Modeling of the inverse z-pinch dynamics

The two-dimensional MHD numerical simulation MHRDR has been applied to develop and investigate a new possible fusion scheme, and design experiments to test it. The confinement of magnetized high-beta plasma directly by material walls holds considerable promise for fusion. An interesting prospective Magnetized Target Fusion (MTF) target plasma is the cylindrical inverse pinch, which is, in theory, an MHD-stable, self-organized plasma. An inverse pinch consists of coaxial, metal, current-carrying cylinders with plasma between them. Important insight into this plasma has been obtained using the MHRDR simulation. First, simulations observe that interchange m=0 modes rearrange the plasma into a pressure profile that is stable to m=0 (the Kadomtsev stable profile). Such plasma self-organization is very encouraging for the development of a robust practical device, since the pressure profile does not have to be created in a very particular manner to satisfy the Kadomtsev criterion. Second, the plasma beta can be adjusted by using an initial bias current on the central conductor to magnetize the gas before it is ionized. In this way, the plasma beta can be kept below 40%, so that, according to theory, the troublesome m=1 mode is also stabilized. (The r-z MHRDR code does not analyze the three-dimensional kink motion.) Although the convection associated with self-organization enhances thermal transport, the kinetic energy of turbulent motion is small compared to the thermal energy, and the energy transport is globally Bohm-like, which is acceptable for MTF. The MHRDR modeling is guiding the design of an experiment on the 2-TW Zebra z-pinch at UNR to test the inverse-pinch concept. For the parameters of the designed experiment, MHRDR simulations predict the 2-MV, 1-MA Marx generator will produce a deuterium plasma with B/spl sim/4T, n/spl sim/10/sup 22/m/sup -3/, T/spl sim/300 eV, and a lifetime of 10-50 microseconds. Understanding of the energy transport in this simple wall-confined plasma will increase confidence in the design of eventual integrated liner-on-plasma experiments.