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Effects of Vapor Shield Expansion on Vapor Shield Effectiveness and Plasma Gun Efficiency

Eric Tucker, J. Gilligan

Fusion Science and Technology

Volume 33 / Number 2 / March 1998 / Pages 118-129


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The vapor shield outward expansion rate can be shown to affect energy transport through the vapor shield, thereby influencing the vapor shield effectiveness. To more accurately determine the divertor plate erosion depth from a tokamak fusion reactor disruption or plasma gun sources, it is then necessary to include source plasma (beam) momentum transfer and beam mass deposition to the expanding vapor shield. Other factors such as incident heat flux and target Z value are shown to influence the vapor shield expansion rate as well. Code calculations show that increasing heat fluxes can increase the fraction of vapor shield kinetic energy and lower the fraction f of incident energy transported to the solid. Low-Z materials give higher kinetic energies as well but result in a higher f due to a lower specific heat. These results can also be applied to plasma gun technology to help increase its efficiency. In an electrothermal gun, the plasma expansion rate (rate at which vaporized material travels out of the gun) can cause differing plasma residence times and differing plasma temperatures as well. Determining the mechanisms that influence the vapor shield expansion rate and showing its sensitivity on f can give us a qualitative way of determining how changing parameters can influence plasma gun efficiency. Low-energy (<200 eV) disruption plasmas add much mass as well as momentum to a vapor shield. Mass addition can cause the vapor shield temperature and f to differ for a given incident heat flux and change the vapor shield expansion rate as well. Also, we find that deuterium's shielding effectiveness differs from carbon.

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