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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

High-quality proton bunch from laser interaction with a gas-filled cone target

Generation of high-energy proton bunch from interaction of an intense short circularly polarized (CP) laser pulse with a gas-filled cone target (GCT) is investigated using two-dimensional particle-in-cell simulation. The GCT target consists of a hollow cone filled with near-critical gas-plasma and a thin foil attached to the tip of the cone. It is observed that as the laser pulse propagates in the gas-plasma, the nonlinear focusing will result in an enhancement of the laser pulse intensity. It is shown that a large number of energetic electrons are generated from the gas-plasma and accelerated by the self-focused laser pulse. The energetic electrons then transports through the foil, forming a backside sheath field which is stronger than that produced by a simple planar target. A quasi-monoenergetic proton beam with maximum energy of 181 MeV is produced from this GCT target irradiated by a CP laser pulse at an intensity of 2.6 x 10{sup 20} W/cm{sup 2}, which is nearly three times higher compared to simple planar target (67 MeV).

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

On electron bunching and stratification of glow discharges

Plasma stratification and excitation of ionization waves is one of the fundamental problems in gas discharge physics. Significant progress in this field is associated with the name of Lev Tsendin. He advocated the need for the kinetic approach to this problem contrary to the traditional hydrodynamic approach, introduced the idea of electron bunching in spatially periodic electric fields, and developed a theory of kinetic resonances for analysis of moving striations in rare gases. The present paper shows how Tsendin's ideas have been further developed and applied for understanding the nature of the well-known S-, P-, and R-striations observed in glow discharges of inert gases at low pressures and currents. We review numerical solutions of a Fokker-Planck kinetic equation in spatially periodic electric fields under the effects of elastic and inelastic collisions of electrons with atoms. We illustrate the formation of kinetic resonances at specific field periods for different shapes of injected Electron Distribution Functions (EDF). Computer simulations illustrate how self-organization of the EDFs occurs under nonlocal conditions and how Gaussian-like peaks moving along resonance trajectories are formed in a certain range of discharge conditions. The calculated EDFs agree well with the experimentally measured EDFs for the S, P, and R striations in noble gases. We discuss how kinetic resonances affect dispersion characteristics of moving striations and mention some non-linear effects associated with glow discharge stratification. We propose further studies of stratification phenomena combining physical kinetics and non-linear physics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Effects of aqueous ammonia treatment on fiber’s surface morphology and enzymatic digestibility of empty fruit bunch fiber (EFBF)

This study was conducted to investigate the effects of aqueous ammonia reflux and soaked treatment on the fiber’s surface morphology and enzymatic digestibility of empty fruit bunch fiber (EFBF). The surface morphological changes of the fiber after aqueous ammonia treatment was linked to the sugars yield by enzymatic hydrolysis. The effectiveness of 6.25% aqueous ammonia treatment in improving enzymatic digestibility of EFBF was initially studied in reflux system and by soaking. The results showed that soaked treatment was more effective than reflux system. Further study on soaked treatment of EFBF was carried out by increasing the ammonia concentration to 12.50%. Soaking in aqueous ammonia was conducted at 30°C and 50°C for 24 hours. The results of enzymatic hydrolysis showed that sugar yield from EFBF soaked in 12.50% aqueous ammonia at 50°C was the highest. Approximately 242.91±15.50 mg/g EFBF of xylose and 320.49±28.31 mg/g EFBF of glucose were produced by the action of enzyme Cellic Ctec 2. Results of scanning electron microscopic showed that aqueous ammonia treatment by soaking had caused a more severe structural distortion on the fiber’s surface and higher removal of silica bodies that embedded on the fiber than those in reflux system. The changes on the fiber’s surface morphology were believed is the contributing factor that improved the enzymatic digestibility of EFBF after aqueous ammonia treatment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

High energy density micro plasma bunch from multiple laser interaction with thin target

Three-dimensional particle-in-cell simulation is used to investigate radiation-pressure driven acceleration and compression of small solid-density plasma by intense laser pulses. It is found that multiple impacts by presently available short-pulse lasers on a small hemispheric shell target can create a long-living tiny quasineutral monoenergetic plasma bunch of very high energy density.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Peculiarities of the coherent spontaneous synchrotron radiation of dense electron bunches

In a short section of homogeneous magnetic field, quasi-plane electron bunches from linear accelerators with laser-driven photo-injectors at moderate particle energies can generate strongly directed, very short and powerful terahertz electromagnetic pulses with a broad frequency spectrum. The formulas for radiation fields, their spectra and efficiency of radiation are presented in a very simple analytical form using expressions for the fields of an arbitrary moving charged plane. The self-action and mutual interaction of thin electron layers are estimated. It is shown that the radiation with frequencies of up to (1–3) THz can be effectively generated by electrons with energies (4–6) MeV in a short and relatively weak magnetic field of (4–10) kOe.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Nanoporous separators for supercapacitor using activated carbon monolith electrode from oil palm empty fruit bunches

Activated porous carbon electrode prepared from fibres of oil palm empty fruit bunches was used for preparing the carbon based supercapacitor cells. The symmetrical supercapacitor cells were fabricated using carbon electrodes, stainless steel current collector, H{sub 2}SO{sub 4} electrolyte, and three types of nanoporous separators. Cells A, B and C were fabricated using polypropylene, eggshell membrane, and filter paper, respectively. Electrochemical characterizations data from Electrochemical Impedance Spectroscopy, Cyclic Voltammetry, and Galvanic Charge Discharge techniques showed that specific capacitance, specific power and specific energy for cell A were 122 F g{sup −1}, 177 W kg{sup −1}, 3.42 Wh kg{sup −1}, cell B; 125 F g{sup −1}, 179 W kg{sup −1}, and 3.64 Wh kg{sup −1}, and cell C; 180 F g{sup −1}, 178 W kg{sup −1}, 4.27 Wh kg{sup −1}. All the micrographs from Field Emission Scanning Electron Microscope showed that the different in nanoporous structure of the separators lead to a significant different in influencing the values of specific capacitance, power and energy of supercapacitors, which is associated with the mobility of ion into the pore network. These results indicated that the filter paper was superior than the eggshell membrane and polypropylene nanoporous separators. However, we found that in terms of acidic resistance, polypropylene was the best nanoporous separator for acidic medium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The effect of plasma radius and profile on the development of self-modulation instability of electron bunches

Plasmas available for plasma wakefield accelerator experiments may have longitudinal and transverse density profiles that could affect the outcome of an experiment. This paper investigates the effect of plasmas with finite radius and inhomogeneous transverse density profiles on the wakefield excitation and the self-modulation instability (SMI) development in overdense plasmas. We focus here on the case of an electron bunch. Simulation results show that such plasmas generate larger focusing force for the propagating electron beam and therefore higher growth rate for the SMI. Although the initial accelerating field (E{sub z}) amplitude is lower in such plasmas, the increased focusing force can dominate the development trend of the SMI, i.e., larger saturated E{sub z} amplitude can be reached over similar plasma lengths.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Generation of high-energy-density ion bunches by ultraintense laser-cone-target interaction

A scheme in which carbon ion bunches are accelerated to a high energy and density by a laser pulse (∼10{sup 21} W/cm{sup 2}) irradiating cone targets is proposed and investigated using particle-in-cell simulations. The laser pulse is focused by the cone and drives forward an ultrathin foil located at the cone's tip. In the course of the work, best results were obtained employing target configurations combining a low-Z cone with a multispecies foil transversely shaped to match the laser intensity profile.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Injection and acceleration of electron bunch in a plasma wakefield produced by a chirped laser pulse

An ultrashort laser pulse propagating in plasma can excite a nonlinear plasma wakefield which can trap and accelerate charged particles up to GeV. One-dimensional analysis of electron injection, trapping, and acceleration by different chirped pulses propagating in plasma is investigated numerically. In this paper, we inject electron bunches in front of the chirped pulses. It is indicated that periodical chirped laser pulse can trap electrons earlier than other pulses. It is shown that periodical chirped laser pulses lead to decrease the minimum momentum necessary to trap the electrons. This is due to the fact that periodical chirped laser pulses are globally much efficient than nonchirped pulses in the wakefield generation. It is found that chirped laser pulses could lead to much larger electron energy than that of nonchirped pulses. Relative energy spread has a lower value in the case of periodical chirped laser pulses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Effect of temperature on pyrolysis product of empty fruit bunches

Pyrolysis of empty fruit bunches (EFB) was performed in a fixed bed reactor equipped with liquid collecting system. Pyrolysis process was conducted by varying the terminal pyrolysis temperature from 300 to 500°C under heating rate of 10°C/min for at least 2 hours. Char yield was obtained highest at 300°C around 55.88 wt%, and started to decrease as temperature increase. The maximum yield of pyrolysis liquid was obtained around 54.75 wt% as pyrolysis temperature reach 450°C. For gas yield percentage, the yield gained as temperature was increased from 300 to 500°C, within the range between 8.44 to 19.32 wt%. The char obtained at 400°C has great potential as an alternative solid fuel, due to its high heating value of 23.37 MJ/kg, low in volatile matter and ash content which are approximately around 40.32 and 11.12 wt%, respectively. The collected pyrolysis liquid within this temperature range found to have high water content of around 16.15 to 18.20 wt%. The high aqueous fraction seemed to cause the pyrolysis liquid to have low HHV which only ranging from 10.81 to 12.94 MJ/kg. These trends of results showed that necessary enhancement should be employ either on the raw biomass or pyrolysis products in order to approach at least the minimum quality of common hydrocarbon solid or liquid fuel. For energy production, both produced bio-char and pyrolysis liquid are considered as sustainable sources of bio-energy since they contained low amounts of nitrogen and sulphur, which are considered as environmental friendly solid and liquid fuel.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Effect of carbonization temperature on the physical and electrochemical properties of supercapacitor electrode from fibers of oil palm empty fruit bunches

Self-adhesive carbon grains (SACG) was prepared from fibers of oil palm empty fruit bunches. The SACG green monoliths were carbonized in N{sub 2} environment at 400, 500, 600 and 700°C to produce carbon monoliths labeled as CM1, CM2, CM3 and CM4 respectively. The CMs were activated in CO{sub 2} surrounding at 800°C for 1 hour to produce activated carbon monolith electrodes (ACM1, ACM2, ACM3 and ACM4). The physical properties of the CMs and ACMs were investigated using X-ray diffraction, field emission scanning electron microscopy (FESEM) and N{sub 2} adsorption-desorption isotherm techniques. ACMs were used as electrode to fabricate symmetry supercapacitor cells and the cells’ performances were investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) standard techniques. In this paper we report the physical and electrochemical properties of the ACM electrodes by analyzing the influence of the carbonization temperature on these properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Effect of electrolyte concentration on performance of supercapacitor carbon electrode from fibers of oil palm empty fruit bunches

Fibers of oil palm empty fruit bunches were used to produce self-adhesive carbon grains (SACG). The SACG green monoliths were carbonized in N{sub 2} environment at 800°C to produce carbon monoliths (CM) and the CM was CO{sub 2} activated at 800°C for 4 hour to produce activated carbon monolith electrodes (ACM). The physical properties of the CMs and ACMs were investigated using X-ray diffraction, field emission scanning electron microscopy and nitrogen adsorption-desorption. ACMs were used as electrode to fabricate symmetry supercapacitor cells and the cells which used H{sub 2}SO{sub 4} electrolyte at 0.5, 1.0 and 1.5 M were investigated using electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge-discharge standard techniques. In this paper we report the physical properties of the ACM electrodes and the effect of electrolyte concentration on the electrochemical properties the ACM electrodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Morphological and spectroscopic analysis of cellulose nanocrystals extracted from oil palm empty fruit bunch fiber

This work evaluates the use of oil palm empty fruit bunch (OPEFB) fiber as a source of cellulose to obtain nanocrystalline cellulose (CNC) by acid hydrolysis reaction. The raw OPEFB fibers were pretreated with aqueous Sodium hydroxide at 80°C followed by bleaching treatment and further hydrolyzed with Sulphuric acid at 45°C with limited range of hydrolysis time and acid concentration. The resulting CNC’s were characterized for spectroscopic, crystallographic and morphological properties using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffractometer (XRD), Transmission Electron Microscope (TEM) and Atomic Force Microscopy (AFM). Finding of this study shows that the properties of CNC’s are strongly dependent on the hydrolysis time and acid concentration.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Delayed bunching for multi-reflection time-of-flight mass separation

Many experiments are handicapped when the ion sources do not only deliver the ions of interest but also contaminations, i.e., unwanted ions of similar mass. In the recent years, multi-reflection time-of-flight mass separation has become a promising method to isolate the ions of interest from the contaminants, in particular for measurements with low-energy short-lived nuclides. To further improve the performance of multi-reflection mass separators with respect to the limitations by space-charge effects, the simultaneously trapped ions are spatially widely distributed in the apparatus. Thus, the ions can propagate with reduced Coulomb interactions until, finally, they are bunched by a change in the trapping conditions for high-resolution mass separation. Proof-of-principle measurements are presented.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Energy spread minimization in a cascaded laser wakefield accelerator via velocity bunching

We propose a scheme to minimize the energy spread of an electron beam (e-beam) in a cascaded laser wakefield accelerator to the one-thousandth-level by inserting a stage to compress its longitudinal spatial distribution. In this scheme, three-segment plasma stages are designed for electron injection, e-beam length compression, and e-beam acceleration, respectively. The trapped e-beam in the injection stage is transferred to the zero-phase region at the center of one wakefield period in the compression stage where the length of the e-beam can be greatly shortened owing to the velocity bunching. After being seeded into the third stage for acceleration, the e-beam can be accelerated to a much higher energy before its energy chirp is compensated owing to the shortened e-beam length. A one-dimensional theory and two-dimensional particle-in-cell simulations have demonstrated this scheme and an e-beam with 0.2% rms energy spread and low transverse emittance could be generated without loss of charge.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Generation of short gamma-ray pulses on electron bunches formed in intense interfering laser beams with tilted fronts

It is shown that in the interference of multiple laser pulses with a relativistic intensity, phase and amplitude fronts of which are tilted at an angle with respect to their wave vector, effective traps of charged particles, which are moving at the velocity of light, are formed. Such traps are capable of capturing and accelerating the electrons produced in the ionisation of low-density gas by means of laser radiation. The accelerated electrons in the traps form a bunch, whose dimensions in all directions are much smaller than the laser radiation wavelength. Calculations show that the energy of accelerated electrons may amount to several hundred GeV at experimentally accessible relativistic laser intensities. As a result of the inverse Compton scattering, gamma-quanta with a high energy and narrow radiation pattern are emitted when these electrons interact with a laser pulse propagating from the opposite direction. The duration of emitted gamma-ray pulses constitutes a few attoseconds. The simulation is performed by solving the relativistic equation of motion for an electron with a relevant Lorentz force. (interaction of radiation with matter)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Effect of the laser spot shape on spatial distribution of the ion bunch accelerated in a superstrong field

We have investigated the effect of the laser spot shape on the spatial distribution of accelerated ions on the front and back sides of a thin target irradiated by a picosecond laser pulse having the intensity of (3 – 4) × 10{sup 18} W cm{sup -2}. Experimental data are compared with numerical calculations. It is shown that the spatial structure of the ion bunch on the front side of the target resembles the laser spot structure rotated by 90°. (interaction of laser radiation with matter. laser plasma)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Generation of laser plasma bunches with a high efficiency of energy concentration for laboratory simulation of collisionless shock waves in magnetised cosmic plasma

We present the results of first experiments on the formation of collisionless shock waves (CSWs) in background plasma by injecting laser plasma bunches transverse to the magnetic field (as a piston) with a maximum energy up to 100 J per unit of solid angle and with a high enough degree of ion magnetisation. With this aim in view, on a unique KI-1 facility at the Institute of Laser Physics, Siberian Branch of the Russian Academy of Sciences (ILP), a plastic (polyethylene) target irradiated by a CO{sub 2} laser in the most energy-efficient regime (near the plasma formation threshold) and a highly ionised hydrogen plasma with a high concentration in a large volume (not less than 1 m{sup 3}) have been employed. As a result of model experiments performed on the basis of a model of collisionless interaction of plasma flows, developed at the VNIIEF and being adequate to the problem under consideration, not only an intensive, background-induced, deceleration of a super-Alfven laser plasma flow, but also the formation in that flow of a strong perturbation having the properties of a subcritical CSW and propagating transverse to the magnetic field, have been first registered in the laboratory conditions. (extreme laser radiation: physics and fundamental applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗