voltage pulses (50 - 60 kV), decrease the rise time from 20 to below 10 ns, and maintain the high pulse repetition capabilities. These new capabilities have applications to pseudospark generation, corona production, liquid discharges, and nonlinear transmission line driving for microwave production. This work is supported in part by the US Navy SBIR program.

Theory of step on leading edge of negative corona current pulse

NASA Astrophysics Data System (ADS)

Gupta, Deepak K.; Mahajan, Sangeeta; John, P. I.

2000-03-01

Theoretical models taking into account different feedback source terms (e.g., ion-impact electron emission, photo-electron emission, field emission, etc) have been proposed for the existence and explanation of the shape of negative corona current pulse, including the step on the leading edge. In the present work, a negative corona current pulse with the step on the leading edge is obtained in the presence of ion-impact electron emission feedback source only. The step on the leading edge is explained in terms of the plasma formation process and enhancement of the feedback source. Ionization wave-like movement toward the cathode is observed after the step. The conditions for the existence of current pulse, with and without the step on the leading edge, are also described. A qualitative comparison with earlier theoretical and experimental work is also included.

Isolated terawatt attosecond hard X-ray pulse generated from single current spike.

PubMed

Shim, Chi Hyun; Parc, Yong Woon; Kumar, Sandeep; Ko, In Soo; Kim, Dong Eon

2018-05-10

Isolated terawatt (TW) attosecond (as) hard X-ray pulse is greatly desired for four-dimensional investigations of natural phenomena with picometer spatial and attosecond temporal resolutions. Since the demand for such sources is continuously increasing, the possibility of generating such pulse by a single current spike without the use of optical or electron delay units in an undulator line is addressed. The conditions of a current spike (width and height) and a modulation laser pulse (wavelength and power) is also discussed. We demonstrate that an isolated TW-level as a hard X-ray can be produced by a properly chosen single current spike in an electron bunch with simulation results. By using realistic specifications of an electron bunch of the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), we show that an isolated, >1.0 TW and ~36 as X-ray pulse at 12.4 keV can be generated in an optimized-tapered undulator line. This result opens a new vista for current XFEL operation: the attosecond XFEL.

Optimization of a Two Stage Pulse Tube Refrigerator for the Integrated Current Lead System

NASA Astrophysics Data System (ADS)

Maekawa, R.; Matsubara, Y.; Okada, A.; Takami, S.; Konno, M.; Tomioka, A.; Imayoshi, T.; Hayashi, H.; Mito, T.

2008-03-01

Implementation of a conventional current lead with a pulse tube refrigerator has been validated to be working as an Integrated Current Lead (ICL) system for the Superconducting Magnetic Energy Storage (SMES). Realization of the system is primarily accounted for the flexibility of a pulse tube refrigerator, which does not posses any mechanical piston and/or displacer. As for an ultimate version of the ICL system, a High Temperature Superconducting (HTS) lead links a superconducting coil with a conventional copper lead. To ensure the minimization of heat loads to the superconducting coil, a pulse tube refrigerator has been upgraded to have a second cooling stage. This arrangement reduces not only the heat loads to the superconducting coil but also the operating cost for a SMES system. A prototype two-stage pulse tube refrigerator, series connected arrangement, was designed and fabricated to satisfy the requirements for the ICL system. Operation of the first stage refrigerator is a four-valve mode, while the second stage utilizes a double inlet configuration to ensure its confined geometry. The paper discusses the optimization of second stage cooling to validate the conceptual design

The detailed characteristics of positive corona current pulses in the line-to-plane electrodes

NASA Astrophysics Data System (ADS)

Xuebao, LI; Dayong, LI; Qian, ZHANG; Yinfei, LI; Xiang, CUI; Tiebing, LU

2018-05-01

The corona current pulses generated by corona discharge are the sources of the radio interference from transmission lines and the detailed characteristics of the corona current pulses from conductor should be investigated in order to reveal their generation mechanism. In this paper, the line-to-plane electrodes are designed to measure and analyze the characteristics of corona current pulses from positive corona discharges. The influences of inter-electrode gap and line diameters on the detail characteristics of corona current pulses, such as pulse amplitude, rise time, duration time and repetition frequency, are carefully analyzed. The obtained results show that the pulse amplitude and the repetition frequency increase with the diameter of line electrode when the electric fields on the surface of line electrodes are same. With the increase of inter-electrode gap, the pulse amplitude and the repetition frequency first decrease and then turn to be stable, while the rise time first increases and finally turns to be stable. The distributions of electric field and space charges under the line electrodes are calculated, and the influences of inter-electrode gap and line electrode diameter on the experimental results are qualitatively explained.

[Rehabilitative treatment of patients with ureterolithiasis using pulsed vacuum depression, pulsed low-frequency electric current, and radon therapy].

PubMed

Li, A A; Karpukhin, I V; Korchazhkina, N B; Gusarov, I I; Kotenko, K V; Slepushkina, T G; Dubovskiĭ, A V

2009-01-01

The authors report results of the treatment of 60 patients with ureterolithiasis using a combination of pulsed vacuum depression (local vibrotherapy), low-frequency pulsed (alternating sinusoidal) current, radon water and radon baths. Clinical efficiency of combined therapy is estimated at 93.3%.

Dual amplitude pulse generator for radiation detectors

DOEpatents

Hoggan, Jerry M.; Kynaston, Ronnie L.; Johnson, Larry O.

2001-01-01

A pulsing circuit for producing an output signal having a high amplitude pulse and a low amplitude pulse may comprise a current source for providing a high current signal and a low current signal. A gate circuit connected to the current source includes a trigger signal input that is responsive to a first trigger signal and a second trigger signal. The first trigger signal causes the gate circuit to connect the high current signal to a pulse output terminal whereas the second trigger signal causes the gate circuit to connect the low current signal to the pulse output terminal.

Microcrack healing in non-ferrous metal tubes through eddy current pulse treatment.

PubMed

Xu, Wenchen; Yang, Chuan; Yu, Haiping; Jin, Xueze; Guo, Bin; Shan, Debin

2018-04-16

This study proposed a novel method to heal microcrack within Mg alloy tubes using high density eddy current pulse treatment (ECPT). Through electromagnetic induction inside a copper coil connected with a high density pulse power source supply, the high density (greater than 5 × 10 9  A/m 2 ) and short duration eddy current was generated in tube specimens of Mg alloy. The results show that the microcracks in tube specimens was healed evidently and the mechanical properties of the tubes subjected to ECPT were improved simultaneously. The crack healing during ECPT was ascribed to not only the thermal stress around the microcrack tips and the softening or melting of metals in the vicinity of microcrack tips, but also the squeezing action acted by the Lorentz force. In the inward-discharging scheme, both the compressive radial stress and tangential stress induced by the Lorentz force contributed to more sufficient crack healing and thus better mechanical properties of tube specimens after the ECPT experiment, compared to the outward-discharging scheme. The ECPT can heal microcracks automatically without directly contacting tubular specimens and is not limited by the length of tubular workpieces, exhibiting great potential for crack healing in non-ferrous alloy tubes.

Transient Response of Arc Temperature and Iron Vapor Concentration Affected by Current Frequency with Iron Vapor in Pulsed Arc

NASA Astrophysics Data System (ADS)

Tanaka, Tatsuro; Maeda, Yoshifumi; Yamamoto, Shinji; Iwao, Toru

2016-10-01

TIG arc welding is chemically a joining technology with melting the metallic material and it can be high quality. However, this welding should not be used in high current to prevent cathode melting. Thus, the heat transfer is poor. Therefore, the deep penetration cannot be obtained and the weld defect sometimes occurs. The pulsed arc welding has been used for the improvement of this defect. The pulsed arc welding can control the heat flux to anode. The convention and driving force in the weld pool are caused by the arc. Therefore, it is important to grasp the distribution of arc temperature. The metal vapor generate from the anode in welding. In addition, the pulsed current increased or decreased periodically. Therefore, the arc is affected by such as a current value and current frequency, the current rate of increment and the metal vapor. In this paper, the transient response of arc temperature and the iron vapor concentration affected by the current frequency with iron vapor in pulsed arc was elucidated by the EMTF (ElectroMagnetic Thermal Fluid) simulation. As a result, the arc temperature and the iron vapor were transient response as the current frequency increase. Thus, the temperature and the electrical conductivity decreased. Therefore, the electrical field increased in order to maintain the current continuity. The current density and electromagnetic force increased at the axial center. In addition, the electronic flow component of the heat flux increased at the axial center because the current density increased. However, the heat conduction component of the heat flux decreased.

Pulse Detonation Engines for High Speed Flight

NASA Technical Reports Server (NTRS)

Povinelli, Louis A.

2002-01-01

Revolutionary concepts in propulsion are required in order to achieve high-speed cruise capability in the atmosphere and for low cost reliable systems for earth to orbit missions. One of the advanced concepts under study is the air-breathing pulse detonation engine. Additional work remains in order to establish the role and performance of a PDE in flight applications, either as a stand-alone device or as part of a combined cycle system. In this paper, we shall offer a few remarks on some of these remaining issues, i.e., combined cycle systems, nozzles and exhaust systems and thrust per unit frontal area limitations. Currently, an intensive experimental and numerical effort is underway in order to quantify the propulsion performance characteristics of this device. In this paper, we shall highlight our recent efforts to elucidate the propulsion potential of pulse detonation engines and their possible application to high-speed or hypersonic systems.

A compact, low jitter, nanosecond rise time, high voltage pulse generator with variable amplitude.

PubMed

Mao, Jiubing; Wang, Xin; Tang, Dan; Lv, Huayi; Li, Chengxin; Shao, Yanhua; Qin, Lan

2012-07-01

In this paper, a compact, low jitter, nanosecond rise time, command triggered, high peak power, gas-switch pulse generator system is developed for high energy physics experiment. The main components of the system are a high voltage capacitor, the spark gap switch and R = 50 Ω load resistance built into a structure to obtain a fast high power pulse. The pulse drive unit, comprised of a vacuum planar triode and a stack of avalanche transistors, is command triggered by a single or multiple TTL (transistor-transistor logic) level pulses generated by a trigger pulse control unit implemented using the 555 timer circuit. The control unit also accepts user input TTL trigger signal. The vacuum planar triode in the pulse driving unit that close the first stage switches is applied to drive the spark gap reducing jitter. By adjusting the charge voltage of a high voltage capacitor charging power supply, the pulse amplitude varies from 5 kV to 10 kV, with a rise time of <3 ns and the maximum peak current up to 200 A (into 50 Ω). The jitter of the pulse generator system is less than 1 ns. The maximum pulse repetition rate is set at 10 Hz that limited only by the gas-switch and available capacitor recovery time.

The efficacy of pulsed ultrahigh current for the stunning of cattle prior to slaughter.

PubMed

Robins, A; Pleiter, H; Latter, M; Phillips, C J C

2014-03-01

We present results from the development of a new system of reversible electrical stunning of cattle. A single-pulse ultra-high current (SPUC) was generated from a capacitance discharge current spike of at least 5000 V at 70 A, for approximately 50 ms. Ninety-seven cattle were stunned in three experimental protocols. With improvements made to the design of the stun box and charge delivered, 38 cattle were either stunned and immediately jugulated or monitored for signs of reappearance of brain stem reflexes at which point a concussion stun was administered. This use of the SPUC charge, provided as a biphasic-pulse waveform, resulted in a high level of stunning efficacy, with unconsciousness lasting for up to 4 min. These results were supported by EEG data taken from a subsequent cohort of stunned cattle. The SPUC stun also apparently eliminated post-stun grand mal seizures that can occur following short-acting conventional electrical stun, with its associated negative consequences on operator safety and meat quality. © 2013.

High velocity pulsed wire-arc spray

NASA Technical Reports Server (NTRS)

Kincaid, Russell W. (Inventor); Witherspoon, F. Douglas (Inventor); Massey, Dennis W. (Inventor)

1999-01-01

Wire arc spraying using repetitively pulsed, high temperature gas jets, usually referred to as plasma jets, and generated by capillary discharges, substantially increases the velocity of atomized and entrained molten droplets. The quality of coatings produced is improved by increasing the velocity with which coating particles impact the coated surface. The effectiveness of wire-arc spraying is improved by replacing the usual atomizing air stream with a rapidly pulsed high velocity plasma jet. Pulsed power provides higher coating particle velocities leading to improved coatings. 50 micron aluminum droplets with velocities of 1500 m/s are produced. Pulsed plasma jet spraying provides the means to coat the insides of pipes, tubes, and engine block cylinders with very high velocity droplet impact.

High Current Systems for HyperV and PLX Plasma Railguns

NASA Astrophysics Data System (ADS)

Brockington, S.; Case, A.; Messer, S.; Elton, R.; Witherspoon, F. D.

2011-10-01

HyperV is developing gas fed, pulsed, plasma railgun accelerators for PLX and other high momentum plasma applications. The present 2.5 cm square-bore plasma railgun forms plasma armatures from high density neutral gas (argon), preionizes it electrothermally, and accelerates the armature with 30 cm long parallel-plate railgun electrodes driven by a pulse forming network (PFN). Recent experiments have successfully formed and accelerated plasma armatures of ~4 mg at 40 km/s, with PFN currents of ~400 kA. In order to further increase railgun performance to the PLX design goal of 8 mg at 50 km/s, the PFN was upgraded to support currents of up to ~750 kA. A high voltage, high current linear array spark-gap switch and flexible, low-inductance transmission line were designed and constructed to handle the increased current load. We will describe these systems and present initial performance data from high current operation of the plasma rail gun from spectroscopy, interferometry, and imaging systems as well as pressure, magnetic field, and optical diagnostics. High current performance of railgun bore materials for electrodes and insulators will also be discussed as well as plans for upcoming experimentation with advanced materials. Supported by the U.S. DOE Joint Program in HEDLP.

Muscle oxygenation of vastus lateralis and medialis muscles during alternating and pulsed current electrical stimulation.

PubMed

Aldayel, Abdulaziz; Muthalib, Makii; Jubeau, Marc; McGuigan, Michael; Nosaka, Kazunori

2011-05-01

This study compared between alternating and pulsed current electrical muscle stimulation (EMS) for muscle oxygenation and blood volume during isometric contractions. Nine healthy men (23-48 years) received alternating current EMS (2500 Hz) modulated at 75 Hz on the knee extensors of one leg, and pulsed current EMS (75 Hz) for the other leg separated by 2 weeks in a randomised, counter-balanced order. Pulse duration (400 μs), on-off ratio (5-15 s) and other stimulation parameters were matched between conditions and 30 isometric contractions were induced at the knee joint angle of 100° (0° full extension). Changes in tissue oxygenation index (∆TOI) and total hemoglobin volume (∆tHb) of vastus lateralis and medialis muscles over 30 contractions were assessed by a near-infrared spectroscopy, and were compared between conditions by a two-way repeated measures ANOVA. Peak torque produced during EMS increased over 30 contractions in response to the increase in the stimulation intensity for pulsed current, but not for the alternating current EMS. The torque during each isometric contraction was less stable in alternating than pulsed current EMS. The changes in ∆TOI amplitude during relaxation phases and ∆tHb amplitude were not significantly different between conditions. However, the decreases in ∆TOI amplitude during contraction phases from baseline were significantly (P < 0.05) greater for the pulsed current than alternating current from the 18th contraction (-15.6 ± 2.3 vs. -8.9 ± 1.8%) to 30th contraction (-10.7 ± 1.8 vs. -4.8 ± 1.5%). These results suggest that the muscles were less activated in the alternating current EMS when compared with the pulsed current EMS.

Modelling the transient behaviour of pulsed current tungsten-inert-gas weldpools

NASA Astrophysics Data System (ADS)

Wu, C. S.; Zheng, W.; Wu, L.

1999-01-01

A three-dimensional model is established to simulate the pulsed current tungsten-inert-gas (TIG) welding process. The goal is to analyse the cyclic variation of fluid flow and heat transfer in weldpools under periodic arc heat input. To this end, an algorithm, which is capable of handling the transience, nonlinearity, multiphase and strong coupling encountered in this work, is developed. The numerical simulations demonstrate the transient behaviour of weldpools under pulsed current. Experimental data are compared with numerical results to show the effectiveness of the developed model.

Pulsed Direct Current Electrospray: Enabling Systematic Analysis of Small Volume Sample by Boosting Sample Economy.

PubMed

Wei, Zhenwei; Xiong, Xingchuang; Guo, Chengan; Si, Xingyu; Zhao, Yaoyao; He, Muyi; Yang, Chengdui; Xu, Wei; Tang, Fei; Fang, Xiang; Zhang, Sichun; Zhang, Xinrong

2015-11-17

We had developed pulsed direct current electrospray ionization mass spectrometry (pulsed-dc-ESI-MS) for systematically profiling and determining components in small volume sample. Pulsed-dc-ESI utilized constant high voltage to induce the generation of single polarity pulsed electrospray remotely. This method had significantly boosted the sample economy, so as to obtain several minutes MS signal duration from merely picoliter volume sample. The elongated MS signal duration enable us to collect abundant MS(2) information on interested components in a small volume sample for systematical analysis. This method had been successfully applied for single cell metabolomics analysis. We had obtained 2-D profile of metabolites (including exact mass and MS(2) data) from single plant and mammalian cell, concerning 1034 components and 656 components for Allium cepa and HeLa cells, respectively. Further identification had found 162 compounds and 28 different modification groups of 141 saccharides in a single Allium cepa cell, indicating pulsed-dc-ESI a powerful tool for small volume sample systematical analysis.

Advanced electrical current measurements of microdischarges: evidence of sub-critical pulses and ion currents in barrier discharge in air

NASA Astrophysics Data System (ADS)

Synek, Petr; Zemánek, Miroslav; Kudrle, Vít; Hoder, Tomáš

2018-04-01

Electrical current measurements in corona or barrier microdischarges are a challenge as they require both high temporal resolution and a large dynamic range of the current probe used. In this article, we apply a simple self-assembled current probe and compare it to commercial ones. An analysis in the time and frequency domain is carried out. Moreover, an improved methodology is presented, enabling both temporal resolution in sub-nanosecond times and current sensitivity in the order of tens of micro-amperes. Combining this methodology with a high-tech oscilloscope and self-developed software, a unique statistical analysis of currents in volume barrier discharge driven in atmospheric-pressure air is made for over 80 consecutive periods of a 15 kHz applied voltage. We reveal the presence of repetitive sub-critical current pulses and conclude that these can be identified with the discharging of surface charge microdomains. Moreover, extremely low, long-lasting microsecond currents were detected which are caused by ion flow, and are analysed in detail. The statistical behaviour presented gives deeper insight into the discharge physics of these usually undetectable current signals.

Numerical calculation and experimental research on crack arrest by detour effect and joule heating of high pulsed current in remanufacturing

NASA Astrophysics Data System (ADS)

Yu, Jing; Zhang, Hongchao; Deng, Dewei; Hao, Shengzhi; Iqbal, Asif

2014-07-01

The remanufacturing blanks with cracks were considered as irreparable. With utilization of detour effect and Joule heating of pulsed current, a technique to arrest the crack in martensitic stainless steel FV520B is developed. According to finite element theory, the finite element(FE) model of the cracked rectangular specimen is established firstly. Then, based on electro-thermo-structure coupled theory, the distributions of current density, temperature field, and stress field are calculated for the instant of energizing. Furthermore, the simulation results are verified by some corresponding experiments performed on high pulsed current discharge device of type HCPD-I. Morphology and microstructure around the crack tip before and after electro pulsing treatment are observed by optical microscope(OM) and scanning electron microscope(SEM), and then the diameters of fusion zone and heat affected zone(HAZ) are measured in order to contrast with numerical calculation results. Element distribution, nano-indentation hardness and residual stress in the vicinity of the crack tip are surveyed by energy dispersive spectrometer(EDS), scanning probe microscopy(SPM) and X-ray stress gauge, respectively. The results show that the obvious partition and refined grain around the crack tip can be observed due to the violent temperature change. The contents of carbon and oxygen in fusion zone and HAZ are higher than those in matrix, and however the hardness around the crack tip decreases. Large residual compressive stress is induced in the vicinity of the crack tip and it has the same order of magnitude for measured results and numerical calculation results that is 100 MPa. The relational curves between discharge energies and diameters of the fusion zone and HAZ are obtained by experiments. The difference of diameter of fusion zone between measured and calculated results is less than 18.3%. Numerical calculation is very useful to define the experimental parameters. An effective method

Effect of pulsed current charging on the performance of nickel-cadium cells

NASA Technical Reports Server (NTRS)

Bedrossian, A. A.; Cheh, H. Y.

1977-01-01

The effect of pulsed current charging on the charge acceptance of NiCd cells in terms of mass transfer, kinetic, and structural considerations was investigated. A systemic investigation on the performance of Ni-Cd cells by pulsed current charging was conducted under a variety of well-defined charge-discharge conditions. Experiments were carried out with half cells and film electrodes. The system behavior was studied by charge acceptance, mechanistic, and structural measurements.

The effects of return current and target charging in short pulse high intensity laser interactions

NASA Astrophysics Data System (ADS)

Beg, Farhat

2003-10-01

Since the introduction of the technique of chirped pulse amplification (CPA), peak laser intensities have increased dramatically. It is now possible to perform laser-plasma interaction experiments at intensities approaching 1021 Wcm-2. The electrons in the field of such lasers are highly relativistic (gamma 31) and the temperature of the hot electron distribution produced in a plasma at such extreme intensities can exceed 10 MeV. Since the resulting beam current exceeds the Alfvén limit, a neutralizing return current of cold plasma electrons moving in the opposite direction is produced. Another source of return current is that due to the escape of very energetic electrons from the target, which then creates a large electrostatic potential due to charge separation. These return currents can cause significant ohmic heating. We present results from experiments performed at Rutherford Appleton Laboratory using the VULCAN laser facility (I> 5 x1019 Wcm-2). Single wire targets were used and in some shots a secondary wire or foil was placed near the target. Three main observations were made: (i) generation of a Z-pinch in the wire due to the return current, (ii) optical transition radiation at 2w and (iii) proton emission from both the primary wire target and the secondary wire or foil. The Z-pinch was observed to be m=0 unstable. The current was estimated to be about 0.8 MA using simple energy balance considerations. Intense second harmonic emission due to coherent optical transition radiation from both the primary target and secondary objects was observed and is likely due to electron bunches accelerated by the ponderomotive jxB force of the laser. The proton emission from the secondary wire or foil was likely due to field emission of electrons from the these objects in response to the large potential produced from charging of the primary target. Results of simulations to model these interactions will also be presented.

Simple method enabling pulse on command from high power, high frequency lasers

NASA Astrophysics Data System (ADS)

Baer, David J.; Marshall, Graham D.; Coutts, David W.; Mildren, Richard P.; Withford, Michael J.

2006-09-01

A method for addressing individual laser pulses in high repetition frequency systems using an intracavity optical chopper and novel electronic timing system is reported. This "pulse on command" capability is shown to enable free running and both subharmonic pulse rate and burst mode operation of a high power, high pulse frequency copper vapor laser while maintaining a fixed output pulse energy. We demonstrate that this technique can be used to improve feature finish when laser micromachining metal.

Influence of waveform and current direction on short-interval intracortical facilitation: a paired-pulse TMS study.

PubMed

Delvendahl, Igor; Lindemann, Hannes; Jung, Nikolai H; Pechmann, Astrid; Siebner, Hartwig R; Mall, Volker

2014-01-01

Transcranial magnetic stimulation (TMS) of the human primary motor hand area (M1-HAND) can produce multiple descending volleys in fast-conducting corticospinal neurons, especially so-called indirect waves (I-waves) resulting from trans-synaptic excitation. Facilitatory interaction between these I-waves can be studied non-invasively using a paired-pulse paradigm referred to as short-interval intracortical facilitation (SICF). We examined whether SICF depends on waveform and current direction of the TMS pulses. In young healthy volunteers, we applied single- and paired-pulse TMS to M1-HAND. We probed SICF by pairs of monophasic or half-sine pulses at suprathreshold stimulation intensity and inter-stimulus intervals (ISIs) between 1.0 and 5.0 ms. For monophasic paired-pulse stimulation, both pulses had either a posterior-anterior (PA) or anterior-posterior (AP) current direction (AP-AP or PA-PA), whereas current direction was reversed between first and second pulse for half-sine paired-pulse stimulation (PA-AP and AP-PA). Monophasic AP-AP stimulation resulted in stronger early SICF at 1.4 ms relative to late SICF at 2.8 and 4.4 ms, whereas monophasic PA-PA stimulation produced SICF of comparable size at all three peaks. With half-sine stimulation the third SICF peak was reduced for PA-AP current orientation compared with AP-PA. SICF elicited using monophasic as well as half-sine pulses is affected by current direction at clearly suprathreshold intensities. The impact of current orientation is stronger for monophasic compared with half-sine pulses. The direction-specific effect of paired-pulse TMS on the strength of early versus late SICF shows that different cortical circuits mediate early and late SICF. Copyright © 2014 Elsevier Inc. All rights reserved.

Fiber optic cables for transmission of high-power laser pulses in spaceflight applications

NASA Astrophysics Data System (ADS)

Thomes, W. J.; Ott, M. N.; Chuska, R. F.; Switzer, R. C.; Blair, D. E.

2017-11-01

Lasers with high peak power pulses are commonly used in spaceflight missions for a wide range of applications, from LIDAR systems to optical communications. Due to the high optical power needed, the laser has to be located on the exterior of the satellite or coupled through a series of free space optics. This presents challenges for thermal management, radiation resistance, and mechanical design. Future applications will require multiple lasers located close together, which further complicates the design. Coupling the laser energy into a fiber optic cable allows the laser to be relocated to a more favorable position on the spacecraft. Typical fiber optic termination procedures are not sufficient for injection of these high-power laser pulses without catastrophic damage to the fiber endface. In the current study, we will review the causes of fiber damage during high-power injection and discuss our new manufacturing procedures that overcome these issues to permit fiber use with high reliability in these applications. We will also discuss the proper methods for launching the laser pulses into the fiber to avoid damage and how this is being implemented for current spaceflight missions.

Fiber Optic Cables for Transmission of High-Power Laser Pulses in Spaceflight Applications

NASA Technical Reports Server (NTRS)

Thomes, W. J., Jr.; Ott, M. N.; Chuska, R. F.; Switzer, R. C.; Blair, D. E.

2010-01-01

Lasers with high peak power pulses are commonly used in spaceflight missions for a wide range of applications, from LIDAR systems to optical communications. Due to the high optical power needed, the laser has to be located on the exterior of the satellite or coupled through a series of free space optics. This presents challenges for thermal management, radiation resistance, and mechanical design. Future applications will require multiple lasers located close together, which further complicates the design. Coupling the laser energy into a fiber optic cable allows the laser to be relocated to a more favorable position on the spacecraft. Typical fiber optic termination procedures are not sufficient for injection of these high-power laser pulses without catastrophic damage to the fiber endface. In the current study, we will review the causes of fiber damage during high-power injection and discuss our new manufacturing procedures that overcome these issues to permit fiber use with high reliability in these applications. We will also discuss the proper methods for launching the laser pulses into the fiber to avoid damage and how this is being implemented for current spaceflight missions.

Electrodeposition of Gold to Conformally Fill High Aspect Ratio Nanometric Silicon Grating Trenches: A Comparison of Pulsed and Direct Current Protocols

PubMed Central

Znati, Sami A.; Chedid, Nicholas; Miao, Houxun; Chen, Lei; Bennett, Eric E.; Wen, Han

2016-01-01

Filling high-aspect-ratio trenches with gold is a frequent requirement in the fabrication of x-ray optics as well as micro-electronic components and other fabrication processes. Conformal electrodeposition of gold in sub-micron-width silicon trenches with an aspect ratio greater than 35 over a grating area of several square centimeters is challenging and has not been described in the literature previously. A comparison of pulsed plating and constant current plating led to a gold electroplating protocol that reliably filled trenches for such structures. PMID:27042384

Strong electromagnetic pulses generated in high-intensity short-pulse laser interactions with thin foil targets

NASA Astrophysics Data System (ADS)

Rączka, P.; Dubois, J.-L.; Hulin, S.; Tikhonchuk, V.; Rosiński, M.; Zaraś-Szydłowska, A.; Badziak, J.

2017-12-01

Measurements are reported of the target neutralization current, the target charge, and the tangential component of the magnetic field generated as a result of laser-target interaction by pulses with the energy in the range of 45 mJ to 92 mJ on target and the pulse duration from 39 fs to 1000 fs. The experiment was performed at the Eclipse facility in CELIA, Bordeaux. The aim of the experiment was to extend investigations performed for the thick (mm scale) targets to the case of thin (micrometer thickness) targets in a way that would allow for a straightforward comparison of the results. We found that thin foil targets tend to generate 20 to 50 percent higher neutralization current and the target charge than the thick targets. The measurement of the tangential component of the magnetic field had shown that the initial spike is dominated by the 1 ns pulse consistent with the 1 ns pulse of the neutralization current, but there are some differences between targets of different type on sub-ns scale, which is an effect going beyond a simple picture of the target acting as an antenna. The sub-ns structure appears to be reproducible to surprising degree. We found that there is in general a linear correlation between the maximum value of the magnetic field and the maximum neutralization current, which supports the target-antenna picture, except for pulses hundreds of fs long.

Subnanosecond breakdown development in high-voltage pulse discharge: Effect of secondary electron emission

NASA Astrophysics Data System (ADS)

Alexandrov, A. L.; Schweigert, I. V.; Zakrevskiy, Dm. E.; Bokhan, P. A.; Gugin, P.; Lavrukhin, M.

2017-10-01

A subnanosecond breakdown in high-voltage pulse discharge may be a key tool for superfast commutation of high power devices. The breakdown in high-voltage open discharge at mid-high pressure in helium was studied in experiment and in kinetic simulations. The kinetic model of electron avalanche development was constructed, based on PIC-MCC simulations, including dynamics of electrons, ions and fast helium atoms, produced by ions scattering. Special attention was paid to electron emission processes from cathode, such as: photoemission by Doppler-shifted resonant photons, produced in excitation processes involving fast atoms; electron emission by ions and fast atoms bombardment of cathode; the secondary electron emission (SEE) by hot electrons from bulk plasma. The simulations show that the fast atoms accumulation is the main reason of emission growth at the early stage of breakdown, but at the final stage, when the voltage on plasma gap diminishes, namely the SEE is responsible for subnanosecond rate of current growth. It was shown that the characteristic time of the current growth can be controlled by the SEE yield. The influence of SEE yield for three types of cathode material (titanium, SiC, and CuAlMg-alloy) was tested. By changing the pulse voltage amplitude and gas pressure, the area of existence of subnanosecond breakdown is identified. It is shown that in discharge with SiC and CuAlMg-alloy cathodes (which have enhanced SEE) the current can increase with a subnanosecond characteristic time value as small as τs = 0.4 ns, for the pulse voltage amplitude of 5÷12 kV. An increase of gas pressure from 15 Torr to 30 Torr essentially decreases the time of of current front growth, whereas the pulse voltage variation weakly affects the results.

CO2-Tea pulse clipping using pulsed high voltage preionization for high spatial resolution I.R. Lidar systems

NASA Astrophysics Data System (ADS)

Gasmi, Taieb

2018-04-01

An extra-cavity CO2-TEA laser pulse clipper for high spatial resolution atmospheric monitoring is presented. The clipper uses pulsed high voltageto facilitate the breakdown of the gas within the clipper cell. Complete extinction of the nitrogen tail, that degrades the range resolution of LIDARS, is obtained at pressures from 375 up to 1500 Torr for nitrogen and argon gases whereas an attenuation coefficient of almost 102 is achieved for helium. Excellent energy stability and pulse width repeatability were achieved using high voltage pre-ionized gas technique.

Transient thermoelectric supercooling: Isosceles current pulses from a response surface perspective and the performance effects of pulse cooling a heat generating mass

NASA Astrophysics Data System (ADS)

Piggott, Alfred J., III

With increased public interest in protecting the environment, scientists and engineers aim to improve energy conversion efficiency. Thermoelectrics offer many advantages as thermal management technology. When compared to vapor compression refrigeration, above approximately 200 to 600 watts, cost in dollars per watt as well as COP are not advantageous for thermoelectrics. The goal of this work was to determine if optimized pulse supercooling operation could improve cooling capacity or efficiency of a thermoelectric device. The basis of this research is a thermal-electrical analogy based modeling study using SPICE. Two models were developed. The first model, a standalone thermocouple with no attached mass to be cooled. The second, a system that includes a module attached to a heat generating mass. With the thermocouple study, a new approach of generating response surfaces with characteristic parameters was applied. The current pulse height and pulse on-time was identified for maximizing Net Transient Advantage, a newly defined metric. The corresponding pulse height and pulse on-time was utilized for the system model. Along with the traditional steady state starting current of Imax, Iopt was employed. The pulse shape was an isosceles triangle. For the system model, metrics new to pulse cooling were Qc, power consumption and COP. The effects of optimized current pulses were studied by changing system variables. Further studies explored time spacing between pulses and temperature distribution in the thermoelement. It was found net Q c over an entire pulse event can be improved over Imax steady operation but not over steady I opt operation. Qc can be improved over Iopt operation but only during the early part of the pulse event. COP is reduced in transient pulse operation due to the different time constants of Qc and Pin. In some cases lower performance interface materials allow more Qc and better COP during transient operation than higher performance interface materials

The current-density distribution in a pulsed dc magnetron deposition discharge

NASA Astrophysics Data System (ADS)

Vetushka, Alena; Bradley, James W.

2007-04-01

Using a carefully constructed magnetic probe (a B-dot probe) the spatial and temporal evolution of the perturbation in the magnetic field ΔB in an unbalanced pulsed dc magnetron has been determined. The plasma was run in argon at a pressure of 0.74 Pa and the plasma ions sputtered a pure graphite target. The pulse frequency and duty were set at 100 kHz and 55%, respectively. From the ΔB measurements (measured with magnitudes up to about 0.01 mT) the axial, azimuthal and radial components of the total current density j in the plasma bulk were determined. In the plasma 'on' phase, the axial current density jz has a maximum value of approximately 200 A m-2 above the racetrack region, while high values in the azimuthal current density jΦ are distributed in a region from 1 to 3 cm into the bulk plasma with jΦ exceeding 350 A m-2. In the 'off' phase of the plasma, jz decays almost instantaneously (at least within the 100 ns time-resolution of the ΔB measurements) as the electric field collapses; however, jΦ decays with a characteristic time constant of about 1 µs. This slow decay can be attributed to the presence of decaying Grad-B and curvature drifts, with their rates controlled by the decay in the plasma density. A comparison between axial and azimuthal current densities in the plasma 'on' time, when the plasma is being driven, strongly indicates that classical transport does not operate in the magnetron discharge.

Characteristics of a velvet cathode under high repetition rate pulse operation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xun Tao; Zhang Jiande; Yang Hanwu

2009-10-15

As commonly used material for cold cathodes, velvet works well in single shot and low repetition rate (rep-rate) high-power microwave (HPM) sources. In order to determine the feasibility of velvet cathodes under high rep-rate operation, a series of experiments are carried out on a high-power diode, driven by a {approx}300 kV, {approx}6 ns, {approx}100 {omega}, and 1-300 Hz rep-rate pulser, Torch 02. Characteristics of vacuum compatibility and cathode lifetime under different pulse rep-rate are focused on in this paper. Results of time-resolved pressure history, diode performance, shot-to-shot reproducibility, and velvet microstructure changes are presented. As the rep-rate increases, the equilibriummore » pressure grows hyperlinearly and the velvet lifetime decreases sharply. At 300 Hz, the pressure in the given diode exceeded 1 Pa, and the utility shots decreased to 2000 pulses for nonstop mode. While, until the velvet begins to degrade, the pulse-to-pulse instability of diode voltage and current is quite small, even under high rep-rate conditions. Possible reasons for the operation limits are discussed, and methods to improve the performance of a rep-rate velvet cathode are also suggested. These results may be of interest to the repetitive HPM systems with cold cathodes.« less

Dynamics of a high-current relativistic electron beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strelkov, P. S., E-mail: strelkov@fpl.gpi.ru; Tarakanov, V. P., E-mail: karat@gmail.ru; Ivanov, I. E., E-mail: iei@fpl.gpi.ru

2015-06-15

The dynamics of a high-current relativistic electron beam is studied experimentally and by numerical simulation. The beam is formed in a magnetically insulated diode with a transverse-blade explosive-emission cathode. It is found experimentally that the radius of a 500-keV beam with a current of 2 kA and duration of 500 ns decreases with time during the beam current pulse. The same effect was observed in numerical simulations. This effect is explained by a change in the shape of the cathode plasma during the current pulse, which, according to calculations, leads to a change in the beam parameters, such as themore » electron pitch angle and the spread over the longitudinal electron momentum. These parameters are hard to measure experimentally; however, the time evolution of the radial profile of the beam current density, which can be measured reliably, coincides with the simulation results. This allows one to expect that the behavior of the other beam parameters also agrees with numerical simulations.« less

Producing High Intense Attosecond Pulse Train by Interaction of Three-Color Pulse and Overdense Plasma

NASA Astrophysics Data System (ADS)

Salehi, M.; Mirzanejad, S.

2017-05-01

Amplifying the attosecond pulse by the chirp pulse amplification method is impossible. Furthermore, the intensity of attosecond pulse is low in the interaction of laser pulse and underdense plasma. This motivates us to propose using a multi-color pulse to produce the high intense attosecond pulse. In the present study, the relativistic interaction of a three-color linearly-polarized laser-pulse with highly overdense plasma is studied. We show that the combination of {{ω }}1, {{ω }}2 and {{ω }}3 frequencies decreases the instance full width at half maximum reflected attosecond pulse train from the overdense plasma surface. Moreover, we show that the three-color pulse increases the intensity of generated harmonics, which is explained by the relativistic oscillating mirror model. The obtained results demonstrate that if the three-color laser pulse interacts with overdense plasma, it will enhance two orders of magnitude of intensity of ultra short attosecond pulses in comparison with monochromatic pulse.

Investigation on Microstructure and Mechanical Properties of Continuous and Pulsed Current Gas Tungsten Arc Welded alloy 600

NASA Astrophysics Data System (ADS)

Srikanth, A.; Manikandan, M.

2018-02-01

The present study investigates the microstructure and mechanical properties of joints fabricated by Continuous and pulsed current gas tungsten arc welded alloy 600. Welding was done by autogenous mode. The macro examination was carried out to evaluate the welding defects in the weld joints. Optical and Scanning Electron Microscope (SEM) were performed to assess the microstructural changes in the fusion zone. Energy Dispersive Spectroscopy (EDS) analysis was carried to evaluate the microsegregation of alloying elements in the fusion zone. The tensile test was conducted to assess the strength of the weld joints. The results show that no welding defects were observed in the fusion zones of Continuous and Pulsed current Gas Tungsten Arc Welding. The refined microstructure was found in the pulsed current compared to continuous current mode. Microsegregation was not noticed in the weld grain boundary of continuous and pulsed current mode. The pulsed current shows improved mechanical properties compared to the continuous current mode.

Coaxial-type water load for measuring high voltage, high current and short pulse of a compact Marx system for a high power microwave source

NASA Astrophysics Data System (ADS)

Han, Jaeeun; Kim, Jung-ho; Park, Sang-duck; Yoon, Moohyun; Park, Soo Yong; Choi, Do Won; Shin, Jin Woo; So, Joon Ho

2009-11-01

A coaxial-type water load was used to measure the voltage output from a Marx generator for a high power microwave source. This output had a rise time of 20 ns, a pulse duration of a few hundred ns, and an amplitude up to 500 kV. The design of the coaxial water load showed that it is an ideal resistive divider and can also accurately measure a short pulse. Experiments were performed to test the performance of the Marx generator with the calibrated coaxial water load.

A Robust High Current Density Electron Gun

NASA Astrophysics Data System (ADS)

Mako, F.; Peter, W.; Shiloh, J.; Len, L. K.

1996-11-01

Proof-of-principle experiments are proposed to validate a new concept for a robust, high-current density Pierce electron gun (RPG) for use in klystrons and high brightness electron sources for accelerators. This rugged, long-life electron gun avoids the difficulties associated with plasma cathodes, thermionic emitters, and field emission cathodes. The RPG concept employs the emission of secondary electrons in a transmission mode as opposed to the conventional mode of reflection, i.e., electrons exit from the back face of a thin negative electron affinity (NEA) material, and in the same direction as the incident beam. Current amplification through one stage of a NEA material could be over 50 times. The amplification is accomplished in one or more stages consisting of one primary emitter and one or more secondary emitters. The primary emitter is a low current density robust emitter (e.g., thoriated tungsten). The secondary emitters are thin NEA electrodes which emit secondary electrons in the same direction as the incident beam. Specific application is targeted for a klystron gun to be used by SLAC with a cold cathode at 30-40 amps/cm^2 output from the secondary emission stage, a ~2 μs pulse length, and ~200 pulses/second.

Electron cyclotron resonance plasma production by using pulse mode microwaves and dependences of ion beam current and plasma parameters on the pulse condition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kiriyama, Ryutaro; Takenaka, Tomoya; Kurisu, Yousuke

2012-02-15

We measure the ion beam current and the plasma parameters by using the pulse mode microwave operation in the first stage of a tandem type ECRIS. The time averaged extracted ion beam current in the pulse mode operation is larger than that of the cw mode operation with the same averaged microwave power. The electron density n{sub e} in the pulse mode is higher and the electron temperature T{sub e} is lower than those of the cw mode operation. These plasma parameters are considered to cause in the increase of the ion beam current and are suitable to produce molecularmore » or cluster ions.« less

Extreme degree of ionization in homogenous micro-capillary plasma columns heated by ultrafast current pulses.

PubMed

Avaria, G; Grisham, M; Li, J; Tomasel, F G; Shlyaptsev, V N; Busquet, M; Woolston, M; Rocca, J J

2015-03-06

Homogeneous plasma columns with ionization levels typical of megaampere discharges are created by rapidly heating gas-filled 520-μm-diameter channels with nanosecond rise time current pulses of 40 kA. Current densities of up to 0.3  GA cm^{-2} greatly increase Joule heating with respect to conventional capillary discharge Z pinches, reaching unprecedented degrees of ionization for a high-Z plasma column heated by a current pulse of remarkably low amplitude. Dense xenon plasmas are ionized to Xe^{28+}, while xenon impurities in hydrogen discharges reach Xe^{30+}. The unique characteristics of these hot, ∼300:1 length-to-diameter aspect ratio plasmas allow the observation of unexpected spectroscopic phenomena. Axial spectra show the unusual dominance of the intercombination line over the resonance line of He-like Al by nearly an order of magnitude, caused by differences in opacities in the axial and radial directions. These plasma columns could enable the development of sub-10-nm x-ray lasers.

A 70 kV solid-state high voltage pulse generator based on saturable pulse transformer.

PubMed

Fan, Xuliang; Liu, Jinliang

2014-02-01

High voltage pulse generators are widely applied in many fields. In recent years, solid-state and operating at repetitive mode are the most important developing trends of high voltage pulse generators. A solid-state high voltage pulse generator based on saturable pulse transformer is proposed in this paper. The proposed generator is consisted of three parts. They are charging system, triggering system, and the major loop. Saturable pulse transformer is the key component of the whole generator, which acts as a step-up transformer and main switch during working process of this generator. The circuit and working principles of the proposed pulse generator are introduced first in this paper, and the saturable pulse transformer used in this generator is introduced in detail. Circuit of the major loop is simulated to verify the design of the system. Demonstration experiments are carried out, and the results show that when the primary energy storage capacitor is charged to a high voltage, such as 2.5 kV, a voltage with amplitude of 86 kV can be achieved on the secondary winding. The magnetic core of saturable pulse transformer is saturated deeply and the saturable inductance of the secondary windings is very small. The switch function of the saturable pulse transformer can be realized ideally. Therefore, a 71 kV output voltage pulse is formed on the load. Moreover, the magnetic core of the saturable pulse transformer can be reset automatically.

The effect of pulsed current electrodeposition parameters of calcium phosphates coating on Ti6Al4V ELI

NASA Astrophysics Data System (ADS)

Sierra-Herrera, D. K.; Sandoval-Amador, A.; Montañez-Supelano, N. D.; Y Peña-Ballesteros, D.

2017-12-01

Pulse current electrodeposition is a technique of special interest, due to the advantages it has, like easy operation, high control in the amount, homogeneity and purity of the deposited material, and low cost. This work studies the influence of the pulsed electrodeposition parameters variation on the characteristics of calcium phosphates coatings, including the composition, crystallinity and morphology. The influence of the current density and pulse on and off time on the physicochemical properties of the obtained coatings were evaluated. The coatings were electrodeposited on Ti6Al4V using Ca(NO3)2·H2O and NH4H2PO4 with a Ca/P molar ratio of 1.67. The coatings were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The analysis of DRX confirmed the formation of HAP. The results revealed that the variation of the current density modified the morphology of the coating. Also, the amount of material deposited increases as the off-time pulse increases, allowing the diffusion of the ions in the solution towards the working electrode.

Observation of Dust Stream Formation Produced by Low Current, High Voltage Cathode Spots

NASA Technical Reports Server (NTRS)

Foster, John E.

2004-01-01

Macro-particle acceleration driven by low current, high voltage cathode spots has been investigated. The phenomenon was observed to occur when nanometer and micrometer-sized particles in the presence of a discharge plasma were exposed to a high voltage pulse. The negative voltage pulse initiates the formation of multiple, high voltage, low current cathode spots which provides the mechanism of actual acceleration of the charged dust particles. Dust streams generated by this process were detected using laser scattering techniques. The particle impact craters observed at the surface of downstream witness badges were documented using SEM and light microscopy.

Physicochemical assessment criteria for high-voltage pulse capacitors

NASA Astrophysics Data System (ADS)

Darian, L. A.; Lam, L. Kh.

2016-12-01

In the paper, the applicability of decomposition products of internal insulation of high-voltage pulse capacitors is considered (aging is the reason for decomposition products of internal insulation). Decomposition products of internal insulation of high-voltage pulse capacitors can be used to evaluate their quality when in operation and in service. There have been three generations of markers of aging of insulation as in the case with power transformers. The area of applicability of markers of aging of insulation for power transformers has been studied and the area can be extended to high-voltage pulse capacitors. The research reveals that there is a correlation between the components and quantities of markers of aging of the first generation (gaseous decomposition products of insulation) dissolved in insulating liquid and the remaining life of high-voltage pulse capacitors. The application of markers of aging to evaluate the remaining service life of high-voltage pulse capacitor is a promising direction of research, because the design of high-voltage pulse capacitors keeps stability of markers of aging of insulation in high-voltage pulse capacitors. It is necessary to continue gathering statistical data concerning development of markers of aging of the first generation. One should also carry out research aimed at estimation of the remaining life of capacitors using markers of the second and the third generation.

Physicochemical assessment criteria for high-voltage pulse capacitors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Darian, L. A., E-mail: LDarian@rambler.ru; Lam, L. Kh.

In the paper, the applicability of decomposition products of internal insulation of high-voltage pulse capacitors is considered (aging is the reason for decomposition products of internal insulation). Decomposition products of internal insulation of high-voltage pulse capacitors can be used to evaluate their quality when in operation and in service. There have been three generations of markers of aging of insulation as in the case with power transformers. The area of applicability of markers of aging of insulation for power transformers has been studied and the area can be extended to high-voltage pulse capacitors. The research reveals that there is amore » correlation between the components and quantities of markers of aging of the first generation (gaseous decomposition products of insulation) dissolved in insulating liquid and the remaining life of high-voltage pulse capacitors. The application of markers of aging to evaluate the remaining service life of high-voltage pulse capacitor is a promising direction of research, because the design of high-voltage pulse capacitors keeps stability of markers of aging of insulation in high-voltage pulse capacitors. It is necessary to continue gathering statistical data concerning development of markers of aging of the first generation. One should also carry out research aimed at estimation of the remaining life of capacitors using markers of the second and the third generation.« less

Characterization of carbon fiber polymer matrix composites subjected to simultaneous application of electric current pulse and low velocity impact

NASA Astrophysics Data System (ADS)

Hart, Robert James

2011-12-01

The use of composite materials in aerospace, electronics, and wind industries has become increasingly common, and these composite components are required to carry mechanical, electrical, and thermal loads simultaneously. A unique property of carbon fiber composites is that when an electric current is applied to the specimen, the mechanical strength of the specimen increases. Previous studies have shown that the higher the electric current, the greater the increase in impact strength. However, as current passes through the composite, heat is generated through Joule heating. This Joule heating can cause degradation of the composite and thus a loss in strength. In order to minimize the negative effects of heating, it is desired to apply a very high current for a very short duration of time. This thesis investigated the material responses of carbon fiber composite plates subjected to electrical current pulse loads of up to 1700 Amps. For 32 ply unidirectional IM7/977-3 specimens, the peak impact load and absorbed energy increased slightly with the addition of a current pulse at the time of an impact event. In 16 ply cross-ply IM7/977-2 specimens, the addition of the current pulse caused detrimental effects due to electrical arcing at the interface between the composite and electrodes. Further refinement of the experimental setup should minimize the risk of electrical arcing and should better elucidate the effects of a current pulse on the impact strength of the specimens.

High Current, Multi-Filament Photoconductive Semiconductor Switching

DTIC Science & Technology

2011-06-01

linear PCSS triggered with a 100 fs laser pulse . Figure 1. A generic photoconductive semiconductor switch rapidly discharges a charged capacitor...switching is the most critical challenge remaining for photoconductive semiconductor switch (PCSS) applications in Pulsed Power. Many authors have...isolation and control, pulsed or DC charging, and long device lifetime, provided the current per filament is limited to 20-30A for short pulse (10

Generating high-current monoenergetic proton beams by a circularly polarized laser pulse in the phase-stable acceleration regime.

PubMed

Yan, X Q; Lin, C; Sheng, Z M; Guo, Z Y; Liu, B C; Lu, Y R; Fang, J X; Chen, J E

2008-04-04

A new ion acceleration method, namely, phase-stable acceleration, using circularly-polarized laser pulses is proposed. When the initial target density n(0) and thickness D satisfy a(L) approximately (n(0)/n(c))D/lambda(L) and D>l(s) with a(L), lambda(L), l(s), and n(c) the normalized laser amplitude, the laser wavelength in vacuum, the plasma skin depth, and the critical density of the incident laser pulse, respectively, a quasiequilibrium for the electrons is established by the light pressure and the space charge electrostatic field at the interacting front of the laser pulse. The ions within the skin depth of the laser pulse are synchronously accelerated and bunched by the electrostatic field, and thereby a high-intensity monoenergetic proton beam can be generated. The proton dynamics is investigated analytically and the results are verified by one- and two-dimensional particle-in-cell simulations.

A new high intensity and short-pulse molecular beam valve

NASA Astrophysics Data System (ADS)

Yan, B.; Claus, P. F. H.; van Oorschot, B. G. M.; Gerritsen, L.; Eppink, A. T. J. B.; van de Meerakker, S. Y. T.; Parker, D. H.

2013-02-01

In this paper, we report on the design and performance of a new home-built pulsed gas valve, which we refer to as the Nijmegen Pulsed Valve (NPV). The main output characteristics include a short pulse width (as short as 20 μs) combined with operating rates up to 30 Hz. The operation principle of the NPV is based on the Lorentz force created by a pulsed current passing through an aluminum strip located within a magnetic field, which opens the nozzle periodically. The amplitude of displacement of the opening mechanism is sufficient to allow the use of nozzles with up to 1.0 mm diameter. To investigate the performance of the valve, several characterizations were performed with different experimental methods. First, a fast ionization gauge was used to measure the beam intensity of the free jet emanating from the NPV. We compare free jets from the NPV with those from several other pulsed valves in current use in our laboratory. Results showed that a high intensity and short pulse-length beam could be generated by the new valve. Second, the NPV was tested in combination with a skimmer, where resonance enhanced multiphoton ionization combined with velocity map imaging was used to show that the NPV was able to produce a pulsed molecular beam with short pulse duration (˜20 μs using 0.1% NO/He at 6 bars) and low rotational temperature (˜1 K using 0.5% NO/Ar at 6 bars). Third, a novel two-point pump-probe method was employed which we label double delay scan. This method allows a full kinematic characterization of the molecular beam, including accurate speed ratios at different temporal positions. It was found that the speed ratio was maximum (S = 50 using 0.1% NO/He at 3 bars) at the peak position of the molecular beam and decreased when it was on the leading or falling edge.

Pulsed high energy synthesis of fine metal powders

NASA Technical Reports Server (NTRS)

Witherspoon, F. Douglas (Inventor); Massey, Dennis W. (Inventor)

1999-01-01

Repetitively pulsed plasma jets generated by a capillary arc discharge at high stagnation pressure (>15,000 psi) and high temperature (>10,000 K) are utilized to produce 0.1-10 .mu.m sized metal powders and decrease cost of production. The plasma jets impact and atomize melt materials to form the fine powders. The melt can originate from a conventional melt stream or from a pulsed arc between two electrodes. Gas streams used in conventional gas atomization are replaced with much higher momentum flux plasma jets. Delivering strong incident shocks aids in primary disintegration of the molten material. A series of short duration, high pressure plasma pulses fragment the molten material. The pulses introduce sharp velocity gradients in the molten material which disintegrates into fine particles. The plasma pulses have peak pressures of approximately one kilobar. The high pressures improve the efficiency of disintegration. High gas flow velocities and pressures are achieved without reduction in gas density. Repetitively pulsed plasma jets will produce powders with lower mean size and narrower size distribution than conventional atomization techniques.

Traceability validation of a high speed short-pulse testing method used in LED production

NASA Astrophysics Data System (ADS)

Revtova, Elena; Vuelban, Edgar Moreno; Zhao, Dongsheng; Brenkman, Jacques; Ulden, Henk

2017-12-01

Industrial processes of LED (light-emitting diode) production include LED light output performance testing. Most of them are monitored and controlled by optically, electrically and thermally measuring LEDs by high speed short-pulse measurement methods. However, these are not standardized and a lot of information is proprietary that it is impossible for third parties, such as NMIs, to trace and validate. It is known, that these techniques have traceability issue and metrological inadequacies. Often due to these, the claimed performance specifications of LEDs are overstated, which consequently results to manufacturers experiencing customers' dissatisfaction and a large percentage of failures in daily use of LEDs. In this research a traceable setup is developed to validate one of the high speed testing techniques, investigate inadequacies and work out the traceability issues. A well-characterised short square pulse of 25 ms is applied to chip-on-board (CoB) LED modules to investigate the light output and colour content. We conclude that the short-pulse method is very efficient in case a well-defined electrical current pulse is applied and the stabilization time of the device is "a priori" accurately determined. No colour shift is observed. The largest contributors to the measurement uncertainty include badly-defined current pulse and inaccurate calibration factor.

Observation of dark pulses in 10 nm thick YBCO nanostrips presenting hysteretic current voltage characteristics

NASA Astrophysics Data System (ADS)

Ejrnaes, M.; Parlato, L.; Arpaia, R.; Bauch, T.; Lombardi, F.; Cristiano, R.; Tafuri, F.; Pepe, G. P.

2017-12-01

We have fabricated several 10 nm thick and 65 nm wide YBa2Cu3O7-δ (YBCO) nanostrips. The nanostrips with the highest critical current densities are characterized by hysteretic current voltage characteristics (IVCs) with a direct bistable switch from the zero-voltage to the finite voltage state. The presence of hysteretic IVCs allowed the observation of dark pulses due to fluctuations phenomena. The key role of the bistable behavior is its ability to transform a small disturbance (e.g. an intrinsic fluctuation) into a measurable transient signal, i.e. a dark pulse. On the contrary, in devices characterized by lower critical current density values, the IVCs are non-hysteretic and dark pulses have not been observed. To investigate the physical origin of the dark pulses, we have measured the bias current dependence of the dark pulse rate: the observed exponential increase with the bias current is compatible with mechanisms based on thermal activation of magnetic vortices in the nanostrip. We believe that the successful amplification of small fluctuation events into measurable signals in nanostrips of ultrathin YBCO is a milestone for further investigation of YBCO nanostrips for superconducting nanostrip single photon detectors and other quantum detectors for operation at higher temperatures.

Saturation current and collection efficiency for ionization chambers in pulsed beams.

PubMed

DeBlois, F; Zankowski, C; Podgorsak, E B

2000-05-01

Saturation currents and collection efficiencies in ionization chambers exposed to pulsed megavoltage photon and electron beams are determined assuming a linear relationship between 1/I and 1/V in the extreme near-saturation region, with I and V the chamber current and polarizing voltage, respectively. Careful measurements of chamber current against polarizing voltage in the extreme near-saturation region reveal a current rising faster than that predicted by the linear relationship. This excess current combined with conventional "two-voltage" technique for determination of collection efficiency may result in an up to 0.7% overestimate of the saturation current for standard radiation field sizes of 10X10 cm2. The measured excess current is attributed to charge multiplication in the chamber air volume and to radiation-induced conductivity in the stem of the chamber (stem effect). These effects may be accounted for by an exponential term used in conjunction with Boag's equation for collection efficiency in pulsed beams. The semiempirical model follows the experimental data well and accounts for both the charge recombination as well as for the charge multiplication effects and the chamber stem effect.

Analytical description of generation of the residual current density in the plasma produced by a few-cycle laser pulse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silaev, A. A., E-mail: silaev@appl.sci-nnov.ru; Vvedenskii, N. V., E-mail: vved@appl.sci-nnov.ru; University of Nizhny Novgorod, Nizhny Novgorod 603950

2015-05-15

When a gas is ionized by a few-cycle laser pulse, some residual current density (RCD) of free electrons remains in the produced plasma after the passage of the laser pulse. This quasi-dc RCD is an initial impetus to plasma polarization and excitation of the plasma oscillations which can radiate terahertz (THz) waves. In this work, the analytical model for calculation of RCD excited by a few-cycle laser pulse is developed for the first time. The dependences of the RCD on the carrier-envelope phase (CEP), wavelength, duration, and intensity of the laser pulse are derived. It is shown that maximum RCDmore » corresponding to optimal CEP increases with the laser pulse wavelength, which indicates the prospects of using mid-infrared few-cycle laser pulses in the schemes of generation of high-power THz pulses. Analytical formulas for optimal pulse intensity and maximum efficiency of excitation of the RCD are obtained. Basing on numerical solution of the 3D time-dependent Schrödinger equation for hydrogen atoms, RCD dependence on CEP is calculated in a wide range of wavelengths. High accuracy of analytical formulas is demonstrated at the laser pulse parameters which correspond to the tunneling regime of ionization.« less

High-efficiency, broad band, high-damage threshold high-index gratings for femtosecond pulse compression.

PubMed

Canova, Frederico; Clady, Raphael; Chambaret, Jean-Paul; Flury, Manuel; Tonchev, Svtelen; Fechner, Renate; Parriaux, Olivier

2007-11-12

High efficiency, broad-band TE-polarization diffraction over a wavelength range centered at 800 nm is obtained by high index gratings placed on a non-corrugated mirror. More than 96% efficiency wide band top-hat diffraction efficiency spectra, as well as more than 1 J/cm(2) damage threshold under 50 fs pulses are demonstrated experimentally. This opens the way to high-efficiency Chirped Pulse Amplification for high average power laser machining by means of all-dielectric structures as well as for ultra-short high energy pulses by means of metal-dielectric structures.

Direct coupling of pulsed radio frequency and pulsed high power in novel pulsed power system for plasma immersion ion implantation.

PubMed

Gong, Chunzhi; Tian, Xiubo; Yang, Shiqin; Fu, Ricky K Y; Chu, Paul K

2008-04-01

A novel power supply system that directly couples pulsed high voltage (HV) pulses and pulsed 13.56 MHz radio frequency (rf) has been developed for plasma processes. In this system, the sample holder is connected to both the rf generator and HV modulator. The coupling circuit in the hybrid system is composed of individual matching units, low pass filters, and voltage clamping units. This ensures the safe operation of the rf system even when the HV is on. The PSPICE software is utilized to optimize the design of circuits. The system can be operated in two modes. The pulsed rf discharge may serve as either the seed plasma source for glow discharge or high-density plasma source for plasma immersion ion implantation (PIII). The pulsed high-voltage glow discharge is induced when a rf pulse with a short duration or a larger time interval between the rf and HV pulses is used. Conventional PIII can also be achieved. Experiments conducted on the new system confirm steady and safe operation.

Electrothermal Action of the Pulse of the Current of a Short Artificial-Lightning Stroke on Test Specimens of Wires and Cables of Electric Power Objects

NASA Astrophysics Data System (ADS)

Baranov, M. I.; Rudakov, S. V.

2018-03-01

The authors have given results of investigations of the electrothermal action of aperiodic pulses of temporal shape 10/350 μs of the current of a short artificial-lightning stroke on test specimens of electric wires and cables with copper and aluminum cores and sheaths with polyvinylchloride and polyethylene insulations of power circuits of industrial electric power objects. It has been shown that the thermal stability of such wires and cables is determined by the action integral of the indicated current pulse. The authors have found the maximum permissible and critical densities of this pulse in copper and aluminum current-carrying parts of the wires and cables. High-current experiments conducted under high-voltage laboratory conditions on a unique generator of 10/350 μs pulses of an artificial-lightning current with amplitude-time parameters normalized according to the existing requirements of international and national standards and with tolerances on them have confirmed the reliability of the proposed calculated estimate for thermal lightning resistance of cabling and wiring products.

Electrothermal Action of the Pulse of the Current of a Short Artificial-Lightning Stroke on Test Specimens of Wires and Cables of Electric Power Objects

NASA Astrophysics Data System (ADS)

Baranov, M. I.; Rudakov, S. V.

2018-05-01

The authors have given results of investigations of the electrothermal action of aperiodic pulses of temporal shape 10/350 μs of the current of a short artificial-lightning stroke on test specimens of electric wires and cables with copper and aluminum cores and sheaths with polyvinylchloride and polyethylene insulations of power circuits of industrial electric power objects. It has been shown that the thermal stability of such wires and cables is determined by the action integral of the indicated current pulse. The authors have found the maximum permissible and critical densities of this pulse in copper and aluminum current-carrying parts of the wires and cables. High-current experiments conducted under high-voltage laboratory conditions on a unique generator of 10/350 μs pulses of an artificial-lightning current with amplitude-time parameters normalized according to the existing requirements of international and national standards and with tolerances on them have confirmed the reliability of the proposed calculated estimate for thermal lightning resistance of cabling and wiring products.

Conductivity tomography based on pulsed eddy current with SQUID magnetometer

NASA Astrophysics Data System (ADS)

Panaitov, G. I.; Krause, H.-J.; Zhang, Y.

2002-05-01

Pulsed eddy current (EC) techniques have the advantage of potentially covering a broader depth range than standard single frequency EC testing. We developed a novel pulsed EC technique using a liquid-nitrogen cooled SQUID magnetometer. For two reasons, SQUID magnetometers are particularly well suited as sensors: first they constitute an extremely sensitive magnetic field sensor, second they measure the field directly which decays more slowly than its time derivative picked up by induction coils. A square waveform transmitter signal was used, with alternating slopes in order to eliminate drift effect, and stacking synchronous to the power line frequency in order to improve signal-to-noise. The early time (high frequency) data of the recorded transient correspond to the upper layers of the conducting medium, while late time data or low frequencies deliver information on deep layers. Measurements of cracks at different depths in a stacked aluminum sample are presented. From the measured data, the apparent conductivity of the sample was calculated for each position and depth by applying a technique known from geophysical data interpretation. Thus, the position and depth of the crack was determined from the tomographic conductivity image of the sample.

Electric breakdown during the pulsed current spreading in the sand

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vasilyak, L. M., E-mail: vasilyak@ihed.ras.ru; Vetchinin, S. P.; Panov, V. A.

2016-03-15

Processes of spreading of the pulsed current from spherical electrodes and an electric breakdown in the quartz sand are studied experimentally. When the current density on the electrode exceeds the critical value, a nonlinear reduction occurs in the grounding resistance as a result of sparking in the soil. The critical electric field strengths for ionization and breakdown are determined. The ionization-overheating instability is shown to develop on the electrode, which leads to the current contraction and formation of plasma channels.

Pulse-Width-Modulating Driver for Brushless dc Motor

NASA Technical Reports Server (NTRS)

Salomon, Phil M.

1991-01-01

High-current pulse-width-modulating driver for brushless dc motor features optical coupling of timing signals from low-current control circuitry to high-current motor-driving circuitry. Provides high electrical isolation of motor-power supply, helping to prevent fast, high-current motor-driving pulses from being coupled through power supplies into control circuitry, where they interfere with low-current control signals.

Control of the electrode metal transfer by means of the welding current pulse generator

NASA Astrophysics Data System (ADS)

Knyaz'kov, A.; Pustovykh, O.; Verevkin, A.; Terekhin, V.; Shachek, A.; Knyaz'kov, S.; Tyasto, A.

2016-04-01

The paper presents a generator of welding current pulses to transfer an electrode metal into the molten pool. A homogeneous artificial line is used to produce near rectangular pulses. The homogeneous artificial line provides the minimum heat input with in the pulse to transfer the electrode metal, and it significantly decreases the impact of disturbances affecting this transfer. The pulse frequency does not exceed 300 Hz, and the duration is 0.6 ÷ 0.9 ms.

Experimental investigation of powerful pulse current generators based on capacitive storage and explosive magnetic generators

NASA Astrophysics Data System (ADS)

Shurupov, A. V.; Zavalova, V. E.; Kozlov, A. V.; Shurupov, M. A.; Povareshkin, M. N.; Kozlov, A. A.; Shurupova, N. P.

2018-01-01

Experimental models of microsecond duration powerful generators of current pulses on the basis of explosive magnetic generators and voltage impulse generator have been developed for the electromagnetic pulse effects on energy facilities to verify their stability. Exacerbation of voltage pulse carried out through the use of electro explosive current interrupter made of copper wires with diameters of 80 and 120 μm. Experimental results of these models investigation are represented. Voltage fronts about 100 ns and the electric field strength of 800 kV/m are registered.

Development and characterization of a high yield transportable pulsed neutron source with efficient and compact pulsed power system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verma, Rishi, E-mail: rishiv9@gmail.com, E-mail: rishiv@barc.gov.in; Mishra, Ekansh; Dhang, Prosenjit

2016-09-15

The results of characterization experiments carried out on a newly developed dense plasma focus device based intense pulsed neutron source with efficient and compact pulsed power system are reported. Its high current sealed pseudospark switch based low inductance capacitor bank with maximum stored energy of ∼10 kJ is segregated into four modules of ∼2.5 kJ each and it cumulatively delivers peak current in the range of 400 kA–600 kA (corresponding to charging voltage range of 14 kV–18 kV) in a quarter time period of ∼2 μs. The neutron yield performance of this device has been optimized by discretely varying deuteriummore » filling gas pressure in the range of 6 mbar–11 mbar at ∼17 kV/550 kA discharge. At ∼7 kJ/8.5 mbar operation, the average neutron yield has been measured to be in the order of ∼4 × 10{sup 9} neutrons/pulse which is the highest ever reported neutron yield from a plasma focus device with the same stored energy. The average forward to radial anisotropy in neutron yield is found to be ∼2. The entire system is contained on a moveable trolley having dimensions 1.5 m × 1 m × 0.7 m and its operation and control (up to the distance of 25 m) are facilitated through optically isolated handheld remote console. The overall compactness of this system provides minimum proximity to small as well as large samples for irradiation. The major intended application objective of this high neutron yield dense plasma focus device development is to explore the feasibility of active neutron interrogation experiments by utilization of intense pulsed neutron sources.« less

Development and characterization of a high yield transportable pulsed neutron source with efficient and compact pulsed power system.

PubMed

Verma, Rishi; Mishra, Ekansh; Dhang, Prosenjit; Sagar, Karuna; Meena, Manraj; Shyam, Anurag

2016-09-01

The results of characterization experiments carried out on a newly developed dense plasma focus device based intense pulsed neutron source with efficient and compact pulsed power system are reported. Its high current sealed pseudospark switch based low inductance capacitor bank with maximum stored energy of ∼10 kJ is segregated into four modules of ∼2.5 kJ each and it cumulatively delivers peak current in the range of 400 kA-600 kA (corresponding to charging voltage range of 14 kV-18 kV) in a quarter time period of ∼2 μs. The neutron yield performance of this device has been optimized by discretely varying deuterium filling gas pressure in the range of 6 mbar-11 mbar at ∼17 kV/550 kA discharge. At ∼7 kJ/8.5 mbar operation, the average neutron yield has been measured to be in the order of ∼4 × 10 9 neutrons/pulse which is the highest ever reported neutron yield from a plasma focus device with the same stored energy. The average forward to radial anisotropy in neutron yield is found to be ∼2. The entire system is contained on a moveable trolley having dimensions 1.5 m × 1 m × 0.7 m and its operation and control (up to the distance of 25 m) are facilitated through optically isolated handheld remote console. The overall compactness of this system provides minimum proximity to small as well as large samples for irradiation. The major intended application objective of this high neutron yield dense plasma focus device development is to explore the feasibility of active neutron interrogation experiments by utilization of intense pulsed neutron sources.

Low and High-Power Inductive Pulsed Plasma Thruster Development Testing at NASA-MSFC

NASA Technical Reports Server (NTRS)

Polzin, Kurt A.; Martin, Adam K.; Greve, Christine M.; Riley, Daniel P.

2017-01-01

The inductive pulsed plasma thruster (IPPT) is an electromagnetic plasma accelerator that has been identified in NASA roadmaps as an enabling propulsion technology for some niche low-power missions and for high-power in-space propulsion needs. The IPPT is an electrodeless space propulsion device where a capacitor is charged to an initial voltage and then discharged producing a high current pulse through a coil. The field produced by this pulse ionizes propellant, inductively driving current in a plasma located near the face of the coil. Once the plasma is formed it can be accelerated and expelled at a high exhaust velocity by the electromagnetic Lorentz body force arising from the interaction of the induced plasma current and the magnetic field produced by the current in the coil. Thrusters of this type possess many demonstrated and potential benefits that make them worthy of continued investigation. The electrodeless nature of these thrusters eliminates the lifetime and contamination issues associated with electrode erosion in conventional electric thrusters. Also, a wider variety of propellants are accessible when compatibility with metallic electrodes in no longer an issue. IPPTs have been successfully operated using propellants like ammonia, hydrazine, and CO2, and there is no fundamental reason why they would not operate on other in situ propellants like H2O. It is well-known that pulsed accelerators can maintain constant specific impulse (I(sub sp)) and thrust efficiency (eta(sub t)) over a wide range of input power levels by adjusting the pulse rate to hold the discharge energy per pulse constant. It has also been demonstrated that an inductive pulsed plasma thruster can operate in a regime where eta(sub t) is relatively constant over a wide range of I(sub sp) values (3000-8000 s). Finally, thrusters in this class have operated in single-pulse mode at high energy per pulse, and by increasing the pulse rate they offer the potential to process very high levels

Uncertainties in cylindrical anode current inferences on pulsed power drivers

NASA Astrophysics Data System (ADS)

Porwitzky, Andrew; Brown, Justin

2018-06-01

For over a decade, velocimetry based techniques have been used to infer the electrical current delivered to dynamic materials properties experiments on pulsed power drivers such as the Z Machine. Though originally developed for planar load geometries, in recent years, inferring the current delivered to cylindrical coaxial loads has become a valuable diagnostic tool for numerous platforms. Presented is a summary of uncertainties that can propagate through the current inference technique when applied to expanding cylindrical anodes. An equation representing quantitative uncertainty is developed which shows the unfold method to be accurate to a few percent above 10 MA of load current.

High-voltage pulsed generator for dynamic fragmentation of rocks

NASA Astrophysics Data System (ADS)

Kovalchuk, B. M.; Kharlov, A. V.; Vizir, V. A.; Kumpyak, V. V.; Zorin, V. B.; Kiselev, V. N.

2010-10-01

A portable high-voltage (HV) pulsed generator has been designed for rock fragmentation experiments. The generator can be used also for other technological applications. The installation consists of low voltage block, HV block, coaxial transmission line, fragmentation chamber, and control system block. Low voltage block of the generator, consisting of a primary capacitor bank (300 μF) and a thyristor switch, stores pulse energy and transfers it to the HV block. The primary capacitor bank stores energy of 600 J at the maximum charging voltage of 2 kV. HV block includes HV pulsed step up transformer, HV capacitive storage, and two electrode gas switch. The following technical parameters of the generator were achieved: output voltage up to 300 kV, voltage rise time of ˜50 ns, current amplitude of ˜6 kA with the 40 Ω active load, and ˜20 kA in a rock fragmentation regime (with discharge in a rock-water mixture). Typical operation regime is a burst of 1000 pulses with a frequency of 10 Hz. The operation process can be controlled within a wide range of parameters. The entire installation (generator, transmission line, treatment chamber, and measuring probes) is designed like a continuous Faraday's cage (complete shielding) to exclude external electromagnetic perturbations.

High-voltage pulsed generator for dynamic fragmentation of rocks.

PubMed

Kovalchuk, B M; Kharlov, A V; Vizir, V A; Kumpyak, V V; Zorin, V B; Kiselev, V N

2010-10-01

A portable high-voltage (HV) pulsed generator has been designed for rock fragmentation experiments. The generator can be used also for other technological applications. The installation consists of low voltage block, HV block, coaxial transmission line, fragmentation chamber, and control system block. Low voltage block of the generator, consisting of a primary capacitor bank (300 μF) and a thyristor switch, stores pulse energy and transfers it to the HV block. The primary capacitor bank stores energy of 600 J at the maximum charging voltage of 2 kV. HV block includes HV pulsed step up transformer, HV capacitive storage, and two electrode gas switch. The following technical parameters of the generator were achieved: output voltage up to 300 kV, voltage rise time of ∼50 ns, current amplitude of ∼6 kA with the 40 Ω active load, and ∼20 kA in a rock fragmentation regime (with discharge in a rock-water mixture). Typical operation regime is a burst of 1000 pulses with a frequency of 10 Hz. The operation process can be controlled within a wide range of parameters. The entire installation (generator, transmission line, treatment chamber, and measuring probes) is designed like a continuous Faraday's cage (complete shielding) to exclude external electromagnetic perturbations.

Measurement of positive direct current corona pulse in coaxial wire-cylinder gap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, Han, E-mail: hanyin1986@gmail.com; Zhang, Bo, E-mail: shizbcn@mail.tsinghua.edu.cn; He, Jinliang, E-mail: hejl@tsinghua.edu.cn

In this paper, a system is designed and developed to measure the positive corona current in coaxial wire-cylinder gaps. The characteristic parameters of corona current pulses, such as the amplitude, rise time, half-wave time, and repetition frequency, are statistically analyzed and a new set of empirical formulas are derived by numerical fitting. The influence of space charges on corona currents is tested by using three corona cages with different radii. A numerical method is used to solve a simplified ion-flow model to explain the influence of space charges. Based on the statistical results, a stochastic model is developed to simulatemore » the corona pulse trains. And this model is verified by comparing the simulated frequency-domain responses with the measured ones.« less

Method for exciting inductive-resistive loads with high and controllable direct current

DOEpatents

Hill, Jr., Homer M.

1976-01-01

Apparatus and method for transmitting dc power to a load circuit by applying a dc voltage from a standard waveform synthesizer to duration modulate a bipolar rectangular wave generator. As the amplitude of the dc voltage increases, the widths of the rectangular wave generator output pulses increase, and as the amplitude of the dc voltage decreases, the widths of the rectangular wave generator output pulses decrease. Thus, the waveform synthesizer selectively changes the durations of the rectangular wave generator bipolar output pulses so as to produce a rectangular wave ac carrier that is duration modulated in accordance with and in direct proportion to the voltage amplitude from the synthesizer. Thereupon, by transferring the carrier to the load circuit through an amplifier and a rectifier, the load current also corresponds directly to the voltage amplitude from the synthesizer. To this end, the rectified wave at less than 100% duty factor, amounts to a doubled frequency direct voltage pulse train for applying a direct current to the load, while the current ripple is minimized by a high L/R in the load circuit. In one embodiment, a power transmitting power amplifier means having a dc power supply is matched to the load circuit through a transformer for current magnification without sacrificing load current duration capability, while negative voltage and current feedback are provided in order to insure good output fidelity.

Effect of pulsed current GTA welding parameters on the fusion zone microstructure of AA 6061 aluminium alloy

NASA Astrophysics Data System (ADS)

Kumar, T. Senthil; Balasubramanian, V.; Babu, S.; Sanavullah, M. Y.

2007-08-01

AA6061 aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of food processing equipment, chemical containers, passenger cars, road tankers, and railway transport systems. The preferred process for welding these aluminium alloys is frequently Gas Tungsten Arc (GTA) welding due to its comparatively easy applicability and lower cost. In the case of single pass GTA welding of thinner sections of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current processes. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. In this investigation, an attempt has been made to develop a mathematical model to predict the fusion zone grain diameter incorporating pulsed current welding parameters. Statistical tools such as design of experiments, analysis of variance, and regression analysis are used to develop the mathematical model. The developed model can be effectively used to predict the fusion grain diameter at a 95% confidence level for the given pulsed current parameters. The effect of pulsed current GTA welding parameters on the fusion zone grain diameter of AA 6061 aluminium alloy welds is reported in this paper.

Training Effects of Alternated and Pulsed Currents on the Quadriceps Muscles of Athletes.

PubMed

Oliveira, Pedro; Modesto, Karenina Arrais Guida; Bottaro, Martim; Babault, Nicolas; Durigan, João Luiz Quagliotti

2018-05-22

The aim of the study was to evaluate the effects of 6 weeks training with different neuromuscular electrical stimulation (NMES) currents (medium alternated and low-frequency pulsed current) on muscle architecture and neuromuscular performance of competitive athletes. A double-blind controlled and randomized experimental study was carried out with 33 athletes (22.2±2.6 yrs, 74.7±9.8 kg, 176.8±6.0 cm), divided into 3 groups: mid-frequency current (MF, n=12), pulsed current (PC, n=11) and the control group (CG, n=10). Quadriceps maximal voluntary peak torque (PT) and corresponding vastus lateralis electromyographic activity, evoked torque (PT-NMES), vastus lateralis muscle thickness, fascicle length, pennation angle, and level of discomfort were assessed before and after the interventions. NMES training was performed 3 times per week and consisted of 18 sessions, 15 min/session, 6 s duration in each contraction interspersed with 18 s rest. After the training period, muscle thickness increased in the MF and PC groups (p<0.05). PT-NMES increased only in the PC group (p<0.05). All currents produced similar levels of discomfort (p>0.05). Quadriceps NMES training applied through alternated or pulsed currents produced similar effects in architecture and neuromuscular performance in competitive athletes. © Georg Thieme Verlag KG Stuttgart · New York.

Carbon-oxygen reaction efficiency in air gap switch with graphite electrodes under high current pulse discharge

NASA Astrophysics Data System (ADS)

Dai, Hongyu; Li, Lee; Peng, Ming-yang; Xiong, Jiaming; Wu, Haibo; Yu, Bin

2017-12-01

In order to reduce the effect of residual carbon on the insulation performance, after the GW-hundreds kiloampere graphite-electrode switch turning on, the chemical kinetics of the carbon-oxygen reaction is analyzed. The capacitive pulsed experimental circuit is used to reconstruct the actual condition of high power and high current discharge. The carbon-oxygen reaction efficiency is analyzed using a Fourier transform infrared spectrometer and a flue gas analyzer. The research shows that the gas products include NOX, O3, CH4, and COX. Through the quantitative analysis, the conversion efficiency of COX increases with the augment of the accumulated transferred charge, and the change law of the CO generation efficiency has an extreme value. With the corresponding calculation and the observation of the scanning electron microscope, it is found that most of the carbon consumed from the graphite electrodes is converted to amorphous elemental carbon, and the insufficiency of the carbon-oxygen reaction leads to the problem of carbon residue, for 20%-45% of elemental carbon is not oxidized. The size of amorphous elemental carbon is about several micrometers to tens micrometers by the analysis of metallographic microscope. In the condition of compressed air, changing the amount of transferred charge is helpful to improve the carbon-oxygen reaction efficiency and inhibit the problem of carbon residue.

Pulsed Eddy Current Probe Design Based on Transient Circuit Analysis

NASA Astrophysics Data System (ADS)

Cadeau, Trevor J.; Krause, Thomas W.

2009-03-01

Probe design parameters affecting depth of penetration of pulsed eddy currents in multi-layer aluminum 2024-T3 were examined. Several probe designs were evaluated for their ability to detect a discontinuity at the bottom of a stack of aluminum plates. The reflection type probes, consisting of pick-up coil and encircling drive coil, were characterized based on their transient response to a square pulse excitation. Probes with longer fundamental time constants, equivalent to a lower driving frequency, generated greater depth of penetration. However, additional factors such as inductive and resistive load, and excessive coil heating were also factors that limited signal-to-noise response with increasing layer thickness.

A compact high-voltage pulse generator based on pulse transformer with closed magnetic core.

PubMed

Zhang, Yu; Liu, Jinliang; Cheng, Xinbing; Bai, Guoqiang; Zhang, Hongbo; Feng, Jiahuai; Liang, Bo

2010-03-01

A compact high-voltage nanosecond pulse generator, based on a pulse transformer with a closed magnetic core, is presented in this paper. The pulse generator consists of a miniaturized pulse transformer, a curled parallel strip pulse forming line (PFL), a spark gap, and a matched load. The innovative design is characterized by the compact structure of the transformer and the curled strip PFL. A new structure of transformer windings was designed to keep good insulation and decrease distributed capacitance between turns of windings. A three-copper-strip structure was adopted to avoid asymmetric coupling of the curled strip PFL. When the 31 microF primary capacitor is charged to 2 kV, the pulse transformer can charge the PFL to 165 kV, and the 3.5 ohm matched load can deliver a high-voltage pulse with a duration of 9 ns, amplitude of 84 kV, and rise time of 5.1 ns. When the load is changed to 50 ohms, the output peak voltage of the generator can be 165 kV, the full width at half maximum is 68 ns, and the rise time is 6.5 ns.

Preconditioned wire array Z-pinches driven by a double pulse current generator

NASA Astrophysics Data System (ADS)

Wu, Jian; Lu, Yihan; Sun, Fengju; Li, Xingwen; Jiang, Xiaofeng; Wang, Zhiguo; Zhang, Daoyuan; Qiu, Aici; Lebedev, Sergey

2018-07-01

Suppression of the core-corona structure and wire ablation in wire array Z-pinches is investigated using a novel double pulse current generator ‘Qin-1’ facility. The ‘Qin-1’ facility allows coupling a ∼10 kA 20 ns prepulse generator with a ∼0.8 MA 160 ns main current generator. The tailored prepulse current preheats wires to a gaseous state and the time interval between the prepulse and the main current pulse allows formation of a more uniform mass distribution for the implosion. The implosion of a gasified two aluminum-wire array showed no ablation phase and allowed all array mass to participate in the implosion. The initial perturbations formed from the inhomogeneous ablation were suppressed, however, the magneto Rayleigh–Taylor (MRT) instability during the implosion was still significant and further researches on the generation and development of the MRT instabilities of this gasified wire array are needed.

Taguchi Optimization of Pulsed Current GTA Welding Parameters for Improved Corrosion Resistance of 5083 Aluminum Welds

NASA Astrophysics Data System (ADS)

Rastkerdar, E.; Shamanian, M.; Saatchi, A.

2013-04-01

In this study, the Taguchi method was used as a design of experiment (DOE) technique to optimize the pulsed current gas tungsten arc welding (GTAW) parameters for improved pitting corrosion resistance of AA5083-H18 aluminum alloy welds. A L9 (34) orthogonal array of the Taguchi design was used, which involves nine experiments for four parameters: peak current ( P), base current ( B), percent pulse-on time ( T), and pulse frequency ( F) with three levels was used. Pitting corrosion resistance in 3.5 wt.% NaCl solution was evaluated by anodic polarization tests at room temperature and calculating the width of the passive region (∆ E pit). Analysis of variance (ANOVA) was performed on the measured data and S/ N (signal to noise) ratios. The "bigger is better" was selected as the quality characteristic (QC). The optimum conditions were found as 170 A, 85 A, 40%, and 6 Hz for P, B, T, and F factors, respectively. The study showed that the percent pulse-on time has the highest influence on the pitting corrosion resistance (50.48%) followed by pulse frequency (28.62%), peak current (11.05%) and base current (9.86%). The range of optimum ∆ E pit at optimum conditions with a confidence level of 90% was predicted to be between 174.81 and 177.74 mVSCE. Under optimum conditions, the confirmation test was carried out, and the experimental value of ∆ E pit of 176 mVSCE was in agreement with the predicted value from the Taguchi model. In this regard, the model can be effectively used to predict the ∆ E pit of pulsed current gas tungsten arc welded joints.

Closed-loop pulsed helium ionization detector

DOEpatents

Ramsey, Roswitha S.; Todd, Richard A.

1987-01-01

A helium ionization detector for gas chromatography is operated in a constant current, pulse-modulated mode by configuring the detector, electrometer and a high voltage pulser in a closed-loop control system. The detector current is maintained at a fixed level by varying the frequency of fixed-width, high-voltage bias pulses applied to the detector. An output signal proportional to the pulse frequency is produced which is indicative of the charge collected for a detected species.

Modified Johnson-Cook model incorporated with electroplasticity for uniaxial tension under a pulsed electric current

NASA Astrophysics Data System (ADS)

Kim, Moon-Jo; Jeong, Hye-Jin; Park, Ju-Won; Hong, Sung-Tae; Han, Heung Nam

2018-01-01

An empirical expression describing the electroplastic deformation behavior is suggested based on the Johnson-Cook (JC) model by adding several functions to consider both thermal and athermal electric current effects. Tensile deformation behaviors are carried out for an AZ31 magnesium alloy and an Al-Mg-Si alloy under pulsed electric current at various current densities with a fixed duration of electric current. To describe the flow curves under electric current, a modified JC model is proposed to take the electric current effect into account. Phenomenological descriptions of the adopted parameters in the equation are made. The modified JC model suggested in the present study is capable of describing the tensile deformation behaviors under pulsed electric current reasonably well.

Comparison of high-voltage ac and pulsed operation of a surface dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Williamson, James M.; Trump, Darryl D.; Bletzinger, Peter; Ganguly, Biswa N.

2006-10-01

A surface dielectric barrier discharge (DBD) in atmospheric pressure air was excited either by low frequency (0.3-2 kHz) high-voltage ac or by short, high-voltage pulses at repetition rates from 50 to 600 pulses s-1. The short-pulse excited discharge was more diffuse and did not have the pronounced bright multiple cathode spots observed in the ac excited discharge. The discharge voltage, current and average power deposited into the discharge were calculated for both types of excitation. As a measure of plasma-chemical efficiency, the ozone number density was measured by UV absorption as a function of average deposited power. The density of ozone produced by ac excitation did not increase so rapidly as that produced by short-pulse excitation as a function of average power, with a maximum measured density of ~3 × 1015 cm-3 at 25 W. The maximum ozone production achieved by short-pulse excitation was ~8.5 × 1015 cm-3 at 20 W, which was four times greater than that achieved by ac excitation at the same power level.

Pulsed-Current Electrochemical Codeposition and Heat Treatment of Ti-Dispersed Ni-Matrix Layers

NASA Astrophysics Data System (ADS)

Janetaisong, Pathompong; Boonyongmaneerat, Yuttanant; Techapiesancharoenkij, Ratchatee

2016-08-01

An electrochemical deposition is a fast and cost-efficient process to produce film or coating. In this research, Ni-Ti electrodeposition is developed by codepositing a Ti-dispersed Ni-matrix layer from a Ni-plating solution suspended with Ti particles. To enhance the coating uniformity and control the atomic composition, the pulsed current was applied to codeposit Ni-Ti layers with varying pulse duty cycles (10 to 100 pct) and frequencies (10 to 100 Hz). The microstructures and compositions of the codeposited layers were analyzed by scanning electron microscopy, X-ray diffraction, and X-ray fluorescent techniques. The pulsed current significantly improved the quality of the Ni-Ti layer as compared to a direct current. The Ni-Ti layers could be electroplated with a controlled composition within 48 to 51 at. pct of Ti. The optimal pulse duty cycle and frequency are 50 pct and 10 Hz, respectively. The standalone Ni-49Ti layers were removed from copper substrates by selective etching method and subsequently heat-treated under Ar-fed atmosphere at 1423 K (1150 °C) for 5 hours. The phase and microstructures of the post-annealed samples exhibit different Ni-Ti intermetallic compounds, including NiTi, Ni3Ti, and NiTi2. Yet, the contamination of TiN and TiO2 was also present in the post-annealed samples.

High-speed photorefractive keratectomy with femtosecond ultraviolet pulses

NASA Astrophysics Data System (ADS)

Danieliene, Egle; Gabryte, Egle; Vengris, Mikas; Ruksenas, Osvaldas; Gutauskas, Algimantas; Morkunas, Vaidotas; Danielius, Romualdas

2015-05-01

Femtosecond near-infrared lasers are widely used for a number of ophthalmic procedures, with flap cutting in the laser-assisted in situ keratomileusis (LASIK) surgery being the most frequent one. At the same time, lasers of this type, equipped with harmonic generators, have been shown to deliver enough ultraviolet (UV) power for the second stage of the LASIK procedure, the stromal ablation. However, the speed of the ablation reported so far was well below the currently accepted standards. Our purpose was to perform high-speed photorefractive keratectomy (PRK) with femtosecond UV pulses in rabbits and to evaluate its predictability, reproducibility and healing response. The laser source delivered femtosecond 206 nm pulses with a repetition rate of 50 kHz and an average power of 400 mW. Transepithelial PRK was performed using two different ablation protocols, to a total depth of 110 and 150 μm. The surface temperature was monitored during ablation; haze dynamics and histological samples were evaluated to assess outcomes of the PRK procedure. For comparison, analogous excimer ablation was performed. Increase of the ablation speed up to 1.6 s/diopter for a 6 mm optical zone using femtosecond UV pulses did not significantly impact the healing process.

Pulse measurement of the hot spot current in a NbTiN superconducting filament

NASA Astrophysics Data System (ADS)

Harrabi, K.; Mekki, A.; Kunwar, S.; Maneval, J. P.

2018-02-01

We have studied the voltage response of superconducting NbTiN filaments to a step-pulse of over-critical current I > Ic. The current induces the destruction of the Cooper pairs and initiates different mechanisms of dissipation depending on the bath temperature T. For the sample investigated, and for T above a certain T*, not far from Tc, the resistance manifests itself in the form of a phase-slip center, which turns into a normal hot spot (HS) as the step-pulse is given larger amplitudes. However, at all temperatures below T*, the destruction of superconductivity still occurs at Ic(T), but leads directly to an ever-growing HS. By lowering the current amplitude during the pulse, one can produce a steady HS and thus define a threshold HS current Ih(T). That is achieved by combining two levels of current, the first and larger one to initiate an HS, the second one to search for constant voltage response. The double diagram of the functions Ic(T) and Ih(T) was plotted in the T-range Tc/2 < T < Tc, and their crossing found at T* = (8.07 ± 0.07) K.

Some Experimental and Monte Carlo Investigations of the Plastic Scintillators for the Current Mode Measurements at Pulsed Neutron Sources

NASA Astrophysics Data System (ADS)

Rogov, A.; Pepyolyshev, Yu.; Carta, M.; d'Angelo, A.

Scintillation detector (SD) is widely used in neutron and gamma-spectrometry in a count mode. The organic scintillators for the count mode of the detector operation are investigated rather well. Usually, they are applied for measurement of amplitude and time distributions of pulses caused by single interaction events of neutrons or gamma's with scintillator material. But in a large area of scientific research scintillation detectors can alternatively be used on a current mode by recording the average current from the detector. For example,the measurements of the neutron pulse shape at the pulsed reactors or another pulsed neutron sources. So as to get a rather large volume of experimental data at pulsed neutron sources, it is necessary to use the current mode detector for registration of fast neutrons. Many parameters of the SD are changed with a transition from an accounting mode to current one. For example, the detector efficiency is different in counting and current modes. Many effects connected with time accuracy become substantial. Besides, for the registration of solely fast neutrons, as must be in many measurements, in the mixed radiation field of the pulsed neutron sources, SD efficiency has to be determined with a gamma-radiation shield present. Here is no calculations or experimental data on SD current mode operation up to now. The response functions of the detectors can be either measured in high-precision reference fields or calculated by a computer simulation. We have used the MCNP code [1] and carried out some experiments for investigation of the plastic performances in a current mode. There are numerous programs performing simulating similar to the MCNP code. For example, for neutrons there are [2-4], for photons - [5-8]. However, all known codes to use (SCINFUL, NRESP4, SANDYL, EGS49) have more stringent restrictions on the source, geometry and detector characteristics. In MCNP code a lot of these restrictions are absent and you need only to write

High-energy ultra-short pulse thin-disk lasers: new developments and applications

NASA Astrophysics Data System (ADS)

Michel, Knut; Klingebiel, Sandro; Schultze, Marcel; Tesseit, Catherine Y.; Bessing, Robert; Häfner, Matthias; Prinz, Stefan; Sutter, Dirk; Metzger, Thomas

2016-03-01

We report on the latest developments at TRUMPF Scientific Lasers in the field of ultra-short pulse lasers with highest output energies and powers. All systems are based on the mature and industrialized thin-disk technology of TRUMPF. Thin Yb:YAG disks provide a reliable and efficient solution for power and energy scaling to Joule- and kW-class picosecond laser systems. Due to its efficient one dimensional heat removal, the thin-disk exhibits low distortions and thermal lensing even when pumped under extremely high pump power densities of 10kW/cm². Currently TRUMPF Scientific Lasers develops regenerative amplifiers with highest average powers, optical parametric amplifiers and synchronization schemes. The first few-ps kHz multi-mJ thin-disk regenerative amplifier based on the TRUMPF thindisk technology was developed at the LMU Munich in 20081. Since the average power and energy have continuously been increased, reaching more than 300W (10kHz repetition rate) and 200mJ (1kHz repetition rate) at pulse durations below 2ps. First experiments have shown that the current thin-disk technology supports ultra-short pulse laser solutions >1kW of average power. Based on few-picosecond thin-disk regenerative amplifiers few-cycle optical parametric chirped pulse amplifiers (OPCPA) can be realized. These systems have proven to be the only method for scaling few-cycle pulses to the multi-mJ energy level. OPA based few-cycle systems will allow for many applications such as attosecond spectroscopy, THz spectroscopy and imaging, laser wake field acceleration, table-top few-fs accelerators and laser-driven coherent X-ray undulator sources. Furthermore, high-energy picosecond sources can directly be used for a variety of applications such as X-ray generation or in atmospheric research.

A Wearable and Highly Sensitive Graphene Strain Sensor for Precise Home-Based Pulse Wave Monitoring.

PubMed

Yang, Tingting; Jiang, Xin; Zhong, Yujia; Zhao, Xuanliang; Lin, Shuyuan; Li, Jing; Li, Xinming; Xu, Jianlong; Li, Zhihong; Zhu, Hongwei

2017-07-28

Profuse medical information about cardiovascular properties can be gathered from pulse waveforms. Therefore, it is desirable to design a smart pulse monitoring device to achieve noninvasive and real-time acquisition of cardiovascular parameters. The majority of current pulse sensors are usually bulky or insufficient in sensitivity. In this work, a graphene-based skin-like sensor is explored for pulse wave sensing with features of easy use and wearing comfort. Moreover, the adjustment of the substrate stiffness and interfacial bonding accomplish the optimal balance between sensor linearity and signal sensitivity, as well as measurement of the beat-to-beat radial arterial pulse. Compared with the existing bulky and nonportable clinical instruments, this highly sensitive and soft sensing patch not only provides primary sensor interface to human skin, but also can objectively and accurately detect the subtle pulse signal variations in a real-time fashion, such as pulse waveforms with different ages, pre- and post-exercise, thus presenting a promising solution to home-based pulse monitoring.

Healing of damaged metal by a pulsed high-energy electromagnetic field

NASA Astrophysics Data System (ADS)

Kukudzhanov, K. V.; Levitin, A. L.

2018-04-01

The processes of defect (intergranular micro-cracks) transformation are investigated for metal samples in a high-energy short-pulsed electromagnetic field. This investigation is based on a numerical coupled model of the impact of high-energy electromagnetic field on the pre-damaged thermal elastic-plastic material with defects. The model takes into account the melting and evaporation of the metal and the dependence of its physical and mechanical properties on the temperature. The system of equations is solved numerically by finite element method with an adaptive mesh using the arbitrary Euler–Lagrange method. The calculations show that the welding of the crack and the healing of micro-defects under treatment by short pulses of the current takes place. For the macroscopic description of the healing process, the healing and damage parameters of the material are introduced. The healing of micro-cracks improves the material healing parameter and reduces its damage. The micro-crack shapes practically do not affect the time-dependence of the healing and damage under the treatment by the current pulses. These changes are affected only by the value of the initial damage of the material and the initial length of the micro-crack. The time-dependence of the healing and the damage is practically the same for all different shapes of micro-defects, provided that the initial lengths of micro-cracks and the initial damages are the same for these different shapes of defects.

Formation of short high-power laser radiation pulses in excimer mediums

NASA Astrophysics Data System (ADS)

Losev, V. F., Sr.; Ivanov, N. G.; Panchenko, Yu. N.

2007-06-01

Presently an excimer mediums continue are examined as one of variants for formation of powerful and over powerful pulses of laser radiation with duration from units of nanosecond up to tens femtosecond. The researches on such powerful installations as "NIKE" (USA) and << SUPER ASHURA >>, Japan) proceed in this direction. The main advantage of excimer mediums is the opportunity to work in a frequency mode, absence of restriction on the size of active area, high uniformity of a gas working medium, high efficiency (up to 10 %) and wide spectral range of laser radiation (KrF, XeCl ~ 2nm, XeF (C-A), Xe IICl ~ 50-100 nanometers). Research in area of high quality laser beams formation in excimer mediums and its amplification in high power amplifiers are carried out the long time in Institute of High Current Electronics SB RAS, Tomsk, Russia. The wide aperture XeCl laser system of MELS-4k is used for these investigations. Last time we take part in program on development of high power excimer laser system with a petawatt level of power. This system supposes the formation and amplification high quality laser beams with different pulse duration from units of nanosecond up to tens femtosecond. We research the possibility of laser beams formation in excimer mediums with ps-ns pulse duration having the low noise and divergence near to diffraction limit. In other hand, we are developing the wide aperture XeF(C-A) amplifier with optical pump on base electron accelerator. According to our estimations of the XeF(C-A) amplifier based on the converter of e-beam energy to the Xe II* fluorescence at 172 nm will allow to obtain up to 100 TW peak power in a 30 fs pulse.

High beam quality and high energy short-pulse laser with MOPA

NASA Astrophysics Data System (ADS)

Jin, Quanwei; Pang, Yu; Jiang, JianFeng; Tan, Liang; Cui, Lingling; Wei, Bin; Sun, Yinhong; Tang, Chun

2018-03-01

A high energy, high beam quality short-pulse diode-pumped Nd:YAG master oscillator power-amplifier (MOPA) laser with two amplifier stages is demonstrated. The two-rod birefringence compensation was used as beam quality controlling methods, which presents a short-pulse energy of 40 mJ with a beam quality value of M2 = 1.2 at a repetition rate of 400Hz. The MOPA system delivers a short-pulse energy of 712.5 mJ with a pulse width of 12.4 ns.The method of spherical aberration compensation is improved the beam quality, a M2 factor of 2.3 and an optical-to-optical efficiency of 27.7% is obtained at the maximum laser out power.The laser obtained 1.4J out energy with polarization integration.

A compact submicrosecond, high current generator

NASA Astrophysics Data System (ADS)

Kovalchuk, B. M.; Kharlov, A. V.; Zorin, V. B.; Zherlitsyn, A. A.

2009-08-01

Pulsed current generator was developed for experiments with current carrying pulsed plasma. Main parts of the generator are capacitor bank, low inductive current driving lines, and central load part. Generator consists of four identical sections, connected in parallel to one load. Capacitor bank is assembled from 24 capacitor blocks (100 kV, 80 nF), connected in parallel. It stores 9.6 kJ at 100 kV charging voltage. Each capacitor block incorporates a multigap spark switch, which is able to commute by six parallel channels. Switches operate in dry air at atmospheric pressure. The generator was tested with an inductive load and a liner load. At 17.5 nH inductive load and 100 kV of charging voltage it provides 650 kA of current amplitude with 390 ns rise time with 0.6 Ω damping resistors in discharge circuit of each capacitor block. The net generator inductance without a load was optimized to be as low as 15 nH, which results in extremely low impedance of the generator (˜0.08 Ω). It ensures effective energy coupling with a low impedance load such as Z pinch. The generator operates reliably without any adjustments in 70-100 kV range of charging voltage. Jitter in delay between output pulse and triggering pulse is less than 5 ns at 70-100 kV charging voltage. Operation and handling are very simple, because no oil or purified gases are required for the generator. The generator has dimensions 5.24×1.2×0.18 m3 and total weight about 1400 kg, thus manifesting itself as simple, robust, and cost effective apparatus.

High-gradient, pulsed operation of superconducting niobium cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campisi, I.E.; Farkas, Z.D.

1984-02-01

Tests performed on several Niobium TM/sub 010/ cavities at frequencies of about 2856 MHz using a high-power, pulsed method indicate that, at the end of the charging pulse, peak surface magnetic fields of up to approx. 1300 Oe, corresponding to a peak surface electric field of approx. 68 MV/m, can be reached at 4.2/sup 0/K without appreciable average losses. Further studies of the properties of superconductors under pulsed operation might shed light on fundamental properties of rf superconductivity, as well as lead to the possibility of applying the pulse method to the operation of high-gradient linear colliders. 7 references, 30more » figures, 2 tables.« less

Giant Pulse Phenomena in a High Gain Erbium Doped Fiber Amplifier

NASA Technical Reports Server (NTRS)

Li, Stephen X.; Merritt, Scott; Krainak, Michael A.; Yu, Anthony

2018-01-01

High gain Erbium Doped Fiber Amplifiers (EDFAs), while revolutionizing optical communications, remain vulnerable to optical damage when unseeded, e.g. due to nonlinear effects that produce random pulses with high peak power, i.e. giant pulses. Giant pulses can damage the components in a high gain EDFA or external components and systems coupled to the EDFA. We explore the conditions under which a reflective, polarization-maintaining (PM), core-pumped high gain EDFA generates giant pulses, provide details on conditions under which normal pulses evolve into giant pulses, and provide results on the transient effects of giant pulses on amplifier's fused-fiber couplers, an effect which we call Fiber Overload Induced Leakage (FOIL). While FOIL's effect on fused-fiber couplers is temporary, its damage to forward pump lasers in a high gain EDFA can be permanent.

High power pulsed sources based on fiber amplifiers

NASA Astrophysics Data System (ADS)

Canat, Guillaume; Jaouën, Yves; Mollier, Jean-Claude; Bouzinac, Jean-Pierre; Cariou, Jean-Pierre

2017-11-01

Cladding-pumped rare-earth-doped fiber laser technologies are currently among the best sources for high power applications. Theses extremely compact and robust sources appoint them as good candidate for aeronautical and space applications. The double-clad (DC) fiber converts the poor beamquality of high-power large-area pump diodes from the 1st cladding to laser light at another wavelength guided in an active single-mode core. High-power coherent MOPA (Master Oscillator Power Amplifier) sources (several 10W CW or several 100W in pulsed regime) will soon be achieved. Unfortunately it also brings nonlinear effects which quickly impairs output signal distortions. Stimulated Brillouin scattering (SBS) and optical parametric amplification (OPA) have been shown to be strong limitations. Based on amplifier modeling and experiments we discuss the performances of these sources.

Electrical characteristics of thin Ta2O5 films deposited by reactive pulsed direct-current magnetron sputtering

NASA Astrophysics Data System (ADS)

Kim, J.-Y.; Nielsen, M. C.; Rymaszewski, E. J.; Lu, T.-M.

2000-02-01

Room temperature deposition of tantalum oxide films on metallized silicon substrates was investigated by reactive pulsed magnetron sputtering of Ta in an Ar/O2 ambient. The dielectric constant of the tantalum oxide ranged from 19 to 31 depending on the oxygen percentage [P(%)=PO2/(PO2+PAr)] used during sputtering. The leakage current density was less than 10 nA/cm2 at 0.5 MV/cm electric field and the dielectric breakdown field was greater than 3.8 MV/cm for P=60%. A charge storage as high as 3.3 μF/cm2 was achieved for 70-Å-thick film. Pulse frequency variation (from 20 to 200 kHz) did not give a significant effect in the electrical properties (dielectric constant or leakage current density) of the Ta2O5 films.

SFOL Pulse: A High Accuracy DME Pulse for Alternative Aircraft Position and Navigation.

PubMed

Kim, Euiho; Seo, Jiwon

2017-09-22

In the Federal Aviation Administration's (FAA) performance based navigation strategy announced in 2016, the FAA stated that it would retain and expand the Distance Measuring Equipment (DME) infrastructure to ensure resilient aircraft navigation capability during the event of a Global Navigation Satellite System (GNSS) outage. However, the main drawback of the DME as a GNSS back up system is that it requires a significant expansion of the current DME ground infrastructure due to its poor distance measuring accuracy over 100 m. The paper introduces a method to improve DME distance measuring accuracy by using a new DME pulse shape. The proposed pulse shape was developed by using Genetic Algorithms and is less susceptible to multipath effects so that the ranging error reduces by 36.0-77.3% when compared to the Gaussian and Smoothed Concave Polygon DME pulses, depending on noise environment.

Blocking and guiding adult sea lamprey with pulsed direct current from vertical electrodes

USGS Publications Warehouse

Johnson, Nicholas S.; Thompson, Henry T.; Holbrook, Christopher M.; Tix, John A.

2014-01-01

Controlling the invasion front of aquatic nuisance species is of high importance to resource managers. We tested the hypothesis that adult sea lamprey (Petromyzon marinus), a destructive invasive species in the Laurentian Great Lakes, would exhibit behavioral avoidance to dual-frequency pulsed direct current generated by vertical electrodes and that the electric field would not injure or kill sea lamprey or non-target fish. Laboratory and in-stream experiments demonstrated that the electric field blocked sea lamprey migration and directed sea lamprey into traps. Rainbow trout (Oncorhynchus mykiss) and white sucker (Catostomus commersoni), species that migrate sympatrically with sea lamprey, avoided the electric field and had minimal injuries when subjected to it. Vertical electrodes are advantageous for fish guidance because (1) the electric field produced varies minimally with depth, (2) the electric field is not grounded, reducing power consumption to where portable and remote deployments powered by solar, wind, hydro, or a small generator are feasible, and (3) vertical electrodes can be quickly deployed without significant stream modification allowing rapid responses to new invasions. Similar dual-frequency pulsed direct current fields produced from vertical electrodes may be advantageous for blocking or trapping other invasive fish or for guiding valued fish around dams.

Giant Pulse Phenomena in a High Gain Erbium Doped Fiber Amplifier

NASA Technical Reports Server (NTRS)

Li, Stephen X.; Merritt, Scott; Krainak, Michael A.; Yu, Anthony

2018-01-01

High gain Erbium Doped Fiber Amplifiers (EDFAs) are vulnerable to optical damage when unseeded, e.g. due to nonlinear effects that produce random, spontaneous Q-switched (SQS) pulses with high peak power, i.e. giant pulses. Giant pulses can damage either the components within a high gain EDFA or external components and systems coupled to the EDFA. We explore the conditions under which a reflective, polarization-maintaining (PM), core-pumped high gain EDFA generates giant pulses, provide details on the evolution of normal pulses into giant pulses, and provide results on the transient effects of giant pulses on an amplifier's fused-fiber couplers, an effect which we call Fiber Overload Induced Leakage (FOIL). While FOIL's effect on fused-fiber couplers is temporary, its damage to forward pump lasers in a high gain EDFA can be permanent.

Reduction of pressure ulcer size with high-voltage pulsed current and high-frequency ultrasound: a randomised trial.

PubMed

Polak, A; Taradaj, J; Nawrat-Szoltysik, A; Stania, M; Dolibog, P; Blaszczak, E; Zarzeczny, R; Juras, G; Franek, A; Kucio, C

2016-12-02

International guidelines recommend the use of ultrasound (US) and electrical stimulation (ES) for treating chronic and recurrent pressure ulcers (PUs). The methodology of these procedures, however, still needs elaboration and confirmation by clinical studies. This parallel-group, randomised, single-blind, prospective, controlled clinical trial was conducted to determine whether by using high-frequency ultrasound (HFUS) and high-voltage monophasic pulsed current (HVMPC), the rate of change in the area of older patients' PUs can be accelerated. Patients were randomly assigned to receive either: standard wound care (SWC) involving supportive care and topical treatments; SWC+US (1MHz; 0.5 W/cm 2 ; 20%; 1-3 minutes/cm2); or SWC+ES (HVMPC, 154 µs, 100 pps, 100 V, 250 µC/sec, 50 minutes/day). US and ES were administered once a day, 5 days a week. The primary outcome was change in PU surface area measured against baseline after 6 weeks of treatment with SWC, SWC+US, and SWC+ES. We recruited 77 patients, aged 60-95 years (80% aged over 70 years of age), with 88 Category II, III and IV PUs were enrolled in the study. The percentage reduction in the surface area of PUs at the end of treatment was significantly greater in the SWC+US group (mean ± standard deviation, 77.48±11.59 %; p=0.024) and the SWC+ES group (76.19±32.83%; p=0.030) versus the control group (48.97±53.42%). The SWC+ES group also had a significantly greater proportion of PUs that decreased in area by at least 50% or closed than the control group (p=0.05 and 0.031, respectively). The SWC+US and SWC+ES groups were not statistically significant different regarding treatment results. Clinical side effects were not recorded. The results show that HFUS and HVMPC are comparable regarding their effectiveness in reducing the size of PUs in older people. The authors have nothing to disclose. All research activities were funded by the Academy of Physical Education, Katowice, Poland.

Reversing-counterpulse repetitive-pulse inductive storage circuit

DOEpatents

Honig, E.M.

1987-02-10

A high-power reversing-counterpulse repetitive-pulse inductive storage and transfer circuit includes an opening switch, a main energy storage coil, a counterpulse capacitor and a small inductor. After counterpulsing the opening switch off, the counterpulse capacitor is recharged by the main energy storage coil before the load pulse is initiated. This gives the counterpulse capacitor sufficient energy for the next counterpulse operation, although the polarity of the capacitor's voltage must be reversed before that can occur. By using a current-zero switch as the counterpulse start switch, the capacitor is disconnected from the circuit (with a full charge) when the load pulse is initiated, preventing the capacitor from depleting its energy store by discharging through the load. After the load pulse is terminated by reclosing the main opening switch, the polarity of the counterpulse capacitor voltage is reversed by discharging the capacitor through a small inductor and interrupting the discharge current oscillation at zero current and peak reversed voltage. The circuit enables high-power, high-repetition-rate operation with reusable switches and features total control (pulse-to-pulse) over output pulse initiation, duration, repetition rate, and, to some extent, risetime. 10 figs.

Reversing-counterpulse repetitive-pulse inductive storage circuit

DOEpatents

Honig, Emanuel M.

1987-01-01

A high-power reversing-counterpulse repetitive-pulse inductive storage and transfer circuit includes an opening switch, a main energy storage coil, a counterpulse capacitor and a small inductor. After counterpulsing the opening switch off, the counterpulse capacitor is recharged by the main energy storage coil before the load pulse is initiated. This gives the counterpulse capacitor sufficient energy for the next counterpulse operation, although the polarity of the capacitor's voltage must be reversed before that can occur. By using a current-zero switch as the counterpulse start switch, the capacitor is disconnected from the circuit (with a full charge) when the load pulse is initiated, preventing the capacitor from depleting its energy store by discharging through the load. After the load pulse is terminated by reclosing the main opening switch, the polarity of the counterpulse capacitor voltage is reversed by discharging the capacitor through a small inductor and interrupting the discharge current oscillation at zero current and peak reversed voltage. The circuit enables high-power, high-repetition-rate operation with reusable switches and features total control (pulse-to-pulse) over output pulse initiation, duration, repetition rate, and, to some extent, risetime.

Reversing-counterpulse repetitive-pulse inductive storage circuit

DOEpatents

Honig, E.M.

1984-06-05

A high power reversing-counterpulse repetitive-pulse inductive storage and transfer circuit includes an opening switch, a main energy storage coil, a counterpulse capacitor and a small inductor. After counterpulsing the opening switch off, the counterpulse capacitor is recharged by the main energy storage coil before the load pulse is initiated. This gives the counterpulse capacitor sufficient energy for the next counterpulse operation, although the polarity of the capacitor's voltage must be reversed before that can occur. By using a current-zero switch as the counterpulse start switch, the capacitor is disconnected from the circuit (with a full charge) when the load pulse is initiated, preventing the capacitor from depleting its energy store by discharging through the load. After the load pulse is terminated by reclosing the main opening switch, the polarity of the counterpulse capacitor voltage is reversed by discharging the capacitor through a small inductor and interrupting the discharge current oscillation at zero current and peak reversed voltage. The circuit enables high-power, high-repetition-rate operation with reusable switches and features total control (pulse-to-pulse) over output pulse initiation, duration, repetition rate, and, to some extent, risetime.

Nanosecond pulsed laser welding of high carbon steels

NASA Astrophysics Data System (ADS)

Ascari, Alessandro; Fortunato, Alessandro

2014-03-01

The present paper deals with the possibility to exploit low-cost, near infra-red, nanosecond pulsed laser sources in welding of high carbon content thin sheets. The exploitation of these very common sources allows to achieve sound weld beads with a good depth-to-width ratio and very small heat affected zones when the proper process parameters are involved. In particular the role of pulse frequency, pulse duration, peak power and welding speed on the characteristics of the weld beads is studied and the advantage of the application of short-pulse laser sources over traditional long-pulse or continuous wave one is assessed.

A Tesla-pulse forming line-plasma opening switch pulsed power generator.

PubMed

Novac, B M; Kumar, R; Smith, I R

2010-10-01

A pulsed power generator based on a high-voltage Tesla transformer which charges a 3.85 Ω/55 ns water-filled pulse forming line to 300 kV has been developed at Loughborough University as a training tool for pulsed power students. The generator uses all forms of insulation specific to pulsed power technology, liquid (oil and water), gas (SF(6)), and magnetic insulation in vacuum, and a number of fast voltage and current sensors are implemented for diagnostic purposes. A miniature (centimeter-size) plasma opening switch has recently been coupled to the output of the pulse forming line, with the overall system comprising the first phase of a program aimed at the development of a novel repetitive, table-top generator capable of producing 15 GW pulses for high power microwave loads. Technical details of all the generator components and the main experimental results obtained during the program and demonstrations of their performance are presented in the paper, together with a description of the various diagnostic tools involved. In particular, it is shown that the miniature plasma opening switch is capable of reducing the rise time of the input current while significantly increasing the load power. Future plans are outlined in the conclusions.

High yield neutron generator based on a high-current gasdynamic electron cyclotron resonance ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skalyga, V.; Sidorov, A.; Lobachevsky State University of Nizhny Novgorod

2015-09-07

In present paper, an approach for high yield compact D-D neutron generator based on a high current gasdynamic electron cyclotron resonance ion source is suggested. Results on dense pulsed deuteron beam production with current up to 500 mA and current density up to 750 mA/cm{sup 2} are demonstrated. Neutron yield from D{sub 2}O and TiD{sub 2} targets was measured in case of its bombardment by pulsed 300 mA D{sup +} beam with 45 keV energy. Neutron yield density at target surface of 10{sup 9} s{sup −1} cm{sup −2} was detected with a system of two {sup 3}He proportional counters. Estimations based on obtained experimental resultsmore » show that neutron yield from a high quality TiD{sub 2} target bombarded by D{sup +} beam demonstrated in present work accelerated to 100 keV could reach 6 × 10{sup 10} s{sup −1} cm{sup −2}. It is discussed that compact neutron generator with such characteristics could be perspective for a number of applications like boron neutron capture therapy, security systems based on neutron scanning, and neutronography.« less

Effects of Pulse Current on Endurance Exercise and Its Anti-Fatigue Properties in the Hepatic Tissue of Trained Rats

PubMed Central

Ju, Xiaowei; Zhu, Lvgang; Huang, Changlin; Huang, Tao; Zuo, Xincheng; Gao, Chunfang

2013-01-01

Fatigue is synonymous with a wide spectrum of familiar physiological conditions, from pathology and general health, to sport and physical exercise. Strenuous, prolonged exercise training causes fatigue. Although several studies have investigated the effects of electrical stimulation frequency on muscle fatigue, the effects of percutaneous pulse current stimulation on fatigue in the hepatic tissue of trained rats is still unclear. In order to find an effective strategy to prevent fatigue or enhance recovery, the effects of pulse current on endurance exercise and its anti-fatigue properties in exercised rats were studied. Rats were subjected to one, three or five weeks of swimming exercise training. After exercise training, rats in the treated group received daily applications of pulse current. All rats were sacrificed after one, three or five weeks of swimming exercise, and the major biochemical indexes were measured in serum and liver. The results demonstrate that pulse current could prolong the exhaustion swimming time, as well as decrease serum ALT, AST and LD levels and liver MDA content. It also elevated serum LDH activity, liver SOD activity and glycogen content. Furthermore, pulse current increased the expression of Bcl-2 and decreased the expression of Bax. Taken together, these results show that pulse current can elevate endurance capacity and facilitate recovery from fatigue. PMID:24116026

High-repetition-rate short-pulse gas discharge.

PubMed

Tulip, J; Seguin, H; Mace, P N

1979-09-01

A high-average-power short-pulse gas discharge is described. This consists of a volume-preionized transverse discharge of the type used in gas lasers driven by a Blumlein energy storage circuit. The Blumlein circuit is fabricated from coaxial cable, is pulse-charged from a high-repetition-rate Marx-bank generator, and is switched by a high-repetition-rate segmented rail gap. The operation of this discharge under conditions typical of rare-gas halide lasers is described. A maximum of 900 pps was obtained, giving a power flow into the discharge of 30 kW.

High voltage pulse generator. [Patent application

DOEpatents

Fasching, G.E.

1975-06-12

An improved high-voltage pulse generator is described which is especially useful in ultrasonic testing of rock core samples. An N number of capacitors are charged in parallel to V volts and at the proper instance are coupled in series to produce a high-voltage pulse of N times V volts. Rapid switching of the capacitors from the paralleled charging configuration to the series discharging configuration is accomplished by using silicon-controlled rectifiers which are chain self-triggered following the initial triggering of the first rectifier connected between the first and second capacitors. A timing and triggering circuit is provided to properly synchronize triggering pulses to the first SCR at a time when the charging voltage is not being applied to the parallel-connected charging capacitors. The output voltage can be readily increased by adding additional charging networks. The circuit allows the peak level of the output to be easily varied over a wide range by using a variable autotransformer in the charging circuit.

[Atomic/ionic fluorescence in microwave plasma torch discharge excited by high current microsecond pulsed hollow cathode lamp-europium atomic/ionic fluorescence spectrometry].

PubMed

Gong, Z; Liang, F; Yang, P; Jin, Q; Huang, B

1999-06-01

Eu atomic and ionic fluorescence spectrometry in microwave plasma torch discharge excited by high current microsecond pulsed hollow cathode lamp (HCMP HCL-MPT AFS/IFS) was studied. Operating conditions were optimized. The best detection limits for AFS and IFS obtained with a desolvated ultrasonic nebulization system were 42.0 ng/mL for Eu I 462.7 nm and 21.8 ng/mL for Eu II 381.97 nm, respectively, both were better than those given by the instruction manual of a Baird ICP AFS-2000 spectrometer using pneumatic concentric nebulizer with desolvation for AFS, but were significantly higher than those obtained by using the Baird spectrometer with a mini-monochromator and a ultrasonic nebulzer system.

Influence of a falling edge on high power microwave pulse combination

NASA Astrophysics Data System (ADS)

Li, Jiawei; Huang, Wenhua; Zhu, Qi; Xiao, Renzhen; Shao, Hao

2016-07-01

This paper presents an explanation of the influence of a microwave falling edge on high-power microwave pulse combination. Through particle-in-cell simulations, we discover that the falling edge is the driving factor that limits the output power of the combined pulses. We demonstrate that the space charge field, which accumulates to become comparable to the E-field at the falling edge of the former pulse, will trap the electrons in the gas layer and decrease its energy to attain a high ionization rate. Hence, avalanche discharge, caused by trapped electrons, makes the plasma density to approach the critical density and cuts off the latter microwave pulse. An X-band combination experiment is conducted with different pulse intervals. This experiment confirms that the high density plasma induced by the falling edge can cut off the latter pulse, and that the time required for plasma recombination in the transmission channel is several microseconds. To ensure a high output power for combined pulses, the latter pulse should be moved ahead of the falling edge of the former one, and consequently, a beat wave with high peak power becomes the output by adding two pulses with normal amplitudes.

A high current pulsed power generator CQ-3-MMAF with co-axial cable transmitting energy for material dynamics experiments

NASA Astrophysics Data System (ADS)

Wang, Guiji; Chen, Xuemiao; Cai, Jintao; Zhang, Xuping; Chong, Tao; Luo, Binqiang; Zhao, Jianheng; Sun, Chengwei; Tan, Fuli; Liu, Cangli; Wu, Gang

2016-06-01

A high current pulsed power generator CQ-3-MMAF (Multi-Modules Assembly Facility, MMAF) was developed for material dynamics experiments under ramp wave and shock loadings at the Institute of Fluid Physics (IFP), which can deliver 3 MA peak current to a strip-line load. The rise time of the current is 470 ns (10%-90%). Different from the previous CQ-4 at IFP, the CQ-3-MMAF energy is transmitted by hundreds of co-axial high voltage cables with a low impedance of 18.6 mΩ and low loss, and then hundreds of cables are reduced and converted to tens of cables into a vacuum chamber by a cable connector, and connected with a pair of parallel metallic plates insulated by Kapton films. It is composed of 32 capacitor and switch modules in parallel. The electrical parameters in short circuit are with a capacitance of 19.2 μF, an inductance of 11.7 nH, a resistance of 4.3 mΩ, and working charging voltage of 60 kV-90 kV. It can be run safely and stable when charged from 60 kV to 90 kV. The vacuum of loading chamber can be up to 10-2 Pa, and the current waveforms can be shaped by discharging in time sequences of four groups of capacitor and switch modules. CQ-3-MMAF is an adaptive machine with lower maintenance because of its modularization design. The COMSOL Multi-physics® code is used to optimize the structure of some key components and calculate their structural inductance for designs, such as gas switches and cable connectors. Some ramp wave loading experiments were conducted to check and examine the performances of CQ-3-MMAF. Two copper flyer plates were accelerated to about 3.5 km/s in one shot when the working voltage was charged to 70 kV. The velocity histories agree very well. The dynamic experiments of some polymer bonded explosives and phase transition of tin under ramp wave loadings were also conducted. The experimental data show that CQ-3-MMAF can be used to do material dynamics experiments in high rate and low cost shots. Based on this design concept, the peak

A high current pulsed power generator CQ-3-MMAF with co-axial cable transmitting energy for material dynamics experiments.

PubMed

Wang, Guiji; Chen, Xuemiao; Cai, Jintao; Zhang, Xuping; Chong, Tao; Luo, Binqiang; Zhao, Jianheng; Sun, Chengwei; Tan, Fuli; Liu, Cangli; Wu, Gang

2016-06-01

A high current pulsed power generator CQ-3-MMAF (Multi-Modules Assembly Facility, MMAF) was developed for material dynamics experiments under ramp wave and shock loadings at the Institute of Fluid Physics (IFP), which can deliver 3 MA peak current to a strip-line load. The rise time of the current is 470 ns (10%-90%). Different from the previous CQ-4 at IFP, the CQ-3-MMAF energy is transmitted by hundreds of co-axial high voltage cables with a low impedance of 18.6 mΩ and low loss, and then hundreds of cables are reduced and converted to tens of cables into a vacuum chamber by a cable connector, and connected with a pair of parallel metallic plates insulated by Kapton films. It is composed of 32 capacitor and switch modules in parallel. The electrical parameters in short circuit are with a capacitance of 19.2 μF, an inductance of 11.7 nH, a resistance of 4.3 mΩ, and working charging voltage of 60 kV-90 kV. It can be run safely and stable when charged from 60 kV to 90 kV. The vacuum of loading chamber can be up to 10(-2) Pa, and the current waveforms can be shaped by discharging in time sequences of four groups of capacitor and switch modules. CQ-3-MMAF is an adaptive machine with lower maintenance because of its modularization design. The COMSOL Multi-physics® code is used to optimize the structure of some key components and calculate their structural inductance for designs, such as gas switches and cable connectors. Some ramp wave loading experiments were conducted to check and examine the performances of CQ-3-MMAF. Two copper flyer plates were accelerated to about 3.5 km/s in one shot when the working voltage was charged to 70 kV. The velocity histories agree very well. The dynamic experiments of some polymer bonded explosives and phase transition of tin under ramp wave loadings were also conducted. The experimental data show that CQ-3-MMAF can be used to do material dynamics experiments in high rate and low cost shots. Based on this design concept, the peak

Effect of secondary electron emission on subnanosecond breakdown in high-voltage pulse discharge

NASA Astrophysics Data System (ADS)

Schweigert, I. V.; Alexandrov, A. L.; Gugin, P.; Lavrukhin, M.; Bokhan, P. A.; Zakrevsky, Dm E.

2017-11-01

The subnanosecond breakdown in open discharge may be applied for producing superfast high power switches. Such fast breakdown in high-voltage pulse discharge in helium was explored both in experiment and in kinetic simulations. The kinetic model of electron avalanche development was developed using PIC-MCC technique. The model simulates motion of electrons, ions and fast helium atoms, appearing due to ions scattering. It was shown that the mechanism responsible for ultra-fast breakdown development is the electron emission from cathode. The photoemission and emission by ions or fast atoms impact is the main reason of current growth at the early stage of breakdown, but at the final stage, when the voltage on discharge gap drops, the secondary electron emission (SEE) is responsible for subnanosecond time scale of current growth. It was also found that the characteristic time of the current growth τS depends on the SEE yield of the cathode material. Three types of cathode material (titanium, SiC, and CuAlMg-alloy) were tested. It is shown that in discharge with SiC and CuAlMg-alloy cathodes (which have enhanced SEE) the current can increase with a subnanosecond characteristic time as small as τS = 0.4 ns, for the pulse voltage amplitude of 5- 12 kV..

SFOL Pulse: A High Accuracy DME Pulse for Alternative Aircraft Position and Navigation

PubMed Central

Kim, Euiho

2017-01-01

In the Federal Aviation Administration’s (FAA) performance based navigation strategy announced in 2016, the FAA stated that it would retain and expand the Distance Measuring Equipment (DME) infrastructure to ensure resilient aircraft navigation capability during the event of a Global Navigation Satellite System (GNSS) outage. However, the main drawback of the DME as a GNSS back up system is that it requires a significant expansion of the current DME ground infrastructure due to its poor distance measuring accuracy over 100 m. The paper introduces a method to improve DME distance measuring accuracy by using a new DME pulse shape. The proposed pulse shape was developed by using Genetic Algorithms and is less susceptible to multipath effects so that the ranging error reduces by 36.0–77.3% when compared to the Gaussian and Smoothed Concave Polygon DME pulses, depending on noise environment. PMID:28937615

High power parallel ultrashort pulse laser processing

NASA Astrophysics Data System (ADS)

Gillner, Arnold; Gretzki, Patrick; Büsing, Lasse

2016-03-01

The class of ultra-short-pulse (USP) laser sources are used, whenever high precession and high quality material processing is demanded. These laser sources deliver pulse duration in the range of ps to fs and are characterized with high peak intensities leading to a direct vaporization of the material with a minimum thermal damage. With the availability of industrial laser source with an average power of up to 1000W, the main challenge consist of the effective energy distribution and disposition. Using lasers with high repetition rates in the MHz region can cause thermal issues like overheating, melt production and low ablation quality. In this paper, we will discuss different approaches for multibeam processing for utilization of high pulse energies. The combination of diffractive optics and conventional galvometer scanner can be used for high throughput laser ablation, but are limited in the optical qualities. We will show which applications can benefit from this hybrid optic and which improvements in productivity are expected. In addition, the optical limitations of the system will be compiled, in order to evaluate the suitability of this approach for any given application.

Highly Efficient Vector-Inversion Pulse Generators

NASA Technical Reports Server (NTRS)

Rose, Franklin

2004-01-01

Improved transmission-line pulse generators of the vector-inversion type are being developed as lightweight sources of pulsed high voltage for diverse applications, including spacecraft thrusters, portable x-ray imaging systems, impulse radar systems, and corona-discharge systems for sterilizing gases. In this development, more than the customary attention is paid to principles of operation and details of construction so as to the maximize the efficiency of the pulse-generation process while minimizing the sizes of components. An important element of this approach is segmenting a pulse generator in such a manner that the electric field in each segment is always below the threshold for electrical breakdown. One design of particular interest, a complete description of which was not available at the time of writing this article, involves two parallel-plate transmission lines that are wound on a mandrel, share a common conductor, and are switched in such a manner that the pulse generator is divided into a "fast" and a "slow" section. A major innovation in this design is the addition of ferrite to the "slow" section to reduce the size of the mandrel needed for a given efficiency.

Oriented graphite layer formation in Ti/C and TiC/C multilayers deposited by high current pulsed cathodic arc

DOE Office of Scientific and Technical Information (OSTI.GOV)

Persson, P. O. A.; Ryves, L.; Tucker, M. D.

2008-10-01

Ti/C and TiC/C multilayers with periods ranging from 2 to 18 nm were grown by filtered high current pulsed cathodic arc. The growth was monitored in situ by ellipsometry and cantilever stress measurements. The ellipsometry results reveal that the optical properties of the carbon vary as a function of thickness. Correspondingly, the stress in each carbon layer as measured in situ exhibits two well defined values: initially the stress is low and then takes on a higher value for the remainder of the layer. Transmission electron microscopy shows that the initial growth of carbon on Ti or TiC layer ismore » oriented with graphitic basal planes aligned parallel to the interface. After 2-4 nm of growth, the graphitic structure transforms to amorphous carbon. Electron energy loss spectroscopy shows that the carbon layer simultaneously undergoes a transition from sp{sup 2} rich to sp{sup 3} rich material.« less

Membrane permeabilization of mammalian cells using bursts of high magnetic field pulses

PubMed Central

Grainys, Audrius; Kranjc, Matej; Miklavčič, Damijan

2017-01-01

Background Cell membrane permeabilization by pulsed electromagnetic fields (PEMF) is a novel contactless method which results in effects similar to conventional electroporation. The non-invasiveness of the methodology, independence from the biological object homogeneity and electrical conductance introduce high flexibility and potential applicability of the PEMF in biomedicine, food processing, and biotechnology. The inferior effectiveness of the PEMF permeabilization compared to standard electroporation and the lack of clear description of the induced transmembrane transport are currently of major concern. Methods The PEMF permeabilization experiments have been performed using a 5.5 T, 1.2 J pulse generator with a multilayer inductor as an applicator. We investigated the feasibility to increase membrane permeability of Chinese Hamster Ovary (CHO) cells using short microsecond (15 µs) pulse bursts (100 or 200 pulses) at low frequency (1 Hz) and high dB/dt (>106 T/s). The effectiveness of the treatment was evaluated by fluorescence microscopy and flow cytometry using two different fluorescent dyes: propidium iodide (PI) and YO-PRO®-1 (YP). The results were compared to conventional electroporation (single pulse, 1.2 kV/cm, 100 µs), i.e., positive control. Results The proposed PEMF protocols (both for 100 and 200 pulses) resulted in increased number of permeable cells (70 ± 11% for PI and 67 ± 9% for YP). Both cell permeabilization assays also showed a significant (8 ± 2% for PI and 35 ± 14% for YP) increase in fluorescence intensity indicating membrane permeabilization. The survival was not affected. Discussion The obtained results demonstrate the potential of PEMF as a contactless treatment for achieving reversible permeabilization of biological cells. Similar to electroporation, the PEMF permeabilization efficacy is influenced by pulse parameters in a dose-dependent manner. PMID:28462057

Spheromak Formation and Current Sustainment Using a Repetitively Pulsed Source

NASA Astrophysics Data System (ADS)

Woodruff, S.; Macnab, A. I. D.; Ziemba, T. M.; Miller, K. E.

2009-06-01

By repeated injection of magnetic helicity ( K = 2φψ) on time-scales short compared with the dissipation time (τinj << τ K ), it is possible to produce toroidal currents relevant to POP-level experiments. Here we discuss an effective injection rate, due to the expansion of a series of current sheets and their subsequent reconnection to form spheromaks and compression into a copper flux-conserving chamber. The benefits of repeated injection are that the usual limits to current amplification can be exceeded, and an efficient quasi-steady sustainment scenario is possible (within minimum impact on confinement). A new experiment designed to address the physics of pulsed formation and sustainment is described.

Influence of a falling edge on high power microwave pulse combination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jiawei; Huang, Wenhua; Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024

This paper presents an explanation of the influence of a microwave falling edge on high-power microwave pulse combination. Through particle-in-cell simulations, we discover that the falling edge is the driving factor that limits the output power of the combined pulses. We demonstrate that the space charge field, which accumulates to become comparable to the E-field at the falling edge of the former pulse, will trap the electrons in the gas layer and decrease its energy to attain a high ionization rate. Hence, avalanche discharge, caused by trapped electrons, makes the plasma density to approach the critical density and cuts offmore » the latter microwave pulse. An X-band combination experiment is conducted with different pulse intervals. This experiment confirms that the high density plasma induced by the falling edge can cut off the latter pulse, and that the time required for plasma recombination in the transmission channel is several microseconds. To ensure a high output power for combined pulses, the latter pulse should be moved ahead of the falling edge of the former one, and consequently, a beat wave with high peak power becomes the output by adding two pulses with normal amplitudes.« less

Dose rate in brachytherapy using after-loading machine: pulsed or high-dose rate?

PubMed

Hannoun-Lévi, J-M; Peiffert, D

2014-10-01

Since February 2014, it is no longer possible to use low-dose rate 192 iridium wires due to the end of industrial production of IRF1 and IRF2 sources. The Brachytherapy Group of the French society of radiation oncology (GC-SFRO) has recommended switching from iridium wires to after-loading machines. Two types of after-loading machines are currently available, based on the dose rate used: pulsed-dose rate or high-dose rate. In this article, we propose a comparative analysis between pulsed-dose rate and high-dose rate brachytherapy, based on biological, technological, organizational and financial considerations. Copyright © 2014 Société française de radiothérapie oncologique (SFRO). Published by Elsevier SAS. All rights reserved.

Pulse switching for high energy lasers

NASA Technical Reports Server (NTRS)

Laudenslager, J. B.; Pacala, T. J. (Inventor)

1981-01-01

A saturable inductor switch for compressing the width and sharpening the rise time of high voltage pulses from a relatively slow rise time, high voltage generator to an electric discharge gas laser (EDGL) also provides a capability for efficient energy transfer from a high impedance primary source to an intermediate low impedance laser discharge network. The switch is positioned with respect to a capacitive storage device, such as a coaxial cable, so that when a charge build-up in the storage device reaches a predetermined level, saturation of the switch inductor releases or switches energy stored in the capactive storage device to the EDGL. Cascaded saturable inductor switches for providing output pulses having rise times of less than ten nanoseconds and a technique for magnetically biasing the saturable inductor switch are disclosed.

Domain wall dynamics along curved strips under current pulses: The influence of Joule heating

NASA Astrophysics Data System (ADS)

Raposo, Victor; Moretti, Simone; Hernandez, Maria Auxiliadora; Martinez, Eduardo

2016-01-01

The current-induced domain wall dynamics along curved ferromagnetic strips is studied by coupling the magnetization dynamics to the heat transport. Permalloy strips with uniform and non-uniform cross section are evaluated, taking into account the influence of the electrical contacts used to inject the current pulses and the substrate on top of which the ferromagnetic strip is sited. Micromagnetic simulations indicate that the geometry and the non-ferromagnetic materials in the system play a significant role in the current-induced domain wall dynamics. Due to the natural pinning, domain walls are hardly affected by the spin-transfer torques when placed in uniform cross section strips under current pulses with reduced magnitude. On the contrary, the current-induced domain wall displacement is significantly different in strips with non-uniform cross section, where thermal gradients emerge as due to the Joule heating. It is found that these thermal gradients can assist or act against the pure spin-transfer torques, in agreement with the recent experimental observations.

Cellular response to high pulse repetition rate nanosecond pulses varies with fluorescent marker identity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steelman, Zachary A., E-mail: zachary.steelman@duke.edu; Tolstykh, Gleb P.; Beier, Hope T.

Nanosecond electric pulses (nsEP's) are a well-studied phenomena in biophysics that cause substantial alterations to cellular membrane dynamics, internal biochemistry, and cytoskeletal structure, and induce apoptotic and necrotic cell death. While several studies have attempted to measure the effects of multiple nanosecond pulses, the effect of pulse repetition rate (PRR) has received little attention, especially at frequencies greater than 100 Hz. In this study, uptake of Propidium Iodide, FM 1–43, and YO-PRO-1 fluorescent dyes in CHO-K1 cells was monitored across a wide range of PRRs (5 Hz–500 KHz) using a laser-scanning confocal microscope in order to better understand how high frequency repetition ratesmore » impact induced biophysical changes. We show that frequency trends depend on the identity of the dye under study, which could implicate transmembrane protein channels in the uptake response due to their chemical selectivity. Finally, YO-PRO-1 fluorescence was monitored in the presence of Gadolinium (Gd{sup 3+}), Ruthenium Red, and in calcium-free solution to elucidate a mechanism for its unique frequency trend. - Highlights: • Pulse repetition rate (PRR) is understudied in nanosecond electric pulsing. • 200 V pulses were applied to CHO-K1 cells from 5 Hz to 500 KHz. • Pulsing was repeated using a variety of fluorophores and imaging conditions. • The response is highly dependent on the fluorophore and the imaging conditions. • This may implicate protein channels in the nanoporation response.« less

Analytical modeling of eddy-current losses caused by pulse-width-modulation switching in permanent-magnet brushless direct-current motors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, F.; Nehl, T.W.

1998-09-01

Because of their high efficiency and power density the PM brushless dc motor is a strong candidate for electric and hybrid vehicle propulsion systems. An analytical approach is developed to predict the inverter high frequency pulse width modulation (PWM) switching caused eddy-current losses in a permanent magnet brushless dc motor. The model uses polar coordinates to take curvature effects into account, and is also capable of including the space harmonic effect of the stator magnetic field and the stator lamination effect on the losses. The model was applied to an existing motor design and was verified with the finite elementmore » method. Good agreement was achieved between the two approaches. Hence, the model is expected to be very helpful in predicting PWM switching losses in permanent magnet machine design.« less

Excitation of low-frequency residual currents at combination frequencies of an ionising two-colour laser pulse

NASA Astrophysics Data System (ADS)

Vvedenskii, N. V.; Kostin, V. A.; Laryushin, I. D.; Silaev, A. A.

2016-05-01

We have studied the processes of excitation of low-frequency residual currents in a plasma produced through ionisation of gases by two-colour laser pulses in laser-plasma schemes for THz generation. We have developed an analytical approach that allows one to find residual currents in the case when one of the components of a two-colour pulse is weak enough. The derived analytical expressions show that the effective generation of the residual current (and hence the effective THz generation) is possible if the ratio of the frequencies in the two-colour laser pulse is close to a rational fraction with a not very big odd sum of the numerator and denominator. The results of numerical calculations (including those based on the solution of the three-dimensional time-dependent Schrödinger equation) agree well with the analytical results.

A 1 MA, variable risetime pulse generator for high energy density plasma research

NASA Astrophysics Data System (ADS)

Greenly, J. B.; Douglas, J. D.; Hammer, D. A.; Kusse, B. R.; Glidden, S. C.; Sanders, H. D.

2008-07-01

COBRA is a 0.5Ω pulse generator driving loads of order 10nH inductance to >1MA current. The design is based on independently timed, laser-triggered switching of four water pulse-forming lines whose outputs are added in parallel to drive the load current pulse. The detailed design and operation of the switching to give a wide variety of current pulse shapes and rise times from 95to230ns is described. The design and operation of a simple inductive load voltage monitor are described which allows good accounting of load impedance and energy dissipation. A method of eliminating gas bubbles on the underside of nearly horizontal insulator surfaces in water was required for reliable operation of COBRA; a novel and effective solution to this problem is described.

High current multicharged metal ion source using high power gyrotron heating of vacuum arc plasma.

PubMed

Vodopyanov, A V; Golubev, S V; Khizhnyak, V I; Mansfeld, D A; Nikolaev, A G; Oks, E M; Savkin, K P; Vizir, A V; Yushkov, G Yu

2008-02-01

A high current, multi charged, metal ion source using electron heating of vacuum arc plasma by high power gyrotron radiation has been developed. The plasma is confined in a simple mirror trap with peak magnetic field in the plug up to 2.5 T, mirror ratio of 3-5, and length variable from 15 to 20 cm. Plasma formed by a cathodic vacuum arc is injected into the trap either (i) axially using a compact vacuum arc plasma gun located on axis outside the mirror trap region or (ii) radially using four plasma guns surrounding the trap at midplane. Microwave heating of the mirror-confined, vacuum arc plasma is accomplished by gyrotron microwave radiation of frequency 75 GHz, power up to 200 kW, and pulse duration up to 150 micros, leading to additional stripping of metal ions by electron impact. Pulsed beams of platinum ions with charge state up to 10+, a mean charge state over 6+, and total (all charge states) beam current of a few hundred milliamperes have been formed.

Study of Ni-Mo electrodeposition in direct and pulse-reverse current

NASA Astrophysics Data System (ADS)

Stryuchkova, Yu M.; Rybin, N. B.; Suvorov, D. V.; Gololobov, G. P.; Tolstoguzov, A. B.; Tarabrin, D. Yu; Serpova, M. A.; Korotchenko, V. A.; Slivkin, E. V.

2017-05-01

Process of electrochemical deposition of the coating based on a binary nickel-molybdenum alloy onto a nickel substrate under pulse mode with current reverse within the range of current density change from 2 to 9 A/dm2 has been researched. Coating structure and its surface morphology have been studied. Method of X-ray energy dispersive spectroscopy has determined a percentage ratio of alloy components in the coating. Mode to obtain the densest and smoothest deposits has been identified under considered terms.

Radial current high power dummy load for characterizing the high power laser triggered transformer-type accelerator.

PubMed

Yin, Yi; Zhong, Hui-Huang; Liu, Jin-Liang; Ren, He-Ming; Yang, Jian-Hua; Zhang, Xiao-Ping; Hong, Zhi-qiang

2010-09-01

A radial-current aqueous resistive solution load was applied to characterize a laser triggered transformer-type accelerator. The current direction in the dummy load is radial and is different from the traditional load in the axial. Therefore, this type of dummy load has smaller inductance and fast response characteristic. The load was designed to accommodate both the resistance requirement of accelerator and to allow optical access for the laser. Theoretical and numerical calculations of the load's inductance and capacitance are given. The equivalent circuit of the dummy load is calculated in theory and analyzed with a PSPICE code. The simulation results agree well with the theoretical analysis. At last, experiments of the dummy load applied to the high power spiral pulse forming line were performed; a quasisquare pulse voltage is obtained at the dummy load.

Radial current high power dummy load for characterizing the high power laser triggered transformer-type accelerator

NASA Astrophysics Data System (ADS)

Yin, Yi; Zhong, Hui-Huang; Liu, Jin-Liang; Ren, He-Ming; Yang, Jian-Hua; Zhang, Xiao-Ping; Hong, Zhi-qiang

2010-09-01

A radial-current aqueous resistive solution load was applied to characterize a laser triggered transformer-type accelerator. The current direction in the dummy load is radial and is different from the traditional load in the axial. Therefore, this type of dummy load has smaller inductance and fast response characteristic. The load was designed to accommodate both the resistance requirement of accelerator and to allow optical access for the laser. Theoretical and numerical calculations of the load's inductance and capacitance are given. The equivalent circuit of the dummy load is calculated in theory and analyzed with a PSPICE code. The simulation results agree well with the theoretical analysis. At last, experiments of the dummy load applied to the high power spiral pulse forming line were performed; a quasisquare pulse voltage is obtained at the dummy load.

Pulsed Laser Illumination of Photovoltaic Cells

NASA Technical Reports Server (NTRS)

Yater, Jane A.; Lowe, Roland; Jenkins, Philip; Landis, Geoffrey A.

1994-01-01

In future space missions, free electron lasers (FEL) may be used to illuminate photovoltaic array receivers to provide remote power. The induction FEL and the radio-frequency (RF) FEL both produce pulsed rather than continuous output. In this work, we investigate cell response to pulsed laser light which simulates the RF FEL format, producing 50 ps pulses at a frequency of 78 MHz. A variety of Si, GaAs, CaSb and CdInSe2 (CIS) solar cells are tested at average incident powers between 4 mW/sq cm and 425 mW/sq cm. The results indicate that if the pulse repetition is high, cell efficiencies are only slightly reduced by using a pulsed laser source compared to constant illumination at the same wavelength. Because the pulse separation is less than or approximately equal to the minority carrier lifetime, the illumination conditions are effectively those of a continuous wave laser. The time dependence of the voltage and current response of the cells are also measured using a sampling oscilloscope equipped with a high frequency voltage probe and current transformer. The frequency response of the cells is weak, with both voltage and current outputs essentially dc in nature. Comparison with previous experiments shows that the RF FEL pulse format yields much more efficient photovoltaic conversion of light than does an induction FEL pulse format.

Thermal imaging diagnostics of high-current electron beams.

PubMed

Pushkarev, A; Kholodnaya, G; Sazonov, R; Ponomarev, D

2012-10-01

The thermal imaging diagnostics of measuring pulsed electron beam energy density is presented. It provides control of the electron energy spectrum and a measure of the density distribution of the electron beam cross section, the spatial distribution of electrons with energies in the selected range, and the total energy of the electron beam. The diagnostics is based on the thermal imager registration of the imaging electron beam thermal print in a material with low bulk density and low thermal conductivity. Testing of the thermal imaging diagnostics has been conducted on a pulsed electron accelerator TEU-500. The energy of the electrons was 300-500 keV, the density of the electron current was 0.1-0.4 kA/cm(2), the duration of the pulse (at half-height) was 60 ns, and the energy in the pulse was up to 100 J. To register the thermal print, a thermal imager Fluke-Ti10 was used. Testing showed that the sensitivity of a typical thermal imager provides the registration of a pulsed electron beam heat pattern within one pulse with energy density over 0.1 J/cm(2) (or with current density over 10 A/cm(2), pulse duration of 60 ns and electron energy of 400 keV) with the spatial resolution of 0.9-1 mm. In contrast to the method of using radiosensitive (dosimetric) materials, thermal imaging diagnostics does not require either expensive consumables, or plenty of processing time.

Irreversible electroporation ablation area enhanced by synergistic high- and low-voltage pulses.

PubMed

Yao, Chenguo; Lv, Yanpeng; Dong, Shoulong; Zhao, Yajun; Liu, Hongmei

2017-01-01

Irreversible electroporation (IRE) produced by a pulsed electric field can ablate tissue. In this study, we achieved an enhancement in ablation area by using a combination of short high-voltage pulses (HVPs) to create a large electroporated area and long low-voltage pulses (LVPs) to ablate the electroporated area. The experiments were conducted in potato tuber slices. Slices were ablated with an array of four pairs of parallel steel electrodes using one of the following four electric pulse protocols: HVP, LVP, synergistic HVP+LVP (SHLVP) or LVP+HVP. Our results showed that the SHLVPs more effectively necrotized tissue than either the HVPs or LVPs, even when the SHLVP dose was the same as or lower than the HVP or LVP doses. The HVP and LVP order mattered and only HVPs+LVPs (SHLVPs) treatments increased the size of the ablation zone because the HVPs created a large electroporated area that was more susceptible to the subsequent LVPs. Real-time temperature change monitoring confirmed that the tissue was non-thermally ablated by the electric pulses. Theoretical calculations of the synergistic effects of the SHLVPs on tissue ablation were performed. Our proposed SHLVP protocol provides options for tissue ablation and may be applied to optimize the current clinical IRE protocols.

Irreversible electroporation ablation area enhanced by synergistic high- and low-voltage pulses

PubMed Central

2017-01-01

Irreversible electroporation (IRE) produced by a pulsed electric field can ablate tissue. In this study, we achieved an enhancement in ablation area by using a combination of short high-voltage pulses (HVPs) to create a large electroporated area and long low-voltage pulses (LVPs) to ablate the electroporated area. The experiments were conducted in potato tuber slices. Slices were ablated with an array of four pairs of parallel steel electrodes using one of the following four electric pulse protocols: HVP, LVP, synergistic HVP+LVP (SHLVP) or LVP+HVP. Our results showed that the SHLVPs more effectively necrotized tissue than either the HVPs or LVPs, even when the SHLVP dose was the same as or lower than the HVP or LVP doses. The HVP and LVP order mattered and only HVPs+LVPs (SHLVPs) treatments increased the size of the ablation zone because the HVPs created a large electroporated area that was more susceptible to the subsequent LVPs. Real-time temperature change monitoring confirmed that the tissue was non-thermally ablated by the electric pulses. Theoretical calculations of the synergistic effects of the SHLVPs on tissue ablation were performed. Our proposed SHLVP protocol provides options for tissue ablation and may be applied to optimize the current clinical IRE protocols. PMID:28253331

Characteristics of H+ current transients induced by adverse H+ gradient pulses in toad bladder.

PubMed

Nero, A C; Schwartz, J H; Furtado, M R

1987-10-01

Acidification in the toad bladder occurs as a result of electrogenic H+ secretion (JH). When a pH gradient is applied in a stepwise fashion in the absence of exogenous CO2, JH decreases linearly with the mucosal (M) solution pH and is null when pHm is approximately 4.5. When pHm is returned to initial values (7.4) in a stepwise fashion, JH increases linearly with pHm. However, on this return, higher values of JH are initially obtained. To investigate this hysteresis, hemibladders mounted in chambers were used to measure the change in the H+ current before and after acid pulses were applied to the mucosal solution. In the absence of exogenous CO2, the application of graded acid pulses to mucosa for 1, 2, 4, and 8 min resulted in a graded decrease in JH. The restoration of pHm to 7.4 was followed by an immediate transient overshoot of reversed short-circuit current (Irsc), which was related to the time of exposure and the magnitude of the acid pulse. The longer the acid pulse or the larger the pulse, the greater the Irsc overshoot. The addition of protonophores, dinitrophenol, or salicylate, into the mucosal solution enhanced this overshoot. Similar Irsc overshoots could be obtained with the application of pulses of adverse electrical gradients. Introduction of exogenous CO2 into the system (3%) completely inhibited the overshoot in JH after an acid pulse. In conclusion, when pHm is decreased JH is reduced and the cell pH presumably decreases because of continued exit of alkali at the serosal side of the cell and entry of H+ from the mucosal solution. The decrease in cell pH then triggers the pump to produce a sharp overshoot in JH when pHm returns to 7.4.

Control of pulse format in high energy per pulse all-fiber erbium/ytterbium laser systems

NASA Astrophysics Data System (ADS)

Klopfer, Michael; Block, Matthew K.; Deffenbaugh, James; Fitzpatrick, Zak G.; Urioste, Michael T.; Henry, Leanne J.; Jain, Ravinder

2017-02-01

A multi-stage linearly polarized (PM) (15 dB) pulsed fiber laser system at 1550 nm capable of operating at repetition rates between 3 and 20 kHz was investigated. A narrow linewidth seed source was linewidth broadened to approximately 20 GHz and pulses were created and shaped via an electro-optic modulator (EOM) in conjunction with a home built arbitrary waveform generator. As expected, a high repetition rate pulse train with a near diffraction limited beam quality (M2 1.12) was achieved. However, the ability to store energy was limited by the number of active ions within the erbium/ytterbium doped gain fiber within the various stages. As a result, the maximum energy per pulse achievable from the system was approximately 0.3 and 0.38 mJ for 300 ns and 1 μs pulses, respectively, at 3 kHz. Because the system was operated at high inversion, the erbium/ytterbium doped optical fiber preferred to lase at 1535 nm versus 1550 nm resulting in amplified spontaneous emission (ASE) both intra- and inter-pulse. For the lower power stages, the ASE was controllable via a EOM whose function was to block the energy between pulses as well as ASE filters whose purpose was to block spectral components outside of the 1550 nm passband. For the higher power stages, the pump diodes were pulsed to enable strategic placement of an inversion resulting in higher intrapulse energies as well as an improved spectrum of the signal. When optimized, this system will be used to seed higher power solid state amplifier stages.

The Rogowski Coil Sensor in High Current Application: A Review

NASA Astrophysics Data System (ADS)

Nazmy Nanyan, Ayob; Isa, Muzamir; Hamid, Haziah Abdul; Nur Khairul Hafizi Rohani, Mohamad; Ismail, Baharuddin

2018-03-01

Rogowski coil is used for measuring the alternating current (AC) and high-speed current pulses. However, the technology makes the Rogowski coil (RC) come out with more improvement, modification and until today it’s still being studied for the new application. The Rogowski coil has a few advantages compared to the high frequency current transformer (HFCT). A brief review on the basic theory and the application of Rogowski coil as a current sensor measurement that been done by previous researchers are presented and discussed in this paper. Additionally, the review also focused on the capability of Rogowski coil for high current sensor measurement and their application for fault detection, over voltage current sensor, lightning current sensor and high impulse current detection. The experimental set up, techniques and measurement parameters in models also been discussed. Finally, a brief review on the performance analysis of current sensor measurement of Rogowski coil likes sensitivity, the maximum and current detection which could be used as a guideline to another researcher in order to develop an advanced RC as high current sensor in future is presented. This review reveal that the RC has a very good performance in high current sensor detection in term of sensitivity which is up to a few nanosecond, higher bandwidth, excellent in detection of high fault and also could measuring lightning current up to 400kA and has many advantages compare to conventional current transformer(CT).

Detection of cracks beneath rivet heads via pulsed eddy current technique

NASA Astrophysics Data System (ADS)

Giguère, J. S. R.; Lepine, B. A.; Dubois, J. M. S.

2002-05-01

Improving the detectability of fatigue cracks under installed fasteners is one of the many goals of the aging aircraft nondestructive evaluation (NDE) community. The pulsed eddy current offers new capabilities to address this requirement. The aim of the paper is to evaluate the potential of this technique for detecting and quantifying notches under installed fasteners.

Method for generating high-energy and high repetition rate laser pulses from CW amplifiers

DOEpatents

Zhang, Shukui

2013-06-18

A method for obtaining high-energy, high repetition rate laser pulses simultaneously using continuous wave (CW) amplifiers is described. The method provides for generating micro-joule level energy in pico-second laser pulses at Mega-hertz repetition rates.

Ion mass spectrometry investigations of the discharge during reactive high power pulsed and direct current magnetron sputtering of carbon in Ar and Ar/N{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, S.; Greczynski, G.; Jensen, J.

2012-07-01

Ion mass spectrometry was used to investigate discharges formed during high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) of a graphite target in Ar and Ar/N{sub 2} ambient. Ion energy distribution functions (IEDFs) were recorded in time-averaged and time-resolved mode for Ar{sup +}, C{sup +}, N{sub 2}{sup +}, N{sup +}, and C{sub x}N{sub y}{sup +} ions. An increase of N{sub 2} in the sputter gas (keeping the deposition pressure, pulse width, pulse frequency, and pulse energy constant) results for the HiPIMS discharge in a significant increase in C{sup +}, N{sup +}, and CN{sup +} ion energies.more » Ar{sup +}, N{sub 2}{sup +}, and C{sub 2}N{sup +} ion energies, in turn, did not considerably vary with the changes in working gas composition. The HiPIMS process showed higher ion energies and fluxes, particularly for C{sup +} ions, compared to DCMS. The time evolution of the plasma species was analyzed for HiPIMS and revealed the sequential arrival of working gas ions, ions ejected from the target, and later during the pulse-on time molecular ions, in particular CN{sup +} and C{sub 2}N{sup +}. The formation of fullerene-like structured CN{sub x} thin films for both modes of magnetron sputtering is explained by ion mass-spectrometry results and demonstrated by transmission electron microscopy as well as diffraction.« less

Low Voltage Electrolytic Capacitor Pulse Forming Inductive Network for Electric Weapons

DTIC Science & Technology

2006-06-01

reliable high- current, high-energy pulses of many megawatts. Pulsed alternators potentially have the same maintenance issues as other motor ...high-energy pulses of many megawatts. Pulsed alternators potentially have the same maintenance issues as other motor -generator sets, so a solid...Rotating Flywheel) Pulse Forming Network Compensated Pulsed Alternators, or Compulsators as they are called, are essentially large motor -generator

Parametric Study of High Frequency Pulse Detonation Tubes

NASA Technical Reports Server (NTRS)

Cutler, Anderw D.

2008-01-01

This paper describes development of high frequency pulse detonation tubes similar to a small pulse detonation engine (PDE). A high-speed valve injects a charge of a mixture of fuel and air at rates of up to 1000 Hz into a constant area tube closed at one end. The reactants detonate in the tube and the products exit as a pulsed jet. High frequency pressure transducers are used to monitor the pressure fluctuations in the device and thrust is measured with a balance. The effects of injection frequency, fuel and air flow rates, tube length, and injection location are considered. Both H2 and C2H4 fuels are considered. Optimum (maximum specific thrust) fuel-air compositions and resonant frequencies are identified. Results are compared to PDE calculations. Design rules are postulated and applications to aerodynamic flow control and propulsion are discussed.

High intensity, pulsed thermal neutron source

DOEpatents

Carpenter, J.M.

1973-12-11

This invention relates to a high intensity, pulsed thermal neutron source comprising a neutron-producing source which emits pulses of fast neutrons, a moderator block adjacent to the last neutron source, a reflector block which encases the fast neutron source and the moderator block and has a thermal neutron exit port extending therethrough from the moderator block, and a neutron energy- dependent decoupling reflector liner covering the interior surfaces of the thermal neutron exit port and surrounding all surfaces of the moderator block except the surface viewed by the thermal neutron exit port. (Official Gazette)

Modification of polymer velvet cathode via metallic Mo coating for enhancement of high-current electron emission performances

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiong, Ying; Wang, Bing; Yi, Yong

2013-09-15

The effect of surface Mo coating on the high-current electron emission performances for polymer velvet cathode has been investigated in a diode with A-K gap of 11.5 cm by the combination of time-resolved electrical diagnostic and temporal pressure variation. Compared with uncoated polymer velvet cathode under the single-pulsed emission mode, the Mo-coated one shows lower outgassing levels (∼0.40 Pa L), slower cathode plasma expansion velocity (∼2.30 cm/μs), and higher emission stability as evidences by the change in cathode current, temporal pressure variation, and diode perveance. Moreover, after Mo coating, the emission consistency of the polymer velvet cathode between two adjacentmore » pulses is significantly improved in double-pulsed emission mode with ∼500 ns interval between two pulses, which further confirms the effectiveness of Mo coating for enhancement of electron emission performance of polymer velvet cathodes. These results should be of interest to the high-repetitive high-power microwave systems with cold cathodes.« less

Investigation of a high power electromagnetic pulse source.

PubMed

Wang, Yuwei; Chen, Dongqun; Zhang, Jiande; Cao, Shengguang; Li, Da; Liu, Chebo

2012-09-01

A high power electromagnetic pulse source with a resonant antenna driven by a compact power supply was investigated in this paper. To match the impedance of the resonant antenna and initial power source, a compact power conditioning circuit based on electro exploding opening switch (EEOS) and pulsed transformer was adopted. In the preliminary experiments, an impulse capacitor was used to drive the system. With the opening of the EEOS at the current of 15 kA flowing trough the primary of the transformer, the resonant antenna was rapidly charged to about -370 kV within a time of about 100 ns. When the switch in the resonant antenna closed at the charging voltage of about -202 kV, the peak intensity of the detected electric field at a distance of about 10 m from the center of the source was 7.2 kV∕m. The corresponding peak power of the radiated electromagnetic field reached 76 MW, while the total radiated electromagnetic energy was about 0.65 J. The total energy efficiency of the resonant antenna was about 22% which can be improved by increasing the closing rapidity of the switch in the antenna.

Single-shot, high-resolution, fiber-based phase-diversity photodetection of optical pulses

NASA Astrophysics Data System (ADS)

Dorrer, C.; Waxer, L. J.; Kalb, A.; Hill, E. M.; Bromage, J.

2016-03-01

Temporally characterizing optical pulses is an important task when building, optimizing, and using optical sources. Direct photodetection with high-bandwidth photodiodes and real-time oscilloscopes is only adequate for optical pulses longer than ~10 ps; diagnostics based on indirect strategies are required to characterize femtosecond and sub-10-ps coherent sources. Most of these diagnostics are based on nonlinear optics and can be difficult to implement for the single-shot characterization of nonrepetitive events. A temporal diagnostic based on phase diversity is demonstrated in the context of picosecond high-energy laser systems, where single-shot pulse measurements are required for system safety and interpretation of experimental results. A plurality of ancillary optical pulses obtained by adding known amounts of chromatic dispersion to the pulse under test are directly measured by photodetection and processed to reconstruct the input pulse shape. This high-sensitivity (~50-pJ) diagnostic is based on a pulse replicator composed of fiber splitters and delay fibers, making it possible to operate with fiber sources and free-space sources after fiber coupling. Experimental data obtained with a high-bandwidth real-time oscilloscope demonstrate accurate characterization of pulses from a high-energy chirped-pulse amplification system, even for pulses shorter than the photodetection impulse response.

Research on defects inspection of solder balls based on eddy current pulsed thermography.

PubMed

Zhou, Xiuyun; Zhou, Jinlong; Tian, Guiyun; Wang, Yizhe

2015-10-13

In order to solve tiny defect detection for solder balls in high-density flip-chip, this paper proposed feasibility study on the effect of detectability as well as classification based on eddy current pulsed thermography (ECPT). Specifically, numerical analysis of 3D finite element inductive heat model is generated to investigate disturbance on the temperature field for different kind of defects such as cracks, voids, etc. The temperature variation between defective and non-defective solder balls is monitored for defects identification and classification. Finally, experimental study is carried on the diameter 1mm tiny solder balls by using ECPT and verify the efficacy of the technique.

Effects of high voltage nanosecond electric pulses on eukaryotic cells (in vitro): A systematic review.

PubMed

Batista Napotnik, Tina; Reberšek, Matej; Vernier, P Thomas; Mali, Barbara; Miklavčič, Damijan

2016-08-01

For this systematic review, 203 published reports on effects of electroporation using nanosecond high-voltage electric pulses (nsEP) on eukaryotic cells (human, animal, plant) in vitro were analyzed. A field synopsis summarizes current published data in the field with respect to publication year, cell types, exposure configuration, and pulse duration. Published data were analyzed for effects observed in eight main target areas (plasma membrane, intracellular, apoptosis, calcium level and distribution, survival, nucleus, mitochondria, stress) and an additional 107 detailed outcomes. We statistically analyzed effects of nsEP with respect to three pulse duration groups: A: 1-10ns, B: 11-100ns and C: 101-999ns. The analysis confirmed that the plasma membrane is more affected with longer pulses than with short pulses, seen best in uptake of dye molecules after applying single pulses. Additionally, we have reviewed measurements of nsEP and evaluations of the electric fields to which cells were exposed in these reports, and we provide recommendations for assessing nanosecond pulsed electric field effects in electroporation studies. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Development of a Pulsed Combustion Actuator For High-Speed Flow Control

NASA Technical Reports Server (NTRS)

Cutler, Andrew D.; Beck, B. Terry; Wilkes, Jennifer A.; Drummond, J. Philip; Alderfer, David W.; Danehy, Paul M.

2005-01-01

This paper describes the flow within a prototype actuator, energized by pulsed combustion or detonations, that provides a pulsed jet suitable for flow control in high-speed applications. A high-speed valve, capable of delivering a pulsed stream of reactants a mixture of H2 and air at rates of up to 1500 pulses per second, has been constructed. The reactants burn in a resonant chamber, and the products exit the device as a pulsed jet. High frequency pressure transducers have been used to monitor the pressure fluctuations in the device at various reactant injection frequencies, including both resonant and off-resonant conditions. The combustion chamber has been constructed with windows, and the flow inside it has been visualized using Planar Laser-Induced Fluorescence (PLIF). The pulsed jet at the exit of the device has been observed using schlieren.

Collimated Propagation of Fast Electron Beams Accelerated by High-Contrast Laser Pulses in Highly Resistive Shocked Carbon.

PubMed

Vaisseau, X; Morace, A; Touati, M; Nakatsutsumi, M; Baton, S D; Hulin, S; Nicolaï, Ph; Nuter, R; Batani, D; Beg, F N; Breil, J; Fedosejevs, R; Feugeas, J-L; Forestier-Colleoni, P; Fourment, C; Fujioka, S; Giuffrida, L; Kerr, S; McLean, H S; Sawada, H; Tikhonchuk, V T; Santos, J J

2017-05-19

Collimated transport of ultrahigh intensity electron current was observed in cold and in laser-shocked vitreous carbon, in agreement with simulation predictions. The fast electron beams were created by coupling high-intensity and high-contrast laser pulses onto copper-coated cones drilled into the carbon samples. The guiding mechanism-observed only for times before the shock breakout at the inner cone tip-is due to self-generated resistive magnetic fields of ∼0.5-1  kT arising from the intense currents of fast electrons in vitreous carbon, by virtue of its specific high resistivity over the range of explored background temperatures. The spatial distribution of the electron beams, injected through the samples at different stages of compression, was characterized by side-on imaging of hard x-ray fluorescence.

Polarization control of isolated high-harmonic pulses

NASA Astrophysics Data System (ADS)

Huang, Pei-Chi; Hernández-García, Carlos; Huang, Jen-Ting; Huang, Po-Yao; Lu, Chih-Hsuan; Rego, Laura; Hickstein, Daniel D.; Ellis, Jennifer L.; Jaron-Becker, Agnieszka; Becker, Andreas; Yang, Shang-Da; Durfee, Charles G.; Plaja, Luis; Kapteyn, Henry C.; Murnane, Margaret M.; Kung, A. H.; Chen, Ming-Chang

2018-06-01

High-harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, thus far, the shortest isolated attosecond pulses have only been produced with linear polarization, which limits the range of physics that can be explored. Here, we demonstrate robust polarization control of isolated extreme-ultraviolet pulses by exploiting non-collinear high-harmonic generation driven by two counter-rotating few-cycle laser beams. The circularly polarized supercontinuum is produced at a central photon energy of 33 eV with a transform limit of 190 as and a predicted linear chirp of 330 as. By adjusting the ellipticity of the two counter-rotating driving pulses simultaneously, we control the polarization state of isolated extreme-ultraviolet pulses—from circular through elliptical to linear polarization—without sacrificing conversion efficiency. Access to the purely circularly polarized supercontinuum, combined with full helicity and ellipticity control, paves the way towards attosecond metrology of circular dichroism.

Compact submicrosecond, high current generator for wire explosion experiments

NASA Astrophysics Data System (ADS)

Aranchuk, L. E.; Chuvatin, A. S.; Larour, J.

2004-01-01

The PIAF generator was designed for low total energy and high energy density experiments with liners, X-pinch or fiber Z-pinch loads. These studies are of interest for such applications as surface and material science, microscopy of biological specimens, lithography of x-ray sensitive resists, and x-ray backlighting of pulsed-power plasmas. The generator is based on an RLC circuit that includes six NWL 180 nF-50 kV capacitors that store up to 1.3 kJ. The capacitors are connected in parallel to a single multispark switch designed to operate at atmospheric pressure. The switch allows reaching a time delay between the trigger pulse and the current pulse of less than 80 ns and has jitter of 6 ns. The total inductance without a load compartment was optimized to be as low as 16 nH, which leads to extremely low impedance of ˜0.12 Ω. A 40 kV initial voltage provides 250 kA maximum current in a 6 nH inductive load with a 180 ns current rise time. PIAF has dimensions of 660×660×490 mm and weight of less than 100 kg, thus manifesting itself as robust, simple to operate, and cost effective. A description of the PIAF generator and the initial experimental results on PIAF with an X-pinch type load are reported. The generator was demonstrated to operate successfully with an X-pinch type load. The experiments first started with investigation of the previously unexplored X-pinch conduction time range, 100 ns-1 μs. A single short radiation pulse was obtained that came from a small, point-like plasma. The following x-ray source characteristics were achieved: typical hot spot size of 50-100 μm, radiation pulse duration of 1.5-2 ns, and radiation yield of about 250-500 mJ in the softer spectral range (hν⩾700 eV) and 50-100 mJ in the harder one (hν⩾1 keV). These results provide the potential for further application of this source, such as use as a backlight diagnostic tool.

High pulse rate high resolution optical radar system

NASA Technical Reports Server (NTRS)

Goss, W. C.; Burns, R. H.; Chi, K. (Inventor)

1973-01-01

The system is composed of an optical cavity with a laser and a mode locking means to build up an optical pulse. An optical switch is also provided within the cavity to convert the polarization of the optical pulse generated within the cavity. The optical switch comprises an electro-optical crystal driven by a time delayed driver circuit which is triggered by a coincident signal made from an optical pulse signal and a gating pulse signal. The converted optical pulse strikes a polarization sensitive prism and is deflected out of the cavity toward the pending target in the form of a pulse containing most of the optical energy generated by the laser in the pulse build-up period. After striking the target, the reflected energy is picked up by a transceiver with the total travel time of the pulse being recorded.

Strain sensors for high field pulse magnets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez, Christian; Zheng, Yan; Easton, Daniel

2009-01-01

In this paper we present an investigation into several strain sensing technologies that are being considered to monitor mechanical deformation within the steel reinforcement shells used in high field pulsed magnets. Such systems generally operate at cryogenic temperatures to mitigate heating issues that are inherent in the coils of nondestructive, high field pulsed magnets. The objective of this preliminary study is to characterize the performance of various strain sensing technologies at liquid nitrogen temperatures (-196 C). Four sensor types are considered in this investigation: fiber Bragg gratings (FBG), resistive foil strain gauges (RFSG), piezoelectric polymers (PVDF), and piezoceramics (PZT). Threemore » operational conditions are considered for each sensor: bond integrity, sensitivity as a function of temperature, and thermal cycling effects. Several experiments were conducted as part of this study, investigating adhesion with various substrate materials (stainless steel, aluminum, and carbon fiber), sensitivity to static (FBG and RFSG) and dynamic (RFSG, PVDF and PZT) load conditions, and sensor diagnostics using PZT sensors. This work has been conducted in collaboration with the National High Magnetic Field Laboratory (NHMFL), and the results of this study will be used to identify the set of sensing technologies that would be best suited for integration within high field pulsed magnets at the NHMFL facility.« less

Petawatt pulsed-power accelerator

DOEpatents

Stygar, William A.; Cuneo, Michael E.; Headley, Daniel I.; Ives, Harry C.; Ives, legal representative; Berry Cottrell; Leeper, Ramon J.; Mazarakis, Michael G.; Olson, Craig L.; Porter, John L.; Wagoner; Tim C.

2010-03-16

A petawatt pulsed-power accelerator can be driven by various types of electrical-pulse generators, including conventional Marx generators and linear-transformer drivers. The pulsed-power accelerator can be configured to drive an electrical load from one- or two-sides. Various types of loads can be driven; for example, the accelerator can be used to drive a high-current z-pinch load. When driven by slow-pulse generators (e.g., conventional Marx generators), the accelerator comprises an oil section comprising at least one pulse-generator level having a plurality of pulse generators; a water section comprising a pulse-forming circuit for each pulse generator and a level of monolithic triplate radial-transmission-line impedance transformers, that have variable impedance profiles, for each pulse-generator level; and a vacuum section comprising triplate magnetically insulated transmission lines that feed an electrical load. When driven by LTD generators or other fast-pulse generators, the need for the pulse-forming circuits in the water section can be eliminated.

The Implementation Of Solid State Switches In A Parallel Configuration To Gain Output Current Capacity In A High Current Capacitive Discharge Unit (CDU).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chaves, Mario Paul

2017-07-01

For my project I have selected to research and design a high current pulse system, which will be externally triggered from a 5V pulse. The research will be conducted in the region of paralleling the solid state switches for a higher current output, as well as to see if there will be any other advantages in doing so. The end use of the paralleled solid state switches will be used on a Capacitive Discharge Unit (CDU). For the first part of my project, I have set my focus on the design of the circuit, selection of components, and simulation ofmore » the circuit.« less

Megavolt, Multigigawatt Pulsed Plasma Switch

NASA Technical Reports Server (NTRS)

Lee, Ja H.; Choi, Sang H.; Song, Kyo D.

1996-01-01

Plasma switch proposed for use in high-voltage, high-current pulse power system. Designed not only to out-perform conventional spark-gap switch but also relatively compact and lightweight. Features inverse-pinch configuration to prevent constriction of current sheets into filaments, plus multiple-ring-electrode structure to resist high-voltage breakdown.

High-pulse-energy mode-locked picosecond oscillator

NASA Astrophysics Data System (ADS)

Chao, Yang; Chen, Meng; Li, Gang

2014-02-01

We report on a high-pulse-energy solid-state picosecond Nd:YVO4 oscillator with cavity-dumping. The laser is end-pumped by an 808 nm laser diode and passively mode-locked with a semiconductor saturable absorption mirror (SESAM). In pure cw-mode-locking, this laser produced 2.5 W of average power at a pulse repetition rate of 40 MHz and pulse duration around 12 ps. A cavity dumping technique using an intra-cavity BBO electro-optic crystal to which bidirectional voltage was applied was adopted, effectively improving the cavity-dumping rate. Tunable high repetition rate from 100 kHz to 1 MHz was achieved. With electro-optic cavity dumper working at 1 MHz repetition rate, we achieved average power 594 mW. The laser includes a 5 mm long, a-cut, 0.5% doped Nd:YVO4 crystal with a 5-degree angle at one end face. Laser radiation is coupled out from the crystal end face with a 5-degree angle, without requiring insertion of a thin-film polarizer (TFP), thus simplifying the laser structure. This picosecond laser system has the advantages of compact structure and high stability, providing a good oscillator for regenerative amplifiers.

High current superconductors for tokamak toroidal field coils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fietz, W.A.

1976-01-01

Conductors rated at 10,000 A for 8 T and 4.2 K are being purchased for the first large coil segment tests at ORNL. Requirements for these conductors, in addition to the high current rating, are low pulse losses, cryostatic stability, and acceptable mechanical properties. The conductors are required to have losses less than 0.4 W/m under pulsed fields of 0.5 T with a rise time of 1 sec in an ambient 8-T field. Methods of calculating these losses and techniques for verifying the performance by direct measurement are discussed. Conductors stabilized by two different cooling methods, pool boiling and forcedmore » helium flow, have been proposed. Analysis of these conductors is presented and a proposed definition and test of stability is discussed. Mechanical property requirements, tensile and compressive, are defined and test methods are discussed.« less

Pulsed eddy current differential probe to detect the defects in a stainless steel pipe

NASA Astrophysics Data System (ADS)

Angani, C. S.; Park, D. G.; Kim, C. G.; Leela, P.; Kishore, M.; Cheong, Y. M.

2011-04-01

Pulsed eddy current (PEC) is an electromagnetic nondestructive technique widely used to detect and quantify the flaws in conducting materials. In the present study a differential Hall-sensor probe which is used in the PEC system has been fabricated for the detection of defects in stainless steel pipelines. The differential probe has an exciting coil with two Hall-sensors. A stainless steel test sample with electrical discharge machining (EDM) notches under different depths of 1-5 mm was made and the sample was laminated by plastic insulation having uniform thickness to simulate the pipelines in nuclear power plants (NPPs). The driving coil in the probe is excited by a rectangular current pulse and the resultant response, which is the difference of the two Hall-sensors, has been detected as the PEC probe signal. The discriminating time domain features of the detected pulse such as peak value and time to zero are used to interpret the experimental results with the defects in the test sample. A feature extraction technique such as spectral power density has been devised to infer the PEC response.

Long Pulse Homopolar Generator

DTIC Science & Technology

1988-08-01

AD-A205 452 AFWAL-TR-88-2045 LONG PULSE HOMOPOLAR GENERATOR Edward A. Knoth David P. Bauer lAP Research, Inc. 2763 Culver Avenue Dayton OH 45429-3723...TASK WORK UNIT ELEMENT NO. NO. NO ACCESSION NO. 61101F ILIR P3 01 11. TITLE (include Security Classiflcation) Long Pulse Homopolar Generator 12. PERSONAL...FIELD GROUP SUB-GROUP C6 6; y .- o- , -, ’, - 20 07 homopolar , high current, high power, high speed, generator, 19. ABIT!CT (Contkwe on rer if =ray and

High energy protons generation by two sequential laser pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xiaofeng; Shen, Baifei, E-mail: bfshen@mail.shcnc.ac.cn, E-mail: zhxm@siom.ac.cn; Zhang, Xiaomei, E-mail: bfshen@mail.shcnc.ac.cn, E-mail: zhxm@siom.ac.cn

2015-04-15

The sequential proton acceleration by two laser pulses of relativistic intensity is proposed to produce high energy protons. In the scheme, a relativistic super-Gaussian (SG) laser pulse followed by a Laguerre-Gaussian (LG) pulse irradiates dense plasma attached by underdense plasma. A proton beam is produced from the target and accelerated in the radiation pressure regime by the short SG pulse and then trapped and re-accelerated in a special bubble driven by the LG pulse in the underdense plasma. The advantages of radiation pressure acceleration and LG transverse structure are combined to achieve the effective trapping and acceleration of protons. Inmore » a two-dimensional particle-in-cell simulation, protons of 6.7 GeV are obtained from a 2 × 10{sup 22 }W/cm{sup 2} SG laser pulse and a LG pulse at a lower peak intensity.« less

PCF based high power narrow line width pulsed fiber laser

NASA Astrophysics Data System (ADS)

Chen, H.; Yan, P.; Xiao, Q.; Wang, Y.; Gong, M.

2012-09-01

Based on semiconductor diode seeded multi-stage cascaded fiber amplifiers, we have obtained 88-W average power of a 1063-nm laser with high repetition rate of up to 1.5 MHz and a constant 2-ns pulse duration. No stimulated Brillouin scattering pulse or optical damage occurred although the maximum pulse peak power has exceeded 112 kW. The output laser exhibits excellent beam quality (M2x = 1.24 and M2y = 1.18), associated with a spectral line width as narrow as 0.065 nm (FWHM). Additionally, we demonstrate high polarization extinction ratio of 18.4 dB and good pulse stabilities superior to 1.6 % (RMS).

Compact pulsed high-energy Er:glass laser

NASA Astrophysics Data System (ADS)

Wan, Peng; Liu, Jian

2012-03-01

Bulk Erbium-doped lasers are widely used for long-distance telemetry and ranging. In some applications such as coherent Doppler radars, laser outputs with a relatively long pulse width, good beam profile and pulse shape are required. High energy Q-switched Er:glass lasers were demonstrated by use of electro-optic (E/O) Q-switching or frustrated total internal reflection (FTIR) Q-switching. However, the output pulse durations in these lasers were fixed to relatively small values and extremely hard to tune. We report here on developing a novel and compact Q-switched Er:Yb co-doped phosphate glass laser at an eye-safe wavelength of 1.5 μm. A rotating mirror was used as a Q-switch. Co-linear pump scheme was used to maintain a good output beam profile. Near-perfect Gaussian temporal shape was obtained in our experiment. By changing motor rotation speed, pulse duration was tunable and up to 240 ns was achieved. In our preliminary experiment, output pulse energies of 44 mJ and 4.5 mJ were obtained in free-running and Q-switched operation modes respectively.

Experimental research of different plasma cathodes for generation of high-current electron beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shafir, G.; Kreif, M.; Gleizer, J. Z.

2015-11-21

The results of experimental studies of different types of cathodes—carbon-epoxy rods, carbon-epoxy capillary, edged graphite, and metal-dielectric—under the application of high-voltage pulses with an amplitude of several hundreds of kV and pulse duration of several nanoseconds are presented. The best diode performance was achieved with the edged graphite and carbon-epoxy-based cathodes characterized by uniform and fast (<1 ns) formation of explosive emission plasma spots and quasi-constant diode impedance. This result was achieved for both annular cathodes in a strong magnetic field and planar cathodes of a similar diameter (∼2 cm) with no external magnetic field. The cathodes based on carbon-epoxy rods andmore » carbon-epoxy capillaries operating with an average current density up to 1 kA/cm{sup 2} showed insignificant erosion along 10{sup 6} pulses of the generator and the generated electron beam current showed excellent reproducibility in terms of the amplitude and waveform.« less

High Performance Pulse Tube Cryocoolers

NASA Astrophysics Data System (ADS)

Olson, J. R.; Roth, E.; Champagne, P.; Evtimov, B.; Nast, T. C.

2008-03-01

Lockheed Martin's Advanced Technology Center has been developing pulse tube cryocoolers for more than ten years. Recent innovations include successful testing of four-stage coldheads, no-load temperature below 4 K, and the recent development of a high-efficiency compressor. This paper discusses the predicted performance of single and multiple stage pulse tube coldheads driven by our new 6 kg "M5Midi" compressor, which is capable of 90% efficiency with 200 W input power, and a maximum input power of 1000 W. This compressor retains the simplicity of earlier LM-ATC compressors: it has a moving magnet and an external electrical coil, minimizing organics in the working gas and requiring no electrical penetrations through the pressure wall. Motor losses were minimized during design, resulting in a simple, easily-manufactured compressor with state-of-the-art motor efficiency. The predicted cryocooler performance is presented as simple formulae, allowing an engineer to include the impact of a highly-optimized cryocooler into a full system analysis. Performance is given as a function of the heat rejection temperature and the cold tip temperatures and cooling loads.

Robust, easily shaped, and epoxy-free carbon-fiber-aluminum cathodes for generating high-current electron beams.

PubMed

Liu, Lie; Li, Limin; Wen, Jianchun; Wan, Hong

2009-02-01

This paper presents the construction of carbon-fiber-aluminum (CFA) cathode by squeezing casting and its applications for generating high-current electron beams to drive high-power microwave sources. The fabrication process avoided using epoxy, a volatile deteriorating the vacuum system. These cathodes had a higher hardness than conventional aluminum, facilitating machining. After surface treatment, carbon fibers became the dominator determining emission property. A multineedle CFA cathode was utilized in a triode virtual cathode oscillator (vircator), powered by a approximately 450 kV, approximately 400 ns pulse. It was found that 300-400 MW, approximately 250 ns microwave was radiated at a dominant frequency of 2.6 GHz. Further, this cathode can endure high-current-density emission without detectable degradation in performance as the pulse shot proceeded, showing the robust nature of carbon fibers as explosive emitters. Overall, this new class of cold cathodes offers a potential prospect of developing high-current electron beam sources.

Methods of high current magnetic field generator for transcranial magnetic stimulation application

NASA Astrophysics Data System (ADS)

Bouda, N. R.; Pritchard, J.; Weber, R. J.; Mina, M.

2015-05-01

This paper describes the design procedures and underlying concepts of a novel High Current Magnetic Field Generator (HCMFG) with adjustable pulse width for transcranial magnetic stimulation applications. This is achieved by utilizing two different switching devices, the MOSFET and insulated gate bipolar transistor (IGBT). Results indicate that currents as high as ±1200 A can be generated with inputs of +/-20 V. Special attention to tradeoffs between field generators utilizing IGBT circuits (HCMFG1) and MOSFET circuits (HCMFG2) was considered. The theory of operation, design, experimental results, and electronic setup are presented and analyzed.

High-Field Fast-Risetime Pulse Failures in 4H- and 6H-SiC pn Junction Diodes

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.; Fazi, Christian

1996-01-01

We report the observation of anomalous reverse breakdown behavior in moderately doped (2-3 x 10(exp 17 cm(exp -3)) small-area micropipe-free 4H- and 6H-SiC pn junction diodes. When measured with a curve tracer, the diodes consistently exhibited very low reverse leakage currents and sharp repeatable breakdown knees in the range of 140-150 V. However, when subjected to single-shot reverse bias pulses (200 ns pulsewidth, 1 ns risetime), the diodes failed catastrophically at pulse voltages of less than 100 V. We propose a possible mechanism for this anomalous reduction in pulsed breakdown voltage relative to dc breakdown voltage. This instability must be removed so that SiC high-field devices can operate with the same high reliability as silicon power devices.

Compact high-power optical source for resonant infrared pulsed laser ablation and deposition of polymer materials

NASA Astrophysics Data System (ADS)

Kolev, V. Z.; Duering, M. W.; Luther-Davies, B.; Rode, A. V.

2006-12-01

We propose a novel tuneable table-top optical source as an alternative to the free electron laser currently used for resonant infrared pulsed laser deposition of polymers. It is based on two-stage pulsed optical parametric amplification using MgO doped periodically poled lithium niobate crystals. Gain in excess of 106 in the first stage and pump depletion of 58% in the second stage were achieved when the system was pumped by a high-power Nd:YVO4 picosecond laser source at 1064 nm and seeded by a CW tuneable diode laser at 1530 nm. An average power of 2 W was generated at 3.5 µm corresponding to 1.3 µJ pulse energy.

Pulse-burst PIV in a high-speed wind tunnel

NASA Astrophysics Data System (ADS)

Beresh, Steven; Kearney, Sean; Wagner, Justin; Guildenbecher, Daniel; Henfling, John; Spillers, Russell; Pruett, Brian; Jiang, Naibo; Slipchenko, Mikhail; Mance, Jason; Roy, Sukesh

2015-09-01

Time-resolved particle image velocimetry (TR-PIV) has been achieved in a high-speed wind tunnel, providing velocity field movies of compressible turbulence events. The requirements of high-speed flows demand greater energy at faster pulse rates than possible with the TR-PIV systems developed for low-speed flows. This has been realized using a pulse-burst laser to obtain movies at up to 50 kHz, with higher speeds possible at the cost of spatial resolution. The constraints imposed by use of a pulse-burst laser are limited burst duration of 10.2 ms and a low duty cycle for data acquisition. Pulse-burst PIV has been demonstrated in a supersonic jet exhausting into a transonic crossflow and in transonic flow over a rectangular cavity. The velocity field sequences reveal the passage of turbulent structures and can be used to find velocity power spectra at every point in the field, providing spatial distributions of acoustic modes. The present work represents the first use of TR-PIV in a high-speed ground-test facility.

High-throughput machining using high average power ultrashort pulse lasers and ultrafast polygon scanner

NASA Astrophysics Data System (ADS)

Schille, Joerg; Schneider, Lutz; Streek, André; Kloetzer, Sascha; Loeschner, Udo

2016-03-01

In this paper, high-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (Aluminium, Copper, Stainless steel) and Al2O3 ceramic at unprecedented processing speeds. This is achieved by using a high pulse repetition frequency picosecond laser with maximum average output power of 270 W in conjunction with a unique, in-house developed two-axis polygon scanner. Initially, different concepts of polygon scanners are engineered and tested to find out the optimal architecture for ultrafast and precision laser beam scanning. Remarkable 1,000 m/s scan speed is achieved on the substrate, and thanks to the resulting low pulse overlap, thermal accumulation and plasma absorption effects are avoided at up to 20 MHz pulse repetition frequencies. In order to identify optimum processing conditions for efficient high-average power laser machining, the depths of cavities produced under varied parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. The maximum removal rate is achieved as high as 27.8 mm3/min for Aluminium, 21.4 mm3/min for Copper, 15.3 mm3/min for Stainless steel and 129.1 mm3/min for Al2O3 when full available laser power is irradiated at optimum pulse repetition frequency.

Ferroelectric switch for a high-power Ka-band active pulse compressor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirshfield, Jay L.

2013-12-18

Results are presented for design of a high-power microwave switch for operation at 34.3 GHz, intended for use in an active RF pulse compressor. The active element in the switch is a ring of ferroelectric material, whose dielectric constant can be rapidly changed by application of a high-voltage pulse. As envisioned, two of these switches would be built into a pair of delay lines, as in SLED-II at SLAC, so as to allow 30-MW μs-length Ka-band pulses to be compressed in time by a factor-of-9 and multiplied in amplitude to generate 200 MW peak power pulses. Such high-power pulses couldmore » be used for testing and evaluation of high-gradient mm-wave accelerator structures, for example. Evaluation of the switch design was carried out with an X-band (11.43 GHz) prototype, built to incorporate all the features required for the Ka-band version.« less

Plasma Switch for High-Power Active Pulse Compressor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirshfield, Jay L.

2013-11-04

Results are presented from experiments carried out at the Naval Research Laboratory X-band magnicon facility on a two-channel X-band active RF pulse compressor that employed plasma switches. Experimental evidence is shown to validate the basic goals of the project, which include: simultaneous firing of plasma switches in both channels of the RF circuit, operation of quasi-optical 3-dB hybrid directional coupler coherent superposition of RF compressed pulses from both channels, and operation of the X-band magnicon directly in the RF pulse compressor. For incident 1.2 ?s pulses in the range 0.63 ? 1.35 MW, compressed pulses of peak powers 5.7 ?more » 11.3 MW were obtained, corresponding to peak power gain ratios of 8.3 ? 9.3. Insufficient bakeout and conditioning of the high-power RF circuit prevented experiments from being conducted at higher RF input power levels.« less

The impact of the driving frequency on the output flux of high-power InGaAlP-LEDs during high-current pulsed operation

NASA Astrophysics Data System (ADS)

Schulz, Benjamin; Morgott, Stefan

2017-09-01

Direct red light-emitting diodes based on InGaAlP comprise a strong temperature sensitivity regarding their output flux. In étendue-limited applications, like digital projectors, these LEDs are usually driven at current densities exceeding 3 A/mm2 in pulsed mode. The losses inside the semiconductor lead to a large amount of heat, which has to be removed most efficiently by a heatsink to keep the junction temperature as low as possible and therefore to obtain the maximum output flux. One important performance parameter is the thermal resistance Rth of the LED, which has been improved during the last few years, e.g. by the development of new high-power chips and packages. In our present approach, we investigated the influence of the driving frequency - which is closely related to the thermal impedance Zth - on the luminous and the radiant flux of red LEDs. A simulation model based on the electro-thermal analogies was implemented in SPICE and the optical and electrical characteristics of one LED type (OSRAM OSTAR Projection Power LE A P1W) were measured under application-related driving conditions while varying the parameters frequency, duty cycle, forward current, and heatsink temperature. The experimental results show clearly that the luminous and the radiant flux go up when the driving frequency is increased while the other parameters are maintained. Moreover, it can be noticed that the degree of this effect depends on the other parameters. The largest impact can be observed at the lowest tested duty cycle (30 %) and the highest tested current density (4 A/mm2) and heatsink temperature (80 °C). At this operating point, the luminous and the radiant flux increase by 20 % and 14 % respectively when raising the frequency from 240 Hz to 1920 Hz.

Evidence of Spin-Injection-Induced Cooper Pair Breaking in Perovskite Ferromagnet-Insulator-Superconductor Heterostructures via Pulsed Current Measurements

NASA Technical Reports Server (NTRS)

Yeh, N. C.; Samoilov, A. V.; Veasquez, R. P.; Li, Y.

1998-01-01

The effect of spin-polarized currents on the critical current densities of cuprate superconductors is investigated in perovskite ferromagnet-insulator-superconductor heterostructures with a pulsed current technique.

High-current electron gun with a planar magnetron integrated with an explosive-emission cathode

NASA Astrophysics Data System (ADS)

Kiziridi, P. P.; Ozur, G. E.

2017-05-01

A new high-current electron gun with plasma anode and explosive-emission cathode integrated with planar pulsed powered magnetron is described. Five hundred twelve copper wires 1 mm in diameter and 15 mm in height serve as emitters. These emitters are installed on stainless steel disc (substrate) with 3-mm distance between them. Magnetron discharge plasma provides increased ion density on the periphery of plasma anode formed by high-current Penning discharge ignited within several milliseconds after starting of the magnetron discharge. The increased on the periphery ion density improves the uniformity of high-current electron beam produced in such an electron gun.

Z a Fast Pulsed Power Generator for Ultra-High Magnetic Field Generation

NASA Astrophysics Data System (ADS)

Spielman, R. B.; Stygar, W. A.; Struve, K. W.; Asay, J. R.; Hall, C. A.; Bernard, M. A.; Bailey, J. E.; McDaniel, D. H.

2004-11-01

Advances in fast, pulsed-power technologies have resulted in the development of very high current drivers that have current rise times ~100 ns. The largest such pulsed power driver today is the new Z accelerator located at Sandia National Laboratories in Albuquerque, New Mexico. Z can deliver more than 20 MA with a time-to-peak of 105 ns to low inductance (~1 nH) loads. Such large drivers are capable of directly generating magnetic fields approaching 3 kT in small, 1 cm3 volumes. In addition to direct field generation, Z can be used to compress an applied, axial seed field with a plasma. Flux compression schemes are not new and are, in fact, the basis of all explosive flux-compression generators, but we propose the use of plasma armatures rather than solid, conducting armatures. We present experimental results from the Z accelerator in which magnetic fields of ~2 kT are generated and measured with several diagnostics. Issues such as energy loss in solid conductors and dynamic response of current-carrying conductors to very large magnetic fields are reviewed in context with Z experiments. We describe planned flux-compression experiments that are expected to create the highest-magnitude uniform-field volumes yet attained in the laboratory.

Parametric Study of Pulse-Combustor-Driven Ejectors at High-Pressure

NASA Technical Reports Server (NTRS)

Yungster, Shaye; Paxson, Daniel E.; Perkins, Hugh D.

2015-01-01

Pulse-combustor configurations developed in recent studies have demonstrated performance levels at high-pressure operating conditions comparable to those observed at atmospheric conditions. However, problems related to the way fuel was being distributed within the pulse combustor were still limiting performance. In the first part of this study, new configurations are investigated computationally aimed at improving the fuel distribution and performance of the pulse-combustor. Subsequent sections investigate the performance of various pulse-combustor driven ejector configurations operating at high pressure conditions, focusing on the effects of fuel equivalence ratio and ejector throat area. The goal is to design pulse-combustor-ejector configurations that maximize pressure gain while achieving a thermal environment acceptable to a turbine, and at the same time maintain acceptable levels of NO(x) emissions and flow non-uniformities. The computations presented here have demonstrated pressure gains of up to 2.8.

Improved pulse laser ranging algorithm based on high speed sampling

NASA Astrophysics Data System (ADS)

Gao, Xuan-yi; Qian, Rui-hai; Zhang, Yan-mei; Li, Huan; Guo, Hai-chao; He, Shi-jie; Guo, Xiao-kang

2016-10-01

Narrow pulse laser ranging achieves long-range target detection using laser pulse with low divergent beams. Pulse laser ranging is widely used in military, industrial, civil, engineering and transportation field. In this paper, an improved narrow pulse laser ranging algorithm is studied based on the high speed sampling. Firstly, theoretical simulation models have been built and analyzed including the laser emission and pulse laser ranging algorithm. An improved pulse ranging algorithm is developed. This new algorithm combines the matched filter algorithm and the constant fraction discrimination (CFD) algorithm. After the algorithm simulation, a laser ranging hardware system is set up to implement the improved algorithm. The laser ranging hardware system includes a laser diode, a laser detector and a high sample rate data logging circuit. Subsequently, using Verilog HDL language, the improved algorithm is implemented in the FPGA chip based on fusion of the matched filter algorithm and the CFD algorithm. Finally, the laser ranging experiment is carried out to test the improved algorithm ranging performance comparing to the matched filter algorithm and the CFD algorithm using the laser ranging hardware system. The test analysis result demonstrates that the laser ranging hardware system realized the high speed processing and high speed sampling data transmission. The algorithm analysis result presents that the improved algorithm achieves 0.3m distance ranging precision. The improved algorithm analysis result meets the expected effect, which is consistent with the theoretical simulation.

Study to evaluate the effect of low-intensity pulsed electrical currents on levels of oedema in chronic non-healing wounds.

PubMed

Young, S; Hampton, S; Tadej, M

2011-08-01

To evaluate the efficacy of a medical device, Accel-Heal, which generates a low-intensity pulsed direct current, on the management of oedema in chronic leg ulcers, using high-frequency diagnostic ultrasound. High-frequency diagnostic ultrasound (20MHz) with an axial resolution of 60um was used to assess the effect of an electrical stimulation device delivering a low-intensity pulsed current on levels of oedema in chronic non-healing venous and mixed aetiology leg ulcers for a period of 10 days. Thirty patients' wounds were monitored over a 3-month period, during which time changes in levels of oedema in the wound bed and surrounding tissues were imaged and measured. A significant fall in the, previously high level, of periwound oedema was noted in the patient population after 10 days of device application. By 20 days after the first application of the device the level of periwound oedema had decreased by approximately 60% of the original level, which was maintained up to the 90-day follow-up. Occurring in parallel with this, scans of the wound bed showed a rapid decrease in the levels of oedema as the new wound matrix was laid down. The electrical stimulation device appeared to be effective in reducing oedema levels in a range of chronic wounds and their surrounding tissues. The study was funded by a grant from Synapse micro-current Ltd.

Completely explosive ultracompact high-voltage nanosecond pulse-generating system

NASA Astrophysics Data System (ADS)

Shkuratov, Sergey I.; Talantsev, Evgueni F.; Baird, Jason; Rose, Millard F.; Shotts, Zachary; Altgilbers, Larry L.; Stults, Allen H.

2006-04-01

A conventional pulsed power technology has been combined with an explosive pulsed power technology to produce an autonomous high-voltage power supply. The power supply contained an explosive-driven high-voltage primary power source and a power-conditioning stage. The ultracompact explosive-driven primary power source was based on the physical effect of shock-wave depolarization of high-energy Pb (Zr52Ti48)O3 ferroelectric material. The volume of the energy-carrying ferroelectric elements in the shock-wave ferroelectric generators (SWFEGs) varied from 1.2 to 2.6cm3. The power-conditioning stage was based on the spiral vector inversion generator (VIG). The SWFEG-VIG system demonstrated successful operation and good performance. The amplitude of the output voltage pulse of the SWFEG-VIG system exceeded 90kV, with a rise time of 5.2ns.

Modeling of high efficiency solar cells under laser pulse for power beaming applications

NASA Technical Reports Server (NTRS)

Jain, Raj K.; Landis, Geoffrey A.

1994-01-01

Solar cells have been used to convert sunlight to electrical energy for many years and also offer great potential for non-solar energy conversion applications. Their greatly improved performance under monochromatic light compared to sunlight, makes them suitable as photovoltaic (PV) receivers in laser power beaming applications. Laser beamed power to a PV array receiver could provide power to satellites, an orbital transfer vehicle, or a lunar base. Gallium arsenide (GaAs) and indium phosphide (InP) solar cells have calculated efficiencies of more than 50 percent under continuous illumination at the optimum wavelength. Currently high power free-electron lasers are being developed which operate in pulsed conditions. Understanding cell behavior under a laser pulse is important in the selection of the solar cell material and the laser. An experiment by NAsA lewis and JPL at the AVLIS laser facility in Livermore, CA presented experimental data on cell performance under pulsed laser illumination. Reference 5 contains an overview of technical issues concerning the use of solar cells for laser power conversion, written before the experiments were performed. As the experimental results showed, the actual effects of pulsed operation are more complicated. Reference 6 discusses simulations of the output of GaAs concentrator solar cells under pulsed laser illumination. The present paper continues this work, and compares the output of Si and GaAs solar cells.

Methods of high current magnetic field generator for transcranial magnetic stimulation application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bouda, N. R., E-mail: nybouda@iastate.edu; Pritchard, J.; Weber, R. J.

This paper describes the design procedures and underlying concepts of a novel High Current Magnetic Field Generator (HCMFG) with adjustable pulse width for transcranial magnetic stimulation applications. This is achieved by utilizing two different switching devices, the MOSFET and insulated gate bipolar transistor (IGBT). Results indicate that currents as high as ±1200 A can be generated with inputs of +/−20 V. Special attention to tradeoffs between field generators utilizing IGBT circuits (HCMFG{sub 1}) and MOSFET circuits (HCMFG{sub 2}) was considered. The theory of operation, design, experimental results, and electronic setup are presented and analyzed.

Analysis and fabrication of tungsten CERMET materials for ultra-high temperature reactor applications via pulsed electric current sintering

NASA Astrophysics Data System (ADS)

Webb, Jonathan A.

The optimized development path for the fabrication of ultra-high temperature W-UO2 CERMET fuel elements were explored within this dissertation. A robust literature search was conducted, which concluded that a W-UO 2 fuel element must contain a fine tungsten microstructure and spherical UO2 kernels throughout the entire consolidation process. Combined Monte Carlo and Computational Fluid Dynamics (CFD) analysis were used to determine the effects of rhenium and gadolinia additions on the performance of W-UO 2 fuel elements at refractory temperatures and in dry and water submerged environments. The computational analysis also led to the design of quasi-optimized fuel elements that can meet thermal-hydraulic and neutronic requirements A rigorous set of experiments were conducted to determine if Pulsed Electric Current Sintering (PECS) can fabricate tungsten and W-Ce02 specimens to the required geometries, densities and microstructures required for high temperature fuel elements as well as determine the mechanisms involved within the PECS consolidation process. The CeO2 acts as a surrogate for UO 2 fuel kernels in these experiments. The experiments seemed to confirm that PECS consolidation takes place via diffusional mass transfer methods; however, the densification process is rapidly accelerated due to the effects of current densities within the consolidating specimen. Fortunately the grain growth proceeds at a traditional rate and the PECS process can yield near fully dense W and W-Ce02 specimens with a finer microstructure than other sintering techniques. PECS consolidation techniques were also shown to be capable of producing W-UO2 segments at near-prototypic geometries; however, great care must be taken to coat the fuel particles with tungsten prior to sintering. Also, great care must be taken to ensure that the particles remain spherical in geometry under the influence of a uniaxial stress as applied during PECS, which involves mixing different fuel kernel sizes in

REX, a 5-MV pulsed-power source for driving high-brightness electron beam diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlson, R.L.; Kauppila, T.J.; Ridlon, R.N.

1991-01-01

The Relativistic Electron-beam Experiment, or REX accelerator, is a pulsed-power source capable of driving a 100-ohm load at 5 MV, 50 kA, 45 ns (FWHM) with less than a 10-ns rise and 15-ns fall time. This paper describes the pulsed-power modifications, modelling, and extensive measurements on REX to allow it to drive high impedance (100s of ohms) diode loads with a shaped voltage pulse. A major component of REX is the 1.83-m-diam {times} 25.4-cm-thick Lucite insulator with embedded grading rings that separates the output oil transmission line from the vacuum vessel that contains the re-entrant anode and cathode assemblies. Amore » radially tailored, liquid-based resistor provides a stiff voltage source that is insensitive to small variations of the diode current and, in addition, optimizes the electric field stress across the vacuum side of the insulator. The high-current operation of REX employs both multichannel peaking and point-plane diverter switches. This mode reduces the prepulse to less than 2 kV and the postpulse to less than 5% of the energy delivered to the load. Pulse shaping for the present diode load is done through two L-C transmission line filters and a tapered, glycol-based line adjacent to the water PFL and output switch. This has allowed REX to drive a diode producing a 4-MV, 4.5-kA, 55-ns flat-top electron beam with a normalized Lapostolle emittance of 0.96 mm-rad corresponding to a beam brightness in excess of 4.4 {times} 10{sup 8} A/m{sup 2} {minus}rad{sup 2}. 6 refs., 13 figs.« less

Strong electromagnetic pulses generated in high-intensity laser-matter interactions

NASA Astrophysics Data System (ADS)

Rączka, P.; Dubois, J.-L.; Hulin, S.; Rosiński, M.; Zaraś-Szydłowska, A.; Badziak, J.

2018-01-01

Results are reported of an experiment performed at the Eclipse laser facility in CELIA, Bordeaux, on the generation of strong electromagnetic pulses. Measurements were performed of the target neutralization current, the total target charge and the tangential component of the magnetic field for the laser energies ranging from 45 mJ to 92 mJ with the pulse duration approximately 40 fs, and for the pulse durations ranging from 39 fs to 1000 fs, with the laser energy approximately 90 mJ. It was found that the values obtained for thick (mm scale) Cu targets are visibly higher than values reported in previous experiments, which is argued to be a manifestation of a strong dependence of the target electric polarization process on the laser contrast and hence on the amount of preplasma. It was also found that values obtained for thin (μm scale) Al foils were visibly higher than values for thick Cu targets, especially for pulse durations longer than 100 fs. The correlations between the total target charge versus the maximum value of the target neutralization current, and the maximum value of the tangential component of the magnetic field versus the total target charge were analysed. They were found to be in very good agreement with correlations seen in data from previous experiments, which provides a good consistency check on our experimental procedures.

Cycle life improvement of alkaline batteries via optimization of pulse current deposition of manganese dioxide under low bath temperatures

NASA Astrophysics Data System (ADS)

Adelkhani, H.; Ghaemi, M.; Jafari, S. M.

Pulse current electrodeposition (PCD) method has been applied to the preparation of novel electrolytic manganese dioxide (EMD) in order to enhance the cycle life of rechargeable alkaline MnO 2-Zn batteries (RAM). The investigation was carried out under atmospheric pressure through a systematic variation of pulse current parameters using additive free sulfuric acid-MnSO 4 electrolyte solutions. On time (t on) was varied from 0.1 to 98.5 ms, off time (t off) from 0.25 to 19.5 ms, pulse frequencies (f) from 10 to 1000 Hz and duty cycles (θ) from 0.02 to 0.985. A constant pulse current density (I p) of 0.8 A dm -2 and average current densities (I a) in the range of 0.08-0.8 A dm -2 were applied in all experiments. Resultant materials were characterized by analyzing their chemical compositions, X-ray diffractions (XRD) and scanning electron microscopy (SEM). Electrochemical characterizations carried out by charge/discharge cycling of samples in laboratory designed RAM batteries and cyclic voltammetric experiments (CV). It has been proved that specific selection of duty cycle, in the order of 0.25, and a pulse frequency of 500 Hz, results in the production of pulse deposited samples (pcMDs) with more uniform distribution of particles and more compact structure than those obtained by direct current techniques (dcMDs). Results of the test batteries demonstrated that, in spite of reduction of bath temperature in the order of 40 °C, the cycle life of batteries made of pcMDs (bath temperature: 60 °C) was rather higher than those made of conventional dcMDs (boiling electrolyte solution). Under the same conditions of EMD synthesis temperature of 80 °C and battery testing, the maximum obtainable cycle life of optimized pcMD was nearly 230 cycles with approximately 30 mAh g -1 MnO 2, compared to that of dcMD, which did not exceed 20 cycles. In accordance to these results, CV has confirmed that the pulse duty cycle is the most influential parameter on the cycle life than the

Spatial-time-state fusion algorithm for defect detection through eddy current pulsed thermography

NASA Astrophysics Data System (ADS)

Xiao, Xiang; Gao, Bin; Woo, Wai Lok; Tian, Gui Yun; Xiao, Xiao Ting

2018-05-01

Eddy Current Pulsed Thermography (ECPT) has received extensive attention due to its high sensitive of detectability on surface and subsurface cracks. However, it remains as a difficult challenge in unsupervised detection as to identify defects without knowing any prior knowledge. This paper presents a spatial-time-state features fusion algorithm to obtain fully profile of the defects by directional scanning. The proposed method is intended to conduct features extraction by using independent component analysis (ICA) and automatic features selection embedding genetic algorithm. Finally, the optimal feature of each step is fused to obtain defects reconstruction by applying common orthogonal basis extraction (COBE) method. Experiments have been conducted to validate the study and verify the efficacy of the proposed method on blind defect detection.

High-throughput machining using a high-average power ultrashort pulse laser and high-speed polygon scanner

NASA Astrophysics Data System (ADS)

Schille, Joerg; Schneider, Lutz; Streek, André; Kloetzer, Sascha; Loeschner, Udo

2016-09-01

High-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (aluminum, copper, and stainless steel) and Al2O3 ceramic at unprecedented processing speeds. This is achieved by using a high-average power picosecond laser in conjunction with a unique, in-house developed polygon mirror-based biaxial scanning system. Therefore, different concepts of polygon scanners are engineered and tested to find the best architecture for high-speed and precision laser beam scanning. In order to identify the optimum conditions for efficient processing when using high-average laser powers, the depths of cavities made in the samples by varying the processing parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. For overlapping pulses of optimum fluence, the removal rate is as high as 27.8 mm3/min for aluminum, 21.4 mm3/min for copper, 15.3 mm3/min for stainless steel, and 129.1 mm3/min for Al2O3, when a laser beam of 187 W average laser powers irradiates. On stainless steel, it is demonstrated that the removal rate increases to 23.3 mm3/min when the laser beam is very fast moving. This is thanks to the low pulse overlap as achieved with 800 m/s beam deflection speed; thus, laser beam shielding can be avoided even when irradiating high-repetitive 20-MHz pulses.

Note: High temperature pulsed solenoid valve.

PubMed

Shen, Wei; Sulkes, Mark

2010-01-01

We have developed a high temperature pulsed solenoid valve with reliable long term operation to at least 400 degrees C. As in earlier published designs, a needle extension sealing a heated orifice is lifted via solenoid actuation; the solenoid is thermally isolated from the heated orifice region. In this new implementation, superior sealing and reliability were attained by choosing a solenoid that produces considerably larger lifting forces on the magnetically actuated plunger. It is this property that facilitates easily attainable sealing and reliability, albeit with some tradeoff in attainable gas pulse durations. The cost of the solenoid valve employed is quite low and the necessary machining quite simple. Our ultimate level of sealing was attained by making a simple modification to the polished seal at the needle tip. The same sealing tip modification could easily be applied to one of the earlier high T valve designs, which could improve the attainability and tightness of sealing for these implementations.

Status of Pulsed Inductive Thruster Research

NASA Technical Reports Server (NTRS)

Hrbud, Ivana; LaPointe, Michael; Vondra, Robert; Lovberg, Ralph; Dailey, C. Lee; Schafer, Charles (Technical Monitor)

2002-01-01

The TRW Pulsed Inductive Thruster (PIT) is an electromagnetic propulsion system that can provide high thrust efficiency over a wide range of specific impulse values. In its basic form, the PIT consists of a flat spiral coil covered by a thin dielectric plate. A pulsed gas injection nozzle distributes a thin layer of gas propellant across the plate surface at the same time that a pulsed high current discharge is sent through the coil. The rising current creates a time varying magnetic field, which in turn induces a strong azimuthal electric field above the coil. The electric field ionizes the gas propellant and generates an azimuthal current flow in the resulting plasma. The current in the plasma and the current in the coil flow in opposite directions, providing a mutual repulsion that rapidly blows the ionized propellant away from the plate to provide thrust. The thrust and specific impulse can be tailored by adjusting the discharge power, pulse repetition rate, and propellant mass flow, and there is minimal if any erosion due to the electrodeless nature of the discharge. Prior single-shot experiment,; performed with a Diameter diameter version of the PIT at TRW demonstrated specific impulse values between 2,000 seconds and 8,000 seconds, with thruster efficiencies of about 52% for ammonia. This paper outlines current and planned activities to transition the single shot device into a multiple repetition rate thruster capable of supporting NASA strategic enterprise missions.

Effect of Continuous and Pulsed Current Gas Tungsten Arc Welding on Dissimilar Weldments Between Hastelloy C-276/AISI 321 Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Sharma, Sumitra; Taiwade, Ravindra V.; Vashishtha, Himanshu

2017-03-01

In the present investigation, an attempt has been made to join Hastelloy C-276 nickel-based superalloy and AISI 321 austenitic stainless steel using ERNiCrMo-4 filler. The joints were fabricated by continuous and pulsed current gas tungsten arc welding processes. Experimental studies to ascertain the structure-property co-relationship with or without pulsed current mode were carried out using an optical microscope and scanning electron microscope. Further, the energy-dispersive spectroscope was used to evaluate the extent of microsegregation. The microstructure of fusion zone was obtained as finer cellular dendritic structure for pulsed current mode, whereas columnar structure was formed with small amount of cellular structure for continuous current mode. The scanning electron microscope examination witnessed the existence of migrated grain boundaries at the weld interfaces. Moreover, the presence of secondary phases such as P and μ was observed in continuous current weld joints, whereas they were absent in pulsed current weld joints, which needs to be further characterized. Moreover, pulsed current joints resulted in narrower weld bead, refined morphology, reduced elemental segregation and improved strength of the welded joints. The outcomes of the present investigation would help in obtaining good quality dissimilar joints for industrial applications and AISI 321 ASS being cheaper consequently led to cost-effective design also.

A highly efficient and compact long pulse Nd:YAG rod laser with 540 J of pulse energy for welding application.

PubMed

Choubey, Ambar; Vishwakarma, S C; Misra, Pushkar; Jain, R K; Agrawal, D K; Arya, R; Upadhyaya, B N; Oak, S M

2013-07-01

We have developed an efficient and high average power flash lamp pumped long pulse Nd:YAG laser capable of generating 1 kW of average output power with maximum 540 J of single pulse energy and 20 kW of peak power. The laser pulse duration can be varied from 1 to 40 ms and repetition rate from 1 to 100 Hz. A compact and robust laser pump chamber and resonator was designed to achieve this high average and peak power. It was found that this laser system provides highest single pulse energy as compared to other long pulsed Nd:YAG laser systems of similar rating. A slope efficiency of 5.4% has been achieved, which is on higher side for typical lamp pumped solid-state lasers. This system will be highly useful in laser welding of materials such as aluminium and titanium. We have achieved 4 mm deep penetration welding of these metals under optimized conditions of output power, pulse energy, and pulse duration. The laser resonator was optimized to provide stable operation from single shot to 100 Hz of repetition rate. The beam quality factor was measured to be M(2) ~ 91 and pulse-to-pulse stability of ±3% for the multimode operation. The laser beam was efficiently coupled through an optical fiber of 600 μm core diameter and 0.22 numerical aperture with power transmission of 90%.

A cavity-dumped and regenerative amplifier system for generating high-energy, high-repetition-rate picosecond pulses

NASA Astrophysics Data System (ADS)

Peng, ZhiGang; Chen, Meng; Yang, Chao; Chang, Liang; Li, Gang

2015-02-01

We report a high-energy, high-repetition CW pumped Nd:YVO4 amplifier system, that produces 10.5 W, 14.2 ps pulses at 1064 nm wavelength and 5 W pulses at 532 nm wavelength with a repetition rate of 10 kHz. Pulses from a passively mode-locked Nd:YVO4 oscillator are first generated by cavity dumping, and then further amplified in a regenerative amplifier from 545 nJ to 1 mJ with a CW diode-pumped Nd:YVO4. After frequency doubling, 0.5 mJ pulses are obtained with a wavelength of 532 nm.

Pulsed characterization of a UV LED for pulsed power applications on a silicon carbide photoconductive semiconductor switch

NASA Astrophysics Data System (ADS)

Wilson, Nicholas; Mauch, Daniel; Meyers, Vincent; Feathers, Shannon; Dickens, James; Neuber, Andreas

2017-08-01

The electrical and optical characteristics of a high-power UV light emitting diode (LED) (365 nm wavelength) were evaluated under pulsed operating conditions at current amplitudes several orders of magnitude beyond the LED's manufacturer specifications. Geared towards triggering of photoconductive semiconductor switches (PCSSs) for pulsed power applications, measurements were made over varying pulse widths (25 ns-100 μs), current (0 A-250 A), and repetition rates (single shot-5 MHz). The LED forward voltage was observed to increase linearly with increasing current (˜3.5 V-53 V) and decrease with increasing pulse widths. The peak optical power observed was >30 W, and a maximum system efficiency of 23% was achieved. The evaluated LED and auxiliary hardware were successfully used as the optical trigger source for a 4H-SiC PCSS. The lowest measured on-resistance of SiC was approximately 67 kΩ.

Pulsed characterization of a UV LED for pulsed power applications on a silicon carbide photoconductive semiconductor switch.

PubMed

Wilson, Nicholas; Mauch, Daniel; Meyers, Vincent; Feathers, Shannon; Dickens, James; Neuber, Andreas

2017-08-01

The electrical and optical characteristics of a high-power UV light emitting diode (LED) (365 nm wavelength) were evaluated under pulsed operating conditions at current amplitudes several orders of magnitude beyond the LED's manufacturer specifications. Geared towards triggering of photoconductive semiconductor switches (PCSSs) for pulsed power applications, measurements were made over varying pulse widths (25 ns-100 μs), current (0 A-250 A), and repetition rates (single shot-5 MHz). The LED forward voltage was observed to increase linearly with increasing current (∼3.5 V-53 V) and decrease with increasing pulse widths. The peak optical power observed was >30 W, and a maximum system efficiency of 23% was achieved. The evaluated LED and auxiliary hardware were successfully used as the optical trigger source for a 4H-SiC PCSS. The lowest measured on-resistance of SiC was approximately 67 kΩ.

Current indications and new applications of intense pulsed light.

PubMed

González-Rodríguez, A J; Lorente-Gual, R

2015-06-01

Intense pulsed light (IPL) systems have evolved since they were introduced into medical practice 20 years ago. Pulsed light is noncoherent, noncollimated, polychromatic light energy emitted at different wavelengths that target specific chromophores. This selective targeting capability makes IPL a versatile therapy with many applications, from the treatment of pigmented or vascular lesions to hair removal and skin rejuvenation. Its large spot size ensures a high skin coverage rate. The nonablative nature of IPL makes it an increasingly attractive alternative for patients unwilling to accept the adverse effects associated with other procedures, which additionally require prolonged absence from work and social activities. In many cases, IPL is similar to laser therapy in effectiveness, and its versatility, convenience, and safety will lead to an expanded range of applications and possibilities in coming years. Copyright © 2014 Elsevier España, S.L.U. and AEDV. All rights reserved.

SU-C-201-03: Ionization Chamber Collection Efficiency in Pulsed Radiation Fields of High Pulse Dose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gotz, M; Karsch, L; Pawelke, J

Purpose: To investigate the reduction of collection efficiency of ionization chambers (IC) by volume recombination and its correction in pulsed fields of very high pulse dose. Methods: Measurements of the collection efficiency of a plane-parallel advanced Markus IC (PTW 34045, 1mm electrode spacing, 300V nominal voltage) were obtained for collection voltages of 100V and 300V by irradiation with a pulsed electron beam (20MeV) of varied pulse dose up to approximately 600mGy (0.8nC liberated charge). A reference measurement was performed with a Faraday cup behind the chamber. It was calibrated for the liberated charge in the IC by a linear fitmore » of IC measurement to reference measurement at low pulse doses. The results were compared to the commonly used two voltage approximation (TVA) and to established theories for volume recombination, with and without considering a fraction of free electrons. In addition, an equation system describing the charge transport and reactions in the chamber was solved numerically. Results: At 100V collection voltage and moderate pulse doses the established theories accurately predict the observed collection efficiency, but at extreme pulse doses a fraction of free electrons needs to be considered. At 300V the observed collection efficiency deviates distinctly from that predicted by any of the established theories, even at low pulse doses. However, the numeric solution of the equation system is able to reproduce the measured collection efficiency across the entire dose range of both voltages with a single set of parameters. Conclusion: At high electric fields (3000V/cm here) the existing theoretical descriptions of collection efficiency, including the TVA, are inadequate to predict pulse dose dependency. Even at low pulse doses they might underestimate collection efficiency. The presented, more accurate numeric solution, which considers additional effects like electric shielding by the charges, might provide a valuable tool for

Loss Analysis of High Power Stirling-Type Pulse Tube Cryocooler

NASA Astrophysics Data System (ADS)

Nakano, K.; Hiratsuka, Y.

2015-12-01

For the purpose of cooling high-temperature superconductor (HTS) devices, such as superconductor motors, superconducting magnetic energy storage (SMES) and current fault limiters, cryocoolers should be compact in size, light-weight, and have high efficiency and reliability. In order to meet the demand of HTS devices world-wide, the cryocooler needs to have COP efficiency >0.1. We have developed a high power Stirling-type pulse tube cryocooler (SPTC) with an in-line expander. The experimental results were reported in June 2012[1]. The cooling capacity was 210 W at 77 K and the minimum temperature was 37 K when the compressor input power was 3.8 kW. Accordingly, the COP was about 0.055. To further improve the efficiency, the energy losses in the cryocooler were analyzed. The experimental results and the numerical calculation results are reported in this paper.

Ultrashort pulse high repetition rate laser system for biological tissue processing

DOEpatents

Neev, Joseph; Da Silva, Luiz B.; Matthews, Dennis L.; Glinsky, Michael E.; Stuart, Brent C.; Perry, Michael D.; Feit, Michael D.; Rubenchik, Alexander M.

1998-01-01

A method and apparatus is disclosed for fast, efficient, precise and damage-free biological tissue removal using an ultrashort pulse duration laser system operating at high pulse repetition rates. The duration of each laser pulse is on the order of about 1 fs to less than 50 ps such that energy deposition is localized in a small depth and occurs before significant hydrodynamic motion and thermal conduction, leading to collateral damage, can take place. The depth of material removed per pulse is on the order of about 1 micrometer, and the minimal thermal and mechanical effects associated with this ablation method allows for high repetition rate operation, in the region 10 to over 1000 Hertz, which, in turn, achieves high material removal rates. The input laser energy per ablated volume of tissue is small, and the energy density required to ablate material decreases with decreasing pulse width. The ablation threshold and ablation rate are only weakly dependent on tissue type and condition, allowing for maximum flexibility of use in various biological tissue removal applications. The use of a chirped-pulse amplified Titanium-doped sapphire laser is disclosed as the source in one embodiment.

Ultrashort pulse high repetition rate laser system for biological tissue processing

DOEpatents

Neev, J.; Da Silva, L.B.; Matthews, D.L.; Glinsky, M.E.; Stuart, B.C.; Perry, M.D.; Feit, M.D.; Rubenchik, A.M.

1998-02-24

A method and apparatus are disclosed for fast, efficient, precise and damage-free biological tissue removal using an ultrashort pulse duration laser system operating at high pulse repetition rates. The duration of each laser pulse is on the order of about 1 fs to less than 50 ps such that energy deposition is localized in a small depth and occurs before significant hydrodynamic motion and thermal conduction, leading to collateral damage, can take place. The depth of material removed per pulse is on the order of about 1 micrometer, and the minimal thermal and mechanical effects associated with this ablation method allows for high repetition rate operation, in the region 10 to over 1000 Hertz, which, in turn, achieves high material removal rates. The input laser energy per ablated volume of tissue is small, and the energy density required to ablate material decreases with decreasing pulse width. The ablation threshold and ablation rate are only weakly dependent on tissue type and condition, allowing for maximum flexibility of use in various biological tissue removal applications. The use of a chirped-pulse amplified Titanium-doped sapphire laser is disclosed as the source in one embodiment. 8 figs.

High-mechanical-strength single-pulse draw tower gratings

NASA Astrophysics Data System (ADS)

Rothhardt, Manfred W.; Chojetzki, Christoph; Mueller, Hans Rainer

2004-11-01

The inscription of fiber Bragg gratings during the drawing process is a very useful method to realize sensor arrays with high numbers of gratings and excellent mechanical strength and also type II gratings with high temperature stability. Results of single pulse grating arrays with numbers up to 100 and definite wavelengths and positions for sensor applications were achieved at 1550 nm and 830 nm using new photosensitive fibers developed in IPHT. Single pulse type I gratings at 1550 nm with more than 30% reflectivity were shown first time to our knowledge. The mechanical strength of this fiber with an Ormocer coating with those single pulse gratings is the same like standard telecom fibers. Weibull plots of fiber tests will be shown. At 830 nm we reached more than 10% reflectivity with single pulse writing during the fiber drawing in photosensitive fibers with less than 16 dB/km transmission loss. These gratings are useful for stress and vibration sensing applications. Type II gratings with reflectivity near 100% and smooth spectral shape and spectral width of about 1 nm are temperature stable up to 1200 K for short time. They are also realized in the fiber drawing process. These gratings are useful for temperature sensor applications.

ICPP: Relativistic Plasma Physics with Ultra-Short High-Intensity Laser Pulses

NASA Astrophysics Data System (ADS)

Meyer-Ter-Vehn, Juergen

2000-10-01

Recent progress in generating ultra-short high-intensity laser pulses has opened a new branch of relativistic plasma physics, which is discussed in this talk in terms of particle-in-cell (PIC) simulations. These pulses create small plasma volumes of high-density plasma with plasma fields above 10^12 V/m and 10^8 Gauss. At intensities beyond 10^18 W/cm^2, now available from table-top systems, they drive relativistic electron currents in self-focussing plasma channels. These currents are close to the Alfven limit and allow to study relativistic current filamentation. A most remarkable feature is the generation of well collimated relativistic electron beams emerging from the channels with energies up to GeV. In dense matter they trigger cascades of gamma-rays, e^+e^- pairs, and a host of nuclear and particle processes. One of the applications may be fast ignition of compressed inertial fusion targets. Above 10^23 W/cm^2, expected to be achieved in the future, solid-density matter becomes relativistically transparent for optical light, and the acceleration of protons to multi-GeV energies is predicted in plasma layers less than 1 mm thick. These results open completely new perspectives for plasma-based accelerator schemes. Three-dimensional PIC simulations turn out to be the superior tool to explore the relativistic plasma kinetics at such intensities. Results obtained with the VLPL code [1] are presented. Different mechanisms of particle acceleration are discussed. Both laser wakefield and direct laser acceleration in plasma channels (by a mechanism similar to inverse free electron lasers) have been identified. The latter describes recent MPQ experimental results. [1] A. Pukhov, J. Plasma Physics 61, 425 - 433 (1999): Three-dimensional electromagnetic relativistic particle-in-cell code VLPL (Virtual Laser Plasma Laboratory).

Cardiac transient outward potassium current: a pulse chemistry model of frequency-dependent properties.

PubMed

Liu, L; Krinsky, V I; Grant, A O; Starmer, C F

1996-01-01

Recent voltage-clamp studies of isolated myocytes have demonstrated widespread occurrence of a transient outward current (I(to)) carried by potassium ions. In the canine ventricle, this current is well developed in epicardial cells but not in endocardial cells. The resultant spatial dispersion of refractoriness is potentially proarrhythmic and may be amplified by channel blockade. The inactivation and recovery time constants of this channel are in excess of several hundred milliseconds, and consequently channel availability is frequency dependent at physiological stimulation rates. When the time constants associated with transitions between different channel conformations are rapid relative to drug binding kinetics, the interactions between drugs and an ion channel can be approximated by a sequence of first-order reactions, in which binding occurs in pulses in response to pulse train stimulation (pulse chemistry). When channel conformation transition time constants do not meet this constraint, analytical characterizations of the drug-channel interaction must then be modified to reflect the channel time-dependent properties. Here we report that the rate and steady-state amount of frequency-dependent inactivation of I(to) are consistent with a generalization of the channel blockade model: channel availability is reduced in a pulsatile exponential pattern as the stimulation frequency is increased, and the rate of reduction is a linear function of the pulse train depolarizing and recovery intervals. I(to) was reduced in the presence of quinidine. After accounting for the use-dependent availability of I(to) channels, we found little evidence of an additional use-dependent component of block after exposure to quinidine, suggesting that quinidine reacts with both open and closed I(to) channels as though the binding site is continuously accessible. The model provides a useful tool for assessing drug-channel interactions when the reaction cannot be continuously monitored.

A Fiber-Optic System Generating Pulses of High Spectral Density

NASA Astrophysics Data System (ADS)

Abramov, A. S.; Zolotovskii, I. O.; Korobko, D. A.; Fotiadi, A. A.

2018-03-01

A cascade fiber-optic system that generates pulses of high spectral density by using the effect of nonlinear spectral compression is proposed. It is demonstrated that the shape of the pulse envelope substantially influences the degree of compression of its spectrum. In so doing, maximum compression is achieved for parabolic pulses. The cascade system includes an optical fiber exhibiting normal dispersion that decreases along the fiber length, thereby ensuring that the pulse envelope evolves toward a parabolic shape, along with diffraction gratings and a fiber spectral compressor. Based on computer simulation, we determined parameters of cascade elements leading to maximum spectral density of radiation originating from a subpicosecond laser pulse of medium energy.

Pulsed current activated synthesis and rapid consolidation of a nanostructured Mg2Al4Si5O18 and its mechanical properties

NASA Astrophysics Data System (ADS)

Shon, In-Jin; Kang, Hyun-Su; Doh, Jung-Mann; Yoon, Jin-Kook

2015-03-01

Nanocrystalline materials have received much attention as advanced engineering materials, with improved mechanical properties. Attention has been directed to the application of nanomaterials, as they possess excellent mechanical properties (high strength, high hardness, excellent ductility and toughness). A singlestep synthesis and consolidation of nanostructured Mg2Al4Si5O18 was achieved by pulsed current heating, using the stoichiometric mixture of MgO, Al2O3 and SiO2 powders. Before sintering, the powder mixture was high-energy ball milled for 10 h. From the milled powder mixture, a highly dense nanostructured Mg2Al4Si5O18 compound could be obtained within one minute, under the simultaneous application of 80 MPa pressure, and a pulsed current. The advantage of this process is that it allows an instant densification to the near theoretical density, while sustaining the nanosized microstructure of raw powders. The sintering behavior, microstructure and mechanical properties of Mg2Al4Si5O18 were evaluated. The fracture toughness of a nanostructured Mg2Al4Si5O18 compound was higher than that of sub-micron Mg2Al4Si5O18 compound.

High voltage pulse ignition of mercury discharge hollow cathodes

NASA Technical Reports Server (NTRS)

Wintucky, E. G.

1973-01-01

A high voltage pulse generated by a capacitor discharge into a step-up transformer has been demonstrated capable of consistently igniting hollow cathode mercury discharges at propellant flows and heater power levels much below those required by conventional cathode starting. Results are presented for 3.2-mm diameter enclosed and open keeper cathodes. Starting characteristics are shown to depend on keeper voltage, mercury flow rate, heater power, keeper orifice size, emissive materials, and electrode to which the pulse is applied. This starting technique has been used to start a cathode over 10,000 times without any degradation of starting capability. The starting reliability, propellant and power savings offered by the high voltage pulse start should favorably impact performance of electron bombardment thrusters in missions requiring many on-off duty cycles.

Multifunctional pulse generator for high-intensity focused ultrasound system

NASA Astrophysics Data System (ADS)

Tamano, Satoshi; Yoshizawa, Shin; Umemura, Shin-Ichiro

2017-07-01

High-intensity focused ultrasound (HIFU) can achieve high spatial resolution for the treatment of diseases. A major technical challenge in implementing a HIFU therapeutic system is to generate high-voltage high-current signals for effectively exciting a multichannel HIFU transducer at high efficiencies. In this paper, we present the development of a multifunctional multichannel generator/driver. The generator can produce a long burst as well as an extremely high-voltage short pulse of pseudosinusoidal waves (trigger HIFU) and second-harmonic superimposed waves for HIFU transmission. The transmission timing, waveform, and frequency can be controlled using a field-programmable gate array (FPGA) via a universal serial bus (USB) microcontroller. The hardware is implemented in a compact printed circuit board. The test results of trigger HIFU reveal that the power consumption and the temperature rise of metal-oxide semiconductor field-effect transistors were reduced by 19.9% and 38.2 °C, respectively, from the previous design. The highly flexible performance of the novel generator/driver is demonstrated in the generation of second-harmonic superimposed waves, which is useful for cavitation-enhanced HIFU treatment, although the previous design exhibited difficulty in generating it.

Pulse charging of lead-acid traction cells

NASA Technical Reports Server (NTRS)

Smithrick, J. J.

1980-01-01

Pulse charging, as a method of rapidly and efficiently charging 300 amp-hour lead-acid traction cells for an electric vehicle application was investigated. A wide range of charge pulse current square waveforms were investigated and the results were compared to constant current charging at the time averaged pulse current values. Representative pulse current waveforms were: (1) positive waveform-peak charge pulse current of 300 amperes (amps), discharge pulse-current of zero amps, and a duty cycle of about 50%; (2) Romanov waveform-peak charge pulse current of 300 amps, peak discharge pulse current of 15 amps, and a duty of 50%; and (3) McCulloch waveform peak charge pulse current of 193 amps, peak discharge pulse current of about 575 amps, and a duty cycle of 94%. Experimental results indicate that on the basis of amp-hour efficiency, pulse charging offered no significant advantage as a method of rapidly charging 300 amp-hour lead-acid traction cells when compared to constant current charging at the time average pulse current value. There were, however, some disadvantages of pulse charging in particular a decrease in charge amp-hour and energy efficiencies and an increase in cell electrolyte temperature. The constant current charge method resulted in the best energy efficiency with no significant sacrifice of charge time or amp-hour output. Whether or not pulse charging offers an advantage over constant current charging with regard to the cell charge/discharge cycle life is unknown at this time.

Band-selective shaped pulse for high fidelity quantum control in diamond

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Yan-Chun; Xing, Jian; Liu, Gang-Qin

High fidelity quantum control of qubits is crucially important for realistic quantum computing, and it becomes more challenging when there are inevitable interactions between qubits. We introduce a band-selective shaped pulse, refocusing BURP (REBURP) pulse, to cope with the problems. The electron spin of nitrogen-vacancy centers in diamond is flipped with high fidelity by the REBURP pulse. In contrast with traditional rectangular pulses, the shaped pulse has almost equal excitation effect in a sharply edged region (in frequency domain). So the three sublevels of host {sup 14}N nuclear spin can be flipped accurately simultaneously, while unwanted excitations of other sublevelsmore » (e.g., of a nearby {sup 13}C nuclear spin) is well suppressed. Our scheme can be used for various applications such as quantum metrology, quantum sensing, and quantum information process.« less

Determination of diffusion coefficients in polypyrrole thin films using a current pulse relaxation method

NASA Technical Reports Server (NTRS)

Penner, Reginald M.; Vandyke, Leon S.; Martin, Charles R.

1987-01-01

The current pulse E sub oc relaxation method and its application to the determination of diffusion coefficients in electrochemically synthesized polypyrrole thin films is described. Diffusion coefficients for such films in Et4NBF4 and MeCN are determined for a series of submicron film thicknesses. Measurement of the double-layer capacitance, C sub dl, and the resistance, R sub u, of polypyrrole thin films as a function of potential obtained with the galvanostatic pulse method is reported. Measurements of the electrolyte concentration in reduced polypyrrole films are also presented to aid in the interpretation of the data.

Damage effect and mechanism of the GaAs pseudomorphic high electron mobility transistor induced by the electromagnetic pulse

NASA Astrophysics Data System (ADS)

Xiao-Wen, Xi; Chang-Chun, Chai; Gang, Zhao; Yin-Tang, Yang; Xin-Hai, Yu; Yang, Liu

2016-04-01

The damage effect and mechanism of the electromagnetic pulse (EMP) on the GaAs pseudomorphic high electron mobility transistor (PHEMT) are investigated in this paper. By using the device simulation software, the distributions and variations of the electric field, the current density and the temperature are analyzed. The simulation results show that there are three physical effects, i.e., the forward-biased effect of the gate Schottky junction, the avalanche breakdown, and the thermal breakdown of the barrier layer, which influence the device current in the damage process. It is found that the damage position of the device changes with the amplitude of the step voltage pulse. The damage appears under the gate near the drain when the amplitude of the pulse is low, and it also occurs under the gate near the source when the amplitude is sufficiently high, which is consistent with the experimental results. Project supported by the National Basic Research Program of China (Grant No. 2014CB339900), and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (CAEP) (Grant No. 2015-0214.XY.K).

Investigations Of A Pulsed Cathodic Vacuum Arc

NASA Astrophysics Data System (ADS)

Oates, T. W. H.; Pigott, J.; Denniss, P.; Mckenzie, D. R.; Bilek, M. M. M.

2003-06-01

Cathodic vacuum arcs are well established as a method for producing thin films for coatings and as a source of metal ions. Research into DC vacuum arcs has been going on for over ten years in the School of Physics at the University of Sydney. Recently a project was undertaken in the school to design and build a pulsed CVA for use in the investigation of plasma sheaths and plasma immersion ion implantation. Pulsed cathodic vacuum arcs generally have a higher current and plasma density and also provide a more stable and reproducible plasma density than their DC counterparts. Additionally it has been shown that if a high repetition frequency can be established the deposition rate of pulsed arcs is equal to or greater than that of DC arcs with a concomitant reduction in the rate of macro-particle formation. We present here results of our investigations into the building of a center-triggered pulsed cathodic vacuum arc. The design of the power supply and trigger mechanism and the geometry of the anode and cathode are examined. Observations of type I and II arc spots using a CCD camera, and cathode spot velocity dependence on arc current will be presented. The role of retrograde motion in a high current pulsed arc is discussed.

High single-spatial-mode pulsed power from 980 nm emitting diode lasers

NASA Astrophysics Data System (ADS)

Hempel, Martin; Tomm, Jens W.; Elsaesser, Thomas; Bettiati, Mauro

2012-11-01

Single-spatial-mode pulsed powers as high as 13 W and 20 W in 150 and 50 ns pulses, respectively, are reported for 980 nm emitting lasers. In terms of energy, single-spatial-mode values of up to 2 μJ within 150 ns pulses are shown. In this high-power pulsed operation, the devices shield themselves from facet degradation, being the main degradation source in continuous wave (cw) operation. Our results pave the way towards additional applications while employing available standard devices, which have originally been designed as very reliable cw fiber pumps.

Characteristics of Extra Narrow Gap Weld of HSLA Steel Welded by Single-Seam per Layer Pulse Current GMA Weld Deposition

NASA Astrophysics Data System (ADS)

Agrawal, B. P.; Ghosh, P. K.

2017-03-01

Butt weld joints are produced using pulse current gas metal arc welding process by employing the technique of centrally laid multi-pass single-seam per layer weld deposition in extra narrow groove of thick HSLA steel plates. The weld joints are prepared by using different combination of pulse parameters. The selection of parameter of pulse current gas metal arc welding is done considering a summarized influence of simultaneously interacting pulse parameters defined by a dimensionless hypothetical factor ϕ. The effect of diverse pulse parameters on the characteristics of weld has been studied. Weld joint is also prepared by using commonly used multi-pass multi-seam per layer weld deposition in conventional groove. The extra narrow gap weld joints have been found much superior to the weld joint prepared by multi-pass multi-seam per layer deposition in conventional groove with respect to its metallurgical characteristics and mechanical properties.

A high dynamic range pulse counting detection system for mass spectrometry.

PubMed

Collings, Bruce A; Dima, Martian D; Ivosev, Gordana; Zhong, Feng

2014-01-30

A high dynamic range pulse counting system has been developed that demonstrates an ability to operate at up to 2e8 counts per second (cps) on a triple quadrupole mass spectrometer. Previous pulse counting detection systems have typically been limited to about 1e7 cps at the upper end of the systems dynamic range. Modifications to the detection electronics and dead time correction algorithm are described in this paper. A high gain transimpedance amplifier is employed that allows a multi-channel electron multiplier to be operated at a significantly lower bias potential than in previous pulse counting systems. The system utilises a high-energy conversion dynode, a multi-channel electron multiplier, a high gain transimpedance amplifier, non-paralysing detection electronics and a modified dead time correction algorithm. Modification of the dead time correction algorithm is necessary due to a characteristic of the pulse counting electronics. A pulse counting detection system with the capability to count at ion arrival rates of up to 2e8 cps is described. This is shown to provide a linear dynamic range of nearly five orders of magnitude for a sample of aprazolam with concentrations ranging from 0.0006970 ng/mL to 3333 ng/mL while monitoring the m/z 309.1 → m/z 205.2 transition. This represents an upward extension of the detector's linear dynamic range of about two orders of magnitude. A new high dynamic range pulse counting system has been developed demonstrating the ability to operate at up to 2e8 cps on a triple quadrupole mass spectrometer. This provides an upward extension of the detector's linear dynamic range by about two orders of magnitude over previous pulse counting systems. Copyright © 2013 John Wiley & Sons, Ltd.

Laser High-Cycle Thermal Fatigue of Pulse Detonation Engine Combustor Materials Tested

NASA Technical Reports Server (NTRS)

Zhu, Dong-Ming; Fox, Dennis S.; Miller, Robert A.

2001-01-01

Pulse detonation engines (PDE's) have received increasing attention for future aerospace propulsion applications. Because the PDE is designed for a high-frequency, intermittent detonation combustion process, extremely high gas temperatures and pressures can be realized under the nearly constant-volume combustion environment. The PDE's can potentially achieve higher thermodynamic cycle efficiency and thrust density in comparison to traditional constant-pressure combustion gas turbine engines (ref. 1). However, the development of these engines requires robust design of the engine components that must endure harsh detonation environments. In particular, the detonation combustor chamber, which is designed to sustain and confine the detonation combustion process, will experience high pressure and temperature pulses with very short durations (refs. 2 and 3). Therefore, it is of great importance to evaluate PDE combustor materials and components under simulated engine temperatures and stress conditions in the laboratory. In this study, a high-cycle thermal fatigue test rig was established at the NASA Glenn Research Center using a 1.5-kW CO2 laser. The high-power laser, operating in the pulsed mode, can be controlled at various pulse energy levels and waveform distributions. The enhanced laser pulses can be used to mimic the time-dependent temperature and pressure waves encountered in a pulsed detonation engine. Under the enhanced laser pulse condition, a maximum 7.5-kW peak power with a duration of approximately 0.1 to 0.2 msec (a spike) can be achieved, followed by a plateau region that has about one-fifth of the maximum power level with several milliseconds duration. The laser thermal fatigue rig has also been developed to adopt flat and rotating tubular specimen configurations for the simulated engine tests. More sophisticated laser optic systems can be used to simulate the spatial distributions of the temperature and shock waves in the engine. Pulse laser high

Oxidized nanocrystalline Fe-Cu pseudoalloy subjected to high pressure and electrodischarge pulses: Mössbauer and x-ray investigations

NASA Astrophysics Data System (ADS)

Gavriliuk, A. G.; Voitkovsky, V. S.; Sidorov, V. A.; Filonenko, V. P.; Tsiok, O. B.; Khvostantsev, L. G.

1998-05-01

Nanocrystalline Fe15Cu85 pseudoalloy has been subjected to pulsed heating up to 1500 K at high pressure (8 GPa). Two regimes were studied: the direct heating using electrodischarge through the sample and indirect heating with the use of cylindrical heater around the sample. The temperature and time conditions in both types of experiments were adjusted to be equivalent. The discharge parameters (stored energy, discharge time, and magnitude of current pulse) were sufficient to move defects by conduction electrons, but insufficient to melt the sample. The properties of treated samples were studied using Mössbauer absorption spectra and x-ray diffraction for three types of samples: (a) primary powder treated by high pressure up to 8 GPa, (b) powder subjected to indirect pulsed heating at 8 GPa, (c) powder treated by electrical pulses at 8 GPa. The x-ray diffraction pattern of primary powder exhibits peaks of copper, iron, and copper oxide (CuO). The Mössbauer spectrum of primary powder exhibits six peaks of alpha iron and some peaks near zero velocity due to the small iron clusters in the copper matrix and ultrafine clusters of paramagnetic phase x-Fe2O3. The transformation of CuO to Cu2O takes place in the course of indirect heating, the Mössbauer spectrum being almost unchanged. The direct electrodischarge heating causes the appearance of new magnetic phase with the magnetic field on iron nucleus 505 kOe, which corresponds to α-Fe2O3. The formation of α-Fe2O3 was confirmed by x-ray diffraction. At the same time the transformation of CuO to Cu2O is incomplete. These experiments demonstrate that high density current pulses, causing the electron wind, can be a useful tool to influence the structure of nanocrystalline powder.

Optimization of Experimental Conditions of the Pulsed Current GTAW Parameters for Mechanical Properties of SDSS UNS S32760 Welds Based on the Taguchi Design Method

NASA Astrophysics Data System (ADS)

Yousefieh, M.; Shamanian, M.; Saatchi, A.

2012-09-01

Taguchi design method with L9 orthogonal array was implemented to optimize the pulsed current gas tungsten arc welding parameters for the hardness and the toughness of super duplex stainless steel (SDSS, UNS S32760) welds. In this regard, the hardness and the toughness were considered as performance characteristics. Pulse current, background current, % on time, and pulse frequency were chosen as main parameters. Each parameter was varied at three different levels. As a result of pooled analysis of variance, the pulse current is found to be the most significant factor for both the hardness and the toughness of SDSS welds by percentage contribution of 71.81 for hardness and 78.18 for toughness. The % on time (21.99%) and the background current (17.81%) had also the next most significant effect on the hardness and the toughness, respectively. The optimum conditions within the selected parameter values for hardness were found as the first level of pulse current (100 A), third level of background current (70 A), first level of % on time (40%), and first level of pulse frequency (1 Hz), while they were found as the second level of pulse current (120 A), second level of background current (60 A), second level of % on time (60%), and third level of pulse frequency (5 Hz) for toughness. The Taguchi method was found to be a promising tool to obtain the optimum conditions for such studies. Finally, in order to verify experimental results, confirmation tests were carried out at optimum working conditions. Under these conditions, there were good agreements between the predicted and the experimental results for the both hardness and toughness.

A high voltage pulse generator based on silicon-controlled rectifier for field-reversed configuration experiment.

PubMed

Lin, Munan; Liu, Ming; Zhu, Guanghui; Wang, Yanpeng; Shi, Peiyun; Sun, Xuan

2017-08-01

A high voltage pulse generator based on a silicon-controlled rectifier has been designed and implemented for a field reversed configuration experiment. A critical damping circuit is used in the generator to produce the desired pulse waveform. Depending on the load, the rise time of the output trigger signal can be less than 1 μs, and the peak amplitudes of trigger voltage and current are up to 8 kV and 85 A in a single output. The output voltage can be easily adjusted by changing the voltage on a capacitor of the generator. In addition, the generator integrates an electrically floating heater circuit so it is capable of triggering either pseudosparks (TDI-type hydrogen thyratron) or ignitrons. Details of the circuits and their implementation are described in the paper. The trigger generator has successfully controlled the discharging sequence of the pulsed power supply for a field reversed configuration experiment.

A high voltage pulse generator based on silicon-controlled rectifier for field-reversed configuration experiment

NASA Astrophysics Data System (ADS)

Lin, Munan; Liu, Ming; Zhu, Guanghui; Wang, Yanpeng; Shi, Peiyun; Sun, Xuan

2017-08-01

A high voltage pulse generator based on a silicon-controlled rectifier has been designed and implemented for a field reversed configuration experiment. A critical damping circuit is used in the generator to produce the desired pulse waveform. Depending on the load, the rise time of the output trigger signal can be less than 1 μs, and the peak amplitudes of trigger voltage and current are up to 8 kV and 85 A in a single output. The output voltage can be easily adjusted by changing the voltage on a capacitor of the generator. In addition, the generator integrates an electrically floating heater circuit so it is capable of triggering either pseudosparks (TDI-type hydrogen thyratron) or ignitrons. Details of the circuits and their implementation are described in the paper. The trigger generator has successfully controlled the discharging sequence of the pulsed power supply for a field reversed configuration experiment.

Energy-Saving Sintering of Electrically Conductive Powders by Modified Pulsed Electric Current Heating Using an Electrically Nonconductive Die

NASA Astrophysics Data System (ADS)

Ito, Mikio; Kawahara, Kenta; Araki, Keita

2014-04-01

Sintering of Cu and thermoelectric Ca3Co4O9 was tried using a modified pulsed electric current sintering (PECS) process, where an electrically nonconductive die was used instead of a conventional graphite die. The pulsed electric current flowed through graphite punches and sample powder, which caused the Joule heating of the powder compact itself, resulting in sintering under smaller power consumption. Especially for the Ca3Co4O9 powder, densification during sintering was also accelerated by this modified PECS process.

Characterization of an electrochemical mercury sensor using alternating current, cyclic, square wave and differential pulse voltammetry.

PubMed

Guerreiro, Gabriela V; Zaitouna, Anita J; Lai, Rebecca Y

2014-01-31

Here we report the characterization of an electrochemical mercury (Hg(2+)) sensor constructed with a methylene blue (MB)-modified and thymine-containing linear DNA probe. Similar to the linear probe electrochemical DNA sensor, the resultant sensor behaved as a "signal-off" sensor in alternating current voltammetry and cyclic voltammetry. However, depending on the applied frequency or pulse width, the sensor can behave as either a "signal-off" or "signal-on" sensor in square wave voltammetry (SWV) and differential pulse voltammetry (DPV). In SWV, the sensor showed "signal-on" behavior at low frequencies and "signal-off" behavior at high frequencies. In DPV, the sensor showed "signal-off" behavior at short pulse widths and "signal-on" behavior at long pulse widths. Independent of the sensor interrogation technique, the limit of detection was found to be 10nM, with a linear dynamic range between 10nM and 500nM. In addition, the sensor responded to Hg(2+) rather rapidly; majority of the signal change occurred in <20min. Overall, the sensor retains all the characteristics of this class of sensors; it is reagentless, reusable, sensitive, specific and selective. This study also highlights the feasibility of using a MB-modified probe for real-time sensing of Hg(2+), which has not been previously reported. More importantly, the observed "switching" behavior in SWV and DPV is potentially generalizable and should be applicable to most sensors in this class of dynamics-based electrochemical biosensors. Copyright © 2013 Elsevier B.V. All rights reserved.

High-current fast electron beam propagation in a dielectric target.

PubMed

Klimo, Ondrej; Tikhonchuk, V T; Debayle, A

2007-01-01

Recent experiments demonstrate an efficient transformation of high intensity laser pulse into a relativistic electron beam with a very high current density exceeding 10(12) A cm(-2). The propagation of such a beam inside the target is possible if its current is neutralized. This phenomenon is not well understood, especially in dielectric targets. In this paper, we study the propagation of high current density electron beam in a plastic target using a particle-in-cell simulation code. The code includes both ionization of the plastic and collisions of newborn electrons. The numerical results are compared with a relatively simple analytical model and a reasonable agreement is found. The temporal evolution of the beam velocity distribution, the spatial density profile, and the propagation velocity of the ionization front are analyzed and their dependencies on the beam density and energy are discussed. The beam energy losses are mainly due to the target ionization induced by the self-generated electric field and the return current. For the highest beam density, a two-stream instability is observed to develop in the plasma behind the ionization front and it contributes to the beam energy losses.

High-energy, high-repetition-rate picosecond pulses from a quasi-CW diode-pumped Nd:YAG system.

PubMed

Noom, Daniel W E; Witte, Stefan; Morgenweg, Jonas; Altmann, Robert K; Eikema, Kjeld S E

2013-08-15

We report on a high-power quasi-CW pumped Nd:YAG laser system, producing 130 mJ, 64 ps pulses at 1064 nm wavelength with a repetition rate of 300 Hz. Pulses from a Nd:YVO(4) oscillator are first amplified by a regenerative amplifier to the millijoule level and then further amplified in quasi-CW diode-pumped Nd:YAG modules. Pulsed diode pumping enables a high gain at repetition rates of several hundred hertz, while keeping thermal effects manageable. Birefringence compensation and multiple thermal-lensing-compensated relay-imaging stages are used to maintain a top-hat beam profile. After frequency doubling, 75 mJ pulses are obtained at 532 nm. The intensity stability is better than 1.1%, which makes this laser an attractive pump source for a high-repetition-rate optical parametric amplification system.

Pulsed x-ray imaging of high-density objects using a ten picosecond high-intensity laser driver

NASA Astrophysics Data System (ADS)

Rusby, D. R.; Brenner, C. M.; Armstrong, C.; Wilson, L. A.; Clarke, R.; Alejo, A.; Ahmed, H.; Butler, N. M. H.; Haddock, D.; Higginson, A.; McClymont, A.; Mirfayzi, S. R.; Murphy, C.; Notley, M.; Oliver, P.; Allott, R.; Hernandez-Gomez, C.; Kar, S.; McKenna, P.; Neely, D.

2016-10-01

Point-like sources of X-rays that are pulsed (sub nanosecond), high energy (up to several MeV) and bright are very promising for industrial and security applications where imaging through large and dense objects is required. Highly penetrating X-rays can be produced by electrons that have been accelerated by a high intensity laser pulse incident onto a thin solid target. We have used a pulse length of 10ps to accelerate electrons to create a bright x-ray source. The bremsstrahlung temperature was measured for a laser intensity from 8.5-12×1018 W/cm2. These x-rays have sequentially been used to image high density materials using image plate and a pixelated scintillator system.

High-power, high-brightness pseudospark-produced electron beam driven by improved pulse line accelerator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Junbino Zhu; Mingchang Wang; Zhijiang Wang

1995-12-31

A high power (200KV), intense current density, low emittance (71mmmrad), high brightness (8x10{sup 10}A/m rad) electron beam was generated in the 10cm long, high-voltage-resistive multi-gap hollow cathode pseudospark chamber filled with 15pa nitrogen and driven by an improved pulse line accelerator. The beam was ejected with the 1mm diameter, the 2.2KA beam current, and the 400ns pulse length, and could propagated 20cm in the drift tube. At a distance of 5cm from the anode it penetrated consecutively an acid-sensitive discoloring film and a 0.05mm-thick copper foil both stuck closely, left 0.6mm and 0.3mm holes on them, respectively. That 10 shotsmore » on an acid-sensitive film produced a hole of 1.6mm at 7cm downstream of anode showed its good repeatability. After 60 shots the pseudospark discharge chamber was disassembled and observed that almost no destructive damage traces left on the surfaces of its various electrodes and insulators. But on almost all the surfaces of changeable central hole parts installed on intermediate electrodes there are traces of electron emission from the sides facing the anode and of bombardment on the sides facing the cathode, in contrast with which on the front- and back-surfaces of hollow cathode no visible traces of electron emission from then was observed. In addition, there were different tints, strip-like regions on the side of anode facing the cathode. Another interesting phenomenon was that there were a set of concentric circular or elliptical ring pattern on the acid-sensitive discoloring film got at 5cm from the anode and observed tinder a metallograph. It seems that the pseudospark electron beam is Laminar beam i.e, being possessed of a multi-layer structure, at least in the case of multi-gap pseudospark discharge chamber. It was found experimentally that the quality of pseudospark electron beam is much better than that of the cold-cathode electron beam.« less

The high-speed after-pulse measurement system for PMT

NASA Astrophysics Data System (ADS)

Cheng, Y.; Qian, S.; Ning, Z.; Xia, J.; Wang, Z.

2018-05-01

A system employing a desktop FADC has been developed to investigate the features of 8-inch Hamamatsu PMT R5912. The system stands out for its high-speed and informative results as a consequence of adopting fast waveform sampling technology. Recording the full waveforms allows us to perform pulse shape analysis. High-precision after-pulse time and charge distribution results are presented in this manuscript. Other characteristics of the photomultiplier tube, such as the gain of charge, dark rate and transit time spread, can be also obtained by this system.

Half radiofrequency pulse excitation with a dedicated prescan to correct eddy current effect and gradient delay.

PubMed

Abe, Takayuki

2013-03-01

To improve the slice profile of the half radiofrequency (RF) pulse excitation and image quality of ultrashort echo time (UTE) imaging by compensating for an eddy current effect. The dedicated prescan has been developed to measure the phase accumulation due to eddy currents induced by the slice-selective gradient. The prescan measures two one-dimensional excitation k-space profiles, which can be acquired with a readout gradient in the slice-selection direction by changing the polarity of the slice-selective gradient. The time shifts due to the phase accumulation in the excitation k-space were calculated. The time shift compensated for the start time of the slice-selective gradient. The total prescan time was 6-15 s. The slice profile and the UTE image with the half RF pulse excitation were acquired to evaluate the slice selectivity and the image quality. Improved slice selectivity was obtained. The simple method proposed in this paper can eliminate eddy current effect. Good UTE images were obtained. The slice profile of the half RF pulse excitation and the image quality of UTE images have been improved by using a dedicated prescan. This method has a possibility that can improve the image quality of a clinical UTE imaging.

Heavy-Ion Injector for the High Current Experiment

NASA Astrophysics Data System (ADS)

Bieniosek, F. M.; Henestroza, E.; Kwan, J. W.; Prost, L.; Seidl, P.

2001-10-01

We report on progress in development of the Heavy-Ion Injector at LBNL, which is being prepared for use as an injector for the High Current Experiment (HCX). It is composed of a 10-cm-diameter surface ionization source, an extraction diode, and an electrostatic quadrupole (ESQ) accelerator, with a typical operating current of 0.6 A of potassium ions at 1.8 MeV, and a beam pulse length of 4.5 microsecs. We have improved the Injector equipment and diagnostics, and have characterized the source emission and radial beam profiles at the diode and ESQ regions. We find improved agreement with EGUN predictions, and improved compatibility with the downstream matching section. Plans are to attach the matching section and the initial ESQ transport section of HCX. Results will be presented and compared with EGUN and WARP simulations.

Pulsed high-energy gamma rays from PSR 1055-52

NASA Technical Reports Server (NTRS)

Fierro, J. M.; Bertsch, D. L.; Brazier, K. T.; Chiang, J.; D'Amico, N.; Fichtel, C. E.; Hartman, R. C.; Hunter, S. D.; Johnston, S.; Kanbach, G.

1993-01-01

The Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory has detected a high-energy gamma-ray source at a position coincident with that of the radio pulsar PSR 1055-52. Analysis of the EGRET data at the radio pulsar period of 197 ms has revealed pulsed gamma-radiation at energies above 300 MeV, making PSR 1055-52 the fifth detected high-energy gamma-ray pulsar. The pulsed radiation from PSR 1055-52 has a very hard photon spectral index of -1.18 +/- 0.16 and a high efficiency for converting its rotational energy into gamma-rays. No unpulsed emission was observed.

Depinning of the transverse domain wall trapped at magnetic impurities patterned in planar nanowires: Control of the wall motion using low-intensity and short-duration current pulses

NASA Astrophysics Data System (ADS)

Paixão, E. L. M.; Toscano, D.; Gomes, J. C. S.; Monteiro, M. G.; Sato, F.; Leonel, S. A.; Coura, P. Z.

2018-04-01

Understanding and controlling of domain wall motion in magnetic nanowires is extremely important for the development and production of many spintronic devices. It is well known that notches are able to pin domain walls, but their pinning potential strength are too strong and it demands high-intensity current pulses to achieve wall depinning in magnetic nanowires. However, traps of pinning can be also originated from magnetic impurities, consisting of located variations of the nanowire's magnetic properties, such as exchange stiffness constant, saturation magnetization, anisotropy constant, damping parameter, and so on. In this work, we have performed micromagnetic simulations to investigate the depinning mechanism of a transverse domain wall (TDW) trapped at an artificial magnetic defect using spin-polarized current pulses. In order to create pinning traps, a simplified magnetic impurity model, only based on a local reduction of the exchange stiffness constant, have been considered. In order to provide a background for experimental studies, we have varied the parameter related to the pinning potential strength of the magnetic impurity. By adjusting the pinning potential of magnetic impurities and choosing simultaneously a suitable current pulse, we have found that it is possible to obtain domain wall depinning by applying low-intensity and short-duration current pulses. Furthermore, it was considered a planar magnetic nanowire containing a linear distribution of equally-spaced magnetic impurities and we have demonstrated the position control of a single TDW by applying sequential current pulses; that means the wall movement from an impurity to another.

Lead paint removal with high-intensity light pulses.

PubMed

Grapperhaus, Michael J; Schaefer, Raymond B

2006-12-15

This paper presents the results of an initial investigation into using high-intensity incoherent light pulses to strip paint. Measurements of light pulse characteristics, the reflectivity of different paints and initial experiments on the threshold for paint removal, and paint removal are presented, along with an approximate model consistent with experimental results. Paint removal tests include lead paint, the reduction of lead levels to below levels required for lead abatement, as well as air and light emissions measurements that are within regulatory guidelines.

Self-channeling of high-power laser pulses through strong atmospheric turbulence

NASA Astrophysics Data System (ADS)

Peñano, J.; Palastro, J. P.; Hafizi, B.; Helle, M. H.; DiComo, G. P.

2017-07-01

We present an unusual example of truly long-range propagation of high-power laser pulses through strong atmospheric turbulence. A form of nonlinear self-channeling is achieved when the laser power is close to the self-focusing power of air and the transverse dimensions of the pulse are smaller than the coherence diameter of turbulence. In this mode, nonlinear self-focusing counteracts diffraction, and turbulence-induced spreading is greatly reduced. Furthermore, the laser intensity is below the ionization threshold so that multiphoton absorption and plasma defocusing are avoided. Simulations show that the pulse can propagate many Rayleigh lengths (several kilometers) while maintaining a high intensity. In the presence of aerosols, or other extinction mechanisms that deplete laser energy, the pulse can be chirped to maintain the channeling.

Temporally Shaped Current Pulses on a Two-Cavity Linear Transformer Driver System

DTIC Science & Technology

2011-06-01

essentially at a fraction of the total switch voltage. Non-uniform corona current characteristics of the different corona needles could cause imperfect...withstand twice the capacitor voltage. A pulse applied to the switch trigger electrodes initiate closure of each switch. We have arranged triggering in...internal cavity potential to ground, allows the trigger electrode of the spark gaps to be at ground potential during charging, and eliminates a

Pulsed power accelerator for material physics experiments

DOE PAGES

Reisman, D.  B.; Stoltzfus, B.  S.; Stygar, W.  A.; ...

2015-09-01

We have developed the design of Thor: a pulsed power accelerator that delivers a precisely shaped current pulse with a peak value as high as 7 MA to a strip-line load. The peak magnetic pressure achieved within a 1-cm-wide load is as high as 100 GPa. Thor is powered by as many as 288 decoupled and transit-time isolated bricks. Each brick consists of a single switch and two capacitors connected electrically in series. The bricks can be individually triggered to achieve a high degree of current pulse tailoring. Because the accelerator is impedance matched throughout, capacitor energy is delivered tomore » the strip-line load with an efficiency as high as 50%. We used an iterative finite element method (FEM), circuit, and magnetohydrodynamic simulations to develop an optimized accelerator design. When powered by 96 bricks, Thor delivers as much as 4.1 MA to a load, and achieves peak magnetic pressures as high as 65 GPa. When powered by 288 bricks, Thor delivers as much as 6.9 MA to a load, and achieves magnetic pressures as high as 170 GPa. We have developed an algebraic calculational procedure that uses the single brick basis function to determine the brick-triggering sequence necessary to generate a highly tailored current pulse time history for shockless loading of samples. Thor will drive a wide variety of magnetically driven shockless ramp compression, shockless flyer plate, shock-ramp, equation of state, material strength, phase transition, and other advanced material physics experiments.« less

High Power Particle Beams and Pulsed Power for Industrial Applications

NASA Astrophysics Data System (ADS)

Bluhm, Hansjoachim; An, Wladimir; Engelko, Wladimir; Giese, Harald; Frey, Wolfgang; Heinzel, Annette; Hoppé, Peter; Mueller, Georg; Schultheiss, Christoph; Singer, Josef; Strässner, Ralf; Strauß, Dirk; Weisenburger, Alfons; Zimmermann, Fritz

2002-12-01

Several industrial scale projects with economic and ecologic potential are presently emanating from research and development in the fields of high power particle beams and pulsed power in Europe. Material surface modifications with large area pulsed electron beams are used to protect high temperature gas turbine blades and steel structures in Pb/Bi cooled accelerator driven nuclear reactor systems against oxidation and corrosion respectively. Channel spark electron beams are applied to deposit bio-compatible or bio-active layers on medical implants. Cell membranes are perforated with strong pulsed electric fields to extract nutritive substances or raw materials from the cells and to kill bacteria for sterilization of liquids. Eletrodynamic fragmentation devices are developed to reutilize concrete aggregates for the production of high quality secondary concrete. All activities have a large potential to contribute to a more sustainable economy.

Energy dissipation of composite multifilamentary superconductors for high-current ramp-field magnet applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gung, C.Y.

1993-01-01

Energy dissipation, which is also called AC loss, of a composite multifilamentary superconducting wire is one of the most fundamental concerns in building a stable superconducting magnet. Characterization and reduction of AC losses are especially important in designing a superconducting magnet for generating transient magnetic fields. The goal of this thesis is to improve the understanding of AC-loss properties of superconducting wires developed for high-current ramp-field magnet applications. The major tasks include: (1) building an advanced AC-loss measurement system, (2) measuring AC losses of superconducting wires under simulated pulse magnet operations, (3) developing an analytical model for explaining the newmore » AC-loss properties found in the experiment, and (4) developing a computational methodology for comparing AC losses of a superconducting wire with those of a cable for a superconducting pulse magnet. A new experimental system using an isothermal calorimetric method was designed and constructed to measure the absolute AC losses in a composite superconductor. This unique experimental setup is capable of measuring AC losses of a brittle Nb{sub 3}Sn wire carrying high AC current in-phase with a large-amplitude pulse magnetic field. Improvements of the accuracy and the efficiency of this method are discussed. Three different types of composite wire have been measured: a Nb{sub 3}Sn modified jelly-roll (MJR) internal-tin wire used in a prototype ohmic heating coil, a Nb{sub 3}Sn internal-tin wire developed for a fusion reactor ohmic heating coil, and a NbTi wire developed for the magnets in a particle accelerator. The cross sectional constructions of these wires represent typical commercial wires manufactured for pulse magnet applications.« less

Investigation of a pulsed current annealing method in reusing MOSFET dosimeters for in vivo IMRT dosimetry.

PubMed

Luo, Guang-Wen; Qi, Zhen-Yu; Deng, Xiao-Wu; Rosenfeld, Anatoly

2014-05-01

To explore the feasibility of pulsed current annealing in reusing metal oxide semiconductor field-effect transistor (MOSFET) dosimeters for in vivo intensity modulated radiation therapy (IMRT) dosimetry. Several MOSFETs were irradiated at d(max) using a 6 MV x-ray beam with 5 V on the gate and annealed with zero bias at room temperature. The percentage recovery of threshold voltage shift during multiple irradiation-annealing cycles was evaluated. Key dosimetry characteristics of the annealed MOSFET such as the dosimeter's sensitivity, reproducibility, dose linearity, and linearity of response within the dynamic range were investigated. The initial results of using the annealed MOSFETs for IMRT dosimetry practice were also presented. More than 95% of threshold voltage shift can be recovered after 24-pulse current continuous annealing in 16 min. The mean sensitivity degradation was found to be 1.28%, ranging from 1.17% to 1.52%, during multiple annealing procedures. Other important characteristics of the annealed MOSFET remained nearly consistent before and after annealing. Our results showed there was no statistically significant difference between the annealed MOSFETs and their control samples in absolute dose measurements for IMRT QA (p = 0.99). The MOSFET measurements agreed with the ion chamber results on an average of 0.16% ± 0.64%. Pulsed current annealing provides a practical option for reusing MOSFETs to extend their operational lifetime. The current annealing circuit can be integrated into the reader, making the annealing procedure fully automatic.

5.8kV SiC PiN Diode for Switching of High-Efficiency Inductive Pulsed Plasma Thruster Circuits

NASA Technical Reports Server (NTRS)

Toftul, Alexandra; Polzin, Kurt A.; Hudgins, Jerry L.

2014-01-01

Inductive Pulsed Plasma Thruster (IPPT) pulse circuits, such as those needed to operate the Pulsed Inductive Thruster (PIT), are required to quickly switch capacitor banks operating at a period of µs while conducting current at levels on the order of at least 10 kA. [1,2] For all iterations of the PIT to date, spark gaps have been used to discharge the capacitor bank through an inductive coil. Recent availability of fast, high-power solid state switching devices makes it possible to consider the use of semiconductor switches in modern IPPTs. In addition, novel pre-ionization schemes have led to a reduction in discharge energy per pulse for electric thrusters of this type, relaxing the switching requirements for these thrusters. [3,4] Solid state switches offer the advantage of greater controllability and reliability, as well as decreased drive circuit dimensions and mass relative to spark gap switches. The use of solid state devices such as Integrated Gate Bipolar Transistors (IGBTs), Gate Turn-off Thyristors (GTOs) and Silicon-Controlled Rectifiers (SCRs) often involves the use of power diodes. These semiconductor devices may be connected antiparallel to the switch for protection from reverse current, or used to reduce power loss in a circuit by clamping off current ringing. In each case, higher circuit efficiency may be achieved by using a diode that is able to transition, or 'switch,' from the forward conducting state ('on' state) to the reverse blocking state ('off' state) in the shortest amount of time, thereby minimizing current ringing and switching losses. Silicon Carbide (SiC) PiN diodes offer significant advantages to conventional fast-switching Silicon (Si) diodes for high power and fast switching applications. A wider band gap results in a breakdown voltage 10 times that of Si, so that a SiC device may have a thinner drift region for a given blocking voltage. [5] This leads to smaller, lighter devices for high voltage applications, as well as reduced

High Pulse Repetition Rate, Eye Safe, Visible Wavelength Lidar Systems: Design, Results and Potential

NASA Technical Reports Server (NTRS)

Spinhirne, James; Berkoff, Timothy; Welton, Elsworth; Campbell, James; OCStarr, David (Technical Monitor)

2002-01-01

In 1993 the first of the eye safe visible wavelength lidar systems known now as Micro Pulse Lidar (MPL) became operational. Since that time there have been several dozen of these systems produced and applied for full time profiling of atmospheric cloud and aerosol structure. There is currently an observational network of MPL sites to support global climate research. In the course of application of these instruments there have been significant improvements in understanding, design and performance of the systems. There are addition potential and applications beyond current practice for the high repetition rate, eye safe designs. The MPL network and the current capability, design and future potential of MPL systems are described.

The R&D progress of 4 MW EAST-NBI high current ion source.

PubMed

Xie, Yahong; Hu, Chundong; Liu, Sheng; Xu, Yongjian; Liang, Lizhen; Xie, Yuanlai; Sheng, Peng; Jiang, Caichao; Liu, Zhimin

2014-02-01

A high current ion source, which consists of the multi-cusp bucket plasma generator and tetrode accelerator with multi-slot apertures, is developed and tested for the Experimental Advanced Superconducting Tokamak neutral beam injector. Three ion sources are tested on the test bed with arc power of 80 kW, beam voltage of 80 keV, and beam power of 4 MW. The arc regulation technology with Langmuir probes is employed for the long pulse operation of ion source, and the long pulse beam of 50 keV @ 15.5 A @ 100 s and 80 keV @ 52A @ 1s are extracted, respectively.

Vacuum Outgassing Behavior of Carbon Nanotube Cathode with High-Intensity Pulsed Electron Emission

NASA Astrophysics Data System (ADS)

Shen, Yi; Zhang, Huang; Xia, Liansheng; Liu, Xingguang; Pan, Haifeng; Lv, Lu; Yang, Anmin; Shi, Jinshui; Zhang, Linwen; Deng, Jianjun

2015-02-01

Experimental investigations on the vacuum outgassing of a carbon nanotube (CNT) cathode with high-intensity pulsed electron emission on a 2 MeV linear induction accelerator injector are presented. Under the 1.60 MV diode voltage, the CNT cathode could provide 1.67 kA electron beam with the amount of outgassing of about 0.51 Pa·L. It is found that the amount of outgassing, which determines the cathode emission current, depends on the diode voltage and the vacuum.

Monolithic polarization maintaining fiber chirped pulse amplification (CPA) system for high energy femtosecond pulse generation at 1.03 µm.

PubMed

Kim, Kyungbum; Peng, Xiang; Lee, Wangkuen; Gee, Sangyoun; Mielke, Michael; Luo, Tao; Pan, Lei; Wang, Qing; Jiang, Shibin

2015-02-23

A monolithic polarization maintaining fiber chirped pulse amplification system with 25 cm Yb(3+)-doped high efficiency media fiber that generates 62 µJ sub-400 fs pulses with 25 W at 1.03 µm has recently been demonstrated.

1W frequency-doubled VCSEL-pumped blue laser with high pulse energy

NASA Astrophysics Data System (ADS)

Van Leeuwen, Robert; Chen, Tong; Watkins, Laurence; Xu, Guoyang; Seurin, Jean-Francois; Wang, Qing; Zhou, Delai; Ghosh, Chuni

2015-02-01

We report on a Q-switched VCSEL side-pumped 946 nm Nd:YAG laser that produces high average power blue light with high pulse energy after frequency doubling in BBO. The gain medium was water cooled and symmetrically pumped by three 1 kW 808 nm VCSEL pump modules. More than 1 W blue output was achieved at 210 Hz with 4.9 mJ pulse energy and at 340 Hz with 3.2 mJ pulse energy, with 42% and 36% second harmonic conversion efficiency respectively. Higher pulse energy was obtained at lower repetition frequencies, up to 9.3 mJ at 70 Hz with 52% conversion efficiency.

Pulsed laser illumination of photovoltaic cells

NASA Technical Reports Server (NTRS)

Yater, Jane A.; Lowe, Roland A.; Jenkins, Phillip P.; Landis, Geoffrey A.

1994-01-01

In future space missions, free electron lasers (FEL) may be used to illuminate photovoltaic array receivers to provide remote power. Both the radio-frequency (RF) and induction FEL provide FEL produce pulsed rather than continuous output. In this work we investigate cell response to pulsed laser light which simulates the RF FEL format. The results indicate that if the pulse repetition is high, cell efficiencies are only slightly reduced compared to constant illumination at the same wavelength. The frequency response of the cells is weak, with both voltage and current outputs essentially dc in nature. Comparison with previous experiments indicates that the RF FEL pulse format yields more efficient photovoltaic conversion than does an induction FEL pulse format.

Parametric Study of Pulse-Combustor-Driven Ejectors at High-Pressure

NASA Technical Reports Server (NTRS)

Yungster, Shaye; Paxson, Daniel E.; Perkins, Hugh D.

2015-01-01

Pulse-combustor configurations developed in recent studies have demonstrated performance levels at high-pressure operating conditions comparable to those observed at atmospheric conditions. However, problems related to the way fuel was being distributed within the pulse combustor were still limiting performance. In the first part of this study, new configurations are investigated computationally aimed at improving the fuel distribution and performance of the pulse-combustor. Subsequent sections investigate the performance of various pulse-combustor driven ejector configurations operating at highpressure conditions, focusing on the effects of fuel equivalence ratio and ejector throat area. The goal is to design pulse-combustor-ejector configurations that maximize pressure gain while achieving a thermal environment acceptable to a turbine, and at the same time maintain acceptable levels of NOx emissions and flow non-uniformities. The computations presented here have demonstrated pressure gains of up to 2.8%.

Development and fabrication of low ON resistance high current vertical VMOS power FETs

NASA Technical Reports Server (NTRS)

Kay, S.

1979-01-01

The design of a VMOS Power FET exhibiting low ON resistance, high current as well as high breakdown voltage and fast switching speeds is described. The design which is based on a 1st-order device model, features a novel polysilicon-gate structure and fieldplated groove termination to achieve high packing density and high breakdown voltage, respectively. One test chip, named VNTKI, can block 180 V at an ON resistence of 2.5 ohm. A 150 mil x 200 mil (.19 sq cm) experimental chip has demonstrated a breakdown voltage of 200v, an ON resistance of 0.12 ohm, a switching time of less than 100 ns, and a pulse drain - current of 50 A with 10 V gate drive.

Avoiding the side effects of electric current pulse application to electroporated cells in disposable small volume cuvettes assures good cell survival.

PubMed

Grys, Maciej; Madeja, Zbigniew; Korohoda, Włodzimierz

2017-01-01

The harmful side effects of electroporation to cells due to local changes in pH, the appearance of toxic electrode products, temperature increase, and the heterogeneity of the electric field acting on cells in the cuvettes used for electroporation were observed and discussed in several laboratories. If cells are subjected to weak electric fields for prolonged periods, for example in experiments on cell electrophoresis or galvanotaxis the same effects are seen. In these experiments investigators managed to reduce or eliminate the harmful side effects of electric current application. For the experiments, disposable 20 μl cuvettes with two walls made of dialysis membranes were constructed and placed in a locally focused electric field at a considerable distance from the electrodes. Cuvettes were mounted into an apparatus for horizontal electrophoresis and the cells were subjected to direct current electric field (dcEF) pulses from a commercial pulse generator of exponentially declining pulses and from a custom-made generator of double and single rectangular pulses. More than 80% of the electroporated cells survived the dcEF pulses in both systems. Side effects related to electrodes were eliminated in both the flow through the dcEF and in the disposable cuvettes placed in the focused dcEFs. With a disposable cuvette system, we also confirmed the sensitization of cells to a dcEF using procaine by observing the loading of AT2 cells with calceine and using a square pulse generator, applying 50 ms single rectangular pulses. We suggest that the same methods of avoiding the side effects of electric current pulse application as in cell electrophoresis and galvanotaxis should also be used for electroporation. This conclusion was confirmed in our electroporation experiments performed in conditions assuring survival of over 80% of the electroporated cells. If the amplitude, duration, and shape of the dcEF pulse are known, then electroporation does not depend on the type of

Generation of plasma X-ray sources via high repetition rate femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Baguckis, Artūras; Plukis, Artūras; Reklaitis, Jonas; Remeikis, Vidmantas; Giniūnas, Linas; Vengris, Mikas

2017-12-01

In this study, we present the development and characterization of Cu plasma X-ray source driven by 20 W average power high repetition rate femtosecond laser in ambient atmosphere environment. The peak Cu- Kα photon flux of 2.3 × 109 photons/s into full solid angle is demonstrated (with a process conversion efficiency of 10-7), using pulses with peak intensity of 4.65 × 1014 W/cm2. Such Cu- Kα flux is significantly larger than others found in comparable experiments, performed in air environment. The effects of resonance plasma absorption process, when optimized, are shown to increase measured flux by the factor of 2-3. The relationship between X-ray photon flux and plasma-driving pulse repetition rate is quasi-linear, suggesting that fluxes could further be increased to 1010 photons/s using even higher average powers of driving radiation. These results suggest that to fully utilize the potential of high repetition rate laser sources, novel target material delivery systems (for example, jet-based ones) are required. On the other hand, this study demonstrates that high energy lasers currently used for plasma X-ray sources can be conveniently and efficiently replaced by high average power and repetition rate laser radiation, as a way to increase the brightness of the generated X-rays.

Alternative Solder Bond Packaging Approach for High-Voltage (HV) Pulsed Power Devices

DTIC Science & Technology

2016-09-01

DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT The silicon carbide...the pulse evaluation circuit used to evaluate a SiC SGTO device under extreme pulsed current switching conditions. 15. SUBJECT TERMS silicon carbide...development effort. We would also like to thank Dr Sei-Hyung Ryu and Dr Jon Zhang of Cree, Inc., for providing the silicon carbide “super” gate-turn

High-average-power 2-kHz laser for generation of ultrashort x-ray pulses.

PubMed

Jiang, Yan; Lee, Taewoo; Li, Wei; Ketwaroo, Gyanprakash; Rose-Petruck, Christoph G

2002-06-01

We describe a Ti:sapphire-based laser-x-ray system specifically designed for generation of ultrafast x-ray pulses in the tenths-of-nanometers spectral range at a 2-kHz repetition rate. To obtain high-contrast laser pulses we divide the laser system into a section for generation of microjoule, high-contrast pulses with pulse cleaning and a subsequent section for chirped-pulse amplification and pulse compression. This laser section operates in conjunction with an x-ray-generation section based on a moving copper wire in a He atmosphere. The high reliability of the entire system permits maintenance-free production of x-ray pulses over tens of hours. Average x-ray fluxes of 10(13) photons/(s 4pi sr 1 keV) at 3 keV and 10(9) photons/(s 4pi sr) above 5 keV of photon energy are produced.

Long pulse acceleration of MeV class high power density negative H{sup −} ion beam for ITER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Umeda, N., E-mail: umeda.naotaka@jaea.go.jp; Kojima, A.; Kashiwagi, M.

2015-04-08

R and D of high power density negative ion beam acceleration has been carried out at MeV test facility in JAEA to realize ITER neutral beam accelerator. The main target is H{sup −} ion beam acceleration up to 1 MeV with 200 A/m{sup 2} for 60 s whose pulse length is the present facility limit. For long pulse acceleration at high power density, new extraction grid (EXG) has been developed with high cooling capability, which electron suppression magnet is placed under cooling channel similar to ITER. In addition, aperture size of electron suppression grid (ESG) is enlarged from 14 mmmore » to 16 mm to reduce direct interception on the ESG and emission of secondary electron which leads to high heat load on the upstream acceleration grid. By enlarging ESG aperture, beam current increased 10 % at high current beam and total acceleration grid heat load reduced from 13 % to 10 % of input power at long pulse beam. In addition, heat load by back stream positive ion into the EXG is measured for the first time and is estimated as 0.3 % of beam power, while heat load by back stream ion into the source chamber is estimated as 3.5 ~ 4.0 % of beam power. Beam acceleration up to 60 s which is the facility limit, has achieved at 683 keV, 100 A/m{sup 2} of negative ion beam, whose energy density increases two orders of magnitude since 2011.« less

An overview of LLNL high-energy short-pulse technology for advanced radiography of laser fusion experiments

NASA Astrophysics Data System (ADS)

Barty, C. P. J.; Key, M.; Britten, J.; Beach, R.; Beer, G.; Brown, C.; Bryan, S.; Caird, J.; Carlson, T.; Crane, J.; Dawson, J.; Erlandson, A. C.; Fittinghoff, D.; Hermann, M.; Hoaglan, C.; Iyer, A.; Jones, L., II; Jovanovic, I.; Komashko, A.; Landen, O.; Liao, Z.; Molander, W.; Mitchell, S.; Moses, E.; Nielsen, N.; Nguyen, H.-H.; Nissen, J.; Payne, S.; Pennington, D.; Risinger, L.; Rushford, M.; Skulina, K.; Spaeth, M.; Stuart, B.; Tietbohl, G.; Wattellier, B.

2004-12-01

The technical challenges and motivations for high-energy, short-pulse generation with NIF and possibly other large-scale Nd : glass lasers are reviewed. High-energy short-pulse generation (multi-kilojoule, picosecond pulses) will be possible via the adaptation of chirped pulse amplification laser techniques on NIF. Development of metre-scale, high-efficiency, high-damage-threshold final optics is a key technical challenge. In addition, deployment of high energy petawatt (HEPW) pulses on NIF is constrained by existing laser infrastructure and requires new, compact compressor designs and short-pulse, fibre-based, seed-laser systems. The key motivations for HEPW pulses on NIF is briefly outlined and includes high-energy, x-ray radiography, proton beam radiography, proton isochoric heating and tests of the fast ignitor concept for inertial confinement fusion.

Evidence for breathing modes in direct current, pulsed, and high power impulse magnetron sputtering plasmas