Z-Pinch Driven Isentropic Compression for Inertial Fusion

The achievement of high gain with inertial fusion requires the compression of hydrogen isotopes to high density and temperatures. High densities can be achieved most efficiently by isentropic compression. This requires relatively slow pressure pulses on the order of 10-20 nanoseconds; however, the pressure profile must have the appropriate time history [J. Nuckolls et. al. Nature, 239, 139, 1972]. We present 1-D numerical simulations that indicate such a pressure profile can be generated by using pulsed power driven z pinches. Although high compression is calculated, the fuel temperature is too low for ignition. Ignition could be achieved by heating a small portion of this compressed fuel with a short (-10 ps) high power laser pulse as previously described [M. Tabak et. al. Phys. Plasmas 1, 1626, 1994]. Our 1-D calculations indicate that the existing Z-accelerator could provide the driving current (~20 MA) necessary to compress fuel to roughly 1500 times solid density. At this density the required laser energy is approximately 10 kJ. Multidimensional effects such as the Rayleigh-Taylor were not addressed in this brief numerical study. These effects will undoubtedly lower fuel compression for a given drive current. Therefore it is necessary to perform z-pinch driven compression experiments. Finally, we present preliminary experimental data from the Z-accelerator indicating that current can be efficiently delivered to appropriately small loads (~ 5 mm radius) and that VISAR can be used measure high pressure during isentropic compression.