Laser Heating of Solid Hydrogen for Production of Vibrationally Excited Molecules for Use in Negative Hydrogen Ion Sources
Guttman, Jeffrey Lynn
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https://hdl.handle.net/2142/69237
Description
Title
Laser Heating of Solid Hydrogen for Production of Vibrationally Excited Molecules for Use in Negative Hydrogen Ion Sources
Author(s)
Guttman, Jeffrey Lynn
Issue Date
1982
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Abstract
An experiment has been performed in which laser light was used to heat hydrogen pellets on a metallic substrate. The purpose of heating the hydrogen is to create a vibrationally excited population of hydrogen for use in negative hydrogen ion sources. The desired heating temperature is 3000-6000 K.
A dye laser with an energy of 1-3 J with a pulse length of 1 (mu)s was used to heat the solid hydrogen. The temperature of the heated hydrogen was measured indirectly by time-of-flight techniques which relate the velocities of hydrogen particles to their initial temperature. A Faraday cup probe was used to measure the velocity of hydrogen ions and a piezoelectric probe was used to measure the velocity of neutral hydrogen.
Fast-framing, streak and shadow photography using an image converter camera was used to observe the motion of the heated hydrogen both during and after the laser pulse.
A heating model, based on thermal conduction processes, is presented. This model involves anywhere from one to three heating stages, depending on the laser intensity and the thickness of the solid hydrogen. In the first stage heating process, the laser energy goes into heating a volume of hydrogen gas between the metallic substrate and the solid hydrogen. The heated gas causes ablation of solid hydrogen and the pressure associated with the heated gas drives a shock wave into the solid hydrogen. When the pressure reaches a certain threshold, the strength of the shock wave is great enough so that the energy imparted to the shocked hydrogen is sufficient to vaporize it. At this time, the laser energy still goes into heating the hydrogen gas, but now the amount of hydrogen gas is much greater due to vaporization by the shock wave. When all the solid hydrogen is vaporized, the final heating stage begins.
The experimental results for two thicknesses of solid hydrogen are compared to results obtained from the heating model.
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