Heating of on-axis plasma heating for keV X-ray production with Z-pinches

Abstract

We discuss a new opportunity of using Z-pinch plasma radiation sources for generating Ar K-shell radiation and harder keV quanta. Our approach to keV X-ray generation is based upon an analogy with laser fusion, where the imploding shell compressionally heats the low-density inner mass. The suggested design of a Z-pinch load consists then of one or two heavy outer shell(s) with a lower mass on-axis fill (i.e., central gas jet) producing most of the radiation. The outer shell is not supposed to radiate and thus does not need to have high specific energy characterized by the large parameter (Whitney et al., 1990). Thus, the heavy outer shell does not need to have a very large initial diameter for its implosion to be matched to the long-pulse current driver. Rather, we want to have a large amount of energy from the driver coupled to this shell by the moment when the shell collides with the low-density fill and eventually converts much of this energy to the thermal energy of the on-axis plasma. This configuration is investigated numerically in the framework of a one-dimensional radiation-magneto-hydrodynamics model for the case of Ar K-shell radiators. It is demonstrated that the Ar fill is heated in two stages. The first stage corresponds to the shock heating and thermal conduction in an initially low-density fill, and it allows preheating the fill while avoiding significant losses in soft radiation. The fill radiator is then compressed quasi-adiabatically and is heated-up to the temperature optimum for K-shell quanta generation. Diffusion of the driving magnetic field is shown to always suppress the conductive heat losses from the hot on-axis plasma to the cold outer shell. Absorption of the K-lines emitted near the axis in the surrounding plasma could be avoided by filling the outer shell with a different gas (like N-on-Ar), which allows a substantial increase in the observed keV X-ray radiation yields.

Numerical and experimental investigations on the interaction of light wire-array Z-pinches with embedded heavy foam converters

“…The initial tungsten plasma is assumed as a shell-like profile, which can reproduce the essential characteristics of Z-pinch implosions in the simulations, 17,18 although wire initiation and ablation are important for the final implosion quality. 19 In our simulations, an initial 1 mm wide plasma shell with an initial temperature of 3 eV, containing 94% of the mass of the wire-array is assumed.…”

Gas puff Z-pinch implosions with external Bz field on COBRA

“…The dense center jet plasma is first pre-heated by a converging shock wave when the imploding plasma approaches the axis, and is then heated quasiadiabatically as long as the implosion continues. 2 We have tested three type load configurations, an outer Ne shell imploding on an inner Ar shell with a center Ar jet (relatively stable), the outer Ne shell without the inner Ar shell (unstable implosion) and the second configuration with an external magnetic field (less unstable).…”

Study of the precursor and non-precursor implosion regimes in wire array Z-pinches

“…32 A small amount of on-axis mass, however, may enhance x-ray output by providing a target for shock heating and compression. 33 The effect of the precursor in the implosion process and on the x-ray yield can be complicated, but the relevant physical processes can be studied in experiments. Furthermore, there are wire array configurations that implode without a central precursor.…”