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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Selective laser melting of Co-29Cr-6Mo alloy with laser power 180–360 W: Cellular growth, intercellular spacing and the related thermal condition

Highlights: • Increasing laser power increases the track size but not the track shape significantly. • Solidification mode and texture are similar over the range of laser power used. • Intercellular spacing is not affected by laser power but decreases slightly with growth angle. • Thermal gradient and cooling rate have been estimated to be ~ 2 × 10{sup 7} K/m and ~ 2 × 10{sup 6} K/s, respectively. - Abstract: A feature of solidification during selective laser melting (SLM) is cellular growth. Thus, how growth direction and cell size may be affected and possibly be controlled by SLM parameters are important to be understood. Furthermore, intercellular spacing (λ{sub 1}) is suggestive of the thermal condition during solidification which needs to be known for advancing the understanding of SLM. In this work, grain solidification orientation and λ{sub 1} of a Co-Cr-Mo alloy produced by SLM over a range of laser power (P = 180–360 W) with other parameters kept unchanged have been evaluated. It has been found that the overall preferred growth of cellular solidification is not significantly affected by P. This is because, over the range of P values used, the shape of track did not change sufficiently to result in a significant variation of growth direction during epitaxial growth. It has also been found that P does not affect λ{sub 1}. This suggests, since growth rate (R) relates to scan speed (v) which is unchanged, P does not significantly affect the temperature gradient of the solidification front (G). From the measured λ{sub 1} and estimated R, G and thus cooling rate ( T-dot ) can be estimated following the commonly used primary arm spacing model. The estimated G and T-dot which could not be directly measured will be compared with those predicted by simulation and the estimated T-dot will also be compared with those determined by using an emperical relationship from literature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Relationship between laser energy input, microstructures and magnetic properties of selective laser melted Fe-6.9%wt Si soft magnets

Highlights: • Effect of laser energy input on magnetic properties of SLM Fe-6.9%wt.Si is described; • Magnetic properties can be described as function of as-built microstructure after stress-relief post-treatment; • Samples with density >99% and strong crystallographic texture along BD have the best magnetic properties; • At very high laser energy, a strong cube texture forms that deteriorates the magnetic properties. - Abstract: Selective Laser Melting (SLM), a powder-bed Additive Manufacturing technology, can be used in combination with high temperature post-annealing to produce high-silicon steel parts characterised by quasi-static magnetic properties comparable to those of commercial electrical steel. However, the role of the as-built microstructure on the magnetic properties is still unexplored. Therefore, in this study the effect of the energy input of the processing laser on the magnetic properties of the material is investigated. The magnetic properties are determined for 4 mm-high rings obtained using three laser energy input values that provide a good compromise in terms of porosity and crack formation. The best magnetic properties are obtained for the rings built using a value of energy input that produces a strong fibrous crystallographic texture, in which one of the crystallographic <001> axes is preferentially aligned along the build direction. Whether the magnetic properties change with sample direction as a result of the crystallographic texture will be the subject of future research.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of laser power on oxygen and nitrogen concentration of commercially pure titanium manufactured by selective laser melting

Highlights: • The hardness and strength of pure titanium fabricated by SLM were increased with increasing the laser power. • During the SLM processing, the concentrations of oxygen and nitrogen in the SLM parts were increased. • The oxidation and nitriding were thermodynamically possible under SLM. - Abstract: This study analyzed the variation of mechanical properties and its causes with increasing the laser power in the fabrication of pure titanium by selective laser melting (SLM). SLM samples were fabricated using commercially pure titanium grade 1 powder when the scan speed was 1000 mm/s and the laser power as 120, 200, 280, 360, and 440 W, respectively. As the laser power increased, the hardness and strength of the samples increased gradually. During the SLM processing, the concentrations of oxygen and nitrogen in the SLM samples were increased, which resulted in the increase of hardness and strength. The SLM equipment used in this study removed oxygen in the chamber by flowing high purity argon gas and fabricates the sample while preserving the oxygen concentration in the atmosphere to 0.2%. Evaluating the possibility of oxidation and nitriding during the SLM process by thermodynamic analysis, it was found that the process occurred under conditions in which temperature and residual oxygen and nitrogen partial pressure led to oxidation and nitriding.

36 MATERIALS SCIENCE↗
DOE OSTI2012

New laser setup for the selective isotope production and investigation in a laser ion source at the IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) facility

New laser installation for the resonance ionization spectroscopy in a laser ion source and for rare isotope production has been recently put into operation at the IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) facility (Petersburg Nuclear Physics Institute, Gatchina). This is a significant improvement of a previous target-laser ion source device of the IRIS mass-separator, working on-line with 1 GeV proton beam of PNPI (Petersburg Nuclear Physics Institute) synchrocyclotron. It makes possible for us to get the isobarically clean radioactive isotope beams of a great number of chemical elements. New laser setup provides the two- or three-resonance step ionization in the range of wavelength of 265-850 nm. The first results obtained at the laser setup for Tl isotopes are presented.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2012

Dependence of terahertz power from laser-produced plasma on laser intensity

Power of terahertz radiation from plasma which is generated from air irradiated by coupled ({omega}, 2{omega}) femtosecond laser pulses is analyzed for high laser intensities, for which non-linear plasma effects on the pulse propagation become essential, with multidimensional particle-in-cell simulations including the self-consistent plasma kinetics. The growth rate of THz power becomes slower as the laser intensity increases. A reason of such a lowering of efficiency in THz emission is found to be ionization of air by the laser pulse, which results in poor focusing of laser pulses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Tailoring the laser pulse shape to improve the quality of the self-injected electron beam in laser wakefield acceleration

In laser wakefield acceleration, tailoring the shape of the laser pulse is one way of influencing the laser-plasma interaction and, therefore, of improving the quality of the self-injected electron beam in the bubble regime. Using three-dimensional particle-in-cell simulations, the evolution dynamics of the laser pulse and the quality of the self-injected beam, for a Gaussian pulse, a positive skew pulse (i.e., one with sharp rise and slow fall), and a negative skew pulse (i.e., one with a slow rise and sharp fall) are studied. It is observed that with a negative skew laser pulse there is a substantial improvement in the emittance (by around a factor of two), and a modest improvement in the energy-spread, compared to Gaussian as well as positive skew pulses. However, the injected charge is less in the negative skew pulse compared to the other two. It is also found that there is an optimal propagation distance that gives the best beam quality; beyond this distance, though the energy increases, the beam quality deteriorates, but this deterioration is least for the negative skew pulse. Thus, the negative skew pulse gives an improvement in terms of beam quality (emittance and energy spread) over what one can get with a Gaussian or positive skew pulse. In part, this is because of the lesser injected charge, and the strong suppression of continuous injection for the negative skew pulse.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

The phase-lock dynamics of the laser wakefield acceleration with an intensity-decaying laser pulse

An electron beam with the maximum energy extending up to 1.8 GeV, much higher than the dephasing limit, is experimentally obtained in the laser wakefield acceleration with the plasma density of 3.5 × 10{sup 18} cm{sup −3}. With particle in cell simulations and theoretical analysis, we find that the laser intensity evolution plays a major role in the enhancement of the electron energy gain. While the bubble length decreases due to the intensity-decay of the laser pulse, the phase of the electron beam in the wakefield can be locked, which contributes to the overcoming of the dephasing. Moreover, the laser intensity evolution is described for the phase-lock acceleration of electrons in the uniform plasma, confirmed with our own simulation. Since the decaying of the intensity is unavoidable in the long distance propagation due to the pump depletion, the energy gain of the high energy laser wakefield accelerator can be greatly enhanced if the current process is exploited.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Investigation of variation of energy of laser beam on structural, electrical and optical properties of pulsed laser deposited CuO thin films

In this paper, copper oxide (CuO) thin films have been deposited successfully by pulsed laser deposition technique using copper metal as target material. Thin films have been prepared under different energy of laser pulses ranging from 100mJ/pulse to 250 mJ/pulse. These films have been characterized for their structural, electrical and optical properties by using X-Ray Diffractometer (XRD), Four probe method and UV spectroscopy. Morphological and structural studies show that there is increase in crystallite size with the increase in energy of laser beam. Thus resulting in improved crystallinity and degree of orientation of the CuO thin films. Optoelectrical properties show direct relation between conductivity and energy of laser beam. Optical analysis of CuO thin films prepared under different energy of laser beam shows good agreement with structural analysis. The prepared CuO thin films show high absorbance in the UV and visible range and thus are suitable candidate for thin films solar cell application.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Formation of laser-induced periodic surface structures on niobium by femtosecond laser irradiation

The surface morphology of a Niobium sample, irradiated in air by a femtosecond laser with a wavelength of 800 nm and pulse duration of 100 fs, was examined. The period of the micro/nanostructures, parallel and perpendicularly oriented to the linearly polarized fs-laser beam, was studied by means of 2D Fast Fourier Transform analysis. The observed Laser-Induced Periodic Surface Structures (LIPSS) were classified as Low Spatial Frequency LIPSS (periods about 600 nm) and High Spatial Frequency LIPSS, showing a periodicity around 300 nm, both of them perpendicularly oriented to the polarization of the incident laser wave. Moreover, parallel high spatial frequency LIPSS were observed with periods around 100 nm located at the peripheral areas of the laser fingerprint and overwritten on the perpendicular periodic gratings. The results indicate that this method of micro/nanostructuring allows controlling the Niobium grating period by the number of pulses applied, so the scan speed and not the fluence is the key parameter of control. A discussion on the mechanism of the surface topology evolution was also introduced.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Dynamics of laser mass-limited foil interaction at ultra-high laser intensities

By using three-dimensional particle-in-cell simulations with synchrotron radiation damping incorporated, dynamics of ultra-intense laser driven mass-limited foils is presented. When a circularly polarized laser pulse with a peak intensity of ∼10{sup 22} W/cm{sup 2} irradiates a mass-limited nanofoil, electrons are pushed forward collectively and a strong charge separation field forms which acts as a “light sail” and accelerates the protons. When the laser wing parts overtake the foil from the foil boundaries, electrons do a betatron-like oscillation around the center proton bunch. Under some conditions, betatron-like resonance takes place, resulting in energetic circulating electrons. Finally, bright femto-second x rays are emitted in a small cone. It is also shown that the radiation damping does not alter the foil dynamics radically at considered laser intensities. The effects of the transverse foil size and laser polarization on x-ray emission and foil dynamics are also discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Multi-dimensional dynamics of stimulated Brillouin scattering in a laser speckle: Ion acoustic wave bowing, breakup, and laser-seeded two-ion-wave decay

Two- and three-dimensional particle-in-cell simulations of stimulated Brillouin scattering (SBS) in laser speckle geometry have been analyzed to evaluate the relative importance of competing nonlinear processes in the evolution and saturation of SBS. It is found that ion-trapping-induced wavefront bowing and breakup of ion acoustic waves (IAW) and the associated side-loss of trapped ions dominate electron-trapping-induced IAW wavefront bowing and breakup, as well as the two-ion-wave decay instability over a range of ZTe/Ti conditions and incident laser intensities. In the simulations, the latter instability does not govern the nonlinear saturation of SBS; however, evidence of two-ion-wave decay is seen, appearing as a modulation of the ion acoustic wavefronts. This modulation is periodic in the laser polarization plane, anti-symmetric across the speckle axis, and of a wavenumber matching that of the incident laser pulse. A simple analytic model is provided for how spatial “imprinting” from a high frequency inhomogeneity (in this case, the density modulation from the laser) in an unstable system with continuum eigenmodes can selectively amplify modes with wavenumbers that match that of the inhomogeneity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Acceleration and evolution of a hollow electron beam in wakefields driven by a Laguerre-Gaussian laser pulse

We show that a ring-shaped hollow electron beam can be injected and accelerated by using a Laguerre-Gaussian laser pulse and ionization-induced injection in a laser wakefield accelerator. The acceleration and evolution of such a hollow, relativistic electron beam are investigated through three-dimensional particle-in-cell simulations. We find that both the ring size and the beam thickness oscillate during the acceleration. The beam azimuthal shape is angularly dependent and evolves during the acceleration. The beam ellipticity changes resulting from the electron angular momenta obtained from the drive laser pulse and the focusing forces from the wakefield. The dependence of beam ring radius on the laser-plasma parameters (e.g., laser intensity, focal size, and plasma density) is studied. Such a hollow electron beam may have potential applications for accelerating and collimating positively charged particles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Laser intensity scaling of the magnetic field from a laser-driven coil target

In this paper, we report on the first direct voltage and current measurements from a laser-generated magnetic field coil target. The magnetic field was observed to scale with the laser intensity as $B ∝ \mathcal{I}^{0.66±0.13}_\text{laser}$. This scaling relation can be derived from the measured voltage approximated by the laser-heated plasma electron temperature $T_e$. The experiments used a 1053 nm laser with pulse lengths ranging from 0.5 to 20 ns and intensities ranging from 10 9 to 10 14 W/cm 2 to generate an electric potential that drives current through the coil. We show that the behavior of the coil can be described with a lumped-element circuit model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Scaling of laser-driven electron and proton acceleration as a function of laser pulse duration, energy, and intensity in the multi-picosecond regime

A scaling study of short-pulse laser-driven proton and electron acceleration was conducted as a function of pulse duration, laser energy, and laser intensity in the multi-picosecond (ps) regime (~0.8 ps–20 ps). Furthermore, maximum proton energies significantly greater than established scaling laws were observed, consistent with observations at other multi-ps laser facilities. In addition, maximum proton energies and electron temperatures in this regime were found to be strongly dependent on the laser pulse duration and preplasma conditions. A modified proton scaling model is presented that is able to better represent the accelerated proton characteristics in this multi-ps regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Scaling laser preheat for MagLIF with the Z-Beamlet laser

Optimizing the performance of the Magnetized Liner Inertial Fusion (MagLIF) platform on the Z pulsed power facility requires coupling greater than 2 kJ of preheat energy to an underdense fuel in the presence of an applied axial magnetic field ranging from 10 to 30 T. Achieving the suggested optimal preheat energies has not been experimentally achieved so far. In this work, we explore the preheat design space for cryogenically cooled MagLIF targets, which represent a viable candidate for increasing preheat energies. Using 2D and 3D HYDRA MHD simulations, we first discuss the various physical effects that occur during laser preheat, such as laser energy deposition, self-focusing, and filamentation. After identifying the changes that different phase plates, gas-fill densities, and magnetic fields bring to the aforementioned physical effects, we, then, consider higher laser energies that are achievable with modest upgrades to the Z Beamlet laser. Lastly, with a 6.0-kJ upgraded laser, 3D calculations suggest that it is possible to deliver 4.25 kJ into the MagLIF fuel, resulting in an expected deuterium neutron yield of Y DD ≃ 1.5 × 10 14 , or roughly 50 kJ of DT equivalent yield, at 20-MA current drive. This represents a 10-fold increase in the currently achieved yields for MagLIF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

A confocal laser-induced fluorescence diagnostic with an annular laser beam

Here, in this work, we report an annular beam confocal laser-induced fluorescence (LIF) configuration, which allows for high spatial resolution measurements of plasma properties in plasma setups and sources with limited optical access. The proposed LIF configuration utilizes the annular laser beam generated by a pair of diffractive axicons. The LIF signal is collected along the main optical axis within the ring region. It is shown experimentally that at a focal distance of 300 mm, a spatial resolution of ~5.3 mm can be achieved. Using geometric optics estimations, we showed that ~1 mm resolution at the same focal distance could potentially be achieved by modifying laser beam parameters. This approaches the localization accuracy of conventional LIF collection methods (with crossing laser beam injection and fluorescence collection optical paths). Measurements of the ion velocity distribution function in an argon plasma using both the confocal LIF with an annular laser beam and conventional LIF demonstrate a satisfactory agreement. The proposed LIF setup has potential applications for diagnostics in various plasma processing equipment and plasma sources, such as hollow cathodes, microplasmas, electric propulsion, etc.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Laser cooling of electron – ion plasma in the case of optimal scanning of the laser frequency

Laser cooling of ions of electron – ion plasma is studied under the action of spontaneous radiation pressure forces. It is shown that the use of a constant detuning of the laser frequency from the quantum transition frequency w0 in ions significantly limits the conditions under which the ions are cooled. To extend the range of initial temperatures of possible cooling of ions and to increase the cooling efficiency we suggest scanning the laser frequency detuning so that the cooling rate remained maximal in the process of changing the temperature of ions. In the case of an optimal detuning, we have found an asymptotic expression for the cooling rate and identified intervals of electron concentrations and temperatures, where cooling of ions is possible. (interaction of laser radiation with matter. laser plasma)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Room-temperature Fe{sup 2+}:ZnS single crystal laser pumped by an electric-discharge HF laser

A room-temperature laser based on a Fe{sup 2+}:ZnS single crystal has been studied. The crystal was pumped by a nonchain electric-discharge HF laser with a light pulse FWHM of ∼140 ns. The pump spot diameter on the crystal surface (d) varied from 3.9 to 11.6 mm. The slope efficiency at these values of d was 37% – 39 %, respectively. The maximum laser energy was 380 mJ (at d=11.6 mm) with the total efficiency with respect to the absorbed pump energy of ∼19%. A further increase in the laser energy was not achieved because the crystal was destroyed at an incident pump energy and power of 3.4 J and ∼24 MW, respectively. The damaged region has a form of a long narrow channel shifted from the entrance surface inside the active element. (lasers)

42 ENGINEERING↗