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(EXP3/07) The Production and Confinement of Runaway Electrons with Impurity ``Killer'' Pellets in DIII-D

   
T. E. Evans , P. L. Taylor , A. G. Kellman , P. Parks , D. A. Humphreys , M. J. Schaffer , A. W. Hyatt , R. L. Lee , J. A. Leuer 
General Atomics, P.O. Box 85608, San Diego, California, U.S.A.
 
D. G. Whyte , S. C. Luckhardt , D. Gray , J. Zhang 
University of California, San Diego, La Jolla, California, U.S.A.
 
R. W. Harvey 
CompX, Del Mar, California, U.S.A.
 
T. Jernigan , L. R. Baylor 
Oak Ridge National Lasboratory, Oak Ridge, Tennessee, U.S.A.

Abstract
Prompt runaway electron bursts, generated by rapidly cooling DIII-D  plasmas with argon ``killer'' pellets, are used to test a recent knock-on avalanche theory describing the growth of multi-MeV runaway electron currents during disruptions in tokamaks. Runaway current amplitudes, observed during some but not all DIII-D current quenches, are consistent with growth rates predicted by the theory assuming a pre-current quench runaway electron density of approximately $\rm 10^{15} m^{-3}$. Argon ``killer'' pellet modeling yields runaway densities of between $\rm 10^{15}$ - $\rm 10^{15} m^{-3}$ in these discharges. Although knock-on avalanching appears to agree rather well with the measurements, relatively small avalanche amplification factors combined with uncertainties in the spatial distribution of pellet mass and cooling rates make it difficult to unambiguously confirm the proposed theory with existing data. Additional measurements are proposed which should enable us to definitively test the theory.

   

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