Peter Trogdon Sheehey

Two‐dimensional direct simulation of deuterium‐fiber‐initiated Z pinches with detailed comparison to experiment

Deuterium‐fiber‐initiated Z‐pinch experiments have been simulated using a two‐dimensional resistive magnetohydrodynamic model, which includes many important experimental details, such as ‘‘cold‐start’’ initial conditions, thermal conduction, radiation, actual discharge current versus time, and grids of sufficient size and resolution to allow realistic development of the plasma. When the fiber becomes fully ionized (at a time depending on current ramp and fiber thickness), the simulations show rapidly developing m=0 instabilities, which originated in the corona surrounding the fiber, drive intense nonuniform heating and rapid expansion of the plasma column. Diagnostics generated from the simulation results, such as shadowgrams and interferograms, are in good agreement with experiment.

Computational modeling of wall-supported dense Z-pinches

In our previous computational modeling of deuterium-fiber-initiated Z-pinches intended for ohmic self-heating to fusion conditions, instability-driven expansion caused densities to drop far below those desired for fusion applications; such behavior has been observed on experiments such as Los Alamos` HDZP-II. A new application for deuterium-fiber-initiated Z-pinches is Magnetized Target Fusion (MTF), in which a preheated and magnetized target plasma is hydrodynamically compressed, by a separately driven liner, to fusion conditions. Although the conditions necessary for suitable target plasma--density O(10{sup 18} cm{sup -3}), temperature O(100 eV), magnetic field O(100 kG)--are less extreme than those required for the previous ohmically heated fusion scheme, the plasma must remain magnetically insulated and clean long enough to be compressed by the imploding liner to fusion conditions, e.g., several microseconds. A fiber-initiated Z-pinch in a 2-cm-radius, 2-cm long conducting liner has been built at Los Alamos to investigate its suitability as an MTF target plasma. Two-dimensional magnetohydrodynamic modeling of this experiment shows early instability similar to that seen on HDZP-II; however, when plasma finds support and stabilization at the outer radial wall, a relatively stable profile forms and persists. Comparison of experimental results and computations, and computational inclusion of additional experimental details is being done. Analytic and computational investigation is also being done on possible instability-driven cooling of the plasma by Benard-like convective cells adjacent to the cold wall.

MHD Simulation of Deuterium‐Fiber‐Initiated Z‐Pinches with Two‐Fluid Effects

Two-dimensional cold-start resistive MHD computations of formation and evolution of deuterium-fiber-initiated Z-pinches have been extended to include separate ion and electron energy equations and finite-Larmor-radius ordered terms. In the Ohms Law (magnetic field evolution) equation, Hall and diamagnetic pressure terms have been added, and corresponding terms have been added to the energy equations. Comparison is made of the results of these computations with previous computations and with experiments.