Imaging and Characterization of Plasma Plumes Produced during Laser Ablation of Zirconium Carbide
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IMAGING AND CHARACTERIZATION OF PLASMA PLUMES PRODUCED DURING LASER ABLATION OF ZIRCONIUM CARBIDE DARRYL P. BUTT* AND PAUL J. WANTUCK**
*Nuclear Materials Technology Division, M.S. E505 "**Chemicaland Laser Sciences Division, M.S. J565 P.O. Box 1663, Los Alamos National Laboratory, Los Alamos, NM 87545
ABSTRACT Laser diagnostic methods are developed and used to characterize the behavior of laser ablated zirconium carbide (ZrC). Emission from zirconium atoms dominates the total emission of the plasma plumes, which are estimated to have excitation temperatures of 9000 to 12,000 K under the conditions studied. Emission from species such as C, C2, and C 3 were absent from the spectra due to the inherently low emission intensities of these species compared with that of Zr. Using a CCD camera, images of the plasma plumes are obtained from the emission and through the use of planar laser induced fluorescence of zirconium atoms.
INTRODUCTION Understanding the vaporization behavior of nuclear fuel materials in high temperature environments is critical for several proposed nuclear thermal propulsion (NTP) concepts. In particular, the uranium-zirconium-carbon (U-Zr-C) system is of importance due to the potential application of (UyZrl.y)Cx as the nuclear fuel for the proposed manned mission to Mars. 1 In a nuclear thermal rocket, a gas passes over a nuclear fuel, is heated and expands through an appropriate nozzle thus propelling the craft. To minimize flight times, most advanced NTP concepts propose using hydrogen as the propellant and require very high gas temperatures with associated fuel temperatures near or above 2800 K. The (UyZrl-y)Cx and (UyZrtly)Cx + C systems are attractive for such applications because of their excellent neutronic properties and thermal stability. Although mechanical integrity and melting point behavior are an issue, it has been suggested that corrosion will be the life-limiting factor for these fuels during rocket 2 operation. The ability to monitor the fuel corrosion products is important for understanding the corrosion kinetics and for assessing the performance of NTP systems during operation. A space NTP system will require instrumentation that can provide data on operating parameters such as gas temperature and pressure. Because the environment in the core of the rocket will be extremely harsh, many common diagnostic instruments (e.g., thermocouples) can not easily be used. Laser diagnostic methods provide several unique advantages over other diagnostic techniques. In particular, measurements can be done in situ with all the hardware located remotely. Laser diagnostics provide imaging ability, excellent temporal and spatial resolution, and are relatively unaffected by high temperatures. A diagnostic specific to a certain corrosion product could, when probing a rocket's exhaust, supply information on local gas stream concentrations and temperatures. This information could then be used, for example, to adjust the reactor operating temperature or propellant flow rate, both of which influence th
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