Wire array Z-pinches

wire array
Gorgon simulation of an 8-wire array Z-pinch

Wire array Z-pinches are the worlds’ most powerful X-ray sources. When a cylindrical array of thin wires is subjected to a large, fast rising current, the wires heat up and become plasma, the magnetic field created then pulls the plasma to the common axis, with implosion velocities of several hundred kilometers per second. 

Upon arrival at the axis, the kinetic energy is transformed to thermal energy resulting in a plasma of very high temperature (~1keV) and density (~1020 ions/cm3). The X-ray production in such plasmas is enormous, experiments at Sandia National Laboratory produce ~2 MJ of X-rays with peak powers of ~290 TW. These X-ray pulses are used to energise hohlraums both for inertial confinement fusion experiments and as a testbed for experiments investigating the opacity of stellar material, the instabilities of exploding supernovae and the equation of state of strongly coupled plasmas.

X-Pinches

An X-pinch is a variation of a wire array Z-pinch and consists of two or more thin metallic wires crossed in the shape of an “X”. By applying a large (100 – 500 kA), fast rising current (~ 100 ns) through the wires, several rapid bursts (~ 1 ns) of soft x-rays are produced from micron sized hot-spots forming at the cross-point between the wires. Here the plasma densitiy exceeds 1022 cm-3 and temperatures of ~ 1 keV are achieved. Because of the temporal and spatial characteristics of the X-ray emission, X-pinches are routinely used as backlighter diagnostics.

The complex physical evolution of an x-pinch is studied in detail using the three-dimensional resistive magneto-hydrodynamic code Gorgon. X-ray emission is preceded by the formation of jet-like structures and a miniature z-pinch plasma column. A combination of radiative collapse and axial flow drive the initial radial implosion of the z-pinch until the onset of MHD instabilities further compresses regions of the plasma producing the x-ray bursts. 

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