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.

A compact high current pulsed electron gun with subnanosecond electron pulse widths

NASA Technical Reports Server (NTRS)

Khakoo, M. A.; Srivastava, S. K.

1984-01-01

A magnetically-collimated, double-pulsed electron gun capable of generating electron pulses with a peak instantaneous current of approximately 70 microamps and a temporal width of 0.35 ns (FWHM) has been developed. Calibration is accomplished by measuring the lifetime of the well known 2(1P)-to-1(1S) transition in helium (58.4nm) at a near-threshold electron-impact energy by use of the delayed-coincidence technique.

Generation of spectrally stable continuous-wave emission and ns pulses with a peak power of 4 W using a distributed Bragg reflector laser and a ridge-waveguide power amplifier.

PubMed

Klehr, A; Wenzel, H; Fricke, J; Bugge, F; Erbert, G

2014-10-06

We have developed a diode-laser based master oscillator power amplifier (MOPA) light source which emits high-power spectrally stabilized and nearly-diffraction limited optical pulses in the nanoseconds range as required by many applications. The MOPA consists of a distributed Bragg reflector (DBR) laser as master oscillator driven by a constant current and a ridge waveguide power amplifier (PA) which can be driven by a constant current (DC) or by rectangular current pulses with a width of 5 ns at a repetition frequency of 200 kHz. Under pulsed operation the amplifier acts as an optical gate, converting the CW input beam emitted by the DBR laser into a train of short amplified optical pulses. With this experimental MOPA arrangement no relaxation oscillations occur. A continuous wave power of 1 W under DC injection and a pulse power of 4 W under pulsed operation are reached. For both operational modes the optical spectrum of the emission of the amplifier exhibits a peak at a constant wavelength of 973.5 nm with a spectral width < 10 pm.

Particle in cell simulation of peaking switch for breakdown evaluation

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

Umbarkar, Sachin B.; Bindu, S.; Mangalvedekar, H.A.

2014-07-01

Marx generator connected to peaking capacitor and peaking switch can generate Ultra-Wideband (UWB) radiation. A new peaking switch is designed for converting the existing nanosecond Marx generator to a UWB source. The paper explains the particle in cell (PIC) simulation for this peaking switch, using MAGIC 3D software. This peaking switch electrode is made up of copper tungsten material and is fixed inside the hermitically sealed derlin material. The switch can withstand a gas pressure up to 13.5 kg/cm{sup 2}. The lower electrode of the switch is connected to the last stage of the Marx generator. Initially Marx generator (withoutmore » peaking stage) in air; gives the output pulse with peak amplitude of 113.75 kV and pulse rise time of 25 ns. Thus, we design a new peaking switch to improve the rise time of output pulse and to pressurize this peaking switch separately (i.e. Marx and peaking switch is at different pressure). The PIC simulation gives the particle charge density, current density, E counter plot, emitted electron current, and particle energy along the axis of gap between electrodes. The charge injection and electric field dependence on ionic dissociation phenomenon are briefly analyzed using this simulation. The model is simulated with different gases (N{sub 2}, H{sub 2}, and Air) under different pressure (2 kg/cm{sup 2}, 5 kg/cm{sup 2}, 10 kg/cm{sup 2}). (author)« less

Self-stimulation in the rat: quantitative characteristics of the reward pathway.

PubMed

Gallistel, C R

1978-12-01

Quantitative characteristics of the neural pathway that carries the reinforcing signal in electrical self-stimulation of the brain were established by finding which combinations of stimulation parameters give the same performance in a runway. The reward for each run was a train of evenly spaced monophasic cathodal pulses from a monopolar electrode. With train duration and pulse frequency held constant, the required current was a hyperbolic function of pulse duration, with chronaxie c approximately 1.5 msec. With pulse duration held constant, the required strength of the train (the charge delivered per second) was a hyperbolic function of train duration, with chronaxie C approximately 500 msec. To a first approximation, the values of c and C were independent of the choice either of train duration and pulse frequency or of pulse duration, respectively. Hence, the current intensity required by any choice of train duration, pulse frequency, and pulse duration dependent on only two basic parameters, c and C, and one quantity, Qi, the required impulse charge. These may reflect, respectively, current integration by directly excited neurons; temporal integration of neural activity by synaptic processes in a neural network; and the peak of the impulse response of the network, assuming that the network has linear dynamics and that the reward depends on the peak of the output of the network.

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.

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.

Characteristics of NLDN-Reported Radio Frequency Emissions Associated with Terrestrial Gamma-ray Flashes

NASA Astrophysics Data System (ADS)

Mailyan, B. G.; Nag, A.; Murphy, M. J.; Briggs, M. S.; Dwyer, J. R.; Cramer, E.; Stanbro, M.; Roberts, O. J.; Rassoul, H.

2017-12-01

Electric and magnetic field signals in the radio frequency range associated with Terrestrial Gamma-ray Flashes (TGFs) have become important measurements for studying this high-energy atmospheric phenomenon. These signals can be used to geolocate the source of TGFs, but they also provide insights into the TGF production mechanism, and the relationship between particle fluxes and lightning. In this study, we analyze 32 TGFs detected by the Fermi Gamma-ray Burst Monitor (GBM) occurring in 2014-2016 in conjunction with data from the U.S. National Lightning Detection Network (NLDN). We examine the characteristics of magnetic field waveforms measured by NLDN sensors for 48 pulses occurring within 5 ms of the peak-time of the gamma-ray photon flux. The -3 dB bandwidth of the NLDN sensors are from about 400 Hz to 400 KHz. For 15 (out of 32) TGFs, the associated NLDN pulse occurred almost simultaneously with (that is, within 300 μs of) the TGF. It is possible that these near-simultaneous low frequency magnetic field pulses were produced by relativistic electron beams. The median time interval between the beginning of these near-simultaneous NLDN pulses and the peak-times of the TGF flux is 38 μs. 3 out of 16 ( 19%) of these pulses had negative initial polarity. The absolute value of NLDN-estimated peak currents, which can be viewed as a quantity proportional to the peak magnetic radiation field of these pulses, ranges from 17 kA to 166 kA, with the median being 32 kA. Twelve pulses had peak currents less than 50 kA. Additionally, we will compare the characteristics of GBM-reported gamma-ray signatures of the two categories of TGFs, those with a near-simultaneous NLDN-detected pulse and those with no such pulse (but with other pulses detected by the NLDN occurring within 5 ms of the TGF). Also, one of the TGFs occurred within the coverage region of the Kennedy Space Center Lightning Mapping Array (LMA). We will examine in detail the LMA, NLDN, and NEXRAD radar data for this TGF.

MRR and TWR evaluation on electrical discharge machining of Ti-6Al-4V using tungsten : copper composite electrode

NASA Astrophysics Data System (ADS)

Prasanna, J.; Rajamanickam, S.; Amith Kumar, O.; Karthick Raj, G.; Sathya Narayanan, P. V. V.

2017-05-01

In this paper Ti-6Al-4V used as workpiece material and it is keenly seen in variety of field including medical, chemical, marine, automotive, aerospace, aviation, electronic industries, nuclear reactor, consumer products etc., The conventional machining of Ti-6Al-4V is very difficult due to its distinctive properties. The Electrical Discharge Machining (EDM) is right choice of machining this material. The tungsten copper composite material is employed as tool material. The gap voltage, peak current, pulse on time and duty factor is considered as the machining parameter to analyze the machining characteristics Material Removal Rate (MRR) and Tool Wear Rate (TWR). The Taguchi method is provided to work for finding the significant parameter of EDM. It is found that for MRR significant parameters rated in the following order Gap Voltage, Pulse On-Time, Peak Current and Duty Factor. On the other hand for TWR significant parameters are listed in line of Gap Voltage, Duty Factor, Peak Current and Pulse On-Time.

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 superconductivity at the edges due to penetration of magnetic field in superconducting core during the pulse.

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.

Studies on sildenafil citrate (Viagra) interaction with DNA using electrochemical DNA biosensor.

PubMed

Rauf, Sakandar; Nawaz, Haq; Akhtar, Kalsoom; Ghauri, Muhammad A; Khalid, Ahmad M

2007-05-15

The interaction of sildenafil citrate (Viagra) with DNA was studied by using an electrochemical DNA biosensor. The binding mechanism of sildenafil citrate was elucidated by using constant current potentiometry and differential pulse voltammetry at DNA-modified glassy carbon electrode. The decrease in the guanine oxidation peak area or peak current was used as an indicator for the interaction in 0.2M acetate buffer (pH 5). The binding constant (K) values obtained were 2.01+/-0.05 x 10(5) and 1.97+/-0.01 x 10(5)M(-1) with constant current potentiometry and differential pulse voltammetry, respectively. A linear dependence of the guanine peak area or peak current was observed within the range of 1-40 microM sildenafil citrate with slope=-2.74 x 10(-4)s/microM, r=0.989 and slope=-2.78 x 10(-3)microA/microM, r=0.995 by using constant current potentiometry and differential pulse voltammetry, respectively. Additionally, binding constant values for sildenafil citrate-DNA interaction were determined for the pH range of 4-8 and in biological fluids (serum and urine) at pH 5. The influence of sodium and calcium ions was also studied to elucidate the mechanism of sildenafil citrate-DNA interaction under different solution conditions. The present study may prove to be helpful in extending our understanding of the anticancer activity of sildenafil citrate from cellular to DNA level.

Ultrafast disk technology enables next generation micromachining laser sources

NASA Astrophysics Data System (ADS)

Heckl, Oliver H.; Weiler, Sascha; Luzius, Severin; Zawischa, Ivo; Sutter, Dirk

2013-02-01

Ultrashort pulsed lasers based on thin disk technology have entered the 100 W regime and deliver several tens of MW peak power without chirped pulse amplification. Highest uptime and insensitivity to back reflections make them ideal tools for efficient and cost effective industrial micromachining. Frequency converted versions allow the processing of a large variety of materials. On one hand, thin disk oscillators deliver more than 30 MW peak power directly out of the resonator in laboratory setups. These peak power levels are made possible by recent progress in the scaling of the pulse energy in excess of 40 μJ. At the corresponding high peak intensity, thin disk technology profits from the limited amount of material and hence the manageable nonlinearity within the resonator. Using new broadband host materials like for example the sesquioxides will eventually reduce the pulse duration during high power operation and further increase the peak power. On the other hand industry grade amplifier systems deliver even higher peak power levels. At closed-loop controlled 100W, the TruMicro Series 5000 currently offers the highest average ultrafast power in an industry proven product, and enables efficient micromachining of almost any material, in particular of glasses, ceramics or sapphire. Conventional laser cutting of these materials often requires UV laser sources with pulse durations of several nanoseconds and an average power in the 10 W range. Material processing based on high peak power laser sources makes use of multi-photon absorption processes. This highly nonlinear absorption enables micromachining driven by the fundamental (1030 nm) or frequency doubled (515 nm) wavelength of Yb:YAG. Operation in the IR or green spectral range reduces the complexity and running costs of industrial systems initially based on UV light sources. Where UV wavelength is required, the TruMicro 5360 with a specified UV crystal life-time of more than 10 thousand hours of continues operation at 15W is an excellent choice. Currently this is the world's most powerful industrial sub-10 ps UV laser.

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

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

Effect of Pulse Parameters on Weld Quality in Pulsed Gas Metal Arc Welding: A Review

NASA Astrophysics Data System (ADS)

Pal, Kamal; Pal, Surjya K.

2011-08-01

The weld quality comprises bead geometry and its microstructure, which influence the mechanical properties of the weld. The coarse-grained weld microstructure, higher heat-affected zone, and lower penetration together with higher reinforcement reduce the weld service life in continuous mode gas metal arc welding (GMAW). Pulsed GMAW (P-GMAW) is an alternative method providing a better way for overcoming these afore mentioned problems. It uses a higher peak current to allow one molten droplet per pulse, and a lower background current to maintain the arc stability. Current pulsing refines the grains in weld fusion zone with increasing depth of penetration due to arc oscillations. Optimum weld joint characteristics can be achieved by controlling the pulse parameters. The process is versatile and easily automated. This brief review illustrates the effect of pulse parameters on weld quality.

Numerical simulation of passively mode-locked fiber laser based on semiconductor optical amplifier

NASA Astrophysics Data System (ADS)

Yang, Jingwen; Jia, Dongfang; Zhang, Zhongyuan; Chen, Jiong; Liu, Tonghui; Wang, Zhaoying; Yang, Tianxin

2013-03-01

Passively mode-locked fiber laser (MLFL) has been widely used in many applications, such as optical communication system, industrial production, information processing, laser weapons and medical equipment. And many efforts have been done for obtaining lasers with small size, simple structure and shorter pulses. In recent years, nonlinear polarization rotation (NPR) in semiconductor optical amplifier (SOA) has been studied and applied as a mode-locking mechanism. This kind of passively MLFL has faster operating speed and makes it easier to realize all-optical integration. In this paper, we had a thorough analysis of NPR effect in SOA. And we explained the principle of mode-locking by SOA and set up a numerical model for this mode-locking process. Besides we conducted a Matlab simulation of the mode-locking mechanism. We also analyzed results under different working conditions and several features of this mode-locking process are presented. Our simulation shows that: Firstly, initial pulse with the peak power exceeding certain threshold may be amplified and compressed, and stable mode-locking may be established. After about 25 round-trips, stable mode-locked pulse can be obtained which has peak power of 850mW and pulse-width of 780fs.Secondly, when the initial pulse-width is greater, narrowing process of pulse is sharper and it needs more round-trips to be stable. Lastly, the bias currents of SOA affect obviously the shape of mode-locked pulse and the mode-locked pulse with high peak power and narrow width can be obtained through adjusting reasonably the bias currents of SOA.

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

Kilohertz and Low-Frequency Electrical Stimulation With the Same Pulse Duration Have Similar Efficiency for Inducing Isometric Knee Extension Torque and Discomfort.

PubMed

Medeiros, Flávia Vanessa; Bottaro, Martim; Vieira, Amilton; Lucas, Tiago Pires; Modesto, Karenina Arrais; Bo, Antonio Padilha L; Cipriano, Gerson; Babault, Nicolas; Durigan, João Luiz Quagliotti

2017-06-01

To test the hypotheses that, as compared with pulsed current with the same pulse duration, kilohertz frequency alternating current would not differ in terms of evoked-torque production and perceived discomfort, and as a result, it would show the same current efficiency. A repeated-measures design with 4 stimuli presented in random order was used to test 25 women: (1) 500-microsecond pulse duration, (2) 250-microsecond pulse duration, (3) 500-microsecond pulse duration and low carrier frequency (1 kHz), (4) 250-microsecond pulse duration and high carrier frequency (4 kHz). Isometric peak torque of quadriceps muscle was measured using an isokinetic dynamometer. Discomfort was measured using a visual analog scale. Currents with long pulse durations induced approximately 21% higher evoked torque than short pulse durations. In addition, currents with 500 microseconds delivered greater amounts of charge than stimulation patterns using 250-microsecond pulse durations (P < 0.05). All currents presented similar discomfort. There was no difference on stimulation efficiency with the same pulse duration. Both kilohertz frequency alternating current and pulsed current, with the same pulse duration, have similar efficiency for inducing isometric knee extension torque and discomfort. However, neuromuscular electrical stimulation (NMES) with longer pulse duration induces higher NMES-evoked torque, regardless of the carrier frequency. Pulse duration is an important variable that should receive more attention for an optimal application of NMES in clinical settings.

Retinal ganglion cell responses to voltage and current stimulation in wild-type and rd1 mouse retinas

NASA Astrophysics Data System (ADS)

Goo, Yong Sook; Ye, Jang Hee; Lee, Seokyoung; Nam, Yoonkey; Ryu, Sang Baek; Kim, Kyung Hwan

2011-06-01

Retinal prostheses are being developed to restore vision for those with retinal diseases such as retinitis pigmentosa or age-related macular degeneration. Since neural prostheses depend upon electrical stimulation to control neural activity, optimal stimulation parameters for successful encoding of visual information are one of the most important requirements to enable visual perception. In this paper, we focused on retinal ganglion cell (RGC) responses to different stimulation parameters and compared threshold charge densities in wild-type and rd1 mice. For this purpose, we used in vitro retinal preparations of wild-type and rd1 mice. When the neural network was stimulated with voltage- and current-controlled pulses, RGCs from both wild-type and rd1 mice responded; however the temporal pattern of RGC response is very different. In wild-type RGCs, a single peak within 100 ms appears, while multiple peaks (approximately four peaks) with ~10 Hz rhythm within 400 ms appear in RGCs in the degenerated retina of rd1 mice. We find that an anodic phase-first biphasic voltage-controlled pulse is more efficient for stimulation than a biphasic current-controlled pulse based on lower threshold charge density. The threshold charge densities for activation of RGCs both with voltage- and current-controlled pulses are overall more elevated for the rd1 mouse than the wild-type mouse. Here, we propose the stimulus range for wild-type and rd1 retinas when the optimal modulation of a RGC response is possible.

Optimization of Surface Roughness Parameters of Al-6351 Alloy in EDC Process: A Taguchi Coupled Fuzzy Logic Approach

NASA Astrophysics Data System (ADS)

Kar, Siddhartha; Chakraborty, Sujoy; Dey, Vidyut; Ghosh, Subrata Kumar

2017-10-01

This paper investigates the application of Taguchi method with fuzzy logic for multi objective optimization of roughness parameters in electro discharge coating process of Al-6351 alloy with powder metallurgical compacted SiC/Cu tool. A Taguchi L16 orthogonal array was employed to investigate the roughness parameters by varying tool parameters like composition and compaction load and electro discharge machining parameters like pulse-on time and peak current. Crucial roughness parameters like Centre line average roughness, Average maximum height of the profile and Mean spacing of local peaks of the profile were measured on the coated specimen. The signal to noise ratios were fuzzified to optimize the roughness parameters through a single comprehensive output measure (COM). Best COM obtained with lower values of compaction load, pulse-on time and current and 30:70 (SiC:Cu) composition of tool. Analysis of variance is carried out and a significant COM model is observed with peak current yielding highest contribution followed by pulse-on time, compaction load and composition. The deposited layer is characterised by X-Ray Diffraction analysis which confirmed the presence of tool materials on the work piece surface.

Evaluation of the shock-wave pattern for endoscopic electrohydraulic lithotripsy.

PubMed

Vorreuther, R; Engelmann, Y

1995-01-01

We evaluated the electrical events and the resulting shock waves of the spark discharge for electrohydraulic lithotripsy at the tip of a 3.3F probe. Spark generation was achieved by variable combinations of voltage and capacity. The effective electrical output was determined by means of a high-voltage probe, a current coil, and a digital oscilloscope. Peak pressures, rise times, and pulse width of the pressure profiles were recorded using a polyvinylidene difluoride needle hydrophone in 0.9% NaCl solution at a distance of 10 mm. The peak pressure and the slope of the shock front depend solely on the voltage, while the pulse width was correlated with the capacity. Pulses of less than 1-microsecond duration can be obtained when low capacity is applied and the inductivity of the cables and plugs is kept at a low level. Using chalk as a stone model it was proven that short pulses of high peak pressure provided by a low capacity and a high voltage have a greater impact on fragmentation than the corresponding broader shock waves of lower peak pressure carrying the same energy.

Cellular effects of acute exposure to high peak power microwave systems: Morphology and toxicology.

PubMed

Ibey, Bennett L; Roth, Caleb C; Ledwig, Patrick B; Payne, Jason A; Amato, Alayna L; Dalzell, Danielle R; Bernhard, Joshua A; Doroski, Michael W; Mylacraine, Kevin S; Seaman, Ronald L; Nelson, Gregory S; Woods, Clifford W

2016-03-15

Electric fields produced by advanced pulsed microwave transmitter technology now readily exceed the Institute of Electrical and Electronic Engineers (IEEE) C.95.1 peak E-field limit of 100 kV/m, highlighting a need for scientific validation of such a specific limit. Toward this goal, we exposed Jurkat Clone E-6 human lymphocyte preparations to 20 high peak power microwave (HPPM) pulses (120 ns duration) with a mean peak amplitude of 2.3 MV/m and standard deviation of 0.1 with the electric field at cells predicted to range from 0.46 to 2.7 MV/m, well in excess of current standard limit. We observed that membrane integrity and cell morphology remained unchanged 4 h after exposure and cell survival 24 h after exposure was not statistically different from sham exposure or control samples. Using flow cytometry to analyze membrane disruption and morphological changes per exposed cell, no changes were observed in HPPM-exposed samples. Current IEEE C95.1-2005 standards for pulsed radiofrequency exposure limits peak electric field to 100 kV/m for pulses shorter than 100 ms [IEEE (1995) PC95.1-Standard for Safety Levels with Respect to Human Exposure to Electric, Magnetic and Electromagnetic Fields, 0 Hz to 300 GHz, Institute of Electrical and Electronic Engineers: Piscataway, NJ, USA]. This may impose large exclusion zones that limit HPPM technology use. In this study, we offer evidence that maximum permissible exposure of 100 kV/m for peak electric field may be unnecessarily restrictive for HPPM devices. Bioelectromagnetics. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

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.

Intense terahertz pulses from SLAC electron beams using coherent transition radiation.

PubMed

Wu, Ziran; Fisher, Alan S; Goodfellow, John; Fuchs, Matthias; Daranciang, Dan; Hogan, Mark; Loos, Henrik; Lindenberg, Aaron

2013-02-01

SLAC has two electron accelerators, the Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET), providing high-charge, high-peak-current, femtosecond electron bunches. These characteristics are ideal for generating intense broadband terahertz (THz) pulses via coherent transition radiation. For LCLS and FACET respectively, the THz pulse duration is typically 20 and 80 fs RMS and can be tuned via the electron bunch duration; emission spectra span 3-30 THz and 0.5 THz-5 THz; and the energy in a quasi-half-cycle THz pulse is 0.2 and 0.6 mJ. The peak electric field at a THz focus has reached 4.4 GV/m (0.44 V/Å) at LCLS. This paper presents measurements of the terahertz pulses and preliminary observations of nonlinear materials response.

Assessment of the magnetic field exposure due to the battery current of digital mobile phones.

PubMed

Jokela, Kari; Puranen, Lauri; Sihvonen, Ari-Pekka

2004-01-01

Hand-held digital mobile phones generate pulsed magnetic fields associated with the battery current. The peak value and the waveform of the battery current were measured for seven different models of digital mobile phones, and the results were applied to compute approximately the magnetic flux density and induced currents in the phone-user's head. A simple circular loop model was used for the magnetic field source and a homogeneous sphere consisting of average brain tissue equivalent material simulated the head. The broadband magnetic flux density and the maximal induced current density were compared with the guidelines of ICNIRP using two various approaches. In the first approach the relative exposure was determined separately at each frequency and the exposure ratios were summed to obtain the total exposure (multiple-frequency rule). In the second approach the waveform was weighted in the time domain with a simple low-pass RC filter and the peak value was divided by a peak limit, both derived from the guidelines (weighted peak approach). With the maximum transmitting power (2 W) the measured peak current varied from 1 to 2.7 A. The ICNIRP exposure ratio based on the current density varied from 0.04 to 0.14 for the weighted peak approach and from 0.08 to 0.27 for the multiple-frequency rule. The latter values are considerably greater than the corresponding exposure ratios 0.005 (min) to 0.013 (max) obtained by applying the evaluation based on frequency components presented by the new IEEE standard. Hence, the exposure does not seem to exceed the guidelines. The computed peak magnetic flux density exceeded substantially the derived peak reference level of ICNIRP, but it should be noted that in a near-field exposure the external field strengths are not valid indicators of exposure. Currently, no biological data exist to give a reason for concern about the health effects of magnetic field pulses from mobile phones.

Development and testing of a pulsed helium ion source for probing materials and warm dense matter studies

NASA Astrophysics Data System (ADS)

Ji, Q.; Seidl, P. A.; Waldron, W. L.; Takakuwa, J. H.; Friedman, A.; Grote, D. P.; Persaud, A.; Barnard, J. J.; Schenkel, T.

2016-02-01

The neutralized drift compression experiment was designed and commissioned as a pulsed, linear induction accelerator to drive thin targets to warm dense matter (WDM) states with peak temperatures of ˜1 eV using intense, short pulses (˜1 ns) of 1.2 MeV lithium ions. At that kinetic energy, heating a thin target foil near the Bragg peak energy using He+ ions leads to more uniform energy deposition of the target material than Li+ ions. Experiments show that a higher current density of helium ions can be delivered from a plasma source compared to Li+ ions from a hot plate type ion source. He+ beam pulses as high as 200 mA at the peak and 4 μs long were measured from a multi-aperture 7-cm-diameter emission area. Within ±5% variation, the uniform beam area is approximately 6 cm across. The accelerated and compressed pulsed ion beams can be used for materials studies and isochoric heating of target materials for high energy density physics experiments and WDM studies.

Development and testing of a pulsed helium ion source for probing materials and warm dense matter studies.

PubMed

Ji, Q; Seidl, P A; Waldron, W L; Takakuwa, J H; Friedman, A; Grote, D P; Persaud, A; Barnard, J J; Schenkel, T

2016-02-01

The neutralized drift compression experiment was designed and commissioned as a pulsed, linear induction accelerator to drive thin targets to warm dense matter (WDM) states with peak temperatures of ∼1 eV using intense, short pulses (∼1 ns) of 1.2 MeV lithium ions. At that kinetic energy, heating a thin target foil near the Bragg peak energy using He(+) ions leads to more uniform energy deposition of the target material than Li(+) ions. Experiments show that a higher current density of helium ions can be delivered from a plasma source compared to Li(+) ions from a hot plate type ion source. He(+) beam pulses as high as 200 mA at the peak and 4 μs long were measured from a multi-aperture 7-cm-diameter emission area. Within ±5% variation, the uniform beam area is approximately 6 cm across. The accelerated and compressed pulsed ion beams can be used for materials studies and isochoric heating of target materials for high energy density physics experiments and WDM studies.

Development and testing of a pulsed helium ion source for probing materials and warm dense matter studies

DOE PAGES

Ji, Q.; Seidl, P. A.; Waldron, W. L.; ...

2015-11-12

In this paper, the neutralized drift compression experiment was designed and commissioned as a pulsed, linear induction accelerator to drive thin targets to warm dense matter (WDM) states with peak temperatures of ~1 eV using intense, short pulses (~1 ns) of 1.2 MeV lithium ions. At that kinetic energy, heating a thin target foil near the Bragg peak energy using He + ions leads to more uniform energy deposition of the target material than Li + ions. Experiments show that a higher current density of helium ions can be delivered from a plasma source compared to Li + ions frommore » a hot plate type ion source. He + beam pulses as high as 200 mA at the peak and 4 μs long were measured from a multi-aperture 7-cm-diameter emission area. Within ±5% variation, the uniform beam area is approximately 6 cm across. Finally, the accelerated and compressed pulsed ion beams can be used for materials studies and isochoric heating of target materials for high energy density physics experiments and WDM studies.« less

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.

Transport simulation of EAST long-pulse H-mode discharge with integrated modeling

NASA Astrophysics Data System (ADS)

Wu, M. Q.; Li, G. Q.; Chen, J. L.; Du, H. F.; Gao, X.; Ren, Q. L.; Li, K.; Chan, Vincent; Pan, C. K.; Ding, S. Y.; Jian, X.; Zhu, X.; Lian, H.; Qian, J. P.; Gong, X. Z.; Zang, Q.; Duan, Y. M.; Liu, H. Q.; Lyu, B.

2018-04-01

In the 2017 EAST experimental campaign, a steady-state long-pulse H-mode discharge lasting longer than 100 s has been obtained using only radio frequency heating and current drive, and the confinement quality is slightly better than standard H-mode, H98y2 ~ 1.1, with stationary peaked electron temperature profiles. Integrated modeling of one long-pulse H-mode discharge in the 2016 EAST experimental campaign has been performed with equilibrium code EFIT, and transport codes TGYRO and ONETWO under integrated modeling framework OMFIT. The plasma current is fully-noninductively driven with a combination of ~2.2 MW LHW, ~0.3 MW ECH and ~1.1 MW ICRF. Time evolution of the predicted electron and ion temperature profiles through integrated modeling agree closely with that from measurements. The plasma current (I p ~ 0.45 MA) and electron density are kept constantly. A steady-state is achieved using integrated modeling, and the bootstrap current fraction is ~28%, the RF drive current fraction is ~72%. The predicted current density profile matches the experimental one well. Analysis shows that electron cyclotron heating (ECH) makes large contribution to the plasma confinement when heating in the core region while heating in large radius does smaller improvement, also a more peaked LHW driven current profile is got when heating in the core. Linear analysis shows that the high-k modes instability (electron temperature gradient driven modes) is suppressed in the core region where exists weak electron internal transport barriers. The trapped electron modes dominates in the low-k region, which is mainly responsible for driving the electron energy flux. It is found that the ECH heating effect is very local and not the main cause to sustained the good confinement, the peaked current density profile has the most important effect on plasma confinement improvement. Transport analysis of the long-pulse H-mode experiments on EAST will be helpful to build future experiments.

Area scaling investigations of charging phenomena. [discharge pulse characteristics of Teflon thermal control tape

NASA Technical Reports Server (NTRS)

Aron, P. R.; Staskus, J. V.

1979-01-01

The charging and discharging behavior of square, planar samples of silvered, fluorinated ethylene-propylene (FEP) Teflon thermal control tape was measured. The equilibrium voltage profiles scaled with the width of the sample. A wide range of discharge pulse characteristics was observed, and the area dependences of the peak current, charge, and pulse widths are described. The observed scaling of the peak currents with area was weaker than that previously reported. The discharge parameters were observed to depend strongly on the grounding impedance and the beam voltage. Preliminary results suggest that measuring only the return-current-pulse characteristics is not adequate to describe the spacecraft discharging behavior of this material. The seams between strips of tape appear to play a fundamental role in determining the discharging behavior. An approximate propagation velocity for the charge cleanoff was extracted from the data. The samples - 232, 1265, and 5058 square centimeters in area - were exposed at ambient temperature to a 1- to 2-nA/sq cm electron beam at energies of 10, 15, and 20 kilovolts in a 19-meter-long by 4.6-meter-diameter simulation facility at the Lewis Research Center.

On the road to self-sputtering in high power impulse magnetron sputtering: particle balance and discharge characteristics

NASA Astrophysics Data System (ADS)

Huo, Chunqing; Lundin, Daniel; Raadu, Michael A.; Anders, André; Tomas Gudmundsson, Jon; Brenning, Nils

2014-04-01

The onset and development of self-sputtering (SS) in a high power impulse magnetron sputtering (HiPIMS) discharge have been studied using a plasma chemical model and a set of experimental data, taken with an aluminum target and argon gas. The model is tailored to duplicate the discharge in which the data are taken. The pulses are long enough to include both an initial transient and a following steady state. The model is used to unravel how the internal discharge physics evolves with pulse power and time, and how it is related to features in the discharge current-voltage-time characteristics such as current densities, maxima, kinks and slopes. The connection between the self-sputter process and the discharge characteristics is quantified and discussed in terms of three parameters: a critical target current density Jcrit based on the maximum refill rate of process (argon) gas above the target, an SS recycling factor ΠSS-recycle, and an approximation \\tilde{\\alpha} of the probabilities of ionization of species that come from the target (both sputtered metal and embedded argon atoms). For low power pulses, discharge voltages UD ⩽ 380 V with peak current densities below ≈ 0.2 A cm-2, the discharge is found to be dominated by process gas sputtering. In these pulses there is an initial current peak in time, associated with partial gas rarefaction, which is followed by a steady-state-like plateau in all parameters similar to direct current magnetron sputtering. In contrast, high power pulses, with UD ⩾ 500 V and peak current densities above JD ≈ 1.6 A cm-2, make a transition to a discharge mode where SS dominates. The transition is found not to be driven by process gas rarefaction which is only about 10% at this time. Maximum gas rarefaction is found later in time and always after the initial peak in the discharge current. With increasing voltage, and pulse power, the discharge can be described as following a route where the role of SS increases in four steps: process gas sputtering, gas-sustained SS, self-sustained SS and SS runaway. At the highest voltage, 1000 V, the discharge is very close to, but does not go into, the SS runaway mode. This absence of runaway is proposed to be connected to an unexpected finding: that twice ionized ions of the target species play almost no role in this discharge, not even at the highest powers. This reduces ionization by secondary-emitted energetic electrons almost to zero in the highest power range of the discharge.

Intense Ion Pulses for Radiation Effects Research

DTIC Science & Technology

2017-04-01

station; here, the time dependent beam current can be measured with a fast Faraday cup (ə ns time resolution). The transverse distribution of the...focused into a spot with a diameter of about 2 mm [8]. The helium ion current and the integrated charge ver- sus time, measured with the fast Faraday cup...target measured with the fast Faraday cup. The sharp peak in the current measurement shows the beam pulse compression from 1 μs to a few ns. The full

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

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.

Solid state modulator for klystron power supply XFEL TDS INJ

NASA Astrophysics Data System (ADS)

Zavadtsev, A. A.; Zavadtsev, D. A.; Zybin, D. A.; Churanov, D. V.; Shemarykin, P. V.

2016-09-01

The transverse deflecting system XFEL TDS INJ for European X-ray Free Electron Laser includes power supply for the CPI VKS-8262HS klystron. It has been designed for pulse high-voltage, cathode heating, solenoid and klystron ion pump. The klystron power supply includes solid state modulator, pulse transformer, controlled power supply for cathode heating and commercial power supplies for solenoid and ion pump. Main parameters of the modulator are 110 kV of peak voltage, 72 A peak current, and pulse length up to 6 μs. The klystron power supply has been developed, designed, manufactured, tuned, tested and installed in the XFEL building. All designed parameters are satisfied.

Cladding-pumped 70-kW-peak-power 2-ns-pulse Er-doped fiber amplifier

NASA Astrophysics Data System (ADS)

Khudyakov, M. M.; Bubnov, M. M.; Senatorov, A. K.; Lipatov, D. S.; Guryanov, A. N.; Rybaltovsky, A. A.; Butov, O. V.; Kotov, L. V.; Likhachev, M. E.

2018-02-01

An all-fiber pulsed erbium laser with pulse width of 2.4 ns working in a MOPA configuration has been created. Cladding pumped double clad erbium doped large mode area fiber was used in the final stage amplifier. Peculiarity of the current work is utilization of custom-made multimode diode wavelength stabilized at 981+/-0.5 nm - wavelength of maximum absorption by Er ions. It allowed us to shorten Er-doped fiber down to 1.7 m and keep a reasonably high pump-to signal conversion efficiency of 8.4%. The record output peak power for all-fiber amplifiers of 84 kW was achieved within 1555.9+/-0.15 nm spectral range.

Color Doppler Sonographic Evaluation of Peak Systolic Velocity and Pulsatility Index in Artery after Pulsed HIFU Exposure

NASA Astrophysics Data System (ADS)

Yang, Feng-Yi; Chiu, Wei-Hsiu; Yeh, Chi-Fang

2011-09-01

The objective of current study was to investigate the functional changes in arteries induced by pulsed-HIFU with or without microbubbles. Sonication was applied at an ultrasound frequency of 1 MHz with a burst length of 50 ms and a repetition frequency of 1 Hz. The duration of the whole sonication was 6s. The abdominal aortas of Sprague-Dawley rats were surgically exposed and sonicated with pulsed HIFU; the pulsed HIFU beam was aimed using color images of the blood flow. There was no obvious normalized peak systolic velocity (PSV) change at various acoustic powers of pulsed-HIFU exposure in the absence of ultrasound contrast agent (UCA). However, the normalized PSV change induced by pulsed-HIFU decreased with the injected dose of UCA at acoustic powers. At this time, the normalized pulsatility index (PI) change in the vessel subjected to pulsed-HIFU increased in proportion to UCA dose. Additional research is needed to investigate the detailed mechanical effects of pulsed-HIFU exposure on blood flow and the structure of vessel walls.

SWIFT OBSERVATIONS OF GAMMA-RAY BURST PULSE SHAPES: GRB PULSE SPECTRAL EVOLUTION CLARIFIED

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

Hakkila, Jon; Lien, Amy; Sakamoto, Takanori

Isolated Swift gamma-ray burst (GRB) pulses, like their higher-energy BATSE counterparts, emit the bulk of their pulsed emission as a hard-to-soft component that can be fitted by the Norris et al. empirical pulse model. This signal is overlaid by a fainter, three-peaked signal that can be modeled by the residual fit of Hakkila and Preece: the two fits combine to reproduce GRB pulses with distinctive three-peaked shapes. The precursor peak appears on or before the pulse rise and is often the hardest component, the central peak is the brightest, and the decay peak converts exponentially decaying emission into a long,more » soft, power-law tail. Accounting for systematic instrumental differences, the general characteristics of the fitted pulses are remarkably similar. Isolated GRB pulses are dominated by hard-to-soft evolution; this is more pronounced for asymmetric pulses than for symmetric ones. Isolated GRB pulses can also exhibit intensity tracking behaviors that, when observed, are tied to the timing of the three peaks: pulses with the largest maximum hardnesses are hardest during the precursor, those with smaller maximum hardnesses are hardest during the central peak, and all pulses can re-harden during the central peak and/or during the decay peak. Since these behaviors are essentially seen in all isolated pulses, the distinction between “hard-to-soft and “intensity-tracking” pulses really no longer applies. Additionally, the triple-peaked nature of isolated GRB pulses seems to indicate that energy is injected on three separate occasions during the pulse duration: theoretical pulse models need to account for this.« less

Generation of spectrally-stable continuous-wave emission and ns pulses at 800 nm and 975 nm with a peak power of 4 W using a distributed Bragg reflector laser and a ridge-waveguide power amplifier

NASA Astrophysics Data System (ADS)

Klehr, A.; Wenzel, H.; Fricke, J.; Bugge, F.; Liero, A.; Hoffmann, Th.; Erbert, G.; Tränkle, G.

2015-03-01

Semiconductor based sources which emit high-power spectrally stable nearly diffraction-limited optical pulses in the nanosecond range are ideally suited for a lot of applications, such as free-space communications, metrology, material processing, seed lasers for fiber or solid state lasers, spectroscopy, LIDAR and frequency doubling. Detailed experimental investigations of 975 nm and 800 nm diode lasers based on master oscillator power amplifier (MOPA) light sources are presented. The MOPA systems consist of distributed Bragg reflector lasers (DBR) as master oscillators driven by a constant current and ridge waveguide power amplifiers which can be driven DC and by current pulses. In pulse regime the amplifiers modulated with rectangular current pulses of about 5 ns width and a repetition frequency of 200 kHz act as optical gates, converting the continuous wave (CW) input beam emitted by the DBR lasers into a train of short optical pulses which are amplified. With these experimental MOPA arrangements no relaxation oscillations in the pulse power occur. With a seed power of about 5 mW at a wavelength of 973 nm output powers behind the amplifier of about 1 W under DC injection and 4 W under pulsed operation, corresponding to amplification factors of 200 (amplifier gain 23 dB) and 800 (gain 29 dB) respectively, are reached. At 800 nm a CW power of 1 W is obtained for a seed power of 40 mW. The optical spectra of the emission of the amplifiers exhibit a single peak at a constant wavelength with a line width < 10 pm in the whole investigated current ranges. The ratios between laser and ASE levels were > 50 dB. The output beams are nearly diffraction limited with beam propagation ratios M2lat ~ 1.1 and M2ver ~ 1.2 up to 4 W pulse power.

A contraction-related component of slow inward current in dog ventricular muscle and its relation to Na(+)-Ca2+ exchange.

PubMed Central

Simurda, J; Simurdová, M; Bravený, P; Sumbera, J

1992-01-01

1. The slow inward current component related to contraction (Isic) was studied in voltage clamp experiments on canine ventricular trabeculae at 30 degrees C with the aims of (a) estimating its relation to electrogenic Na(+)-Ca2+ exchange and (b) comparing it with similar currents as reported in cardiac myocytes. 2. Isic may be recorded under conditions of augmented contractility in response to depolarizing pulses below the threshold of the classic slow inward current (presumably mediated by L-type Ca2+ channels). In responses to identical depolarizing clamp pulses the peak value of Isic is directly related to the amplitude of contraction (Fmax). Isic peaks about 60 ms after the onset of depolarization and declines with a half-time of about 110 ms. 3. The voltage threshold of Isic activation is the same as the threshold of contraction. The positive inotropic clamp preconditions shift both thresholds to more negative values of membrane voltage, i.e. below the threshold of the classic slow inward current. 4. Isic may also be recorded as a slowly decaying inwardly directed current 'tail' after depolarizing pulses. In this representation the peak value of Isic changes with duration of the depolarizing pulses, again in parallel with Fmax. In response to pulses shorter than 100 ms both variables increase with depolarization time. If initial conditions remain constant, further prolongation of the pulse does not significantly influence either one (tail currents follow a common envelope). 5. Isic differs from classic slow inward current by: (a) its direct relation to contraction, (b) the slower decay of the current tail on repolarization, (c) slower restitution corresponding to the mechanical restitution, (d) its relative insensitivity to Ca(2+)-blocking agents (the decrease of Isic is secondary to the negative inotropic of Ca(2+)-blocking agents (the decrease of Isic is secondary to the negative inotropic effect) and (e) its disappearance after Sr2+ substitution for Ca2+. 6. The manifestations of Isic in multicellular preparations do not differ significantly from those reported in isolated myocytes (in contrast to calcium current). 7. The analysis of the correlation between Isic and Fmax transients during trains of identical test depolarizing pulses at variable extra- and intracellular ionic concentrations (changes of [Ca2+]o, 50% Li+ substitution for Na+, strophanthidin) indicate that the observed effects conform to the predictions based on a quantitative model of Na(+)-Ca2+ exchange. 8. It is concluded that Isic is activated by a transient increase of [Ca2+]i, in consequence of the release from the reticular stores.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:1293284

Time resolved Thomson scattering diagnostic of pulsed gas metal arc welding (GMAW) process

NASA Astrophysics Data System (ADS)

Kühn-Kauffeldt, M.; Marquès, J. L.; Schein, J.

2014-11-01

In this work a Thomson scattering diagnostic technique was applied to obtain time resolved electron temperature and density values during a gas metal arc welding (GMAW) process. The investigated GMAW process was run with aluminum wire (AlMg 4,5 Mn) with 1.2 mm diameter as a wire electrode, argon as a shielding gas and peak currents in the range of 400 A. Time resolved measurements could be achieved by triggering the laser pulse at shifted time positions with respect to the current pulse driving the process. Time evaluation of resulting electron temperatures and densities is used to investigate the state of the plasma in different phases of the current pulse and to determine the influence of the metal vapor and droplets on the plasma properties.

Effect of plasma arc welding variables on fusion zone grain size and hardness of AISI 321 austenitic stainless steel

NASA Astrophysics Data System (ADS)

Kondapalli, S. P.

2017-12-01

In the present work, pulsed current microplasma arc welding is carried out on AISI 321 austenitic stainless steel of 0.3 mm thickness. Peak current, Base current, Pulse rate and Pulse width are chosen as the input variables, whereas grain size and hardness are considered as output responses. Response surface method is adopted by using Box-Behnken Design, and in total 27 experiments are performed. Empirical relation between input and output response is developed using statistical software and analysis of variance (ANOVA) at 95% confidence level to check the adequacy. The main effect and interaction effect of input variables on output response are also studied.

Doppler indexes of left ventricular systolic and diastolic flow and central pulse pressure in relation to renal resistive index.

PubMed

Kuznetsova, Tatiana; Cauwenberghs, Nicholas; Knez, Judita; Thijs, Lutgarde; Liu, Yan-Ping; Gu, Yu-Mei; Staessen, Jan A

2015-04-01

The cardio-renal interaction occurs via hemodynamic and humoral factors. Noninvasive assessment of renal hemodynamics is currently possible by assessment of renal resistive index (RRI) derived from intrarenal Doppler arterial waveforms as ((peak systolic velocity - end-diastolic velocity)/peak systolic velocity). Limited information is available regarding the relationship between RRI and cardiac hemodynamics. We investigated these associations in randomly recruited subjects from a general population. In 171 participants (48.5% women; mean age, 52.2 years), using pulsed wave Doppler, we measured RRI (mean, 0.60) and left ventricular outflow tract (LVOT) and transmitral (E and A) blood flow peak velocities and its velocity time integrals (VTI). Using carotid applanation tonometry, we measured central pulse pressure and arterial stiffness indexes such as augmentation pressure and carotid-femoral pulse wave velocity. In stepwise regression analysis, RRI independently and significantly increased with female sex, age, body weight, brachial pulse pressure, and use of β-blockers, whereas it decreased with body height and mean arterial pressure. In multivariable-adjusted models with central pulse pressure and arterial stiffness indexes as the explanatory variables, we observed a significant and positive correlation of RRI only with central pulse pressure (P < 0.0001). Among the Doppler indexes of left ventricular blood flow, RRI was significantly and positively associated with LVOT and E peak velocities (P ≤ 0.012) and VTIs (P ≤ 0.010). We demonstrated that in unselected subjects RRI was significantly associated with central pulse pressure and left ventricular systolic and diastolic Doppler blood flow indexes. Our findings imply that in addition to the anthropometric characteristics, cardiac hemodynamic factors influence the intrarenal arterial Doppler waveform patterns. © American Journal of Hypertension, Ltd 2014. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

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.

Ultrapulse welding: A new joining technique. [for automotive industry

NASA Technical Reports Server (NTRS)

Anderson, D. G.

1972-01-01

The ultrapulse process is a resistance welding process that utilizes unidirectional current of high magnitude for a very short time with a precisely controlled dynamic force pulse. Peak currents of up to 220,000 amperes for two to ten milliseconds are used with synchronized force pulses of up to nine thousand pounds. The welding current passing through the relatively high resistance of the interface between the parts that are being joined results in highly localized heating. Described is the UPW process as it applies to the automotive industry.

Performance of the LANSCE H^- Source and Low Energy Transport at Higher Peak Current

NASA Astrophysics Data System (ADS)

Pillai, Chandra; Stevens, Ralph; Fitzgerald, Daniel; Garnett, Robert; Ingllas, William; Merrill, Frank; Rybarcyk, Larry; Sander, Oscar

1997-05-01

The Los Alamos Neutron Science Center (LANSCE) 800 MeV linac facility uses a multicusp field, surface ion source to produce H^- beam for delivery to the Proton Storage Ring (PSR) and to the Weapon Neutron Research (WNR) areas. The source typically operates at a duty factor of 9.4% delivering a peak current of about 14 mA into the 750 keV LEBT. Each beam macropulse is chopped to create a sequence of 360 ns pulse, each with a 100 ns ``extraction notch'' for injection into PSR. The average current delivered to the short-pulse spallation target is nominally 70μA. One goal of the present PSR upgrade projects is an increase in the average beam current to 200μA. This will be accomplished by a combination of increased repetition rate (to 30 Hz), upgraded PSR bunchers, and a brighter H^- ion source that will produce higher peak current with lower beam emittance. The present ion source and injector system was studied to investigate the beam qualities of the source and the performance of the low energy transpot. The performance of the ion source at higher currents and the change in beam parameters in the low energy transport compared to those in the standard source conditions will be presented.

Transverse beam motion on the second axis of the dual axis radiographic hydrodynamic test facility

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

Caporaso, G J; Chen, Y J; Fawley, W M

1999-03-23

The accelerator on the second-axis of the Dual-Axis Radiographic Hydrodynamic Test (DARHT-II) facility will generate a 20 MeV, 2-4 kA, 2 µs long electron beam with an energy variation {<=} ± 0.5%. Four short current pulses with various lengths will be selected out of this 2 µs long current pulse and delivered to an x-ray converter target. The DARHT-II radiographic resolution requires these electron pulses to be focused to sub-millimeter spots on Bremsstrahlung targets with peak-to-peak transverse beam motion less than a few hundred microns. We have modeled the transverse beam motion, including the beam breakup instability, corkscrew motion, transversemore » resistive wall instability and beam induced transverse deflection in the kicker system, from the DARHT-II injector exit to the x-ray converter target. Simulations show that the transverse motion at the x-ray converters satisfies the DARHT-II radiographic requirements.« less

An innovative high-power constant-current pulsed-arc power-supply for a high-density pulsed-arc-plasma ion-source using a LaB6-filament.

PubMed

Ueno, A; Oguri, H; Ikegami, K; Namekawa, Y; Ohkoshi, K; Tokuchi, A

2010-02-01

An innovative high-power constant-current (CC) pulsed-arc (PA) power-supply (PS) indispensable for a high-density PA plasma ion-source using a lanthanum hexaboride (LaB(6)) filament was devised by combining a constant-voltage (CV) PA-PS, which is composed of an insulated gate bipolar transistor (IGBT) switch, a CV direct-current (dc) PS and a 270 mF capacitor with a CC-PA-PS, which is composed of an IGBT-switch, a CC-dc-PS and a 400 microH inductor, through the inductor. The hybrid-CC-PA-PS succeeded in producing a flat arc-pulse with a peak power of 56 kW (400 A x 140 V) and a duty factor of more than 1.5% (600 micros x 25 Hz) for Japan Proton Accelerator Research Complex (J-PARC) H(-) ion-source stably. It also succeeded in shortening the 99% rising-time of the arc-pulse-current to about 20 micros and tilting up or down the arc-pulse-current arbitrarily and almost linearly by changing the setting voltage of its CV-dc-PS.

Ion heating and characteristics of ST plasma used by double-pulsing CHI on HIST

NASA Astrophysics Data System (ADS)

Hanao, Takafumi; Hirono, Hidetoshi; Hyobu, Takahiro; Ito, Kengo; Matsumoto, Keisuke; Nakayama, Takashi; Oki, Nobuharu; Kikuchi, Yusuke; Fukumoto, Naoyuki; Nagata, Masayoshi

2013-10-01

Multi-pulsing Coaxial Helicity Injection (M-CHI) is an efficient current drive and sustainment method used in spheromak and spherical torus (ST). We have observed plasma current/flux amplification by double pulsing CHI. Poloidal ion temperature measured by Ion Doppler Spectrometer (IDS) has a peak at plasma core region. In this region, radial electric field has a negative peak. At more inboard side that is called separatrix between closed flux region and inner open flux region, poloidal flow has a large shear and radial electric field changes the polarity. After the second CHI pulse, we observed sharp and rapid ion heating at plasma core region and separatrix. In this region, the poloidal ion temperature is selective heating because electron temperature is almost uniform. At this time, flow shear become larger and radial electric field is amplified at separatorix. These effects produce direct heating of ion through the viscous flow damping. Furthermore, we observed decrease of electron density at separatrix. Decreased density makes Hall dynamo electric field as two-fluid effect. When the ion temperature is increasing, dynamo electric field is observed at separatrix. It may have influence with the ion heating. We will discuss characteristic of double pulsing CHI driven ST plasmas and correlation of direct heating of ion with dynamo electric field and any other parameters.

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.

A Study of Applying Pulsed Remote Field Eddy Current in Ferromagnetic Pipes Testing

PubMed Central

Luo, Qingwang; Shi, Yibing; Wang, Zhigang; Zhang, Wei; Li, Yanjun

2017-01-01

Pulsed Remote Field Eddy Current Testing (PRFECT) attracts the attention in the testing of ferromagnetic pipes because of its continuous spectrum. This paper simulated the practical PRFECT of pipes by using ANSYS software and employed Least Squares Support Vector Regression (LSSVR) to extract the zero-crossing time to analyze the pipe thickness. As a result, a secondary peak is found in zero-crossing time when transmitter passed by a defect. The secondary peak will lead to wrong quantification and the localization of defects, especially when defects are found only at the transmitter location. Aiming to eliminate the secondary peaks, double sensing coils are set in the transition zone and Wiener deconvolution filter is applied. In the proposed method, position dependent response of the differential signals from the double sensing coils is calibrated by employing zero-mean normalization. The methods proposed in this paper are validated by analyzing the simulation signals and can improve the practicality of PRFECT of ferromagnetic pipes. PMID:28475141

A Study of Applying Pulsed Remote Field Eddy Current in Ferromagnetic Pipes Testing.

PubMed

Luo, Qingwang; Shi, Yibing; Wang, Zhigang; Zhang, Wei; Li, Yanjun

2017-05-05

Pulsed Remote Field Eddy Current Testing (PRFECT) attracts the attention in the testing of ferromagnetic pipes because of its continuous spectrum. This paper simulated the practical PRFECT of pipes by using ANSYS software and employed Least Squares Support Vector Regression (LSSVR) to extract the zero-crossing time to analyze the pipe thickness. As a result, a secondary peak is found in zero-crossing time when transmitter passed by a defect. The secondary peak will lead to wrong quantification and the localization of defects, especially when defects are found only at the transmitter location. Aiming to eliminate the secondary peaks, double sensing coils are set in the transition zone and Wiener deconvolution filter is applied. In the proposed method, position dependent response of the differential signals from the double sensing coils is calibrated by employing zero-mean normalization. The methods proposed in this paper are validated by analyzing the simulation signals and can improve the practicality of PRFECT of ferromagnetic pipes.

Two Ca current components of the receptor current in the electroreceptors of the marine catfish Plotosus.

PubMed

Sugawara, Y

1989-02-01

In the isolated sensory epithelium of the Plotosus electroreceptor, the receptor current has been dissected into inward Ca current, ICa, and superimposed outward transient of Ca-gated K current, IK(Ca). In control saline (170 mM/liter Na), with IK(Ca) abolished by K blockers, ICa declined in two successive exponential phases with voltage-dependent time constants. Double-pulse experiments revealed that the test ICa was partially depressed by prepulses, maximally near voltage levels for the control ICa maximum, which suggests current-dependent inactivation. In low Na saline (80 mM/liter), ICa declined in a single phase with time constants similar to those of the slower phase in control saline. The test ICa was then unaffected by prepulses. The implied presence of two Ca current components, the fast and slow ICa's, were further examined. In control saline, the PSP externally recorded from the afferent nerve showed a fast peak and a slow tonic phase. The double-pulse experiments revealed that IK(Ca) and the peak PSP were similarly depressed, i.e., secondarily to inactivation of the peak current. The steady inward current, however, was unaffected by prolonged prepulses that were stepped to 0 mV, the in situ DC level. Therefore, the fast ICa seems to initiate IK(Ca) and phasic release of transmitter, which serves for phasic receptor responses. The slow ICa may provide persistent active current, which has been shown to maintain tonic receptor operation.

Modular compact solid-state modulators for particle accelerators

NASA Astrophysics Data System (ADS)

Zavadtsev, A. A.; Zavadtsev, D. A.; Churanov, D. V.

2017-12-01

The building of the radio frequency (RF) particle accelerator needs high-voltage pulsed modulator as a power supply for klystron or magnetron to feed the RF accelerating system. The development of a number of solid-state modulators for use in linear accelerators has allowed to develop a series of modular IGBT based compact solid-state modulators with different parameters. This series covers a wide range of needs in accelerator technology to feed a wide range of loads from the low power magnetrons to powerful klystrons. Each modulator of the series is built on base of a number of unified solid-state modules connected to the pulse transformer, and covers a wide range of modulators: voltage up to 250 kV, a peak current up to 250 A, average power up to 100 kW and the pulse duration up to 20 μsec. The parameters of the block with an overall dimensions 880×540×250 mm are: voltage 12 kV, peak current 1600 A, pulse duration 20 μsec, average power 10 kW with air-cooling and 40 kW with liquidcooling. These parameters do not represent a physical limit, and modulators to parameters outside these ranges can be created on request.

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.

Influence of Substrate, Additives, and Pulse Parameters on Electrodeposition of Gold Nanoparticles from Potassium Dicyanoaurate

NASA Astrophysics Data System (ADS)

Vahdatkhah, Parisa; Sadrnezhaad, Sayed Khatiboleslam

2015-12-01

Gold nanoparticles (AuNPs) of less than 50 nm diameter were electrodeposited from cyanide solution by pulsating electric current on modified copper and indium tin oxide (ITO) films coated on glass. Morphology, size, and composition of the deposited AuNPs were studied by X-ray photoelectron spectroscopy, atomic force microscopy, and field emission scanning electron microscopy. Effects of peak current density, pulse frequency, potassium iodide and cysteine on grain size, and morphology of the AuNPs were determined. Experiments showed that cathode current efficiency increases with the pulse frequency and the iodide ion. Size of the AuNPs increased with the current density. The number of nucleation sites was larger on ITO than on Cu layer; while the average diameter of the crystallites on ITO was smaller than on Cu layer.

Towards sub-100 fs multi-GW pulses directly emitted from a Thulium-doped fiber CPA system

NASA Astrophysics Data System (ADS)

Gaida, C.; Gebhardt, M.; Stutzki, F.; Jauregui, C.; Limpert, J.; Tünnermann, A.

2017-02-01

Experimental demonstrations of Tm-doped fiber amplifiers (typically in CW- or narrow-band pulsed operation) span a wavelength range going from about 1700 nm to well beyond 2000 nm. Thus, it should be possible to obtain a bandwidth of more than 100 nm, which would enable sub-100 fs pulse duration in an efficient, linear amplification scheme. In fact, this would allow the emission of pulses with less than 20 optical cycles directly from a Tm-doped fiber system, something that seems to be extremely challenging for other dopants in a fused silica fiber. In this contribution, we summarize the current development of our Thulium-doped fiber CPA system, demonstrate preliminary experiments for further scaling and discuss important design factors for the next steps. The current single-channel laser system presented herein delivers a pulse-peak power of 2 GW and a nearly transform-limited pulse duration of 200 fs in combination with 28.7 W of average power. Special care has been taken to reduce the detrimental impact of water vapor absorption by placing the whole system in a dry atmosphere housing (<0.1% rel. humidity) and by using a sufficiently long wavelength (1920-1980 nm). The utilization of a low-pressure chamber in the future will allow for the extension of the amplification bandwidth. Preliminary experiments demonstrating a broader amplification bandwidth that supports almost 100 fs pulse duration and average power scaling to < 100W have already been performed. Based on these results, a Tm-doped fiber CPA with sub-100 fs pulse duration, multi-GW pulse peak power and >100 W average power can be expected in the near future.

Ferroelectric Emission Cathodes for Low-Power Electric Propulsion

NASA Technical Reports Server (NTRS)

Kovaleski, Scott D.; Burke, Tom (Technical Monitor)

2002-01-01

Low- or no-flow electron emitters are required for low-power electric thrusters, spacecraft plasma contactors, and electrodynamic tether systems to reduce or eliminate the need for propellant/expellant. Expellant-less neutralizers can improve the viability of very low-power colloid thrusters, field emission electric propulsion devices, ion engines, Hall thrusters, and gridded vacuum arc thrusters. The NASA Glenn Research Center (GRC) is evaluating ferroelectric emission (FEE) cathodes as zero expellant flow rate cathode sources for the applications listed above. At GRC, low voltage (100s to approx. 1500 V) operation of FEE cathodes is examined. Initial experiments, with unipolar, bipolar, and RF burst applied voltage, have produced current pulses 250 to 1000 ns in duration with peak currents of up to 2 A at voltages at or below 1500 V. In particular, FEE cathodes driven by RF burst voltages from 1400 to 2000 V peak to peak, at burst frequencies from 70 to 400 kHz, emitted average current densities from 0.1 to 0.7 A/sq cm. Pulse repeatability as a function of input voltage has been initially established. Reliable emission has been achieved in air background at pressures as high as 10(exp -6) Torr.

Characteristics and instabilities of mode-locked quantum-dot diode lasers.

PubMed

Li, Yan; Lester, Luke F; Chang, Derek; Langrock, Carsten; Fejer, M M; Kane, Daniel J

2013-04-08

Current pulse measurement methods have proven inadequate to fully understand the characteristics of passively mode-locked quantum-dot diode lasers. These devices are very difficult to characterize because of their low peak powers, high bandwidth, large time-bandwidth product, and large timing jitter. In this paper, we discuss the origin for the inadequacies of current pulse measurement techniques while presenting new ways of examining frequency-resolved optical gating (FROG) data to provide insight into the operation of these devices. Under the assumptions of a partial coherence model for the pulsed laser, it is shown that simultaneous time-frequency characterization is a necessary and sufficient condition for characterization of mode-locking. Full pulse characterization of quantum dot passively mode-locked lasers (QD MLLs) was done using FROG in a collinear configuration using an aperiodically poled lithium niobate waveguide-based FROG pulse measurement system.

A 7.8 kV nanosecond pulse generator with a 500 Hz repetition rate

NASA Astrophysics Data System (ADS)

Lin, M.; Liao, H.; Liu, M.; Zhu, G.; Yang, Z.; Shi, P.; Lu, Q.; Sun, X.

2018-04-01

Pseudospark switches are widely used in pulsed power applications. In this paper, we present the design and performance of a 500 Hz repetition rate high-voltage pulse generator to drive TDI-series pseudospark switches. A high-voltage pulse is produced by discharging an 8 μF capacitor through a primary windings of a setup isolation transformer using a single metal-oxide-semiconductor field-effect transistor (MOSFET) as a control switch. In addition, a self-break spark gap is used to steepen the pulse front. The pulse generator can deliver a high-voltage pulse with a peak trigger voltage of 7.8 kV, a peak trigger current of 63 A, a full width at half maximum (FWHM) of ~30 ns, and a rise time of 5 ns to the trigger pin of the pseudospark switch. During burst mode operation, the generator achieved up to a 500 Hz repetition rate. Meanwhile, we also provide an AC heater power circuit for heating a H2 reservoir. This pulse generator can be used in circuits with TDI-series pseudospark switches with either a grounded cathode or with a cathode electrically floating operation. The details of the circuits and their implementation are described in the paper.

FAST TRACK COMMUNICATION: Asymmetric surface barrier discharge plasma driven by pulsed 13.56 MHz power in atmospheric pressure air

NASA Astrophysics Data System (ADS)

Dedrick, J.; Boswell, R. W.; Charles, C.

2010-09-01

Barrier discharges are a proven method of generating plasmas at high pressures, having applications in industrial processing, materials science and aerodynamics. In this paper, we present new measurements of an asymmetric surface barrier discharge plasma driven by pulsed radio frequency (rf 13.56 MHz) power in atmospheric pressure air. The voltage, current and optical emission of the discharge are measured temporally using 2.4 kVp-p (peak to peak) 13.56 MHz rf pulses, 20 µs in duration. The results exhibit different characteristics to plasma actuators, which have similar discharge geometry but are typically driven at frequencies of up to about 10 kHz. However, the electrical measurements are similar to some other atmospheric pressure, rf capacitively coupled discharge systems with symmetric electrode configurations and different feed gases.

On Both Spatial And Velocity Distribution Of Sputtered Particles In Magnetron Discharge

NASA Astrophysics Data System (ADS)

Vitelaru, C.; Pohoata, V.; Tiron, V.; Costin, C.; Popa, G.

2012-12-01

The kinetics of the sputtered atoms from the metallic target as well as the time-space distribution of the argon metastable atoms have been investigated for DC and high power pulse magnetron discharge by means of Tunable Diode - Laser Absorption Spectroscopy (TD-LAS) and Tunable Diode - Laser Induced Fluorescence (TD-LIF). The discharge was operated in argon (5-30 mTorr) with two different targets, tungsten and aluminum, for pulses of 1 to 20 μs, at frequencies of 0.2 to 1 kHz. Peak current intensity of ~100 A has been attained at cathode peak voltage of ~1 kV. The mean velocity distribution functions and particle fluxes of the sputtered metal atoms, in parallel and perpendicular direction to the target, have been obtained and compared for DC and pulse mode.

Nondestructive evaluation of fatigue damage on low alloy steel by magnetomechanical acoustic emission technique

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

Hiraasawa, T.; Saito, K.; Komura, I.

1995-08-01

A modified magnetomechanical acoustic emission (MAE) technique, denoted Pulse-MAE, in which the magnetization by current pulse was adopted, was newly developed and its applicability was assessed for the nondestructive detection and evaluation of fatigue damage in reactor pressure vessel steel SFVV2 and SA508 class2. MAE signals were measured with both conventional MAE and Pulse-MAE technique for fatigue damaged specimens having several damage fractions, and peak voltage ratio Vp/Vo, where Vp and Vo were the peak voltage for damaged and undamaged specimen respectively, was chosen as a measure. Vp/Vo was found to increase monotonously at the early stage of fatigue processmore » and the rate of increase in Vp/Vo during the fatigue process was larger in Pulse-MAE than conventional MAE. Therefore, Pulse-MAE technique proved to have higher sensitivity for the detection of fatigue damage compared with the conventional MAE and to have the potential of a practical technique for nondestructive detection and evaluation of fatigue damage in actual components.« less

Direct electron-impact mechanism of excitation of mercury monobromide in a double-pulse dielectric-barrier-discharge HgBr lamp

NASA Astrophysics Data System (ADS)

Datsyuk, V. V.; Izmailov, I. A.; Naumov, V. V.; Kochelap, V. A.

2016-08-01

In a nonequlibrium plasma of a gas-discharge HgBr lamp, the terminal electronic state of the HgBr(B-X) radiative transition with a peak wavelength of 502 nm remains populated for a relatively long time and is repeatedly excited to the B state in collisions with plasma electrons. This transfer of the HgBr molecules from the ground state X to the excited state B is the main mechanism of formation of the light-emitting molecules especially when the lamp is excited by double current pulses. According to our simulations, due to the electron-induced transitions between HgBr(X) and HgBr(B), the output characteristics of the DBD lamp operating in a double-pulse regime are better than those of the lamp operating in a single-pulse regime. In the considered case, the peak power is calculated to increase by a factor of about 2 and the lamp efficiency increases by about 50%.

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.

A large-area diffuse air discharge plasma excited by nanosecond pulse under a double hexagon needle-array electrode.

PubMed

Liu, Zhi-Jie; Wang, Wen-Chun; Yang, De-Zheng; Wang, Sen; Zhang, Shuai; Tang, Kai; Jiang, Peng-Chao

2014-01-01

A large-area diffuse air discharge plasma excited by bipolar nanosecond pulse is generated under a double hexagon needle-array electrode at atmospheric pressure. The images of the diffuse discharge, electric characteristics, and the optical emission spectra emitted from the diffuse air discharge plasma are obtained. Based on the waveforms of pulse voltage and current, the power consumption, and the power density of the diffuse air discharge plasma are investigated under different pulse peak voltages. The electron density and the electron temperature of the diffuse plasma are estimated to be approximately 1.42×10(11) cm(-3) and 4.4 eV, respectively. The optical emission spectra are arranged to determine the rotational and vibrational temperatures by comparing experimental with simulated spectra. Meanwhile, the rotational and vibrational temperatures of the diffuse discharge plasma are also discussed under different pulse peak voltages and pulse repetition rates, respectively. In addition, the diffuse air discharge plasma can form an area of about 70×50 mm(2) on the surface of dielectric layer and can be scaled up to the required size. Crown Copyright © 2013. Published by Elsevier B.V. All rights reserved.

Design of a variable width pulse generator feasible for manual or automatic control

NASA Astrophysics Data System (ADS)

Vegas, I.; Antoranz, P.; Miranda, J. M.; Franco, F. J.

2017-01-01

A variable width pulse generator featuring more than 4-V peak amplitude and less than 10-ns FWHM is described. In this design the width of the pulses is controlled by means of the control signal slope. Thus, a variable transition time control circuit (TTCC) is also developed, based on the charge and discharge of a capacitor by means of two tunable current sources. Additionally, it is possible to activate/deactivate the pulses when required, therefore allowing the creation of any desired pulse pattern. Furthermore, the implementation presented here can be electronically controlled. In conclusion, due to its versatility, compactness and low cost it can be used in a wide variety of applications.

New laser glass for short pulsed laser applications: the BLG80 (Conference Presentation)

NASA Astrophysics Data System (ADS)

George, Simi A.

2017-03-01

For achieving highest peak powers in a solid state laser (SSL) system, significant energy output and short pulses are necessary. For mode-locked lasers, it is well-known from the Fourier theorem that the largest gain bandwidths produce the narrowest pulse-widths; thus are transform limited. For an inhomogeneously broadened line width of a laser medium, if the intensity of pulses follow a Gaussian function, then the resulting mode-locked pulse will have a Gaussian shape with the emission bandwidth/pulse duration relationship of pulse ≥ 0.44?02/c. Thus, for high peak power SSL systems, laser designers incorporate gain materials capable of broad emission bandwidths. Available energy outputs from a phosphate glass host doped with rare-earth ions are unparalleled. Unfortunately, the emission bandwidths achievable from glass based gain materials are typically many factors smaller when compared to the Ti:Sapphire crystal. In order to overcome this limitation, a hybrid "mixed" laser glass amplifier - OPCPA approach was developed. The Texas petawatt laser that is currently in operation at the University of Texas-Austin and producing high peak powers uses this hybrid architecture. In this mixed-glass laser design, a phosphate and a silicate glass is used in series to achieve a broader bandwidth required before compression. Though proven, this technology is still insufficient for the future compact petawatt and exawatt systems capable of producing high energies and shorter pulse durations. New glasses with bandwidths that are two and three times larger than what is now available from glass hosts is needed if there is to be an alternative to Ti:Sapphire for laser designers. In this paper, we present new materials that may meet the necessary characteristics and demonstrate the laser and emission characteristics these through the internal and external studies.

Terahertz emission from ultrafast ionizing air in symmetry-broken laser fields

NASA Astrophysics Data System (ADS)

Kim, Ki-Yong; Glownia, James H.; Taylor, Antoinette J.; Rodriguez, George

2007-04-01

A transient photocurrent model is developed to explain coherent terahertz emission from air irradiated by a symmetry-broken laser field composed of the fundamental and its second harmonic laser pulses. When the total laser field is asymmetric across individual optical cycles, a nonvanishing electron current surge can arise during optical field ionization of air, emitting a terahertz electromagnetic pulse. Terahertz power scalability is also investigated, and with optical pump energy of tens of millijoules per pulse, peak terahertz field strengths in excess of 150 kV/cm are routinely produced.

Terahertz emission from ultrafast ionizing air in symmetry-broken laser fields.

PubMed

Kim, Ki-Yong; Glownia, James H; Taylor, Antoinette J; Rodriguez, George

2007-04-16

A transient photocurrent model is developed to explain coherent terahertz emission from air irradiated by a symmetry-broken laser field composed of the fundamental and its second harmonic laser pulses. When the total laser field is asymmetric across individual optical cycles, a nonvanishing electron current surge can arise during optical field ionization of air, emitting a terahertz electromagnetic pulse. Terahertz power scalability is also investigated, and with optical pump energy of tens of millijoules per pulse, peak terahertz field strengths in excess of 150 kV/cm are routinely produced.

Intense ion beam generator

DOEpatents

Humphries, Jr., Stanley; Sudan, Ravindra N.

1977-08-30

Methods and apparatus for producing intense megavolt ion beams are disclosed. In one embodiment, a reflex triode-type pulsed ion accelerator is described which produces ion pulses of more than 5 kiloamperes current with a peak energy of 3 MeV. In other embodiments, the device is constructed so as to focus the beam of ions for high concentration and ease of extraction, and magnetic insulation is provided to increase the efficiency of operation.

Correcting for strong eddy current induced B0 modulation enables two-spoke RF pulse design with parallel transmission: demonstration at 9.4T in the human brain.

PubMed

Wu, Xiaoping; Adriany, Gregor; Ugurbil, Kamil; Van de Moortele, Pierre-Francois

2013-01-01

Successful implementation of homogeneous slice-selective RF excitation in the human brain at 9.4T using 16-channel parallel transmission (pTX) is demonstrated. A novel three-step pulse design method incorporating fast real-time measurement of eddy current induced B0 variations as well as correction of resulting phase errors during excitation is described. To demonstrate the utility of the proposed method, phantom and in-vivo experiments targeting a uniform excitation in an axial slice were conducted using two-spoke pTX pulses. Even with the pre-emphasis activated, eddy current induced B0 variations with peak-to-peak values greater than 4 kHz were observed on our system during the rapid switches of slice selective gradients. This large B0 variation, when not corrected, resulted in drastically degraded excitation fidelity with the coefficient of variation (CV) of the flip angle calculated for the region of interest being large (~ 12% in the phantom and ~ 35% in the brain). By comparison, excitation fidelity was effectively restored, and satisfactory flip angle uniformity was achieved when using the proposed method, with the CV value reduced to ~ 3% in the phantom and ~ 8% in the brain. Additionally, experimental results were in good agreement with the numerical predictions obtained from Bloch simulations. Slice-selective flip angle homogenization in the human brain at 9.4T using 16-channel 3D spoke pTX pulses is achievable despite of large eddy current induced excitation phase errors; correcting for the latter was critical in this success.

Drilling of Hybrid Titanium Composite Laminate (HTCL) with Electrical Discharge Machining.

PubMed

Ramulu, M; Spaulding, Mathew

2016-09-01

An experimental investigation was conducted to determine the application of die sinker electrical discharge machining (EDM) as it applies to a hybrid titanium thermoplastic composite laminate material. Holes were drilled using a die sinker EDM. The effects of peak current, pulse time, and percent on-time on machinability of hybrid titanium composite material were evaluated in terms of material removal rate (MRR), tool wear rate, and cut quality. Experimental models relating each process response to the input parameters were developed and optimum operating conditions with a short cutting time, achieving the highest workpiece MRR, with very little tool wear were determined to occur at a peak current value of 8.60 A, a percent on-time of 36.12%, and a pulse time of 258 microseconds. After observing data acquired from experimentation, it was determined that while use of EDM is possible, for desirable quality it is not fast enough for industrial application.

Drilling of Hybrid Titanium Composite Laminate (HTCL) with Electrical Discharge Machining

PubMed Central

Ramulu, M.; Spaulding, Mathew

2016-01-01

An experimental investigation was conducted to determine the application of die sinker electrical discharge machining (EDM) as it applies to a hybrid titanium thermoplastic composite laminate material. Holes were drilled using a die sinker EDM. The effects of peak current, pulse time, and percent on-time on machinability of hybrid titanium composite material were evaluated in terms of material removal rate (MRR), tool wear rate, and cut quality. Experimental models relating each process response to the input parameters were developed and optimum operating conditions with a short cutting time, achieving the highest workpiece MRR, with very little tool wear were determined to occur at a peak current value of 8.60 A, a percent on-time of 36.12%, and a pulse time of 258 microseconds. After observing data acquired from experimentation, it was determined that while use of EDM is possible, for desirable quality it is not fast enough for industrial application. PMID:28773866

Dosimetric response for crystalline and nanostructured aluminium oxide to a high-current pulse electron beam.

PubMed

Nikiforov, S V; Kortov, V S

2014-11-01

The main thermoluminescent (TL) and dosimetric properties of the detectors based on anion-defective crystalline and nanostructured aluminium oxide after exposure to a high-current pulse electron beam are studied. TL peaks associated with deep-trapping centres are registered. It is shown that the use of deep-trap TL at 200-600°С allows registering absorbed doses up to 750 kGy for single-crystalline detectors and those up to 6 kGy for nanostructured ones. A wide range of the doses registered, high reproducibility of the TL signal and low fading contribute to a possibility of using single-crystalline and nanostructured aluminium oxide for the dosimetry of high-current pulse electron beams. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Influence of angular acceleration-deceleration pulse shapes on regional brain strains.

PubMed

Yoganandan, Narayan; Li, Jianrong; Zhang, Jiangyue; Pintar, Frank A; Gennarelli, Thomas A

2008-07-19

Recognizing the association of angular loading with brain injuries and inconsistency in previous studies in the application of the biphasic loads to animal, physical, and experimental models, the present study examined the role of the acceleration-deceleration pulse shapes on region-specific strains. An experimentally validated two-dimensional finite element model representing the adult male human head was used. The model simulated the skull and falx as a linear elastic material, cerebrospinal fluid as a hydrodynamic material, and cerebrum as a linear viscoelastic material. The angular loading matrix consisted coronal plane rotation about a center of rotation that was acceleration-only (4.5 ms duration, 7.8 krad/s/s peak), deceleration-only (20 ms, 1.4 krad/s/s peak), acceleration-deceleration, and deceleration-acceleration pulses. Both biphasic pulses had peaks separated by intervals ranging from 0 to 25 ms. Principal strains were determined at the corpus callosum, base of the postcentral sulcus, and cerebral cortex of the parietal lobe. The cerebrum was divided into 17 regions and peak values of average maximum principal strains were determined. In all simulations, the corpus callosum responded with the highest strains. Strains were the least under all simulations in the lower parietal lobes. In all regions peak strains were the same for both monophase pulses suggesting that the angular velocity may be a better metric than peak acceleration or deceleration. In contrast, for the biphasic pulse, peak strains were region- and pulse-shape specific. Peak values were lower in both biphasic pulses when there was no time separation between the pulses than the corresponding monophase pulse. Increasing separation time intervals increased strains, albeit non-uniformly. Acceleration followed by deceleration pulse produced greater strains in all regions than the other form of biphasic pulse. Thus, pulse shape appears to have an effect on regional strains in the brain.

Experimental launcher facility - ELF-I: Design and operation

NASA Astrophysics Data System (ADS)

Deis, D. W.; Ross, D. P.

1982-01-01

In order to investigate the general area of ultra-high-current density, high-velocity sliding contacts as applied to electromagnetic launcher armatures, a small experimental launcher, ELF-I, has been developed, and preliminary experiments have been performed. The system uses a 36 kJ, 5 kV capacitor bank as a primary pulse power source. When used in conjunction with a 5-microhenry pulse conditioning coil, a 100-kA peak current and 10-ms-wide pulse is obtained. A three-station 150 kV flash X-ray system is operational for obtaining in-bore photographs of the projectiles. Experimental results obtained for both metal and plasma armatures at sliding velocities of up to 1 km/s are discussed with emphasis on armature-rail interactions.

Role of vanguard counter-potential in terahertz emission due to surface currents explicated by three-dimensional ensemble Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Cortie, D. L.; Lewis, R. A.

2011-10-01

The discovery that short pulses of near-infrared radiation striking a semiconductor may lead to emission of radiation at terahertz frequencies paved the way for terahertz time-domain spectroscopy. Previous modeling has allowed the physical mechanisms to be understood in general terms but it has not fully explored the role of key physical parameters of the emitter material nor has it fully revealed the competing nature of the surface-field and photo-Dember effects. In this context, our purpose has been to more fully explicate the mechanisms of terahertz emission from transient currents at semiconductor surfaces and to determine the criteria for efficient emission. To achieve this purpose we employ an ensemble Monte Carlo simulation in three dimensions. To ground the calculations, we focus on a specific emitter, InAs. We separately vary distinct physical parameters to determine their specific contribution. We find that scattering as a whole has relatively little impact on the terahertz emission. The emission is found to be remarkably resistant to alterations of the dark surface potential. Decreasing the band gap leads to a strong increase in terahertz emission, as does decreasing the electron mass. Increasing the absorption dramatically influences the peak-peak intensity and peak shape. We conclude that increasing absorption is the most direct path to improve surface-current semiconductor terahertz emitters. We find for longer pump pulses that the emission is limited by a newly identified vanguard counter-potential mechanism: Electrons at the leading edge of longer laser pulses repel subsequent electrons. This discovery is the main result of our work.

A closer look at the relationships between meridional mass circulation pulses in the stratosphere and cold air outbreak patterns in northern hemispheric winter

NASA Astrophysics Data System (ADS)

Yu, Yueyue; Cai, Ming; Ren, Rongcai; Rao, Jian

2018-01-01

The relationship between continental-scale cold air outbreaks (CAOs) in the mid-latitudes and pulse signals in the stratospheric mass circulation in Northern Hemisphere winter (December-February) is investigated using ERA-Interim data for the 32 winters from 1979 to 2011. Pulse signals in the stratospheric mass circulation include "PULSE_TOT", "PULSE_W1", and "PULSE_W2" events, defined as a period of stronger meridional mass transport into the polar stratosphere by total flow, wavenumber-1, and wavenumber-2, respectively. Each type of PULSE event occurs on average 4-6 times per winter. A robust relationship is found between two dominant patterns of winter CAOs and PULSE_W1 and PULSE_W2 events. Cold temperature anomalies tend to occur over Eurasia with the other continent anomalously warm during the 2 weeks before the peak dates of PULSE_W1 events, while the opposite temperature anomaly pattern can be found after the peak dates; and during the 1-2 weeks centered on the peak dates of PULSE_W2 events, a higher probability of occurrence of CAOs is found over both continents. These relationships become more robust for PULSE_W1 and PULSE_W2 events of larger peak intensity. PULSE_TOT events are classified into five types, which have a distinct coupling relationship with PULSE_W1 and PULSE_W2 events. The specific pattern of CAOs associated with each type of PULSE_TOT event is found to be a combination of the CAO patterns associated with PULSE_W1 and PULSE_W2 events. The percentage of PULSE_TOT events belonging to the types that are dominated by PULSE_W2 events increases with the peak intensity of PULSE_TOT events. Accordingly, the related CAO pattern is close to that associated with PULSE_W1 for PULSE_TOT events with small-to-medium intensity, but tends to resemble that associated with PULSE_W2 events as the peak intensity of PULSE_TOT events increases.

Homogenization of Vehicle Fleet Frontal Crash Pulses from 2000–2010

PubMed Central

Locey, Caitlin M.; Garcia-Espana, J. Felipe; Toh, Akira; Belwadi, Aditya; Arbogast, Kristy B.; Maltese, Matthew R.

2012-01-01

Full-scale vehicle crash tests are performed globally to assess vehicle structure and restraint system performance. The crash pulse, captured by accelerometers mounted within the occupant compartment, measures the motion of the vehicle during the impact event. From an occupant’s perspective, the crash pulse is the inertial event to which the vehicle’s restraint systems must respond in order to mitigate the forces and accelerations that act on a passenger, and thus reduce injury risk. The objective of this study was to quantify the characteristics of crash pulses for different vehicle types in the contemporary North American fleet, and delineate current trends in crash pulse evolution. NHTSA and Transport Canada crash test databases were queried for full-frontal rigid barrier crash tests of passenger vehicles model year 2000–2010 with impact angle equaling zero degrees. Acceleration-time histories were analyzed for all accelerometers attached to the vehicle structure within the occupant compartment. Custom software calculated the following crash pulse characteristics (CPCs): peak deceleration, time of peak deceleration, onset rate, pulse duration, and change in velocity. Vehicle body types were classified by adapting the Highway Loss Data Institute (HLDI) methodology, and vehicles were assigned a generation start year in place of model year in order to more accurately represent structural change over time. 1094 vehicle crash tests with 2795 individual occupant compartment-mounted accelerometers were analyzed. We found greater peak decelerations and and shorter pulse durations across multiple vehicle types in newer model years as compared to older. For midsize passenger cars, large passenger cars, and large SUVs in 56 km/h rigid barrier tests, maximum deceleration increased by 0.40, 0.96, and 1.57 g/year respectively, and pulse duration decreased by 0.74, 1.87, and 2.51 ms/year. We also found that the crash pulse characteristics are becoming more homogeneous in the modern vehicle fleet; the range of peak deceleration values for all vehicle classes decreased from 17.1 g in 1997–1999 generation start years to 10.7 g in 2009–2010 generation years, and the pulse duration range decreased from 39.5 ms to 13.4 ms for the same generation year groupings. This latter finding suggests that the designs of restraint systems may become more universally applicable across vehicle body types, since the occupant compartment accelerations are not as divergent for newer vehicles. PMID:23169139

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.

Ozone generation in a kHz-pulsed He-O2 capillary dielectric barrier discharge operated in ambient air

NASA Astrophysics Data System (ADS)

Sands, Brian L.; Ganguly, Biswa N.

2013-12-01

The generation of reactive oxygen species using nonequilibrium atmospheric pressure plasma jet devices has been a subject of recent interest due to their ability to generate localized concentrations from a compact source. To date, such studies with plasma jet devices have primarily utilized radio-frequency excitation. In this work, we characterize ozone generation in a kHz-pulsed capillary dielectric barrier discharge configuration comprised of an active discharge plasma jet operating in ambient air that is externally grounded. The plasma jet flow gas was composed of helium with an admixture of up to 5% oxygen. A unipolar voltage pulse train with a 20 ns pulse risetime was used to drive the discharge at repetition rates between 2-25 kHz. Using UVLED absorption spectroscopy centered at 255 nm near the Hartley-band absorption peak, ozone was detected over 1 cm from the capillary axis. We observed roughly linear scaling of ozone production with increasing pulse repetition rate up to a "turnover frequency," beyond which ozone production steadily dropped and discharge current and 777 nm O(5P→5S°) emission sharply increased. The turnover in ozone production occurred at higher pulse frequencies with increasing flow rate and decreasing applied voltage with a common energy density of 55 mJ/cm3 supplied to the discharge. The limiting energy density and peak ozone production both increased with increasing O2 admixture. The power dissipated in the discharge was obtained from circuit current and voltage measurements using a modified parallel plate dielectric barrier discharge circuit model and the volume-averaged ozone concentration was derived from a 2D ozone absorption measurement. From these measurements, the volume-averaged efficiency of ozone production was calculated to be 23 g/kWh at conditions for peak ozone production of 41 mg/h at 11 kV applied voltage, 3% O2, 2 l/min flow rate, and 13 kHz pulse repetition rate, with 1.79 W dissipated in the discharge.

Acoustic time-of-flight for proton range verification in water

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

Jones, Kevin C.; Avery, Stephen, E-mail: Stephen.A

2016-09-15

Purpose: Measurement of the arrival times of thermoacoustic waves induced by pulsed proton dose depositions (protoacoustics) may provide a proton range verification method. The goal of this study is to characterize the required dose and protoacoustic proton range (distance) verification accuracy in a homogeneous water medium at a hospital-based clinical cyclotron. Methods: Gaussian-like proton pulses with 17 μs widths and instantaneous currents of 480 nA (5.6 × 10{sup 7} protons/pulse, 3.4 cGy/pulse at the Bragg peak) were generated by modulating the cyclotron proton source with a function generator. After energy degradation, the 190 MeV proton pulses irradiated a water phantom,more » and the generated protoacoustic emissions were measured by a hydrophone. The detector position and proton pulse characteristics were varied. The experimental results were compared to simulations. Different arrival time metrics derived from acoustic waveforms were compared, and the accuracy of protoacoustic time-of-flight distance calculations was assessed. Results: A 27 mPa noise level was observed in the treatment room during irradiation. At 5 cm from the proton beam, an average maximum pressure of 5.2 mPa/1 × 10{sup 7} protons (6.1 mGy at the Bragg peak) was measured after irradiation with a proton pulse with 10%–90% rise time of 11 μs. Simulation and experiment arrival times agreed well, and the observed 2.4 μs delay between simulation and experiment is attributed to the difference between the hydrophone’s acoustic and geometric centers. Based on protoacoustic arrival times, the beam axis position was measured to within (x, y) = (−2.0,  0.5) ± 1 mm. After deconvolution of the exciting proton pulse, the protoacoustic compression peak provided the most consistent measure of the distance to the Bragg peak, with an error distribution with mean = − 4.5 mm and standard deviation = 2.0 mm. Conclusions: Based on water tank measurements at a clinical hospital-based cyclotron, protoacoustics is a potential method for measuring the beam’s position (x and y within 2.0 mm) and Bragg peak range (2.0 mm standard deviation), although range verification will require simulation or experimental calibration to remove systematic error. Based on extrapolation, a protoacoustic arrival time reproducibility of 1.5 μs (2.2 mm) is achievable with 2 Gy of total deposited dose. Of the compared methods, deconvolution of the excitation proton pulse is the best technique for extracting protoacoustic arrival times, particularly if there is variation in the proton pulse shape.« less

Acoustic time-of-flight for proton range verification in water.

PubMed

Jones, Kevin C; Vander Stappen, François; Sehgal, Chandra M; Avery, Stephen

2016-09-01

Measurement of the arrival times of thermoacoustic waves induced by pulsed proton dose depositions (protoacoustics) may provide a proton range verification method. The goal of this study is to characterize the required dose and protoacoustic proton range (distance) verification accuracy in a homogeneous water medium at a hospital-based clinical cyclotron. Gaussian-like proton pulses with 17 μs widths and instantaneous currents of 480 nA (5.6 × 10(7) protons/pulse, 3.4 cGy/pulse at the Bragg peak) were generated by modulating the cyclotron proton source with a function generator. After energy degradation, the 190 MeV proton pulses irradiated a water phantom, and the generated protoacoustic emissions were measured by a hydrophone. The detector position and proton pulse characteristics were varied. The experimental results were compared to simulations. Different arrival time metrics derived from acoustic waveforms were compared, and the accuracy of protoacoustic time-of-flight distance calculations was assessed. A 27 mPa noise level was observed in the treatment room during irradiation. At 5 cm from the proton beam, an average maximum pressure of 5.2 mPa/1 × 10(7) protons (6.1 mGy at the Bragg peak) was measured after irradiation with a proton pulse with 10%-90% rise time of 11 μs. Simulation and experiment arrival times agreed well, and the observed 2.4 μs delay between simulation and experiment is attributed to the difference between the hydrophone's acoustic and geometric centers. Based on protoacoustic arrival times, the beam axis position was measured to within (x, y) = (-2.0,  0.5) ± 1 mm. After deconvolution of the exciting proton pulse, the protoacoustic compression peak provided the most consistent measure of the distance to the Bragg peak, with an error distribution with mean = - 4.5 mm and standard deviation = 2.0 mm. Based on water tank measurements at a clinical hospital-based cyclotron, protoacoustics is a potential method for measuring the beam's position (x and y within 2.0 mm) and Bragg peak range (2.0 mm standard deviation), although range verification will require simulation or experimental calibration to remove systematic error. Based on extrapolation, a protoacoustic arrival time reproducibility of 1.5 μs (2.2 mm) is achievable with 2 Gy of total deposited dose. Of the compared methods, deconvolution of the excitation proton pulse is the best technique for extracting protoacoustic arrival times, particularly if there is variation in the proton pulse shape.

Transit time of optical pulses propagating through a finite length medium.

PubMed

Bloemer, Mark; Myneni, Krishna; Centini, Marco; Scalora, Michael; D'Aguanno, Giuseppe

2002-05-01

We present experimental and theoretical results on the transit time of optical pulses propagating through bulk media of finite length, specifically GaAs and silica. The transit time of the peak of the pulse varies with the central wavelength due to the étalon effects caused by the reflectivity at the air/medium boundaries. For transform limited optical pulses, the transit time as a function of wavelength follows the transmittance spectrum, that is, the longest transit time occurs at the transmittance maxima where the cavity dwell time is the longest and the shortest transit time occurs at the transmittance minima. The results are dramatically different for chirped pulses obtained by modulating the injection current of a diode laser. The range in the transit times for chirped pulses is a factor of four times larger compared with transform limited pulses. In addition, the transit time for chirped pulses propagating through the GaAs sample is negative at certain wavelengths. Also, the transmitted pulse is not distorted. Although modulating the injection current of a diode laser is the most common method for generating optical pulses, to our knowledge this is the first reported observation of the transit time of these chirped optical pulses propagating through a simple étalon structure.

Influence of driving frequency on discharge modes in a dielectric-barrier discharge with multiple current pulses

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

Jiang, Weiman; Tang, Jie; Wang, Yishan

2013-07-15

A one-dimensional self-consistent fluid model was employed to investigate the effect of the driving frequency on the discharge modes in atmospheric-pressure argon discharge with multiple current pulses. The discharge mode was discussed in detail not only at current peaks but also between two adjacent peaks. The simulation results show that different transitions between the Townsend and glow modes during the discharge take place with the driving frequency increased. A complicated transition from the Townsend mode, through glow, Townsend, and glow, and finally back to the Townsend one is found in the discharge with the driving frequency of 8 kHz. Theremore » is a tendency of transition from the Townsend to glow mode for the discharge both at the current peaks and troughs with the increasing frequency. The discharge in the half period can all along operate in the glow mode with the driving frequency high enough. This is resulted from the preservation of more electrons in the gas gap and acquisition of more electron energy from the swiftly varying electric field with the increase in driving frequency. Comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increment of the driving frequency allows the plasma chemistry to be enhanced. This electrical characteristic is important for the applications, such as surface treatment and biomedical sterilization.« less

Light sources based on semiconductor current filaments

DOEpatents

Zutavern, Fred J.; Loubriel, Guillermo M.; Buttram, Malcolm T.; Mar, Alan; Helgeson, Wesley D.; O'Malley, Martin W.; Hjalmarson, Harold P.; Baca, Albert G.; Chow, Weng W.; Vawter, G. Allen

2003-01-01

The present invention provides a new type of semiconductor light source that can produce a high peak power output and is not injection, e-beam, or optically pumped. The present invention is capable of producing high quality coherent or incoherent optical emission. The present invention is based on current filaments, unlike conventional semiconductor lasers that are based on p-n junctions. The present invention provides a light source formed by an electron-hole plasma inside a current filament. The electron-hole plasma can be several hundred microns in diameter and several centimeters long. A current filament can be initiated optically or with an e-beam, but can be pumped electrically across a large insulating region. A current filament can be produced in high gain photoconductive semiconductor switches. The light source provided by the present invention has a potentially large volume and therefore a potentially large energy per pulse or peak power available from a single (coherent) semiconductor laser. Like other semiconductor lasers, these light sources will emit radiation at the wavelength near the bandgap energy (for GaAs 875 nm or near infra red). Immediate potential applications of the present invention include high energy, short pulse, compact, low cost lasers and other incoherent light sources.

A z-gradient array for simultaneous multi-slice excitation with a single-band RF pulse.

PubMed

Ertan, Koray; Taraghinia, Soheil; Sadeghi, Alireza; Atalar, Ergin

2018-07-01

Multi-slice radiofrequency (RF) pulses have higher specific absorption rates, more peak RF power, and longer pulse durations than single-slice RF pulses. Gradient field design techniques using a z-gradient array are investigated for exciting multiple slices with a single-band RF pulse. Two different field design methods are formulated to solve for the required current values of the gradient array elements for the given slice locations. The method requirements are specified, optimization problems are formulated for the minimum current norm and an analytical solution is provided. A 9-channel z-gradient coil array driven by independent, custom-designed gradient amplifiers is used to validate the theory. Performance measures such as normalized slice thickness error, gradient strength per unit norm current, power dissipation, and maximum amplitude of the magnetic field are provided for various slice locations and numbers of slices. Two and 3 slices are excited by a single-band RF pulse in simulations and phantom experiments. The possibility of multi-slice excitation with a single-band RF pulse using a z-gradient array is validated in simulations and phantom experiments. Magn Reson Med 80:400-412, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

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.

Design and testing of a magnetically driven implosion peak current diagnostic

NASA Astrophysics Data System (ADS)

Hess, M. H.; Peterson, K. J.; Ampleford, D. J.; Hutsel, B. T.; Jennings, C. A.; Gomez, M. R.; Dolan, D. H.; Robertson, G. K.; Payne, S. L.; Stygar, W. A.; Martin, M. R.; Sinars, D. B.

2018-04-01

A critical component of the magnetically driven implosion experiments at Sandia National Laboratories is the delivery of high-current, 10s of MA, from the Z pulsed power facility to a target. In order to assess the performance of the experiment, it is necessary to measure the current delivered to the target. Recent Magnetized Liner Inertial Fusion (MagLIF) experiments have included velocimetry diagnostics, such as PDV (Photonic Doppler Velocimetry) or Velocity Interferometer System for Any Reflector, in the final power feed section in order to infer the load current as a function of time. However, due to the nonlinear volumetrically distributed magnetic force within a velocimetry flyer, a complete time-dependent load current unfold is typically a time-intensive process and the uncertainties in the unfold can be difficult to assess. In this paper, we discuss how a PDV diagnostic can be simplified to obtain a peak current by sufficiently increasing the thickness of the flyer. This effectively keeps the magnetic force localized to the flyer surface, resulting in fast and highly accurate measurements of the peak load current. In addition, we show the results of experimental peak load current measurements from the PDV diagnostic in recent MagLIF experiments.

Method and apparatus for providing pulse pile-up correction in charge quantizing radiation detection systems

DOEpatents

Britton, Jr., Charles L.; Wintenberg, Alan L.

1993-01-01

A radiation detection method and system for continuously correcting the quantization of detected charge during pulse pile-up conditions. Charge pulses from a radiation detector responsive to the energy of detected radiation events are converted to voltage pulses of predetermined shape whose peak amplitudes are proportional to the quantity of charge of each corresponding detected event by means of a charge-sensitive preamplifier. These peak amplitudes are sampled and stored sequentially in accordance with their respective times of occurrence. Based on the stored peak amplitudes and times of occurrence, a correction factor is generated which represents the fraction of a previous pulses influence on a preceding pulse peak amplitude. This correction factor is subtracted from the following pulse amplitude in a summing amplifier whose output then represents the corrected charge quantity measurement.

A study pertaining to inertial energy storage machine designs for space applications

NASA Technical Reports Server (NTRS)

Zowarka, R. C.

1981-01-01

The preliminary design of a counterrotating fast discharge homopolar generator (HPG) and a counterrotating active rotary flux compressor (CARFC) for space application is reported. The HPG is a counterrotating spool-type homopolar with superconducting field coil excitation. It delivers a 20-ms, 145-kJ pulse to a magnetoplasmahydrodynamic thruster. The peak output current is 42.7 kA at 240 V. After 20 ms the current is 29.7 kA at 167 V. The CARFC delivers ten 50-kJ, 250 microsecond pulses at 50-ms interval to six Xenon flash lamps pumping an Nd glass laser. The flux compressor is counterrotating for torque compensation. Current is started in the machine with a 5-kV, 5-kJ pulse-charged capacitor. Both designs were based upon demonstrated technology. The sensitivity of the designs to technology that may be available in five to ten years was determined.

Generating coherent broadband continuum soft-x-ray radiation by attosecond ionization gating.

PubMed

Pfeifer, Thomas; Jullien, Aurélie; Abel, Mark J; Nagel, Phillip M; Gallmann, Lukas; Neumark, Daniel M; Leone, Stephen R

2007-12-10

The current paradigm of isolated attosecond pulse production requires a few-cycle pulse as the driver for high-harmonic generation that has a cosine-like electric field stabilized with respect to the peak of the pulse envelope. Here, we present simulations and experimental evidence that the production of high-harmonic light can be restricted to one or a few cycles on the leading edge of a laser pulse by a gating mechanism that employs time-dependent ionization of the conversion medium. This scheme enables the generation of broadband and tunable attosecond pulses. Instead of fixing the carrier-envelope phase to produce a cosine driver pulse, the phase becomes a control parameter for the center frequency of the attosecond pulse. A method to assess the multiplicity of attosecond pulses in the pulse train is also presented. The results of our study suggest an avenue towards relaxing the requirement of few-cycle pulses for isolated attosecond pulse generation.

Scaling magnetized liner inertial fusion on Z and future pulsed-power accelerators

DOE PAGES

Slutz, Stephen A.; Stygar, William A.; Gomez, Matthew R.; ...

2016-02-04

In this study, the MagLIF (Magnetized Liner Inertial Fusion) concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] has demonstrated fusion–relevant plasma conditions [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z accelerator with a peak drive current of about 18 MA. We present 2D numerical simulations of the scaling of MagLIF on Z as a function of drive current, preheat energy, and applied magnetic field. The results indicate that deuterium-tritium (DT) fusion yields greater than 100 kJ could be possible on Z when all of these parameters are at the optimum values:more » i.e., peak current = 25 MA, deposited preheat energy = 5 kJ, and B z = 30 T. Much higher yields have been predicted [S. A. Slutz and R. A. Vesey, Phys. Rev. Lett. 108, 025003 (2012)] for MagLIF driven with larger peak currents. Two high performance pulsed-power accelerators (Z300 and Z800) based on linear-transformer-driver technology have been designed [W. A. Stygar et al., Phys. Rev. ST Accel. Beams 18, 110401 (2015)]. The Z300 design would provide 48 MA to a MagLIF load, while Z800 would provide 65 MA. Parameterized Thevenin-equivalent circuits were used to drive a series of 1D and 2D numerical MagLIF simulations with currents ranging from what Z can deliver now to what could be achieved by these conceptual future pulsed-power accelerators. 2D simulations of simple MagLIF targets containing just gaseous DT have yields of 18 MJ for Z300 and 440 MJ for Z800. The 2D simulated yield for Z800 is increased to 7 GJ by adding a layer of frozen DT ice to the inside of the liner.« less

Scaling magnetized liner inertial fusion on Z and future pulsed-power accelerators

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

Slutz, Stephen A.; Stygar, William A.; Gomez, Matthew R.

In this study, the MagLIF (Magnetized Liner Inertial Fusion) concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] has demonstrated fusion–relevant plasma conditions [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z accelerator with a peak drive current of about 18 MA. We present 2D numerical simulations of the scaling of MagLIF on Z as a function of drive current, preheat energy, and applied magnetic field. The results indicate that deuterium-tritium (DT) fusion yields greater than 100 kJ could be possible on Z when all of these parameters are at the optimum values:more » i.e., peak current = 25 MA, deposited preheat energy = 5 kJ, and B z = 30 T. Much higher yields have been predicted [S. A. Slutz and R. A. Vesey, Phys. Rev. Lett. 108, 025003 (2012)] for MagLIF driven with larger peak currents. Two high performance pulsed-power accelerators (Z300 and Z800) based on linear-transformer-driver technology have been designed [W. A. Stygar et al., Phys. Rev. ST Accel. Beams 18, 110401 (2015)]. The Z300 design would provide 48 MA to a MagLIF load, while Z800 would provide 65 MA. Parameterized Thevenin-equivalent circuits were used to drive a series of 1D and 2D numerical MagLIF simulations with currents ranging from what Z can deliver now to what could be achieved by these conceptual future pulsed-power accelerators. 2D simulations of simple MagLIF targets containing just gaseous DT have yields of 18 MJ for Z300 and 440 MJ for Z800. The 2D simulated yield for Z800 is increased to 7 GJ by adding a layer of frozen DT ice to the inside of the liner.« less

Correcting for Strong Eddy Current Induced B0 Modulation Enables Two-Spoke RF Pulse Design with Parallel Transmission: Demonstration at 9.4T in the Human Brain

PubMed Central

Wu, Xiaoping; Adriany, Gregor; Ugurbil, Kamil; Van de Moortele, Pierre-Francois

2013-01-01

Successful implementation of homogeneous slice-selective RF excitation in the human brain at 9.4T using 16-channel parallel transmission (pTX) is demonstrated. A novel three-step pulse design method incorporating fast real-time measurement of eddy current induced B0 variations as well as correction of resulting phase errors during excitation is described. To demonstrate the utility of the proposed method, phantom and in-vivo experiments targeting a uniform excitation in an axial slice were conducted using two-spoke pTX pulses. Even with the pre-emphasis activated, eddy current induced B0 variations with peak-to-peak values greater than 4 kHz were observed on our system during the rapid switches of slice selective gradients. This large B0 variation, when not corrected, resulted in drastically degraded excitation fidelity with the coefficient of variation (CV) of the flip angle calculated for the region of interest being large (∼12% in the phantom and ∼35% in the brain). By comparison, excitation fidelity was effectively restored, and satisfactory flip angle uniformity was achieved when using the proposed method, with the CV value reduced to ∼3% in the phantom and ∼8% in the brain. Additionally, experimental results were in good agreement with the numerical predictions obtained from Bloch simulations. Slice-selective flip angle homogenization in the human brain at 9.4T using 16-channel 3D spoke pTX pulses is achievable despite of large eddy current induced excitation phase errors; correcting for the latter was critical in this success. PMID:24205098

Field-Oriented Control Of Induction Motors

NASA Technical Reports Server (NTRS)

Burrows, Linda M.; Roth, Mary Ellen; Zinger, Don S.

1993-01-01

Field-oriented control system provides for feedback control of torque or speed or both. Developed for use with commercial three-phase, 400-Hz, 208-V, 5-hp motor. Systems include resonant power supply operating at 20 kHz. Pulse-population-modulation subsystem selects individual pulses of 20-kHz single-phase waveform as needed to synthesize three waveforms of appropriate lower frequency applied to three phase windings of motor. Electric actuation systems using technology currently being built to peak powers of 70 kW. Amplitude of voltage of effective machine-frequency waveform determined by momentary frequency of pulses, while machine frequency determined by rate of repetition of overall temporal pattern of pulses. System enables independent control of both voltage and frequency.

RF synchronized short pulse laser ion source

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

Fuwa, Yasuhiro, E-mail: fuwa@kyticr.kuicr.kyoto-u.ac.jp; Iwashita, Yoshihisa; Tongu, Hiromu

A laser ion source that produces shortly bunched ion beam is proposed. In this ion source, ions are extracted immediately after the generation of laser plasma by an ultra-short pulse laser before its diffusion. The ions can be injected into radio frequency (RF) accelerating bucket of a subsequent accelerator. As a proof-of-principle experiment of the ion source, a RF resonator is prepared and H{sub 2} gas was ionized by a short pulse laser in the RF electric field in the resonator. As a result, bunched ions with 1.2 mA peak current and 5 ns pulse length were observed at themore » exit of RF resonator by a probe.« less

Integrator Circuitry for Single Channel Radiation Detector

NASA Technical Reports Server (NTRS)

Holland, Samuel D. (Inventor); Delaune, Paul B. (Inventor); Turner, Kathryn M. (Inventor)

2008-01-01

Input circuitry is provided for a high voltage operated radiation detector to receive pulses from the detector having a rise time in the range of from about one nanosecond to about ten nanoseconds. An integrator circuit, which utilizes current feedback, receives the incoming charge from the radiation detector and creates voltage by integrating across a small capacitor. The integrator utilizes an amplifier which closely follows the voltage across the capacitor to produce an integrator output pulse with a peak value which may be used to determine the energy which produced the pulse. The pulse width of the output is stretched to approximately 50 to 300 nanoseconds for use by subsequent circuits which may then use amplifiers with lower slew rates.

A photon-counting photodiode array detector for far ultraviolet (FUV) astronomy

NASA Technical Reports Server (NTRS)

Hartig, G. F.; Moos, H. W.; Pembroke, R.; Bowers, C.

1982-01-01

A compact, stable, single-stage intensified photodiode array detector designed for photon-counting, far ultraviolet astronomy applications employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain pulses with a narrowly peaked pulse height distribution. The P-20 output phosphor exhibits a very short decay time, due to the high current density of the electron pulses. This intensifier is being coupled to a self-scanning linear photodiode array which has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location.

Characteristics of Currents and Electric Fields Associated with the Initial Stage of Upward Lightning

NASA Astrophysics Data System (ADS)

Watanabe, N.; Nag, A.; Diendorfer, G.; Pichler, H.; Schulz, W.

2017-12-01

There is increasing interest in understanding processes associated with the initiation of upward lightning from tall structures. Characterization of such processes is essential for the development of appropriate models. We examine current and electric field waveforms for 15 negative upward flashes occurring in 2007-2009 initiated from the Gaisberg Tower located in Salzburg, Austria. Current was measured at the top of the tower using a 0.25 mΩ shunt. Electric field was measured simultaneously at close (170 m from the tower) and far (79 km from the tower in 2007 and 109 km in 2008-2009) distances. The initial stage (IS) of these flashes comprised of relatively slowly varying "background" current (having durations ranging from 132 to 692 ms), with faster, more impulsive current variations (pulses having durations ranging from 4.7 µs to 22.9 ms) overlaid on this background current. In five of the 15 (33%) flashes, this IS background current was negative while in the other ten (67%) flashes, the current was bipolar (changing between negative and positive values). 150 current pulses occurred during the IS of these 15 flashes, of which 28 (19%) were positive bipolar (positive initial polarity with a negative opposite polarity overshoot), 5 (3.3%) were positive unipolar (positive initial polarity with no opposite polarity overshoot), and 117 (78%) were negative unipolar. No negative bipolar pulses were found. The median peak current and risetime for the 28 bipolar pulses were 0.74 kA and 2.8 µs, respectively, and those for the 122 unipolar pulses were 0.87 kA and 70 µs, respectively. Generally speaking, majority of the pulses occurring at the beginning of the initial stage were lower-amplitude positive bipolar, while higher-amplitude unipolar pulses were more likely to occur at later times. These 150 IS current pulses produced 133 detectable electric field change signatures at the near station and 59 at the far station (all recorded at 79 km in 12 flashes occurring in 2007). We will examine in detail the characteristics of these electric field pulses in order to gain insights into the mechanisms of the underlying processes.

High performance mode locking characteristics of single section quantum dash lasers.

PubMed

Rosales, Ricardo; Murdoch, S G; Watts, R T; Merghem, K; Martinez, Anthony; Lelarge, Francois; Accard, Alain; Barry, L P; Ramdane, Abderrahim

2012-04-09

Mode locking features of single section quantum dash based lasers are investigated. Particular interest is given to the static spectral phase profile determining the shape of the mode locked pulses. The phase profile dependence on cavity length and injection current is experimentally evaluated, demonstrating the possibility of efficiently using the wide spectral bandwidth exhibited by these quantum dash structures for the generation of high peak power sub-picosecond pulses with low radio frequency linewidths.

A transportable 50 kA dual mode lightning simulator

NASA Technical Reports Server (NTRS)

Salisbury, K.; Lloyd, S.; Chen, Y. G.

1991-01-01

A transportable lightning simulator was designed, built and tested, which is capable of delivering more than 50 kA to an 8 micro-H test object. The simulator was designed to be a versatile device in the lightning laboratory while meeting the requirements of MIL-STD-1757A for component E current waveforms. The system is capable of operating in either a ringing mode with a Q greater than 5 and a nominal frequency of 160 kHz, or a unipolar mode with no hardware configuration changes. The ringing mode is obtained by the LCR series circuit formed by the pulse generator and test object. The unipolar mode is obtained by closing an electrically triggered crowbar switch at peak current. The simulator exceeds the peak current requirement and rate of rise requirements for MIL-STD-1757A in both the ringing and unipolar modes. The pulse half width in the unipolar mode is in excess of 50 microsec and the action is in excess of 10(exp 5) A(exp 2)s. The design, component values, and test results are presented.

Long-Lag, Wide-pulse Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Norris, J. P.; Bonnell, J. T.; Kazanas, D.; Scargle, . D.; Hakkila, J.; Giblin, T. W.

2004-01-01

Currently, the best available probe of the early phase of gamma-ray burst (GRB) jet attributes is the prompt gamma-ray emission, in which several intrinsic and extrinsic variables determine GRB pulse evolution. Bright, usually complex bursts have many narrow pulses that are difficult to model due to overlap. However, the relatively simple, long spectral lag, wide-pulse bursts may have simpler physics and are easier to model. In this work we analyze the temporal and spectral behavior of wide pulses in 24 long-lag bursts, using a pulse model with two shape parameters - width and asymmetry - and the Band spectral model with three shape parameters. We find that pulses in long-lag bursts are distinguished both temporally and spectrally from those in bright bursts: the pulses in long spectral lag bursts are few in number, and approximately 100 times wider (10s of seconds), have systematically lower peaks in vF(v), harder low-energy spectra and softer high-energy spectra. We find that these five pulse descriptors are essentially uncorrelated for our long-lag sample, suggesting that at least approximately 5 parameters are needed to model burst temporal and spectral behavior. However, pulse width is strongly correlated with spectral lag; hence these two parameters may be viewed as mutual surrogates. We infer that accurate formulations for estimating GRB luminosity and total energy will depend on several gamma-ray attributes, at least for long-lag bursts. The prevalence of long-lag bursts near the BATSE trigger threshold, their predominantly low vF(v) spectral peaks, and relatively steep upper power-law spectral indices indicate that Swift will detect many such bursts.

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.

Nanosecond pulsed power generator for a voltage amplitude up to 300 kV and a repetition rate up to 16 Hz for fine disintegration of quartz

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

Krastelev, E. G., E-mail: ekrastelev@yandex.ru; Sedin, A. A.; Tugushev, V. I.

2015-12-15

A generator of high-power high-voltage nanosecond pulses is intended for electrical discharge disintegration of mineral quartz and other nonconducting minerals. It includes a 320 kV Marx pulsed voltage generator, a high-voltage glycerin-insulated coaxial peaking capacitor, and an output gas spark switch followed by a load, an electric discharge disintegration chamber. The main parameters of the generator are as follows: a voltage pulse amplitude of up to 300 kV, an output impedance of ≈10 Ω, a discharge current amplitude of up to 25 kA for a half-period of 80–90 ns, and a pulse repetition rate of up to 16 Hz.

Development of 600 kV triple resonance pulse transformer.

PubMed

Li, Mingjia; Zhang, Faqiang; Liang, Chuan; Xu, Zhou

2015-06-01

In this paper, a triple-resonance pulse transformer based on an air-core transformer is introduced. The voltage across the high-voltage winding of the air-core transformer is significantly less than the output voltage; instead, the full output voltage appears across the tuning inductor. The maximum ratio of peak load voltage to peak transformer voltage is 2.77 in theory. By analyzing pulse transformer's lossless circuit, the analytical expression for the output voltage and the characteristic equation of the triple-resonance circuit are presented. Design method for the triple-resonance pulse transformer (iterated simulation method) is presented, and a triple-resonance pulse transformer is developed based on the existing air-core transformer. The experimental results indicate that the maximum ratio of peak voltage across the load to peak voltage across the high-voltage winding of the air-core transformer is approximately 2.0 and the peak output voltage of the triple-resonance pulse transformer is approximately 600 kV.

Optimization of current waveform tailoring for magnetically driven isentropic compression experiments

NASA Astrophysics Data System (ADS)

Waisman, E. M.; Reisman, D. B.; Stoltzfus, B. S.; Stygar, W. A.; Cuneo, M. E.; Haill, T. A.; Davis, J.-P.; Brown, J. L.; Seagle, C. T.; Spielman, R. B.

2016-06-01

The Thor pulsed power generator is being developed at Sandia National Laboratories. The design consists of up to 288 decoupled and transit time isolated capacitor-switch units, called "bricks," that can be individually triggered to achieve a high degree of pulse tailoring for magnetically driven isentropic compression experiments (ICE) [D. B. Reisman et al., Phys. Rev. Spec. Top.-Accel. Beams 18, 090401 (2015)]. The connecting transmission lines are impedance matched to the bricks, allowing the capacitor energy to be efficiently delivered to an ICE strip-line load with peak pressures of over 100 GPa. Thor will drive experiments to explore equation of state, material strength, and phase transition properties of a wide variety of materials. We present an optimization process for producing tailored current pulses, a requirement for many material studies, on the Thor generator. This technique, which is unique to the novel "current-adder" architecture used by Thor, entirely avoids the iterative use of complex circuit models to converge to the desired electrical pulse. We begin with magnetohydrodynamic simulations for a given material to determine its time dependent pressure and thus the desired strip-line load current and voltage. Because the bricks are connected to a central power flow section through transit-time isolated coaxial cables of constant impedance, the brick forward-going pulses are independent of each other. We observe that the desired equivalent forward-going current driving the pulse must be equal to the sum of the individual brick forward-going currents. We find a set of optimal brick delay times by requiring that the L2 norm of the difference between the brick-sum current and the desired forward-going current be a minimum. We describe the optimization procedure for the Thor design and show results for various materials of interest.

Optimization of current waveform tailoring for magnetically driven isentropic compression experiments.

PubMed

Waisman, E M; Reisman, D B; Stoltzfus, B S; Stygar, W A; Cuneo, M E; Haill, T A; Davis, J-P; Brown, J L; Seagle, C T; Spielman, R B

2016-06-01

The Thor pulsed power generator is being developed at Sandia National Laboratories. The design consists of up to 288 decoupled and transit time isolated capacitor-switch units, called "bricks," that can be individually triggered to achieve a high degree of pulse tailoring for magnetically driven isentropic compression experiments (ICE) [D. B. Reisman et al., Phys. Rev. Spec. Top.-Accel. Beams 18, 090401 (2015)]. The connecting transmission lines are impedance matched to the bricks, allowing the capacitor energy to be efficiently delivered to an ICE strip-line load with peak pressures of over 100 GPa. Thor will drive experiments to explore equation of state, material strength, and phase transition properties of a wide variety of materials. We present an optimization process for producing tailored current pulses, a requirement for many material studies, on the Thor generator. This technique, which is unique to the novel "current-adder" architecture used by Thor, entirely avoids the iterative use of complex circuit models to converge to the desired electrical pulse. We begin with magnetohydrodynamic simulations for a given material to determine its time dependent pressure and thus the desired strip-line load current and voltage. Because the bricks are connected to a central power flow section through transit-time isolated coaxial cables of constant impedance, the brick forward-going pulses are independent of each other. We observe that the desired equivalent forward-going current driving the pulse must be equal to the sum of the individual brick forward-going currents. We find a set of optimal brick delay times by requiring that the L2 norm of the difference between the brick-sum current and the desired forward-going current be a minimum. We describe the optimization procedure for the Thor design and show results for various materials of interest.

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.

Influence of stroke volume and exercise tolerance on peak oxygen pulse in patients with and without beta-adrenergic receptor blockers in patients with heart disease.

PubMed

Murata, Makoto; Adachi, Hitoshi; Oshima, Shigeru; Kurabayashi, Masahiko

2017-01-01

In a given individual, a consistent relationship exists between oxygen uptake (V˙O 2 ) and heart rate (HR) during exercise. The quotient of V˙O 2 and HR (V˙O 2 /HR) is called the oxygen pulse (O 2 pulse), and its value is dependent on stroke volume (SV). However, it is difficult to believe that the O 2 pulse would indicate the SV when HR has been modified as with the use of beta-adrenergic receptor blockers (BB). Until now, the effect of BB on peak O 2 pulse has not been precisely studied. We tried to clarify the effect of BB on the relationship between O 2 pulse and SV. Of 699 consecutive heart disease subjects who performed cardiopulmonary exercise tests (CPX) from 2012 to 2014, we enrolled 430 subjects who had sinus rhythm and could perform CPX until exhaustion. One hundred and fifty-seven subjects were taking BB. SV was evaluated during CPX using impedance cardiography, and we compared the peak O 2 pulse with peak SV between patients without BB (Group A) and with BB (Group B). The HRs at rest and peak exercise in Group A were greater than those in Group B (74.4±13.0/min vs. 71.8±11.3/min, p<0.01, 134.9±21.7/min vs. 124.9±23.6/min, p<0.01, respectively). The regression line of the peak O 2 pulse against the peak SV was steeper in Group B than in Group A. When we divided the patients into two groups according to the average values of the peak SV and peak V˙O 2 , O 2 pulse/SV ratio in Group B above the average was greater than that in Group A, whereas it was similar in the two groups that were below average. We found that the increase in the O 2 pulse was disproportionately greater than the SV that was measured by impedance cardiography when a BB was used in patients with preserved SV and exercise tolerance. Copyright © 2016. Published by Elsevier Ltd.

Scaling laws and edge effects for polymer surface discharges

NASA Technical Reports Server (NTRS)

Balmain, K. G.

1979-01-01

Specimens of Mylar sheet were exposed to a 20 kV electron beam. The resulting surface discharge arcs were photographed and the discharge current into a metal backing plate measured as a function of time. The area of the Mylar sheet was defined by a round aperture in a close-fitting metal mask, and the current pulse characteristics were plotted against area on log-log paper. The plots appear as straight lines (due to power-law behavior) with slopes of 0.50 for the peak current, 1.00 for the charge released, 1.49 for the energy and 0.55 for the pulse duration. Evidence is presented for the occurrence of banded charge distributions near grounded edges, on both Teflon and Mylar.

Measuring 20-100 T B-fields using Zeeman splitting of sodium emission lines on a 500 kA pulsed power machine

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

Banasek, J. T., E-mail: jtb254@cornell.edu; Engelbrecht, J. T.; Pikuz, S. A.

2016-11-15

We have shown that Zeeman splitting of the sodium (Na) D-lines at 5890 and 5896 Å can be used to measure the magnetic field (B-field) produced in high current pulsed power experiments. We have measured the B-field next to a return current conductor in a hybrid X-pinch experiment near a peak current of about 500 kA. Na is deposited on the conductor and then is desorbed and excited by radiation from the hybrid X-pinch. The D-line emission spectrum implies B-fields of about 20 T with a return current post of 4 mm diameter or up to 120 T with amore » return current wire of 0.455 mm diameter. These measurements were consistent or lower than the expected B-field, thereby showing that basic Zeeman splitting can be used to measure the B-field in a pulsed-power-driven high-energy-density (HED) plasma experiment. We hope to extend these measurement techniques using suitable ionized species to measurements within HED plasmas.« less

Dynamic chirp control of all-optical format-converted pulsed data from a multi-wavelength inverse-optical-comb injected semiconductor optical amplifier.

PubMed

Lin, Gong-Ru; Pan, Ci-Ling; Yu, Kun-Chieh

2007-10-01

By spectrally and temporally reshaping the gain-window of a traveling-wave semiconductor optical amplifier (TWSOA) with a backward injected multi- or single-wavelength inverse-optical-comb, we theoretically and experimentally investigate the dynamic frequency chirp of the all-optical 10GBit/s Return-to-Zero (RZ) data-stream format-converted from the TWSOA under strong cross-gain depletion scheme. The multi-wavelength inverse-optical-comb injection effectively depletes the TWSOA gain spectrally and temporally, remaining a narrow gain-window and a reduced spectral linewidth and provide a converted RZ data with a smaller peak-to-peak frequency chirp of 6.7 GHz. Even at high inverse-optical-comb injection power and highly biased current condition for improving the operational bit-rate, the chirp of the multi-wavelength-injection converted RZ pulse is still 2.1-GHz smaller than that obtained by using single-wavelength injection at a cost of slight pulse-width broadening by 1 ps.

Electrochromic and optical properties of tungsten oxide films deposited with DC sputtering by introducing hydrogen.

PubMed

Chen, Hsi-Chao; Jan, Der-Jun; Luo, Yu-Siang; Huang, Kuo-Ting

2014-02-01

Research was undertaken to investigate the electrochromic and optical properties of tungsten oxide (WO3) films deposited by introducing hydrogen with a direct current (DC) and pulsed DC sputtering. The results show that WO3 films have optimum electrochromic properties at a hydrogen flow of 4 and 3 sccm for DC and pulsed DC, respectively. In the Raman spectra, the peak intensity increased with the increase of hydrogen flow at both 770  cm1 and 950  cm(-1) peaks, which resulted in bonds of W(6+)-O and W(6+)=O, respectively. Simultaneously, the transmittance (ΔT550  nm) variations were 65.6% and 64.4%, and the average transmittance (ΔT400-500  nm) variations were 56.7% and 56.4% for DC and pulsed DC, respectively. The bleached/colored ability of the cyclic voltammograms (CVs) was DC>pulsed DC, and the resistances of AC impedance were pulsed DC>DC.

Photon counting photodiode array detector for far ultraviolet (FUV) astronomy

NASA Technical Reports Server (NTRS)

Hartig, G. F.; Moos, H. W.; Pembroke, R.; Bowers, C.

1982-01-01

A compact, stable, single-stage intensified photodiode array detector designed for photon-counting, far ultraviolet astronomy applications employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain pulses with a narrowly peaked pulse height distribution. The P-20 output phosphor exhibits a very short decay time, due to the high current density of the electron pulses. This intensifier is being coupled to a self-scanning linear photodiode array which has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location. Previously announced in STAR as N82-19118

Method and apparatus for analog pulse pile-up rejection

DOEpatents

De Geronimo, Gianluigi

2013-12-31

A method and apparatus for pulse pile-up rejection are disclosed. The apparatus comprises a delay value application constituent configured to receive a threshold-crossing time value, and provide an adjustable value according to a delay value and the threshold-crossing time value; and a comparison constituent configured to receive a peak-occurrence time value and the adjustable value, compare the peak-occurrence time value with the adjustable value, indicate pulse acceptance if the peak-occurrence time value is less than or equal to the adjustable value, and indicate pulse rejection if the peak-occurrence time value is greater than the adjustable value.

Method and apparatus for analog pulse pile-up rejection

DOEpatents

De Geronimo, Gianluigi

2014-11-18

A method and apparatus for pulse pile-up rejection are disclosed. The apparatus comprises a delay value application constituent configured to receive a threshold-crossing time value, and provide an adjustable value according to a delay value and the threshold-crossing time value; and a comparison constituent configured to receive a peak-occurrence time value and the adjustable value, compare the peak-occurrence time value with the adjustable value, indicate pulse acceptance if the peak-occurrence time value is less than or equal to the adjustable value, and indicate pulse rejection if the peak-occurrence time value is greater than the adjustable value.

Observation of Gigawatt-Class THz Pulses from a Compact Laser-Driven Particle Accelerator

NASA Astrophysics Data System (ADS)

Gopal, A.; Herzer, S.; Schmidt, A.; Singh, P.; Reinhard, A.; Ziegler, W.; Brömmel, D.; Karmakar, A.; Gibbon, P.; Dillner, U.; May, T.; Meyer, H.-G.; Paulus, G. G.

2013-08-01

We report the observation of subpicosecond terahertz (T-ray) pulses with energies ≥460μJ from a laser-driven ion accelerator, thus rendering the peak power of the source higher even than that of state-of-the-art synchrotrons. Experiments were performed with intense laser pulses (up to 5×1019W/cm2) to irradiate thin metal foil targets. Ion spectra measured simultaneously showed a square law dependence of the T-ray yield on particle number. Two-dimensional particle-in-cell simulations show the presence of transient currents at the target rear surface which could be responsible for the strong T-ray emission.

Scaling magnetized liner inertial fusion on Z and future pulsed-power accelerators

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

Slutz, S. A.; Stygar, W. A.; Gomez, M. R.

The MagLIF (Magnetized Liner Inertial Fusion) concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] has demonstrated fusion–relevant plasma conditions [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z accelerator with a peak drive current of about 18 MA. We present 2D numerical simulations of the scaling of MagLIF on Z as a function of drive current, preheat energy, and applied magnetic field. The results indicate that deuterium-tritium (DT) fusion yields greater than 100 kJ could be possible on Z when all of these parameters are at the optimum values: i.e., peak current = 25 MA, deposited preheatmore » energy = 5 kJ, and B{sub z} = 30 T. Much higher yields have been predicted [S. A. Slutz and R. A. Vesey, Phys. Rev. Lett. 108, 025003 (2012)] for MagLIF driven with larger peak currents. Two high performance pulsed-power accelerators (Z300 and Z800) based on linear-transformer-driver technology have been designed [W. A. Stygar et al., Phys. Rev. ST Accel. Beams 18, 110401 (2015)]. The Z300 design would provide 48 MA to a MagLIF load, while Z800 would provide 65 MA. Parameterized Thevenin-equivalent circuits were used to drive a series of 1D and 2D numerical MagLIF simulations with currents ranging from what Z can deliver now to what could be achieved by these conceptual future pulsed-power accelerators. 2D simulations of simple MagLIF targets containing just gaseous DT have yields of 18 MJ for Z300 and 440 MJ for Z800. The 2D simulated yield for Z800 is increased to 7 GJ by adding a layer of frozen DT ice to the inside of the liner.« less

The influence of superimposed DC current on electrical and spectroscopic characteristics of HiPIMS discharge

NASA Astrophysics Data System (ADS)

Zuo, Xiao; Chen, Rende; Liu, Jingzhou; Ke, Peiling; Wang, Aiying

2018-01-01

The electrical characteristics and spectroscopic properties have been comprehensively investigated in a DC superimposed high power impulse magnetron sputtering (DC-HiPIMS) deposition system in this paper. The influence of superimposed DC current on the variation of target and substrate current waveforms, active species and electron temperatures with pulse voltages are focused. The peak target currents in DC-HiPIMS are lower than in HiPIMS. The time scales of the two main discharge processes like ionization and gas rarefaction in DC-HiPIMS are analyzed. When the pulse voltage is higher than 600 V, the gas rarefaction effect becomes apparent. Overall, the ionization process is found to be dominant in the initial ˜100 μs during each pulse. The active species of Ar and Cr in DC-HiPIMS are higher than in HiPIMS unless that the pulse voltage reaches 900 V. However, the ionization degree in HiPIMS exceeds that in DC-HiPIMS at around 600 V. The electron temperature calculated by modified Boltzmann plot method based on corona model has a precipitous increase from 0.87 to 25.0 eV in HiPIMS, but varies mildly after the introduction of the superimposed DC current. Additionally, the current from plasma flowing to the substrate is improved when a DC current is superimposed with HiPIMS.

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.

Design of parallel transmission pulses for simultaneous multislice with explicit control for peak power and local specific absorption rate.

PubMed

Guérin, Bastien; Setsompop, Kawin; Ye, Huihui; Poser, Benedikt A; Stenger, Andrew V; Wald, Lawrence L

2015-05-01

To design parallel transmit (pTx) simultaneous multislice (SMS) spokes pulses with explicit control for peak power and local and global specific absorption rate (SAR). We design SMS pTx least-squares and magnitude least squares spokes pulses while constraining local SAR using the virtual observation points (VOPs) compression of SAR matrices. We evaluate our approach in simulations of a head (7T) and a body (3T) coil with eight channels arranged in two z-rows. For many of our simulations, control of average power by Tikhonov regularization of the SMS pTx spokes pulse design yielded pulses that violated hardware and SAR safety limits. On the other hand, control of peak power alone yielded pulses that violated local SAR limits. Pulses optimized with control of both local SAR and peak power satisfied all constraints and therefore had the best excitation performance under limited power and SAR constraints. These results extend our previous results for single slice pTx excitations but are more pronounced because of the large power demands and SAR of SMS pulses. Explicit control of local SAR and peak power is required to generate optimal SMS pTx excitations satisfying both the system's hardware limits and regulatory safety limits. © 2014 Wiley Periodicals, Inc.

Electron-Beam Switches For A High Peak Power Sled-II Pulse Compressor

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

Hirshfield, Jay, L.

2015-12-02

Omega-P demonstrated triggered electron-beam switches on the L=2 m dual-delay-line X-band pulse compressor at Naval Research Laboratory (NRL). In those experiments, with input pulses of up to 9 MW from the Omega-P/NRL X-band magnicon, output pulses having peak powers of 140-165 MW and durations of 16-20 ns were produced, with record peak power gains M of 18-20. Switch designs are described based on the successful results that should be suitable for use with the existing SLAC SLED-II delay line system, to demonstrate C=9, M=7, and n>>78%, yielding 173ns compressed pulses with peak powers up to 350MW with input of amore » single 50-MW.« less

THE TEMPORAL AND SPECTRAL CHARACTERISTICS OF 'FAST RISE AND EXPONENTIAL DECAY' GAMMA-RAY BURST PULSES

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

Peng, Z. Y.; Ma, L.; Yin, Y.

2010-08-01

In this paper, we have analyzed the temporal and spectral behavior of 52 fast rise and exponential decay (FRED) pulses in 48 long-duration gamma-ray bursts (GRBs) observed by the CGRO/BATSE, using a pulse model with two shape parameters and the Band model with three shape parameters, respectively. It is found that these FRED pulses are distinguished both temporally and spectrally from those in the long-lag pulses. In contrast to the long-lag pulses, only one parameter pair indicates an evident correlation among the five parameters, which suggests that at least four parameters are needed to model burst temporal and spectral behavior.more » In addition, our studies reveal that these FRED pulses have the following correlated properties: (1) long-duration pulses have harder spectra and are less luminous than short-duration pulses and (2) the more asymmetric the pulses are, the steeper are the evolutionary curves of the peak energy (E{sub p}) in the {nu}f{sub {nu}} spectrum within the pulse decay phase. Our statistical results give some constraints on the current GRB models.« less

Solid-state repetitive generator with a gyromagnetic nonlinear transmission line operating as a peak power amplifier

NASA Astrophysics Data System (ADS)

Gusev, A. I.; Pedos, M. S.; Rukin, S. N.; Timoshenkov, S. P.

2017-07-01

In this work, experiments were made in which gyromagnetic nonlinear transmission line (NLTL) operates as a peak power amplifier of the input pulse. At such an operating regime, the duration of the input pulse is close to the period of generated oscillations, and the main part of the input pulse energy is transmitted only to the first peak of the oscillations. Power amplification is achieved due to the voltage amplitude of the first peak across the NLTL output exceeding the voltage amplitude of the input pulse. In the experiments, the input pulse with an amplitude of 500 kV and a half-height pulse duration of 7 ns is applied to the NLTL with a natural oscillation frequency of ˜300 MHz. At the output of the NLTL in 40 Ω coaxial transmission line, the pulse amplitude is increased to 740 kV and the pulse duration is reduced to ˜2 ns, which correspond to power amplification of the input pulse from ˜6 to ˜13 GW. As a source of input pulses, a solid-state semiconductor opening switch generator was used, which allowed carrying out experiments at pulse repetition frequency up to 1 kHz in the burst mode of operation.

Q-switched dual-wavelength pumped 3.5-μm erbium-doped mid-Infrared fiber laser

NASA Astrophysics Data System (ADS)

Bawden, Nathaniel; Matsukuma, Hiraku; Henderson-Sapir, Ori; Klantsataya, Elizaveta; Tokita, Shigeki; Ottaway, David J.

2018-02-01

Short pulse operation of fiber lasers operating at wavelengths up 3 micron have been reported in recent years. At longer wavelengths, fiber lasers have only been demonstrated with a continuous operation mode. Short pulse operation in the mid-IR is necessary for utilizing such lasers in laser radars and for medical applications. Our previous numerical work suggested that Q-switching is possible on the 3.5 μm transition in erbium-doped ZBLAN in a similar manner to work demonstrated on the 2.8 μm transition in erbium. In this work we report on initial experimental results of a Q-switched, dualwavelength pumped fiber laser operating on the 3.5 μm transition in erbium-doped ZBLAN glass fibers. Using a hybrid fiber and open resonator configuration utilizing an acousto-optic modulator we demonstrated stable single pulse Q-switching while operating at repetition rates of 20 kHz and up to 120 kHz. The laser achieved a peak power of 8 W with pulse energy of 7 μJ while operating at 25 kHz. Long pulse widths on the order of 1 μs were obtained. The low peak power and long pulses are likely the result of both low gain of the transition and additional losses in the resonator which are currently being investigated. Our latest results will be presented.

Baird's beaked whale echolocation signals.

PubMed

Baumann-Pickering, Simone; Yack, Tina M; Barlow, Jay; Wiggins, Sean M; Hildebrand, John A

2013-06-01

Echolocation signals from Baird's beaked whales were recorded during visual and acoustic shipboard surveys of cetaceans in the California Current ecosystem and with autonomous, long-term recorders in the Southern California Bight. The preliminary measurement of the visually validated Baird's beaked whale echolocation signals from towed array data were used as a basis for identifying Baird's signals in the autonomous recorder data. Two distinct signal types were found, one being a beaked whale-like frequency modulated (FM) pulse, the other being a dolphin-like broadband click. The median FM inter-pulse interval was 230 ms. Both signal types showed a consistent multi-peak structure in their spectra with peaks at ~9, 16, 25, and 40 kHz. Depending on signal type, as well as recording aspect and distance to the hydrophone, these peaks varied in relative amplitude. The description of Baird's echolocation signals will allow for studies of their distribution and abundance using towed array data without associated visual sightings and from autonomous seafloor hydrophones.

Two-dimensional time-dependent modelling of fume formation in a pulsed gas metal arc welding process

NASA Astrophysics Data System (ADS)

Boselli, M.; Colombo, V.; Ghedini, E.; Gherardi, M.; Sanibondi, P.

2013-06-01

Fume formation in a pulsed gas metal arc welding (GMAW) process is investigated by coupling a time-dependent axi-symmetric two-dimensional model, which takes into account both droplet detachment and production of metal vapour, with a model for fume formation and transport based on the method of moments for the solution of the aerosol general dynamic equation. We report simulative results of a pulsed process (peak current = 350 A, background current 30 A, period = 9 ms) for a 1 mm diameter iron wire, with Ar shielding gas. Results showed that metal vapour production occurs mainly at the wire tip, whereas fume formation is concentrated in the fringes of the arc in the spatial region close to the workpiece, where metal vapours are transported by convection. The proposed modelling approach allows time-dependent tracking of fumes also in plasma processes where temperature-time variations occur faster than nanoparticle transport from the nucleation region to the surrounding atmosphere, as is the case for most pulsed GMAW processes.

ECCM Waveform Investigation

DTIC Science & Technology

1977-08-01

period, duration/ peak power, and side lobe levels. A recommended waveform library is presented. One of the program results is that an optimum waveform...Areas a. Coding b. Pulse Repetition Period c. Peak Power/Pulse Duration d. Sidelobes 3. Performance Dependence Upon Bandwidth/Bandspan a... peak power and pulse duration, and range and Doppler sldelobe levels. The constraints upon waveforms due to the In- ability of the radar components

Effects of pulsed magnetic stimulation on tumor development and immune functions in mice.

PubMed

Yamaguchi, Sachiko; Ogiue-Ikeda, Mari; Sekino, Masaki; Ueno, Shoogo

2006-01-01

We investigated the effects of pulsed magnetic stimulation on tumor development processes and immune functions in mice. A circular coil (inner diameter = 15 mm, outer diameter = 75 mm) was used in the experiments. Stimulus conditions were pulse width = 238 micros, peak magnetic field = 0.25 T (at the center of the coil), frequency = 25 pulses/s, 1,000 pulses/sample/day and magnetically induced eddy currents in mice = 0.79-1.54 A/m(2). In an animal study, B16-BL6 melanoma model mice were exposed to the pulsed magnetic stimulation for 16 days from the day of injection of cancer cells. A tumor growth study revealed a significant tumor weight decrease in the stimulated group (54% of the sham group). In a cellular study, B16-BL6 cells were also exposed to the magnetic field (1,000 pulses/sample, and eddy currents at the bottom of the dish = 2.36-2.90 A/m(2)); however, the magnetically induced eddy currents had no effect on cell viabilities. Cytokine production in mouse spleens was measured to analyze the immunomodulatory effect after the pulsed magnetic stimulation. tumor necrosis factor (TNF-alpha) production in mouse spleens was significantly activated after the exposure of the stimulus condition described above. These results showed the first evidence of the anti-tumor effect and immunomodulatory effects brought about by the application of repetitive magnetic stimulation and also suggested the possible relationship between anti-tumor effects and the increase of TNF-alpha levels caused by pulsed magnetic stimulation.

Research on improvement of power quality of Micro - grid based on SVG pulse load

NASA Astrophysics Data System (ADS)

Lv, Chuang; Xie, Pu

2017-05-01

Pulse load will make the micro-grid public bus power to produce a high peak pulse due to its cyclical pulsation characteristics,, and make the micro-grid voltage fluctuations, frequency fluctuations, voltage and current distortion, power factor reduction and other adverse effects. In order to suppress the adverse effects of the pulse load on the microgrid and improve the power quality of the microgrid, this paper established the SVG simulation model in Matlab / Simulink environment, the superiority of SVG is verified by comparing the improvement of power quality before and after adding the SVG to microgrid system. The results show that the SVG model can suppress the adverse effects effectively of the pulse load on the microgrid, which is of great value and significance to the reactive power compensation and harmonic suppression of the microgrid.

A nerve stimulation method to selectively recruit smaller motor-units in rat skeletal muscle.

PubMed

van Bolhuis, A I; Holsheimer, J; Savelberg, H H

2001-05-30

Electrical stimulation of peripheral nerve results in a motor-unit recruitment order opposite to that attained by natural neural control, i.e. from large, fast-fatiguing to progressively smaller, fatigue-resistant motor-units. Yet animal studies involving physiological exercise protocols of low intensity and long duration require minimal fatigue. The present study sought to apply a nerve stimulation method to selectively recruit smaller motor-units in rat skeletal muscle. Two pulse generators were used, independently supplying short supramaximal cathodal stimulating pulses (0.5 ms) and long subthreshold cathodal inactivating pulses (1.5 s) to the sciatic nerve. Propagation of action potentials was selectively blocked in nerve fibres of different diameter by adjusting the strength of the inactivating current. A tensile-testing machine was used to gauge isometric muscle force of the plantaris and both heads of the gastrocnemius muscle. The order of motor-unit recruitment was estimated from twitch characteristics, i.e. peak force and relaxation time. The results showed prolonged relaxation at lower twitch peak forces as the intensity of the inactivating current increased, indicating a reduction of the number of large motor-units to force production. It is shown that the nerve stimulation method described is effective in mimicking physiological muscle control.

High Intensity Mirror-Free Nanosecond Ytterbium Fiber Laser System in Master Oscillator Power Amplification

NASA Astrophysics Data System (ADS)

Chun-Lin, Louis Chang

Rare-earth-doped fiber lasers and amplifiers are relatively easy to efficiently produce a stable and high quality laser beam in a compact, robust, and alignment-free configuration. Recently, high power fiber laser systems have facilitated wide spread applications in academics, industries, and militaries in replacement of bulk solid-state laser systems. The master oscillator power amplifier (MOPA) composed of a highly-controlled seed, high-gain preamplifiers, and high-efficiency power amplifiers are typically utilized to scale up the pulse energy, peak power, or average power. Furthermore, a direct-current-modulated nanosecond diode laser in single transverse mode can simply provide a compact and highly-controlled seed to result in the flexible output parameters, such as repetition rate, pulse duration, and even temporal pulse shape. However, when scaling up the peak power for high intensity applications, such a versatile diode-seeded nanosecond MOPA laser system using rare-earth-doped fibers is unable to completely save its own advantages compared to bulk laser systems. Without a strong seeding among the amplifiers, the guided amplified spontaneous amplification is easy to become dominant during the amplification, leading to the harmful self-lasing or pulsing effects, and the difficulty of the quantitative numerical comparison. In this dissertation, we study a high-efficiency and intense nanosecond ytterbium fiber MOPA system with good beam quality and stability for high intensity applications. The all-PM-fiber structure is achieved with the output extinction ratio of >12 dB by optimizing the interconnection of high power optical fibers. The diode-seeded MOPA configuration without parasitic stimulated amplification (PAS) is implemented using the double-pass scheme to extract energy efficiently for scaling peak power. The broadband PAS was studied experimentally, which matches well with our numerical simulation. The 1064-nm nanosecond seed was a direct-current-modulated Fabry-Perot diode laser associated with a weak and pulsed noise spanning from 1045 to 1063 nm. Even though the contribution of input noise pulse is only <5%, it becomes a significant transient spike during amplification. The blue-shifted pulsed noise may be caused by band filling effect for quantum-well seed laser driven by high peak current. The study helps the development of adaptive pulse shaping for scaling peak power or energy at high efficiency. On the other hand, the broadband spike with a 3-dB bandwidth of 8.8 nm can support pulses to seed the amplifier for sub-nanosecond giant pulse generation. Because of the very weak seed laser, the design of high-gain preamplifier becomes critical. The utilization of single-mode core-pumped fiber preamplifier can not only improve the mode contrast without fiber coiling effect but also significantly suppress the fiber nonlinearity. The double-pass scheme was therefore studied both numerically and experimentally to improve energy extraction efficiency for the lack of attainable seed and core-pumped power. As a result, a record-high peak power of > 30 kW and energy of > 0.23 mJ was successfully achieved to the best of our knowledge from the output of clad-pumped power amplifier with a beam quality of M2 ˜1.1 in a diode-seeded 15-microm-core fiber MOPA system. After the power amplifier, the MOPA conversion efficiency can be dramatically improved to >56% for an energy gain of >63 dB at a moderate repetition rate of 20 kHz with a beam quality of M 2 <1.5. The output energy of >1.1 mJ with a pulse duration of ˜6.1 ns can result in a peak power up to >116 kW which is limited by fiber fuse in long-term operation. Such a condition able to generate the on-target laser intensity of > 60 GW/cm2 for applications is qualified to preliminarily create a laser-plasma light source. Moreover, the related simulation results also reveal the double-passed power amplifier can further simplify MOPA. Such an intense clad-pumped power amplifier can further become a nonlinear fiber amplifier in all-normal dispersion instead of a nonlinear passive fiber. The combination of laser amplification and nonlinear conversion together can therefore overcome the significant pump depletion during the propagation along the passive fiber for power scaling. As a result, an intense spectrum spanning from 980 to 1600 nm as a high-power nanosecond supercontinuum source can be successfully generated with a conversion efficiency of >65% and a record-high peak power of >116 kW to the best of our knowledge. Because of MOPA structure, the influence of input parameters of nonlinear fiber amplifier on supercontinuum parameters can also be studied. The onset and interplay of fiber nonlinearities can be revealed stage by stage. Such an unique and linearly-polarized light source composed of an intense pump and broad sideband seed is beneficial for efficiently driving the broadband tunable optical parametric amplification free from the bulkiness and timing jitter. Keywords: High power fiber laser and amplifier, ytterbium fiber, master oscillator power amplification, parasitic stimulated amplification, multi-pass fiber amplification, peak power/pulse energy scaling, fiber nonlinear optics, supercontinuum generation.

A Gaussian Model-Based Probabilistic Approach for Pulse Transit Time Estimation.

PubMed

Jang, Dae-Geun; Park, Seung-Hun; Hahn, Minsoo

2016-01-01

In this paper, we propose a new probabilistic approach to pulse transit time (PTT) estimation using a Gaussian distribution model. It is motivated basically by the hypothesis that PTTs normalized by RR intervals follow the Gaussian distribution. To verify the hypothesis, we demonstrate the effects of arterial compliance on the normalized PTTs using the Moens-Korteweg equation. Furthermore, we observe a Gaussian distribution of the normalized PTTs on real data. In order to estimate the PTT using the hypothesis, we first assumed that R-waves in the electrocardiogram (ECG) can be correctly identified. The R-waves limit searching ranges to detect pulse peaks in the photoplethysmogram (PPG) and to synchronize the results with cardiac beats--i.e., the peaks of the PPG are extracted within the corresponding RR interval of the ECG as pulse peak candidates. Their probabilities of being the actual pulse peak are then calculated using a Gaussian probability function. The parameters of the Gaussian function are automatically updated when a new pulse peak is identified. This update makes the probability function adaptive to variations of cardiac cycles. Finally, the pulse peak is identified as the candidate with the highest probability. The proposed approach is tested on a database where ECG and PPG waveforms are collected simultaneously during the submaximal bicycle ergometer exercise test. The results are promising, suggesting that the method provides a simple but more accurate PTT estimation in real applications.

James Webb Space Telescope Mid Infra-Red Instrument Pulse-Tube Cryocooler Electronics

NASA Technical Reports Server (NTRS)

Harvey, D.; Flowers, T.; Liu, N.; Moore, K.; Tran, D.; Valenzuela, P.; Franklin, B.; Michaels, D.

2013-01-01

The latest generation of long life, space pulse-tube cryocoolers require electronics capable of controlling self-induced vibration down to a fraction of a newton and coldhead temperature with high accuracy down to a few kelvin. Other functions include engineering diagnostics, heater and valve control, telemetry and safety protection of the cryocooler subsystem against extreme environments and operational anomalies. The electronics are designed to survive the thermal, vibration, shock and radiation environment of launch and orbit, while providing a design life in excess of 10 years on-orbit. A number of our current generation high reliability radiation-hardened electronics units are in various stages of integration on several space flight payloads. This paper describes the features and performance of our latest flight electronics designed for the pulse-tube cryocooler that is the pre-cooler for a closed cycle Joule-Thomson cooler providing 6K cooling for the James Webb Space Telescope (JWST) Mid Infra-Red Instrument (MIRI). The electronics is capable of highly accurate temperature control over the temperature range from 4K to 15K. Self-induced vibration is controlled to low levels on all harmonics up to the 16th. A unique active power filter controls peak-to-peak reflected ripple current on the primary power bus to a very low level. The 9 kg unit is capable of delivering 360W continuous power to NGAS's 3-stage pulse-tube High-Capacity Cryocooler (HCC).

Electrochemical behavior of phytochelatins and related peptides at the hanging mercury drop electrode in the presence of cobalt(II) ions.

PubMed

Dorcák, Vlastimil; Sestáková, Ivana

2006-01-01

Direct current voltammetry and differential pulse voltammetry have been used to investigate the electrochemical behaviour of two phytochelatins: heptapeptide (gamma-Glu-Cys)3-Gly and pentapeptide (gamma-Glu-Cys)2-Gly, tripeptide glutathione gamma-Glu-Cys-Gly and its fragments: dipeptides Cys-Gly and gamma-Glu-Cys at the hanging mercury drop electrode in the presence of cobalt(II) ions. Most interesting results were obtained with direct current voltammetry in the potential region of -0.80 V up to -1.80 V. Differential pulse voltammetry of the same solutions of Co(II) with peptides gives more complicated voltammograms with overlapping peaks, probably in connection with the influence of adsorption at slow scan rates necessarily used in this method. However, in using Brdicka catalytic currents for analytical purposes, differential pulse voltammograms seem to be more helpful. Presented investigations have shown that particularly the prewave of cobalt(II) allows distinguishing among phytochelatins, glutathione, and its fragments.

Design and Analysis of Nano-Pulse Generator for Industrial Wastewater Application

NASA Astrophysics Data System (ADS)

Jang, Sung-Duck; Son, Yoon-Kyoo; Cho, Moo-Hyun; Norov, Enkhbat

2018-05-01

Recently, the application of a pulsed power system is being extended to environmental and industrial fields. The non-dissolution wastewater pollutants from industrial plants can be processed by applying high-voltage pulses with a fast rising time (a few nanoseconds) and short duration (nano to microseconds) in a pulsed corona discharge reactor. The high-voltage nano-pulse generator with a magnetic switch has been developed. It can be used for a spray type water treatment facility. Its corona current in load can be adjusted by pulse width and repetition rate. We investigated the performance of the nano-pulse generator by using the dummy load that is composed of resistor and capacitor equivalent to the actual reactor. In this paper, the results of design, construction and characterization of a high-voltage nano-pulse generator for an industrial wastewater treatment are reported. Consequently, a pulse width of 1.1 μs at the repetition rate of 200 pps, a peak voltage of 41 kV for the nano-pulse generator were achieved across a 640 Ω load. The simulation results on magnetic switch show reasonable agreement with experimental ones.

Multiple polarization states of vector soliton in fiber laser

NASA Astrophysics Data System (ADS)

Chen, Weicheng; Xu, Wencheng; Cao, Hui; Han, Dingan

2007-11-01

Vector soliton is obtained in erbium-doped fiber laser via nonlinear polarization rotation techniques. In experiment, we observe the every 4- and 7-pulse sinusoidal peak modulation. Temporal pulse sinusoidal peak modulation owes to evolution behavior of vector solitons in multiple polarization states. The polarizer in the laser modulates the mode-locked pulses with different polarization states into periodical pulse train intensities modulation. Moreover, the increasing pumping power lead to the appearance of the harmonic pulses and change the equivalent beat length to accelerate the polarization rotation. When the laser cavity length is the n-th multiple ratios to the beat length to maintain the mode-locking, the mode-locked vector soliton is in n-th multiple polarization states, exhibiting every n-pulse sinusoidal peak modulation.

Conductive graphene as passive saturable absorber with high instantaneous peak power and pulse energy in Q-switched regime

NASA Astrophysics Data System (ADS)

Zuikafly, Siti Nur Fatin; Khalifa, Ali; Ahmad, Fauzan; Shafie, Suhaidi; Harun, SulaimanWadi

2018-06-01

The Q-switched pulse regime is demonstrated by integrating conductive graphene as passive saturable absorber producing relatively high instantaneous peak power and pulse energy. The fabricated conductive graphene is investigated using Raman spectroscopy. The single wavelength Q-switching operates at 1558.28 nm at maximum input pump power of 151.47 mW. As the pump power is increased from threshold power of 51.6 mW to 151.47 mW, the pulse train repetition rate increases proportionally from 47.94 kHz to 67.8 kHz while the pulse width is reduced from 9.58 μs to 6.02 μs. The generated stable pulse produced maximum peak power and pulse energy of 32 mW and 206 nJ, respectively. The first beat node of the measured signal-to-noise ratio is about 62 dB indicating high pulse stability.

Temporal differentiation of pH-dependent capacitive current from dopamine.

PubMed

Yoshimi, Kenji; Weitemier, Adam

2014-09-02

Voltammetric recording of dopamine (DA) with fast-scan cyclic voltammetry (FSCV) on carbon fiber microelectrodes have been widely used, because of its high sensitivity to dopamine. However, since an electric double layer on a carbon fiber surface in a physiological ionic solution behaves as a capacitor, fast voltage manipulation in FSCV induces large capacitive current. The faradic current from oxidation/reduction of target chemicals must be extracted from this large background current. It is known that ionic shifts, including H(+), influence this capacitance, and pH shift can cause confounding influences on the FSCV recordings within a wide range of voltage. Besides FSCV with a triangular waveform, we have been using rectangular pulse voltammetry (RPV) for dopamine detection in the brain. In this method, the onset of a single pulse causes a large capacitive current, but unlike FSCV, the capacitive current is restricted to a narrow temporal window of just after pulse onset (<5 ms). In contrast, the peak of faradic current from dopamine oxidation occurs after a delay of more than a few milliseconds. Taking advantage of the temporal difference, we show that RPV could distinguish dopamine from pH shifts clearly and easily. In addition, the early onset current was useful to evaluate pH shifts. The narrow voltage window of our RPV pulse allowed a clear differentiation of dopamine and serotonin (5-HT), as we have shown previously. Additional recording with RPV, alongside FSCV, would improve identification of chemicals such as dopamine, pH, and 5-HT.

Investigation of a Gallium MPD Thruster with an Ablating Cathode

NASA Technical Reports Server (NTRS)

Thomas, Robert E.; Burton, Rodney L.; Polzin, Kurt A.

2010-01-01

Arc impedance, exhaust velocity, and plasma probe measurements are presented. The thruster is driven by a 50 microsecond pulse from a 6.2 milliohm pulse forming network, and gallium is supplied to the discharge by evaporation of the cathode. The arc voltage is found to vary linearly with the discharge current with an arc impedance of 6.5 milliohms. Electrostatic probes yield an exhaust velocity that is invariant with the discharge current and has a peak value of 20 kilometers per second, which is in reasonable agreement with the value (16 plus or minus 1 kilometer per second) calculated from the mass bit and discharge current data. Triple probe measurements yield on axis electron temperatures in the range of 0.8-3.8 eV, electron densities in the range of 1.6 x 10(exp 21) to 2.1 x 10(exp 22) per cubic meter, and a divergence half angle of 16 degrees. Measurements within the interelectrode region yield a peak magnetic field of 0.8 T, and the observed radial trends are consistent with an azimuthally symmetric current distribution. A cathode power balance model is coupled with an ablative heat conduction model predicting mass bit values that are within 20% of the experimental values.

EXCESS OPTICAL ENHANCEMENT OBSERVED WITH ARCONS FOR EARLY CRAB GIANT PULSES

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

Strader, M. J.; Mazin, B. A.; Spiro Jaeger, G. V.

2013-12-10

We observe an extraordinary link in the Crab pulsar between the enhancement of an optical pulse and the timing of the corresponding giant radio pulse. At optical through infrared wavelengths, our observations use the high time resolution of ARray Camera for Optical to Near-IR Spectrophotometry, a unique superconducting energy-resolving photon-counting array at the Palomar 200 inch telescope. At radio wavelengths, we observe with the Robert C. Byrd Green Bank Telescope and the Green Bank Ultimate Pulsar Processing Instrument backend. We see an 11.3% ± 2.5% increase in peak optical flux for pulses that have an accompanying giant radio pulse arrivingmore » near the peak of the optical main pulse, in contrast to a 3.2% ± 0.5% increase when an accompanying giant radio pulse arrives soon after the optical peak. We also observe that the peak of the optical main pulse is 2.8% ± 0.8% enhanced when there is a giant radio pulse accompanying the optical interpulse. We observe no statistically significant spectral differences between optical pulses accompanied by and not accompanied by giant radio pulses. Our results extend previous observations of optical-radio correlation to the time and spectral domains. Our refined temporal correlation suggests that optical and radio emission are indeed causally linked, and the lack of spectral differences suggests that the same mechanism is responsible for all optical emission.« less

High-peak-power microwave pulses: effects on heart rate and blood pressure in unanesthetized rats.

PubMed

Jauchem, J R; Frei, M R

1995-10-01

Exposure sources capable of generating high-peak-power microwave pulses, with relatively short pulse widths, have recently been developed. Studies of the effect of these sources on the cardiovascular systems of animals have not been reported previously. We exposed 14 unanesthetized male Sprague-Dawley rats to 10 high-peak-power microwave pulses generated by a transformer-energized megawatt pulsed output (TEMPO) microwave source, at frequencies ranging from 1.2-1.8 GHz. Peak power densities were as high as 51.6 kW/cm2. At 14 d prior to irradiation, the animals were implanted with chronic aortic cannulae. With appropriate shielding of the transducer, blood pressure recordings were obtained during microwave pulsing. In a preliminary series of exposures at 1.7-1.8 GHz (peak power density 3.3-6.5 kW/cm2), an immediate but transient increase in mean arterial blood pressure (significant) and decrease in heart rate (non-significant) were observed. A loud noise was associated with each pulse produced by the TEMPO; this factor was subsequently attenuated. In a second series of exposures at 1.2-1.4 GHz (peak power density 14.6-51.6 kW/cm2), there were no significant changes in mean arterial blood pressure or heart rate during microwave exposure. The earlier significant increase in blood pressure that occurred during microwave exposure appeared to be related to the sharp noise produced by the TEMPO source. After appropriate sound attenuation, there were no significant effects of exposure to the microwave pulses.

Discharge mode transition and temporal-spatial evolution of an air-water plasma jet generated by pulsating DC power

NASA Astrophysics Data System (ADS)

Lei, J.; Geng, Y.; Liu, K.; Zhu, W.; Zheng, Z.; Hu, H.

2017-12-01

In this paper, pulsating direct current air-water plasma jet, which can increase the production of •OH and decrease the temperature, is studied. The results show that the discharge mode changes in one cycle from corona discharge with steep Trichel current pulse to glow-like discharge. It is unknown whether the different discharge modes and water ratio have an effect on the transient process of the excited O and •OH production and the mechanism of plasma propagation. So, a series of experiments are done in this paper. The results show that the changing rules of both the excited state O and the discharge current reach their two peak values synchronously. And its maximum appears at the time of the first peak current value in corona mode. However, the change of the excited state •OH is different. It increases to its maximum at the time of the second peak current value in glow-like mode. Besides, the intensified charge coupled device photographs show that the luminous intensity of the discharge zone at the first peak current value in corona mode is stronger than the second peak current value in glow-like mode. At the same time, the discharge area of the former is larger than the latter. Nevertheless, with the increase in water ratio, the discharge area change reversed. Additionally, the air plasma plume propagation depends on the gas flow. The initial propagation velocity decreases with the increase in water ratio.

Voltammetric Behavior of o-Nitrophenol and Damage to DNA

PubMed Central

Zhang, Da-Peng; Wu, Wei-Li; Long, Hai-Yan; Liu, Yun-Chun; Yang, Zhou-Sheng

2008-01-01

The electrochemical behavior of o-nitrophenol was studied in detail with a glassy carbon electrode (GCE). The dependence of peak potential on pH indicated that equivalent electrons and protons were involved in the process of o-nitrophenol reduction. The interaction of o-nitrophenol with calf thymus DNA was investigated by adding DNA to the o-nitrophenol solution and by immobilizing DNA on GCE, respectively. The peak current decrement and peak potential shift in presence of DNA indicated that o-nitrophenol could interact with DNA. The result was demonstrated that the in situ DNA damage was detected by differential pulse voltammetry after the o-nitrophenol was electrochemically reduced. PMID:19325751

Direct space-time observation of pulse tunneling in an electromagnetic band gap

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

Doiron, Serge; Hache, Alain; Winful, Herbert G.

2007-08-15

We present space-time-resolved measurements of electromagnetic pulses tunneling through a coaxial electromagnetic band gap structure. The results show that during the tunneling process the field distribution inside the barrier is an exponentially decaying standing wave whose amplitude increases and decreases as it slowly follows the temporal evolution of the input pulse. At no time is a pulse maximum found inside the barrier, and hence the transmitted peak is not the incident peak that has propagated to the exit. The results support the quasistatic interpretation of tunneling dynamics and confirm that the group delay is not the traversal time of themore » input pulse peak.« less

Picosecond pulse generation in a hybrid Q-switched laser source by using a microelectromechanical mirror.

PubMed

Couderc, Vincent; Crunteanu, Aurelian; Fabert, Marc; Doutre, Florent; El Bassri, Farid; Pagnoux, Dominique; Jalocha, Alain

2012-02-27

We present a novel Q-switched laser source using a micro-optical-electromechanical mirror (MOEM) designed for short pulse emission. It is based on a hybrid configuration including a passively Q-switched microchip laser coupled to a fiber cavity closed by a cantilever type MOEM acting as an active modulator. This specially designed mirror with a single reflecting gold membrane is switched by low bias voltage ~50 V (peak to peak). This device emits pulses at tunable repetition rates up to 1.6 kHz, with ~564 ps duration and 3.4 kW peak power, which constitutes the shortest pulse duration ever reported with MOEMs based pulsed lasers.

X-ray Pulsations from AXP 1E 1547-5407 Detected with RXTE

NASA Astrophysics Data System (ADS)

Dib, R.; Kaspi, V. M.; Gavriil, F. P.; Woods, P. M.

2008-10-01

We observed AXP 1E 1547-5407 which is currently in outburst (see ATELs #1756, #1761, #1763) with RXTE on October 4 (4 ks), and 6 (1.4 ks, 1.6 ks). The 2-20 keV pulse profile of these observations (October 04 UT 21:51:04, October 06 UT 01:46:04, and October 06 UT 23:31:04) shows a single broad pulse that is qualitatively similar to that reported in Halpern et al. (2008, ApJ, 676, 1178), though there is a possible hint of additional peaks.

Electrical filtering in gerbil isolated type I semicircular canal hair cells

NASA Technical Reports Server (NTRS)

Rennie, K. J.; Ricci, A. J.; Correia, M. J.

1996-01-01

1. Membrane potential responses of dissociated gerbil type I semicircular canal hair cells to current injections in whole cell current-clamp have been measured. The input resistance of type I cells was 21.4 +/- 14.3 (SD) M omega, (n = 25). Around the zero-current potential (Vz = -66.6 +/- 9.3 mV, n = 25), pulsed current injections (from approximately -200 to 750 pA) produced only small-amplitude, pulse-like changes in membrane potential. 2. Injecting constant current to hyperpolarize the membrane to around -100 mV resulted in a approximately 10-fold increase in membrane resistance. Current pulses superimposed on this constant hyperpolarization produced larger and more complex membrane potential changes. Depolarizing currents > or = 200 pA caused a rapid transient peak voltage before a plateau. 3. Membrane voltage was able to faithfully follow sine-wave current injections around Vz over the range 1-1,000 Hz with < 25% attenuation at 1 kHz. A previously described K conductance, IKI, which is active at Vz, produces the low input resistance and frequency response. This was confirmed by pharmacologically blocking IKI. This conductance, present in type I cells but not type II hair cells, would appear to confer on type I cells a lower gain, but a much broader bandwidth at Vz, than seen in type II cells.

High quality ultrafast transmission electron microscopy using resonant microwave cavities.

PubMed

Verhoeven, W; van Rens, J F M; Kieft, E R; Mutsaers, P H A; Luiten, O J

2018-05-01

Ultrashort, low-emittance electron pulses can be created at a high repetition rate by using a TM 110 deflection cavity to sweep a continuous beam across an aperture. These pulses can be used for time-resolved electron microscopy with atomic spatial and temporal resolution at relatively large average currents. In order to demonstrate this, a cavity has been inserted in a transmission electron microscope, and picosecond pulses have been created. No significant increase of either emittance or energy spread has been measured for these pulses. At a peak current of 814 ± 2 pA, the root-mean-square transverse normalized emittance of the electron pulses is ɛ n,x =(2.7±0.1)·10 -12  m rad in the direction parallel to the streak of the cavity, and ɛ n,y =(2.5±0.1)·10 -12  m rad in the perpendicular direction for pulses with a pulse length of 1.1-1.3 ps. Under the same conditions, the emittance of the continuous beam is ɛ n,x =ɛ n,y =(2.5±0.1)·10 -12  m rad. Furthermore, for both the pulsed and the continuous beam a full width at half maximum energy spread of 0.95 ± 0.05 eV has been measured. Copyright © 2018 Elsevier B.V. All rights reserved.

Generation of mechanical vibrations in metal samples by the use of the pinch effect

NASA Astrophysics Data System (ADS)

Troitskiy, O. A.; Skvortsov, O. B.; Stashenko, V. I.

2017-07-01

The article presents the recent research in electrodynamic processes for metal samples exposed to current pulses. The pinch effect and the skin effect cause the vibration of the metal rods. The results of these studies show how current and magnetic field interact with material samples of gold, silver and copper. The analysis allowed establishing the dependences of peak acceleration on current density and conductor diameter. The dependencies can be used in metal workings and for nondestructive testing.

THz field engineering in two-color femtosecond filaments using chirped and delayed laser pulses

NASA Astrophysics Data System (ADS)

Nguyen, A.; González de Alaiza Martínez, P.; Thiele, I.; Skupin, S.; Bergé, L.

2018-03-01

We numerically study the influence of chirping and delaying several ionizing two-color light pulses in order to engineer terahertz (THz) wave generation in air. By means of comprehensive 3D simulations, it is shown that two chirped pulses can increase the THz yield when they are separated by a suitable time delay for the same laser energy in focused propagation geometry. To interpret these results, the local current theory is revisited and we propose an easy, accessible all-optical criterion that predicts the laser-to-THz conversion efficiencies given any input laser spectrum. In the filamentation regime, numerical simulations display evidence that a chirped pulse is able to produce more THz radiation due to propagation effects, which maintain the two colors of the laser field more efficiently coupled over long distances. A large delay between two pulses promotes multi-peaked THz spectra as well as conversion efficiencies above 10‑4.

Induction linear accelerators

NASA Astrophysics Data System (ADS)

Birx, Daniel

1992-03-01

Among the family of particle accelerators, the Induction Linear Accelerator is the best suited for the acceleration of high current electron beams. Because the electromagnetic radiation used to accelerate the electron beam is not stored in the cavities but is supplied by transmission lines during the beam pulse it is possible to utilize very low Q (typically<10) structures and very large beam pipes. This combination increases the beam breakup limited maximum currents to of order kiloamperes. The micropulse lengths of these machines are measured in 10's of nanoseconds and duty factors as high as 10-4 have been achieved. Until recently the major problem with these machines has been associated with the pulse power drive. Beam currents of kiloamperes and accelerating potentials of megavolts require peak power drives of gigawatts since no energy is stored in the structure. The marriage of liner accelerator technology and nonlinear magnetic compressors has produced some unique capabilities. It now appears possible to produce electron beams with average currents measured in amperes, peak currents in kiloamperes and gradients exceeding 1 MeV/meter, with power efficiencies approaching 50%. The nonlinear magnetic compression technology has replaced the spark gap drivers used on earlier accelerators with state-of-the-art all-solid-state SCR commutated compression chains. The reliability of these machines is now approaching 1010 shot MTBF. In the following paper we will briefly review the historical development of induction linear accelerators and then discuss the design considerations.

Direct observation of electron emission and recombination processes by time domain measurements of charge pumping current

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

Hori, Masahiro, E-mail: hori@eng.u-toyama.ac.jp; Watanabe, Tokinobu; Ono, Yukinori

2015-01-26

To analyze the charge pumping (CP) sequence in detail, the source/drain electron current and the substrate hole current under the CP mode of transistors are simultaneously monitored in the time domain. Peaks are observed in both the electron and hole currents, which are, respectively, attributed to the electron emission from the interface defects and to the recombination with holes. The peak caused by the electron emission is found to consist of two components, strongly suggesting that the present time-domain measurement can enable us to resolve different kinds of interface defects. Investigating the correlation between the number of emitted and recombinedmore » electrons reveals that only one of the two components contributes to the CP current for the gate-pulse fall time from 6.25 × 10{sup −4} to 1.25 × 10{sup −2} s.« less

1030-nm diode-laser-based light source delivering pulses with nanojoule energies and picosecond duration adjustable by mode locking or pulse gating operation

NASA Astrophysics Data System (ADS)

Klehr, A.; Liero, A.; Wenzel, H.; Bugge, F.; Brox, O.; Fricke, J.; Ressel, P.; Knigge, A.; Heinrich, W.; Tränkle, G.

2017-02-01

A new compact 1030 nm picosecond light source which can be switched between pulse gating and mode locking operation is presented. It consists of a multi-section distributed Bragg reflector (DBR) laser, an ultrafast multisection optical gate and a flared power amplifier (PA), mounted together with high frequency electronics and optical elements on a 5×4 cm micro bench. The master oscillator (MO) is a 10 mm long ridge wave-guide (RW) laser consisting of 200 μm long saturable absorber, 1500 μm long gain, 8000 μm long cavity, 200 μm long DBR and 100 μm long monitor sections. The 2 mm long optical gate consisting of several RW sections is monolithically integrated with the 4 mm long gain-guided tapered amplifier on a single chip. The light source can be switched between pulse gating and passive mode locking operation. For pulse gating all sections of the MO (except of the DBR and monitor sections) are forward biased and driven by a constant current. By injecting electrical pulses into one section of the optical gate the CW beam emitted by the MO is converted into a train of optical pulses with adjustable widths between 250 ps and 1000 ps. Peak powers of 20 W and spectral linewidths in the MHz range are achieved. Shorter pulses with widths between 4 ps and 15 ps and peak powers up to 50 W but larger spectral widths of about 300 pm are generated by mode locking where the saturable absorber section of the MO is reversed biased. The repetition rate of 4.2 GHz of the pulse train emitted by the MO can be reduced to values between 1 kHz and 100 MHz by utilizing the optical gate as pulse picker. The pulse-to-pulse distance can be controlled by an external trigger source.

Excess optical enhancement observed with arcons for early crab giant pulses

DOE PAGES

Strader, M. J.; Johnson, M. D.; Mazin, B. A.; ...

2013-11-26

Here, we observe an extraordinary link in the Crab pulsar between the enhancement of an optical pulse and the timing of the corresponding giant radio pulse. At optical through infrared wavelengths, our observations use the high time resolution of ARray Camera for Optical to Near-IR Spectrophotometry, a unique superconducting energy-resolving photon-counting array at the Palomar 200 inch telescope. At radio wavelengths, we observe with the Robert C. Byrd Green Bank Telescope and the Green Bank Ultimate Pulsar Processing Instrument backend. We see an 11.3% ± 2.5% increase in peak optical flux for pulses that have an accompanying giant radio pulsemore » arriving near the peak of the optical main pulse, in contrast to a 3.2% ± 0.5% increase when an accompanying giant radio pulse arrives soon after the optical peak. We also observe that the peak of the optical main pulse is 2.8% ± 0.8% enhanced when there is a giant radio pulse accompanying the optical interpulse. We also observe no statistically significant spectral differences between optical pulses accompanied by and not accompanied by giant radio pulses. These results extend previous observations of optical-radio correlation to the time and spectral domains. Our refined temporal correlation suggests that optical and radio emission are indeed causally linked, and the lack of spectral differences suggests that the same mechanism is responsible for all optical emission.« less

Synthesis of monopolar ultrasound pulses for therapy: the frequency-compounding transducer.

PubMed

Lin, Kuang-Wei; Hall, Timothy L; McGough, Robert J; Xu, Zhen; Cain, Charles A

2014-07-01

In diagnostic ultrasound, broadband transducers capable of short acoustic pulse emission and reception can improve axial resolution and provide sufficient bandwidth for harmonic imaging and multi-frequency excitation techniques. In histotripsy, a cavitation-based ultrasound therapy, short acoustic pulses (<2 cycles) can produce precise tissue ablation wherein lesion formation only occurs when the applied peak negative pressure exceeds an intrinsic threshold of the medium. This paper investigates a frequency compounding technique to synthesize nearly monopolar (half-cycle) ultrasound pulses. More specifically, these pulses were generated using a custom transducer composed of 23 individual relatively-broadband piezoceramic elements with various resonant frequencies (0.5, 1, 1.5, 2, and 3 MHz). Each frequency component of the transducer was capable of generating 1.5-cycle pulses with only one high-amplitude negative half-cycle using a custom 23-channel high-voltage pulser. By varying time delays of individual frequency components to allow their principal peak negative peaks to arrive at the focus of the transducer constructively, destructive interference occurs elsewhere in time and space, resulting in a monopolar pulse approximation with a dominant negative phase (with measured peak negative pressure [P-]: peak positive pressure [P+] = 4.68: 1). By inverting the excitation pulses to individual elements, monopolar pulses with a dominant positive phase can also be generated (with measured P+: P- = 4.74: 1). Experiments in RBC phantoms indicated that monopolar pulses with a dominant negative phase were able to produce very precise histotripsy-type lesions using the intrinsic threshold mechanism. Monopolar pulses with a dominant negative phase can inhibit shock scattering during histotripsy, leading to more predictable lesion formation using the intrinsic threshold mechanism, while greatly reducing any constructive interference, and potential hot-spots elsewhere. Moreover, these monopolar pulses could have many potential benefits in ultrasound imaging, including axial resolution improvement, speckle reduction, and contrast enhancement in pulse inversion imaging.

How proton pulse characteristics influence protoacoustic determination of proton-beam range: simulation studies.

PubMed

Jones, Kevin C; Seghal, Chandra M; Avery, Stephen

2016-03-21

The unique dose deposition of proton beams generates a distinctive thermoacoustic (protoacoustic) signal, which can be used to calculate the proton range. To identify the expected protoacoustic amplitude, frequency, and arrival time for different proton pulse characteristics encountered at hospital-based proton sources, the protoacoustic pressure emissions generated by 150 MeV, pencil-beam proton pulses were simulated in a homogeneous water medium. Proton pulses with Gaussian widths ranging up to 200 μs were considered. The protoacoustic amplitude, frequency, and time-of-flight (TOF) range accuracy were assessed. For TOF calculations, the acoustic pulse arrival time was determined based on multiple features of the wave. Based on the simulations, Gaussian proton pulses can be categorized as Dirac-delta-function-like (FWHM < 4 μs) and longer. For the δ-function-like irradiation, the protoacoustic spectrum peaks at 44.5 kHz and the systematic error in determining the Bragg peak range is <2.6 mm. For longer proton pulses, the spectrum shifts to lower frequencies, and the range calculation systematic error increases (⩽ 23 mm for FWHM of 56 μs). By mapping the protoacoustic peak arrival time to range with simulations, the residual error can be reduced. Using a proton pulse with FWHM = 2 μs results in a maximum signal-to-noise ratio per total dose. Simulations predict that a 300 nA, 150 MeV, FWHM = 4 μs Gaussian proton pulse (8.0 × 10(6) protons, 3.1 cGy dose at the Bragg peak) will generate a 146 mPa pressure wave at 5 cm beyond the Bragg peak. There is an angle dependent systematic error in the protoacoustic TOF range calculations. Placing detectors along the proton beam axis and beyond the Bragg peak minimizes this error. For clinical proton beams, protoacoustic detectors should be sensitive to <400 kHz (for -20 dB). Hospital-based synchrocyclotrons and cyclotrons are promising sources of proton pulses for generating clinically measurable protoacoustic emissions.

Hybrid Ion-Detector/Data-Acquisition System for a TOF-MS

NASA Technical Reports Server (NTRS)

Burton, William D., Jr.; Schultz, J. Albert; Vaughn, Valentine; McCully, Michael; Ulrich, Steven; Egan, Thomas F.

2006-01-01

A modified ion-detector/data-acquisition system has been devised to increase the dynamic range of a time-of-flight mass spectrometer (TOF-MS) that, previously, included a microchannel-plate detector and a data-acquisition system based on counting pulses and time-tagging them by use of a time-to-digital converter (TDC). The dynamic range of the TOF-MS was limited by saturation of the microchannel plate detector, which can handle no more than a few million counts per second. The modified system includes (1) a combined microchannel plate/discrete ion multiplier and (2) a hybrid data-acquisition system that simultaneously performs analog current or voltage measurements and multianode single-ion-pulse-counting time-of-flight measurements to extend the dynamic range of a TDC into the regime in which a mass peak comprises multiple ions arriving simultaneously at the detector. The multianode data are used to determine, in real time, whether the detector is saturated. When saturation is detected, the data-acquisition system selectively enables circuitry that simultaneously determines the ion-peak intensity by measuring the time profile of the analog current or voltage detector-output signal.

Electroanalytical study of proflavine intercalation in 5-methyl or inosine-containing amplicons.

PubMed

Alexiadou, Despina K; Ioannou, Andrea K; Kouidou-Andreou, Sofia A; Voulgaropoulos, Anastasios N; Girousi, Stella Th

2008-10-01

Amplicons corresponding to the GC-rich p53 exon 5 and its analogues, synthesized by substituting 60% of cytosine by 5-methyl-cytosine, or 60% of guanosine by inosine and GC-poor p53 exon 6 were synthesized and investigated electrochemically, in the presence and absence of proflavine, by differential pulse voltammetry (DPV). Incorporation of base analogues and the thermal stability of the resulting amplicons were tested in the presence of a fluorescent probe (Sybr-Green). Peak current at 1.0 V was lower for methylated than for unmethylated PCR amplicons and was similarly affected by proflavine intercalation. In contrast, considerable peak current differences were observed in the presence of proflavine for unmodified exon 5 v.s. exon 6 or inosine-containing amplicons. Thermal analysis verified the expected shifts in melting temperature (T (m)) due to the base analogue incorporation and GC-content variations. In conclusion, methylated and unmethylated PCR amplicons could be distinguished in model DNA systems using differential pulse voltammetry (DPV) and use of proflavine could serve as an electrochemical probe for identifying different DNA conformations.

The light ion pulsed power induction accelerator for ETF

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

Mazarakis, M.G.; Olson, R.E.; Olson, C.L.

1994-12-31

Our Engineering Test Facility (ETF) driver concept is based on HERMES III and RHEPP technologies. Actually, it is a scaled-down version of the LMF design incorporating repetition rate capabilities of up to 10 Hz CW. The preconceptual design presented here provides 200-TW peak power to the ETF target during 10 ns, equal to 2-MJ total ion beam energy. Linear inductive voltage addition driving a self-magnetically insulated transmission line (MITL) is utilized to generate the 36-MV peak voltage needed for lithium ion beams. The {approximately} 3-MA ion current is achieved by utilizing many accelerating modules in parallel. Since the current permore » module is relatively modest ({approximately}300 kA), two-stage or one-stage extraction diodes can be utilized for the generation of singly charged lithium ions. The accelerating modules are arranged symmetrically around the fusion chamber in order to provide uniform irradiation onto the ETF target. In addition, the modules are fired in a programmed sequence in order to generate the optimum power pulse shape onto the target. This design utilizes RHEPP accelerator modules as the principal power source.« less

FORTE Compact Intra-cloud Discharge Detection parameterized by Peak Current

NASA Astrophysics Data System (ADS)

Heavner, M. J.; Suszcynsky, D. M.; Jacobson, A. R.; Heavner, B. D.; Smith, D. A.

2002-12-01

The Los Alamos Sferic Array (EDOT) has recorded over 3.7 million lightning-related fast electric field change data records during April 1 - August 31, 2001 and 2002. The events were detected by three or more stations, allowing for differential-time-of-arrival location determination. The waveforms are characterized with estimated peak currents as well as by event type. Narrow Bipolar Events (NBEs), the VLF/LF signature of Compact Intra-cloud Discharges (CIDs), are generally isolated pulses with identifiable ionospheric reflections, permitting determination of event source altitudes. We briefly review the EDOT characterization of events. The FORTE satellite observes Trans-Ionospheric Pulse Pairs (TIPPs, the VHF satellite signature of CIDs). The subset of coincident EDOT and FORTE CID observations are compared with the total EDOT CID database to characterize the VHF detection efficiency of CIDs. The NBE polarity and altitude are also examined in the context of FORTE TIPP detection. The parameter-dependent detection efficiencies are extrapolated from FORTE orbit to GPS orbit in support of the V-GLASS effort (GPS based global detection of lightning).

Differential pulse voltammetric determination of acyclovir in pharmaceutical preparations using a pencil graphite electrode.

PubMed

Dilgin, Didem Giray; Karakaya, Serkan

2016-06-01

In this study, a new selective and sensitive voltammetric procedure for determination of acyclovir (ACV) was proposed using a disposable electrode, pencil graphite electrode (PGE). Cyclic and differential pulse voltammograms of ACV were recorded in Britton-Robinson buffer solution containing 0.10 M KCl with pH of 4.0 at PGE. The PGE displayed a very good electrochemical behavior with significant enhancement of the peak current compared to a glassy carbon electrode (GCE). Under experimental conditions, the PGE had a linear response range from 1.0 μM to 100.0 μM ACV with a detection limit of 0.3 μM (based on 3 Sb). Relative standard deviations of 4.8 and 3.6% were obtained for five successive determinations of 10.0 and 50.0 μM ACV, respectively, which indicate acceptable repeatability. This voltammetric method was successfully applied to the direct determination of ACV in real pharmaceutical samples. The effect of various interfering compounds on the ACV peak current was studied. Copyright © 2016 Elsevier B.V. All rights reserved.

The Lethality Test System

NASA Astrophysics Data System (ADS)

Parsons, W. M.; Sims, J. R.; Parker, J. V.

1986-11-01

The Lethality Test System (LTS) under construction at Los Alamos is an electromagnetic launcher facility designed to perform impact experiments at velocities up to 15 km/sec. The launcher is a 25 mm round bore, plasma armature railgun 22 m in length. Preinjection is accomplished with a two-stage light gas gun capable of 7 km/sec. The railgun power supply utilizes traction motors, vacuum interrupters, and pulse transformers. An assembly of 28 traction motors, equipped with flywheels, stores approximately 80 MJ at 92 percent of full speed and energizes the primary windings of three pulse transformers at a current of 50 kA. At peak current an array of vacuum interrupters disconnects the transformer primary windings and forces the current to flow in the secondary windings. The secondary windings are connected to the railgun, and by staging the vacuum interrupter openings, a 1-1.3 MA ramped current waveform will be delivered to the railgun.

Validation of neoclassical bootstrap current models in the edge of an H-mode plasma.

PubMed

Wade, M R; Murakami, M; Politzer, P A

2004-06-11

Analysis of the parallel electric field E(parallel) evolution following an L-H transition in the DIII-D tokamak indicates the generation of a large negative pulse near the edge which propagates inward, indicative of the generation of a noninductive edge current. Modeling indicates that the observed E(parallel) evolution is consistent with a narrow current density peak generated in the plasma edge. Very good quantitative agreement is found between the measured E(parallel) evolution and that expected from neoclassical theory predictions of the bootstrap current.

Optimization of current waveform tailoring for magnetically driven isentropic compression experiments

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

Waisman, E. M.; Reisman, D. B.; Stoltzfus, B. S.

2016-06-15

The Thor pulsed power generator is being developed at Sandia National Laboratories. The design consists of up to 288 decoupled and transit time isolated capacitor-switch units, called “bricks,” that can be individually triggered to achieve a high degree of pulse tailoring for magnetically driven isentropic compression experiments (ICE) [D. B. Reisman et al., Phys. Rev. Spec. Top.–Accel. Beams 18, 090401 (2015)]. The connecting transmission lines are impedance matched to the bricks, allowing the capacitor energy to be efficiently delivered to an ICE strip-line load with peak pressures of over 100 GPa. Thor will drive experiments to explore equation of state,more » material strength, and phase transition properties of a wide variety of materials. We present an optimization process for producing tailored current pulses, a requirement for many material studies, on the Thor generator. This technique, which is unique to the novel “current-adder” architecture used by Thor, entirely avoids the iterative use of complex circuit models to converge to the desired electrical pulse. We begin with magnetohydrodynamic simulations for a given material to determine its time dependent pressure and thus the desired strip-line load current and voltage. Because the bricks are connected to a central power flow section through transit-time isolated coaxial cables of constant impedance, the brick forward-going pulses are independent of each other. We observe that the desired equivalent forward-going current driving the pulse must be equal to the sum of the individual brick forward-going currents. We find a set of optimal brick delay times by requiring that the L{sub 2} norm of the difference between the brick-sum current and the desired forward-going current be a minimum. We describe the optimization procedure for the Thor design and show results for various materials of interest.« less

Acceleration and Pickup Ring of Energetic Electrons Observed in Relativistic Magnetic Reconnection Simulations

NASA Astrophysics Data System (ADS)

Ping, Y. L.; Zhong, J. Y.; Wang, X. G.; Sheng, Z. M.; Zhao, G.

2017-11-01

Pickup ring of energetic electrons found in relativistic magnetic reconnection (MR) driven by two relativistic intense femtosecond laser pulses is investigated by particle simulation in 3D geometry. Magnetic reconnection processes and configurations are characterized by plasma current density distributions at different axial positions. Two helical structures associated with the circular polarization of laser pulses break down in the reconnection processes to form a current sheet between them, where energetic electrons are found to pile up and the outflow relativistic electron jets are observed. In the field line diffusion region, electrons are accelerated to multi-MeV with a flatter power-law spectrum due to MR. The development of the pickup ring of energetic electrons is strongly dependent upon laser peak intensities.

Switching power supply

DOEpatents

Mihalka, A.M.

1984-06-05

The invention is a repratable capacitor charging, switching power supply. A ferrite transformer steps up a dc input. The transformer primary is in a full bridge configuration utilizing power MOSFETs as the bridge switches. The transformer secondary is fed into a high voltage, full wave rectifier whose output is connected directly to the energy storage capacitor. The transformer is designed to provide adequate leakage inductance to limit capacitor current. The MOSFETs are switched to the variable frequency from 20 to 50 kHz to charge a capacitor from 0.6 kV. The peak current in a transformer primary and secondary is controlled by increasing the pulse width as the capacitor charges. A digital ripple counter counts pulses and after a preselected desired number is reached an up-counter is clocked.

Development of a compact, rf-driven, pulsed ion source for neutron generation

NASA Astrophysics Data System (ADS)

Perkins, L. T.; Celata, C.; Lee, Y.; Leung, K. N.; Picard, D. S.; Vilaithong, R.; Williams, M. D.; Wutte, D.

1997-02-01

Lawrence Berkeley National Laboratory is currently developing a compact, sealed-accelerator-tube neutron generator capable of producing a neutron flux in the range of 109 to 1010 D-T neutrons per second. The ion source, a miniaturized variation of earlier radio-frequency (rf)-driven multicusp ion sources, is designed to fit within a ˜5 cm diameter borehole. Typical operating parameters include repetition rates up to 100 pps, with pulse widths between 10 and 80 μs (limited only by the available rf power supply) and source pressures as low as ˜5 mTorr. In this configuration, peak extractable hydrogen current densities exceeding 1180 mA/cm2 with H1+ yields over 94% having been achieved.

Terahertz generation from laser-driven ultrafast current propagation along a wire target

NASA Astrophysics Data System (ADS)

Zhuo, H. B.; Zhang, S. J.; Li, X. H.; Zhou, H. Y.; Li, X. Z.; Zou, D. B.; Yu, M. Y.; Wu, H. C.; Sheng, Z. M.; Zhou, C. T.

2017-01-01

Generation of intense coherent THz radiation by obliquely incidenting an intense laser pulse on a wire target is studied using particle-in-cell simulation. The laser-accelerated fast electrons are confined and guided along the surface of the wire, which then acts like a current-carrying line antenna and under appropriate conditions can emit electromagnetic radiation in the THz regime. For a driving laser intensity ˜3 ×1018W /cm2 and pulse duration ˜10 fs, a transient current above 10 KA is produced on the wire surface. The emission-cone angle of the resulting ˜0.15 mJ (˜58 GV/m peak electric field) THz radiation is ˜30∘ . The conversion efficiency of laser-to-THz energy is ˜0.75 % . A simple analytical model that well reproduces the simulated result is presented.

Absorption spectrum of a two-level system subjected to a periodic pulse sequence

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

Fotso, H. F.; Dobrovitski, V. V.

We investigate how the quantum control of a two-level system (TLS) coupled to photons can modify and tune the TLS’s photon absorption spectrum. Tuning and controlling the emission and the absorption is of much interest e.g. for the development of efficient interfaces between stationary and flying qubits in modern architectures for quantum computation and quantum communication. We consider the periodic pulse control, where the TLS is subjected to a periodic sequence of the near-resonant Rabi driving pulses, each pulse implementing a 180° rotation. For small inter-pulse delays, the absorption spectrum features a pronounced peak of stimulated emission at the pulsemore » frequency, as well as equidistant satellite peaks with smaller spectral weights. As long as the detuning between the carrier frequency of the driving and the TLS transition frequency remains moderate, this spectral shape shows little change. Therefore, the quantum control allows shifting the absorption peak to a desired position, and locks the absorption peak to the carrier frequency of the driving pulses. Detailed description of the spectrum, and its evolution as a function time, the inter-pulse spacing and the detuning, is presented.« less

Absorption spectrum of a two-level system subjected to a periodic pulse sequence

DOE PAGES

Fotso, H. F.; Dobrovitski, V. V.

2017-06-01

We investigate how the quantum control of a two-level system (TLS) coupled to photons can modify and tune the TLS’s photon absorption spectrum. Tuning and controlling the emission and the absorption is of much interest e.g. for the development of efficient interfaces between stationary and flying qubits in modern architectures for quantum computation and quantum communication. We consider the periodic pulse control, where the TLS is subjected to a periodic sequence of the near-resonant Rabi driving pulses, each pulse implementing a 180° rotation. For small inter-pulse delays, the absorption spectrum features a pronounced peak of stimulated emission at the pulsemore » frequency, as well as equidistant satellite peaks with smaller spectral weights. As long as the detuning between the carrier frequency of the driving and the TLS transition frequency remains moderate, this spectral shape shows little change. Therefore, the quantum control allows shifting the absorption peak to a desired position, and locks the absorption peak to the carrier frequency of the driving pulses. Detailed description of the spectrum, and its evolution as a function time, the inter-pulse spacing and the detuning, is presented.« less

Partial tripolar cochlear implant stimulation: Spread of excitation and forward masking in the inferior colliculus.

PubMed

Bierer, Julie Arenberg; Bierer, Steven M; Middlebrooks, John C

2010-12-01

This study examines patterns of neural activity in response to single biphasic electrical pulses, presented alone or following a forward masking pulse train, delivered by a cochlear implant. Recordings were made along the tonotopic axis of the central nucleus of the inferior colliculus (ICC) in ketamine/xylazine anesthetized guinea pigs. The partial tripolar electrode configuration was used, which provided a systematic way to vary the tonotopic extent of ICC activation between monopolar (broad) and tripolar (narrow) extremes while maintaining the same peak of activation. The forward masking paradigm consisted of a 200 ms masker pulse train (1017 pulses per second) followed 10 ms later by a single-pulse probe stimulus; the current fraction of the probe was set to 0 (monopolar), 1 (tripolar), or 0.5 (hybrid), and the fraction of the masker was fixed at 0.5. Forward masking tuning profiles were derived from the amount of masking current required to just suppress the activity produced by a fixed-level probe. These profiles were sharper for more focused probe configurations, approximating the pattern of neural activity elicited by single (non-masked) pulses. The result helps to bridge the gap between previous findings in animals and recent psychophysical data. Copyright © 2010 Elsevier B.V. All rights reserved.

Partial tripolar cochlear implant stimulation: Spread of excitation and forward masking in the inferior colliculus

PubMed Central

Bierer, Julie Arenberg; Bierer, Steven M.; Middlebrooks, John C.

2010-01-01

This study examines patterns of neural activity in response to single biphasic electrical pulses, presented alone or following a forward masking pulse train, delivered by a cochlear implant. Recordings were made along the tonotopic axis of the central nucleus of the inferior colliculus (ICC) in ketamine/xylazine anesthetized guinea pigs. The partial tripolar electrode configuration was used, which provided a systematic way to vary the tonotopic extent of ICC activation between monopolar (broad) and tripolar (narrow) extremes while maintaining the same peak of activation. The forward masking paradigm consisted of a 200-ms masker pulse train (1017 pulses per second) followed 10 ms later by a single-pulse probe stimulus; the current fraction of the probe was set to 0 (monopolar), 1 (tripolar), or 0.5 (hybrid), and the fraction of the masker was fixed at 0.5. Forward masking tuning profiles were derived from the amount of masking current required to just suppress the activity produced by a fixed-level probe. These profiles were sharper for more focused probe configurations, approximating the pattern of neural activity elicited by single (non-masked) pulses. The result helps to bridge the gap between previous findings in animals and recent psychophysical data. PMID:20727397

Hysteresis in Lanthanide Zirconium Oxides Observed Using a Pulse CV Technique and including the Effect of High Temperature Annealing.

PubMed

Lu, Qifeng; Zhao, Chun; Mu, Yifei; Zhao, Ce Zhou; Taylor, Stephen; Chalker, Paul R

2015-07-29

A powerful characterization technique, pulse capacitance-voltage (CV) technique, was used to investigate oxide traps before and after annealing for lanthanide zirconium oxide thin films deposited on n-type Si (111) substrates at 300 °C by liquid injection Atomic Layer Deposition (ALD). The results indicated that: (1) more traps were observed compared to the conventional capacitance-voltage characterization method in LaZrO x ; (2) the time-dependent trapping/de-trapping was influenced by the edge time, width and peak-to-peak voltage of a gate voltage pulse. Post deposition annealing was performed at 700 °C, 800 °C and 900 °C in N₂ ambient for 15 s to the samples with 200 ALD cycles. The effect of the high temperature annealing on oxide traps and leakage current were subsequently explored. It showed that more traps were generated after annealing with the trap density increasing from 1.41 × 10 12 cm -2 for as-deposited sample to 4.55 × 10 12 cm -2 for the 800 °C annealed one. In addition, the leakage current density increase from about 10 - ⁶ A/cm² at V g = +0.5 V for the as-deposited sample to 10 -3 A/cm² at V g = +0.5 V for the 900 °C annealed one.

Pulsed hybrid dual wavelength Y-branch-DFB laser-tapered amplifier system suitable for water vapor detection at 965 nm with 16 W peak power

NASA Astrophysics Data System (ADS)

Vu, Thi N.; Klehr, Andreas; Sumpf, Bernd; Hoffmann, Thomas; Liero, Armin; Tränkle, Günther

2016-03-01

A master oscillator power amplifier system emitting alternatingly at two neighbored wavelengths around 965 nm is presented. As master oscillator (MO) a Y-branch DFB-laser is used. The two branches, which can be individually controlled, deliver the two wavelengths needed for a differential absorption measurement of water vapor. Adjusting the current through the DFB sections, the wavelength can be adjusted with respect to the targeted either "on" or "off" resonance, respectively wavelength λon or wavelength λoff. The emission of this laser is amplified in a tapered amplifier (TA). The ridge waveguide section of the TA acts as optical gate to generate short pulses with duration of 8 ns at a repetition rate of 25 kHz, the flared section is used for further amplification to reach peak powers up to 16 W suitable for micro-LIDAR (Light Detection and Ranging). The necessary pulse current supply user a GaN-transistor based driver electronics placed close to the power amplifier (PA). The spectral properties of the emission of the MO are preserved by the PA. A spectral line width smaller than 10 pm and a side mode suppression ratio (SMSR) of 37 dB are measured. These values meet the demands for water vapor absorption measurements under atmospheric conditions.

Study and development of 22 kW peak power fiber coupled short pulse Nd:YAG laser for cleaning applications

NASA Astrophysics Data System (ADS)

Choubey, Ambar; Vishwakarma, S. C.; Vachhani, D. M.; Singh, Ravindra; Misra, Pushkar; Jain, R. K.; Arya, R.; Upadhyaya, B. N.; Oak, S. M.

2014-11-01

Free running short pulse Nd:YAG laser of microsecond pulse duration and high peak power has a unique capability to ablate material from the surface without heat propagation into the bulk. Applications of short pulse Nd:YAG lasers include cleaning and restoration of marble, stones, and a variety of metals for conservation. A study on the development of high peak power short pulses from Nd:YAG laser along with its cleaning and conservation applications has been performed. A pulse energy of 1.25 J with 55 μs pulse duration and a maximum peak power of 22 kW has been achieved. Laser beam has an M2 value of ~28 and a pulse-to-pulse stability of ±2.5%. A lower value of M2 means a better beam quality of the laser in multimode operation. A top hat spatial profile of the laser beam was achieved at the exit end of 200 μm core diameter optical fiber, which is desirable for uniform cleaning. This laser system has been evaluated for efficient cleaning of surface contaminations on marble, zircaloy, and inconel materials for conservation with cleaning efficiency as high as 98%. Laser's cleaning quality and efficiency have been analysed by using a microscope, a scanning electron microscope (SEM), and X-ray photon spectroscopy (XPS) measurements.

Generation of subterawatt-attosecond pulses in a soft x-ray free-electron laser

DOE PAGES

Huang, Senlin; Ding, Yuantao; Huang, Zhirong; ...

2016-08-15

Here, we propose a novel scheme to generate attosecond soft x rays in a self-seeded free-electron laser (FEL) suitable for enabling attosecond spectroscopic investigations. A time-energy chirped electron bunch with additional sinusoidal energy modulation is adopted to produce a short seed pulse through a self-seeding monochromator. This short seed pulse, together with high electron current spikes and a cascaded delay setup, enables a high-efficiency FEL with a fresh bunch scheme. Simulations show that using the Linac Coherent Light Source (LCLS) parameters, soft x-ray pulses with a FWHM of 260 attoseconds and a peak power of 0.5 TW can be obtained.more » This scheme also has the feature of providing a stable central wavelength determined by the self-seeding monochromator.« less

Radially polarized, half-cycle, attosecond pulses from laser wakefields through coherent synchrotronlike radiation.

PubMed

Li, F Y; Sheng, Z M; Chen, M; Yu, L L; Meyer-ter-Vehn, J; Mori, W B; Zhang, J

2014-10-01

Attosecond bursts of coherent synchrotronlike radiation are found when driving ultrathin relativistic electron disks in a quasi-one-dimensional regime of wakefield acceleration, in which the laser waist is larger than the wake wavelength. The disks of overcritical density shrink radially due to focusing wakefields, thus providing the transverse currents for the emission of an intense, radially polarized, half-cycle pulse of about 100 attoseconds in duration. The electromagnetic pulse first focuses to a peak intensity (7×10(20)W/cm(2)) 10 times larger than the driving pulse and then emerges as a conical beam. Basic dynamics of the radiative process are derived analytically and in agreement with particle-in-cell simulations. By making use of gas targets instead of solids to form the ultrathin disks, this method allows for high repetition rates required for applications.

Pulsed power systems for environmental and industrial applications

NASA Astrophysics Data System (ADS)

Neau, E. L.

1994-10-01

The development of high peak power simulators, laser drivers, free electron lasers, and Inertial Confinement Fusion drivers is being extended to high average power short-pulse machines with the capabilities of performing new roles in environmental cleanup and industrial manufacturing processes. We discuss a new class of short-pulse, high average power accelerator that achieves megavolt electron and ion beams with 10's of kiloamperes of current and average power levels in excess of 100 kW. Large treatment areas are possible with these systems because kilojoules of energy are available in each output pulse. These systems can use large area x-ray converters for applications requiring grater depth of penetration such as food pasteurization and waste treatment. The combined development of this class of accelerators and applications, and Sandia National Laboratories, is called Quantum Manufacturing.

Biointerfacial Property of Plasma-Treated Single-Walled Carbon Nanotube Film Electrodes for Electrochemical Biosensors

NASA Astrophysics Data System (ADS)

Kim, Joon Hyub; Lee, Jun-Yong; Jin, Joon-Hyung; Park, Eun Jin; Min, Nam Ki

2013-01-01

The single-walled carbon nanotube (SWCNT)-based thin film was spray-coated on the Pt support and functionalized using O2 plasma. The effects of plasma treatment on the biointerfacial properties of the SWCNT films were analyzed by cyclic voltammogram (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). The plasma-functionalized (pf) SWCNT electrodes modified with Legionella pneumophila-specific probe DNA strands showed a much higher peak current and a smaller peak separation in differential pulse voltammetry and a lower charge transfer resistance, compared to the untreated samples. These results suggest that the pf-SWCNT films have a better electrocatalytic character and an electron transfer capability faster than the untreated SWCNTs, due to the fact that the oxygen-containing functional groups promote direct electron transfer in the biointerfacial region of the electrocatalytic activity of redox-active biomolecules.

Laser generation of Au ions with charge states above 50+

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

Laska, L.; Jungwirth, K.; Krasa, J.

2008-02-15

Results of recent studies on highly charged Au ion generation, using the intense long pulses of the PALS high power iodine laser ({lambda}=1.315 {mu}m, E{sub L}=800 J/400 ps), operating under variable experimental conditions (1{omega}, 3{omega}, varying target thickness and changing focus positions), are presented. Both the ion collectors and the ion electrostatic analyzers were applied for the identification of ions in a large distance from the target. The time-of-flight collector signals were treated by a means of peak deconvolution assuming a shifted Maxwell-Boltzmann form of the constituent ion current peaks. Attention was paid to the influence of pulse precursor, whichmore » becomes evident, especially, if using thinner targets and 1{omega}. The results for 3{omega} point to the presence of several groups of ions with the highest recorded charge state Au{sup 53+}.« less

High average/peak power linearly polarized all-fiber picosecond MOPA seeded by mode-locked noise-like pulses

NASA Astrophysics Data System (ADS)

Yu, H. L.; Ma, P. F.; Tao, R. M.; Wang, X. L.; Zhou, P.; Chen, J. B.

2015-06-01

The characteristics of mode-locked noise-like pulses generated from a passively mode-locked fiber oscillator are experimentally investigated. By carefully adjusting the two polarization controllers, stable mode-locked noise-like pulse emission with a high radio frequency signal/noise ratio of  >55 dB is successfully achieved, ensuring the safety and possibility of high power amplification. To investigate the amplification characteristics of such pulses, one all-fiber master oscillator power amplifier (MOPA) is built to boost the power and energy of such pulses. Amplified noise-like pulses with average output power of 423 W, repetition rate of 18.71 MHz, pulse energy of 22.61 μJ, pulse duration of 72.1 ps and peak power of 314 kW are obtained. Near diffraction-limited beam is also demonstrated with M2 factor measured at full power operation of ~1.2 in the X and Y directions. The polarization extinction ratio at output power of 183 W is measured to be ~13 dB. To the best of our knowledge, this is the first demonstration of high-power amplification of noise-like pulses and the highest peak power ever reported in all-fiber picosecond MOPAs. The temporal self-compression process of such pulses and high peak power when amplified make it an ideal pump source for generation of high-power supercontinuum. Other potential applications, such as material processing and optical coherent tomography, could also be foreseen.

20 T portable bipolar magnetic pulser.

PubMed

Wolf Cruz, R R; Dias, A L B; Bonfim, M J C

2010-06-01

High magnetic fields are required for the study of hard magnetic materials and, in many cases, the reversal of these fields is essential. This paper describes a portable pulse generator capable of producing bipolar magnetic fields up to 20 T into a copper coil. The peak current around 7 kA is achieved by discharging two capacitor banks through a combination of thyristors and fast diodes. Each pulse polarity has a semisinusoidal shape with 18 mus base width. Pulse triggering is computer controlled and magnetic measurements are done by an induction coil or Kerr effect acquired by a sampling oscilloscope. The whole apparatus weighs less than 2 kg. Hysteresis loops of NdFeB magnets were done to demonstrate the viability of the system.

The Phelix Pulsed Power Project: Bringing Portable Magnetic Drive to World Class Radiography

DTIC Science & Technology

2011-06-01

vitreous carbon damping resistors are used on the output headers of each module for a total of 25.1 mΩ of resistance. Figure 6. The PHELIX portable...4 MA peak current in the secondary winding for driving a liner. In order to not produce too much reverse voltage on the capacitors, reticulated

Characterization of fast photoelectron packets in weak and strong laser fields in ultrafast electron microscopy.

PubMed

Plemmons, Dayne A; Tae Park, Sang; Zewail, Ahmed H; Flannigan, David J

2014-11-01

The development of ultrafast electron microscopy (UEM) and variants thereof (e.g., photon-induced near-field electron microscopy, PINEM) has made it possible to image atomic-scale dynamics on the femtosecond timescale. Accessing the femtosecond regime with UEM currently relies on the generation of photoelectrons with an ultrafast laser pulse and operation in a stroboscopic pump-probe fashion. With this approach, temporal resolution is limited mainly by the durations of the pump laser pulse and probe electron packet. The ability to accurately determine the duration of the electron packets, and thus the instrument response function, is critically important for interpretation of dynamics occurring near the temporal resolution limit, in addition to quantifying the effects of the imaging mode. Here, we describe a technique for in situ characterization of ultrashort electron packets that makes use of coupling with photons in the evanescent near-field of the specimen. We show that within the weakly-interacting (i.e., low laser fluence) regime, the zero-loss peak temporal cross-section is precisely the convolution of electron packet and photon pulse profiles. Beyond this regime, we outline the effects of non-linear processes and show that temporal cross-sections of high-order peaks explicitly reveal the electron packet profile, while use of the zero-loss peak becomes increasingly unreliable. Copyright © 2014 Elsevier B.V. All rights reserved.

Experimental Study of Magnetic Field Production and Dielectric Breakdown of Auto-Magnetizing Liners

NASA Astrophysics Data System (ADS)

Shipley, Gabriel; Awe, Thomas; Hutchinson, Trevor; Hutsel, Brian; Slutz, Stephen; Lamppa, Derek

2017-10-01

AutoMag liners premagnetize the fuel in MagLIF targets and provide enhanced x-ray diagnostic access and increased current delivery without requiring external field coils. AutoMag liners are composite liners made with discrete metallic helical conduction paths separated by insulating material. First, a low dI/dt ``foot'' current pulse (1 MA in 100 ns) premagnetizes the fuel. Next, a higher dI/dt pulse with larger induced electric field initiates breakdown on the composite liner's; surface, switching the current from helical to axial to implode the liner. Experiments on MYKONOS have tested the premagnetization and breakdown phases of AutoMag and demonstrate axial magnetic fields above 90 Tesla for a 550 kA peak current pulse. Electric fields of 17 MV/m have been generated before breakdown. AutoMag may enhance MagLIF performance by increasing the premagnetization strength significantly above 30 T, thus reducing thermal-conduction losses and mitigating anomalous diffusion of magnetic field out of hotter fuel regions, by, for example, the Nernst thermoelectric effect. This project was funded in part by Sandia's Laboratory Directed Research and Development Program (Projects No. 200169 and 195306).

Low-noise pulse conditioner

DOEpatents

Bird, David A.

1983-01-01

A low-noise pulse conditioner is provided for driving electronic digital processing circuitry directly from differentially induced input pulses. The circuit uses a unique differential-to-peak detector circuit to generate a dynamic reference signal proportional to the input peak voltage. The input pulses are compared with the reference signal in an input network which operates in full differential mode with only a passive input filter. This reduces the introduction of circuit-induced noise, or jitter, generated in ground referenced input elements normally used in pulse conditioning circuits, especially speed transducer processing circuits.

Calcium currents in a fast-twitch skeletal muscle of the rat.

PubMed

Donaldson, P L; Beam, K G

1983-10-01

Slow ionic currents were measured in the rat omohyoid muscle with the three-microelectrode voltage-clamp technique. Sodium and delayed rectifier potassium currents were blocked pharmacologically. Under these conditions, depolarizing test pulses elicited an early outward current, followed by a transient slow inward current, followed in turn by a late outward current. The early outward current appeared to be a residual delayed rectifier current. The slow inward current was identified as a calcium current on the basis that (a) its magnitude depended on extracellular calcium concentration, (b) it was blocked by the addition of the divalent cations cadmium or nickel, and reduced in magnitude by the addition of manganese or cobalt, and (c) barium was able to replace calcium as an inward current carrier. The threshold potential for inward calcium current was around -20 mV in 10mM extracellular calcium and about -35 mV in 2 mM calcium. Currents were net inward over part of their time course for potentials up to at least +30 mV. At temperatures of 20-26 degrees C, the peak inward current (at approximately 0 mV) was 139 +/- 14 microA/cm2 (mean +/- SD), increasing to 226 +/- 28 microA/cm2 at temperatures of 27-37 degrees C. The late outward current exhibited considerable fiber-to-fiber variability. In some fibers it was primarily a time-independent, nonlinear leakage current. In other fibers it was primarily a time-independent, nonlinear leakage current. In other fibers it appeared to be the sum of both leak and a slowly activated outward current. The rate of activation of inward calcium current was strongly temperature dependent. For example, in a representative fiber, the time-to-peak inward current for a +10-mV test pulse decreased from approximately 250 ms at 20 degrees C to 100 ms at 30 degrees C. At 37 degrees C, the time-to-peak current was typically approximately 25 ms. The earliest phase of activation was difficult to quantify because the ionic current was partially obscured by nonlinear charge movement. Nonetheless, at physiological temperatures, the rate of calcium channel activation in rat skeletal muscle is about five times faster than activation of calcium channels in frog muscle. This pathway may be an important source of calcium entry in mammalian muscle.

Controlling Gilbert damping in a YIG film using nonlocal spin currents

NASA Astrophysics Data System (ADS)

Haidar, M.; Dürrenfeld, P.; Ranjbar, M.; Balinsky, M.; Fazlali, M.; Dvornik, M.; Dumas, R. K.; Khartsev, S.; Åkerman, J.

2016-11-01

We demonstrate the control of Gilbert damping in 65-nm-thick yttrium iron garnet (YIG) films using a spin-polarized current generated by a direct current through a nanocontact, spin filtered by a thin Co layer. The magnetodynamics of both the YIG and the Co layers can be excited by a pulse-modulated microwave current injected through the nanocontact and the response detected as a lock-in amplified voltage over the device. The spectra show three clear peaks, two associated with the ferromagnetic resonance (FMR) in each layer, and an additional Co mode with a higher wave vector proportional to the inverse of the nanocontact diameter. By varying the sign and magnitude of the direct nanocontact current, we can either increase or decrease the linewidth of the YIG FMR peak consistent with additional positive or negative damping being exerted by the nonlocal spin current injected into the YIG film. Our nanocontact approach thus offers an alternative route in the search for auto-oscillations in YIG films.

Optical chirped beam amplification and propagation

DOEpatents

Barty, Christopher P.

2004-10-12

A short pulse laser system uses dispersive optics in a chirped-beam amplification architecture to produce high peak power pulses and high peak intensities without the potential for intensity dependent damage to downstream optical components after amplification.

Theoretical detection threshold of the proton-acoustic range verification technique.

PubMed

Ahmad, Moiz; Xiang, Liangzhong; Yousefi, Siavash; Xing, Lei

2015-10-01

Range verification in proton therapy using the proton-acoustic signal induced in the Bragg peak was investigated for typical clinical scenarios. The signal generation and detection processes were simulated in order to determine the signal-to-noise limits. An analytical model was used to calculate the dose distribution and local pressure rise (per proton) for beams of different energy (100 and 160 MeV) and spot widths (1, 5, and 10 mm) in a water phantom. In this method, the acoustic waves propagating from the Bragg peak were generated by the general 3D pressure wave equation implemented using a finite element method. Various beam pulse widths (0.1-10 μs) were simulated by convolving the acoustic waves with Gaussian kernels. A realistic PZT ultrasound transducer (5 cm diameter) was simulated with a Butterworth bandpass filter with consideration of random noise based on a model of thermal noise in the transducer. The signal-to-noise ratio on a per-proton basis was calculated, determining the minimum number of protons required to generate a detectable pulse. The maximum spatial resolution of the proton-acoustic imaging modality was also estimated from the signal spectrum. The calculated noise in the transducer was 12-28 mPa, depending on the transducer central frequency (70-380 kHz). The minimum number of protons detectable by the technique was on the order of 3-30 × 10(6) per pulse, with 30-800 mGy dose per pulse at the Bragg peak. Wider pulses produced signal with lower acoustic frequencies, with 10 μs pulses producing signals with frequency less than 100 kHz. The proton-acoustic process was simulated using a realistic model and the minimal detection limit was established for proton-acoustic range validation. These limits correspond to a best case scenario with a single large detector with no losses and detector thermal noise as the sensitivity limiting factor. Our study indicated practical proton-acoustic range verification may be feasible with approximately 5 × 10(6) protons/pulse and beam current.

Theoretical detection threshold of the proton-acoustic range verification technique

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

Ahmad, Moiz; Yousefi, Siavash; Xing, Lei, E-mail: lei@stanford.edu

2015-10-15

Purpose: Range verification in proton therapy using the proton-acoustic signal induced in the Bragg peak was investigated for typical clinical scenarios. The signal generation and detection processes were simulated in order to determine the signal-to-noise limits. Methods: An analytical model was used to calculate the dose distribution and local pressure rise (per proton) for beams of different energy (100 and 160 MeV) and spot widths (1, 5, and 10 mm) in a water phantom. In this method, the acoustic waves propagating from the Bragg peak were generated by the general 3D pressure wave equation implemented using a finite element method.more » Various beam pulse widths (0.1–10 μs) were simulated by convolving the acoustic waves with Gaussian kernels. A realistic PZT ultrasound transducer (5 cm diameter) was simulated with a Butterworth bandpass filter with consideration of random noise based on a model of thermal noise in the transducer. The signal-to-noise ratio on a per-proton basis was calculated, determining the minimum number of protons required to generate a detectable pulse. The maximum spatial resolution of the proton-acoustic imaging modality was also estimated from the signal spectrum. Results: The calculated noise in the transducer was 12–28 mPa, depending on the transducer central frequency (70–380 kHz). The minimum number of protons detectable by the technique was on the order of 3–30 × 10{sup 6} per pulse, with 30–800 mGy dose per pulse at the Bragg peak. Wider pulses produced signal with lower acoustic frequencies, with 10 μs pulses producing signals with frequency less than 100 kHz. Conclusions: The proton-acoustic process was simulated using a realistic model and the minimal detection limit was established for proton-acoustic range validation. These limits correspond to a best case scenario with a single large detector with no losses and detector thermal noise as the sensitivity limiting factor. Our study indicated practical proton-acoustic range verification may be feasible with approximately 5 × 10{sup 6} protons/pulse and beam current.« less

Theoretical detection threshold of the proton-acoustic range verification technique

PubMed Central

Ahmad, Moiz; Xiang, Liangzhong; Yousefi, Siavash; Xing, Lei

2015-01-01

Purpose: Range verification in proton therapy using the proton-acoustic signal induced in the Bragg peak was investigated for typical clinical scenarios. The signal generation and detection processes were simulated in order to determine the signal-to-noise limits. Methods: An analytical model was used to calculate the dose distribution and local pressure rise (per proton) for beams of different energy (100 and 160 MeV) and spot widths (1, 5, and 10 mm) in a water phantom. In this method, the acoustic waves propagating from the Bragg peak were generated by the general 3D pressure wave equation implemented using a finite element method. Various beam pulse widths (0.1–10 μs) were simulated by convolving the acoustic waves with Gaussian kernels. A realistic PZT ultrasound transducer (5 cm diameter) was simulated with a Butterworth bandpass filter with consideration of random noise based on a model of thermal noise in the transducer. The signal-to-noise ratio on a per-proton basis was calculated, determining the minimum number of protons required to generate a detectable pulse. The maximum spatial resolution of the proton-acoustic imaging modality was also estimated from the signal spectrum. Results: The calculated noise in the transducer was 12–28 mPa, depending on the transducer central frequency (70–380 kHz). The minimum number of protons detectable by the technique was on the order of 3–30 × 106 per pulse, with 30–800 mGy dose per pulse at the Bragg peak. Wider pulses produced signal with lower acoustic frequencies, with 10 μs pulses producing signals with frequency less than 100 kHz. Conclusions: The proton-acoustic process was simulated using a realistic model and the minimal detection limit was established for proton-acoustic range validation. These limits correspond to a best case scenario with a single large detector with no losses and detector thermal noise as the sensitivity limiting factor. Our study indicated practical proton-acoustic range verification may be feasible with approximately 5 × 106 protons/pulse and beam current. PMID:26429247

Cascaded Raman shifting of high-peak-power nanosecond pulses in As₂S₃ and As₂Se₃ optical fibers.

PubMed

White, Richard T; Monro, Tanya M

2011-06-15

We report efficient cascaded Raman scattering of near-IR nanosecond pulses in large-core (65 μm diameter) As₂S₃ and As₂Se₃ optical fibers. Raman scattering dominates other spectral broadening mechanisms, such as four-wave mixing, modulation instability, and soliton dynamics, because the fibers have large normal group-velocity dispersion in the spectral range of interest. With ~2 ns pump pulses at a wavelength of 1.9 μm, four Stokes peaks, all with peak powers greater than 1 kW, have been measured.

Achievement of radiative feedback control for long-pulse operation on EAST

NASA Astrophysics Data System (ADS)

Wu, K.; Yuan, Q. P.; Xiao, B. J.; Wang, L.; Duan, Y. M.; Chen, J. B.; Zheng, X. W.; Liu, X. J.; Zhang, B.; Xu, J. C.; Luo, Z. P.; Zang, Q.; Li, Y. Y.; Feng, W.; Wu, J. H.; Yang, Z. S.; Zhang, L.; Luo, G.-N.; Gong, X. Z.; Hu, L. Q.; Hu, J. S.; Li, J.

2018-05-01

The active feedback control of radiated power to prevent divertor target plates overheating during long-pulse operation has been developed and implemented on EAST. The radiation control algorithm, with impurity seeding via a supersonic molecular beam injection (SMBI) system, has shown great success in both reliability and stability. By seeding a sequence of short neon (Ne) impurity pulses with the SMBI from the outer mid-plane, the radiated power of the bulk plasma can be well controlled, and the duration of radiative control (feedforward and feedback) is 4.5 s during a discharge of 10 s. Reliable control of the total radiated power of bulk plasma has been successfully achieved in long-pulse upper single null (USN) discharges with a tungsten divertor. The achieved control range of {{f}rad} is 20%–30% in L-mode regimes and 18%–36% in H-mode regimes. The temperature of the divertor target plates was maintained at a low level during the radiative control phase. The peak particle flux on the divertor target was decreased by feedforward Ne injection in the L-mode discharges, while the Ne pulses from the SMBI had no influence on the peak particle flux because of the very small injecting volume. It is shown that although the radiated power increased, no serious reduction of plasma-stored energy or confinement was observed during the control phase. The success of the radiation control algorithm and current experiments in radiated power control represents a significant advance for steady-state divertor radiation and heat flux control on EAST for near-future long-pulse operation.

Rheoencephalographic (REG) Assessment of Head and Neck Cooling for use with Multiple Sclerosis Patients

NASA Technical Reports Server (NTRS)

Montogomery, Leslie D.; Ku, Yu-Tsuan E.; Webbon, Bruce W. (Technical Monitor)

1995-01-01

We have prepared a computer program (RHEOSYS:RHEOencephalographic impedance trace scanning SyStem) that can be used to automate the analysis of segmental impedance blood flow waveforms. This program was developed to assist in the post test analysis of recorded impedance traces from multiple segments of the body. It incorporates many of the blood flow, segmental volume, and vascular state indices reported in the world literature. As it is currently programmed, seven points are selected from each blood flow pulse and associated ECG waveforrn: 1. peak of the first ECG QRS complex, 2. start of systolic slope on the blood flow trace, 3. maximum amplitude of the impedance pulse, 4. position of the dicrotic notch, 5. maximum amplitude of the postdicrotic segment, 6. peak of the second ECG QRS complex, and 7. start of the next blood flow pulse. These points we used to calculate various geometric, area, and time-related values associated with the impedance pulse morphology. RHEOSYS then calculates a series of 34 impedance and cardiac cycle parameters which include pulse amplitudes; areas; pulse propagation times; cardiac cycle times; and various measures of arterial and various tone, contractility, and pulse volume. We used this program to calculate the scalp and intracranial blood flow responses to head and neck cooling as it may be applied to lower the body temperatures of multiple sclerosis patients. Twelve women and twelve men were tested using a commercially available head and neck cooling system operated at its maximum cooling capacity for a period of 30 minutes. Head and neck cooling produced a transient change in scalp blood flow and a significant, (P<0.05) decrease of approx. 30% in intracranial blood flow. Results of this experiment will illustrate how REG and RHEOSYS can be used in biomedical applications.

Terahertz generation from laser-driven ultrafast current propagation along a wire target.

PubMed

Zhuo, H B; Zhang, S J; Li, X H; Zhou, H Y; Li, X Z; Zou, D B; Yu, M Y; Wu, H C; Sheng, Z M; Zhou, C T

2017-01-01

Generation of intense coherent THz radiation by obliquely incidenting an intense laser pulse on a wire target is studied using particle-in-cell simulation. The laser-accelerated fast electrons are confined and guided along the surface of the wire, which then acts like a current-carrying line antenna and under appropriate conditions can emit electromagnetic radiation in the THz regime. For a driving laser intensity ∼3×10^{18}W/cm^{2} and pulse duration ∼10 fs, a transient current above 10 KA is produced on the wire surface. The emission-cone angle of the resulting ∼0.15 mJ (∼58 GV/m peak electric field) THz radiation is ∼30^{∘}. The conversion efficiency of laser-to-THz energy is ∼0.75%. A simple analytical model that well reproduces the simulated result is presented.

Compensated pulsed alternator

DOEpatents

Weldon, William F.; Driga, Mircea D.; Woodson, Herbert H.

1980-01-01

This invention relates to an electromechanical energy converter with inertial energy storage. The device, a single phase, two or multi-pole alternator with stationary field coils, and a rotating armature is provided. The rotor itself may be of laminated steel for slower pulses or for faster pulses should be nonmagnetic and electrically nonconductive in order to allow rapid penetration of the field as the armature coil rotates. The armature coil comprises a plurality of power generating conductors mounted on the rotor. The alternator may also include a stationary or counterrotating compensating coil to increase the output voltage thereof and to reduce the internal impedance of the alternator at the moment of peak outout. As the machine voltage rises sinusoidally, an external trigger switch is adapted to be closed at the appropriate time to create the desired output current from said alternator to an external load circuit, and as the output current passes through zero a self-commutating effect is provided to allow the switch to disconnect the generator from the external circuit.

Photoemission experiments of a large area scandate dispenser cathode

NASA Astrophysics Data System (ADS)

Zhang, Huang; Liu, Xing-guang; Chen, Yi; Chen, De-biao; Jiang, Xiao-guo; Yang, An-min; Xia, Lian-sheng; Zhang, Kai-zhi; Shi, Jin-shui; Zhang, Lin-wen

2010-09-01

A 100-mm-diameter scandate dispenser cathode was tested as a photocathode with a 10 ns Nd:YAG laser (266 nm) on an injector test stand for linear induction accelerators. This thermionic dispenser cathode worked at temperatures ranging from room temperature to 930 °C (below or near the thermionic emission threshold) while the vacuum was better than 4×10 -7 Torr. The laser pulse was synchronized with a 120 ns diode voltage pulse stably and they were in single pulse mode. Emission currents were measured by a Faraday cup. The maximum peak current collected at the anode was about 100 A. The maximum quantum efficiency measured at low laser power was 2.4×10 -4. Poisoning effect due to residual gas was obvious and uninterrupted heating was needed to keep cathode's emission capability. The cathode was exposed to air one time between experiments and recovered after being reconditioned. Photoemission uniformity of the cathode was also explored by changing the laser spot's position.

Effects of solution volume on hydrogen production by pulsed spark discharge in ethanol solution

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

Xin, Y. B.; Sun, B., E-mail: sunb88@dlmu.edu.cn; Zhu, X. M.

2016-07-15

Hydrogen production from ethanol solution (ethanol/water) by pulsed spark discharge was optimized by varying the volume of ethanol solution (liquid volume). Hydrogen yield was initially increased and then decreased with the increase in solution volume, which achieved 1.5 l/min with a solution volume of 500 ml. The characteristics of pulsed spark discharge were studied in this work; the results showed that the intensity of peak current, the rate of current rise, and energy efficiency of hydrogen production can be changed by varying the volume of ethanol solution. Meanwhile, the mechanism analysis of hydrogen production was accomplished by monitoring the process of hydrogenmore » production and the state of free radicals. The analysis showed that decreasing the retention time of gas production and properly increasing the volume of ethanol solution can enhance the hydrogen yield. Through this research, a high-yield and large-scale method of hydrogen production can be achieved, which is more suitable for industrial application.« less

Properties of M components from currents measured at triggered lightning channel base

NASA Astrophysics Data System (ADS)

Thottappillil, Rajeev; Goldberg, Jon D.; Rakov, Vladimir A.; Uman, Martin A.; Fisher, Richard J.; Schnetzer, George H.

1995-12-01

Channel base currents from triggered lightning were measured at the NASA Kennedy Space Center, Florida, during summer 1990 and at Fort McClellan, Alabama, during summer 1991. An analysis of the return stroke data and overall continuing current data has been published by Fisher et al. [1993]. Here an analysis is given of the impulsive processes, called M components, that occur during the continuing current following return strokes. The 14 flashes analyzed contain 37 leader-return stroke sequences and 158 M components, both processes lowering negative charge from cloud to ground. Statistics are presented for the following M current pulse parameters: magnitude, rise time, duration, half-peak width, preceding continuing current level, M interval, elapsed time since the return stroke, and charge transferred by the M current pulse. A typical M component in triggered lightning is characterized by a more or less symmetrical current pulse having an amplitude of 100-200 A (2 orders of magnitude lower than that for a typical return stroke [Fisher et al., 1993]), a 10-90% rise time of 300-500 μs (3 orders of magnitude larger than that for a typical return stroke [Fisher et al., 1993]), and a charge transfer to ground of the order of 0.1 to 0.2 C (1 order of magnitude smaller than that for a typical subsequent return stroke pulse [Berger et al., 1975]). About one third of M components transferred charge greater than the minimum charge reported by Berger et al. [1975] for subsequent leader-return stroke sequences. No correlation was found between either the M charge or the magnitude of the M component current (the two are moderately correlated) and any other parameter considered. M current pulses occurring soon after the return stroke tend to have shorter rise times, shorter durations, and shorter M intervals than those which occur later. M current pulses were observed to be superimposed on continuing currents greater than 30 A or so, with one exception out of 140 cases, wherein the continuing current level was measured to be about 20 A. The first M component virtually always (one exception out of 34 cases) occurred within 4 ms of the return stroke. This relatively short separation time between return stroke and the first M component, coupled with the observation of Fisher et al. [1993] that continuing currents lasting longer than 10 ms never occur without M current pulses, implies that the M component is a necessary feature of the continuing current mode of charge transfer to ground.

Free-beam soliton self-compression in air

NASA Astrophysics Data System (ADS)

Voronin, A. A.; Mitrofanov, A. V.; Sidorov-Biryukov, D. A.; Fedotov, A. B.; Pugžlys, A.; Panchenko, V. Ya; Shumakova, V.; Ališauskas, S.; Baltuška, A.; Zheltikov, A. M.

2018-02-01

We identify a physical scenario whereby soliton transients generated in freely propagating laser beams within the regions of anomalous dispersion in air can be compressed as a part of their free-beam spatiotemporal evolution to yield few-cycle mid- and long-wavelength-infrared field waveforms, whose peak power is substantially higher than the peak power of the input pulses. We show that this free-beam soliton self-compression scenario does not require ionization or laser-induced filamentation, enabling high-throughput self-compression of mid- and long-wavelength-infrared laser pulses within a broad range of peak powers from tens of gigawatts up to the terawatt level. We also demonstrate that this method of pulse compression can be extended to long-range propagation, providing self-compression of high-peak-power laser pulses in atmospheric air within propagation ranges as long as hundreds of meters, suggesting new ways towards longer-range standoff detection and remote sensing.

Maximal exercise oxygen pulse as a predictor of mortality among male veterans referred for exercise testing.

PubMed

Oliveira, Ricardo B; Myers, Jonathan; Araújo, Claudio Gil S; Abella, Joshua; Mandic, Sandra; Froelicher, Victor

2009-06-01

Maximal oxygen pulse (O(2) pulse) mirrors the stroke volume response to exercise, and should therefore be a strong predictor of mortality. Limited and conflicting data are, however, available on this issue. Nine hundred forty-eight participants, classified as those with cardiopulmonary disease (CPD) and those without (non-CPD), underwent cardiopulmonary exercise testing (CPX) for clinical reasons between 1993 and 2003. The ability of maximal O(2) pulse and maximal oxygen uptake (peak VO(2)) to predict mortality was investigated using proportional hazards and Akaike information criterion analyses. All-cause mortality was the endpoint. Over a mean follow-up of 6.3+/-3.2 years, there were 126 deaths. Maximal O(2) pulse, expressed in either absolute or relative to age-predicted terms, and peak VO(2) were significant and independent predictors of mortality in those with and without CPD (P<0.04). Akaike information criterion analysis revealed that the model including both maximal O(2) pulse and peak VO(2) had the highest accuracy for predicting mortality. The optimal cut-points for O(2) pulse and peak VO(2) (<12; > or =12 ml/beat and <16; > or =16 ml/(kg.min) respectively) were established by the area under the receiver-operating-characteristic curve. The relative risks of mortality were 3.4 and 2.2 (CPD and non-CPD, respectively) among participants with both maximal O(2) pulse and peak VO(2) responses below these cut-points compared with participants with both responses above these cut-points. These results indicate that maximal O(2) pulse is a significant predictor of mortality in patients with and without CPD. The addition of absolute and relative O(2) pulse data provides complementary information for risk-stratifying heterogeneous participants referred for CPX and should be routinely included in the CPX report.

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.

A nanoscale vacuum-tube diode triggered by few-cycle laser pulses

NASA Astrophysics Data System (ADS)

Higuchi, Takuya; Maisenbacher, Lothar; Liehl, Andreas; Dombi, Péter; Hommelhoff, Peter

2015-02-01

We propose and demonstrate a nanoscale vacuum-tube diode triggered by few-cycle near-infrared laser pulses. It represents an ultrafast electronic device based on light fields, exploiting near-field optical enhancement at surfaces of two metal nanotips. The sharper of the two tips displays a stronger field-enhancement, resulting in larger photoemission yields at its surface. One laser pulse with a peak intensity of 4.7 × 1011 W/cm2 triggers photoemission of ˜16 electrons from the sharper cathode tip, while emission from the blunter anode tip is suppressed by 19 dB to ˜0.2 electrons per pulse. Thus, the laser-triggered current between two tips exhibit a rectifying behavior, in analogy to classical vacuum-tube diodes. According to the kinetic energy of the emitted electrons and the distance between the tips, the total operation time of this laser-triggered nanoscale diode is estimated to be below 1 ps.

Plasma-filled diode based on the coaxial gun

NASA Astrophysics Data System (ADS)

Zherlitsyn, A. A.; Kovalchuk, B. M.; Pedin, N. N.

2012-10-01

The paper presents the results of studies of a coaxial gun for a plasma-filled electron diode. Effects of the discharge channel diameter and gun current on characteristics of the plasma and pulse generated in the diode were investigated. The electron beam with maximum energy of ≥1 MeV at the current of ≈100 kA was obtained in the experiments with a plasma-filled diode. The energy of ≈5 kJ with the peak power of ≥100 GW dissipated in the diode.

Plasma-filled diode based on the coaxial gun.

PubMed

Zherlitsyn, A A; Kovalchuk, B M; Pedin, N N

2012-10-01

The paper presents the results of studies of a coaxial gun for a plasma-filled electron diode. Effects of the discharge channel diameter and gun current on characteristics of the plasma and pulse generated in the diode were investigated. The electron beam with maximum energy of ≥1 MeV at the current of ≈100 kA was obtained in the experiments with a plasma-filled diode. The energy of ≈5 kJ with the peak power of ≥100 GW dissipated in the diode.

A low power radiofrequency pulse for simultaneous multislice excitation and refocusing.

PubMed

Eichner, Cornelius; Wald, Lawrence L; Setsompop, Kawin

2014-10-01

Simultaneous multislice (SMS) acquisition enables increased temporal efficiency of MRI. Nonetheless, MultiBand (MB) radiofrequency (RF) pulses used for SMS can cause large energy deposition. Power independent of number of slices (PINS) pulses reduce RF power at cost of reduced bandwidth and increased off-resonance dependency. This work improves PINS design to further reduce energy deposition, off-resonance dependency and peak power. Modifying the shape of MB RF-pulses allows for mixing with PINS excitation, creating a new pulse type with reduced energy deposition and SMS excitation characteristics. Bloch Simulations were used to evaluate excitation and off-resonance behavior of this "MultiPINS" pulse. In this work, MultiPINS was used for whole-brain MB = 3 acquisition of high angular and spatial resolution diffusion MRI at 7 Tesla in 3 min. By using MultiPINS, energy transmission and peak power for SMS imaging can be significantly reduced compared with PINS and MB pulses. For MB = 3 acquisition in this work, MultiPINS reduces energy transmission by up to ∼50% compared with PINS pulses. The energy reduction was traded off to shorten the MultiPINS pulse, yielding higher signal at off-resonances for spin-echo acquisitions. MB and PINS pulses can be combined to enable low energy and peak power SMS acquisition. Copyright © 2014 Wiley Periodicals, Inc.

Poster - 25: Neutron Spectral Measurements around a Scanning Proton Beam

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

Kildea, John; Enger, Shirin; Maglieri, Robert

We describe the measurements of neutron spectra that we undertook around a scanning proton beam at the Skandion proton therapy clinic in Uppsala, Sweden. Measurements were undertaken using an extended energy range Nested Neutron Spectrometer (NNS, Detec Inc., Gatineau, QC) operated in pulsed and current mode. Spectra were measured as a function of location in the treatment room and for various Bragg peak depths. Our preliminary unfolded data clearly show the direct, evaporation and thermal neutron peaks and we can show the effect on the neutron spectrum of a water phantom in the primary proton beam.

Femtosecond laser pulse distortion in Ti:sapphire multipass amplifier by atomic phase shifts

NASA Astrophysics Data System (ADS)

Hwang, Seungjin; Jeong, Jihoon; Cho, Seryeyohan; Lee, Jongmin; Yu, Tae Jun

2017-11-01

We have derived modified Frantz-Nodvik equations that simultaneously account for atomic phase shift (APS) and gain depletion as the chirped laser pulse passes through a gain medium, and have analyzed the effect of temporal pulse distortion in a Ti:sapphire multipass amplifier chain. The combination of APS and gain depletion distorted a temporal pulse and decreased the peak power. The pulse width increased from 21.3 fs to 22.8 fs and the peak power reduced to 89% for the PW class Ti:sapphire CPA laser system in the particular conditions.

Spectroscopic investigation of species separation in opening switch plasmas

NASA Astrophysics Data System (ADS)

Jackson, S. L.; Phipps, D. G.; Richardson, A. S.; Commisso, R. J.; Hinshelwood, D. D.; Murphy, D. P.; Schumer, J. W.; Weber, B. V.; Boyer, C. N.; Doron, R.; Biswas, S.; Maron, Y.

2015-11-01

Interactions between magnetic fields and current-carrying plasmas that lead to the separation of plasma species in multi-species plasmas are being studied in a plasma opening switch geometry. Several Marshall guns are used to inject single or multi-species plasmas between coaxial conductors connected to the output of the Naval Research Laboratory's Hawk pulsed-power generator. Following injection of the plasma, the generator is used at roughly half power to apply an electrical pulse with a peak current of 450 kA, a peak voltage of 400 kV, and a rise time of 1.2 μs. The resulting magnetic field interacts with the plasma through a combination of field penetration and magnetohydrodynamic (MHD) pushing that is not well understood but can lead to the separation of plasma species in multi-species plasmas. An ICCD-coupled spectrometer has been used in combination with magnetic probes, a ribbon-beam interferometer, and particle-in-cell (PIC) modeling to diagnose and understand conditions in the plasma from the time it is injected until the end of the conduction phase of the opening switch. This work supported by the Naval Research Laboratory Base Program and the Office of Naval Research.

Development of soft ionization using direct current pulse glow discharge plasma source in mass spectrometry for volatile organic compounds analysis

NASA Astrophysics Data System (ADS)

Nunome, Yoko; Kodama, Kenji; Ueki, Yasuaki; Yoshiie, Ryo; Naruse, Ichiro; Wagatsuma, Kazuaki

2018-01-01

This study describes an ionization source for mass analysis, consisting of glow discharge plasma driven by a pulsed direct-current voltage for soft plasma ionization, to detect toxic volatile organic compounds (VOCs) rapidly and easily. The novelty of this work is that a molecular adduct ion, in which the parent molecule attaches with an NO+ radical, [M + NO]+, can be dominantly detected as a base peak with little or no fragmentation of them in an ambient air plasma at a pressure of several kPa. Use of ambient air as the discharge plasma gas is suitable for practical applications. The higher pressure in an ambient air discharge provided a stable glow discharge plasma, contributing to the soft ionization of organic molecules. Typical mass spectra of VOCs toluene, benzene, o-xylene, chlorobenzene and n-hexane were observed as [M + NO]+ adduct ion whose peaks were detected at m/z 122, 108, 136, 142 and 116, respectively. The NO generation was also confirmed by emission bands of NO γ-system. The ionization reactions were suggested, such that NO+ radical formed in an ambient air discharge could attach with the analyte molecule.

Evaluation of externally heated pulsed MPD thruster cathodes

NASA Astrophysics Data System (ADS)

Myers, Roger M.; Domonkos, Matthew; Gallimore, Alec D.

1993-12-01

Recent interest in solar electric orbit transfer vehicles (SEOTV's) has prompted a reevaluation of pulsed magnetoplasmadynamic (MPD) thruster systems due to their ease of power scaling and reduced test facility requirements. In this work the use of externally heated cathodes was examined in order to extend the lifetime of these thrusters to the 1000 to 3000 hours required for SEOTV missions. A pulsed MPD thruster test facility was assembled, including a pulse-forming network (PFN), ignitor supply and propellant feed system. Results of cold cathode tests used to validate the facility, PFN, and propellant feed system design are presented, as well as a preliminary evaluation of externally heated impregnated tungsten cathodes. The cold cathode thruster was operated on both argon and nitrogen propellants at peak discharge power levels up to 300 kW. The results confirmed proper operation of the pulsed thruster test facility, and indicated that large amounts of gas were evolved from the BaO-CaO-Al2O3 cathodes during activation. Comparison of the expected space charge limited current with the measured vacuum current when using the heated cathode indicate that either that a large temperature difference existed between the heater and the cathode or that the surface work function was higher than expected.

Evaluation of externally heated pulsed MPD thruster cathodes

NASA Technical Reports Server (NTRS)

Myers, Roger M.; Domonkos, Matthew; Gallimore, Alec D.

1993-01-01

Recent interest in solar electric orbit transfer vehicles (SEOTV's) has prompted a reevaluation of pulsed magnetoplasmadynamic (MPD) thruster systems due to their ease of power scaling and reduced test facility requirements. In this work the use of externally heated cathodes was examined in order to extend the lifetime of these thrusters to the 1000 to 3000 hours required for SEOTV missions. A pulsed MPD thruster test facility was assembled, including a pulse-forming network (PFN), ignitor supply and propellant feed system. Results of cold cathode tests used to validate the facility, PFN, and propellant feed system design are presented, as well as a preliminary evaluation of externally heated impregnated tungsten cathodes. The cold cathode thruster was operated on both argon and nitrogen propellants at peak discharge power levels up to 300 kW. The results confirmed proper operation of the pulsed thruster test facility, and indicated that large amounts of gas were evolved from the BaO-CaO-Al2O3 cathodes during activation. Comparison of the expected space charge limited current with the measured vacuum current when using the heated cathode indicate that either that a large temperature difference existed between the heater and the cathode or that the surface work function was higher than expected.

Multi-millijoule few-cycle mid-infrared pulses through nonlinear self-compression in bulk

PubMed Central

Shumakova, V.; Malevich, P.; Ališauskas, S.; Voronin, A.; Zheltikov, A. M.; Faccio, D.; Kartashov, D.; Baltuška, A.; Pugžlys, A.

2016-01-01

The physics of strong-field applications requires driver laser pulses that are both energetic and extremely short. Whereas optical amplifiers, laser and parametric, boost the energy, their gain bandwidth restricts the attainable pulse duration, requiring additional nonlinear spectral broadening to enable few or even single cycle compression and a corresponding peak power increase. Here we demonstrate, in the mid-infrared wavelength range that is important for scaling the ponderomotive energy in strong-field interactions, a simple energy-efficient and scalable soliton-like pulse compression in a mm-long yttrium aluminium garnet crystal with no additional dispersion management. Sub-three-cycle pulses with >0.44 TW peak power are compressed and extracted before the onset of modulation instability and multiple filamentation as a result of a favourable interplay between strong anomalous dispersion and optical nonlinearity around the wavelength of 3.9 μm. As a manifestation of the increased peak power, we show the evidence of mid-infrared pulse filamentation in atmospheric air. PMID:27620117

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.

A novel non-contact radar sensor for affective and interactive analysis.

PubMed

Lin, Hong-Dun; Lee, Yen-Shien; Shih, Hsiang-Lan; Chuang, Bor-Nian

2013-01-01

Currently, many physiological signal sensing techniques have been applied for affective analysis in Human-Computer Interaction applications. Most known maturely developed sensing methods (EEG/ECG/EMG/Temperature/BP etc. al.) replied on contact way to obtain desired physiological information for further data analysis. However, those methods might cause some inconvenient and uncomfortable problems, and not easy to be used for affective analysis in interactive performing. To improve this issue, a novel technology based on low power radar technology (Nanosecond Pulse Near-field Sensing, NPNS) with 300 MHz radio-frequency was proposed to detect humans' pulse signal by the non-contact way for heartbeat signal extraction. In this paper, a modified nonlinear HRV calculated algorithm was also developed and applied on analyzing affective status using extracted Peak-to-Peak Interval (PPI) information from detected pulse signal. The proposed new affective analysis method is designed to continuously collect the humans' physiological signal, and validated in a preliminary experiment with sound, light and motion interactive performance. As a result, the mean bias between PPI (from NPNS) and RRI (from ECG) shows less than 1ms, and the correlation is over than 0.88, respectively.

High peak power actively Q-switched mid-infrared fiber lasers at 3 μm

NASA Astrophysics Data System (ADS)

Shen, Yanlong; Wang, Yishan; Luan, Kunpeng; Chen, Hongwei; Tao, Mengmeng; Si, Jinhai

2017-04-01

Diode-pumped pulsed Er3+-doped ZBLAN fiber lasers at 2.8 μm actively Q-switched by using an mechanical Q-switch with feedbacks of a protected gold mirror and a blazing grating were investigated, respectively. A pulse energy of 0.13 mJ and repetition rate of 10 kHz with a pulse width of 127.3 ns at 2.78 μm was obtained when using a protected gold mirror as the feedback. By replacing the mirror with a blazing grating in Littrow configuration, the wavelength of the Q-switched pulse train was tunable with over 100 nm tuning range from 2.71 to 2.82 μm and a linewidth of 1.5 nm. A maxinmum pulse energy of up to 0.15 mJ and repetition rate of 10 kHz with a pulse width of 92.6 ns was achieved, yielding the maximum peak power of exceeding 1.6 kW. The pulse energy and peak power, to our knowledge, are the highest ever reported in the mid-infrared Q-switched fiber lasers.

Building A Simulation Model For The Prediction Of Temperature Distribution In Pulsed Laser Spot Welding Of Dissimilar Low Carbon Steel 1020 To Aluminum Alloy 6061

NASA Astrophysics Data System (ADS)

Yousef, Adel K. M.; Taha, Ziad. A.; Shehab, Abeer A.

2011-01-01

This paper describes the development of a computer model used to analyze the heat flow during pulsed Nd: YAG laser spot welding of dissimilar metal; low carbon steel (1020) to aluminum alloy (6061). The model is built using ANSYS FLUENT 3.6 software where almost all the environments simulated to be similar to the experimental environments. A simulation analysis was implemented based on conduction heat transfer out of the key hole where no melting occurs. The effect of laser power and pulse duration was studied. Three peak powers 1, 1.66 and 2.5 kW were varied during pulsed laser spot welding (keeping the energy constant), also the effect of two pulse durations 4 and 8 ms (with constant peak power), on the transient temperature distribution and weld pool dimension were predicated using the present simulation. It was found that the present simulation model can give an indication for choosing the suitable laser parameters (i.e. pulse durations, peak power and interaction time required) during pulsed laser spot welding of dissimilar metals.

Transient photothermal spectra of plasmonic nanobubbles.

PubMed

Lukianova-Hleb, Ekaterina Y; Sassaroli, Elisabetta; Jones, Alicia; Lapotko, Dmitri O

2012-03-13

The photothermal efficacy of near-infrared gold nanoparticles (NP), nanoshells, and nanorods was studied under pulsed high-energy optical excitation in plasmonic nanobubble (PNB) mode as a function of the wavelength and duration of the excitation laser pulse. PNBs, transient vapor nanobubbles, were generated around individual and clustered overheated NPs in water and living cells. Transient PNBs showed two photothermal features not previously observed for NPs: the narrowing of the spectral peaks to 1 nm and the strong dependence of the photothermal efficacy upon the duration of the laser pulse. Narrow red-shifted (relative to those of NPs) near-infrared spectral peaks were observed for 70 ps excitation laser pulses, while longer sub- and nanosecond pulses completely suppressed near-infrared peaks and blue shifted the PNB generation to the visual range. Thus, PNBs can provide superior spectral selectivity over gold NPs under specific optical excitation conditions.

High-energy and high-peak-power nanosecond pulse generation with beam quality control in 200-µm core highly multimode Yb-doped fiberamplifiers

NASA Astrophysics Data System (ADS)

Cheng, Ming-Yuan; Chang, Yu-Chung; Galvanauskas, Almantas; Mamidipudi, Pri; Changkakoti, Rupak; Gatchell, Peter

2005-02-01

We explored high-energy and high-peak-power pulse generation in large-core multimode fiber amplifiers, achieving what is to our knowledge the highest reported energies, up to 82 mJ for 500-ns pulses, 27 mJ for 50-ns pulses, and 2.4-MW peak power for 4-ns pulses at 1064 nm, using 200-µm-diameter and 0.062-N.A. core Yb-doped double-clad fiber amplifiers. The highly multimode nature of the fiber core was mitigated by use of a coiling-induced mode-filtering effect to yield a significant improvement in output-beam quality from M^2 = 25 from an uncoiled fiber to M^2 = 6.5 from a properly coiled fiber, with the corresponding reduction in number of propagating transverse modes from >or=200 to <or=20.

Scattering-type scanning near-field optical microscopy with low-repetition-rate pulsed light source through phase-domain sampling

PubMed Central

Wang, Haomin; Wang, Le; Xu, Xiaoji G.

2016-01-01

Scattering-type scanning near-field optical microscopy (s-SNOM) allows spectroscopic imaging with spatial resolution below the diffraction limit. With suitable light sources, s-SNOM is instrumental in numerous discoveries at the nanoscale. So far, the light sources have been limited to continuous wave or high-repetition-rate pulsed lasers. Low-repetition-rate pulsed sources cannot be used, due to the limitation of the lock-in detection mechanism that is required for current s-SNOM techniques. Here, we report a near-field signal extraction method that enables low-repetition-rate pulsed light sources. The method correlates scattering signals from pulses with the mechanical phases of the oscillating s-SNOM probe to obtain near-field signal, by-passing the apparent restriction imposed by the Nyquist–Shannon sampling theorem on the repetition rate. The method shall enable s-SNOM with low-repetition-rate pulses with high-peak-powers, such as femtosecond laser amplifiers, to facilitate investigations of strong light–matter interactions and nonlinear processes at the nanoscale. PMID:27748360

Direct Electrodeposition of Gold Nanoparticles on Glassy Carbon Electrode for Selective Determination Catechol in the Presence of Hydroquinone.

PubMed

Jayakumar, C; Magdalane, C Maria; Kaviyarasu, K; Kulandainathan, M Anbu; Jeyaraj, Boniface; Maaza, M

2018-07-01

A simple and reliable voltammetric sensor for simultaneous determination of Catechol (CT) and Hydroquinone (HQ) was developed by electrodepositing the gold nanoparticles on the surface of the Glassy Carbon Electrode (GCE). The cyclic voltammograms in a mixed solution of CT and HQ have shown that the oxidation peaks become well resolved and were separated by 110 mV, although the bare GCE gave a single broad oxidation peak. Moreover, the oxidation peak currents of both CT and HQ were remarkably increased three times in comparison with the bare GCE. This makes gold nanoparticles deposited GCE a suitable candidate for the determination of these isomers. In the presence of 1 mM HQ isomer, the oxidation peak currents of differential pulse voltammograms are proportional to the concentration of CT in the range of 21 μM to 323 μM with limit of detection 3.0 μM (S/N = 3). The proposed sensor has some important advantages such as low cost, ease of preparation, good stability and high reproducibility.

Characteristics of the pulse waveform during altered nitric oxide synthesis in the rabbit.

PubMed

Weinberg, P D; Habens, F; Kengatharan, M; Barnes, S E; Matz, J; Anggård, E E; Carrier, M J

2001-06-01

Nitrovasodilators produce characteristic changes in the shape of the peripheral pulse wave. Similar changes might also be caused by alteration of endogenous NO activity, which would allow such activity to be assessed in vivo. We investigated whether manipulation of the NO pathway influences the pulse waveform, and the mechanisms involved. The pulse wave in the ear of normal rabbits was examined by reflectance photoplethysmography before and during infusion of vasoactive agents. Pulse wave velocity was assessed by using an additional sensor on the rear foot. A diastolic peak was observed in the ear pulse; its timing was consistent with it being a reflection of the systolic peak from the lower body. The height of the dicrotic notch marking the start of this diastolic wave was decreased by acetylcholine or an NO donor, and further decreased by a phosphodiesterase type V inhibitor. The acetylcholine-induced decreases were blocked by inhibiting NO synthesis with N(G)-nitro-L-arginine methyl ester (L-NAME) but were unaffected by the inactive enantiomer D-NAME. These data demonstrate that NO influences the height of the notch in the pulse wave. Heart rate and blood pressure were altered during acetylcholine or L-NAME infusion, but there were no changes in pulse wave amplitude or velocity, or in the timing of the diastolic peak or dicrotic notch. The slope of the pulse wave between the systolic peak and notch changed substantially. These effects are most convincingly explained by changes in wave reflection, not only from the lower body but also from more proximal sites.

Characteristics of the pulse waveform during altered nitric oxide synthesis in the rabbit

PubMed Central

Weinberg, P D; Habens, F; Kengatharan, M; Barnes, S E; Matz, J; Änggård, E E; Carrier, M J

2001-01-01

Nitrovasodilators produce characteristic changes in the shape of the peripheral pulse wave. Similar changes might also be caused by alteration of endogenous NO activity, which would allow such activity to be assessed in vivo. We investigated whether manipulation of the NO pathway influences the pulse waveform, and the mechanisms involved. The pulse wave in the ear of normal rabbits was examined by reflectance photoplethysmography before and during infusion of vasoactive agents. Pulse wave velocity was assessed by using an additional sensor on the rear foot. A diastolic peak was observed in the ear pulse; its timing was consistent with it being a reflection of the systolic peak from the lower body. The height of the dicrotic notch marking the start of this diastolic wave was decreased by acetylcholine or an NO donor, and further decreased by a phosphodiesterase type V inhibitor. The acetylcholine-induced decreases were blocked by inhibiting NO synthesis with NG-nitro-L-arginine methyl ester (L-NAME) but were unaffected by the inactive enantiomer D-NAME. These data demonstrate that NO influences the height of the notch in the pulse wave. Heart rate and blood pressure were altered during acetylcholine or L-NAME infusion, but there were no changes in pulse wave amplitude or velocity, or in the timing of the diastolic peak or dicrotic notch. The slope of the pulse wave between the systolic peak and notch changed substantially. These effects are most convincingly explained by changes in wave reflection, not only from the lower body but also from more proximal sites. PMID:11375252

High peak current operation of x-ray free-electron laser multiple beam lines by suppressing coherent synchrotron radiation effects

NASA Astrophysics Data System (ADS)

Hara, Toru; Kondo, Chikara; Inagaki, Takahiro; Togawa, Kazuaki; Fukami, Kenji; Nakazawa, Shingo; Hasegawa, Taichi; Morimoto, Osamu; Yoshioka, Masamichi; Maesaka, Hirokazu; Otake, Yuji; Tanaka, Hitoshi

2018-04-01

The parallel operation of multiple beam lines is an important means to expand the opportunity of user experiments at x-ray free-electron laser (XFEL) facilities. At SPring-8 Angstrom free-electron laser (SACLA), the multi-beam-line operation had been tested using two beam lines, but transverse coherent synchrotron radiation (CSR) effects at a dogleg beam transport severely limited the laser performance. To suppress the CSR effects, a new beam optics based on two double bend achromat (DBA) structures was introduced for the dogleg. After the replacement of the beam optics, high peak current bunches of more than 10 kA are now stably transported through the dogleg and the laser pulse output is increased by a factor of 2-3. In the multi-beam-line operation of SACLA, the electron beam parameters, such as the beam energy and peak current, can be adjusted independently for each beam line. Thus the laser output can be optimized and wide spectral tunability is ensured for all beam lines.

Pulse advancement and delay in an integrated-optical two-port ring-resonator circuit: direct experimental observations.

PubMed

Uranus, H P; Zhuang, L; Roeloffzen, C G H; Hoekstra, H J W M

2007-09-01

We report experimental observations of the negative-group-velocity (v(g)) phenomenon in an integrated-optical two-port ring-resonator circuit. We demonstrate that when the v(g) is negative, the (main) peak of output pulse appears earlier than the peak of a reference pulse, while for a positive v(g), the situation is the other way around. We observed that a pulse splitting phenomenon occurs in the neighborhood of the critical-coupling point. This pulse splitting limits the maximum achievable delay and advancement of a single device as well as facilitating a smooth transition from highly advanced to highly delayed pulse, and vice versa, across the critical-coupling point.

Micro-Welding of Copper Plate by Frequency Doubled Diode Pumped Pulsed Nd:YAG Laser

NASA Astrophysics Data System (ADS)

Nakashiba, Shin-Ichi; Okamoto, Yasuhiro; Sakagawa, Tomokazu; Takai, Sunao; Okada, Akira

A pulsed laser of 532 nm wavelength with ms range pulse duration was newly developed by second harmonic generation of diode pumped pulsed Nd:YAG laser. High electro-optical conversion efficiency more than 13% could be achieved, and 1.5 kW peak power green laser pulse was put in optical fiber of 100 μm in diameter. In micro- welding of 1.0 mm thickness copper plate, a keyhole welding was successfully performed by 1.0 kW peak power at spot diameter less than 200 μm. The frequency doubled pulsed laser improved the processing efficiency of copper welding, and narrow and deep weld bead was stably obtained.

TU-FG-BRB-08: Challenges, Limitations and Future Outlook Towards Clinical Translation of Proton Acoustic Range Verification

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

Yousefi, S; Ahmad, M; Xiang, L

Purpose: To report our investigations of proton acoustic imaging, including computer simulations and preliminary experimental studies at clinical facilities. The ultimate achievable accuracy, sensitivity and clinical translation challenges are discussed. Methods: The acoustic pulse due to pressure rise was estimated using finite element model. Since the ionoacoustic pulse is highly dependent on the proton pulse width and energy, multiple pulse widths were studied. Based on the received signal spectrum at piezoelectric ultrasound transducer with consideration of random thermal noise, maximum spatial resolution of the proton-acoustic imaging modality was calculated. The simulation studies defined the design specifications of the system tomore » detect proton acoustic signal from Hitachi and Mevion clinical machines. A 500 KHz hydrophone with 100 dB amplification was set up in a water tank placed in front of the proton nozzle A 40 MHz data acquisition was synchronized by a trigger signal provided by the machine. Results: Given 30–800 mGy dose per pulse at the Bragg peak, the minimum number of protons detectable by the proton acoustic technique was on the order of 10×10^6 per pulse. The broader pulse widths produce signal with lower acoustic frequencies, with 10 µs pulses producing signals with frequency less than 100 kHz. As the proton beam pulse width increases, a higher dose rate is required to measure the acoustic signal. Conclusion: We have established the minimal detection limit for protonacoustic range validation for a variety of pulse parameters. Our study indicated practical proton-acoustic range verification can be feasible with a pulse shorter than 10 µs, 5×10^6 protons/pulse, 50 nA beam current and a highly sensitive ultrasonic transducer. The translational challenges into current clinical machines include proper magnetic shielding of the measurement equipment, providing a clean trigger signal from the proton machine, providing a shorter proton beam pulse and higher dose per pulse.« less

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.

Design and test of a flat-top magnetic field system driven by capacitor banks.

PubMed

Jiang, Fan; Peng, Tao; Xiao, Houxiu; Zhao, Jianlong; Pan, Yuan; Herlach, Fritz; Li, Liang

2014-04-01

An innovative method for generating a flat-top pulsed magnetic field by means of capacitor banks is developed at the Wuhan National High Magnetic Field Center (WHMFC). The system consists of two capacitor banks as they are normally used to generate a pulsed field. The two discharge circuits (the magnet circuit and the auxiliary circuit) are coupled by a pulse transformer such that the electromotive force (EMF) induced via the transformer in the magnet circuit containing the magnet coil is opposed to the EMF of the capacitor bank. At a certain point before the current pulse in the coil reaches its peak, the auxiliary circuit is triggered. With optimized parameters for charging voltage and trigger delay, the current in the magnet circuit can be approximately kept constant to obtain a flat-top. A prototype was developed at the WHMFC; the magnet circuit was energized by seven 1 MJ (3.2 mF/25 kV) capacitor modules and the auxiliary circuit by four 1 MJ modules. Fields up to 41 T with 6 ms flat-top have been obtained with a conventional user magnet used at the WHMFC.

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.

Use of alternating and pulsed direct current electrified fields for zebra mussel control

USGS Publications Warehouse

Luoma, James A.; Dean, Jan C.; Severson, Todd J.; Wise, Jeremy K.; Barbour, Matthew

2017-01-01

Alternatives to chemicals for controlling dreissenid mussels are desirable for environmental compatibility, but few alternatives exist. Previous studies have evaluated the use of electrified fields for stunning and/or killing planktonic life stages of dreissenid mussels, however, the available literature on the use of electrified fields to control adult dreissenid mussels is limited. We evaluated the effects of sinusoidal alternating current (AC) and 20% duty cycle square-wave pulsed direct current (PDC) exposure on the survival of adult zebra mussels at water temperatures of 10, 15, and 22 °C. Peak voltage gradients of ~ 17 and 30 Vp/cm in the AC and PDC exposures, respectively, were continuously applied for 24, 48, or 72 h. Peak power densities ranged from 77,999 to 107,199 µW/cm3 in the AC exposures and 245,320 to 313,945 µW/cm3 in the PDC exposures. The peak dose ranged from 6,739 to 27,298 Joules/cm3 and 21,306 to 80,941 Joules/cm3 in the AC and PDC exposures, respectively. The applied power ranged from 16.6 to 68.9 kWh in the AC exposures and from 22.2 to 86.4 kWh in the PDC exposures. Mortality ranged from 2.7 to 92.7% in the AC exposed groups and from 24.0 to 98.7% in PDC exposed groups. Mortality increased with corresponding increases in water temperature and exposure duration, and we observed more zebra mussel mortality in the PDC exposures. Exposures conducted with AC required less of a peak dose (Joules/cm3) but more applied power (kWh) to achieve the same level of adult zebra mussel mortality as corresponding PDC exposures. The results demonstrate that 20% duty cycle square-wave PDC requires less energy than sinusoidal AC to inducing the same level of adult zebra mussel mortality.

Collimated electron beam accelerated at 12 kV from a Penning discharge.

PubMed

Toader, D; Oane, M; Ticoş, C M

2015-01-01

A pulsed electron beam accelerated at 12 kV with a duration of 40 μs per pulse is obtained from a Penning discharge with a hollow anode and two cathodes. The electrons are extracted through a hole in one of the cathodes and focused by a pair of coils. The electron beam has a diameter of a few mm in the cross section, while the beam current reaches peak values of 400 mA, depending on the magnetic field inside the focussing coils. This relatively inexpensive and compact device is suitable for the irradiation of small material samples placed in high vacuum.

A multi-spectroscopic and molecular docking approach to investigate the interaction of antiviral drug oseltamivir with ct-DNA.

PubMed

Moghadam, Neda Hosseinpour; Salehzadeh, Sadegh; Shahabadi, Nahid; Golbedaghi, Reza

2017-07-03

The possible interaction between the antiviral drug oseltamivir and calf thymus DNA at physiological pH was studied by spectrophotometry, competitive spectrofluorimetry, differential pulse voltammogram (DPV), circular dichroism spectroscopy (CD), viscosity measurements, salt effect, and computational studies. Intercalation of oseltamivir between the base pairs of DNA was shown by a sharp increase in specific viscosity of DNA and a decrease of the peak current and a positive shift in differential pulse voltammogram. Competitive fluorescence experiments were performed using neutral red (NR) as a probe for the intercalation binding mode. The studies showed that oseltamivir is able to release the NR.

Association between ICP pulse waveform morphology and ICP B waves.

PubMed

Kasprowicz, Magdalena; Bergsneider, Marvin; Czosnyka, Marek; Hu, Xiao

2012-01-01

The study aimed to investigate changes in the shape of ICP pulses associated with different patterns of the ICP slow waves (0.5-2.0 cycles/min) during ICP overnight monitoring in hydrocephalus. Four patterns of ICP slow waves were characterized in 44 overnight ICP recordings (no waves - NW, slow symmetrical waves - SW, slow asymmetrical waves - AS, slow waves with plateau phase - PW). The morphological clustering and analysis of ICP pulse (MOCAIP) algorithm was utilized to calculate a set of metrics describing ICP pulse morphology based on the location of three sub-peaks in an ICP pulse: systolic peak (P(1)), tidal peak (P(2)) and dicrotic peak (P(3)). Step-wise discriminant analysis was applied to select the most characteristic morphological features to distinguish between different ICP slow waves. Based on relative changes in variability of amplitudes of P(2) and P(3) we were able to distinguish between the combined groups NW + SW and AS + PW (p < 0.000001). The AS pattern can be differentiated from PW based on respective changes in the mean curvature of P(2) and P(3) (p < 0.000001); however, none of the MOCAIP feature separates between NW and SW. The investigation of ICP pulse morphology associated with different ICP B waves may provide additional information for analysing recordings of overnight ICP.

Electrochemical behavior of an antiviral drug acyclovir at fullerene-C(60)-modified glassy carbon electrode.

PubMed

Shetti, Nagaraj P; Malode, Shweta J; Nandibewoor, Sharanappa T

2012-12-01

Electrochemical oxidation of acyclovir at fullerene-C(60)-modified glassy carbon electrode has been investigated using cyclic and differential pulse voltammetry. In pH 7.4 phosphate buffer, acyclovir showed an irreversible oxidation peak at about 0.96V. The cyclic voltammetric results showed that fullerene-C(60)-modified glassy carbon electrode can remarkably enhance electrocatalytic activity towards the oxidation of acyclovir. The electrocatalytic behavior was further exploited as a sensitive detection scheme for the acyclovir determination by differential pulse voltammetry. Effects of anodic peak potential (E(p)/V), anodic peak current (I(p)/μA) and heterogeneous rate constant (k(0)) have been discussed. Under optimized conditions, the concentration range and detection limit were 9.0×10(-8) to 6.0×10(-6)M and 1.48×10(-8)M, respectively. The proposed method was applied to acyclovir determination in pharmaceutical samples and human biological fluids such as urine and blood plasma as a real sample. This method can also be employed in quality control and routine determination of drugs in pharmaceutical formulations. Copyright © 2012 Elsevier B.V. All rights reserved.

Sub-MW peak power diffraction-limited chirped-pulse monolithic Yb-doped tapered fiber amplifier.

PubMed

Bobkov, Konstantin; Andrianov, Alexey; Koptev, Maxim; Muravyev, Sergey; Levchenko, Andrei; Velmiskin, Vladimir; Aleshkina, Svetlana; Semjonov, Sergey; Lipatov, Denis; Guryanov, Alexey; Kim, Arkady; Likhachev, Mikhail

2017-10-30

We demonstrate a novel amplification regime in a counter-pumped, relatively long (2 meters), large mode area, highly Yb-doped and polarization-maintaining tapered fiber, which offers a high peak power directly from the amplifier. The main feature of this regime is that the amplifying signal propagates through a thin part of the tapered fiber without amplification and experiences an extremely high gain in the thick part of the tapered fiber, where most of the pump power is absorbed. In this regime, we have demonstrated 8 ps pulse amplification to a peak power of up to 0.76 MW, which is limited by appearance of stimulated Raman scattering. In the same regime, 28 ps chirped pulses are amplified to a peak power of 0.35 MW directly from the amplifier and then compressed with 70% efficiency to 315 ± 10 fs, corresponding to an estimated peak power of 22 MW.

Temperature peaking at beginning of breakdown in 2.45 GHz pulsed off-resonance electron cyclotron resonance ion source hydrogen plasma

NASA Astrophysics Data System (ADS)

Cortázar, O. D.; Megía-Macías, A.; Vizcaíno-de-Julián, A.

2012-10-01

An experimental study of temperature and density evolution during breakdown in off-resonance ECR hydrogen plasma is presented. Under square 2.45 GHz microwave excitation pulses with a frequency of 50 Hz and relative high microwave power, unexpected transient temperature peaks that reach 18 eV during 20 μs are reported at very beginning of plasma breakdown. Decays of such peaks reach final stable temperatures of 5 eV at flat top microwave excitation pulse. Evidence of interplay between incoming power and duty cycle giving different kind of plasma parameters evolutions engaged to microwave coupling times is observed. Under relative high power conditions where short microwave coupling times are recorded, high temperature peaks are measured. However, for lower incoming powers and longer coupling times, temperature evolves gradually to a higher final temperature without peaking. On the other hand, the early instant where temperature peaks are observed also suggest a possible connection with preglow processes during breakdown in ECRIS plasmas.

Optimisation of thulium fibre laser parameters with generation of pulses by pump modulation

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

Obronov, I V; Larin, S V; Sypin, V E

2015-07-31

The formation of relaxation pulses of a thulium fibre laser (λ = 1.9 μm) by modulating the power of a pump erbium fibre laser (λ = 1.55 μm) is studied. A theoretical model is developed to find the dependences of pulse duration and peak power on different cavity parameters. The optimal cavity parameters for achieving the minimal pulse duration are determined. The results are confirmed by experimental development of a laser emitting pulses with a duration shorter than 10 ns, a peak power of 1.8 kW and a repetition rate of 50 kHz. (control of radiation parameters)

Coherent Enhancement of 10 s Burst-Mode Ultraviolet Pulses at Megawatt Peak Power

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

Abudureyimu, Reheman; Liu, Yun

2017-01-01

A doubly-resonant optical cavity and its locking technique have been developed to achieve coherent enhancement of 402.5-MHz, 50-ps, megawatt peak power ultraviolet (355 nm) laser pulses operating at a 10- s/10-Hz burst mode.

1.6  MW peak power, 90  ps all-solid-state laser from an aberration self-compensated double-passing end-pumped Nd:YVO₄ rod amplifier.

PubMed

Wang, Chunhua; Liu, Chong; Shen, Lifeng; Zhao, Zhiliang; Liu, Bin; Jiang, Hongbo

2016-03-20

In this paper a delicately designed double-passing end-pumped Nd:YVO₄ rod amplifier is reported that produces 10.2 W average laser output when seeded by a 6 mW Nd:YVO₄ microchip laser at a repetition rate of 70 kHz with pulse duration of 90 ps. A pulse peak power of ∼1.6  MW and pulse energy of ∼143  μJ is achieved. The beam quality is well preserved by a double-passing configuration for spherical-aberration compensation. The laser-beam size in the amplifier is optimized to prevent the unwanted damage from the high pulse peak-power density. This study provides a simple and robust picosecond all-solid-state master oscillator power amplifier system with both high peak power and high beam quality, which shows great potential in the micromachining.

Interaction of ultrashort laser pulses and silicon solar cells under short circuit conditions

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

Mundus, M., E-mail: markus.mundus@ise.fraunhofer.de; Giesecke, J. A.; Fischer, P.

Ultrashort pulse lasers are promising tools for numerous measurement purposes. Among other benefits their high peak powers allow for efficient generation of wavelengths in broad spectral ranges and at spectral powers that are orders of magnitude higher than in conventional light sources. Very recently this has been exploited for the establishment of sophisticated measurement facilities for electrical characterization of photovoltaic (PV) devices. As the high peak powers of ultrashort pulses promote nonlinear optical effects they might also give rise to nonlinear interactions with the devices under test that possibly manipulate the measurement outcome. In this paper, we present a comprehensivemore » theoretical and experimental study of the nonlinearities affecting short circuit current (I{sub SC}) measurements of silicon (Si) solar cells. We derive a set of coupled differential equations describing the radiation-device interaction and discuss the nonlinearities incorporated in those. By a semi-analytical approach introducing a quasi-steady-state approximation and integrating a Green's function we solve the system of equations and obtain simulated I{sub SC} values. We validate the theoretical model by I{sub SC} ratios obtained from a double ring resonator setup capable for reproducible generation of various ultrashort pulse trains. Finally, we apply the model to conduct the most prominent comparison of I{sub SC} generated by ultrashort pulses versus continuous illumination. We conclude by the important finding that the nonlinearities induced by ultrashort pulses are negligible for the most common I{sub SC} measurements. However, we also find that more specialized measurements (e.g., of concentrating PV or Si-multijunction devices as well as highly localized electrical characterizations) will be biased by two-photon-absorption distorting the I{sub SC} measurement.« less

RF pulse compression for future linear colliders

NASA Astrophysics Data System (ADS)

Wilson, Perry B.

1995-07-01

Future (nonsuperconducting) linear colliders will require very high values of peak rf power per meter of accelerating structure. The role of rf pulse compression in producing this power is examined within the context of overall rf system design for three future colliders at energies of 1.0-1.5 TeV, 5 TeV, and 25 TeV. In order to keep the average AC input power and the length of the accelerator within reasonable limits, a collider in the 1.0-1.5 TeV energy range will probably be built at an x-band rf frequency, and will require a peak power on the order of 150-200 MW per meter of accelerating structure. A 5 TeV collider at 34 GHz with a reasonable length (35 km) and AC input power (225 MW) would require about 550 MW per meter of structure. Two-beam accelerators can achieve peak powers of this order by applying dc pulse compression techniques (induction linac modules) to produce the drive beam. Klystron-driven colliders achieve high peak power by a combination of dc pulse compression (modulators) and rf pulse compression, with about the same overall rf system efficiency (30-40%) as a two-beam collider. A high gain (6.8) three-stage binary pulse compression system with high efficiency (80%) is described, which (compared to a SLED-II system) can be used to reduce the klystron peak power by about a factor of two, or alternatively, to cut the number of klystrons in half for a 1.0-1.5 TeV x-band collider. For a 5 TeV klystron-driven collider, a high gain, high efficiency rf pulse compression system is essential.

Coherent (photon) vs incoherent (current) detection of multidimensional optical signals from single molecules in open junctions

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

Agarwalla, Bijay Kumar; Hua, Weijie; Zhang, Yu

2015-06-07

The nonlinear optical response of a current-carrying single molecule coupled to two metal leads and driven by a sequence of impulsive optical pulses with controllable phases and time delays is calculated. Coherent (stimulated, heterodyne) detection of photons and incoherent detection of the optically induced current are compared. Using a diagrammatic Liouville space superoperator formalism, the signals are recast in terms of molecular correlation functions which are then expanded in the many-body molecular states. Two dimensional signals in benzene-1,4-dithiol molecule show cross peaks involving charged states. The correlation between optical and charge current signal is also observed.

Effects of ultrashort laser pulses on angular distributions of photoionization spectra.

PubMed

Ooi, C H Raymond; Ho, W L; Bandrauk, A D

2017-07-27

We study the photoelectron spectra by intense laser pulses with arbitrary time dependence and phase within the Keldysh framework. An efficient semianalytical approach using analytical transition matrix elements for hydrogenic atoms in any initial state enables efficient and accurate computation of the photoionization probability at any observation point without saddle point approximation, providing comprehensive three dimensional photoelectron angular distribution for linear and elliptical polarizations, that reveal the intricate features and provide insights on the photoionization characteristics such as angular dispersions, shift and splitting of photoelectron peaks from the tunneling or above threshold ionization(ATI) regime to non-adiabatic(intermediate) and multiphoton ionization(MPI) regimes. This facilitates the study of the effects of various laser pulse parameters on the photoelectron spectra and their angular distributions. The photoelectron peaks occur at multiples of 2ħω for linear polarization while  odd-ordered peaks are suppressed in the direction perpendicular to the electric field. Short pulses create splitting and angular dispersion where the peaks are strongly correlated to the angles. For MPI and elliptical polarization with shorter pulses the peaks split into doublets and the first peak vanishes. The carrier envelope phase(CEP) significantly affects the ATI spectra while the Stark effect shifts the spectra of intermediate regime to higher energies due to interference.

Numerical simulations of self-focusing of ultrafast laser pulses

NASA Astrophysics Data System (ADS)

Fibich, Gadi; Ren, Weiqing; Wang, Xiao-Ping

2003-05-01

Simulation of nonlinear propagation of intense ultrafast laser pulses is a hard problem, because of the steep spatial gradients and the temporal shocks that form during the propagation. In this study we adapt the iterative grid distribution method of Ren and Wang [J. Comput. Phys. 159, 246 (2000)] to solve the two-dimensional nonlinear Schrödinger equation with normal time dispersion, space-time focusing, and self-steepening. Our simulations show that, after the asymmetric temporal pulse splitting, the rear peak self-focuses faster than the front one. As a result, the collapse of the rear peak is arrested before that of the front peak. Unlike what has sometimes been conjectured, however, collapse of the two peaks is not arrested through multiple splittings, but rather through temporal dispersion.

Waterproof and stretchable triboelectric nanogenerator for biomechanical energy harvesting and self-powered sensing

NASA Astrophysics Data System (ADS)

Chen, Xuexian; Miao, Liming; Guo, Hang; Chen, Haotian; Song, Yu; Su, Zongming; Zhang, Haixia

2018-05-01

We introduce a waterproof and stretchable triboelectric nanogenerator (TENG) that can be attached on the human body, such as fingers and the wrist, to harvest mechanical energy from body movement. The whole device is composed of stretchable material, making it able to endure diverse mechanical deformations and scavenge energy from them. Under gentle mechanical motions of pressing, stretching and bending, the device with an effective area of 1 × 2 cm2 can generate the peak-to-peak output current of 257.5 nA, 50.2 nA, and 33.5 nA, respectively. Besides, the TENG is tightly encapsulated, enabling it to avoid the influence of the external environment like humidity changes and harvest energy under water. Particularly, owing to the thin and soft properties of the encapsulation film, the device can respond to weak vibrations like the wrist pulse and act as a self-powered pulse sensor, which broadens its application prospects in the field of wearable energy harvesting devices and self-powered sensing systems.

High power THz sources for nonlinear imaging

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

Tekavec, Patrick F.; Kozlov, Vladimir G.

2014-02-18

Many biological and chemical compounds have unique absorption features in the THz (0.1 - 10 THz) region, making the use of THz waves attractive for imaging in defense, security, biomedical imaging, and monitoring of industrial processes. Unlike optical radiation, THz frequencies can pass through many substances such as paper, clothing, ceramic, etc. with little attenuation. The use of currently available THz systems is limited by lack of highpower, sources as well as sensitive detectors and detector arrays operating at room temperature. Here we present a novel, high power THz source based on intracavity downconverison of optical pulses. The source deliversmore » 6 ps pulses at 1.5 THz, with an average power of >300 μW and peak powers >450 mW. We propose an imaging method based on frequency upconverison that is ideally suited to use the narrow bandwidth and high peak powers produced by the source. By upconverting the THz image to the infrared, commercially available detectors can be used for real time imaging.« less

High power THz sources for nonlinear imaging

NASA Astrophysics Data System (ADS)

Tekavec, Patrick F.; Kozlov, Vladimir G.

2014-02-01

Many biological and chemical compounds have unique absorption features in the THz (0.1 - 10 THz) region, making the use of THz waves attractive for imaging in defense, security, biomedical imaging, and monitoring of industrial processes. Unlike optical radiation, THz frequencies can pass through many substances such as paper, clothing, ceramic, etc. with little attenuation. The use of currently available THz systems is limited by lack of highpower, sources as well as sensitive detectors and detector arrays operating at room temperature. Here we present a novel, high power THz source based on intracavity downconverison of optical pulses. The source delivers 6 ps pulses at 1.5 THz, with an average power of >300 μW and peak powers >450 mW. We propose an imaging method based on frequency upconverison that is ideally suited to use the narrow bandwidth and high peak powers produced by the source. By upconverting the THz image to the infrared, commercially available detectors can be used for real time imaging.

Ramp compression of a metallic liner driven by a shaped 5 MA current on the SPHINX machine

NASA Astrophysics Data System (ADS)

D'Almeida, Thierry; Lassalle, Francis; Morell, Alain; Grunenwald, Julien; Zucchini, Frédéric; Loyen, Arnaud; Maysonnave, Thomas; Chuvatin, Alexandre

2013-06-01

SPHINX is a 6MA, 1- μs Linear Transformer Driver operated by the CEA Gramat (France) and primarily used for imploding Z-pinch loads for radiation effects studies. Among the options that are currently being considered for improving the generator performances, there is a compact Dynamic Load Current Amplifier (DLCM). A method for performing magnetic ramp compression experiments, without modifying the generator operation scheme, was developed using the DLCM to shape the initial current pulse. We present the overall experimental configuration chosen for these experiments, based on electrical and hydrodynamic simulations. Initial results obtained over a set of experiments on an aluminum cylindrical liner, ramp-compressed to a peak pressure of 23 GPa, are presented. Details of the electrical and Photonic Doppler Velocimetry (PDV) setups used to monitor and diagnose the ramp compression experiments are provided. Current profiles measured at various locations across the system, particularly the load current, agree with simulated current profile and demonstrate adequate pulse shaping by the DLCM. The liner inner free surface velocity measurements agree with the hydrocode results obtained using the measured load current as the input. Higher ramp pressure levels are foreseen in future experiments with an improved DLCM system.

Numerical investigation on the dynamics and evolution mechanisms of multiple-current-pulse behavior in homogeneous helium dielectric-barrier discharges at atmospheric pressure

NASA Astrophysics Data System (ADS)

Zhang, Yuhui; Ning, Wenjun; Dai, Dong

2018-03-01

A systematic investigation on the dynamics and evolution mechanisms of multiple-current-pulse (MCP) behavior in homogeneous dielectric barrier discharge (HDBD) is carried out via fluid modelling. Inspecting the simulation results, two typical discharge regimes, namely the MCP-Townsend regime and MCP-glow regime, are found prevailing in MCP discharges, each with distinctive electrical and dynamic properties. Moreover, the evolution of MCP behavior with external parameters altering are illustrated and explicitly discussed. It is revealed that the discharge undergoes some different stages as external parameters vary, and the discharge in each stage follows a series of distinctive pattern in morphological characteristics and evolution trends. Among those stages, the pulse number per half cycle is perceived to observe non-monotonic variations with applied voltage amplitude (Vam) and gap width (dg) increasing, and a merging effect among pulses, mainly induced by the enhanced contribution of sinusoidal component to the total current, is considered responsible for such phenomenon. The variation of incipient discharge peak phase (Φpm) is dominated by the value of Vam as well as the proportion of total applied voltage that drops across the gas gap. Moreover, an abnormal, dramatic elevation in Jpm with dg increasing is observed, which could be evinced by the strengthened glow discharge structure and therefore enhanced space charge effect.

Resistive Random Access Memory from Materials Development fnd Engineering to Novel Encryption and Neuromorphic Applications

NASA Astrophysics Data System (ADS)

Beckmann, Karsten

Resistive random access memory (ReRAM or RRAM) is a novel form of non-volatile memory that is expected to play a major role in future computing and memory solutions. It has been shown that the resistance state of ReRAM devices can be precisely tuned by modulating switching voltages, by limiting peak current, and by adjusting the switching pulse properties. This enables the realization of novel applications such as memristive neuromorphic computing and neural network computing. I have developed two processes based on 100 and 300mm wafer platforms to demonstrate functional HfO2 based ReRAM devices. The first process is designed for a rapid materials engineering and device characterization, while the second is an advanced hybrid ReRAM/CMOS combination based on the IBM 65nm 10LPe process technology. The 100mm wafer efforts were used to show impacts of etch processes on ReRAM switching performance and the need for a rigorous structural evaluation of ReRAM devices before starting materials development. After an etch development, a bottom electrode comparison between the inert materials Pt, Ru and W was performed where Ru showed superior results with respect to yield and resilience against environmental impacts such as humidity over a 2-month period. A comparison of amorphous and crystalline devices showed no statistical difference in the performance with respect to random telegraph noise. This demonstrates, that the forming process fundamentally alters the crystallographic structure within and around the filament. The 300mm wafer development efforts were aimed towards implementing ReRAM in the FEOL, combined with CMOS, to yield a seamless process flow of 1 transistor 1 ReRAM structures (1T1R). This technology was customized with custom-developed tungsten metal 1 (M1) and dual tungsten/copper via 1 (V1) structures, within which the ReRAM stack is embedded. The ReRAM itself consists of an inert W bottom electrode, HfO2 based active switching layer, a Ti oxygen scavenger layer, and an inert TiN top electrode. Linear sweep and controlled pulse (down to 5 ns) based electrical characterization of 1 transistor 1 ReRAM (1T1R) elements was performed to determine key properties including endurance, reliability, and threshold voltages. We demonstrated endurance values above 1010 cycles with an average on/off ratio of 10, and pulse voltages for set/reset operation of +/-1.5V. The on-chip 1T1R structures show an excellent controllability with respect to the low and high resistive states by manipulating the peak current from 75 up to 350 mu?A resulting in 10 distinct low resistance states (LRS). Our results demonstrate that the set operation (which shifts the ReRAM device from the high to the low resistance state) is only dependent on the voltage of the switching pulse and the peak current limit. The reset operation, however, occurs in an analog fashion and appears to be dependent on the total energy of the applied switching pulse. Pulse energy was modulated by varying the peak voltage resulting in a larger relative change of the ReRAM device resistance. The incremental resistance changes are ideally suited to emulate synaptic weights for future implementation into neuromorphic architectures. Switching results from these devices were also used to develop a model time-delay physical unclonable function (PUF) circuit, which showed excellent performance when compared to a pure CMOS implementation with significant improvements in uniqueness, size and accuracy.

Effect of the solenoid in various conditions of the laser ion source at Brookhaven National Laboratory

NASA Astrophysics Data System (ADS)

Ikeda, S.; Kumaki, M.; Kanesue, T.; Okamura, M.

2016-02-01

In the laser ion source (LIS) at the Brookhaven National Laboratory (BNL), a solenoid is used to guide the laser ablation plasma and modulate the extracted beam current. Many types of ion species are guided. In some cases, the plasma plume is injected into the solenoid away from the solenoidal axis. To investigate the effects of the solenoid on the beam extracted from the plasma that has different properties, the beam current was measured in the setup of the LIS at the BNL. The beam current of Li, Al, Si, Fe, and Au increased when the magnetic field was applied. For most of the species the peak current and the total charge within a single beam pulse increased around 10 times with a magnetic field less than 100 G. In addition, for some species the rate of increase of the peak currents became smaller when the magnetic flux densities were larger than certain values depending on the species. In this case, the current waveforms were distorted. At the same magnetic field value, the field was more effective on lighter species than on heavier ones. When plasma was injected offset from the axis of the solenoid, peak current and total charge became half of those without offset. The experimental data are useful for the operation of the LIS at the BNL.

Effect of the solenoid in various conditions of the laser ion source at Brookhaven National Laboratory

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

Ikeda, S., E-mail: ikeda.s.ae@m.titech.ac.jp; Nishina Center for Accelerator-Based Science, RIKEN, Wako, Saitama 351-0108; Kumaki, M.

In the laser ion source (LIS) at the Brookhaven National Laboratory (BNL), a solenoid is used to guide the laser ablation plasma and modulate the extracted beam current. Many types of ion species are guided. In some cases, the plasma plume is injected into the solenoid away from the solenoidal axis. To investigate the effects of the solenoid on the beam extracted from the plasma that has different properties, the beam current was measured in the setup of the LIS at the BNL. The beam current of Li, Al, Si, Fe, and Au increased when the magnetic field was applied.more » For most of the species the peak current and the total charge within a single beam pulse increased around 10 times with a magnetic field less than 100 G. In addition, for some species the rate of increase of the peak currents became smaller when the magnetic flux densities were larger than certain values depending on the species. In this case, the current waveforms were distorted. At the same magnetic field value, the field was more effective on lighter species than on heavier ones. When plasma was injected offset from the axis of the solenoid, peak current and total charge became half of those without offset. The experimental data are useful for the operation of the LIS at the BNL.« less

Effect of the solenoid in various conditions of the laser ion source at Brookhaven National Laboratory.

PubMed

Ikeda, S; Kumaki, M; Kanesue, T; Okamura, M

2016-02-01

In the laser ion source (LIS) at the Brookhaven National Laboratory (BNL), a solenoid is used to guide the laser ablation plasma and modulate the extracted beam current. Many types of ion species are guided. In some cases, the plasma plume is injected into the solenoid away from the solenoidal axis. To investigate the effects of the solenoid on the beam extracted from the plasma that has different properties, the beam current was measured in the setup of the LIS at the BNL. The beam current of Li, Al, Si, Fe, and Au increased when the magnetic field was applied. For most of the species the peak current and the total charge within a single beam pulse increased around 10 times with a magnetic field less than 100 G. In addition, for some species the rate of increase of the peak currents became smaller when the magnetic flux densities were larger than certain values depending on the species. In this case, the current waveforms were distorted. At the same magnetic field value, the field was more effective on lighter species than on heavier ones. When plasma was injected offset from the axis of the solenoid, peak current and total charge became half of those without offset. The experimental data are useful for the operation of the LIS at the BNL.

Spectral variation of high power microwave pulse propagating in a self-generated plasma

NASA Technical Reports Server (NTRS)

Ren, A.; Kuo, S. P.; Kossey, Paul

1995-01-01

A systematic study to understand the spectral variation of a high power microwave pulse propagating in a self-generated plasma is carried out. It includes the theoretical formulation, experimental demonstration, and computer simulations and computer experiments. The experiment of pulse propagation is conducted in a vacuum chamber filled with dry air (approximately 0.2 torr); the chamber is made of a 2 ft. cube of Plexiglas. A rectangular microwave pulse (1 microsec pulse width and 3.27 GHz carrier frequency) is fed into the cube through an S band microwave horn placed at one side of the chamber. A second S-band horn placed at the opposite side of the chamber is used to receive the transmitted pulse. The spectra of the incident pulse and transmitted pulse are then compared. As the power of the incident pulse is only slightly (less than 15%) above the breakdown threshold power of the background air, the peak of the spectrum of the transmitted pulse is upshifted from the carrier frequency 3.27 GHz of the incident pulse. However, as the power of the incident pulse exceeds the breakdown threshold power of the background air by 30%, a different phenomenon appears. The spectrum of the transmitted pulse begins to have two peaks. One is upshifted and the other one downshifted from the single peak location of the incident pulse. The amount of frequency downshift is comparable to that of the upshifted frequency. A theoretical model describing the experiment of pulse propagation in a self-generated plasma is developed. There are excellent agreements between the experimental results and computer simulations based on this theoretical model, which is also used to further carry out computer experiments identifying the role of plasma introduced wave loss on the result of frequency downshift phenomenon.

Single-pulse picking at kHz repetition rates using a Ge plasma switch at the free-electron laser FELBE.

PubMed

Schmidt, J; Winnerl, S; Seidel, W; Bauer, C; Gensch, M; Schneider, H; Helm, M

2015-06-01

We demonstrate a system for picking of mid-infrared and terahertz (THz) radiation pulses from the free-electron laser (FEL) FELBE operating at a repetition rate of 13 MHz. Single pulses are reflected by a dense electron-hole plasma in a Ge slab that is photoexcited by amplified near-infrared (NIR) laser systems operating at repetition rates of 1 kHz and 100 kHz, respectively. The peak intensity of picked pulses is up to 400 times larger than the peak intensity of residual pulses. The required NIR fluence for picking pulses at wavelengths in the range from 5 μm to 30 μm is discussed. In addition, we show that the reflectivity of the plasma decays on a time scale from 100 ps to 1 ns dependent on the wavelengths of the FEL and the NIR laser. The plasma switch enables experiments with the FEL that require high peak power but lower average power. Furthermore, the system is well suited to investigate processes with decay times in the μs to ms regime, i.e., much longer than the 77 ns long pulse repetition period of FELBE.

Single-pulse picking at kHz repetition rates using a Ge plasma switch at the free-electron laser FELBE

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

Schmidt, J., E-mail: j.schmidt@hzdr.de; Helm, M.; Technische Universität Dresden, 01062 Dresden

2015-06-15

We demonstrate a system for picking of mid-infrared and terahertz (THz) radiation pulses from the free-electron laser (FEL) FELBE operating at a repetition rate of 13 MHz. Single pulses are reflected by a dense electron-hole plasma in a Ge slab that is photoexcited by amplified near-infrared (NIR) laser systems operating at repetition rates of 1 kHz and 100 kHz, respectively. The peak intensity of picked pulses is up to 400 times larger than the peak intensity of residual pulses. The required NIR fluence for picking pulses at wavelengths in the range from 5 μm to 30 μm is discussed. Inmore » addition, we show that the reflectivity of the plasma decays on a time scale from 100 ps to 1 ns dependent on the wavelengths of the FEL and the NIR laser. The plasma switch enables experiments with the FEL that require high peak power but lower average power. Furthermore, the system is well suited to investigate processes with decay times in the μs to ms regime, i.e., much longer than the 77 ns long pulse repetition period of FELBE.« less

Note: Experimental platform for magnetized high-energy-density plasma studies at the omega laser facility

NASA Astrophysics Data System (ADS)

Fiksel, G.; Agliata, A.; Barnak, D.; Brent, G.; Chang, P.-Y.; Folnsbee, L.; Gates, G.; Hasset, D.; Lonobile, D.; Magoon, J.; Mastrosimone, D.; Shoup, M. J.; Betti, R.

2015-01-01

An upgrade of the pulsed magnetic field generator magneto-inertial fusion electrical discharge system [O. Gotchev et al., Rev. Sci. Instrum. 80, 043504 (2009)] is described. The device is used to study magnetized high-energy-density plasma and is capable of producing a pulsed magnetic field of tens of tesla in a volume of a few cubic centimeters. The magnetic field is created by discharging a high-voltage capacitor through a small wire-wound coil. The coil current pulse has a duration of about 1 μs and a peak value of 40 kA. Compared to the original, the updated version has a larger energy storage and improved switching system. In addition, magnetic coils are fabricated using 3-D printing technology which allows for a greater variety of the magnetic field topology.

Note: Experimental platform for magnetized high-energy-density plasma studies at the omega laser facility.

PubMed

Fiksel, G; Agliata, A; Barnak, D; Brent, G; Chang, P-Y; Folnsbee, L; Gates, G; Hasset, D; Lonobile, D; Magoon, J; Mastrosimone, D; Shoup, M J; Betti, R

2015-01-01

An upgrade of the pulsed magnetic field generator magneto-inertial fusion electrical discharge system [O. Gotchev et al., Rev. Sci. Instrum. 80, 043504 (2009)] is described. The device is used to study magnetized high-energy-density plasma and is capable of producing a pulsed magnetic field of tens of tesla in a volume of a few cubic centimeters. The magnetic field is created by discharging a high-voltage capacitor through a small wire-wound coil. The coil current pulse has a duration of about 1 μs and a peak value of 40 kA. Compared to the original, the updated version has a larger energy storage and improved switching system. In addition, magnetic coils are fabricated using 3-D printing technology which allows for a greater variety of the magnetic field topology.

Biased-probe-induced water ion injection into amorphous polymers investigated by electric force microscopy

NASA Astrophysics Data System (ADS)

Knorr, Nikolaus; Rosselli, Silvia; Miteva, Tzenka; Nelles, Gabriele

2009-06-01

Although charging of insulators by atomic force microscopy (AFM) has found widespread interest, often with data storage or nanoxerography in mind, less attention has been paid to the charging mechanism and the nature of the charge. Here we present a systematic study on charging of amorphous polymer films by voltage pulses applied to conducting AFM probes. We find a quadratic space charge limited current law of Kelvin probe force microscopy and electrostatic force microscopy peak volumes in pulse height, offset by a threshold voltage, and a power law in pulse width of positive exponents smaller than one. We interpret the results by a charging mechanism of injection and surface near accumulation of aqueous ions stemming from field induced water adsorption, with threshold voltages linked to the water affinities of the polymers.

[Dependence of anti-inflammatory effects of high peak-power pulsed electromagnetic radiation of extremely high frequency on exposure parameters].

PubMed

Gapeev, A B; Mikhaĭlik, E N; Rubanik, A V; Cheremis, N K

2007-01-01

A pronounced anti-inflammatory effect of high peak-power pulsed electromagnetic radiation of extremely high frequency was shown for the first time in a model of zymosan-induced footpad edema in mice. Exposure to radiation of specific parameters (35, 27 GHz, peak power 20 kW, pulse widths 400-600 ns, pulse repetition frequency 5-500 Hz) decreased the exudative edema and local hyperthermia by 20% compared to the control. The kinetics and the magnitude of the anti-inflammatory effect were comparable with those induced by sodium diclofenac at a dose of 3 mg/kg. It was found that the anti-inflammatory effect linearly increased with increasing pulse width at a fixed pulse repetition frequency and had threshold dependence on the average incident power density of the radiation at a fixed pulse width. When animals were whole-body exposed in the far-field zone of radiator, the optimal exposure duration was 20 min. Increasing the average incident power density upon local exposure of the inflamed paw accelerated both the development of the anti-inflammatory effect and the reactivation time. The results obtained will undoubtedly be of great importance in the hygienic standardization of pulsed electromagnetic radiation and in further studies of the mechanisms of its biological action.

500 MW peak power degenerated optical parametric amplifier delivering 52 fs pulses at 97 kHz repetition rate.

PubMed

Rothhardt, J; Hädrich, S; Röser, F; Limpert, J; Tünnermann, A

2008-06-09

We present a high peak power degenerated parametric amplifier operating at 1030 nm and 97 kHz repetition rate. Pulses of a state-of-the art fiber chirped-pulse amplification (FCPA) system with 840 fs pulse duration and 410 microJ pulse energy are used as pump and seed source for a two stage optical parametric amplifier. Additional spectral broadening of the seed signal in a photonic crystal fiber creates enough bandwidth for ultrashort pulse generation. Subsequent amplification of the broadband seed signal in two 1 mm BBO crystals results in 41 microJ output pulse energy. Compression in a SF 11 prism compressor yields 37 microJ pulses as short as 52 fs. Thus, pulse shortening of more than one order of magnitude is achieved. Further scaling in terms of average power and pulse energy seems possible and will be discussed, since both concepts involved, the fiber laser and the parametric amplifier have the reputation to be immune against thermo-optical effects.

Electro-optically cavity dumped 2 μm semiconductor disk laser emitting 3 ns pulses of 30 W peak power

NASA Astrophysics Data System (ADS)

Kaspar, Sebastian; Rattunde, Marcel; Töpper, Tino; Schwarz, Ulrich T.; Manz, Christian; Köhler, Klaus; Wagner, Joachim

2012-10-01

A 2 μm electro-optically cavity-dumped semiconductor disk laser (SDL) with a pulse full width at half maximum of 3 ns, a pulse peak power of 30 W, and repetition rates adjustable between 87 kHz and 1 MHz is reported. For ns-pulse cavity dumping the SDL was set up with a 35-cm long cavity into which an intra-cavity Brewster-angled polarizer prism and a Pockels cell for rotation of the linear polarization were inserted. By means of internal total reflection in the birefringent polarizer, pulses are coupled out of the cavity sideways. This variant of ns-pulse 2-μm SDL is well suited for applications such as high-precision light detection and ranging or ns-pulse laser materials processing after further power amplification.

Perturbative transport modeling and comparison to cold-pulse and heat-pulse propagation experiments in Alcator C-Mod and DIII-D

NASA Astrophysics Data System (ADS)

Rodriguez Fernandez, P.; White, A. E.; Cao, N. M.; Creely, A. J.; Greenwald, M. J.; Howard, N. T.; Hubbard, A. E.; Hughes, J. W.; Irby, J. H.; Petty, C. C.; Rice, J. E.; Alcator C-Mod Team

2016-10-01

Possible ``non-local'' transport phenomena are often observed in tokamak plasmas. Different models have been proposed to explain fast responses during perturbative transport experiments, including non-diffusive effects. Specific tools to characterize the dynamic behavior and power balance analysis using TRANSP and the quasi-linear trapped gyro-landau fluid code TGLF have been developed to analyze Alcator C-Mod experiments. Recent results from cold pulse experiments show that fast core temperature increases following edge cold-pulse injections (peak within 10ms , while τE 25ms) are not correlated with the direction of intrinsic rotation, and instead the amplitude of the core response depends on density, plasma current and RF input power. The propagation of the cold pulse can be compared with propagation of heat pulses from sawteeth, and both may be used to probe changes in temperature profile stiffness. A Laser Blow Off (LBO) system is being developed for DIII-D that will allow further validation and cross-machine comparison of cold pulse experiments. LBO at DIII-D will also allow for direct comparisons with ECH perturbative heat pulse experiments. Work supported by US DOE under Grants DE-FC02-99ER54512 (C-Mod) and DE-FC02-04ER54698 (DIII-D) and La Caixa Fellowship.

A Novel Low-Ringing Monocycle Picosecond Pulse Generator Based on Step Recovery Diode

PubMed Central

Zhou, Jianming; Yang, Xiao; Lu, Qiuyuan; Liu, Fan

2015-01-01

This paper presents a high-performance low-ringing ultra-wideband monocycle picosecond pulse generator, formed using a step recovery diode (SRD), simulated in ADS software and generated through experimentation. The pulse generator comprises three parts, a step recovery diode, a field-effect transistor and a Schottky diode, used to eliminate the positive and negative ringing of pulse. Simulated results validate the design. Measured results indicate an output waveform of 1.88 peak-to-peak amplitude and 307ps pulse duration with a minimal ringing of -22.5 dB, providing good symmetry and low level of ringing. A high degree of coordination between the simulated and measured results is achieved. PMID:26308450

The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks

NASA Technical Reports Server (NTRS)

Preece, R.; Burgess, J. Michael; von Kienlin, A.; Bhat, P. N.; Briggs, M. S.; Byrne, D.; Chaplin, V.; Cleveland, W.; Collazzi, A. C.; Goldstein, A.;

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

Low-noise pulse conditioner

DOEpatents

Bird, D.A.

1981-06-16

A low-noise pulse conditioner is provided for driving electronic digital processing circuitry directly from differentially induced input pulses. The circuit uses a unique differential-to-peak detector circuit to generate a dynamic reference signal proportional to the input peak voltage. The input pulses are compared with the reference signal in an input network which operates in full differential mode with only a passive input filter. This reduces the introduction of circuit-induced noise, or jitter, generated in ground referenced input elements normally used in pulse conditioning circuits, especially speed transducer processing circuits. This circuit may be used for conditioning the sensor signal from the Fidler coil in a gas centrifuge for separation of isotopic gaseous mixtures.

Increasing Flexibility in Two-Dimensional Liquid Chromatography by Pulsed Elution of the First Dimension: A Proof of Concept.

PubMed

Jakobsen, Simon S; Christensen, Jan H; Verdier, Sylvain; Mallet, Claude R; Nielsen, Nikoline J

2017-09-05

This work demonstrates the development of an online two-dimensional liquid chromatography (2D-LC) method where the first dimension column is eluted by a sequence of pulses of increasing eluotropic strength generated by the LC pumps (pulsed-elution 2D-LC). Between the pulses, the first dimension is kept in a no-elution state using low eluent strength. The eluate from the first dimension is actively modulated using trap columns and subsequently analyzed in the second dimension. We demonstrate that by tuning the length and eluotropic strength of the pulses, peaks with retention factors in water, k w , above 150 can be manipulated to elute in 3-4 pulses. The no-elution state can be kept for 1-10 min with only minor changes as to which and how many pulses the peaks elute in. Pulsed-elution 2D-LC combined with active modulation tackles three of the main challenges encountered in 2D-LC and specifically online comprehensive 2D-LC: undersampling, difficulties in refocusing, and lack of flexibility in the selection of column dimensions and flow rates because the two dimensions constrain each other. The pulsed-elution 2D-LC was applied for the analysis of a basic fraction of vacuum gas oil. Peak capacity was 4018 for a 540 min analysis and 4610 for a 1040 min analysis.

[Increase in the effectiveness of identifying peaks and feet of the photoplethysmographic pulse to be reconstructed it using adaptive filtering].

PubMed

Becerra-Luna, Brayans; Martínez-Memije, Raúl; Cartas-Rosado, Raúl; Infante-Vázquez, Oscar

To improve the identification of peaks and feet in photoplethysmographic (PPG) pulses deformed by myokinetic noise, through the implementation of a modified fingertip and applying adaptive filtering. PPG signals were recordedfrom 10 healthy volunteers using two photoplethysmography systems placed on the index finger of each hand. Recordings lasted three minutes andwere done as follows: during the first minute, both handswere at rest, and for the lasting two minutes only the left hand was allowed to make quasi-periodicmovementsin order to add myokinetic noise. Two methodologies were employed to process the signals off-line. One consisted on using an adaptive filter based onthe Least Mean Square (LMS) algorithm, and the other includeda preprocessing stage in addition to the same LMS filter. Both filtering methods were compared and the one with the lowest error was chosen to assess the improvement in the identification of peaks and feet from PPG pulses. Average percentage errorsobtained wereof 22.94% with the first filtering methodology, and 3.72% withthe second one. On identifying peaks and feet from PPG pulsesbefore filtering, error percentages obtained were of 24.26% and 48.39%, respectively, and once filtered error percentageslowered to 2.02% for peaks and 3.77% for feet. The attenuation of myokinetic noise in PPG pulses through LMS filtering, plusa preprocessing stage, allows increasingthe effectiveness onthe identification of peaks and feet from PPG pulses, which are of great importance for medical assessment. Copyright © 2016 Instituto Nacional de Cardiología Ignacio Chávez. Publicado por Masson Doyma México S.A. All rights reserved.

Interaction of Lightning Electromagnetic Pulse with the Ionosphere as Inferred from Wideband Measurements and Modeling

NASA Astrophysics Data System (ADS)

Somu, Vijaya Bhaskar

Apparent ionospheric reflection heights estimated using the zero-to-zero and peak-to-peak methods to measure skywave delay relative to the groundwave were compared for 108 first and 124 subsequent strokes observed at LOG in 2009. For either metric there was a considerable decrease in average re ection height for subsequent strokes relative to first strokes. Median uncertainties in daytime re ection heights did not exceed 0.7 km. The standard errors in mean re ection heights were less than 3% of the mean value. Apparent changes in re ection height (estimated using the peak-to-peak method) within individual ashes for 54 daytime and 11 nighttime events at distances ranging from 50 km to 330 km were compared. For daytime conditions, the majority of the ashes showed a monotonic decrease in re ection height. For nighttime ashes, the monotonic decrease was found to be considerably less frequent. The apparent ionospheric re ection height tends to increase with return-stroke peak current. In order to increase the sample size for nighttime conditions, additional data for 43 nighttime flashes observed at LOG in 2014 were analyzed. The "fast-break-point" method of measuring skywave delay (McDonald et al., 1979) was additionally used. The 2014 results for return strokes are generally consistent with the 2009 results. The 2014 data were also used for estimating ionospheric re ection heights for elevated sources (6 CIDs and 3 PB pulses) using the double-skywave feature. The results were compared with re ection heights estimated for corresponding return strokes (if any), and fairly good agreement was generally found. It has been shown, using two different FDTD simulation codes, that the observed differences in re ection height cannot be explained by the difference in the frequency content of first and subsequent return-stroke currents. FDTD simulations showed that within 200 km the re ection heights estimated using the peak-to-peak method are close to the hOE parameter of the ionospheric profile for both daytime and nighttime conditions and for both first and second skywaves. The TL model was used to estimate the radial extent of elves produced by the interaction of LEMP with the ionosphere as a function of return-stroke peak current. For a peak current of 100 kA and the speed equal to one-half of the speed of light, the expected radius of elves is 157 km. Skywaves associated with 24 return strokes in 6 lightning ashes triggered at CB in 2015 and recorded at LOG (at a distance of 45 km from CB) were not found for any of the strokes recorded. In contrast, natural-lightning strokes do produce skywaves at comparable distances. One possible reason is the difference in the higher-frequency content (field waveforms for triggered lightning are more narrow than for natural lightning).

Compton suppression in BEGe detectors by digital pulse shape analysis.

PubMed

Mi, Yu-Hao; Ma, Hao; Zeng, Zhi; Cheng, Jian-Ping; Li, Jun-Li; Zhang, Hui

2017-03-01

A new method of pulse shape discrimination (PSD) for BEGe detectors is developed to suppress Compton-continuum by digital pulse shape analysis (PSA), which helps reduce the Compton background level in gamma ray spectrometry. A decision parameter related to the rise time of a pulse shape was presented. The method was verified by experiments using 60 Co and 137 Cs sources. The result indicated that the 60 Co Peak to Compton ratio and the Cs-Peak to Co-Compton ratio could be improved by more than two and three times, respectively. Copyright © 2016 Elsevier Ltd. All rights reserved.

Assessment of left ventricular function using pulsed tissue Doppler imaging in healthy dogs and dogs with spontaneous mitral regurgitation.

PubMed

Teshima, Kenji; Asano, Kazushi; Sasaki, Yukie; Kato, Yuka; Kutara, Kenji; Edamura, Kazuya; Hasegawa, Atsuhiko; Tanaka, Shigeo

2005-12-01

Pulsed tissue Doppler imaging (pulsed TDI) has been demonstrated to be useful for the estimation of left ventricular (LV) systolic and diastolic functions in various human cardiac diseases. The objectives of this study were to investigate the relationship between pulsed TDI and LV function by using cardiac catheterization in healthy dogs and to evaluate the clinical usefulness of pulsed TDI in dogs with spontaneous mitral regurgitation (MR). The peak early diastolic velocity (E'), peak atrial systolic velocity (A'), and peak systolic velocity (S') were detectable in the velocity profiles of the mitral annulus in all the dogs. In the healthy dogs, S' and E' were correlated with LV peak +dP/dt and -dP/dt, respectively. E' was lower in dogs with MR than in dogs without cardiac diseases. E/E' in the MR dogs with decompensated heart failure was significantly increased in comparison with those with compensated heart failure. The sensitivity and specificity of the E/E' cutoff value of 13.0 for identifying decompensated heart failure were 80% and 83%, respectively. In addition, E/E' was significantly correlated with the ratio of left atrial to aortic diameter. These findings suggest that canine pulsed TDI can be applied clinically for estimation of cardiac function and detection of cardiac decompensation and left atrial volume overload in dogs with MR.

MHD-EMP protection guidelines

NASA Astrophysics Data System (ADS)

Barnes, P. R.; Vance, E. F.

A nuclear detonation at altitudes several hundred kilometers above the earth will severely distort the earth's magnetic field and result in a strong magnetohydrodynamic electromagnetic pulse (MHD-EMP). The geomagnetic disturbance interacts with the soil to induce current and horizontal electric gradients. MHD-EMP, also called E3 since it is the third component of the high-altitude EMP (HEMP), lasts over 100 s after an exoatmospheric burst. MHD-EMP is similar to solar geomagnetic storms in it's global and low frequency (less than 1 Hz) nature except that E3 can be much more intense with a far shorter duration. When the MHD-EMP gradients are integrated over great distances by power lines, communication cables, or other long conductors, the induced voltages are significant. (The horizontal gradients in the soil are too small to induce major responses by local interactions with facilities.) The long pulse waveform for MHD-EMP-induced currents on long lines has a peak current of 200 A and a time-to-half-peak of 100 s. If this current flows through transformer windings, it can saturate the magnetic circuit and cause 60 Hz harmonic production. To mitigate the effects of MHD-EMP on a facility, long conductors must be isolated from the building and the commercial power harmonics and voltage swings must be addressed. The transfer switch would be expected to respond to the voltage fluctuations as long as the harmonics have not interfered with the switch control circuitry. The major sources of MHD-EMP induced currents are the commercial power lines and neutral; neutral current indirect coupling to the facility power or ground system via the metal fence, powered gate, parking lights, etc; metal water pipes; phone lines; and other long conductors that enter or come near the facility. The major source of harmonics is the commercial power system.

Electrochemical preparation of MnO2 nanobelts through pulse base-electrogeneration and evaluation of their electrochemical performance

NASA Astrophysics Data System (ADS)

Aghazadeh, Mustafa; Maragheh, Mohammad Ghannadi; Ganjali, Mohammad Reza; Norouzi, Parviz; Faridbod, Farnoush

2016-02-01

Cathodic electrodeposition of MnO2 from a nitrate solution, via pulsed base (OH-) electrogeneration was performed for the first time. The deposition experiments were performed in a pulse current mode in typical on-times and off-times (i.e. ton = 1 s and toff = 1 s) with a peak current density of 2 mA cm-2 (Ia = 2 mA cm-2). The structural characterizations conducted by XRD and FTIR techniques revealed that the prepared MnO2 is composed of both α and γ phases. Morphological observation by SEM and TEM showed that the prepared MnO2 is made up of nanobelts with uniform shapes (an average diameter and length of 50 nm and 1 μm, respectively). Further electrochemical measurements by cyclic voltammetry and charge-discharge techniques revealed that the prepared MnO2 nanostructures have excellent capacitive behaviors, like a specific capacitance of 235.5 F g-1 and capacity retention of 91.3% after 1000 cycling at the scan rate of 25 mV s-1.

Optimization of process parameters of pulsed TIG welded maraging steel C300

NASA Astrophysics Data System (ADS)

Deepak, P.; Jualeash, M. J.; Jishnu, J.; Srinivasan, P.; Arivarasu, M.; Padmanaban, R.; Thirumalini, S.

2016-09-01

Pulsed TIG welding technology provides excellent welding performance on thin sections which helps to increase productivity, enhance weld quality, minimize weld costs, and boost operator efficiency and this has drawn the attention of the welding society. Maraging C300 steel is extensively used in defence and aerospace industry and thus its welding becomes an area of paramount importance. In pulsed TIG welding, weld quality depends on the process parameters used. In this work, Pulsed TIG bead-on-plate welding is performed on a 5mm thick maraging C300 plate at different combinations of input parameters: peak current (Ip), base current (Ib) and pulsing frequency (HZ) as per box behnken design with three-levels for each factor. Response surface methodology is utilized for establishing a mathematical model for predicting the weld bead depth. The effect of Ip, Ib and HZ on the weld bead depth is investigated using the developed model. The weld bead depth is found to be affected by all the three parameters. Surface and contour plots developed from regression equation are used to optimize the processing parameters for maximizing the weld bead depth. Optimum values of Ip, Ib and HZ are obtained as 259 A, 120 A and 8 Hz respectively. Using this optimum condition, maximum bead depth of the weld is predicted to be 4.325 mm.

Kicker field simulation and measurement for the muon g-2 experiment at FNAL

NASA Astrophysics Data System (ADS)

Chang, Seung Pyo; Kim, Young Im; Choi, Jihoon; Semertzidis, Yannis; muon g-2 experiment Collaboration

2017-01-01

In the Muon g-2 experiment, muon beam is injected to the storage ring in a slightly tilted orbit whose center is 77 mm away from the center of the ring. The kicker is needed to send the muon beam to the central orbit. The magnetic kicker is designed for the experiment and about 0.1 Tm field integral is needed. The peak current pulse is 4200 A to make this field integral. This strong kicker pulse could make unwanted eddy current occur. This eddy current could spoil the main magnetic field of the storage ring. This could be a critical threat to the precision of experiment. The kicker field simulation has done using OPERA to estimate the effects. Also the kicker field should be measured based on Faraday effect. The measurement has tested in the lab before install the experiment area. In this presentation, the simulation and measurement results will be discussed. This work was supported by IBS-R017-D1-2016-a00.

Temporal self-splitting of optical pulses

NASA Astrophysics Data System (ADS)

Ding, Chaoliang; Koivurova, Matias; Turunen, Jari; Pan, Liuzhan

2018-05-01

We present mathematical models for temporally and spectrally partially coherent pulse trains with Laguerre-Gaussian and Hermite-Gaussian Schell-model statistics as extensions of the standard Gaussian Schell model for pulse trains. We derive propagation formulas of both classes of pulsed fields in linearly dispersive media and in temporal optical systems. It is found that, in general, both types of fields exhibit time-domain self-splitting upon propagation. The Laguerre-Gaussian model leads to multiply peaked pulses, while the Hermite-Gaussian model leads to doubly peaked pulses, in the temporal far field (in dispersive media) or at the Fourier plane of a temporal system. In both model fields the character of the self-splitting phenomenon depends both on the degree of temporal and spectral coherence and on the power spectrum of the field.

Diode end-pumped passively Q-switched Tm:YAP laser with 1.85-mJ pulse energy.

PubMed

Sebbag, Daniel; Korenfeld, Arik; Ben-Ami, Udi; Elooz, David; Shalom, Eran; Noach, Salman

2015-04-01

Passive Q switching of a Tm:YAP solid-state laser at 1935 nm with Cr:ZnSe and Cr:ZnS polycrystalline saturable absorbers is demonstrated for the first time, to the best of our knowledge. With Cr:ZnS, a maximum pulse energy of 1.85 mJ is obtained for a pulse duration of 35.8 ns, resulting in a peak power of 51.7 kW. With Cr:ZnSe, the achieved pulse energy of 1.55 mJ with a pulse duration of 42.2 ns leads to 36.7-kW peak power. These high pulse energies, together with the unique lasing wavelength at 1935 nm, make this laser a promising tool for biomedical and microsurgery applications.

Artificial stimulation of auroral electron acceleration by intense field aligned currents

NASA Technical Reports Server (NTRS)

Holmgren, G.; Bostrom, R.; Kelley, M. C.; Kintner, P. M.; Lundin, R.; Bering, E. A.; Sheldon, W. R.; Fahleson, U. V.

1979-01-01

A cesium-doped high explosion was detonated at 165 km altitude in the auroral ionosphere during quiet conditions. An Alfven wave pulse with a 200-mV/m electric field was observed, with the peak occurring 135 ms after the explosion at a distance of about 1 km. The count rate of fixed energy 2-keV electron detectors abruptly increased at 140 ms, peaked at 415 ms, and indicated a downward field-aligned beam of accelerated electrons. An anomalously high-field aligned beam of backscattered electrons was also detected. The acceleration is interpreted as due to production of an electrostatic shock or double layer between 300 and 800 km altitude. The structure was probably formed by an instability of the intense field-aligned currents in the Alfven wave launched by the charge-separation electric field due to the explosion.

Pulsed electromagnetic acceleration

NASA Technical Reports Server (NTRS)

Jahn, R. G.; Vonjaskowsky, W. F.; Clark, K. E.

1973-01-01

Direct measurements of the power deposited in the anode of a multimegawatt MPD accelerator using thermocouples attached to a thin shell anode reveal a dramatic decrease in the fractional anode power from 50% at 200 KW input power to less than 10% at 20 MW power. The corresponding local power flux peak at a value of 10,000 W/sq cm at the lip of the anode exhaust orifice, a distribution traced to a corresponding peak in the local current density at the anode. A comparison of voltage-current characteristics and spectral photographs of the MPD discharge using quartz, boron nitride and plexiglas insulators with various mass injection configurations led to the identification of different voltage modes and regions of ablation free operation. The technique of piezoelectric impact pressure measurement in the MPD exhaust flow was refined to account for the effects due to probe yaw angle.

A design of energy detector for ArF excimer lasers

NASA Astrophysics Data System (ADS)

Feng, Zebin; Han, Xiaoquan; Zhou, Yi; Bai, Lujun

2017-08-01

ArF excimer lasers with short wavelength and high photon energy are widely applied in the field of integrated circuit lithography, material processing, laser medicine, and so on. Excimer laser single pulse energy is a very important parameter in the application. In order to detect the single pulse energy on-line, one energy detector based on photodiode was designed. The signal processing circuit connected to the photodiode was designed so that the signal obtained by the photodiode was amplified and the pulse width was broadened. The amplified signal was acquired by a data acquisition card and stored in the computer for subsequent data processing. The peak of the pulse signal is used to characterize the single pulse energy of ArF excimer laser. In every condition of deferent pulse energy value levels, a series of data about laser pulses energy were acquired synchronously using the Ophir energy meter and the energy detector. A data set about the relationship between laser pulse energy and the peak of the pulse signal was acquired. Then, by using the data acquired, a model characterizing the functional relationship between the energy value and the peak value of the pulse was trained based on an algorithm of machine learning, Support Vector Regression (SVR). By using the model, the energy value can be obtained directly from the energy detector designed in this project. The result shows that the relative error between the energy obtained by the energy detector and by the Ophir energy meter is less than 2%.

Sub-cycle light transients for attosecond, X-ray, four-dimensional imaging

NASA Astrophysics Data System (ADS)

Fattahi, Hanieh

2016-10-01

This paper reviews the revolutionary development of ultra-short, multi-TW laser pulse generation made possible by current laser technology. The design of the unified laser architecture discussed in this paper, based on the synthesis of ultrabroadband optical parametric chirped-pulse amplifiers, promises to provide powerful light transients with electromagnetic forces engineerable on the electron time scale. By coherent combination of multiple amplifiers operating in different wavelength ranges, pulses with wavelength spectra extending from less than 1 ?m to more than 10 ?m, with sub-cycle duration at unprecedented peak and average power levels can be generated. It is shown theoretically that these light transients enable the efficient generation of attosecond X-ray pulses with photon flux sufficient to image, for the first time, picometre-attosecond trajectories of electrons, by means of X-ray diffraction and record the electron dynamics by attosecond spectroscopy. The proposed system leads to a tool with sub-atomic spatio-temporal resolution for studying different processes deep inside matter.

Two-Pole Caustic Model for High-Energy Lightcurves of Pulsars

NASA Technical Reports Server (NTRS)

Dyks, J.; Rudak, B.

2003-01-01

We present a new model of high-energy lightcurves from rotation powered pulsars. The key ingredient of the model is the gap region (i.e. the region where particle acceleration is taking place and high-energy photons originate) which satisfies the following assumptions: i) the gap region extends from each polar cap to the light cylinder; ii) the gap is thin and confined to the surface of last open magnetic-field lines; iii) photon emissivity is uniform within the gap region. The model lightcurves are dominated by strong peaks (either double or single) of caustic origin. Unlike in other pulsar models with caustic effects, the double peaks arise due to crossing two caustics, each of which is associated with a different magnetic pole. The generic features of the lightcurves are consistent with the observed characteristics of pulsar lightcurves: 1) the most natural (in terms of probability) shape consists of two peaks (separated by 0.4 to 0.5 in phase for large viewing angles); 2) the peaks possess well developed wings; 3) there is a bridge (inter-peak) emission component; 4) there is a non-vanishing off-pulse emission level; 5) the radio pulse occurs before the leading high-energy peak. The model is well suited for four gamma-ray pulsars - Crab, Vela, Geminga and B1951+32 - with double-peak lightcurves exhibiting the peak separation of 0.4 to 0.5 in phase. Hereby, we apply the model to the Vela pulsar. Moreover, we indicate the limitation of the model in accurate reproducing of the lightcurves with single pulses and narrowly separated (about 0.2 in phase) pulse peaks. We also discuss the optical polarization properties for the Crab pulsar in the context of the two-pole caustic model.

Giant-pulse Nd:YVO4 microchip laser with MW-level peak power by emission cross-sectional control.

PubMed

Kausas, Arvydas; Taira, Takunori

2016-02-22

We present a giant-pulse generation laser realized by the emission cross-section control of a gain medium in a passively Q-switched Nd:YVO4 microchip laser with a Cr4+:YAG saturable absorber. Up to 1.17 MW peak power and 1.03 mJ pulse energy were obtained with a 100 Hz repetition rate. By combining the Nd:YVO4 crystal with a Sapphire plate, lower temperature difference between a pump region in the gain crystal and a crystal holder was obtained which helped to keep the cavity in stability zone at elevated temperatures and allowed the achievement of the high peak power for this laser system.

Passively mode-locked diode-pumped Nd:YVO4 oscillator operating at an ultralow repetition rate.

PubMed

Papadopoulos, D N; Forget, S; Delaigue, M; Druon, F; Balembois, F; Georges, P

2003-10-01

We demonstrate the operation of an ultralow-repetition-rate, high-peak-power, picosecond diode-pumped Nd:YVO4 passively mode-locked laser oscillator. Repetition rates lower than 1 MHz were achieved with the use of a new design for a multiple-pass cavity and a semiconductor saturable absorber. Long-term stable operation at 1.2 MHz with a pulse duration of 16.3 ps and an average output power of 470 mW, corresponding to 24-kW peak-power pulses, is reported. These are to our knowledge the lowest-repetition-rate high-peak-power pulses ever generated directly from apicosecond laser resonator without cavity dumping.

Widely tunable mid-infrared quantum cascade lasers using sampled grating reflectors.

PubMed

Mansuripur, Tobias S; Menzel, Stefan; Blanchard, Romain; Diehl, Laurent; Pflügl, Christian; Huang, Yong; Ryou, Jae-Hyun; Dupuis, Russell D; Loncar, Marko; Capasso, Federico

2012-10-08

We demonstrate a three-section, electrically pulsed quantum cascade laser which consists of a Fabry-Pérot section placed between two sampled grating distributed Bragg reflectors. The device is current-tuned between ten single modes spanning a range of 0.46 μm (63 cm(-1)), from 8.32 to 8.78 μm. The peak optical output power exceeds 280 mW for nine of the modes.

Electro-optic analysis of the influence of target geometry on electromagnetic pulses generated by petawatt laser-matter interactions

NASA Astrophysics Data System (ADS)

Robinson, Timothy; Giltrap, Samuel; Eardley, Samuel; Consoli, Fabrizio; De Angelis, Riccardo; Ingenito, Francesco; Stuart, Nicholas; Verona, Claudio; Smith, Roland A.

2018-01-01

We present an analysis of strong laser-driven electromagnetic pulses using novel electro-optic diagnostic techniques. A range of targets were considered, including thin plastic foils (20-550 nm) and mass-limited, optically-levitated micro-targets. Results from foils indicate a dependence of EMP on target thickness, with larger peak electric fields observed with thinner targets. Spectral analysis suggests high repeatability between shots, with identified spectral features consistently detected with <1 MHz standard deviations of the peak position. This deviation is reduced for shots taken on the same day, suggesting that local conditions, such as movement of metal objects within the target chamber, are more likely to lead to minor spectral modifications, highlighting the role of the local environment in determining the details of EMP production. Levitated targets are electrically isolated from their environment, hence these targets should be unable to draw a neutralization current from the earth following ejection of hot electrons from the plasma, in contrast to predictions for pin-mounted foils in the Poyé EMP generation model. With levitated targets, no EMP was measurable above the noise threshold of any diagnostic, despite observation of protons accelerated to >30 MeV energies, suggesting the discharge current contribution to EMP is dominant.

Application of an impedance matching transformer to a plasma focus.

PubMed

Bures, B L; James, C; Krishnan, M; Adler, R

2011-10-01

A plasma focus was constructed using an impedance matching transformer to improve power transfer between the pulse power and the dynamic plasma load. The system relied on two switches and twelve transformer cores to produce a 100 kA pulse in short circuit on the secondary at 27 kV on the primary with 110 J stored. With the two transformer systems in parallel, the Thevenin equivalent circuit parameters on the secondary side of the driver are: C = 10.9 μF, V(0) = 4.5 kV, L = 17 nH, and R = 5 mΩ. An equivalent direct drive circuit would require a large number of switches in parallel, to achieve the same Thevenin equivalent. The benefits of this approach are replacement of consumable switches with non-consumable transformer cores, reduction of the driver inductance and resistance as viewed by the dynamic load, and reduction of the stored energy to produce a given peak current. The system is designed to operate at 100 Hz, so minimizing the stored energy results in less load on the thermal management system. When operated at 1 Hz, the neutron yield from the transformer matched plasma focus was similar to the neutron yield from a conventional (directly driven) plasma focus at the same peak current.

The Effect of Ethylene and Propylene Pulses on Respiration, Ripening Advancement, Ethylene-Forming Enzyme, and 1-Aminocyclopropane-1-carboxylic Acid Synthase Activity in Avocado Fruit 12

PubMed Central

Starrett, David A.; Laties, George G.

1991-01-01

When early-season avocado fruit (Persea americana Mill. cv Hass) were treated with ethylene or propylene for 24 hours immediately on picking, the time to the onset of the respiratory climacteric, i.e. the lag period, remained unchanged compared with that in untreated fruit. When fruit were pulsed 24 hours after picking, on the other hand, the lag period was shortened. In both cases, however, a 24 hour ethylene or propylene pulse induced a transient increase in respiration, called the pulse-peak, unaccompanied by ethylene production (IL Eaks [1980] Am Soc Hortic Sci 105: 744-747). The pulse also caused a sharp rise in ethylene-forming enzyme activity in both cases, without any increase in the low level of 1-aminocyclopropane-1-carboxylic acid synthase activity. Thus, the shortening of the lag period by an ethylene pulse is not due to an effect of ethylene on either of the two key enzymes in ethylene biosynthesis. A comparison of two-dimensional polyacrylamide gel electrophoresis polypeptide profiles of in vitro translation products of poly(A+) mRNA from control and ethylene-pulsed fruit showed both up- and down-regulation in response to ethylene pulsing of a number of genes expressed during the ripening syndrome. It is proposed that the pulse-peak or its underlying events reflect an intrinsic element in the ripening process that in late-season or continuously ethylene-treated fruit may be subsumed in the overall climacteric response. A computerized system that allows continuous readout of multiple samples has established that the continued presentation of exogeneous ethylene or propylene to preclimacteric fruit elicits a dual respiration response comprising the merged pulse-peak and climacteric peak in series. The sequential removal of cores from a single fruit has proven an unsatisfactory sampling procedure inasmuch as coring induces wound ethylene, evokes a positive respiration response, and advances ripening. PMID:16668073

CaV 3.1 and CaV 3.3 account for T-type Ca2+ current in GH3 cells.

PubMed

Mudado, M A; Rodrigues, A L; Prado, V F; Beirão, P S L; Cruz, J S

2004-06-01

T-type Ca2+ channels are important for cell signaling by a variety of cells. We report here the electrophysiological and molecular characteristics of the whole-cell Ca2+ current in GH3 clonal pituitary cells. The current inactivation at 0 mV was described by a single exponential function with a time constant of 18.32 +/- 1.87 ms (N = 16). The I-V relationship measured with Ca2+ as a charge carrier was shifted to the left when we applied a conditioning pre-pulse of up to -120 mV, indicating that a low voltage-activated current may be present in GH3 cells. Transient currents were first activated at -50 mV and peaked around -20 mV. The half-maximal voltage activation and the slope factors for the two conditions are -35.02 +/- 2.4 and 6.7 +/- 0.3 mV (pre-pulse of -120 mV, N = 15), and -27.0 +/- 0.97 and 7.5 +/- 0.7 mV (pre-pulse of -40 mV, N = 9). The 8-mV shift in the activation mid-point was statistically significant (P < 0.05). The tail currents decayed bi-exponentially suggesting two different T-type Ca2+ channel populations. RT-PCR revealed the presence of alpha1G (CaV3.1) and alpha1I (CaV3.3) T-type Ca2+ channel mRNA transcripts.

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.

Inference and analysis of xenon outflow curves under multi-pulse injection in two-dimensional chromatography.

PubMed

Shu-Jiang, Liu; Zhan-Ying, Chen; Yin-Zhong, Chang; Shi-Lian, Wang; Qi, Li; Yuan-Qing, Fan

2013-10-11

Multidimensional gas chromatography is widely applied to atmospheric xenon monitoring for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). To improve the capability for xenon sampling from the atmosphere, sampling techniques have been investigated in detail. The sampling techniques are designed by xenon outflow curves which are influenced by many factors, and the injecting condition is one of the key factors that could influence the xenon outflow curves. In this paper, the xenon outflow curves of single-pulse injection in two-dimensional gas chromatography has been tested and fitted as a function of exponential modified Gaussian distribution. An inference formula of the xenon outflow curve for six-pulse injection is derived, and the inference formula is also tested to compare with its fitting formula of the xenon outflow curve. As a result, the curves of both the one-pulse and six-pulse injections obey the exponential modified Gaussian distribution when the temperature of the activated carbon column's temperature is 26°C and the flow rate of the carrier gas is 35.6mLmin(-1). The retention time of the xenon peak for one-pulse injection is 215min, and the peak width is 138min. For the six-pulse injection, however, the retention time is delayed to 255min, and the peak width broadens to 222min. According to the inferred formula of the xenon outflow curve for the six-pulse injection, the inferred retention time is 243min, the relative deviation of the retention time is 4.7%, and the inferred peak width is 225min, with a relative deviation of 1.3%. Copyright © 2013 Elsevier B.V. All rights reserved.

A NEW THERMIONIC RF ELECTRON GUN FOR SYNCHROTRON LIGHT SOURCES

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

Kutsaev, Sergey; Agustsson, R.; Hartzell, J

A thermionic RF gun is a compact and efficient source of electrons used in many practical applications. RadiaBeam Systems and the Advanced Photon Source at Argonne National Laboratory collaborate in developing of a reliable and robust thermionic RF gun for synchrotron light sources which would offer substantial improvements over existing thermionic RF guns and allow stable operation with up to 1A of beam peak current at a 100 Hz pulse repetition rate and a 1.5 μs RF pulse length. In this paper, we discuss the electromagnetic and engineering design of the cavity and report the progress towards high power testsmore » of the cathode assembly of the new gun.« less

Laser-photofield emission from needle cathodes for low-emittance electron beams.

PubMed

Ganter, R; Bakker, R; Gough, C; Leemann, S C; Paraliev, M; Pedrozzi, M; Le Pimpec, F; Schlott, V; Rivkin, L; Wrulich, A

2008-02-15

Illumination of a ZrC needle with short laser pulses (16 ps, 266 nm) while high voltage pulses (-60 kV, 2 ns, 30 Hz) are applied, produces photo-field emitted electron bunches. The electric field is high and varies rapidly over the needle surface so that quantum efficiency (QE) near the apex can be much higher than for a flat photocathode due to the Schottky effect. Up to 150 pC (2.9 A peak current) have been extracted by photo-field emission from a ZrC needle. The effective emitting area has an estimated radius below 50 microm leading to a theoretical intrinsic emittance below 0.05 mm mrad.

Laser pulse heating of steel mixing with WC particles in a irradiated region

NASA Astrophysics Data System (ADS)

Shuja, S. Z.; Yilbas, B. S.; Ali, H.; Karatas, C.

2016-12-01

Laser pulse heating of steel mixing with tungsten carbide (WC) particles is carried out. Temperature field in the irradiated region is simulated in line with the experimental conditions. In the analysis, a laser pulse parameter is introduced, which defines the laser pulse intensity distribution at the irradiated surface. The influence of the laser parameter on the melt pool size and the maximum temperature increase in the irradiated region is examined. Surface temperature predictions are compared with the experimental data. In addition, the distribution of WC particles and their re-locations in the treated layer, due to combination of the natural convection and Marangoni currents, are predicted. The findings are compared to the experimental data. It is found that surface temperature predictions agree well with the experimental data. The dislocated WC particles form a streamlining in the near region of the melt pool wall, which agree with the experimental findings. The Gaussian distribution of the laser pulse intensity results in the maximum peak temperature and the maximum flow velocity inside the melt pool. In this case, the melt pool depth becomes the largest as compared to those corresponding to other laser pulse intensity distributions at the irradiated surface.

Accurate step-FMCW ultrasound ranging and comparison with pulse-echo signaling methods

NASA Astrophysics Data System (ADS)

Natarajan, Shyam; Singh, Rahul S.; Lee, Michael; Cox, Brian P.; Culjat, Martin O.; Grundfest, Warren S.; Lee, Hua

2010-03-01

This paper presents a method setup for high-frequency ultrasound ranging based on stepped frequency-modulated continuous waves (FMCW), potentially capable of producing a higher signal-to-noise ratio (SNR) compared to traditional pulse-echo signaling. In current ultrasound systems, the use of higher frequencies (10-20 MHz) to enhance resolution lowers signal quality due to frequency-dependent attenuation. The proposed ultrasound signaling format, step-FMCW, is well-known in the radar community, and features lower peak power, wider dynamic range, lower noise figure and simpler electronics in comparison to pulse-echo systems. In pulse-echo ultrasound ranging, distances are calculated using the transmit times between a pulse and its subsequent echoes. In step-FMCW ultrasonic ranging, the phase and magnitude differences at stepped frequencies are used to sample the frequency domain. Thus, by taking the inverse Fourier transform, a comprehensive range profile is recovered that has increased immunity to noise over conventional ranging methods. Step-FMCW and pulse-echo waveforms were created using custom-built hardware consisting of an arbitrary waveform generator and dual-channel super heterodyne receiver, providing high SNR and in turn, accuracy in detection.

Measurement of OH Radicals in Pulsed Corona and Pulsed Dielectric Barrier Discharge

NASA Astrophysics Data System (ADS)

Ono, Ryo; Oda, Tetsuji

OH radicals are measured in a pulsed corona or a pulsed dielectric barrier discharge (DBD) using laserinduced fluorescence (LIF) method. The pulsed discharges occur in nitrogen-oxygen mixture with 2.4% water vapor at atmospheric pressure. The pulse width is 100ns and the peak voltage is 35kV. The electrode configuration is a needle to plate electrode with 16-mm gap for corona discharge, and with 5-mm gap for DBD where the barrier is 2mm thick glass plate. It is shown that OH density is approximately proportional to the energy consumed by the discharge. The OH density per the discharge energy is about 2-4×1014cm-3/mJ for both discharges in H2O(2.4%)/N2 mixture. It is shown that OH density increases with oxygen content in DBD, whereas OH density reaches a maximum at 3% oxygen content in corona discharge. The existence of oxygen accelerates OH decay rate in both discharges. A trace amount of trichloroethylene (TCE) is added to the ambient gas. It is shown that the addition of 100ppm TCE to corona discharge reduces discharge current by about 50%. That leads to decrease of OH production.

Demonstration of a 140-GHz 1-kW Confocal Gyro-Traveling-Wave Amplifier

PubMed Central

Joye, Colin D.; Shapiro, Michael A.; Sirigiri, Jagadishwar R.; Temkin, Richard J.

2009-01-01

The theory, design, and experimental results of a wideband 140-GHz 1-kW pulsed gyro-traveling-wave amplifier (gyro-TWA) are presented. The gyro-TWA operates in the HE06 mode of an overmoded quasi-optical waveguide using a gyrating electron beam. The electromagnetic theory, interaction theory, design processes, and experimental procedures are described in detail. At 37.7 kV and a 2.7-A beam current, the experiment has produced over 820 W of peak power with a –3-dB bandwidth of 0.8 GHz and a linear gain of 34 dB at 34.7 kV. In addition, the amplifier produced a –3-dB bandwidth of over 1.5 GHz (1.1%) with a peak power of 570 W from a 38.5-kV 2.5-A electron beam. The electron beam is estimated to have a pitch factor of 0.55–0.6, a radius of 1.9 mm, and a calculated perpendicular momentum spread of approximately 9%. The gyro-amplifier was nominally operated at a pulselength of 2 μs but was tested to amplify pulses as short as 4 ns with no noticeable pulse broadening. Internal reflections in the amplifier were identified using these short pulses by time-domain reflectometry. The demonstrated performance of this amplifier shows that it can be applied to dynamic nuclear polarization and electron paramagnetic resonance spectroscopy. PMID:20054451

High peak-power mid-infrared ZnGeP₂ optical parametric oscillator pumped by a Tm:fiber master oscillator power amplifier system.

PubMed

Gebhardt, Martin; Gaida, Christian; Kadwani, Pankaj; Sincore, Alex; Gehlich, Nils; Jeon, Cheonha; Shah, Lawrence; Richardson, Martin

2014-03-01

We report on the utilization of a novel Tm:fiber laser source for mid-IR ZnGeP2 (ZGP) optical parametric oscillator (OPO) pumping. The pump laser is built in a master oscillator power-amplifier configuration delivering up to 3.36 W of polarized, diffraction limited output power with 7 ns pulse duration and 4 kHz repetition rate. This corresponds to a peak power of ∼121  kW and a pulse energy of ∼0.84  mJ. With this source, we generated 27.9 kW of total mid-IR peak power in a doubly resonant oscillator (DRO) configuration. This is, to the best of our knowledge, the highest ever demonstrated mid-IR peak power from a directly Tm:fiber laser pumped ZGP OPO. Moreover, a DRO output with about 284 μJ of total mid-IR pulse energy was demonstrated using 100 ns pump pulses. The wavelength tuning of the idler was extended to 6 μm with lower output power in another OPO experiment.

SIN accelerator, operational experience and improvement programs

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

Joho, W.; Olivo, M.; Stammbach, T.

1977-06-01

The SIN meson facility, in operation since 1974, consists of a 590 MeV ring cyclotron for protons and a 72 MeV injector cyclotron. The average beam current on target is presently about 50 ..mu..A, the peak being 112 ..mu..A. Extraction efficiency, once considered a severe handicap for cyclotrons, is now 99.6 to 99.9% for the ring cyclotron and about 90% for the injector. Many improvements in both accelerators allow single turn extraction in the ring cyclotron. The present current limit is given by the injector, while the ring itself could accept now a 600 ..mu..A beam, with 2 to 4more » mA as an ultimate limit. Some muon experiments require a pulsed beam with on-off times in the order of the lifetime of the muon. First trials with beam pulse frequencies of 200 and 400 kHz and a 50% duty cycle have been successful.« less

Description of an aircraft lightning and simulated nuclear electromagnetic pulse (NEMP) threat based on experimental data

NASA Technical Reports Server (NTRS)

Rustan, Pedro L., Jr.

1987-01-01

Lightning data obtained by measuring the surface electromagnetic fields on a CV-580 research aircraft during 48 lightning strikes between 1500 and 18,000 feet in central Florida during the summers of 1984 and 1985, and nuclear electromagnetic pulse (NEMP) data obtained by surface electromagnetic field measurements using a 1:74 CV-580 scale model, are presented. From one lightning event, maximum values of 3750 T/s for the time rate of change of the surface magnetic flux density, and 4.7 kA for the peak current, were obtained. From the simulated NEMP test, maximum values of 40,000 T/s for the time rate of change of the surface magnetic flux density, and 90 A/sq m for the total normal current density, were found. The data have application to the development of a military aircraft lightning/NEMP standard.

Variable slew-rate spiral design: theory and application to peak B(1) amplitude reduction in 2D RF pulse design.

PubMed

Xu, Dan; King, Kevin F; Liang, Zhi-Pei

2007-10-01

A new class of spiral trajectories called variable slew-rate spirals is proposed. The governing differential equations for a variable slew-rate spiral are derived, and both numeric and analytic solutions to the equations are given. The primary application of variable slew-rate spirals is peak B(1) amplitude reduction in 2D RF pulse design. The reduction of peak B(1) amplitude is achieved by changing the gradient slew-rate profile, and gradient amplitude and slew-rate constraints are inherently satisfied by the design of variable slew-rate spiral gradient waveforms. A design example of 2D RF pulses is given, which shows that under the same hardware constraints the RF pulse using a properly chosen variable slew-rate spiral trajectory can be much shorter than that using a conventional constant slew-rate spiral trajectory, thus having greater immunity to resonance frequency offsets.

Error probability for RFID SAW tags with pulse position coding and peak-pulse detection.

PubMed

Shmaliy, Yuriy S; Plessky, Victor; Cerda-Villafaña, Gustavo; Ibarra-Manzano, Oscar

2012-11-01

This paper addresses the code reading error probability (EP) in radio-frequency identification (RFID) SAW tags with pulse position coding (PPC) and peak-pulse detection. EP is found in a most general form, assuming M groups of codes with N slots each and allowing individual SNRs in each slot. The basic case of zero signal in all off-pulses and equal signals in all on-pulses is investigated in detail. We show that if a SAW-tag with PPC is designed such that the spurious responses are attenuated by more than 20 dB below on-pulses, then EP can be achieved at the level of 10(-8) (one false read per 108 readings) with SNR >17 dB for any reasonable M and N. The tag reader range is estimated as a function of the transmitted power and EP.

Pulsed electrodeposition of two-dimensional Ag nanostructures on Au(111).

PubMed

Borissov, D; Tsekov, R; Freyland, W

2006-08-17

One-step pulsed potential electrodeposition of Ag on Au(111) in the underpotential deposition (UPD) region has been studied in 0.5 mM Ag2SO4 + 0.1 M H2SO4 aqueous electrolyte at various pulse durations from 0.2 to 500 ms. Evolution of the deposited Ag nanostructures was followed by in situ scanning tunneling microscopy (STM) and by measurement of the respective current transients. At short pulse durations a relatively high number density (4 x 10(11) cm(-2)) of two-dimensional Ag clusters with a narrow size and distance distribution is observed. They exhibit a remarkably high stability characterized by a dissolution potential which lies about 200 mV more anodically than the typical potential of Ag-(1 x 1) monolayer dissolution. To elucidate the underlying nucleation and growth mechanism, two models have been considered: two-dimensional lattice incorporation and a newly developed coupled diffusion-adsorption model. The first one yields a qualitative description of the current transients, whereas the second one is in nearly quantitative agreement with the experimental data. In this model the transformation of a Ag-(3 x 3) into a Ag-(1 x 1) structure indicated in the cyclic voltammogram (peaks at 520 vs 20 mV) is taken into account.

Study on the amplifier experiment of end-pumped long pulse slab laser

NASA Astrophysics Data System (ADS)

Jin, Quanwei; Chen, Xiaoming; Jiang, JianFeng; Pang, Yu; Tong, Lixin; Li, Mi; Hu, Hao; Lv, Wenqiang; Gao, Qingsong; Tang, Chun

2018-03-01

The amplifier experiment research of end-pumped long pulse slab laser is developed, the results of out-put energy, optical-optical efficiency and pulse waveform are obtained at different experiment conditions, such as peak pumped power, amplifier power and pumped pulse width. The seed laser is CW fundamental transverse-mode operation fiber laser, the laser medium is composited Nd:YAG slab. Under end-pumped and the 2 passes, the laser obtain 7.65J out-put energy and 43.1% optical-optical efficiency with 45kW peak-pumped power and 386μs pump pulse width. The experimental results provide the basic for the optimization design to high frequency, high energy and high beam-quality slab lasers.

The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks

DOE PAGES

Preece, R.; Burgess, J. Michael; von Kienlin, A.; ...

2013-11-21

Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 seconds is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. But, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. We found it difficult for any of the existing models to account for all of the observedmore » spectral and temporal behaviors simultaneously.« less

Experimental verification of the vaporization's contribution to the shock waves generated by underwater electrical wire explosion under micro-second timescale pulsed discharge

NASA Astrophysics Data System (ADS)

Han, Ruoyu; Zhou, Haibin; Wu, Jiawei; Clayson, Thomas; Ren, Hang; Wu, Jian; Zhang, Yongmin; Qiu, Aici

2017-06-01

This paper studies pressure waves generated by exploding a copper wire in a water medium, demonstrating the significant contribution of the vaporization process to the formation of shock waves. A test platform including a pulsed current source, wire load, chamber, and diagnostic system was developed to study the shock wave and optical emission characteristics during the explosion process. In the experiment, a total of 500 J was discharged through a copper wire load 0.2 mm in diameter and 4 cm in length. A water gap was installed adjacent to the load so that the current was diverted away from the load after breakdown occurred across the water gap. This allows the electrical energy injection into the load to be interrupted at different times and at different stages of the wire explosion process. Experimental results indicate that when the load was bypassed before the beginning of the vaporization phase, the measured peak pressure was less than 2.5 MPa. By contrast, the peak pressure increased significantly to over 6.5 MPa when the water gap broke down after the beginning of the vaporization phase. It was also found that when bypassing the load after the voltage peak, similar shock waves were produced to those from a non-bypassed load. However, the total optical emission of these bypassed loads was at least an order of magnitude smaller. These results clearly demonstrate that the vaporization process is vital to the formation of shock waves and the energy deposited after the voltage collapse may only have a limited effect.

Voltage-Clamp Studies on Uterine Smooth Muscle

PubMed Central

Anderson, Nels C.

1969-01-01

These studies have developed and tested an experimental approach to the study of membrane ionic conductance mechanisms in strips of uterine smooth muscle. The experimental and theoretical basis for applying the double sucrose-gap technique is described along with the limitations of this system. Nonpropagating membrane action potentials were produced in response to depolarizing current pulses under current-clamp conditions. The stepwise change of membrane potential under voltage-clamp conditions resulted in a family of ionic currents with voltage- and time-dependent characteristics. In sodium-free solution the peak transient current decreased and its equilibrium potential shifted along the voltage axis toward a more negative internal potential. These studies indicate a sodium-dependent, regenerative excitation mechanism. PMID:5796366

A gigawatt level repetitive rate adjustable magnetic pulse compressor.

PubMed

Li, Song; Gao, Jing-Ming; Yang, Han-Wu; Qian, Bao-Liang; Li, Ze-Xin

2015-08-01

In this paper, a gigawatt level repetitive rate adjustable magnetic pulse compressor is investigated both numerically and experimentally. The device has advantages of high power level, high repetitive rate achievability, and long lifetime reliability. Importantly, dominate parameters including the saturation time, the peak voltage, and even the compression ratio can be potentially adjusted continuously and reliably, which significantly expands the applicable area of the device and generators based on it. Specifically, a two-stage adjustable magnetic pulse compressor, utilized for charging the pulse forming network of a high power pulse generator, is designed with different compression ratios of 25 and 18 through an optimized design process. Equivalent circuit analysis shows that the modification of compression ratio can be achieved by just changing the turn number of the winding. At the same time, increasing inductance of the grounded inductor will decrease the peak voltage and delay the charging process. Based on these analyses, an adjustable compressor was built and studied experimentally in both the single shot mode and repetitive rate mode. Pulses with peak voltage of 60 kV and energy per pulse of 360 J were obtained in the experiment. The rise times of the pulses were compressed from 25 μs to 1 μs and from 18 μs to 1 μs, respectively, at repetitive rate of 20 Hz with good repeatability. Experimental results show reasonable agreement with analyses.

A simple differential pulse polarographic method for the determination of thymoquinone in black seed oil.

PubMed

Michelitsch, Astrid; Rittmannsberger, Anna

2003-01-01

A reliable and simple differential pulse polarographic method is described for the determination of thymoquinone in black seed oil. The polarographic behaviour of thymoquinone was examined in various buffer systems over the pH range 5.0-10.0. Thymoquinone is reduced in a single, reversible peak at the dropping mercury electrode. The differential pulse polarogram showed a distinct peak in Sörensen buffer:methanol (3:7, v/v; pH 8.5) at a peak potential of -0.095 V (vs. silver/silver chloride electrode), and a plot of peak height against concentration was found to be linear over the range 0.2-15.0 microg/mL (R = 0.9998). The limit of detection was calculated to be 0.054 microg/mL. The polarographic method has been applied to determine thymoquinone in two black seed oil preparations available on the Austrian pharmaceutical market.

Pulsed coherent population trapping with repeated queries for producing single-peaked high contrast Ramsey interference

NASA Astrophysics Data System (ADS)

Warren, Z.; Shahriar, M. S.; Tripathi, R.; Pati, G. S.

2018-02-01

A repeated query technique has been demonstrated as a new interrogation method in pulsed coherent population trapping for producing single-peaked Ramsey interference with high contrast. This technique enhances the contrast of the central Ramsey fringe by nearly 1.5 times and significantly suppresses the side fringes by using more query pulses ( >10) in the pulse cycle. Theoretical models have been developed to simulate Ramsey interference and analyze the characteristics of the Ramsey spectrum produced by the repeated query technique. Experiments have also been carried out employing a repeated query technique in a prototype rubidium clock to study its frequency stability performance.

Oxidation of ammonium sulfite by a multi-needle-to-plate gas phase pulsed corona discharge reactor

NASA Astrophysics Data System (ADS)

Ren, Hua; Lu, Na; Shang, Kefeng; Li, Jie; Wu, Yan

2013-03-01

The oxidation of ammonium sulfite in the ammonia-based flue gas desulfurization (FGD) process was investigated in a multi-needle-to-plate gas phase pulsed corona discharge reactor in this paper. The effect of several parameters, including capacitance and peak pulse voltage of discharge system, electrode gap and bubbling gas flow rate on the oxidation rate of ammonium sulfite was reviewed. The oxidation rate of ammonium sulfite could reach 47.2% at the capacitance, the peak pulse voltage, electrode gap and bubbling gas flow rate equal to 2 nF, -24.6 k V, 35 mm and 4 L min-1 within treatment time of 40 min The experimental results indicate that the gas phase pulsed discharge system with a multi-needle-to-plate electrode can oxide the ammonium sulfite. The oxidation rate increased with the applied capacitance and peak pulse voltage and decreased with the electrode gap. As the bubbling gas flow rate increased, the oxidation rate increased first and then tended to reach a stationary value. These results would be important for the process optimization of the (NH4)2SO3 to (NH4)2SO4 oxidation.

High-temperature thermoluminescence of anion-deficient alumina and possibilities of its application in high-dose dosimetry

NASA Astrophysics Data System (ADS)

Surdo, A. I.; Milman, I. I.; Abashev, R. M.; Vlasov, M. I.

2014-12-01

Results of studies of the thermoluminescence (TL) of anion-deficient alumina (α-Al2O3 - δ) single crystals and based on them TLD-500 detectors exposed to pulsed X-ray and electron radiation in a wide range of doses D, pulsed dose rates P p , and temperatures are described. The TL responses of α-Al2O3 - δ for continuous and pulsed X-ray irradiation at D = 0.05-150 Gy are compared. Unlike continuous irradiation, in the case of pulsed irradiation at P p ≥ 6 × 106 Gy/s, a linear increase in the TL response as a function of D is registered in the main and "chromium" peaks at 450 and 580 K, respectively, with a decrease in the slope of the dose dependence at D > 2 Gy for the peak at 450 K. It is found that high-dose irradiation (>60 Gy) leads to the formation of a new TL peak at 830 K and the preferential redistribution of the stored light sums into this peak. The dose dependence for the TL peak at 830 K is studied. It is established that it is linear in a super-high dose range of 104 to 6 × 106 Gy at P p = 2.6 × 1011 Gy/s.

High resolution, high rate X-ray spectrometer

DOEpatents

Goulding, Frederick S.; Landis, Donald A.

1987-01-01

A pulse processing system (10) for use in an X-ray spectrometer in which a ain channel pulse shaper (12) and a fast channel pulse shaper (13) each produce a substantially symmetrical triangular pulse (f, p) for each event detected by the spectrometer, with the pulse width of the pulses being substantially independent of the magnitude of the detected event and with the pulse width of the fast pulses (p) being substantially shorter than the pulse width of the main channel pulses (f). A pile-up rejector circuit (19) allows output pulses to be generated, with amplitudes linearly related to the magnitude of the detected events, whenever the peak of a main channel pulse (f) is not affected by a preceding or succeeding main channel pulse, while inhibiting output pulses wherein peak magnitudes of main channel pulses are affected by adjacent pulses. The substantially symmetrical triangular main channel pulses (f) are generated by the weighted addition (27-31) of successive RC integrations (24, 25, 26) of an RC differentiated step wave (23). The substantially symmetrical triangular fast channel pulses (p) are generated by the RC integration ( 43) of a bipolar pulse (o) in which the amplitude of the second half is 1/e that of the first half, with the RC time constant of integration being equal to one-half the width of the bipolar pulse.

[Flexible Guidance of Ultra-Short Laser Pulses in Ophthalmic Therapy Systems].

PubMed

Blum, J; Blum, M; Rill, M S; Haueisen, J

2017-01-01

In the last 20 years, the role of ultrashort pulsed lasers in ophthalmology has become increasingly important. However, it is still impossible to guide ultra-short laser pulses with standard glass fibres. The highly energetic femtosecond pulses would destroy the fibre material, and non-linear dispersion effects would significantly change beam parameters. In contrast, photonic crystal fibres mainly guide the laser pulses in air, so that absorption and dispersive pulse broadening have essentially no effect. This article compares classical beam guidance with mirrors, lenses and prisms with photonic crystal fibres and describes the underlying concepts and the current state of technology. A classical mirror arm possesses more variable optical properties, while the HCF (Hollow-Core Photonic Crystal Fibre) must be matched in terms of the laser energy and the laser spectrum. In contrast, the HCF has more advantages in respect of handling, system integration and costs. For applications based on photodisruptive laser-tissue interaction, the relatively low damage threshold of photonic crystal fibres compared to classic beam guiding systems is unacceptable. If, however, pulsed laser radiation has a sufficiently low peak intensity, e.g. as used for plasma-induced ablation, photonic crystal fibres can definitely be considered as an alternative solution to classic beam guidance. Georg Thieme Verlag KG Stuttgart · New York.

Research on Shock Responses of Three Types of Honeycomb Cores

NASA Astrophysics Data System (ADS)

Peng, Fei; Yang, Zhiguang; Jiang, Liangliang; Ren, Yanting

2018-03-01

The shock responses of three kinds of honeycomb cores have been investigated and analyzed based on explicit dynamics analysis. According to the real geometric configuration and the current main manufacturing methods of aluminum alloy honeycomb cores, the finite element models of honeycomb cores with three different cellular configurations (conventional hexagon honeycomb core, rectangle honeycomb core and auxetic honeycomb core with negative Poisson’s ratio) have been established through FEM parametric modeling method based on Python and Abaqus. In order to highlight the impact response characteristics of the above three honeycomb cores, a 5 mm thick panel with the same mass and material was taken as contrast. The analysis results showed that the peak values of longitudinal acceleration history curves of the three honeycomb cores were lower than those of the aluminum alloy panel in all three reference points under the loading of a longitudinal pulse pressure load with the peak value of 1 MPa and the pulse width of 1 μs. It could be concluded that due to the complex reflection and diffraction of stress wave induced by shock in honeycomb structures, the impact energy was redistributed which led to a decrease in the peak values of the longitudinal acceleration at the measuring points of honeycomb cores relative to the panel.

[Current status of the development of wireless sensors for medical applications].

PubMed

Moor, C; Braecklein, M; Jörns, N

2005-01-01

Wireless near-field transmission has been a challenge for scientists developing medical sensors for a long time. Here, instruments which measure a patient's ECG, oxygen saturation, blood pressure, peak flow, weight, blood glucose etc. are to be equipped with suitable transmission technology. Application scenarios for these sensors can be found in all medical areas where cable connections are irritating for the doctor, patient and other care personnel. This problem is especially common in sport medicine, sleep medicine, emergency medicine and intensive care. Based on its beneficial properties with regard to power consumption, range, data security and network capability, the worldwide standard radio technology Bluetooth was selected to transmit measurements. Since digital data is sent to a receiving station via Bluetooth, the measurement pre-processing now takes place in the patient sensor itself, instead of being processed by the monitor. In this article, a Bluetooth ECG, Bluetooth pulse oximeter, Bluetooth peak flow meter and Bluetooth event recorder will be introduced. On the one hand, systems can be realized with these devices, which allow patients to be monitored online (ECG, pulse oximeter). These devices can also be integrated in disease management programs (peak flow meter) and can be used to monitor high-risk patients in their home environment (event recorder).

Pulse sequences for efficient multi-cycle terahertz generation in periodically poled lithium niobate.

PubMed

Ravi, Koustuban; Schimpf, Damian N; Kärtner, Franz X

2016-10-31

The use of laser pulse sequences to drive the cascaded difference frequency generation of high energy, high peak-power and multi-cycle terahertz pulses in cryogenically cooled (100 K) periodically poled Lithium Niobate is proposed and studied. Detailed simulations considering the coupled nonlinear interaction of terahertz and optical waves (or pump depletion), show that unprecedented optical-to-terahertz energy conversion efficiencies > 5%, peak electric fields of hundred(s) of mega volts/meter at terahertz pulse durations of hundred(s) of picoseconds can be achieved. The proposed methods are shown to circumvent laser induced damage limitations at Joule-level pumping by 1µm lasers to enable multi-cycle terahertz sources with pulse energies > 10 milli-joules. Various pulse sequence formats are proposed and analyzed. Numerical calculations for periodically poled structures accounting for cascaded difference frequency generation, self-phase-modulation, cascaded second harmonic generation and laser induced damage are introduced. The physics governing terahertz generation using pulse sequences in this high conversion efficiency regime, limitations and practical considerations are discussed. It is shown that varying the poling period along the crystal length and further reduction of absorption can lead to even higher energy conversion efficiencies >10%. In addition to numerical calculations, an analytic formulation valid for arbitrary pulse formats and closed-form expressions for important cases are presented. Parameters optimizing conversion efficiency in the 0.1-1 THz range, the corresponding peak electric fields, crystal lengths and terahertz pulse properties are furnished.

Nonlinear pulse compression stage delivering 43-W few-cycle pulses with GW peak-power at 2-μm wavelength

NASA Astrophysics Data System (ADS)

Gebhardt, Martin; Gaida, Christian; Heuermann, T.; Stutzki, F.; Jauregui, C.; Antonio-Lopez, J.; Schüuzgen, A.; Amezcua-Correa, R.; Tünnermann, A.; Limpert, J.

2018-02-01

In this contribution we demonstrate the nonlinear pulse compression of an ultrafast thulium-doped fiber laser down to 14 fs FWHM duration (sub-3 optical cycles) at a record average power of 43 W and 34.5 μJ pulse energy. To the best of our knowledge, we present the highest average power few-cycle laser source at 2 μm wavelength. This performance level in combination with GW-class peak power makes our laser source extremely interesting for driving high-harmonic generation or for generating mid-infrared frequency combs via intra-pulse frequency down-conversion at an unprecedented average power. The experiments were enabled by an ultrafast thulium-doped fiber laser delivering 110 fs pulses at high repetition rates, and an argon gas-filled antiresonant hollow-core fiber (ARHCF) with excellent transmission and weak anomalous dispersion, leading to the self-compression of the pulses. We have shown that ARHCFs are well-suited for nonlinear pulse compression around 2 μm wavelength and that this concept features excellent power handling capabilities. Based on this result, we discuss the next steps for energy and average power scaling including upscaling the fiber dimensions in order to fully exploit the capabilities of our laser system, which can deliver several GW of peak power. This way, a 100 W-class laser source with mJ-level few-cycle pulses at 2 μm wavelength is feasible in the near future.

Improved performances of CIBER-X: a new tabletop laser-driven electron and x-ray source

NASA Astrophysics Data System (ADS)

Girardeau-Montaut, Jean-Pierre; Kiraly, Bela; Girardeau-Montaut, Claire

2000-11-01

We present the most recent data concerning the performances of the table-top laser driven electron and x-ray source developed in our laboratory. X-ray pulses are produced by a three-step process which consists of the photoelectron emission from a thin metallic photocathode illuminated by 16 ps duration laser pulse at 213 nm. The e-gun is a standard pierce diode electrode type, in which electrons are accelerated by a cw electric fields of 12 MV/m. The photoinjector produced a train of 90 - 100 keV electron pulses of approximately 1 nC and 40 A peak current at a repetition rate of 10 Hz. The electrons, transported outside the diode, are focused onto a target of thulium by magnetic fields produced by two electromagnetic coils to produce x-rays. Applications to low dose imagery of inert and living materials are also presented.

Emerging opportunities in structural biology with X-ray free-electron lasers

PubMed Central

Schlichting, Ilme; Miao, Jianwei

2012-01-01

X-ray free-electron lasers (X-FELs) produce X-ray pulses with extremely brilliant peak intensity and ultrashort pulse duration. It has been proposed that radiation damage can be “outrun” by using an ultra intense and short X-FEL pulse that passes a biological sample before the onset of significant radiation damage. The concept of “diffraction-before-destruction” has been demonstrated recently at the Linac Coherent Light Source, the first operational hard X-ray FEL, for protein nanocrystals and giant virus particles. The continuous diffraction patterns from single particles allow solving the classical “phase problem” by the oversampling method with iterative algorithms. If enough data are collected from many identical copies of a (biological) particle, its three-dimensional structure can be reconstructed. We review the current status and future prospects of serial femtosecond crystallography (SFX) and single-particle coherent diffraction imaging (CDI) with X-FELs. PMID:22922042

RF extraction issues in the relativistic klystron amplifiers

NASA Astrophysics Data System (ADS)

Serlin, Victor; Friedman, Moshe; Lampe, Martin; Hubbard, Richard F.

1994-05-01

Relativistic klystron amplifiers (RKAs) were successfully operated at NRL in several frequency regimes and power levels. In particular, an L-band RKA was optimized for high- power rf extraction into the atmosphere and an S-band RKA was operated, both in a two-beam and a single-beam configuration. At L-band the rf extraction at maximum power levels (>= 15 GW) was hindered by pulse shortening and poor repeatability. Preliminary investigation showed electron emission in the radiating horn, due to very high voltages associated with the multi-gigawatt rf power levels. This electron current constituted an electric load in parallel with the radiating antenna, and precipitated the rf pulse collapse. At S-band the peak extracted power reached 1.7 GW with power efficiency approximately 50%. However, pulse shortening limited the duration to approximately 50 nanoseconds. The new triaxial RKA promises to solve many of the existing problems.

Note: Experimental platform for magnetized high-energy-density plasma studies at the omega laser facility

DOE PAGES

Fiksel, G.; Agliata, A.; Barnak, D.; ...

2015-01-12

Here, an upgrade of the pulsed magnetic field generator magneto-inertial fusion electrical discharge system [O. Gotchev et al., Rev. Sci. Instrum. 80, 043504 (2009)] is described. The device is used to study magnetized high-energy-density plasma and is capable of producing a pulsed magnetic field of tens of tesla in a volume of a few cubic centimeters. The magnetic field is created by discharging a high-voltage capacitor through a small wire-wound coil. The coil current pulse has a duration of about 1 μs and a peak value of 40 kA. Compared to the original, the updated version has a larger energymore » storage and improved switching system. In addition, magnetic coils are fabricated using 3-D printing technology which allows for a greater variety of the magnetic field topology.« less

2D modeling of DC potential structures induced by RF sheaths with transverse currents in front of ICRF antenna

NASA Astrophysics Data System (ADS)

Faudot, E.; Heuraux, S.; Colas, L.

2005-09-01

Understanding DC potential generation in front of ICRF antennas is crucial for long pulse high RF power systems. DC potentials are produced by sheath rectification of these RF potentials. To reach this goal, near RF parallel electric fields have to be computed in 3D and integrated along open magnetic field lines to yield a 2D RF potential map in a transverse plane. DC potentials are produced by sheath rectification of these RF potentials. As RF potentials are spatially inhomogeneous, transverse polarization currents are created, modifying RF and DC maps. Such modifications are quantified on a `test map' having initially a Gaussian shape and assuming that the map remains Gaussian near its summit,the time behavior of the peak can be estimated analytically in presence of polarization current as a function of its width r0 and amplitude φ0 (normalized to a characteristic length for transverse transport and to the local temperature). A `peaking factor' is built from the DC peak potential normalized to φ0, and validated with a 2D fluid code and a 2D PIC code (XOOPIC). In an unexpected way transverse currents can increase this factor. Realistic situations of a Tore Supra antenna are also studied, with self-consistent near fields provided by ICANT code. Basic processes will be detailed and an evaluation of the `peaking factor' for ITER will be presented for a given configuration.

2D modeling of DC potential structures induced by RF sheaths with transverse currents in front of ICRF antenna

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

Faudot, E.; Heuraux, S.; Colas, L.

2005-09-26

Understanding DC potential generation in front of ICRF antennas is crucial for long pulse high RF power systems. DC potentials are produced by sheath rectification of these RF potentials. To reach this goal, near RF parallel electric fields have to be computed in 3D and integrated along open magnetic field lines to yield a 2D RF potential map in a transverse plane. DC potentials are produced by sheath rectification of these RF potentials. As RF potentials are spatially inhomogeneous, transverse polarization currents are created, modifying RF and DC maps. Such modifications are quantified on a 'test map' having initially amore » Gaussian shape and assuming that the map remains Gaussian near its summit,the time behavior of the peak can be estimated analytically in presence of polarization current as a function of its width r0 and amplitude {phi}0 (normalized to a characteristic length for transverse transport and to the local temperature). A 'peaking factor' is built from the DC peak potential normalized to {phi}0, and validated with a 2D fluid code and a 2D PIC code (XOOPIC). In an unexpected way transverse currents can increase this factor. Realistic situations of a Tore Supra antenna are also studied, with self-consistent near fields provided by ICANT code. Basic processes will be detailed and an evaluation of the 'peaking factor' for ITER will be presented for a given configuration.« less

Experimental observation of acoustic emissions generated by a pulsed proton beam from a hospital-based clinical cyclotron.

PubMed

Jones, Kevin C; Vander Stappen, François; Bawiec, Christopher R; Janssens, Guillaume; Lewin, Peter A; Prieels, Damien; Solberg, Timothy D; Sehgal, Chandra M; Avery, Stephen

2015-12-01

To measure the acoustic signal generated by a pulsed proton spill from a hospital-based clinical cyclotron. An electronic function generator modulated the IBA C230 isochronous cyclotron to create a pulsed proton beam. The acoustic emissions generated by the proton beam were measured in water using a hydrophone. The acoustic measurements were repeated with increasing proton current and increasing distance between detector and beam. The cyclotron generated proton spills with rise times of 18 μs and a maximum measured instantaneous proton current of 790 nA. Acoustic emissions generated by the proton energy deposition were measured to be on the order of mPa. The origin of the acoustic wave was identified as the proton beam based on the correlation between acoustic emission arrival time and distance between the hydrophone and proton beam. The acoustic frequency spectrum peaked at 10 kHz, and the acoustic pressure amplitude increased monotonically with increasing proton current. The authors report the first observation of acoustic emissions generated by a proton beam from a hospital-based clinical cyclotron. When modulated by an electronic function generator, the cyclotron is capable of creating proton spills with fast rise times (18 μs) and high instantaneous currents (790 nA). Measurements of the proton-generated acoustic emissions in a clinical setting may provide a method for in vivo proton range verification and patient monitoring.

Local SAR in Parallel Transmission Pulse Design

PubMed Central

Lee, Joonsung; Gebhardt, Matthias; Wald, Lawrence L.; Adalsteinsson, Elfar

2011-01-01

The management of local and global power deposition in human subjects (Specific Absorption Rate, SAR) is a fundamental constraint to the application of parallel transmission (pTx) systems. Even though the pTx and single channel have to meet the same SAR requirements, the complex behavior of the spatial distribution of local SAR for transmission arrays poses problems that are not encountered in conventional single-channel systems and places additional requirements on pTx RF pulse design. We propose a pTx pulse design method which builds on recent work to capture the spatial distribution of local SAR in numerical tissue models in a compressed parameterization in order to incorporate local SAR constraints within computation times that accommodate pTx pulse design during an in vivo MRI scan. Additionally, the algorithm yields a Protocol-specific Ultimate Peak in Local SAR (PUPiL SAR), which is shown to bound the achievable peak local SAR for a given excitation profile fidelity. The performance of the approach was demonstrated using a numerical human head model and a 7T eight-channel transmit array. The method reduced peak local 10g SAR by 14–66% for slice-selective pTx excitations and 2D selective pTx excitations compared to a pTx pulse design constrained only by global SAR. The primary tradeoff incurred for reducing peak local SAR was an increase in global SAR, up to 34% for the evaluated examples, which is favorable in cases where local SAR constraints dominate the pulse applications. PMID:22083594

Measured close lightning leader-step electric-field-derivative waveforms.

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

Jordan, Doug M.; Hill, Dustin; Biagi, Christopher J.

2010-12-01

We characterize the measured electric field-derivative (dE/dt) waveforms of lightning stepped-leader steps from three negative lightning flashes at distances of tens to hundreds of meters. Electromagnetic signatures of leader steps at such close distances have rarely been documented in previous literature. Individual leader-step three-dimensional locations are determined by a dE/dt TOA system. The leader-step field derivative is typically a bipolar pulse with a sharp initial half-cycle of the same polarity as that of the return stroke, followed by an opposite polarity overshoot that decays relatively slowly to background level. This overshoot increases in amplitude relative to the initial peak andmore » becomes dominant as range decreases. The initial peak is often preceded by a 'slow front,' similar to the slow front that precedes the fast transition to peak in first return stroke dE/dt and E waveforms. The overall step-field waveform duration is typically less than 1 {micro}s. The mean initial peak of dE/dt, range-normalized to 100 km, is 7.4 V m{sup -1} {micro}s{sup -1} (standard deviation (S.D.), 3.7 V m{sup -1} {micro}s{sup -1}, N = 103), the mean half-peak width is 33.5 ns (S.D., 11.9 ns, N = 69), and the mean 10-to-90% risetime is 43.6 ns (S.D., 24.2 ns, N = 69). From modeling, we determine the properties of the leader step currents which produced two typical measured field derivatives, and we use one of these currents to calculate predicted leader step E and dE/dt as a function of source range and height, the results being in good agreement with our observations. The two modeled current waveforms had maximum rates of current rise-to-peak near 100 kA {micro}s{sup -1}, peak currents in the 5-7 kA range, current half-peak widths of about 300 ns, and charge transfers of {approx}3 mC. As part of the modeling, those currents were propagated upward at 1.5 x 10{sup 8} m s{sup -1}, with their amplitudes decaying exponentially with a decay height constant of 25 m.« less

High-sensitive computed tomography system using a silicon-PIN x-ray diode

NASA Astrophysics Data System (ADS)

Sato, Eiichi; Sato, Yuich; Abudurexiti, Abulajiang; Hagiwara, Osahiko; Matsukiyo, Hiroshi; Osawa, Akihiro; Enomoto, Toshiyuki; Watanabe, Manabu; Kusachi, Shinya; Sato, Shigehiro; Ogawa, Akira; Onagawa, Jun

2012-10-01

A low-dose-rate X-ray computed tomography (CT) system is useful for reducing absorbed dose for patients. The CT system with a tube current of 1.91 mA was developed using a silicon-PIN X-ray diode (Si-PIN-XD). The Si-PIN-XD is a selected high-sensitive Si-PIN photodiode (PD) for detecting X-ray photons. X-ray photons are detected directly using the Si-PIN-XD without a scintillator, and the photocurrent from the diode is amplified using current-voltage and voltage-voltage amplifiers. The output voltage is converted into logical pulses using a voltage-frequency converter with maximum frequency of 500 kHz, and the frequency is proportional to the voltage. The pulses from the converter are sent to differentiator with a time constant of 1 μs to generate short positive pulses for counting, and the pulses are counted using a counter card. Tomography is accomplished by repeated linear scans and rotations of an object, and projection curves of the object are obtained by the linear scan. The exposure time for obtaining a tomogram was 5 min at a scan step of 0.5 mm and a rotation step of 3.0°. The tube current and voltage were 1.91 mA and 100 kV, respectively, and gadolinium K-edge CT was carried out using filtered X-ray spectra with a peak energy of 52 keV.

Characterization of an electrothermal plasma source for fusion transient simulations

NASA Astrophysics Data System (ADS)

Gebhart, T. E.; Baylor, L. R.; Rapp, J.; Winfrey, A. L.

2018-01-01

The realization of fusion energy requires materials that can withstand high heat and particle fluxes at the plasma material interface. In this work, an electrothermal (ET) plasma source has been designed as a transient heat flux source for a linear plasma material interaction device. An ET plasma source operates in the ablative arc regime driven by a DC capacitive discharge. The current channel width is defined by the 4 mm bore of a boron nitride liner. At large plasma currents, the arc impacts the liner wall, leading to high particle and heat fluxes to the liner material, which subsequently ablates and ionizes. This results in a high density plasma with a large unidirectional bulk flow out of the source exit. The pulse length for the ET source has been optimized using a pulse forming network to have durations of 1 and 2 ms. The peak currents and maximum source energies seen in this system are 1.9 kA and 1.2 kJ for the 2 ms pulse and 3.2 kA and 2.1 kJ for the 1 ms pulse, respectively. This work is a proof of the principal project to show that an ET source produces electron densities and heat fluxes comparable to those anticipated in transient events in large future magnetic confinement fusion devices. Heat flux, plasma temperature, and plasma density were determined for each shot using infrared imaging and optical spectroscopy techniques. This paper will discuss the assumptions, methods, and results of the experiments.

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.

Testing of Diode-Clamping in an Inductive Pulsed Plasma Thruster Circuit

NASA Technical Reports Server (NTRS)

Toftul, Alexandra; Polzin, Kurt A.; Martin, Adam K.; Hudgins, Jerry L.

2014-01-01

Testing of a 5.5 kV silicon (Si) diode and 5.8 kV prototype silicon carbide (SiC) diode in an inductive pulsed plasma thruster (IPPT) circuit was performed to obtain a comparison of the resulting circuit recapture efficiency,eta(sub r), defined as the percentage of the initial charge energy remaining on the capacitor bank after the diode interrupts the current. The diode was placed in a pulsed circuit in series with a silicon controlled rectifier (SCR) switch, and the voltages across different components and current waveforms were collected over a range of capacitor charge voltages. Reverse recovery parameters, including turn-off time and peak reverse recovery current, were measured and capacitor voltage waveforms were used to determine the recapture efficiency for each case. The Si fast recovery diode in the circuit was shown to yield a recapture efficiency of up to 20% for the conditions tested, while the SiC diode further increased recapture efficiency to nearly 30%. The data presented show that fast recovery diodes operate on a timescale that permits them to clamp the discharge quickly after the first half cycle, supporting the idea that diode-clamping in IPPT circuit reduces energy dissipation that occurs after the first half cycle

Laser plasma interaction at an early stage of laser ablation

NASA Astrophysics Data System (ADS)

Lu, Y. F.; Hong, M. H.; Low, T. S.

1999-03-01

Laser scattering and its interaction with plasma during KrF excimer laser ablation of silicon are investigated by ultrafast phototube detection. There are two peaks in an optical signal with the first peak attributed to laser scattering and the second one to plasma generation. For laser fluence above 5.8 J/cm2, the second peak rises earlier to overlap with the first one. The optical signal is fitted by a pulse distribution for the scattered laser light and a drifted Maxwell-Boltzmann distribution with a center-of-mass velocity for the plasma. Peak amplitude and its arrival time, full width at half maximum (FWHM), starting time, and termination time of the profiles are studied for different laser fluences and detection angles. Laser pulse is scattered from both the substrate and the plasma with the latter part as a dominant factor during the laser ablation. Peak amplitude of the scattered laser signal increases but its FWHM decreases with the laser fluence. Angular distribution of the peak amplitude can be fitted with cosn θ(n=4) while the detection angle has no obvious influence on the FWHM. In addition, FWHM and peak amplitude of plasma signal increase with the laser fluence. However, starting time and peak arrival time of plasma signal reduce with the laser fluence. The time interval between plasma starting and scattered laser pulse termination is proposed as a quantitative parameter to characterize laser plasma interaction. Threshold fluence for the interaction is estimated to be 3.5 J/cm2. For laser fluence above 12.6 J/cm2, the plasma and scattered laser pulse distributions tend to saturate.

Anatomy of a Flash Flood in the Amargosa Desert, U.S.A.

NASA Astrophysics Data System (ADS)

Stonestrom, D. A.; Prudic, D. E.; Glancy, P. A.; Beck, D. A.

2004-12-01

In August 2004, intense convective rainstorms caused flash flooding throughout the Amargosa River drainage network, temporarily closing Death Valley National Park and causing two fatalities when runoff from Furnace Creek and other channels overtopped roadways in the Park. In 1998, we began installing streambed temperature loggers, pressure transducers, and scour chains in the normally dry channel and selected tributaries of the river in the Amargosa Desert and Oasis Valley. The primary objective of this work is to improve understanding of ground-water recharge from ephemeral streamflows under current climatic conditions. Two weeks after the flash flooding, we visited instrumented sites and estimated peak flows by surveying high-water marks and corresponding channel geometries. Time series of temperatures and stages, together with peak-flow estimates, reveal the routing and evolution of distinct flood pulses in the upper Amargosa River basin. The data also reveal previously undocumented details of individual flash-flood hydrographs, including initial and subsequent flood pulses at two sites. Arid environments are prone to flash flooding not only because vegetation is sparse, but also because the surface-water network is decoupled from underlying ground water by a thick unsaturated zone. Nonlinear interactions between runoff (with energy potentials on the order of a meter of head) and the unsaturated zone (with energy potentials on the order of negative hundreds of meters of head) keep advancing fronts of flood pulses sharp. Profiles of water content beneath the main channel before and after the passage of a flood pulse, together with down-channel attenuation of flow volume within individual pulses, show the leaky nature of dry alluvial channels and the efficiency at which flash floods become potential recharge.

SU-C-207A-04: Accuracy of Acoustic-Based Proton Range Verification in Water

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

Jones, KC; Sehgal, CM; Avery, S

2016-06-15

Purpose: To determine the accuracy and dose required for acoustic-based proton range verification (protoacoustics) in water. Methods: Proton pulses with 17 µs FWHM and instantaneous currents of 480 nA (5.6 × 10{sup 7} protons/pulse, 8.9 cGy/pulse) were generated by a clinical, hospital-based cyclotron at the University of Pennsylvania. The protoacoustic signal generated in a water phantom by the 190 MeV proton pulses was measured with a hydrophone placed at multiple known positions surrounding the dose deposition. The background random noise was measured. The protoacoustic signal was simulated to compare to the experiments. Results: The maximum protoacoustic signal amplitude at 5more » cm distance was 5.2 mPa per 1 × 10{sup 7} protons (1.6 cGy at the Bragg peak). The background random noise of the measurement was 27 mPa. Comparison between simulation and experiment indicates that the hydrophone introduced a delay of 2.4 µs. For acoustic data collected with a signal-to-noise ratio (SNR) of 21, deconvolution of the protoacoustic signal with the proton pulse provided the most precise time-of-flight range measurement (standard deviation of 2.0 mm), but a systematic error (−4.5 mm) was observed. Conclusion: Based on water phantom measurements at a clinical hospital-based cyclotron, protoacoustics is a potential technique for measuring the proton Bragg peak range with 2.0 mm standard deviation. Simultaneous use of multiple detectors is expected to reduce the standard deviation, but calibration is required to remove systematic error. Based on the measured background noise and protoacoustic amplitude, a SNR of 5.3 is projected for a deposited dose of 2 Gy.« less

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.

Comprehensive two-dimensional gas chromatography using partial modulation via a pulsed flow valve with a short modulation period.

PubMed

Freye, Chris E; Bahaghighat, H Daniel; Synovec, Robert E

2018-01-15

Partial modulation via a pulsed flow valve for comprehensive two-dimensional (2D) gas chromatography (GC × GC) is demonstrated, producing narrow peak widths, 2 W b , on the secondary separation dimension, 2 D, coupled with short modulation periods, P M , thus producing a high peak capacity on the 2 D dimension, 2 n c . The GC × GC modulator is a pulse flow valve that injects a pulse of carrier gas at the specified P M , at the connection between the primary, 1 D, column and the 2 D column. Using a commercially available pulse flow valve, this injection technique performs a combination of vacancy chromatography and frontal analysis, whereby each pulse disturbance in the analyte concentration profile as it exits the 1 D column results in data that is readily converted into a 2 D separation. A three-step process converts the raw data into a format analogous to a GC × GC separation, incorporating signal differentiation, baseline correction and conversion to a GC × GC chromatogram representation. A 115-component test mixture with a wide range of boiling points (36-372°C) of nine compound classes is demonstrated using modulation periods of P M = 50, 100, 250, and 500ms, respectively. For the test mixture with a P M of 250ms, peak shapes on 2 D are symmetric with apparent 2 W b ranging from 12 to 45ms producing a 2 n c of ~ 10. Based on the average peak width of 0.93s on the 1 D separation for a time window of 400s, the 1 D peak capacity is 1 n c ∼ 430. Thus, the ideal 2D peak capacity n c,2D is 4300 or a peak capacity production of 650 peaks/min using the P M of 250ms. Additionally, for a P M of 50, 100 and 500ms, the 2 n c are 4, 7, and 12, respectively. Retention times on 2 D, 2 t R , are reproducible having standard deviations less than 1ms. Finally, the processed data is shown to be quantitative, with an average RSD of 4.7% for test analytes. Copyright © 2017 Elsevier B.V. All rights reserved.

High peak current acceleration of narrow divergence ions beams with the BELLA-PW laser

NASA Astrophysics Data System (ADS)

Steinke, Sven; Ji, Qing; Treffert, Franziska; Bulanov, Stepan; Bin, Jianhui; Nakamura, Kei; Gonsalves, Anthony; Toth, Csaba; Park, Jaehong; Roth, Markus; Esarey, Eric; Schenkel, Thomas; Leemans, Wim

2017-10-01

We present a parameter study of ion acceleration driven by the BELLA-PW laser. The laser repetition rate of 1Hz allowed for scanning the laser pulse duration, relative focus location and target thickness for the first time at laser peak powers of above 1 petawatt. Further, the long focal length geometry of the experiment (f\\65) and hence, large focus size provided ion beams of reduced divergence and unprecedented charge density. This work was supported by Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and Laboratory Directed Research and Development (LDRD) funding from Lawrence Berkeley National Laboratory.

ON THE PUZZLING HIGH-ENERGY PULSATIONS OF THE ENERGETIC RADIO-QUIET γ-RAY PULSAR J1813–1246

DOE PAGES

Marelli, M.; Harding, A.; Pizzocaro, D.; ...

2014-10-28

In this study, we have analyzed the new deep XMM-Newton and Chandra observations of the energetic, radio-quiet pulsar J1813–1246. The X-ray spectrum is nonthermal, very hard, and absorbed. Based on spectral considerations, we propose that J1813 is located at a distance further than 2.5 kpc. J1813 is highly pulsed in the X-ray domain, with a light curve characterized by two sharp, asymmetrical peaks, separated by 0.5 in phase. We detected no significant X-ray spectral changes during the pulsar phase. We extended the available Fermi ephemeris to five years. We found two glitches. The γ-ray light curve is characterized by twomore » peaks, separated by 0.5 in phase, with a bridge in between and no off-pulse emission. The spectrum shows clear evolution in phase, being softer at the peaks and hardening toward the bridge. Surprisingly, both X-ray peaks lag behind the γ-ray ones by a quarter of phase. We found a hint of detection in the 30-500 keV band with INTEGRAL, which is consistent with the extrapolation of both the soft X-ray and γ-ray emission of J1813. The unique X-ray and γ-ray phasing suggests a singular emission geometry. We discuss some possibilities within the current pulsar emission models. Finally, we develop an alternative geometrical model where the X-ray emission comes from polar cap pair cascades.« less

On the Puzzling High-Energy Pulsations of the Energetic Radio-Quiet -Ray Pulsar J1813-1246

NASA Technical Reports Server (NTRS)

Marelli, M.; Harding, Alice K.; Pizzocaro, D.; De Luca, A.; Wood, K. S.; Caraveo, P.; Salvetti, D.; Parkinson, P. M.; Acero, F.

2014-01-01

We have analyzed the new deep XMM-Newton and Chandra observations of the energetic, radio-quiet pulsar J1813-1246. The X-ray spectrum is nonthermal, very hard, and absorbed. Based on spectral considerations, we propose that J1813 is located at a distance further than 2.5 kpc. J1813 is highly pulsed in the X-ray domain, with a light curve characterized by two sharp, asymmetrical peaks, separated by 0.5 in phase. We detected no significant X-ray spectral changes during the pulsar phase.We extended the available Fermi ephemeris to five years.We found two glitches. The gamma-ray light curve is characterized by two peaks, separated by 0.5 in phase, with a bridge in between and no off-pulse emission. The spectrum shows clear evolution in phase, being softer at the peaks and hardening toward the bridge. Surprisingly, both X-ray peaks lag behind the gamma-ray ones by a quarter of phase. We found a hint of detection in the 30-500 keV band with INTEGRAL, which is consistent with the extrapolation of both the soft X-ray and gamma-ray emission of J1813. The unique X-ray and gamma-ray phasing suggests a singular emission geometry. We discuss some possibilities within the current pulsar emission models. Finally, we develop an alternative geometrical model where the X-ray emission comes from polar cap pair cascades.

Realization and optimization of a 1 ns pulsewidth multi-stage 250 kW peak power monolithic Yb doped fiber amplifier at 1064 nm

NASA Astrophysics Data System (ADS)

Morasse, Bertrand; Plourde, Estéban

2017-02-01

We present a simple way to achieve and optimize hundreds of kW peak power pulsed output using a monolithic amplifier chain based on solid core double cladding fiber tightly packaged. A fiber pigtailed current driven diode is used to produce nanosecond pulses at 1064 nm. We present how to optimize the use of Fabry-Perot versus DFB type diode along with the proper wavelength locking using a fiber Bragg grating. The optimization of the two pre-amplifiers with respect to the pump wavelength and Yb inversions is presented. We explain how to manage ASE using core and cladding pumping and by using single pass and double pass amplifier. ASE rejection within the Yb fiber itself and with the use of bandpass filter is discussed. Maximizing the amplifier conversion efficiency with regards to the fiber parameters, glass matrix and signal wavelength is described in details. We present how to achieve high peak power at the power amplifier stage using large core/cladding diameter ratio highly doped Yb fibers pumped at 975 nm. The effect of pump bleaching on the effective Yb fiber length is analyzed carefully. We demonstrate that counter-pumping brings little advantage in very short length amplifier. Dealing with the self-pulsation limit of stimulated Brillouin scattering is presented with the adjustment of the seed pulsewidth and linewidth. Future prospects for doubling the output peak power are discussed.

INPIStron switched pulsed power for dense plasma pinches

NASA Technical Reports Server (NTRS)

Han, Kwang S.; Lee, Ja H.

1993-01-01

The inverse plasma switch INPIStron was employed for 10kJ/40kV capacitor bank discharge system to produce focused dense plasmas in hypocycloidal-pinch (HCP) devices. A single unit and an array of multiple HCP's were coupled as the load of the pulsed power circuit. The geometry and switching plasma dynamics were found advantageous and convenient for commutating the large current pulse from the low impedance transmission line to the low impedance plasma load. The pulse power system with a single unit HCP, the system A, was used for production of high temperature plasma focus and its diagnostics. The radially running down plasma dynamics, revealed in image converter photographs, could be simulated by a simple snow-plow model with a correction for plasma resistivity. The system B with an array of 8-HCP units which forms a long coaxial discharge chamber was used for pumping a Ti-sapphire laser. The intense UV emission from the plasma was frequency shifted with dye-solution jacket to match the absorption band of the Ti crystal laser near 500 nm. An untuned laser pulse energy of 0.6 J/pulse was obtained for 6.4 kJ/40 kV discharge, or near 103 times of the explosion limit of conventional flash lamps. For both systems the advantages of the INPIStron were well demonstrated: a single unit is sufficient for a large current (greater than 50 kA) without increasing the system impedance, highly reliable and long life operation and implied scalability for the high power ranges above I(sub peak) = 1 MA and V(sub hold) = 100 kV.

Q-switched slab RF discharge CO laser

NASA Astrophysics Data System (ADS)

Ionin, A. A.; Kochetkov, Yu V.; Kozlov, A. Yu; Mokrousova, D. V.; Seleznev, L. V.; Sinitsyn, D. V.; Sunchugasheva, E. S.; Zemtsov, D. S.

2017-05-01

A compact repetitively pulsed cryogenically cooled slab RF discharge CO laser with double path V-type laser resonator equipped with external Q-switching system based on rotating mirror was developed and studied. The laser produced mid-IR (λ ~ 5-7 µm) radiation pulses of ~1 ÷ 2 µs duration (FWHM), peak power up to ~3 kW, and pulse repetition rate up to 130 Hz. Averaged output laser power reached 0.5 W, the laser spectrum consisted of ~80 laser lines with individual peak power up to 80 W.

2.79 μm high peak power LGS electro-optically Q-switched Cr,Er:YSGG laser.

PubMed

Wang, Li; Wang, Jintao; Yang, Jingwei; Wu, Xianyou; Sun, Dunlu; Yin, Shaotang; Jiang, Haihe; Wang, Jiyang; Xu, Changqing

2013-06-15

A flash lamp pumped Cr,Er:YSGG laser utilizing a langasite (LGS) crystal as an electro-optic Q-switch is proposed and demonstrated. It is proved that a LGS crystal with relatively high damage threshold can be used as the electro-optic Q-switch at 2.79 μm, and 216 mJ pulse energy with 14.36 ns pulse width is achieved. Its corresponding peak power of pulse can reach 15 MW, to our knowledge the best result at a 2.79 μm wavelength.

Time of flight emission spectroscopy of laser produced nickel plasma: Short-pulse and ultrafast excitations

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

Smijesh, N.; Chandrasekharan, K.; Joshi, Jagdish C.

2014-07-07

We report the experimental investigation and comparison of the temporal features of short-pulse (7 ns) and ultrafast (100 fs) laser produced plasmas generated from a solid nickel target, expanding into a nitrogen background. When the ambient pressure is varied in a large range of 10⁻⁶Torr to 10²Torr, the plume intensity is found to increase rapidly as the pressure crosses 1 Torr. Time of flight (TOF) spectroscopy of emission from neutral nickel (Ni I) at 361.9 nm (3d⁹(²D) 4p → 3d⁹(²D) 4s transition) reveals two peaks (fast and slow species) in short-pulse excitation and a single peak in ultrafast excitation. Themore » fast and slow peaks represent recombined neutrals and un-ionized neutrals, respectively. TOF emission from singly ionized nickel (Ni II) studied using the 428.5 nm (3p⁶3d⁸(³P) 4s→ 3p⁶3d⁹ 4s) transition shows only a single peak for either excitation. Velocities of the neutral and ionic species are determined from TOF measurements carried out at different positions (i.e., at distances of 2 mm and 4 mm, respectively, from the target surface) on the plume axis. Measured velocities indicate acceleration of neutrals and ions, which is caused by the Coulomb pull of the electrons enveloping the plume front in the case of ultrafast excitation. Both Coulomb pull and laser-plasma interaction contribute to the acceleration in the case of short-pulse excitation. These investigations provide new information on the pressure dependent temporal behavior of nickel plasmas produced by short-pulse and ultrafast laser pulses, which have potential uses in applications such as pulsed laser deposition and laser-induced nanoparticle generation.« less

Peak power ratio generator

DOEpatents

Moyer, Robert D.

1985-01-01

A peak power ratio generator is described for measuring, in combination with a conventional power meter, the peak power level of extremely narrow pulses in the gigahertz radio frequency bands. The present invention in a preferred embodiment utilizes a tunnel diode and a back diode combination in a detector circuit as the only high speed elements. The high speed tunnel diode provides a bistable signal and serves as a memory device of the input pulses for the remaining, slower components. A hybrid digital and analog loop maintains the peak power level of a reference channel at a known amount. Thus, by measuring the average power levels of the reference signal and the source signal, the peak power level of the source signal can be determined.

Peak power ratio generator

DOEpatents

Moyer, R.D.

A peak power ratio generator is described for measuring, in combination with a conventional power meter, the peak power level of extremely narrow pulses in the gigahertz radio frequency bands. The present invention in a preferred embodiment utilizes a tunnel diode and a back diode combination in a detector circuit as the only high speed elements. The high speed tunnel diode provides a bistable signal and serves as a memory device of the input pulses for the remaining, slower components. A hybrid digital and analog loop maintains the peak power level of a reference channel at a known amount. Thus, by measuring the average power levels of the reference signal and the source signal, the peak power level of the source signal can be determined.

A multi-functional high voltage experiment apparatus for vacuum surface flashover switch research.

PubMed

Zeng, Bo; Su, Jian-cang; Cheng, Jie; Wu, Xiao-long; Li, Rui; Zhao, Liang; Fang, Jin-peng; Wang, Li-min

2015-04-01

A multifunctional high voltage apparatus for experimental researches on surface flashover switch and high voltage insulation in vacuum has been developed. The apparatus is composed of five parts: pulse generating unit, axial field unit, radial field unit, and two switch units. Microsecond damped ringing pulse with peak-to-peak voltage 800 kV or unipolar pulse with maximum voltage 830 kV is generated, forming transient axial or radial electrical field. Different pulse waveforms and field distributions make up six experimental configurations in all. Based on this apparatus, preliminary experiments on vacuum surface flashover switch with different flashover dielectric materials have been conducted in the axial field unit, and nanosecond pulse is generated in the radial field unit which makes a pulse transmission line in the experiment. Basic work parameters of this kind of switch such as lifetime, breakdown voltage are obtained.

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 all-fiber cladding-pumped Yb-doped gain-switched laser.

PubMed

Larsen, C; Hansen, K P; Mattsson, K E; Bang, O

2014-01-27

Gain-switching is an alternative pulsing technique of fiber lasers, which is power scalable and has a low complexity. From a linear stability analysis of rate equations the relaxation oscillation period is derived and from it, the pulse duration is defined. Good agreement between the measured pulse duration and the theoretical prediction is found over a wide range of parameters. In particular we investigate the influence of an often present length of passive fiber in the cavity and show that it introduces a finite minimum in the achievable pulse duration. This minimum pulse duration is shown to occur at longer active fibers length with increased passive length of fiber in the cavity. The peak power is observed to depend linearly on the absorbed pump power and be independent of the passive fiber length. Given these conclusions, the pulse energy, duration, and peak power can be estimated with good precision.

1.8  mJ, 3.5  kW single-frequency optical pulses at 1572  nm generated from an all-fiber MOPA system.

PubMed

Lee, Wangkuen; Geng, Jihong; Jiang, Shibin; Yu, Anthony W

2018-05-15

High-energy single-frequency optical pulses at 1572 nm were generated from an all-fiber MOPA system for atmospheric CO 2 LIDAR system application. We report the experimental demonstration of 1.8 mJ, a peak power of 3.5 kW at the pulse repetition of 2.5 kHz, as well as 1.3 mJ, a peak power of 2.5 kW at the pulse repetition of 7.5 kHz single-frequency optical pulses at 1572 nm using single-mode large-core polarization-maintaining Er-Yb co-doped silicate glass fiber amplifiers pumped at 976 nm. To the best of our knowledge, this is the highest pulse energy of single frequency at 1572 nm from an all-fiber amplifier system.

Water impact shock test system

NASA Technical Reports Server (NTRS)

1977-01-01

The basic objective was to design, manufacture, and install a shock test system which, in part, would have the ability to subject test articles weighing up to 1,000 pounds to both half sine and/or full sine pulses having peak levels of up to 50 G's with half sine pulse durations of 100 milliseconds or full sine period duration of 200 milliseconds. The tolerances associated with the aforementioned pulses were +20% and -10% for the peak levels and plus or minus 10% for the pulse durations. The subject shock test system was to be capable of accepting test article sizes of up to 4 feet by 4 feet mounting surface by 4 feet in length.

2.5 TW, two-cycle IR laser pulses via frequency domain optical parametric amplification.

PubMed

Gruson, V; Ernotte, G; Lassonde, P; Laramée, A; Bionta, M R; Chaker, M; Di Mauro, L; Corkum, P B; Ibrahim, H; Schmidt, B E; Legaré, F

2017-10-30

Broadband optical parametric amplification in the IR region has reached a new milestone through the use of a non-collinear Frequency domain Optical Parametric Amplification system. We report a laser source delivering 11.6 fs pulses with 30 mJ of energy at a central wavelength of 1.8 μm at 10 Hz repetition rate corresponding to a peak power of 2.5 TW. The peak power scaling is accompanied by a pulse shortening of about 20% upon amplification due to the spectral reshaping with higher gain in the spectral wings. This source paves the way for high flux soft X-ray pulses and IR-driven laser wakefield acceleration.

Diffraction-limited, 300-kW peak-power pulses from a coiled multimode fiber amplifier

NASA Astrophysics Data System (ADS)

di Teodoro, Fabio; Koplow, Jeffrey P.; Moore, Sean W.; Kliner, Dahv A. V.

2002-04-01

We report a multimode, double-clad, Yb-doped fiber amplifier that produces diffraction-limited, 0.8-ns pulses with energies of 255 μJ and peak powers in excess of 300 kW at a repetition rate of ~8 kHz. Single-transverse-mode operation was obtained by bend-loss-induced mode filtering of the gain fiber.

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.

Observation of emission process in hydrogen-like nitrogen Z-pinch discharge with time integrated soft X-ray spectrum pinhole image

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

Sakai, Y.; Kumai, H.; Nakanishi, Y.

2013-02-15

The emission spectra of hydrogen-like nitrogen Balmer at the wavelength of 13.4 nm in capillary Z-pinch discharge plasma are experimentally examined. Ionization to fully strip nitrogen at the pinch maximum, and subsequent rapid expansion cooling are required to establish the population inversion between the principal quantum number of n = 2 and n = 3. The ionization and recombination processes with estimated plasma parameters are evaluated by utilizing a time integrated spectrum pinhole image containing radial spatial information. A cylindrical capillary plasma is pinched by a triangular pulsed current with peak amplitude of 50 kA and pulse width of 50more » ns.« less

Neon-hydrogen penning plasma laser in a helical hallow-cathode discharge

NASA Astrophysics Data System (ADS)

Pramatarov, P. M.; Stefanova, M. S.; Ganciu, M.; Karelin, A. V.; Yancharina, A. M.; Ivanova, J. P.; Yakovlenko, S. I.

1991-07-01

A Penning plasma laser (PPL) operating at the NeI 585.3 nm and NeI 1.15 μm lines in Ne-H2 mixture has been realized. Helical configuration of the electrodes was used. The dependence of the laser-pulse shape and output power on current pulse duration and amplitude values were investigated. Peak output powers of 1.5 W for the yellow line and 1.2 W for the IR line have been measured. The population inversion mechanism for the 585.3 nm line is discussed in the frames of a model for PPL. The main factor maintaining the population inversion on both lines is depopulation of the Ne(1 s 2) level by Penning reactions with H2.

Neon-hydrogen Penning plasma laser in a helical hallow-cathode discharge

NASA Astrophysics Data System (ADS)

Pramatarov, P. M.; Stefanova, M. S.; Ivanova, J. P.; Ganciu, M.; Karelin, A. V.; Iakovlenko, S. I.; Iancharina, A. M.

1991-07-01

A Penning plasma laser (PPL) operating at the NeI 585.3 nm and NeI 1.15-micron lines in Ne-H2 mixture has been realized. Helical configuration of the electrodes was used. The dependence of the laser-pulse shape and output power on current pulse duration and amplitude values were investigated. Peak output powers of 1.5 W for the yellow line and 1.2 W for the IR line have been measured. The population inversion mechanism for the 585.3 nm line is discussed in the frames of a model for PPL. The main factor maintaining the population inversion on both lines is depopulation of the Ne(1S2) level by Penning reactions with H2.

Field-Distortion Air-Insulated Switches for Next-Generation Pulsed-Power Accelerators

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

Wisher, Matthew Louis; Johns, Owen M.; Breden, Eric Wayne

We have developed two advanced designs of a field-distortion air-insulated spark-gap switch that reduce the size of a linear-transformer-driver (LTD) brick. Both designs operate at 200 kV and a peak current of ~50 kA. At these parameters, both achieve a jitter of less than 2 ns and a prefire rate of ~0.1% over 5000 shots. We have reduced the number of switch parts and assembly steps, which has resulted in a more uniform, design-driven assembly process. We will characterize the performance of tungsten-copper and graphite electrodes, and two different electrode geometries. The new switch designs will substantially improve the electricalmore » and operational performance of next-generation pulsed-power accelerators.« less

Dynamics of Intense Pulsed Proton Beam in the Nagaoka ETIGO-I

NASA Astrophysics Data System (ADS)

Tanaka, Hajime; Konno, Kohji; Masugata, Katsumi; Yatsui, Kiyoshi; Matsui, Masao

1982-10-01

Dynamics of an intense pulsed proton beam have been studied by measuring nuclear reactions as well as by a biased ion-collector (BIC). When the ion-current density (Ji) is small such that Ji<30 A/cm2, the proton number measured by BIC is in good agreement with that by nuclear activation. Good linearity exists between time integrated γ-ray signal and proton number measured by the activation. Hence, it would be possible to obtain the proton number quantitatively even when a target “blow-off” takes place at Ji>1 kA/cm2. Prompt γ-ray is also measured by the time-of-flight method to yield reasonable agreement with the applied peak potential.

Optimisation of wire-cut EDM process parameter by Grey-based response surface methodology

NASA Astrophysics Data System (ADS)

Kumar, Amit; Soota, Tarun; Kumar, Jitendra

2018-03-01

Wire electric discharge machining (WEDM) is one of the advanced machining processes. Response surface methodology coupled with Grey relation analysis method has been proposed and used to optimise the machining parameters of WEDM. A face centred cubic design is used for conducting experiments on high speed steel (HSS) M2 grade workpiece material. The regression model of significant factors such as pulse-on time, pulse-off time, peak current, and wire feed is considered for optimising the responses variables material removal rate (MRR), surface roughness and Kerf width. The optimal condition of the machining parameter was obtained using the Grey relation grade. ANOVA is applied to determine significance of the input parameters for optimising the Grey relation grade.

Hitomi X-ray studies of giant radio pulses from the Crab pulsar

NASA Astrophysics Data System (ADS)

Hitomi Collaboration; Aharonian, Felix; Akamatsu, Hiroki; Akimoto, Fumie; Allen, Steven W.; Angelini, Lorella; Audard, Marc; Awaki, Hisamitsu; Axelsson, Magnus; Bamba, Aya; Bautz, Marshall W.; Blandford, Roger; Brenneman, Laura W.; Brown, Gregory V.; Bulbul, Esra; Cackett, Edward M.; Chernyakova, Maria; Chiao, Meng P.; Coppi, Paolo S.; Costantini, Elisa; de Plaa, Jelle; de Vries, Cor P.; den Herder, Jan-Willem; Done, Chris; Dotani, Tadayasu; Ebisawa, Ken; Eckart, Megan E.; Enoto, Teruaki; Ezoe, Yuichiro; Fabian, Andrew C.; Ferrigno, Carlo; Foster, Adam R.; Fujimoto, Ryuichi; Fukazawa, Yasushi; Furuzawa, Akihiro; Galeazzi, Massimiliano; Gallo, Luigi C.; Gandhi, Poshak; Giustini, Margherita; Goldwurm, Andrea; Gu, Liyi; Guainazzi, Matteo; Haba, Yoshito; Hagino, Kouichi; Hamaguchi, Kenji; Harrus, Ilana M.; Hatsukade, Isamu; Hayashi, Katsuhiro; Hayashi, Takayuki; Hayashida, Kiyoshi; Hiraga, Junko S.; Hornschemeier, Ann; Hoshino, Akio; Hughes, John P.; Ichinohe, Yuto; Iizuka, Ryo; Inoue, Hajime; Inoue, Yoshiyuki; Ishida, Manabu; Ishikawa, Kumi; Ishisaki, Yoshitaka; Iwai, Masachika; Kaastra, Jelle; Kallman, Tim; Kamae, Tsuneyoshi; Kataoka, Jun; Katsuda, Satoru; Kawai, Nobuyuki; Kelley, Richard L.; Kilbourne, Caroline A.; Kitaguchi, Takao; Kitamoto, Shunji; Kitayama, Tetsu; Kohmura, Takayoshi; Kokubun, Motohide; Koyama, Katsuji; Koyama, Shu; Kretschmar, Peter; Krimm, Hans A.; Kubota, Aya; Kunieda, Hideyo; Laurent, Philippe; Lee, Shiu-Hang; Leutenegger, Maurice A.; Limousin, Olivier O.; Loewenstein, Michael; Long, Knox S.; Lumb, David; Madejski, Greg; Maeda, Yoshitomo; Maier, Daniel; Makishima, Kazuo; Markevitch, Maxim; Matsumoto, Hironori; Matsushita, Kyoko; McCammon, Dan; McNamara, Brian R.; Mehdipour, Missagh; Miller, Eric D.; Miller, Jon M.; Mineshige, Shin; Mitsuda, Kazuhisa; Mitsuishi, Ikuyuki; Miyazawa, Takuya; Mizuno, Tsunefumi; Mori, Hideyuki; Mori, Koji; Mukai, Koji; Murakami, Hiroshi; Mushotzky, Richard F.; Nakagawa, Takao; Nakajima, Hiroshi; Nakamori, Takeshi; Nakashima, Shinya; Nakazawa, Kazuhiro; Nobukawa, Kumiko K.; Nobukawa, Masayoshi; Noda, Hirofumi; Odaka, Hirokazu; Ohashi, Takaya; Ohno, Masanori; Okajima, Takashi; Oshimizu, Kenya; Ota, Naomi; Ozaki, Masanobu; Paerels, Frits; Paltani, Stéphane; Petre, Robert; Pinto, Ciro; Porter, Frederick S.; Pottschmidt, Katja; Reynolds, Christopher S.; Safi-Harb, Samar; Saito, Shinya; Sakai, Kazuhiro; Sasaki, Toru; Sato, Goro; Sato, Kosuke; Sato, Rie; Sawada, Makoto; Schartel, Norbert; Serlemtsos, Peter J.; Seta, Hiromi; Shidatsu, Megumi; Simionescu, Aurora; Smith, Randall K.; Soong, Yang; Stawarz, Łukasz; Sugawara, Yasuharu; Sugita, Satoshi; Szymkowiak, Andrew; Tajima, Hiroyasu; Takahashi, Hiromitsu; Takahashi, Tadayuki; Takeda, Shiníchiro; Takei, Yoh; Tamagawa, Toru; Tamura, Takayuki; Tanaka, Takaaki; Tanaka, Yasuo; Tanaka, Yasuyuki T.; Tashiro, Makoto S.; Tawara, Yuzuru; Terada, Yukikatsu; Terashima, Yuichi; Tombesi, Francesco; Tomida, Hiroshi; Tsuboi, Yohko; Tsujimoto, Masahiro; Tsunemi, Hiroshi; Tsuru, Takeshi Go; Uchida, Hiroyuki; Uchiyama, Hideki; Uchiyama, Yasunobu; Ueda, Shutaro; Ueda, Yoshihiro; Uno, Shiníchiro; Urry, C. Megan; Ursino, Eugenio; Watanabe, Shin; Werner, Norbert; Wilkins, Dan R.; Williams, Brian J.; Yamada, Shinya; Yamaguchi, Hiroya; Yamaoka, Kazutaka; Yamasaki, Noriko Y.; Yamauchi, Makoto; Yamauchi, Shigeo; Yaqoob, Tahir; Yatsu, Yoichi; Yonetoku, Daisuke; Zhuravleva, Irina; Zoghbi, Abderahmen; Terasawa, Toshio; Sekido, Mamoru; Takefuji, Kazuhiro; Kawai, Eiji; Misawa, Hiroaki; Tsuchiya, Fuminori; Yamazaki, Ryo; Kobayashi, Eiji; Kisaka, Shota; Aoki, Takahiro

2018-03-01

To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2-300 keV band and the Kashima NICT radio telescope in the 1.4-1.7 GHz band with a net exposure of about 2 ks on 2016 March 25, just before the loss of the Hitomi mission. The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1000 and 100 GRPs were simultaneously observed at the main pulse and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main pulse or inter-pulse phase. All variations are within the 2 σ fluctuations of the X-ray fluxes at the pulse peaks, and the 3 σ upper limits of variations of main pulse or inter-pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2-300 keV band. The values for main pulse or inter-pulse GRPs become 25% or 110%, respectively, when the phase width is restricted to the 0.03 phase. Among the upper limits from the Hitomi satellite, those in the 4.5-10 keV and 70-300 keV bands are obtained for the first time, and those in other bands are consistent with previous reports. Numerically, the upper limits of the main pulse and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) × 10-11 erg cm-2, respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere. Although the number of photon-emitting particles should temporarily increase to account for the brightening of the radio emission, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a >0.02% brightening of the pulse-peak flux under such conditions.

Broadband VHF Interferometer Observations of an Energetic In-cloud Pulse (EIP)

NASA Astrophysics Data System (ADS)

Tilles, J.; Krehbiel, P. R.; Stanley, M. A.; Rison, W.; Lyu, F.; Cummer, S.; Liu, N.; Dwyer, J. R.; Brown, R. G.; Wilson, J. G.

2017-12-01

Energetic in-cloud pulses (EIPs) are a little-known in-cloud subprocess of lightning. While they may be best identified by their large peak current (>200 kA) [Lyu et al., Geophys. Res. Lett., 42, 2015], they differ from narrow bipolar events (NBEs) - another type of in-cloud, high peak-current process - in that the sferic of an EIP lasts an order of magnitude longer ( ˜100 us) than that of a typical NBE ( ˜10 us). To further differentiate them from NBEs, EIPs are generally embedded within other electrical activity, whereas NBEs are known to primarily occur in isolation or as a lightning-initiating event [Smith et al., J. Geophys. Res., 104, D4, 4189-4212, 1999; Rison et al., Nat. Commun., 7, 10721, 2016]. Moreover, EIPs may have an intrinsic connection with the production of terrestrial gamma ray flashes (TGFs) [Cummer et al., Geophys. Res. Lett., 41, 8586-8593, 2014].Here we present coincident broadband VHF interferometer (INTF) observations and electric and magnetic field waveforms of an EIP with an associated NLDN peak current of 247 kA. The EIP occurs nearly 4 ms into a normal-polarity intracloud flash as part of the upward extension of the negative-polarity lightning leader. For this reason, we suspect that EIPs are a more energetic version of initial breakdown pulses (IBPs), which accompany the development of negative stepped leaders [e.g. Marshall et al., J. Geophys. Res. Atmos., 119, 445-460, 2014]. In addition, we show similarities with NBE-producing fast breakdown [Rison et al., 2016; Tilles et al., AE12A-03, AGU Fall Meeting, 2016], in that the breakdown accompanying the EIP propagates over a similar vertical extent ( ˜0.5-1 km) and with similar propagation speed ( ˜3×107 m/s). The INTF was developed by New Mexico Tech and has been deployed at Kennedy Space Center since July 2016. It employed three 100-m baselines in 2016, has a bandwidth of 14-88 MHz and samples at 180 MS/s with 16-bit resolution. A synchronously digitized fast antenna (FA), with 100-μ s decay time constant, samples the electric field, and the whole INTF+FA system is automatically triggered on strong VHF radiation. Coincident VLF/ LF (1-300 kHz, sampled at 1 MS/s) observations are made with Duke University's magnetic sensor network.

Characteristics of exploding metal wires in water with three discharge types

NASA Astrophysics Data System (ADS)

Han, Ruoyu; Wu, Jiawei; Zhou, Haibin; Ding, Weidong; Qiu, Aici; Clayson, Thomas; Wang, Yanan; Ren, Hang

2017-07-01

This paper presents the characteristics of underwater electrical wire explosion (UEWE) with three discharge types, namely, Type-A, Type-B, and Type-C. Experiments were carried out with copper and tungsten wires (4 cm long and 50-300 μm in diameter) driven by a microsecond time-scale pulsed current source with 500 J stored energy. A time-integrated spectrometer and a photodiode were used to measure the optical emission of UEWE. A Polyvinylidene Fluoride probe was adopted to record the pressure waveforms. Experimental results indicate that from Type-A to Type-C, more energy deposits prior to the voltage peak and the first peak power increases drastically. This variation of energy deposition influences the optical emission and shock wave generation process. Specifically, the light intensity decreases by more than 90% and the peak of continuous spectra moves from ˜400 nm to ˜700 nm. In addition, the peak pressure of the first shock wave increases from ˜2 MPa to more than 7.5 MPa.

> 6 MW peak power at 532 nm from passively Q-switched Nd:YAG/Cr4+:YAG microchip laser.

PubMed

Bhandari, Rakesh; Taira, Takunori

2011-09-26

Megawatt peak power, giant pulse microchip lasers are attractive for wavelength conversion, provided their output is linearly polarized. We use a [110] cut Cr(4+):YAG for passively Q-switched Nd:YAG microchip laser to obtain a stable, linearly polarized output. Further, we optimize the conditions for second harmonic generation at 532 nm wavelength to achieve > 6 MW peak power, 1.7 mJ, 265 ps, 100 Hz pulses with a conversion efficiency of 85%. © 2011 Optical Society of America

Gamma-ray spectroscopy and pulse shape discrimination with a plastic scintillator

NASA Astrophysics Data System (ADS)

van Loef, E.; Markosyan, G.; Shirwadkar, U.; McClish, M.; Shah, K.

2015-07-01

The scintillation properties of a novel plastic scintillator loaded with an organolead compound are presented. Under X-ray and gamma-ray excitation, emission is observed peaking at 435 nm. The scintillation light output is 9000 ph/MeV. An energy resolution (full width at half maximum over the peak position) of about 16% was observed for the 662 keV full absorption peak. Excellent pulse shape discrimination between neutrons and gamma-rays with a Figure of Merit of 2.6 at 1 MeVee was observed.

Method and apparatus for signal processing in a sensor system for use in spectroscopy

DOEpatents

O'Connor, Paul [Bellport, NY; DeGeronimo, Gianluigi [Nesconset, NY; Grosholz, Joseph [Natrona Heights, PA

2008-05-27

A method for processing pulses arriving randomly in time on at least one channel using multiple peak detectors includes asynchronously selecting a non-busy peak detector (PD) in response to a pulse-generated trigger signal, connecting the channel to the selected PD in response to the trigger signal, and detecting a pulse peak amplitude. Amplitude and time of arrival data are output in first-in first-out (FIFO) sequence. An apparatus includes trigger comparators to generate the trigger signal for the pulse-receiving channel, PDs, a switch for connecting the channel to the selected PD, and logic circuitry which maintains the write pointer. Also included, time-to-amplitude converters (TACs) convert time of arrival to analog voltage and an analog multiplexer provides FIFO output. A multi-element sensor system for spectroscopy includes detector elements, channels, trigger comparators, PDs, a switch, and a logic circuit with asynchronous write pointer. The system includes TACs, a multiplexer and analog-to-digital converter.

A 800 kV compact peaking capacitor for nanosecond generator.

PubMed

Jia, Wei; Chen, Zhiqiang; Tang, Junping; Chen, Weiqing; Guo, Fan; Sun, Fengrong; Li, Junna; Qiu, Aici

2014-09-01

An extremely compact high voltage peaking capacitor is developed. The capacitor has a pancake structure with a diameter of 315 mm, a thickness of 59 mm, and a mass of 6.1 kg. The novel structural design endows the capacitor with a better mechanical stability and reliability under hundreds of kilovolts pulse voltage and an inner gas pressure of more than 1.5 MPa. The theoretical value of the capacitor self-inductance is near to 17 nH. Proved by series of electrical experiments, the capacitor can endure a high-voltage pulse with a rise time of about 20 ns, a half-width duration of around 25 ns, and an amplitude of up to 800 kV in a single shot model. When the capacitor was used in an electromagnetic pulse simulator as a peaking capacitor, the rise time of the voltage pulse can be reduced from 20 ns to less than 3 ns. The practical value of the capacitor's inductance deduced from the experimental date is no more than 25 nH.

Narrow linewidth picosecond UV pulsed laser with mega-watt peak power.

PubMed

Huang, Chunning; Deibele, Craig; Liu, Yun

2013-04-08

We demonstrate a master oscillator power amplifier (MOPA) burst mode laser system that generates 66 ps/402.5 MHz pulses with mega-watt peak power at 355 nm. The seed laser consists of a single frequency fiber laser (linewidth < 5 KHz), a high bandwidth electro-optic modulator (EOM), a picosecond pulse generator, and a fiber based preamplifier. A very high extinction ratio (45 dB) has been achieved by using an adaptive bias control of the EOM. The multi-stage Nd:YAG amplifier system allows a uniformly temporal shaping of the macropulse with a tunable pulse duration. The light output from the amplifier is converted to 355 nm, and over 1 MW peak power is obtained when the laser is operating in a 5-μs/10-Hz macropulse mode. The laser output has a transform-limited spectrum with a very narrow linewidth of individual longitudinal modes. The immediate application of the laser system is the laser-assisted hydrogen ion beam stripping for the Spallation Neutron Source (SNS).

Improved semi-conductor laser device, operating, at room temperature, with an array of three lasers in the spatially coherent, free running mode

NASA Technical Reports Server (NTRS)

Rutz, E. M.

1975-01-01

The peak pulse power was increased by operating an array of three homostructure Ga As lasers in the laser device. A spatial filter in the laser device selects the spatially coherent, free running, mode. The optical peak power is 5 watts, which is three times the peak power of a single laser in the array. The far-field distribution of the three laser array is a single Gaussian beam of spatial coherence without sidelobes or grating lobes. The length of the optical pulses of spatial coherence was increased to 200 ns by improved heat transfer from the p-n junctions of the lasers to the metal housing of the pulse transformer, and by doubling the core area and increasing the turns of the primary windings of the pulse transformer. The mechanical stability of the laser device was improved and the transition from mechanical alignment to electro-mechanical alignment control, was facilitated.

Use-dependent inhibition of Na+ currents by benzocaine homologs.

PubMed Central

Quan, C; Mok, W M; Wang, G K

1996-01-01

Most local anesthetics (LAs) elicit use-dependent inhibition of Na+ currents when excitable membranes are stimulated repetitively. One exception to this rule is benzocaine, a neutral LA that fails to produce appreciable use-dependent inhibition. In this study, we have examined the use-dependent phenomenon of three benzocaine homologs: ethyl 4-diethylaminobenzoate, ethyl 4-ethoxybenzoate, and ethyl 4-hydroxybenzoate. Ethyl 4-hydroxybenzoate at 1 mM, like benzocaine, elicited little use-dependent inhibition of Na+ currents, whereas ethyl 4-diethylaminobenzoate at 0.15 mM and ethyl 4-ethoxybenzoate at 0.5 mM elicited substantial use-dependent inhibition--up to 55% of peak Na+ currents were inhibited by repetitive depolarizations at 5 Hz. Each of these compounds produced significant tonic block of Na+ currents at rest and shifted the steady-state inactivation curve (h infinity) toward the hyperpolarizing direction. Kinetic analyses showed that the decaying phase of Na+ currents during a depolarizing pulse was significantly accelerated by all drugs, thus suggesting that these drugs also block the activated channel. The recovery time course for the use-dependent inhibition of Na+ currents was relatively slow, with time constants of 6.8 and 4.4 s for ethyl 4-diethylaminobenzoate and ethyl 4-ethoxybenzoate, respectively. We conclude that benzocaine and 4-hydroxybenzoate interact with the open and inactivated channels during repetitive pulses, but during the interpulse the complex dissociates too fast to accumulate sufficient use-dependent block of Na+ currents. In contrast, ethyl 4-diethylaminobenzoate and ethyl 4-ethoxybenzoate dissociate slowly from their binding site and consequently elicit significant use-dependent block. A common LA binding site suffices to explain the presence and absence of use-dependent block by benzocaine homologs during repetitive pulses. PMID:8770198

Effects of pressure characteristics on transfection efficiency in laser-induced stress wave-mediated gene delivery

NASA Astrophysics Data System (ADS)

Ando, Takahiro; Sato, Shunichi; Ashida, Hiroshi; Obara, Minoru

2013-07-01

Laser-induced stress waves (LISWs) generated by irradiating a light-absorbing medium with a pulsed laser can transiently increase the permeability of cell membranes for gene delivery. In this study, we investigated the effects of pressure characteristics of LISWs upon gene transfection efficiency using lasers with different pulse durations: a 6-ns pulsed Nd:YAG laser and 20-ns and 200-µs pulsed ruby lasers. LISWs were generated by irradiating a black rubber disk, on which a transparent plastic sheet was adhered for confinement of the laser-produced plasma. Rat dorsal skin was injected with plasmid DNA coding for luciferase, to which LISWs were applied. With nanosecond laser pulses, transfection efficiency increased linearly with increasing positive peak pressure in the range of 35 to 145 MPa, the corresponding impulse ranging from 10 to 40 Paṡs. With 200-µs laser pulses, on the other hand, efficient gene expression was observed by the application of LISWs even with a 10-fold-lower peak pressure (˜5 MPa), the corresponding impulse being as large as 430 Paṡs. These results indicate that even at low peak pressures, efficient transfection can be achieved by extending the pressure duration and hence by increasing the impulse of LISWs, while the averaged expression efficiencies were relatively low.

Local SAR in parallel transmission pulse design.

PubMed

Lee, Joonsung; Gebhardt, Matthias; Wald, Lawrence L; Adalsteinsson, Elfar

2012-06-01

The management of local and global power deposition in human subjects (specific absorption rate, SAR) is a fundamental constraint to the application of parallel transmission (pTx) systems. Even though the pTx and single channel have to meet the same SAR requirements, the complex behavior of the spatial distribution of local SAR for transmission arrays poses problems that are not encountered in conventional single-channel systems and places additional requirements on pTx radio frequency pulse design. We propose a pTx pulse design method which builds on recent work to capture the spatial distribution of local SAR in numerical tissue models in a compressed parameterization in order to incorporate local SAR constraints within computation times that accommodate pTx pulse design during an in vivo magnetic resonance imaging scan. Additionally, the algorithm yields a protocol-specific ultimate peak in local SAR, which is shown to bound the achievable peak local SAR for a given excitation profile fidelity. The performance of the approach was demonstrated using a numerical human head model and a 7 Tesla eight-channel transmit array. The method reduced peak local 10 g SAR by 14-66% for slice-selective pTx excitations and 2D selective pTx excitations compared to a pTx pulse design constrained only by global SAR. The primary tradeoff incurred for reducing peak local SAR was an increase in global SAR, up to 34% for the evaluated examples, which is favorable in cases where local SAR constraints dominate the pulse applications. Copyright © 2011 Wiley Periodicals, Inc.

Pump-probe studies of radiation induced defects and formation of warm dense matter with pulsed ion beams

NASA Astrophysics Data System (ADS)

Schenkel, T.; Persaud, A.; Gua, H.; Seidl, P. A.; Waldron, W. L.; Gilson, E. P.; Kaganovich, I. D.; Davidson, R. C.; Friedman, A.; Barnard, J. J.; Minior, A. M.

2014-10-01

We report results from the 2nd generation Neutralized Drift Compression Experiment at Berkeley Lab. NDCX-II is a pulsed, linear induction accelerator designed to drive thin foils to warm dense matter (WDM) states with peak temperatures of ~ 1 eV using intense, short pulses of 1.2 MeV lithium ions. Tunability of the ion beam enables pump-probe studies of radiation effects in solids as a function of excitation density, from isolated collision cascades to the onset of phase-transitions and WDM. Ion channeling is an in situ diagnostic of damage evolution during ion pulses with a sensitivity of <0.1% displacements per atom. We will report results from damage evolution studies in thin silicon crystals with Li + and K + beams. Detection of channeled ions tracks lattice disorder evolution with a resolution of ~ 1 ns using fast current measurements. We will discuss pump-probe experiments with pulsed ion beams and the development of diagnostics for WDM and multi-scale (ms to fs) access to the materials physics of collision cascades e.g. in fusion reactor materials. Work performed under auspices of the US DOE under Contract No. DE-AC02-05CH11231.

Design of a quasi-CW laser diode driver for space-based laser transmitter

NASA Astrophysics Data System (ADS)

Singh, Ravindra; Dangwal, Nishma; Chandraprakash, .; Agrawal, Lalita; Pal, Suranjan; Kamlakar, J. A.

2006-12-01

LASTEC Delhi in a joint collaborative activity with LEOS, Bangalore is developing a space qualified diode array pumped Nd:YAG laser transmitter delivering 30 mJ @ 10 pps of 10 ns duration. For space applications laser diodes are preferred because of their excellent reliability with lifetimes exceeding 100,000 hours. However, they are extremely sensitive to electro-static discharge, excessive current levels, and current spikes and transients. Small variations in bias voltage may produce large fluctuations in the current causing instability and damage to the device. Hence instead of the traditional power supplies a current controlled laser diode driver is required. This paper presents the design of a Q-CW laser diode driver based on closed loop current regulator, capable of driving 24 QCW laser diode bars each with 75W peak power at 70 A. The driver can generate up to 100 Amp peak current and 200μsec pulse width operating at 10 Hz. The current source design includes special circuits for low noise operation, slow turn-on and turn-off, circuits for over voltage and transient current protection; and good regulation. Space qualified and radiation hardened components are required to be used to sustain stringent space environment requirements during mission life of two years.

Production of high transient heat and particle fluxes in a linear plasma device

NASA Astrophysics Data System (ADS)

De Temmerman, G.; Zielinski, J. J.; van der Meiden, H.; Melissen, W.; Rapp, J.

2010-08-01

We report on the generation of high transient heat and particle fluxes in a linear plasma device by pulsed operation of the plasma source. A capacitor bank is discharged into the source to transiently increase the discharge current up to 1.7 kA, allowing peak densities and temperature of 70×1020 m-3 and 6 eV corresponding to a surface power density of about 400 MW m-2.

Propagation of ultrashort laser pulses in water: linear absorption and onset of nonlinear spectral transformation.

PubMed

Sokolov, Alexei V; Naveira, Lucas M; Poudel, Milan P; Strohaber, James; Trendafilova, Cynthia S; Buck, William C; Wang, Jieyu; Strycker, Benjamin D; Wang, Chao; Schuessler, Hans; Kolomenskii, Alexandre; Kattawar, George W

2010-01-20

We study propagation of short laser pulses through water and use a spectral hole filling technique to essentially perform a sensitive balanced comparison of absorption coefficients for pulses of different duration. This study is motivated by an alleged violation of the Bouguer-Lambert-Beer law at low light intensities, where the pulse propagation is expected to be linear, and by a possible observation of femtosecond optical precursors in water. We find that at low intensities, absorption of laser light is determined solely by its spectrum and does not directly depend on the pulse duration, in agreement with our earlier work and in contradiction to some work of others. However, as the laser fluence is increased, interaction of light with water becomes nonlinear, causing energy exchange among the pulse's spectral components and resulting in peak-intensity dependent (and therefore pulse-duration dependent) transmission. For 30 fs pulses at 800 nm center wavelength, we determine the onset of nonlinear propagation effects to occur at a peak value of about 0.12 mJ/cm(2) of input laser energy fluence.

Pulsed photothermal interferometry for spectroscopic gas detection with hollow-core optical fibre

PubMed Central

Lin, Yuechuan; Jin, Wei; Yang, Fan; Ma, Jun; Wang, Chao; Ho, Hoi Lut; Liu, Yang

2016-01-01

Gas detection with hollow-core photonic bandgap fibre (HC-PBF) and pulsed photothermal (PT) interferometry spectroscopy are studied theoretically and experimentally. A theoretical model is developed and used to compute the gas-absorption-induced temperature and phase modulation in a HC-PBF filled with low-concentration of C2H2 in nitrogen. The PT phase modulation dynamics for different pulse duration, peak power and energy of pump beam are numerically modelled, which are supported by the experimental results obtained around the P(9) absorption line of C2H2 at 1530.371 nm. Thermal conduction is identified as the main process responsible for the phase modulation dynamics. For a constant peak pump power level, the phase modulation is found to increase with pulse duration up to ~1.2 μs, while it increases with decreasing pulse duration for a constant pulse energy. It is theoretically possible to achieve ppb level detection of C2H2 with ~1 m length HC-PBF and a pump beam with ~10 ns pulse duration and ~100 nJ pulse energy. PMID:28009011

Pulsed photothermal interferometry for spectroscopic gas detection with hollow-core optical fibre.

PubMed

Lin, Yuechuan; Jin, Wei; Yang, Fan; Ma, Jun; Wang, Chao; Ho, Hoi Lut; Liu, Yang

2016-12-23

Gas detection with hollow-core photonic bandgap fibre (HC-PBF) and pulsed photothermal (PT) interferometry spectroscopy are studied theoretically and experimentally. A theoretical model is developed and used to compute the gas-absorption-induced temperature and phase modulation in a HC-PBF filled with low-concentration of C 2 H 2 in nitrogen. The PT phase modulation dynamics for different pulse duration, peak power and energy of pump beam are numerically modelled, which are supported by the experimental results obtained around the P(9) absorption line of C 2 H 2 at 1530.371 nm. Thermal conduction is identified as the main process responsible for the phase modulation dynamics. For a constant peak pump power level, the phase modulation is found to increase with pulse duration up to ~1.2 μs, while it increases with decreasing pulse duration for a constant pulse energy. It is theoretically possible to achieve ppb level detection of C 2 H 2 with ~1 m length HC-PBF and a pump beam with ~10 ns pulse duration and ~100 nJ pulse energy.

Loaded delay lines for future RF pulse compression systems

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

Jones, R.M.; Wilson, P.B.; Kroll, N.M.

1995-05-01

The peak power delivered by the klystrons in the NLCRA (Next Linear Collider Test Accelerator) now under construction at SLAC is enhanced by a factor of four in a SLED-II type of R.F. pulse compression system (pulse width compression ratio of six). To achieve the desired output pulse duration of 250 ns, a delay line constructed from a 36 m length of circular waveguide is used. Future colliders, however, will require even higher peak power and larger compression factors, which favors a more efficient binary pulse compression approach. Binary pulse compression, however, requires a line whose delay time is approximatelymore » proportional to the compression factor. To reduce the length of these lines to manageable proportions, periodically loaded delay lines are being analyzed using a generalized scattering matrix approach. One issue under study is the possibility of propagating two TE{sub o} modes, one with a high group velocity and one with a group velocity of the order 0.05c, for use in a single-line binary pulse compression system. Particular attention is paid to time domain pulse degradation and to Ohmic losses.« less

Above threshold spectral dependence of linewidth enhancement factor, optical duration and linear chirp of quantum dot lasers.

PubMed

Kim, Jimyung; Delfyett, Peter J

2009-12-07

The spectral dependence of the linewidth enhancement factor above threshold is experimentally observed from a quantum dot Fabry-Pérot semiconductor laser. The linewidth enhancement factor is found to be reduced when the quantum dot laser operates approximately 10 nm offset to either side of the gain peak. It becomes significantly reduced on the anti-Stokes side as compared to the Stokes side. It is also found that the temporal duration of the optical pulses generated from quantum dot mode-locked lasers is shorter when the laser operates away from the gain peak. In addition, less linear chirp is impressed on the pulse train generated from the anti-Stokes side whereas the pulses generated from the gain peak and Stokes side possess a large linear chirp. These experimental results imply that enhanced performance characteristics of quantum dot lasers can be achieved by operating on the anti-Stokes side, approximately 10 nm away from the gain peak.

Two-dimensional coherent spectroscopy of a THz quantum cascade laser: observation of multiple harmonics.

PubMed

Markmann, Sergej; Nong, Hanond; Pal, Shovon; Fobbe, Tobias; Hekmat, Negar; Mohandas, Reshma A; Dean, Paul; Li, Lianhe; Linfield, Edmund H; Davies, A Giles; Wieck, Andreas D; Jukam, Nathan

2017-09-04

Two-dimensional spectroscopy is performed on a terahertz (THz) frequency quantum cascade laser (QCL) with two broadband THz pulses. Gain switching is used to amplify the first THz pulse and the second THz pulse is used to probe the system. Fourier transforms are taken with respect to the delay time between the two THz pulses and the sampling time of the THz probe pulse. The two-dimensional spectrum consists of three peaks at (ω τ = 0, ω t = ω 0 ), (ω τ = ω 0 , ω t = ω 0 ), and (ω τ = 2ω 0 , ω t = ω 0 ) where ω 0 denotes the lasing frequency. The peak at ω τ = 0 represents the response of the probe to the zero-frequency (rectified) component of the instantaneous intensity and can be used to measure the gain recovery.

Performance enhancement of sub-nanosecond diode-pumped passively Q-switched Yb:YAG microchip laser with diamond surface cooling.

PubMed

Zhuang, W Z; Chen, Yi-Fan; Su, K W; Huang, K F; Chen, Y F

2012-09-24

We experimentally confirm that diamond surface cooling can significantly enhance the output performance of a sub-nanosecond diode-end-pumped passively Q-switched Yb:YAG laser. It is found that the pulse energy obtained with diamond cooling is approximately 1.5 times greater than that obtained without diamond cooling, where a Cr(4+):YAG absorber with the initial transmission of 84% is employed. Furthermore, the standard deviation of the pulse amplitude peak-to-peak fluctuation is found to be approximately 3 times lower than that measured without diamond cooling. Under a pump power of 3.9 W, the passively Q-switched Yb:YAG laser can generate a pulse train of 3.3 kHz repetition rate with a pulse energy of 287 μJ and with a pulse width of 650 ps.

Detection of cephradine through the electrochemical study of the degradation product of cephradine

NASA Astrophysics Data System (ADS)

Jiang, Qingfeng; Ying, Yibin; Wang, Jianping; Ye, Zunzhong; Li, Yanbin

2005-11-01

The degradation product of cephradine(CEP), a broad spectrum antibiotic, with NaOH was studied in solution by Cyclic Voltammetry and Differential Pulse Voltammetry at a three electrode system (Gold working electrode, Hg/HgCl reference electrode and Platinum counter electrode). Our experiment was based on that the R-SH in degradation product could cause a deoxidization peak at gold working electrode. The response was optimized with respect to accumulation time, ionic strength, drug concentration, reproducibility and other variables. We found that the degradation product of CEP in Na2HPO4-NaH2PO4 buffer could cause a sensitive deoxidization peak at -0.68V. A linear dependence of peak currents on the concentration was observed in the range of 10-7 - 10-6 mol/L, with a detection limit of 0.5*10-7mol/L. This method can achieve satisfactory results in the application of detecting human-made CEP.

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.

Performance of the JT-60SA cryogenic system under pulsed heat loads during acceptance tests

NASA Astrophysics Data System (ADS)

Hoa, C.; Bonne, F.; Roussel, P.; Lamaison, V.; Girard, S.; Fejoz, P.; Goncalves, R.; Vallet, J. C.; Legrand, J.; Fabre, Y.; Pudys, V.; Wanner, M.; Cardella, A.; Di Pietro, E.; Kamiya, K.; Natsume, K.; Ohtsu, K.; Oishi, M.; Honda, A.; Kashiwa, Y.; Kizu, K.

2017-12-01

The JT-60SA cryogenic system a superconducting tokamak currently under assembly at Naka, Japan. After one year of commissioning, the acceptance tests were successfully completed in October 2016 in close collaboration with Air Liquide Advanced Technologies (ALaT), the French atomic and alternative energies commission (CEA), Fusion for Energy (F4E) and the Quantum Radiological Science and Technology (QST). The cryogenic system has several cryogenic users at various temperatures: the superconducting magnets at 4.4 K, the current leads at 50 K, the thermal shields at 80 K and the divertor cryo-pumps at 3.7 K. The cryogenic system has an equivalent refrigeration power of about 9.5 kW at 4.5 K, with peak loads caused by the nuclear heating, the eddy currents in the structures and the AC losses in the magnets during cyclic plasma operation. The main results of the acceptance tests will be reported, with emphasis on the management of the challenging pulsed load operation using a liquid helium volume of 7 m3 as a thermal damper.

Enhanced ozone production in a pulsed dielectric barrier discharge plasma jet with addition of argon to a He-O2 flow gas

NASA Astrophysics Data System (ADS)

Sands, Brian; Ganguly, Biswa; Scofield, James

2013-09-01

Ozone production in a plasma jet DBD driven with a 20-ns risetime unipolar pulsed voltage can be significantly enhanced using helium as the primary flow gas with an O2 coflow. The overvolted discharge can be sustained with up to a 5% O2 coflow at <20 kHz pulse repetition frequency at 13 kV applied voltage. Ozone production scales with the pulse repetition frequency up to a ``turnover frequency'' that depends on the O2 concentration, total gas flow rate, and applied voltage. For example, peak ozone densities >1016 cm-3 were measured with 3% O2 admixture and <3 W input power at a 12 kHz turnover frequency. A further increase in the repetition frequency results in increased discharge current and 777 nm O(5 P) emission, but decreased ozone production and is followed by a transition to a filamentary discharge mode. The addition of argon at concentrations >=5% reduces the channel conductivity and shifts the turnover frequency to higher frequencies. This results in increased ozone production for a given applied voltage and gas flow rate. Time-resolved Ar(1s5) and He(23S1) metastable densities were acquired along with discharge current and ozone density measurements to gain insight into the mechanisms of optimum ozone production.

Quasi-CW diode-pumped self-starting adaptive laser with self-Q-switched output.

PubMed

Smith, G; Damzen, M J

2007-05-14

An investigation is made into a quasi-CW (QCW) diode-pumped holographic adaptive laser utilising an ultra high gain (approximately 10(4)) Nd:YVO(4) bounce amplifier. The laser produces pulses at 1064 nm with energy approximately 0.6 mJ, duration <3 ns and peak power approximately 200 kW, with high stability, via self-Q-switching effects due to the transient dynamics of the writing and replay of the gain hologram for each pump pulse. The system produces a near-diffraction-limited output with M(2)<1.3 and operates with a single longitudinal mode. In a further adaptive laser configuration, the output was amplified to obtain pulses of approximately 5.6 mJ energy, approximately 7 ns duration and approximately 1 MW peak power. The output spatial quality is also M(2)<1.3 with SLM operation. Up to 2.9 mJ pulse energy of frequency doubled green (532 nm) radiation is obtained, using an LBO crystal, representing approximately 61% conversion efficiency. This work shows that QCW diode-pumped self-adaptive holographic lasers can provide a useful source of high peak power, short duration pulses with excellent spatial quality and narrow linewidth spectrum.

LUNG DEFLATION AND OXYGEN PULSE IN COPD: RESULTS FROM THE NETT RANDOMIZED TRIAL

PubMed Central

Come, Carolyn E.; Divo, Miguel J.; Estépar, Raúl San José; Sciurba, Frank C.; Criner, Gerard J.; Marchetti, Nathaniel; Scharf, Steven M.; Mosenifar, Zab; Make, Barry J.; Keller, Cesar A.; Minai, Omar A.; Martinez, Fernando J.; Han, MeiLan K.; Reilly, John J.; Celli, Bartolome R.; Washko, George R.

2011-01-01

Background In COPD patients, hyperinflation impairs cardiac function. We examined whether lung deflation improves oxygen pulse, a surrogate marker of stroke volume. Methods In 129 NETT patients with cardiopulmonary exercise testing (CPET) and arterial blood gases (ABG substudy), hyperinflation was assessed with residual volume to total lung capacity ratio (RV/TLC), and cardiac function with oxygen pulse (O2 pulse=VO2/HR) at baseline and 6 months. Medical and surgical patients were divided into “deflators” and “non-deflators” based on change in RV/TLC from baseline (ΔRV/TLC). We defined deflation as the ΔRV/TLC experienced by 75% of surgical patients. We examined changes in O2 pulse at peak and similar (iso-work) exercise. Findings were validated in 718 patients who underwent CPET without ABGs. Results In the ABG substudy, surgical and medical deflators improved their RV/TLC and peak O2 pulse (median ΔRV/TLC −18.0% vs. −9.3%, p=0.0003; median ΔO2 pulse 13.6% vs. 1.8%, p=0.12). Surgical deflators also improved iso-work O2 pulse (0.53 mL/beat, p=0.04 at 20 watts). In the validation cohort, surgical deflators experienced a greater improvement in peak O2 pulse than medical deflators (mean 18.9% vs. 1.1%). In surgical deflators improvements in O2 pulse at rest and during unloaded pedaling (0.32 mL/beat, p<0.0001 and 0.47 mL/beat, p<0.0001, respectively) corresponded with significant reductions in HR and improvements in VO2. On multivariate analysis, deflators were 88% more likely than non-deflators to have an improvement in O2 pulse (OR 1.88, 95% CI 1.30–2.72, p=0.0008). Conclusion In COPD, decreased hyperinflation through lung volume reduction is associated with improved O2 pulse. PMID:21843930

Lung deflation and oxygen pulse in COPD: results from the NETT randomized trial.

PubMed

Come, Carolyn E; Divo, Miguel J; San José Estépar, Raúl; Sciurba, Frank C; Criner, Gerard J; Marchetti, Nathaniel; Scharf, Steven M; Mosenifar, Zab; Make, Barry J; Keller, Cesar A; Minai, Omar A; Martinez, Fernando J; Han, MeiLan K; Reilly, John J; Celli, Bartolome R; Washko, George R

2012-01-01

In COPD patients, hyperinflation impairs cardiac function. We examined whether lung deflation improves oxygen pulse, a surrogate marker of stroke volume. In 129 NETT patients with cardiopulmonary exercise testing (CPET) and arterial blood gases (ABG substudy), hyperinflation was assessed with residual volume to total lung capacity ratio (RV/TLC), and cardiac function with oxygen pulse (O(2) pulse=VO(2)/HR) at baseline and 6 months. Medical and surgical patients were divided into "deflators" and "non-deflators" based on change in RV/TLC from baseline (∆RV/TLC). We defined deflation as the ∆RV/TLC experienced by 75% of surgical patients. We examined changes in O(2) pulse at peak and similar (iso-work) exercise. Findings were validated in 718 patients who underwent CPET without ABGs. In the ABG substudy, surgical and medical deflators improved their RV/TLC and peak O(2) pulse (median ∆RV/TLC -18.0% vs. -9.3%, p=0.0003; median ∆O(2) pulse 13.6% vs. 1.8%, p=0.12). Surgical deflators also improved iso-work O(2) pulse (0.53 mL/beat, p=0.04 at 20 W). In the validation cohort, surgical deflators experienced a greater improvement in peak O(2) pulse than medical deflators (mean 18.9% vs. 1.1%). In surgical deflators improvements in O(2) pulse at rest and during unloaded pedaling (0.32 mL/beat, p<0.0001 and 0.47 mL/beat, p<0.0001, respectively) corresponded with significant reductions in HR and improvements in VO(2). On multivariate analysis, deflators were 88% more likely than non-deflators to have an improvement in O(2) pulse (OR 1.88, 95% CI 1.30-2.72, p=0.0008). In COPD, decreased hyperinflation through lung volume reduction is associated with improved O(2) pulse. Copyright © 2011 Elsevier Ltd. All rights reserved.

Control of broadband optically generated ultrasound pulses using binary amplitude holograms.

PubMed

Brown, Michael D; Jaros, Jiri; Cox, Ben T; Treeby, Bradley E

2016-04-01

In this work, the use of binary amplitude holography is investigated as a mechanism to focus broadband acoustic pulses generated by high peak-power pulsed lasers. Two algorithms are described for the calculation of the binary holograms; one using ray-tracing, and one using an optimization based on direct binary search. It is shown using numerical simulations that when a binary amplitude hologram is excited by a train of laser pulses at its design frequency, the acoustic field can be focused at a pre-determined distribution of points, including single and multiple focal points, and line and square foci. The numerical results are validated by acoustic field measurements from binary amplitude holograms, excited by a high peak-power laser.

Infrared focal plane performance in the South Atlantic anomaly

NASA Technical Reports Server (NTRS)

Junga, Frank A.

1989-01-01

Proton-induced pulse height distributions (PHD's) in Si:XX detectors were studied analytically and experimentally. In addition, a preliminary design for a flight experiment to characterize the response of Si:XX detectors to the trapped proton environment and verify PHD models was developed. PHD's were computed for two orbit altitudes for a variety of shielding configurations. Most of the proton-induced pulses have amplitudes less that about 3.5 x 10(exp 5) e-h pairs. Shielding has a small effect on the shape of the PHD's. The primary effect of shielding is to reduce the total number of pulses produced. Proton-induced PHD's in a Si:Sb focal plane array bombarded by a unidirectional 67-MeV beam were measured. The maximum pulse height recorded was 6 x 10(exp 5) pairs. The distribution had two peaks: the larger peak corresponded to 3.8 x 10(exp 5) pairs and the smaller peak to 1.2 x 10(exp 5) pairs. The maximum pulse height and the larger peak are within a factor of two of predicted values. The low-energy peak was not expected, but is believed to be an artifact of inefficient charge collection in the detector. The planned flight experiment will be conducted on a Space Shuttle flight. Lockheed's helium extended life dewar (HELD) will be used to provide the required cryogenic environment for the detector. Two bulk Si:Sb arrays and two Si:As impurity band conduction arrays will be tested. The tests will be conducted while the Space Shuttle passes through the South Atlantic Anomaly. PHD's will be recorded and responsivity changes tracked. This experiment will provide a new database on proton-induced PHD's, compare two infrared detector technologies in a space environment, and provide the data necessary to validate PHD modeling.

Relating Silicon Carbide Avalanche Breakdown Diode Design to Pulsed-Energy Capability

DTIC Science & Technology

2017-03-01

Relating Silicon Carbide Avalanche Breakdown Diode Design to Pulsed- Energy Capability Damian Urciuoli, Miguel Hinojosa, and Ronald Green US...were pulse tested in an inductive load circuit at peak powers of over 110 kW. Total pulsed- energy dissipation was kept nearly the same among the...voltages about which design provides the highest pulsed- energy capability. Keywords: Avalanche; Breakdown; Diode; Silicon Carbide Introduction

Characterization of an electrothermal plasma source for fusion transient simulations

DOE PAGES

Gebhart, T. E.; Baylor, Larry R.; Rapp, Juergen; ...

2018-01-21

The realization of fusion energy requires materials that can withstand high heat and particle fluxes at the plasma material interface. Here in this work, an electrothermal (ET) plasma source has been designed as a transient heat flux source for a linear plasma material interaction device. An ET plasma source operates in the ablative arc regime driven by a DC capacitive discharge. The current channel width is defined by the 4 mm bore of a boron nitride liner. At large plasma currents, the arc impacts the liner wall, leading to high particle and heat fluxes to the liner material, which subsequentlymore » ablates and ionizes. This results in a high density plasma with a large unidirectional bulk flow out of the source exit. The pulse length for the ET source has been optimized using a pulse forming network to have durations of 1 and 2 ms. The peak currents and maximum source energies seen in this system are 1.9 kA and 1.2 kJ for the 2 ms pulse and 3.2 kA and 2.1 kJ for the 1 ms pulse, respectively. This work is a proof of the principal project to show that an ET source produces electron densities and heat fluxes comparable to those anticipated in transient events in large future magnetic confinement fusion devices. Heat flux, plasma temperature, and plasma density were determined for each shot using infrared imaging and optical spectroscopy techniques. This paper will discuss the assumptions, methods, and results of the experiments.« less

Characterization of an electrothermal plasma source for fusion transient simulations

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

Gebhart, T. E.; Baylor, Larry R.; Rapp, Juergen

The realization of fusion energy requires materials that can withstand high heat and particle fluxes at the plasma material interface. Here in this work, an electrothermal (ET) plasma source has been designed as a transient heat flux source for a linear plasma material interaction device. An ET plasma source operates in the ablative arc regime driven by a DC capacitive discharge. The current channel width is defined by the 4 mm bore of a boron nitride liner. At large plasma currents, the arc impacts the liner wall, leading to high particle and heat fluxes to the liner material, which subsequentlymore » ablates and ionizes. This results in a high density plasma with a large unidirectional bulk flow out of the source exit. The pulse length for the ET source has been optimized using a pulse forming network to have durations of 1 and 2 ms. The peak currents and maximum source energies seen in this system are 1.9 kA and 1.2 kJ for the 2 ms pulse and 3.2 kA and 2.1 kJ for the 1 ms pulse, respectively. This work is a proof of the principal project to show that an ET source produces electron densities and heat fluxes comparable to those anticipated in transient events in large future magnetic confinement fusion devices. Heat flux, plasma temperature, and plasma density were determined for each shot using infrared imaging and optical spectroscopy techniques. This paper will discuss the assumptions, methods, and results of the experiments.« less

Experimental observation of acoustic emissions generated by a pulsed proton beam from a hospital-based clinical cyclotron

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

Jones, Kevin C.; Solberg, Timothy D.; Avery, Stephen, E-mail: Stephen.Avery@uphs.upenn.edu

Purpose: To measure the acoustic signal generated by a pulsed proton spill from a hospital-based clinical cyclotron. Methods: An electronic function generator modulated the IBA C230 isochronous cyclotron to create a pulsed proton beam. The acoustic emissions generated by the proton beam were measured in water using a hydrophone. The acoustic measurements were repeated with increasing proton current and increasing distance between detector and beam. Results: The cyclotron generated proton spills with rise times of 18 μs and a maximum measured instantaneous proton current of 790 nA. Acoustic emissions generated by the proton energy deposition were measured to be onmore » the order of mPa. The origin of the acoustic wave was identified as the proton beam based on the correlation between acoustic emission arrival time and distance between the hydrophone and proton beam. The acoustic frequency spectrum peaked at 10 kHz, and the acoustic pressure amplitude increased monotonically with increasing proton current. Conclusions: The authors report the first observation of acoustic emissions generated by a proton beam from a hospital-based clinical cyclotron. When modulated by an electronic function generator, the cyclotron is capable of creating proton spills with fast rise times (18 μs) and high instantaneous currents (790 nA). Measurements of the proton-generated acoustic emissions in a clinical setting may provide a method for in vivo proton range verification and patient monitoring.« less

Facile preparation of MnO2 nanorods and evaluation of their supercapacitive characteristics

NASA Astrophysics Data System (ADS)

Aghazadeh, Mustafa; Asadi, Maryam; Maragheh, Mohammad Ghannadi; Ganjali, Mohammad Reza; Norouzi, Parviz; Faridbod, Farnoush

2016-02-01

The first time pulsed base (OH-) electrogeneration to the cathodic electrodeposition of MnO2 in nitrate bath was applied and MnO2 nanorods were obtained. The deposition experiments were performed under a pulse current mode with typical on-times and off-times (ton = 10 ms and toff = 50 ms) and a peak current density of 2 mA cm-2 (Ia = 2 mA cm-2). The structural characterization with XRD and FTIR revealed that the prepared MnO2 is composed of both α and γ phases. Morphological evaluations through SEM and TEM revealed that the prepared MnO2 contains nanorods of relative uniform structures (with an average diameter of 50 nm). The electrochemical measurements through cyclic voltammetry and charge-discharge techniques revealed that the prepared MnO2 nanostructures reveal an excellent capacitive behavior with specific capacitance values of 242, 167 and 98 F g-1 under the applied current densities of 2, 5 and 10 A g-1, respectively. Also, excellent long-term cycling stabilities of 94.8%, 89.1%, and 76.5% were observed after 1000 charge-discharge cycles at the current densities of 2, 5 and 10 A g-1.

Analysis and development of fourth order LCLC resonant based capacitor charging power supply for pulse power applications.

PubMed

Naresh, P; Hitesh, C; Patel, A; Kolge, T; Sharma, Archana; Mittal, K C

2013-08-01

A fourth order (LCLC) resonant converter based capacitor charging power supply (CCPS) is designed and developed for pulse power applications. Resonant converters are preferred t utilize soft switching techniques such as zero current switching (ZCS) and zero voltage switching (ZVS). An attempt has been made to overcome the disadvantages in 2nd and 3rd resonant converter topologies; hence a fourth order resonant topology is used in this paper for CCPS application. In this paper a novel fourth order LCLC based resonant converter has been explored and mathematical analysis carried out to calculate load independent constant current. This topology provides load independent constant current at switching frequency (fs) equal to resonant frequency (fr). By changing switching condition (on time and dead time) this topology has both soft switching techniques such as ZCS and ZVS for better switching action to improve the converter efficiency. This novel technique has special features such as low peak current through switches, DC blocking for transformer, utilizing transformer leakage inductance as resonant component. A prototype has been developed and tested successfully to charge a 100 μF capacitor to 200 V.

High speed imager test station

DOEpatents

Yates, George J.; Albright, Kevin L.; Turko, Bojan T.

1995-01-01

A test station enables the performance of a solid state imager (herein called a focal plane array or FPA) to be determined at high image frame rates. A programmable waveform generator is adapted to generate clock pulses at determinable rates for clock light-induced charges from a FPA. The FPA is mounted on an imager header board for placing the imager in operable proximity to level shifters for receiving the clock pulses and outputting pulses effective to clock charge from the pixels forming the FPA. Each of the clock level shifters is driven by leading and trailing edge portions of the clock pulses to reduce power dissipation in the FPA. Analog circuits receive output charge pulses clocked from the FPA pixels. The analog circuits condition the charge pulses to cancel noise in the pulses and to determine and hold a peak value of the charge for digitizing. A high speed digitizer receives the peak signal value and outputs a digital representation of each one of the charge pulses. A video system then displays an image associated with the digital representation of the output charge pulses clocked from the FPA. In one embodiment, the FPA image is formatted to a standard video format for display on conventional video equipment.

High speed imager test station

DOEpatents

Yates, G.J.; Albright, K.L.; Turko, B.T.

1995-11-14

A test station enables the performance of a solid state imager (herein called a focal plane array or FPA) to be determined at high image frame rates. A programmable waveform generator is adapted to generate clock pulses at determinable rates for clock light-induced charges from a FPA. The FPA is mounted on an imager header board for placing the imager in operable proximity to level shifters for receiving the clock pulses and outputting pulses effective to clock charge from the pixels forming the FPA. Each of the clock level shifters is driven by leading and trailing edge portions of the clock pulses to reduce power dissipation in the FPA. Analog circuits receive output charge pulses clocked from the FPA pixels. The analog circuits condition the charge pulses to cancel noise in the pulses and to determine and hold a peak value of the charge for digitizing. A high speed digitizer receives the peak signal value and outputs a digital representation of each one of the charge pulses. A video system then displays an image associated with the digital representation of the output charge pulses clocked from the FPA. In one embodiment, the FPA image is formatted to a standard video format for display on conventional video equipment. 12 figs.

Theoretical and experimental investigations on high peak power Q-switched Nd:YAG laser at 1112 nm

NASA Astrophysics Data System (ADS)

He, Miao; Yang, Feng; Wang, Zhi-Chao; Gao, Hong-Wei; Yuan, Lei; Li, Chen-Long; Zong, Nan; Shen, Yu; Bo, Yong; Peng, Qin-Jun; Cui, Da-Fu; Xu, Zu-Yan

2018-07-01

We report on the experimental measurement and theoretical analysis on a Q-switched high peak power laser diode (LD) side-pumped 1112 nm Nd:YAG laser by means of special mirrors coating design in cavity. In theory, a numerical model, based on four-wavelength rate equations, is performed to analyze the competition process of different gain lines and the output characteristics of the Q-switched Nd:YAG laser. In the experiment, a maximum output power of 25.2 W with beam quality factor M2 of 1.46 is obtained at the pulse repetition rate of 2 kHz and 210 ns of pulse width, corresponding to a pulse energy and peak power of 12.6 mJ and 60 kW, respectively. The experimental data agree well with the theoretical simulation results.

Relationship between nutritional risk and exercise capacity in severe chronic obstructive pulmonary disease in male patients

PubMed Central

Shan, Xizheng; Liu, Jinming; Luo, Yanrong; Xu, Xiaowen; Han, Zhiqing; Li, Hailing

2015-01-01

Objective The nutritional status of chronic obstructive pulmonary disease (COPD) patients is associated with their exercise capacity. In the present study, we have explored the relationship between nutritional risk and exercise capacity in severe male COPD patients. Methods A total of 58 severe COPD male patients were enrolled in this study. The patients were assigned to no nutritional risk group (n=33) and nutritional risk group (n=25) according to the Nutritional Risk Screening (NRS, 2002) criteria. Blood gas analysis, conventional pulmonary function testing, and cardiopulmonary exercise testing were performed on all the patients. Results Results showed that the weight and BMI of the patients in the nutritional risk group were significantly lower than in the no nutritional risk group (P<0.05). The pulmonary diffusing capacity for carbon monoxide of the no nutritional risk group was significantly higher than that of the nutritional risk group (P<0.05). Besides, the peak VO2 (peak oxygen uptake), peak O2 pulse (peak oxygen pulse), and peak load of the nutritional risk group were significantly lower than those of the no nutritional risk group (P<0.05) and there were significantly negative correlations between the NRS score and peak VO2, peak O2 pulse, or peak load (r<0, P<0.05). Conclusion The association between exercise capacity and nutritional risk based on NRS 2002 in severe COPD male patients is supported by these results of this study. PMID:26150712

Analysis of electromagnetic fields on an F-106B aircraft during lightning strikes

NASA Technical Reports Server (NTRS)

Trost, T. F.; Pitts, F. L.

1982-01-01

Information on the exterior electromagnetic environment of an aircraft when it is struck by lightning has been obtained during thunderstorm penetrations with an F-106B aircraft. Electric and magnetic fields were observed, using mainly time-derivative type sensors, with bandwidths to 50 MHz. Lightning pulse lengths ranging from 25 ns to 7 microsec have been recorded. Sufficient high-frequency content was present to excite electromagnetic resonances of the aircraft, and peaks in the frequency spectra of the waveforms in the range 7 to 23 MHz are in agreement with the resonant frequencies determined in laboratory scale-model tests. Both positively and negatively charged strikes were experienced, and most of the data suggest low values of peak current.

Experimental application of pulsed laser-induced water jet for endoscopic submucosal dissection: mechanical investigation and preliminary experiment in swine.

PubMed

Sato, Chiaki; Nakano, Toru; Nakagawa, Atsuhiro; Yamada, Masato; Yamamoto, Hiroaki; Kamei, Takashi; Miyata, Go; Sato, Akira; Fujishima, Fumiyoshi; Nakai, Masaaki; Niinomi, Mitsuo; Takayama, Kazuyoshi; Tominaga, Teiji; Satomi, Susumu

2013-05-01

A current drawback of endoscopic submucosal dissection (ESD) for early-stage gastrointestinal tumors is the lack of instruments that can safely assist with this procedure. We have developed a pulsed jet device that can be incorporated into a gastrointestinal endoscope. Here, we investigated the mechanical profile of the pulsed jet device and demonstrated the usefulness of this instrument in esophageal ESD in swine. The device comprises a 5-Fr catheter, a 14-mm long stainless steel tube for generating the pulsed water jet, a nozzle and an optical quartz fiber. The pulsed water jet was generated at pulse rates of 3 Hz by irradiating the physiological saline (4°C) within the stainless steel tube with an holmium-doped yttrium-aluminum-garnet (Ho:YAG) laser at 1.1 J/pulse. Mechanical characteristics were evaluated using a force meter. The device was used only for the part of submucosal dissection in the swine ESD model. Tissues removed using the pulsed jet device and a conventional electrocautery device, and the esophagus, were histologically examined to assess thermal damage. The peak impact force was observed at a stand-off distance of 40 mm (1.1 J/pulse). ESD using the pulsed jet device was successful, as the tissue specimens showed precise dissection of the submucosal layer. The extent of thermal injury was significantly lower in the dissected bed using the pulsed jet device. The results showed that the present endoscopic pulsed jet system is a useful alternative for a safe ESD with minimum tissue injury. © 2012 The Authors. Digestive Endoscopy © 2012 Japan Gastroenterological Endoscopy Society.

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.

Research Laboratory of Electronic Progress Report Number 135.

DTIC Science & Technology

1993-06-01

78 @ 1.12 Ultrashort Pulse Generation in Solid State Lasers ...generation the use of intracavity self-phase-modulation and of ultrashort laser pulses is essential for studies of negative group velocity dispersion... pulses . Our studies focus on exploiting mode locked solid state lasers . While the dominant the short pulse durations and high peak intensity of effect of

Sensitivity to microstimulation of somatosensory cortex distributed over multiple electrodes.

PubMed

Kim, Sungshin; Callier, Thierri; Tabot, Gregg A; Tenore, Francesco V; Bensmaia, Sliman J

2015-01-01

Meaningful and repeatable tactile sensations can be evoked by electrically stimulating primary somatosensory cortex. Intracortical microstimulation (ICMS) may thus be a viable approach to restore the sense of touch in individuals who have lost it, for example tetraplegic patients. One of the potential limitations of this approach, however, is that high levels of current can damage the neuronal tissue if the resulting current densities are too high. The limited range of safe ICMS amplitudes thus limits the dynamic range of ICMS-evoked sensations. One way to get around this limitation would be to distribute the ICMS over multiple electrodes in the hopes of intensifying the resulting percept without increasing the current density experienced by the neuronal tissue. Here, we test whether stimulating through multiple electrodes is a viable solution to increase the dynamic range of ICMS-elicited sensations without increasing the peak current density. To this end, we compare the ability of non-human primates to detect ICMS delivered through one vs. multiple electrodes. We also compare their ability to discriminate pulse trains differing in amplitude when these are delivered through one or more electrodes. We find that increasing the number of electrodes through which ICMS is delivered only has a marginal effect on detectability or discriminability despite the fact that 2-4 times more current is delivered overall. Furthermore, the impact of multielectrode stimulation (or lack thereof) is found whether pulses are delivered synchronously or asynchronously, whether the leading phase of the pulses is cathodic or anodic, and regardless of the spatial configuration of the electrode groups.

Attachment process in rocket-triggered lightning strokes

NASA Astrophysics Data System (ADS)

Wang, D.; Rakov, V. A.; Uman, M. A.; Takagi, N.; Watanabe, T.; Crawford, D. E.; Rambo, K. J.; Schnetzer, G. H.; Fisher, R. J.; Kawasaki, Z.-I.

1999-01-01

In order to study the lightning attachment process, we have obtained highly resolved (about 100 ns time resolution and about 3.6 m spatial resolution) optical images, electric field measurements, and channel-base current recordings for two dart leader/return-stroke sequences in two lightning flashes triggered using the rocket-and-wire technique at Camp Blanding, Florida. One of these two sequences exhibited an optically discernible upward-propagating discharge that occurred in response to the approaching downward-moving dart leader and connected to this descending leader. This observation provides the first direct evidence of the occurrence of upward connecting discharges in triggered lightning strokes, these strokes being similar to subsequent strokes in natural lightning. The observed upward connecting discharge had a light intensity one order of magnitude lower than its associated downward dart leader, a length of 7-11 m, and a duration of several hundred nanoseconds. The speed of the upward connecting discharge was estimated to be about 2 × 107 m/s, which is comparable to that of the downward dart leader. In both dart leader/return-stroke sequences studied, the return stroke was inferred to start at the point of junction between the downward dart leader and the upward connecting discharge and to propagate in both upward and downward directions. This latter inference provides indirect evidence of the occurrence of upward connecting discharges in both dart leader/return-stroke sequences even though one of these sequences did not have a discernible optical image of such a discharge. The length of the upward connecting discharges (observed in one case and inferred from the height of the return-stroke starting point in the other case) is greater for the event that is characterized by the larger leader electric field change and the higher return-stroke peak current. For the two dart leader/return-stroke sequences studied, the upward connecting discharge lengths are estimated to be 7-11 m and 4-7 m, with the corresponding return-stroke peak currents being 21 kA and 12 kA, and the corresponding leader electric field changes 30 m from the rocket launcher being 56 kV/m and 43 kV/m. Additionally, we note that the downward dart leader light pulse generally exhibits little variation in its 10-90% risetime and peak value over some tens of meters above the return-stroke starting point, while the following return-stroke light pulse shows an appreciable increase in risetime and a decrease in peak value while traversing the same section of the lightning channel. Our findings regarding (1) the initially bidirectional development of return-stroke process and (2) the relatively strong attenuation of the upward moving return-stroke light (and by inference current) pulse over the first some tens of meters of the channel may have important implications for return-stroke modeling.

Weld pool oscillation during pulsed GTA welding

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

Aendenroomer, A.J.R.; Ouden, G. den

1996-12-31

This paper deals with weld pool oscillation during pulsed GTA welding and with the possibility to use this oscillation for in-process control of weld penetration. Welding experiments were carried out under different welding conditions. During welding the weld pool was triggered into oscillation by the normal welding pulses or by extra current pulses. The oscillation frequency was measured both during the pulse time and during the base time by analyzing the arc voltage variation using a Fast Fourier Transformation program. Optimal results are obtained when full penetration occurs during the pulse time and partial penetration during the base time. Undermore » these conditions elliptical overlapping spot welds are formed. In the case of full penetration the weld pool oscillates in a low frequency mode (membrane oscillation), whereas in the case of partial penetration the weld pool oscillates in a high frequency mode (surface oscillation). Deviation from the optimal welding conditions occurs when high frequency oscillation is observed during both pulse time and base time (underpenetration) or when low frequency oscillation is observed during both pulse time and base time (overpenetration). In line with these results a penetration sensing system with feedback control was designed, based on the criterion that optimal weld penetration is achieved when two peaks are observed in the frequency distribution. The feasibility of this sensing system for orbital tube welding was confirmed by the results of experiments carried out under various welding conditions.« less

Assessing mental stress from the photoplethysmogram: a numerical study

PubMed Central

Charlton, Peter H; Celka, Patrick; Farukh, Bushra; Chowienczyk, Phil; Alastruey, Jordi

2018-01-01

Abstract Objective: Mental stress is detrimental to cardiovascular health, being a risk factor for coronary heart disease and a trigger for cardiac events. However, it is not currently routinely assessed. The aim of this study was to identify features of the photoplethysmogram (PPG) pulse wave which are indicative of mental stress. Approach: A numerical model of pulse wave propagation was used to simulate blood pressure signals, from which simulated PPG pulse waves were estimated using a transfer function. Pulse waves were simulated at six levels of stress by changing the model input parameters both simultaneously and individually, in accordance with haemodynamic changes associated with stress. Thirty-two feature measurements were extracted from pulse waves at three measurement sites: the brachial, radial and temporal arteries. Features which changed significantly with stress were identified using the Mann–Kendall monotonic trend test. Main results: Seventeen features exhibited significant trends with stress in measurements from at least one site. Three features showed significant trends at all three sites: the time from pulse onset to peak, the time from the dicrotic notch to pulse end, and the pulse rate. More features showed significant trends at the radial artery (15) than the brachial (8) or temporal (7) arteries. Most features were influenced by multiple input parameters. Significance: The features identified in this study could be used to monitor stress in healthcare and consumer devices. Measurements at the radial artery may provide superior performance than the brachial or temporal arteries. In vivo studies are required to confirm these observations. PMID:29658894

a Compact, Rf-Driven Pulsed Ion Source for Intense Neutron Generation

NASA Astrophysics Data System (ADS)

Perkins, L. T.; Celata, C. M.; Lee, Y.; Leung, K. N.; Picard, D. S.; Vilaithong, R.; Williams, M. D.; Wutte, D.

1997-05-01

Lawrence Berkeley National Laboratory is currently developing a compact, sealed-accelerator-tube neutron generator capable of producing a neutron flux in the range of 109 to 1010 D-T neutrons per second. The ion source, a miniaturized variation of earlier 2 MHz radio-frequency (rf)-driven multicusp ion sources, is designed to fit within a #197# 5 cm diameter borehole. Typical operating parameters include repetition rates up to 100 pps, with pulse widths between 10 and 80 us and source pressures as low as #197# 5 mTorr. In this configuration, peak extractable hydrogen current exceeding 35 mA from a 2 mm diameter aperture together with H1+ yields over 94% have been achieved. The required rf impedance matching network has been miniaturized to #197# 5 cm diameter. The accelerator column is a triode design using the IGUN ion optics codes and allows for electron suppression. Results from the testing of the integrated matching network-ion source-accelerator system will be presented.

Tide-related variability of TAG hydrothermal activity observed by deep-sea monitoring system and OBSH

NASA Astrophysics Data System (ADS)

Fujioka, Kantaro; Kobayashi, Kazuo; Kato, Kazuhiro; Aoki, Misumi; Mitsuzawa, Kyohiko; Kinoshita, Masataka; Nishizawa, Azusa

1997-12-01

Hydrothermal activities were monitored by an ocean bottom seismometer with hydrophone (OBSH) and a composite measuring system (Manatee) including CTD, current meter, transmission meter and cameras at a small depression on the TAG hydrothermal mound in the Mid-Atlantic Ridge. Low-frequency pressure pulses detected by the hydrophone with semi-diurnal periodicity seem to correspond to cycles of hydrothermal upflow from a small and short-lived smoker vent close to the observing site. The peaks of pressure pulses are synchronous with the maximum gradient of areal strain decrease due to tidal load release. Microearthquakes with very near epicenters occur sporadically and do not appear to be directly correlatable to hydrothermal venting. Temporal variations in bottom water temperature also have semi-diurnal periodicity but are more complicated than the pressure events. Temperatures may be affected both by upwelling of hot water and by lateral flow of the bottom current changing its directions with ocean tide.

A Hybrid Wavelet-Based Method for the Peak Detection of Photoplethysmography Signals.

PubMed

Li, Suyi; Jiang, Shanqing; Jiang, Shan; Wu, Jiang; Xiong, Wenji; Diao, Shu

2017-01-01

The noninvasive peripheral oxygen saturation (SpO 2 ) and the pulse rate can be extracted from photoplethysmography (PPG) signals. However, the accuracy of the extraction is directly affected by the quality of the signal obtained and the peak of the signal identified; therefore, a hybrid wavelet-based method is proposed in this study. Firstly, we suppressed the partial motion artifacts and corrected the baseline drift by using a wavelet method based on the principle of wavelet multiresolution. And then, we designed a quadratic spline wavelet modulus maximum algorithm to identify the PPG peaks automatically. To evaluate this hybrid method, a reflective pulse oximeter was used to acquire ten subjects' PPG signals under sitting, raising hand, and gently walking postures, and the peak recognition results on the raw signal and on the corrected signal were compared, respectively. The results showed that the hybrid method not only corrected the morphologies of the signal well but also optimized the peaks identification quality, subsequently elevating the measurement accuracy of SpO 2 and the pulse rate. As a result, our hybrid wavelet-based method profoundly optimized the evaluation of respiratory function and heart rate variability analysis.

A Hybrid Wavelet-Based Method for the Peak Detection of Photoplethysmography Signals

PubMed Central

Jiang, Shanqing; Jiang, Shan; Wu, Jiang; Xiong, Wenji

2017-01-01

The noninvasive peripheral oxygen saturation (SpO2) and the pulse rate can be extracted from photoplethysmography (PPG) signals. However, the accuracy of the extraction is directly affected by the quality of the signal obtained and the peak of the signal identified; therefore, a hybrid wavelet-based method is proposed in this study. Firstly, we suppressed the partial motion artifacts and corrected the baseline drift by using a wavelet method based on the principle of wavelet multiresolution. And then, we designed a quadratic spline wavelet modulus maximum algorithm to identify the PPG peaks automatically. To evaluate this hybrid method, a reflective pulse oximeter was used to acquire ten subjects' PPG signals under sitting, raising hand, and gently walking postures, and the peak recognition results on the raw signal and on the corrected signal were compared, respectively. The results showed that the hybrid method not only corrected the morphologies of the signal well but also optimized the peaks identification quality, subsequently elevating the measurement accuracy of SpO2 and the pulse rate. As a result, our hybrid wavelet-based method profoundly optimized the evaluation of respiratory function and heart rate variability analysis. PMID:29250135

Simulation study of the sub-terawatt laser wakefield acceleration operated in self-modulated regime

NASA Astrophysics Data System (ADS)

Hsieh, C.-Y.; Lin, M.-W.; Chen, S.-H.

2018-02-01

Laser wakefield acceleration (LWFA) can be accomplished by introducing a sub-terawatt (TW) laser pulse into a thin, high-density gas target. In this way, the self-focusing effect and the self-modulation that happened on the laser pulse produce a greatly enhanced laser peak intensity that can drive a nonlinear plasma wave to accelerate electrons. A particle-in-cell model is developed to study sub-TW LWFA when a 0.6-TW laser pulse interacts with a dense hydrogen plasma. Gas targets having a Gaussian density profile or a flat-top distribution are defined for investigating the properties of sub-TW LWFA when conducting with a gas jet or a gas cell. In addition to using 800-nm laser pulses, simulations are performed with 1030-nm laser pulses, as they represent a viable approach to realize the sub-TW LWFA driven by high-frequency, diode-pumped laser systems. The peak density which allows the laser peak power PL˜2 Pc r of self-focusing critical power is favourable for conducting sub-TW LWFA. Otherwise, an excessively high peak density can induce an undesired filament effect which rapidly disintegrates the laser field envelope and violates the process of plasma wave excitation. The plateau region of a flat-top density distribution allows the self-focusing and the self-modulation of the laser pulse to develop, from which well-established plasma bubbles can be produced to accelerate electrons. The process of electron injection is complicated in such high-density plasma conditions; however, increasing the length of the plateau region represents a straightforward method to realize the injection and acceleration of electrons within the first bubble, such that an improved LWFA performance can be accomplished.

Characterization and compression of dissipative-soliton-resonance pulses in fiber lasers

PubMed Central

Li, Daojing; Li, Lei; Zhou, Junyu; Zhao, Luming; Tang, Dingyuan; Shen, Deyuan

2016-01-01

We report numerical and experimental studies of dissipative-soliton-resonance (DSR) in a fiber laser with a nonlinear optical loop mirror. The DSR pulse presents temporally a flat-top profile and a clamped peak power. Its spectrum has a rectangle profile with characteristic steep edges. It shows a unique behavior as pulse energy increases: The rectangle part of the spectrum is unchanged while the newly emerging spectrum sits on the center part and forms a peak. Experimental observations match well with the numerical results. Moreover, the detailed evolution of the DSR pulse compression is both numerically and experimentally demonstrated for the first time. An experimentally obtained DSR pulse of 63 ps duration is compressed down to 760 fs, with low-intensity pedestals using a grating pair. Before being compressed to its narrowest width, the pulse firstly evolves into a cat-ear profile, and the corresponding autocorrelation trace shows a crown shape, which distinguishes itself from properties of other solitons formed in fiber lasers. PMID:27025189

2.36 J, 50 Hz nanosecond pulses from a diode side-pumped Nd:YAG MOPA system

NASA Astrophysics Data System (ADS)

Li, Chaoyang; Lu, Chengqiang; Li, Chuan; Yang, Ning; Li, Ye; Yang, Zhen; Han, Song; Shi, Junfeng; Zhou, Zewu

2017-07-01

We report on a high-energy high-repetition-rate nanosecond Nd:YAG main oscillator power amplifier (MOPA) system. Maximum output pulse energy of 2.36 J with duration of 9.4 ns at 50 Hz has been achieved. The master oscillator was a LD side-pumped electro-optical Q-switched Nd:YAG rod laser adopting unstable cavity with variable reflectivity mirror (VRM). It delivered a pulse train with energy up to 180 mJ and pulse duration of 10.7 ns. The near-field pattern demonstrated a nearly super Gaussian flat top profile. In the amplification stage, the pulse was boosted via double-pass two Nd:YAG rod amplifiers. Maximum pulse energy was obtained at the peak pump power of 37.5 kW, corresponding to an optical-optical conversion efficiency of 25.2%. The correlative peak power was deduced to be 251 MW. We also presented the result of 100 Hz nanosecond laser with average output power of >100 W.

Measurement and compensation schemes for the pulse front distortion of ultra-intensity ultra-short laser pulses

NASA Astrophysics Data System (ADS)

Wu, Fenxiang; Xu, Yi; Yu, Linpeng; Yang, Xiaojun; Li, Wenkai; Lu, Jun; Leng, Yuxin

2016-11-01

Pulse front distortion (PFD) is mainly induced by the chromatic aberration in femtosecond high-peak power laser systems, and it can temporally distort the pulse in the focus and therefore decrease the peak intensity. A novel measurement scheme is proposed to directly measure the PFD of ultra-intensity ultra-short laser pulses, which can work not only without any extra struggle for the desired reference pulse, but also largely reduce the size of the required optical elements in measurement. The measured PFD in an experimental 200TW/27fs laser system is in good agreement with the calculated result, which demonstrates the validity and feasibility of this method effectively. In addition, a simple compensation scheme based on the combination of concave lens and parabolic lens is also designed and proposed to correct the PFD. Based on the theoretical calculation, the PFD of above experimental laser system can almost be completely corrected by using this compensator with proper parameters.

Sub-50-as isolated extreme ultraviolet continua generated by 1.6-cycle near-infrared pulse combined with double optical gating scheme

NASA Astrophysics Data System (ADS)

Oguri, Katsuya; Mashiko, Hiroki; Ogawa, Tatsuya; Hanada, Yasutaka; Nakano, Hidetoshi; Gotoh, Hideki

2018-04-01

We demonstrate the generation of ultrabroad bandwidth attosecond continua extending to sub-50-as duration in the extreme ultraviolet (EUV) region based on a 1.6-cycle Ti:sapphire laser pulse. The combination of the amplitude gating scheme with a sub-two-cycle driver pulse and the double optical gating scheme achieves the continuum generation with a bandwidth of 70 eV at the full width at half maximum near the peak photon energy of 140 eV, which supports a Fourier-transform-limited pulse duration as short as 32 as. The carrier-envelope-phase (CEP) dependence of the attosecond continua shows a single-peak structure originating from the half-cycle cut-off at appropriate CEP values, which strongly indicates the generation of a single burst of an isolated attosecond pulse. Our approach suggests a possibility for isolated sub-50-as pulse generation in the EUV region by compensating for the intrinsic attosecond chirp with a Zr filter.

Evaluation of a 10 kV, 400 kA Si SGTO at High dI/dt

DTIC Science & Technology

2006-05-01

inspection and high-potting of each component module prior to pulsing. The complete unit was then switched in a low inductance RLC circuit to test...during triggering. A ring down RLC circuit (Fig. 3) was designed with minimum inductance to test for peak dI/dt of anode-cathode flowing current. A...single 860 µF capacitor was charged to a chosen high voltage, then the power supply was disconnected and the switch was triggered to rapidly

Nitride-based stacked laser diodes with a tunnel junction

NASA Astrophysics Data System (ADS)

Okawara, Satoru; Aoki, Yuta; Kuwabara, Masakazu; Takagi, Yasufumi; Maeda, Junya; Yoshida, Harumasa

2018-01-01

We report on nitride-based two-stack laser diodes with a tunnel junction for the first time. The stacked laser diode was monolithically grown by metalorganic vapor phase epitaxy. It was confirmed that the two-stack InGaN/GaN multiple-quantum-well laser diode with an emission wavelength of 394 nm exhibited laser oscillation up to a peak output power of over 10 W in the pulsed current mode. The upper and lower emitters of the device were capable of lasing at different threshold currents of 2.4 and 5.2 A with different slope efficiencies of 0.8 and 0.3 W/A, respectively.

Aggregation effect on absorbance spectrum of laser ablated gold nanoparticles

NASA Astrophysics Data System (ADS)

Isnaeni; Irmaniar; Herbani, Y.

2017-04-01

Plasmon of gold nanoparticles is one of the hot topics nowadays due to various possible applications. The application is determined by plasmon peak in absorbance spectrum. We have fabricated gold nanoparticles using laser ablation technique and studied the influence of CTAB (Cetyl trimethylammonium bromide) effect on the optical characterization of fabricated gold nanoparticles. We ablated a gold plate using NdYAG pulsed laser at 1064 nm wavelength, 10 Hz pulse frequency at low energy density. We found there are two distinctive plasmon peaks, i.e., primary and secondary peaks, where the secondary peak is the main interests of this work. Our simulation results have revealed that the secondary plasmon peak is affected by random aggregation of gold nanoparticles. Our research leads to good techniques on fabrication of colloidal gold nanoparticles in aqueous solution using laser ablation technique.

A remote and non-contact method for obtaining the blood-pulse waveform with a laser Doppler vibrometer

NASA Astrophysics Data System (ADS)

Desjardins, Candida L.; Antonelli, Lynn T.; Soares, Edward

2007-02-01

The use of lasers to remotely and non-invasively detect the blood pressure waveform of humans and animals would provide a powerful diagnostic tool. Current blood pressure measurement tools, such as a cuff, are not useful for burn and trauma victims, and animals require catheterization to acquire accurate blood pressure information. The purpose of our sensor method and apparatus invention is to remotely and non-invasively detect the blood pulse waveform of both animals and humans. This device is used to monitor an animal or human's skin in proximity to an artery using radiation from a laser Doppler vibrometer (LDV). This system measures the velocity (or displacement) of the pulsatile motion of the skin, indicative of physiological parameters of the arterial motion in relation to the cardiac cycle. Tests have been conducted that measures surface velocity with an LDV and a signal-processing unit, with enhanced detection obtained with optional hardware including a retro-reflector dot. The blood pulse waveform is obtained by integrating the velocity signal to get surface displacement using standard signal processing techniques. Continuous recording of the blood pulse waveform yields data containing information on cardiac health and can be analyzed to identify important events in the cardiac cycle, such as heart rate, the timing of peak systole, left ventricular ejection time and aortic valve closure. Experimental results are provided that demonstrates the current capabilities of the optical, non-contact sensor for the continuous, non-contact recording of the blood pulse waveform without causing patient distress.

Short-lived solar burst spectral component at f approximately 100 GHz

NASA Technical Reports Server (NTRS)

Kaufmann, P.; Correia, E.; Costa, J. E. R.; Vaz, A. M. Z.

1986-01-01

A new kind of burst emission component was discovered, exhibiting fast and distinct pulses (approx. 60 ms durations), with spectral peak emission at f approx. 100 GHz, and onset time coincident to hard X-rays to within approx. 128 ms. These features pose serious constraints for the interpretation using current models. One suggestion assumes the f approx. 100 GHz pulses emission by synchrotron mechanism of electrons accelerated to ultrarelativistic energies. The hard X-rays originate from inverse Compton scattering of the electrons on the synchrotron photons. Several crucial observational tests are needed for the understanding of the phenomenon, requiring high sensitivity and high time resolution (approx. 1 ms) simultaneous to high spatial resolution (0.1 arcsec) at f approx. 110 GHz and hard X-rays.

In0.15Ga0.85N visible-light metal-semiconductor-metal photodetector with GaN interlayers deposited by pulsed NH3

NASA Astrophysics Data System (ADS)

Wang, Hongxia; Zhang, Xiaohan; Wang, Hailong; Lv, Zesheng; Li, Yongxian; Li, Bin; Yan, Huan; Qiu, Xinjia; Jiang, Hao

2018-05-01

InGaN visible-light metal-semiconductor-metal photodetectors with GaN interlayers deposited by pulsed NH3 were fabricated and characterized. By periodically inserting the GaN thin interlayers, the surface morphology of InGaN active layer is improved and the phase separation is suppressed. At 5 V bias, the dark current reduced from 7.0 × 10-11 A to 7.0 × 10-13 A by inserting the interlayers. A peak responsivity of 85.0 mA/W was measured at 420 nm and 5 V bias, corresponding to an external quantum efficiency of 25.1%. The insertion of GaN interlayers also lead to a sharper spectral response cutoff.

The study towards high intensity high charge state laser ion sources.

PubMed

Zhao, H Y; Jin, Q Y; Sha, S; Zhang, J J; Li, Z M; Liu, W; Sun, L T; Zhang, X Z; Zhao, H W

2014-02-01

As one of the candidate ion sources for a planned project, the High Intensity heavy-ion Accelerator Facility, a laser ion source has been being intensively studied at the Institute of Modern Physics in the past two years. The charge state distributions of ions produced by irradiating a pulsed 3 J/8 ns Nd:YAG laser on solid targets of a wide range of elements (C, Al, Ti, Ni, Ag, Ta, and Pb) were measured with an electrostatic ion analyzer spectrometer, which indicates that highly charged ions could be generated from low-to-medium mass elements with the present laser system, while the charge state distributions for high mass elements were relatively low. The shot-to-shot stability of ion pulses was monitored with a Faraday cup for carbon target. The fluctuations within ±2.5% for the peak current and total charge and ±6% for pulse duration were demonstrated with the present setup of the laser ion source, the suppression of which is still possible.

Diffraction based Hanbury Brown and Twiss interferometry at a hard x-ray free-electron laser

DOE PAGES

Gorobtsov, O. Yu.; Mukharamova, N.; Lazarev, S.; ...

2018-02-02

X-ray free-electron lasers (XFELs) provide extremely bright and highly spatially coherent x-ray radiation with femtosecond pulse duration. Currently, they are widely used in biology and material science. Knowledge of the XFEL statistical properties during an experiment may be vitally important for the accurate interpretation of the results. Here, for the first time, we demonstrate Hanbury Brown and Twiss (HBT) interferometry performed in diffraction mode at an XFEL source. It allowed us to determine the XFEL statistical properties directly from the Bragg peaks originating from colloidal crystals. This approach is different from the traditional one when HBT interferometry is performed inmore » the direct beam without a sample. Our analysis has demonstrated nearly full (80%) global spatial coherence of the XFEL pulses and an average pulse duration on the order of ten femtoseconds for the monochromatized beam, which is significantly shorter than expected from the electron bunch measurements.« less

Pulsed Plasma Thruster Contamination

NASA Technical Reports Server (NTRS)

Myers, Roger M.; Arrington, Lynn A.; Pencil, Eric J.; Carter, Justin; Heminger, Jason; Gatsonis, Nicolas

1996-01-01

Pulsed Plasma Thrusters (PPT's) are currently baselined for the Air Force Mightysat II.1 flight in 1999 and are under consideration for a number of other missions for primary propulsion, precision positioning, and attitude control functions. In this work, PPT plumes were characterized to assess their contamination characteristics. Diagnostics included planar and cylindrical Langmuir probes and a large number of collimated quartz contamination sensors. Measurements were made using a LES 8/9 flight PPT at 0.24, 0.39, 0.55, and 1.2 m from the thruster, as well as in the backflow region behind the thruster. Plasma measurements revealed a peak centerline ion density and velocity of approx. 6 x 10(exp 12) cm(exp -3) and 42,000 m/s, respectively. Optical transmittance measurements of the quartz sensors after 2 x 10(exp 5) pulses showed a rapid decrease in plume contamination with increasing angle from the plume axis, with a barely measurable transmittance decrease in the ultraviolet at 90 deg. No change in optical properties was detected for sensors in the backflow region.

Diffraction based Hanbury Brown and Twiss interferometry at a hard x-ray free-electron laser

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

Gorobtsov, O. Yu.; Mukharamova, N.; Lazarev, S.

X-ray free-electron lasers (XFELs) provide extremely bright and highly spatially coherent x-ray radiation with femtosecond pulse duration. Currently, they are widely used in biology and material science. Knowledge of the XFEL statistical properties during an experiment may be vitally important for the accurate interpretation of the results. Here, for the first time, we demonstrate Hanbury Brown and Twiss (HBT) interferometry performed in diffraction mode at an XFEL source. It allowed us to determine the XFEL statistical properties directly from the Bragg peaks originating from colloidal crystals. This approach is different from the traditional one when HBT interferometry is performed inmore » the direct beam without a sample. Our analysis has demonstrated nearly full (80%) global spatial coherence of the XFEL pulses and an average pulse duration on the order of ten femtoseconds for the monochromatized beam, which is significantly shorter than expected from the electron bunch measurements.« less

Neutronics and Transient Calculations for the Conversion of the Transient Reactor Rest Facility (TREAT)

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

Kontogeorgakos, Dimitrios C.; Connaway, Heather M.; Papadias, Dionissios D.

2015-01-01

The Transient Reactor Test Facility (TREAT) is a graphite-reflected, graphitemoderated, and air-cooled reactor fueled with 93.1% enriched UO2 particles dispersed in graphite, with a carbon-to-235U ratio of ~10000:1. TREAT was used to simulate accident conditions by subjecting fuel test samples placed at the center of the core to high energy transient pulses. The transient pulse production is based on the core’s selflimiting nature due to the negative reactivity feedback provided by the fuel graphite as the core temperature rises. The analysis of the conversion of TREAT to low enriched uranium (LEU) is currently underway. This paper presents the analytical methodsmore » used to calculate the transient performance of TREAT in terms of power pulse production and resulting peak core temperatures. The validation of the HEU neutronics TREAT model, the calculation of the temperature distribution and the temperature reactivity feedback as well as the number of fissions generated inside fuel test samples are discussed.« less

Schlieren, Phase-Contrast, and Spectroscopy Diagnostics for the LBNL HIF Plasma Channel Experiment

NASA Astrophysics Data System (ADS)

Ponce, D. M.; Niemann, C.; Fessenden, T. J.; Leemans, W.; Vandersloot, K.; Dahlbacka, G.; Yu, S. S.; Sharp, W. M.; Tauschwitz, A.

1999-11-01

The LBNL Plasma Channel experiment has demonstrated stable 42-cm Z-pinch discharge plasma channels with peak currents in excess of 50 kA for a 7 torr nitrogen, 30 kV discharge. These channels offer the possibility of transporting heavy-ion beams for inertial fusion. We postulate that the stability of these channels resides in the existance of a neutral-gas density depresion created by a pre-pulse discharge before the main capacitor bank discharge is created. Here, we present the results and experimental diagnostics setup used for the study of the pre-pulse and main bank channels. Observation of both the plasma and neutral gas dynamics is achieved. Schlieren, Zernike's phase-contrast, and spectroscopic techniques are used. Preliminary Schlieren results show a gas shockwave moving radially at a rate of ≈ 10^6 mm/sec as a result of the fast and localized deposited energy during the evolution of the pre-pulse channel. This data will be used to validate simulation codes (BUCKY and CYCLOPS).

Compact and efficient 2μm Tm:YAP lasers with mechanical or passive Q-switching

NASA Astrophysics Data System (ADS)

Cole, Brian; Goldberg, Lew

2017-02-01

We describe compact and efficient Q-switched diode-pumped, Tm:YAP lasers operating at 1.94μm. Laser CW and Q-switched performance is compared, using both compact mechanical as well as passive Q-switching. For passive Q-switching using a Cr:ZnS saturable absorber (unsaturated transmission of 95%), the laser produced 0.5mJ pulses with an average power of 4.4W and 6.5kW peak power, and had an optical efficiency of 30%. A resonant mirror mechanical Q-switch resulted in a 4 kHz PRF pulse train, with an optical slope efficiency of 52% and an optical-to-optical conversion efficiency of 41%. The laser generated 1.5 mJ, 45 ns FWHM, 33kW peak power pulses, and 6.2W of average output. A second mechanically Q-switched laser operating at 10 kHz PRF produced 1mJ, 35kW peak power pulses, generating 11W average power with an optical efficiency of 46%, and a beam quality of 1.4x diffraction limit.

Distinguishing synchronous and time-varying synergies using point process interval statistics: motor primitives in frog and rat

PubMed Central

Hart, Corey B.; Giszter, Simon F.

2013-01-01

We present and apply a method that uses point process statistics to discriminate the forms of synergies in motor pattern data, prior to explicit synergy extraction. The method uses electromyogram (EMG) pulse peak timing or onset timing. Peak timing is preferable in complex patterns where pulse onsets may be overlapping. An interval statistic derived from the point processes of EMG peak timings distinguishes time-varying synergies from synchronous synergies (SS). Model data shows that the statistic is robust for most conditions. Its application to both frog hindlimb EMG and rat locomotion hindlimb EMG show data from these preparations is clearly most consistent with synchronous synergy models (p < 0.001). Additional direct tests of pulse and interval relations in frog data further bolster the support for synchronous synergy mechanisms in these data. Our method and analyses support separated control of rhythm and pattern of motor primitives, with the low level execution primitives comprising pulsed SS in both frog and rat, and both episodic and rhythmic behaviors. PMID:23675341

Imaging feedback for histotripsy by characterizing dynamics of acoustic radiation force impulse (ARFI)-induced shear waves excited in a treated volume.

PubMed

Wang, Tzu-Yin; Hall, Timothy L; Xu, Zhen; Fowlkes, J Brian; Cain, Charles A

2014-07-01

Our previous study indicated that shear waves decay and propagate at a lower speed as they propagate into a tissue volume mechanically fractionated by histotripsy. In this paper, we hypothesize that the change in the shear dynamics is related to the degree of tissue fractionation, and can be used to predict histotripsy treatment outcomes. To test this hypothesis, lesions with different degrees of tissue fractionation were created in agar-graphite tissue phantoms and ex vivo kidneys with increasing numbers of therapy pulses, from 0 to 2000 pulses per treatment location. The therapy pulses were 3-cycle 750-kHz focused ultrasound delivered at a peak negative/positive pressure of 17/108 MPa and a repetition rate of 50 Hz. The shear waves were excited by acoustic radiation force impulse (ARFI) focused at the center of the lesion. The spatial and temporal behavior of the propagating shear waves was measured with ultrasound plane wave imaging. The temporal displacement profile at a lateral location 10 mm offset to the shear excitation region was detected with M-mode imaging. The decay and delay of the shear waves were quantitatively characterized on the temporal displacement profile. Results showed significant changes in two characteristics on the temporal displacement profile: the peak-to-peak displacement decayed exponentially with increasing numbers of therapy pulses; the relative time-to-peak displacement increased with increasing numbers of therapy pulses, and appeared to saturate at higher numbers of pulses. Correspondingly, the degree of tissues fractionation, as indicated by the percentage of structurally intact cell nuclei, decreased exponentially with increasing numbers of therapy pulses. Strong linear correlations were found between the two characteristics and the degree of tissue fractionation. These results suggest that the characteristics of the shear temporal displacement profile may provide useful feedback information regarding the treatment outcomes.

GaSb-based VECSEL for high-power applications and Ho-pumping

NASA Astrophysics Data System (ADS)

Holl, P.; Rattunde, M.; Adler, S.; Scholle, K.; Lamrini, S.; Fuhrberg, P.; Diwo-Emmer, E.; Aidam, R.; Bronner, W.; Wagner, J.

2017-02-01

The (AlGaIn)(AsSb) material system has been shown to be ideally suited to realize VECSELs for the 2-3 μm wavelength range. In this report we will present results on increasing the output power of the SDL chips with special emphasis on the 2.8 μm emission wavelength by means of low quantum defect pumping. Further on we have investigated concepts for a VECSEL-pumped Q-switched Ho:YAG laser in order to convert the high cw-power of the VECSEL into pulses with a high peak power. Up to 3.3 mJ of pulse energy were achieved with a compact setup (corresponding to a peak power of 30 kW at 110 ns pulse length) combined with stable pulsing behavior.

Investigation of Spectral Lag and Epeak as Joint Luminosity Indicators in GRBs

NASA Technical Reports Server (NTRS)

White, Nicholas E. (Technical Monitor); Norris, Jay P.

2003-01-01

Models for gamma-ray bursts which invoke jetted, colliding shells would appear to have at least two determinants for luminosity, e.g., observer viewing angle and Lorentz factor, or possibly shell mass. The latter two internal physical parameters may vary from pulse to pulse within a burst, and such variation might be reflected in evolution of observables such as spectral lag and peak in the spectral energy distribution. We analyze bright BATSE bursts using the 16-channel medium energy resolution (MER) data, with time resolutions of 16 and 64 ms, measuring spectral lags and peak energies for significant pulse structures within a burst, identified using a Bayesian block algorithm. We then explore correlations between the measured parameters and total flux for the individual pulse structures.

An all-solid-state CO2 laser driver

NASA Astrophysics Data System (ADS)

Birx, Daniel

1991-03-01

New, all-solid-state pulse generators are described which meet military requirements for an efficient, reliable pulsed power source to drive a space based CO2 laser. These SCR-commutated, nonlinear magnetic pulse compressors are fully-compatible with the present Spectra Technologies laser head design planned for use on LOWKATER. By employing SCRs rather than thyratron commutators, these pulsers should provide a significant increase in reliability over the current generation of pulsed power drivers. The first pulser which was designed and constructed was denoted COLD-I. COLD-I was designed to meet the original LOWKATER specifications and delivered at 150 joule, 20 kV pulse into a laser load at 10 to 20 Hz repetition rate. The second pulser, denoted COLD-II, was designed to provide a 45 joule, 500 nsec duration pulse at a voltage of 20 kV and a repetition rate of 1 kHz peak and 50 to 100 Hz average. The electrical efficiency was measured to be 80 percent with an input drive of 500 VDC. This pulse served as a design verification testbed for a third pulser, presently designed but not constructed and denoted COLD-III. COLD-III would be capable of producing 36 joules at the same pulse length and repetition rate at voltages of 20 kV. The Phase-II effort was a high risk, high payoff effort aimed at developing a light weight, high reliability RF power source for advanced RF CO2 laser heads under development. COLD-IV a Branched Magnetic RF Nonlinear Magnetic Pulse Compressor was built as a bread

Experimental demonstration of fiber optical parametric chirped-pulse amplification

NASA Astrophysics Data System (ADS)

Zhou, Yue; Cheung, Kim K. Y.; Chui, P. C.; Wong, Kenneth K. Y.

2010-02-01

A fiber optical parametric chirped-pulse amplifier (FOPCPA) is experimentally demonstrated. A 1.76 ps signal at 1542 nm with a peak power of 20 mW is broadened to 40 ps, and then amplified by a 100-ps pulsed pump at 1560 nm. The corresponding idler at 1578 nm is generated as the FOPCPA output. The same medium used to stretch the signal is deployed to compress the idler to 3.8 ps, and another spool of fiber is deployed to further compress the idler to 1.87 ps. The peak power of the compressed idler is 2 W, which corresponds to a gain of 20 dB.

Supercontinuum optimization for dual-soliton based light sources using genetic algorithms in a grid platform.

PubMed

Arteaga-Sierra, F R; Milián, C; Torres-Gómez, I; Torres-Cisneros, M; Moltó, G; Ferrando, A

2014-09-22

We present a numerical strategy to design fiber based dual pulse light sources exhibiting two predefined spectral peaks in the anomalous group velocity dispersion regime. The frequency conversion is based on the soliton fission and soliton self-frequency shift occurring during supercontinuum generation. The optimization process is carried out by a genetic algorithm that provides the optimum input pulse parameters: wavelength, temporal width and peak power. This algorithm is implemented in a Grid platform in order to take advantage of distributed computing. These results are useful for optical coherence tomography applications where bell-shaped pulses located in the second near-infrared window are needed.

Practical continuous-variable quantum key distribution without finite sampling bandwidth effects.

PubMed

Li, Huasheng; Wang, Chao; Huang, Peng; Huang, Duan; Wang, Tao; Zeng, Guihua

2016-09-05

In a practical continuous-variable quantum key distribution system, finite sampling bandwidth of the employed analog-to-digital converter at the receiver's side may lead to inaccurate results of pulse peak sampling. Then, errors in the parameters estimation resulted. Subsequently, the system performance decreases and security loopholes are exposed to eavesdroppers. In this paper, we propose a novel data acquisition scheme which consists of two parts, i.e., a dynamic delay adjusting module and a statistical power feedback-control algorithm. The proposed scheme may improve dramatically the data acquisition precision of pulse peak sampling and remove the finite sampling bandwidth effects. Moreover, the optimal peak sampling position of a pulse signal can be dynamically calibrated through monitoring the change of the statistical power of the sampled data in the proposed scheme. This helps to resist against some practical attacks, such as the well-known local oscillator calibration attack.

Selective and sensitive determination of uric acid in the presence of ascorbic acid and dopamine by PDDA functionalized graphene/graphite composite electrode.

PubMed

Yu, Yanyan; Chen, Zuanguang; Zhang, Beibei; Li, Xinchun; Pan, Jianbin

2013-08-15

In this work, a facile electrochemical sensor based on poly(diallyldimethylammonium chloride) (PDDA) functionalized graphene (PDDA-G) and graphite was fabricated. The composite electrode exhibited excellent selectivity and sensitivity towards uric acid (UA), owing to the electrocatalytic effect of graphene nanosheets and the electrostatic attractions between PDDA-G and UA. The anodic peak current of UA obtained by cyclic voltammetry (CV) increased over 10-fold compared with bare carbon paste electrode (CPE). And the reversibility of the oxidation process was improved significantly. Differential pulse voltammetry (DPV) was used to determine UA in the presence of ascorbic acid (AA) and dopamine (DA). It was found that all of oxidation peaks of three species could be well resolved, and the peak current of UA was much stronger than the other two components. More importantly, considerable-amount of AA and DA showed negligible interference to UA assay. The calibration curve for UA ranged from 0.5 to 20 μmol L(-1) with a correlation coefficient of 0.9934. The constructed sensor has been employed to quantitatively determine UA in urine samples. Copyright © 2013 Elsevier B.V. All rights reserved.

Diagnostics of an AC driven atmospheric pressure non-thermal plasma jet and its use for radially directed jet array

NASA Astrophysics Data System (ADS)

Zhu, W.; Wang, R.

2017-08-01

An alternating current atmospheric pressure plasma jet is generated with noble gas or noble gas/oxygen admixture as working gas. A "core plasma filament" is observed at the center of the dielectric tube and extends to the plasma jet at higher peak-to-peak voltages. This type of plasma jet is believed to be of the same nature with the reported plasma bullet driven by pulsed DC power sources. Double current probes are used to assess the speed of the plasma bullet and show that the speed is around 104-105 m/s. The time dependence of the downstream bullet speed is attributed to the gas heating and in turn the increase of the reduced electric field E/N. Optical emission spectra show the dependence of helium and oxygen emission intensities on the concentration of oxygen additive in the carrier gas, with peak values found at 0.5% O2. Multiple radial jets are realized on dielectric tubes of different sizes. As a case study, one of these multi-jet devices is used to treat B. aureus on the inner surface of a plastic beaker and is shown to be more effective than a single jet.

Characterization of pulsed flow attenuation on a regulated montane river

NASA Astrophysics Data System (ADS)

Fong, C. S.; Yarnell, S. M.; Fleenor, W. E.; Viers, J. H.

2013-12-01

A major benefit of hydropower is its ability to respond quickly to fluctuating electrical loads. However, the sharp changes in discharge caused by this practice have detrimental environmental effects downstream. This study investigated the effects of hydrograph shape on attenuation of regulated pulsed flow events by first categorizing, then modeling the downstream movement of representative pulses on the upper Tuolumne River below Holm Powerhouse in the Sierra Nevada mountains of California. This system was managed by a public utility and produced flow pulses primarily for hydroelectricity generation and/or whitewater recreation. Operations were highly influenced by a system-wide "Water First" policy, which prioritized drinking water supply and quality over other beneficial uses. Pulses were therefore associated with a spectrum of time scales, from predetermined schedules decided far in advance to hydropeaking operations responding to real-time demands. We extracted underlying hydrograph shape patterns using principal component analysis on individual pulsed flow events released from 1988-2012 (n=4439). From principal component loadings, six shape categories were determined: rectangular, front-step, back-step, goalpost, centered tower, and other. The rectangular and stepped shapes were the most frequent, composing 62% and 24% of total events, respectively. The rectangular shape was often produced by 'standard' hydropeaking or recreational releases, while the stepped shapes were often used for water conservation or were recreational flows bordered by periods of electricity generation. The stepped shape increased in occurrence after the "Water First" policy took effect in 1993 and dominated two drier years (2007 and 2009). After categorization by shape, magnitude and durational indices were used to fabricate representative pulsed flow events. Attenuation of these representative pulses was then modeled using a 1D hydraulic model of 42 river km prepared in HEC-RAS. As no operational measures or physical structures existed within the system to counter the adverse effects of pulsed flow events, natural attenuation was the only potential major mitigation agent. However, model results demonstrated a clear durational threshold for representative pulses (~ 3-5 hrs) over which the degree of attenuation of ramping rates and peak discharge approached a limit. These thresholds were unique to the study reach and were dependent upon river morphology, bed characteristics, and flow rates. Increasing baseflows did not necessarily increase attenuation of pulses, most likely due to minimal increases in bed friction forces in this fairly steep and confined channel. Simulations of front and back-step representative pulses showed trade-offs between attenuation of peak magnitudes and steepness of ramping rates. Finally, a range of rising ramping rates were shown to steepen downstream above initial rates due to the study reach's channel morphology. Reshaping pulses to be more ecologically benign at all points downstream was infeasible if the system was required to maintain current electricity production and recreational service levels.

Influence of different approaches for dynamical performance optimization of monolithic passive colliding-pulse mode-locked laser diodes emitting around 850 nm

NASA Astrophysics Data System (ADS)

Prziwarka, T.; Klehr, A.; Wenzel, H.; Fricke, J.; Bugge, F.; Weyers, M.; Knigge, A.; Tränkle, G.

2018-02-01

Monolithic laser diodes which generate short infrared pulses in the picosecond and sub-picosecond ranges with high peak power are ideal sources for many applications like e.g. THz-time-domain spectroscopy (TDS) scanning systems. The achievable THz bandwidth is limited by the length of the optical pulses. Due to the fact that colliding-pulse mode locking (CPM) leads to the shortest pulses which could reached by passive mode locking, we experimentally investigated in detail the dynamical and electro optical performance of InGaAsP based quantum well CPM laser diodes with well-established vertical layer structures. Simple design modifications whose implementation is technically easy were realized. Improvements of the device performance in terms of pulse duration, output power, and noise properties are presented in dependence on the different adaptions. From the results we extract an optimized configuration with which we have reached pulses with durations of ≍1.5 ps, a peak power of > 1 W and a pulse-to-pulse timing jitter < 200 fs. The laser diodes emit pulses at a wavelength around 850 nm with a repetition frequency of ≍ 12.4 GHz and could be used as pump source for GaAs antennas to generate THz-radiation. Approaches for reducing pulse width, increasing output power, and improving noise performance are described.

Acoustic pressure waves induced in human heads by RF pulses from high-field MRI scanners.

PubMed

Lin, James C; Wang, Zhangwei

2010-04-01

The current evolution toward greater image resolution from magnetic resonance image (MRI) scanners has prompted the exploration of higher strength magnetic fields and use of higher levels of radio frequencies (RFs). Auditory perception of RF pulses by humans has been reported during MRI with head coils. It has shown that the mechanism of interaction for the auditory effect is caused by an RF pulse-induced thermoelastic pressure wave inside the head. We report a computational study of the intensity and frequency of thermoelastic pressure waves generated by RF pulses in the human head inside high-field MRI and clinical scanners. The U.S. Food and Drug Administration (U.S. FDA) guides limit the local specific absorption rate (SAR) in the body-including the head-to 8 W kg(-1). We present results as functions of SAR and show that for a given SAR the peak acoustic pressures generated in the anatomic head model were essentially the same at 64, 300, and 400 MHz (1.5, 7.0, and 9.4 T). Pressures generated in the anatomic head are comparable to the threshold pressure of 20 mPa for sound perception by humans at the cochlea for 4 W kg(-1). Moreover, results indicate that the peak acoustic pressure in the brain is only 2 to 3 times the auditory threshold at the U.S. FDA guideline of 8 W kg(-1). Even at a high SAR of 20 W kg(-1), where the acoustic pressure in the brain could be more than 7 times the auditory threshold, the sound pressure levels would not be more than 17 db above threshold of perception at the cochlea.

Superharmonic microbubble Doppler effect in ultrasound therapy

NASA Astrophysics Data System (ADS)

Pouliopoulos, Antonios N.; Choi, James J.

2016-08-01

The introduction of microbubbles in focused ultrasound therapies has enabled a diverse range of non-invasive technologies: sonoporation to deliver drugs into cells, sonothrombolysis to dissolve blood clots, and blood-brain barrier opening to deliver drugs into the brain. Current methods for passively monitoring the microbubble dynamics responsible for these therapeutic effects can identify the cavitation position by passive acoustic mapping and cavitation mode by spectral analysis. Here, we introduce a new feature that can be monitored: microbubble effective velocity. Previous studies have shown that echoes from short imaging pulses had a Doppler shift that was produced by the movement of microbubbles. Therapeutic pulses are longer (>1 000 cycles) and thus produce a larger alteration of microbubble distribution due to primary and secondary acoustic radiation force effects which cannot be monitored using pulse-echo techniques. In our experiments, we captured and analyzed the Doppler shift during long therapeutic pulses using a passive cavitation detector. A population of microbubbles (5  ×  104-5  ×  107 microbubbles ml-1) was embedded in a vessel (inner diameter: 4 mm) and sonicated using a 0.5 MHz focused ultrasound transducer (peak-rarefactional pressure: 75-366 kPa, pulse length: 50 000 cycles or 100 ms) within a water tank. Microbubble acoustic emissions were captured with a coaxially aligned 7.5 MHz passive cavitation detector and spectrally analyzed to measure the Doppler shift for multiple harmonics above the 10th harmonic (i.e. superharmonics). A Doppler shift was observed on the order of tens of kHz with respect to the primary superharmonic peak and is due to the axial movement of the microbubbles. The position, amplitude and width of the Doppler peaks depended on the acoustic pressure and the microbubble concentration. Higher pressures increased the effective velocity of the microbubbles up to 3 m s-1, prior to the onset of broadband emissions, which is an indicator for high magnitude inertial cavitation. Although the microbubble redistribution was shown to persist for the entire sonication period in dense populations, it was constrained to the first few milliseconds in lower concentrations. In conclusion, superharmonic microbubble Doppler effects can provide a quantitative measure of effective velocities of a sonicated microbubble population and could be used for monitoring ultrasound therapy in real-time.

Superharmonic microbubble Doppler effect in ultrasound therapy

PubMed Central

Pouliopoulos, Antonios N; Choi, James J

2016-01-01

Abstract The introduction of microbubbles in focused ultrasound therapies has enabled a diverse range of non-invasive technologies: sonoporation to deliver drugs into cells, sonothrombolysis to dissolve blood clots, and blood-brain barrier opening to deliver drugs into the brain. Current methods for passively monitoring the microbubble dynamics responsible for these therapeutic effects can identify the cavitation position by passive acoustic mapping and cavitation mode by spectral analysis. Here, we introduce a new feature that can be monitored: microbubble effective velocity. Previous studies have shown that echoes from short imaging pulses had a Doppler shift that was produced by the movement of microbubbles. Therapeutic pulses are longer (>1 000 cycles) and thus produce a larger alteration of microbubble distribution due to primary and secondary acoustic radiation force effects which cannot be monitored using pulse-echo techniques. In our experiments, we captured and analyzed the Doppler shift during long therapeutic pulses using a passive cavitation detector. A population of microbubbles (5  ×  104–5  ×  107 microbubbles ml−1) was embedded in a vessel (inner diameter: 4 mm) and sonicated using a 0.5 MHz focused ultrasound transducer (peak-rarefactional pressure: 75–366 kPa, pulse length: 50 000 cycles or 100 ms) within a water tank. Microbubble acoustic emissions were captured with a coaxially aligned 7.5 MHz passive cavitation detector and spectrally analyzed to measure the Doppler shift for multiple harmonics above the 10th harmonic (i.e. superharmonics). A Doppler shift was observed on the order of tens of kHz with respect to the primary superharmonic peak and is due to the axial movement of the microbubbles. The position, amplitude and width of the Doppler peaks depended on the acoustic pressure and the microbubble concentration. Higher pressures increased the effective velocity of the microbubbles up to 3 m s−1, prior to the onset of broadband emissions, which is an indicator for high magnitude inertial cavitation. Although the microbubble redistribution was shown to persist for the entire sonication period in dense populations, it was constrained to the first few milliseconds in lower concentrations. In conclusion, superharmonic microbubble Doppler effects can provide a quantitative measure of effective velocities of a sonicated microbubble population and could be used for monitoring ultrasound therapy in real-time. PMID:27469394

Ps laser pulse induced stimulated Raman scattering of ammonium nitrate dissolved in water

NASA Astrophysics Data System (ADS)

Kumar, V. Rakesh; Kiran, P. Prem

2018-04-01

An intense picosecond laser pulse focused into a liquid medium generates a shock wave in the focal region. This shock wave while propagating into the medium varies the pressure and temperature of the liquid locally leading to the appearance of novel phases which are manifested by the appearance of Raman peaks. We present the phase changes of ammonium nitrate (AN) dissolved in water by studying the forward and backward stimulated Raman Scattering (FSRS and BSRS) signals due to propagation of 30 ps laser pulse induced shockwaves. The dominant peak corresponding to the NO3- symmetric stretching mode is observed with a Raman shift of 1045 cm-1 which represents phase IV of AN with an orthogonal crystalline structure. Apart from this peak, the dominant mode of liquid phase of water with a Raman shift of 3400 cm-1 and an ice VII peak at a Raman shift of 3050 cm-1 confirming the pressure of 10 GPa is observed. The effect of the concentration and input energy on the appearance of the phases will be presented.

Thermoacoustic range verification using a clinical ultrasound array provides perfectly co-registered overlay of the Bragg peak onto an ultrasound image

NASA Astrophysics Data System (ADS)

Patch, S. K.; Kireeff Covo, M.; Jackson, A.; Qadadha, Y. M.; Campbell, K. S.; Albright, R. A.; Bloemhard, P.; Donoghue, A. P.; Siero, C. R.; Gimpel, T. L.; Small, S. M.; Ninemire, B. F.; Johnson, M. B.; Phair, L.

2016-08-01

The potential of particle therapy due to focused dose deposition in the Bragg peak has not yet been fully realized due to inaccuracies in range verification. The purpose of this work was to correlate the Bragg peak location with target structure, by overlaying the location of the Bragg peak onto a standard ultrasound image. Pulsed delivery of 50 MeV protons was accomplished by a fast chopper installed between the ion source and the cyclotron inflector. The chopper limited the train of bunches so that 2 Gy were delivered in 2 μ \\text{s} . The ion pulse generated thermoacoustic pulses that were detected by a cardiac ultrasound array, which also produced a grayscale ultrasound image. A filtered backprojection algorithm focused the received signal to the Bragg peak location with perfect co-registration to the ultrasound images. Data was collected in a room temperature water bath and gelatin phantom with a cavity designed to mimic the intestine, in which gas pockets can displace the Bragg peak. Phantom experiments performed with the cavity both empty and filled with olive oil confirmed that displacement of the Bragg peak due to anatomical change could be detected. Thermoacoustic range measurements in the waterbath agreed with Monte Carlo simulation within 1.2 mm. In the phantom, thermoacoustic range estimates and first-order range estimates from CT images agreed to within 1.5 mm.

Pulsed laser-deposited VO2 thin films on Pt layers

NASA Astrophysics Data System (ADS)

Sakai, Joe; Zaghrioui, Mustapha; Ta Phuoc, Vinh; Roger, Sylvain; Autret-Lambert, Cécile; Okimura, Kunio

2013-03-01

VO2 films were deposited on Pt (111)/TiO2/SiO2/Si (001) substrates by means of a pulsed laser deposition technique. An x-ray diffraction peak at 2θ = 39.9° was deconvoluted into two pseudo-Voigt profiles of Pt (111) and VOx-originated components. The VOx diffraction peak was more obvious in a VOx/Pt (111)/Al2O3 (0001) sample, having a narrower width compared with a VO2/Al2O3 (0001) sample. Temperature-controlled Raman spectroscopy for the VOx/Pt/TiO2/SiO2/Si sample has revealed the monoclinic VO2 phase at low temperature and the structural phase transition at about 72 °C in a heating process. The electronic conductive nature at the high temperature phase was confirmed by near normal incidence infrared reflectivity measurements. Out-of-plane current-voltage characteristics showed an electric field-induced resistance switching at a voltage as low as 0.2 V for a 50 nm-thick film. A survey of present and previous results suggests an experimental law that the transition voltage of VO2 is proportional to the square root of the electrodes distance.

Attosecond Pulse Carrier-Envelope Phase Effects: Roles of Frequency, Intensity and an Additional IR Pulse

NASA Astrophysics Data System (ADS)

Pronin, Evgeny A.; Peng, Liang-You; Starace, Anthony F.

2008-05-01

The effects of the carrier-envelope phase (CEP) of a few-cycle attosecond pulse on ionized electron momentum and energy spectra are analyzed, both with and without an additional few-cycle IR pulse [1, 2]. In the absence of an IR pulse, the CEP-induced asymmetries in the ionized electron momentum distributions are shown to vary as the 3/2 power of the attosecond pulse intensity. These asymmetries are also found to satisfy an approximate scaling law involving the frequency and intensity of the attosecond pulse. In the presence of even a very weak IR pulse, the attosecond pulse CEP-induced asymmetries are found to be significantly augmented. In addition, for higher IR laser intensities, we observe for low electron energies peaks separated by the IR photon energy in one electron momentum direction along the laser polarization axis; in the opposite direction, we find structured peaks that are spaced by twice the IR photon energy. Possible physical mechanisms for such asymmetric, low-energy structures in the ionized electron momentum distribution are proposed. Our results are based on single-active-electron solutions of the 3D TDSE for H and He. [1] Peng LY, Pronin EA, and Starace AF, New J. Phys. 10, xxx (2008); [2] Peng LY, Starace AF, Phys. Rev. A 76, 043401 (2007)

Thermal modeling for pulsed radiofrequency ablation: analytical study based on hyperbolic heat conduction.

PubMed

López Molina, Juan A; Rivera, María J; Trujillo, Macarena; Berjano, Enrique J

2009-04-01

The objectives of this study were to model the temperature progress of a pulsed radiofrequency (RF) power during RF heating of biological tissue, and to employ the hyperbolic heat transfer equation (HHTE), which takes the thermal wave behavior into account, and compare the results to those obtained using the heat transfer equation based on Fourier theory (FHTE). A theoretical model was built based on an active spherical electrode completely embedded in the biological tissue, after which HHTE and FHTE were analytically solved. We found three typical waveforms for the temperature progress depending on the relations between the dimensionless duration of the RF pulse delta(a) and the expression square root of lambda(rho-1), with lambda as the dimensionless thermal relaxation time of the tissue and rho as the dimensionless position. In the case of a unique RF pulse, the temperature at any location was the result of the overlapping of two different heat sources delayed for a duration delta(a) (each heat source being produced by a RF pulse of limitless duration). The most remarkable feature in the HHTE analytical solution was the presence of temperature peaks traveling through the medium at a finite speed. These peaks not only occurred during the RF power switch-on period but also during switch off. Finally, a physical explanation for these temperature peaks is proposed based on the interaction of forward and reverse thermal waves. All-purpose analytical solutions for FHTE and HHTE were obtained during pulsed RF heating of biological tissues, which could be used for any value of pulsing frequency and duty cycle.

First images of thunder: Acoustic imaging of triggered lightning

NASA Astrophysics Data System (ADS)

Dayeh, M. A.; Evans, N. D.; Fuselier, S. A.; Trevino, J.; Ramaekers, J.; Dwyer, J. R.; Lucia, R.; Rassoul, H. K.; Kotovsky, D. A.; Jordan, D. M.; Uman, M. A.

2015-07-01

An acoustic camera comprising a linear microphone array is used to image the thunder signature of triggered lightning. Measurements were taken at the International Center for Lightning Research and Testing in Camp Blanding, FL, during the summer of 2014. The array was positioned in an end-fire orientation thus enabling the peak acoustic reception pattern to be steered vertically with a frequency-dependent spatial resolution. On 14 July 2014, a lightning event with nine return strokes was successfully triggered. We present the first acoustic images of individual return strokes at high frequencies (>1 kHz) and compare the acoustically inferred profile with optical images. We find (i) a strong correlation between the return stroke peak current and the radiated acoustic pressure and (ii) an acoustic signature from an M component current pulse with an unusual fast rise time. These results show that acoustic imaging enables clear identification and quantification of thunder sources as a function of lightning channel altitude.

Extension of filament propagation in water with Bessel-Gaussian beams

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

Kaya, G.; Sayrac, M.; Boran, Y.

We experimentally studied intense femtosecond pulse filamentation and propagation in water for Bessel-Gaussian beams with different numbers of radial modal lobes. The transverse modes of the incident Bessel-Gaussian beam were created from a Gaussian beam of a Ti:sapphire laser system by using computer generated hologram techniques. We found that filament propagation length increased with increasing number of lobes under the conditions of the same peak intensity, pulse duration, and the size of the central peak of the incident beam, suggesting that the radial modal lobes may serve as an energy reservoir for the filaments formed by the central intensity peak.

Industrial Applications of Pulsed Power Technology

NASA Astrophysics Data System (ADS)

Takaki, Koichi; Katsuki, Sunao

Recent progress of the industrial applications of pulsed power is reviewed in this paper. Repetitively operated pulsed power generators with a moderate peak power have been developed for industrial applications. These generators are reliable and low maintenance. Development of the pulsed power generators helps promote industrial applications of pulsed power for such things as food processing, medical treatment, water treatment, exhaust gas treatment, ozone generation, engine ignition, ion implantation and others. Here, industrial applications of pulsed power are classified by application for biological effects, for pulsed streamer discharges in gases, for pulsed discharges in liquid or liquid-mixture, and for bright radiation sources.

Attosecond control of electronic processes by intense light fields.

PubMed

Baltuska, A; Udem, Th; Uiberacker, M; Hentschel, M; Goulielmakis, E; Gohle, Ch; Holzwarth, R; Yakovlev, V S; Scrinzi, A; Hänsch, T W; Krausz, F

2003-02-06

The amplitude and frequency of laser light can be routinely measured and controlled on a femtosecond (10(-15) s) timescale. However, in pulses comprising just a few wave cycles, the amplitude envelope and carrier frequency are not sufficient to characterize and control laser radiation, because evolution of the light field is also influenced by a shift of the carrier wave with respect to the pulse peak. This so-called carrier-envelope phase has been predicted and observed to affect strong-field phenomena, but random shot-to-shot shifts have prevented the reproducible guiding of atomic processes using the electric field of light. Here we report the generation of intense, few-cycle laser pulses with a stable carrier envelope phase that permit the triggering and steering of microscopic motion with an ultimate precision limited only by quantum mechanical uncertainty. Using these reproducible light waveforms, we create light-induced atomic currents in ionized matter; the motion of the electronic wave packets can be controlled on timescales shorter than 250 attoseconds (250 x 10(-18) s). This enables us to control the attosecond temporal structure of coherent soft X-ray emission produced by the atomic currents--these X-ray photons provide a sensitive and intuitive tool for determining the carrier-envelope phase.

Studies on the optogalvanic effect and isotope-selective excitation of ytterbium in a hollow cathode discharge lamp using a pulsed dye laser.

PubMed

Kumar, Pankaj; Kumar, Jitendra; Prakash, Om; Saini, Vinod K; Dixit, Sudhir K; Nakhe, Shankar V

2013-09-01

This paper presents studies on the pulsed optogalvanic effect and isotope-selective excitation of Yb 555.648 nm (0 cm(-1) → 17 992.007 cm(-1)) and 581.067 nm (17 992.007 cm(-1) → 35 196.98 cm(-1)) transitions, in a Yb/Ne hollow cathode lamp. The Yb atoms were excited by narrow linewidth (500-1000 MHz) Rh110 and Rh6G dye based pulsed lasers. Optogalvanic signal inversion for ground state transition at 555.648 nm was observed beyond a hollow cathode discharge current of 8.5 mA, in contrast to normal optogalvanic signal at 581.067 nm up to maximum current of 14 mA. The isotope-selective excitation studies of Yb were carried out by recording Doppler limited optogalvanic signals as a function of dye laser wavelength. For the 581.067 nm transition, three even isotopes, (172)Yb, (174)Yb, and (176)Yb, and one odd isotope, (171)Yb, were clearly resolved. These data were compared with selective isotope excitation by 10 MHz linewidth continuous-wave dye laser. For 555.648 nm transition, isotopes were not clearly resolved, although isotope peaks of low modulation were observed.

Ionic mechanisms of transient inward current in the absence of Na(+)-Ca2+ exchange in rabbit cardiac Purkinje fibres.

PubMed Central

Han, X; Ferrier, G R

1992-01-01

1. Membrane currents were measured with a two-microelectrode technique in voltage clamped rabbit cardiac Purkinje fibres under conditions known to cause intracellular calcium overload and to eliminate or minimize Na(+)-Ca2+ exchange. 2. Increasing [Ca2+]o from 2.5 to 5 mM or above and substituting external sodium with either sucrose, choline or Li+ induced an oscillatory transient inward current (TI) which peaked 200-300 ms after repolarization from a previous depolarizing pulse. The TI quickly disappeared upon return to normal Tyrode solution. Both the rate and configuration of action potentials of Purkinje fibres also returned to control upon return to Tyrode solution after 30 min of high Ca2+ exposure, if the Ca2+ concentration was 30 mM or less. 3. The TI in Na(+)-free solution was Ca2+ dependent. Either zero or low (2.5 mM) [Ca2+]o, or replacement of [Ca2+]o by BaCl prevented induction of the TI current upon repolarization from a previous depolarizing pulse. 4. In the presence of 30 mM-CaCl2 and with choline chloride as the substitute for NaCl, TI had a distinct reversal potential (Erev) of -25 mV. The time-to-peak TI, either inward or outward, did not shift significantly with change in voltage. Both inward and outward TI were simultaneously abolished by exposure to 1 microM-ryanodine, suggesting they were both activated by transient release of Ca2+ from the sarcoplasmic reticulum. The occurrence of TI in the absence of [Na+]o is not compatible with an electrogenic Na(+)-Ca2+ exchange mechanism. The existence of a clear-cut reversal potential suggests that an ionic channel may be responsible for the TI under these conditions. 5. Both the magnitude of peak TI and the Erev were affected by changes of CaCl2 concentration. (i) Under steady-state conditions, peak inward TI was significantly increased when the [Ca2+]o was elevated from 5 to 15 mM. The peak TI in the outward direction was significantly increased when [Ca2+]o was elevated from 15 to 30 mM; however, the difference in peak inward TI at 15 and 30 mM [Ca2+]o was small. (ii) Clear-cut reversals of TI were found at Ca2+ concentrations of 10 mM (Erev = -19.5 mV) or greater, and elevation of [Ca2+]o to 20, 30, 50 and 105 mM shifted the Erev to more negative potentials. (iii) In the presence of 5 mM [Ca2+]o the inward TI declined to zero at about -30 mV, and test voltages between -55 and +5 mV failed to reveal a distinct outward TI.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:1284077

Aerothermal Analysis of the Project Fire II Afterbody Flow

NASA Technical Reports Server (NTRS)

Wright, Michael J.; Loomis, Mark; Papadopoulos, Periklis; Arnold, James O. (Technical Monitor)

2001-01-01

Computational fluid dynamics (CFD) is used to simulate the wake flow and afterbody heating of the Project Fire II ballistic reentry to Earth at 11.4 km/sec. Laminar results are obtained over a portion of the trajectory between the initial heat pulse and peak afterbody heating. Although non-catalytic forebody convective heating results are in excellent agreement with previous computations, initial predictions of afterbody heating were about a factor of two below the experimental values. Further analysis suggests that significant catalysis may be occurring on the afterbody heat shield. Computations including finite-rate catalysis on the afterbody surface are in good agreement with the data over the early portion of the trajectory, but are conservative near the peak afterbody heating point, especially on the rear portion of the conical frustum. Further analysis of the flight data from Fire II shows that peak afterbody heating occurs before peak forebody heating, a result that contradicts computations and flight data from other entry vehicles. This result suggests that another mechanism, possibly pyrolysis, may be occurring during the later portion of the trajectory, resulting in less total heat transfer than the current predictions.

Development of Thermal Protection Materials for Future Mars Entry, Descent and Landing Systems

NASA Technical Reports Server (NTRS)

Cassell, Alan M.; Beck, Robin A. S.; Arnold, James O.; Hwang, Helen; Wright, Michael J.; Szalai, Christine E.; Blosser, Max; Poteet, Carl C.

2010-01-01

Entry Systems will play a crucial role as NASA develops the technologies required for Human Mars Exploration. The Exploration Technology Development Program Office established the Entry, Descent and Landing (EDL) Technology Development Project to develop Thermal Protection System (TPS) materials for insertion into future Mars Entry Systems. An assessment of current entry system technologies identified significant opportunity to improve the current state of the art in thermal protection materials in order to enable landing of heavy mass (40 mT) payloads. To accomplish this goal, the EDL Project has outlined a framework to define, develop and model the thermal protection system material concepts required to allow for the human exploration of Mars via aerocapture followed by entry. Two primary classes of ablative materials are being developed: rigid and flexible. The rigid ablatives will be applied to the acreage of a 10x30 m rigid mid L/D Aeroshell to endure the dual pulse heating (peak approx.500 W/sq cm). Likewise, flexible ablative materials are being developed for 20-30 m diameter deployable aerodynamic decelerator entry systems that could endure dual pulse heating (peak aprrox.120 W/sq cm). A technology Roadmap is presented that will be used for facilitating the maturation of both the rigid and flexible ablative materials through application of decision metrics (requirements, key performance parameters, TRL definitions, and evaluation criteria) used to assess and advance the various candidate TPS material technologies.

Electrochemical Determination of Chlorpyrifos on a Nano-TiO₂Cellulose Acetate Composite Modified Glassy Carbon Electrode.

PubMed

Kumaravel, Ammasai; Chandrasekaran, Maruthai

2015-07-15

A rapid and simple method of determination of chlorpyrifos is important in environmental monitoring and quality control. Electrochemical methods for the determination of pesticides are fast, sensitive, reproducible, and cost-effective. The key factor in electrochemical methods is the choice of suitable electrode materials. The electrode materials should have good stability, reproducibility, more sensitivity, and easy method of preparation. Mercury-based electrodes have been widely used for the determination of chlorpyrifos. From an environmental point of view mercury cannot be used. In this study a biocompatible nano-TiO2/cellulose acetate modified glassy carbon electrode was prepared by a simple method and used for the electrochemical sensing of chlorpyrifos in aqueous methanolic solution. Electroanalytical techniques such as cyclic voltammetry, differential pulse voltammetry, and amperometry were used in this work. This electrode showed very good stability, reproducibility, and sensitivity. A well-defined peak was obtained for the reduction of chlorpyrifos in cyclic voltammetry and differential pulse voltammetry. A smooth noise-free current response was obtained in amperometric analysis. The peak current obtained was proportional to the concentration of chlorpyrifos and was used to determine the unknown concentration of chlorpyrifos in the samples. Analytical parameters such as LOD, LOQ, and linear range were estimated. Analysis of real samples was also carried out. The results were validated through HPLC. This composite electrode can be used as an alternative to mercury electrodes reported in the literature.

Self-phase-modulation induced spectral broadening in silicon waveguides

NASA Astrophysics Data System (ADS)

Boyraz, Ozdal; Indukuri, Tejaswi; Jalali, Bahram

2004-03-01

The prospect for generating supercontinuum pulses on a silicon chip is studied. Using ~4ps optical pulses with 2.2GW/cm2 peak power, a 2 fold spectral broadening is obtained. Theoretical calculations, that include the effect of two-photon-absorption, indicate up to 5 times spectral broadening is achievable at 10x higher peak powers. Representing a nonlinear loss mechanism at high intensities, TPA limits the maximum optical bandwidth that can be generated.

Self-phase-modulation induced spectral broadening in silicon waveguides.

PubMed

Boyraz, Ozdal; Indukuri, Tejaswi; Jalali, Bahram

2004-03-08

The prospect for generating supercontinuum pulses on a silicon chip is studied. Using ~4ps optical pulses with 2.2GW/cm(2) peak power, a 2 fold spectral broadening is obtained. Theoretical calculations, that include the effect of two-photon-absorption, indicate up to 5 times spectral broadening is achievable at 10x higher peak powers. Representing a nonlinear loss mechanism at high intensities, TPA limits the maximum optical bandwidth that can be generated.

Focusing of shock waves induced by optical breakdown in water

PubMed Central

Sankin, Georgy N.; Zhou, Yufeng; Zhong, Pei

2008-01-01

The focusing of laser-generated shock waves by a truncated ellipsoidal reflector was experimentally and numerically investigated. Pressure waveform and distribution around the first (F1) and second foci (F2) of the ellipsoidal reflector were measured. A neodymium doped yttrium aluminum garnet laser of 1046 nm wavelength and 5 ns pulse duration was used to create an optical breakdown at F1, which generates a spherically diverging shock wave with a peak pressure of 2.1–5.9 MPa at 1.1 mm stand-off distance and a pulse width at half maximum of 36–65 ns. Upon reflection, a converging shock wave is produced which, upon arriving at F2, has a leading compressive wave with a peak pressure of 26 MPa and a zero-crossing pulse duration of 0.1 μs, followed by a trailing tensile wave of −3.3 MPa peak pressure and 0.2 μs pulse duration. The −6 dB beam size of the focused shock wave field is 1.6×0.2 mm2 along and transverse to the shock wave propagation direction. Formation of elongated plasmas at high laser energy levels limits the increase in the peak pressure at F2. General features in the waveform profile of the converging shock wave are in qualitative agreement with numerical simulations based on the Hamilton model. PMID:18537359

Low-Dose-Rate Computed Tomography System Utilizing 25 mm/s-Scan Silicon X-ray Diode and Its Application to Iodine K-Edge Imaging Using Filtered Bremsstrahlung Photons

NASA Astrophysics Data System (ADS)

Matsushita, Ryo; Sato, Eiichi; Yanbe, Yutaka; Chiba, Hiraku; Maeda, Tomoko; Hagiwara, Osahiko; Matsukiyo, Hiroshi; Osawa, Akihiro; Enomoto, Toshiyuki; Watanabe, Manabu; Kusachi, Shinya; Sato, Shigehiro; Ogawa, Akira; Onagawa, Jun

2013-03-01

A low-dose-rate X-ray computed tomography (CT) system is useful for reducing absorbed dose for patients. The CT system with a tube current of sub-mA was developed using a silicon X-ray diode (Si-XD). The Si-XD is a high-sensitivity Si photodiode (PD) selected for detecting X-ray photons, and the X-ray sensitivity of the Si-XD was twice as high as that of Si-PD cerium-doped yttrium aluminum perovskite [YAP(Ce)]. X-ray photons are directly detected using the Si-XD without a scintillator, and the photocurrent from the diode is amplified using current-voltage and voltage-voltage amplifiers. The output voltage is converted into logical pulses using a voltage-frequency converter with a maximum frequency of 500 kHz, and the frequency is proportional to the voltage. The pulses from the converter are sent to the differentiator with a time constant of 500 ns to generate short positive pulses for counting, and the pulses are counted using a counter card. Tomography is accomplished by repeated linear scans and rotations of an object, and projection curves of the object are obtained by the linear scan. The exposure time for obtaining a tomogram was 5 min at a scan step of 0.5 mm and a rotation step of 3.0°. The tube current and voltage were 0.55 mA and 60 kV, respectively, and iodine K-edge CT was carried out using filtered bremsstrahlung X-ray spectra with a peak energy of 38 keV.

Characteristics of retinal reflectance changes induced by transcorneal electrical stimulation in cat eyes.

PubMed

Morimoto, Takeshi; Kanda, Hiroyuki; Miyoshi, Tomomitsu; Hirohara, Yoko; Mihashi, Toshifumi; Kitaguchi, Yoshiyuki; Nishida, Kohji; Fujikado, Takashi

2014-01-01

Transcorneal electrical stimulation (TES) activates retinal neurons leading to visual sensations. How the retinal cells are activated by TES has not been definitively determined. Investigating the reflectance changes of the retina is an established technique and has been used to determine the mechanism of retinal activation. The purpose of this study was to evaluate the reflectance changes elicited by TES in cat eyes. Eight eyes of Eight cats were studied under general anesthesia. Biphasic electrical pulses were delivered transcornealy. The fundus images observed with near-infrared light (800-880 nm) were recorded every 25 ms for 26 s. To improve the signal-to-noise ratio, the images of 10 consecutive recordings were averaged. Two-dimensional topographic maps of the reflective changes were constructed by subtracting images before from those after the TES. The effects of different stimulus parameters, e.g., current intensity, pulse duration, frequency, and stimulus duration, on the reflective changes were studied. Our results showed that after TES, the reflective changes appeared on the retinal vessels and optic disc. The intensity of reflectance changes increased as the current intensity, pulse duration, and stimulation duration increased (P<0.05 for all). The maximum intensity of the reflective change was obtained when the stimulus frequency was 20 Hz. The time course of the reflectance changes was also altered by the stimulation parameters. The response started earlier and returned to the baseline later with higher current intensities, longer pulse durations, but the time of the peak of the response was not changed. These results showed that the reflective changes were due to the activation of retinal neurons by TES and might involve the vascular changes induced by an activation of the retinal neurons.

Initial Testing of the Mark-0 X-Band RF Gun at SLAC

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

Vlieks, Arnold; Adolphsen, C.; Dolgashev, V.

A new X-band RF gun (Mark-0) has been assembled, tuned and was tested in the ASTA facility at SLAC. This gun has been improved from an earlier gun used in Compton-scattering experiments at SLAC by the introduction of a racetrack dual-input coupler to reduce quadrupole fields. Waveguide-to-coupler irises were also redesigned to reduce surface magnetic fields and therefore peak pulse surface heating. Tests of this photocathode gun will allow us to gain early operational experience for beam tests of a new gun with further improvements (Mark-1) being prepared for SLAC's X-Band Test Area (XTA) program and the LLNL MEGa-ray program.more » Results of current testing up to {approx} 200 MV/m peak surface Electric fields are presented.« less