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Results for “LASER-RADIATION HEATING”

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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131 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Comparing the use of mid-infrared versus far-infrared lasers for mitigating damage growth on fused silica

Laser-induced growth of optical damage can limit component lifetime and, therefore, increase operating costs of large-aperture fusion-class laser systems. While far-infrared (IR) lasers have been used previously to treat laser damage on fused silica optics and render it benign, little is known about the effectiveness of less-absorbing mid-IR lasers for this purpose. In this study, we quantitatively compare the effectiveness and efficiency of mid-IR (4.6 {mu}m) versus far-IR (10.6 {mu}m) lasers in mitigating damage growth on fused silica surfaces. The nonlinear volumetric heating due to mid-IR laser absorption is analyzed by solving the heat equation numerically, taking into account the temperature-dependent absorption coefficient {alpha}(T) at {lambda}=4.6 {mu}m, while far-IR laser heating is well described by a linear analytic approximation to the laser-driven temperature rise. In both cases, the predicted results agree well with surface temperature measurements based on IR radiometry, as well as subsurface fictive temperature measurements based on confocal Raman microscopy. Damage mitigation efficiency is assessed using a figure of merit (FOM) relating the crack healing depth to laser power required, under minimally ablative conditions. Based on our FOM, we show that, for cracks up to at least 500 {mu}m in depth, mitigation with a 4.6 {mu}m mid-IR laser is more efficient than mitigation with a 10.6 {mu}m far-IR laser. This conclusion is corroborated by direct application of each laser system to the mitigation of pulsed laser-induced damage possessing fractures up to 225 {mu}m in depth.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Interferometric measurement of laser heating in praseodymium-doped YAG crystal

Temperature measurement is required for many applications but can be difficult in some cases. Laser heating or cooling studies demand accurate measurements of temperature changes. A Michelson interferometer configuration has been used to investigate laser heating in solids. An analytical formula was derived to estimate the temperature change from the fringe count by taking into account the temperature dependence of the sample length and refractive index. When 115 mW of a focused Ar{sup +} laser beam (488 nm) passes through a Pr{sup 3+}-doped YAG sample, its temperature increased by 11.7{+-}1.0 K along the beam path due to nonradiative relaxation. The power dependence of the fringe count/movement was recorded. The temperature change was estimated by the interferometric method and is in agreement with that measured by a thermocouple.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Some Thoughts on the Role of non-LTE Physics in ICF

An effort to develop sub-critical-density high-Z metal-doped and pure metal foams as laser-driven x-ray sources is described. The main idea is that the laser beams preferentially heat the electrons, and if the plasma is sufficiently low density so that the heating rate is greater than the equilibration rate via electron-ion collisions, then the electron temperature in the plasma is much greater than the ion temperature as long as the laser is on. In such a situation the plasma is not in local thermal equilibrium (LTE), it heats supersonically and volumetrically, and the conversion efficiency of laser beam energy to multi-keV L-shell and K-shell radiation is much higher than what it would be in LTE plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Underwater Laser Cutting Technology - 16491

Underwater dismantling is advantageous for the highly radioactive apparatuses such as nuclear reactor internals. The most advantageous point of underwater dismantling is a radiation exposure reduction for workers. Underwater dismantling can take advantage of the water shielding. Then it can make the exposure reduction for workers and contamination reduction for work area be realized. And, underwater laser cutting technology has major three advantages. First advantage is lower action force. Therefore it can be possible that we can use a simple remote device for underwater dismantling operation. Second advantage is to reduce secondary waste. The cutting kerf size of underwater laser cutting is very narrow, so the amount of cutting dross is very small. Third advantage is very simple methods for dismantling. This advantage can reduce process time for cutting. On the other hand, the contaminated off-gas which generates during cutting should be taken care. IHl Corporation (IHI) developed the underwater laser cutting devices. The characteristic of IHI's laser cutting torch is that there is no air habitat. Therefore, the positions of the torch and the access to the narrow space have little limitation. Using the device the series of performance tests were performed in order to verify the ability of it. In the first Laboratory test at 0.2 meter depth of water, we evaluated the optimum cutting parameters. The next underwater demonstration test at 6 meters depth of water was performed. In the test the cutting performance, which the mild steel plate of the thickness of 12 mm can be cut at the speed of 300 mm/min with the horizontal and downward position of torch was verified. Then the hot bubble test using real radioactive test coupons was performed to evaluate the radioactivity carried as air borne and the decontamination factor (DF) of off-gas passing through water. This document provides an overview of the underwater laser cutting device that has been developed by IHI, and the advantage of these devices for the dismantling work of underwater apparatus. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Thermonuclear targets for direct-drive ignition by a megajoule laser pulse

Central ignition of a thin two-layer-shell fusion target that is directly driven by a 2-MJ profiled pulse of Nd laser second-harmonic radiation has been studied. The parameters of the target were selected so as to provide effective acceleration of the shell toward the center, which was sufficient for the onset of ignition under conditions of increased hydrodynamic stability of the ablator acceleration and compression. The aspect ratio of the inner deuterium-tritium layer of the shell does not exceed 15, provided that a major part (above 75%) of the outer layer (plastic ablator) is evaporated by the instant of maximum compression. The investigation is based on two series of numerical calculations that were performed using one-dimensional (1D) hydrodynamic codes. The first 1D code was used to calculate the absorption of the profiled laser-radiation pulse (including calculation of the total absorption coefficient with allowance for the inverse bremsstrahlung and resonance mechanisms) and the spatial distribution of target heating for a real geometry of irradiation using 192 laser beams in a scheme of focusing with a cubo-octahedral symmetry. The second 1D code was used for simulating the total cycle of target evolution under the action of absorbed laser radiation and for determining the thermonuclear gain that was achieved with a given target.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗