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In recent years, series of experiments of Z-pinch dynamic hohlraums were performed on the PTS facility. The radiating shocks were observed and the formation of dynamic hohlraums is affirmed in this 7~8MA pulse power facility. In this paper the implosion dynamics of dynamic hohlraums is numerically investigated using a one-dimensional RMHD code using the same parameters in experiments. It is shown that a local high pressure region, which is generated by the impaction of the tungsten plasma with the converter plasma, is crucial to launch the strongly radiating shock wave and to form the dynamic hohlruam. As the shock propagates to the axis, the hohlraum volume becomes small and the radiation temperature is also increased. Basically, the hohlraum radiation is determined by the detailed profiles of plasma conditions when the wire-array plasma impacts onto the CH converter plasma. Numerical results show that a suitable mass ratio of the wire-array to the CH converter is very important to affect the hohlraum radiation. When this mass ratio is slightly lower than unity, for example 0.75, a relatively optimal dynamic hohlraum can be produced. Also, the ratio of the initial wire-array radius to the converter radius is important to determine the shape of the hohlraum radiation. The radiation transfer largely depends on the radiation temperature and the mass density of the converter. When the mass ratio of the wire-array to the converter is near 1.0, the radiation temperature can be increased to about 120e V with the PTS drive current. In this case, the radiation generated from the interaction region will quickly transfer to the center of the converter. The experimental end-on x-ray images present the overall process of radiation production and transfer of this kind of dynamic hohlraums. As the mass ratio is decreased, the radiation temperature will also be deceased, and the converter will become more opaque to the radiation. In the case of extremely low mass ratio such as lower than 0.3, the peak radiation temperature will be lower than 100e V, and the radiation transfers very slowly to the interior of the converter and presents the large non-uniformity, which is also observed in experiments on the PTS facility. The characteristics of measured radial and axial radiation power, the shock production and propagation, as well as the variation of dynamic parameters also validate our qualitative understanding of dynamic hohraums. |
