CHARACTERIZATION OF ENERGY-FLOW AND INSTABILITY-DEVELOPMENT IN 2-DIMENSIONAL SIMULATIONS OF HOLLOW Z-PINCHES

A two-dimensional (2-D) Eulerian Radiation-Magnetohydrodynamic (RMHD) code has been used to simulate imploding Z pinches for three experimen ts fielded on the Los Alamos Pegasus B capacitor bank [J. C. Cochrane et al., Dense Z-Pinches, Third International Conference, London, Unite d Kingdom 1993 (American Institute of Physics, New York, 1994), p. 381 ] and the Sandia Saturn accelerator [R. B. Spielman et al., Dense Z-Pi nches, Second International Conference, Laguna Beach, 1989 (American I nstitute of Physics, New York, 1989), p. 3] and Z accelerator [R. B. S pielman et al., Phys. Plasmas 5, 2105 (1998)]. These simulations match the experimental results closely and illustrate how the code results may be used to track the flow of energy in the simulation and account for the amount of total radiated energy. The differences between the c alculated radiated energy and power in 2-D simulations and those from zero-dimensional (0-D) and one-dimensional (1-D) Lagrangian simulation s (which typically underpredict the total radiated energy and overpred ict power) are due to the radially extended nature of the plasma shell , an effect which arises from the presence of magnetically driven Rayl eigh-Taylor instabilities. The magnetic Rayleigh-Taylor instabilities differ substantially from hydrodynamically driven instabilities and ty pical measures of instability development such as e-folding times and mixing layer thickness are inapplicable or of limited value. A new mea sure of global instability development is introduced, tied to the impl oding plasma mass, termed ''fractional involved mass.'' Examples of th is quantity are shown for the three experiments along with a discussio n of the applicability of this measure. (C) 1998 American Institute of Physics. [S1070-664X(98)00209-2]