A review of the dense Z-pinch

Plasma Phys. Control. Fusion 53 (2011) 093001
Topical Review
Figure 44. Scheme of the experimental set-up for x-ray backlighting by image of a 20 µm Ti wire
in a 16 wire array at 180 ns on MAGPIE. Reprinted with permission from [578]. Copyright 2001,
American Institute of Physics.
Figure 45. Electron pressure versus density for various temperatures in a modified Thomas–Fermi
model. A typical trajectory for material ablated from the core and expanding into the corona is
shown. Reprinted figure with permission from [336]. Copyright 2000 by the American Physical
Society.
the wire induces a breakdown in the vapour (and desorbed gases) surrounding the wire core.
There is a sharp voltage drop as the current transfers to the highly conducting plasma. Further
experiments by Sinars et al measured the initial energy deposition and expansion rates of
exploding wires [334]. Recently Douglass et al [335] employed multi-frame radiography to
show the development of structure in wire cores.
This heterogeneous core structure has not been modelled and makes realistic calculations
of mass ablation rates very difficult. So far the expanding cores are assumed to be in a
homogeneous state, being a modified Thomas–Fermi equation of state as shown in figure 45
and used by Chittenden et al [336]. Here single wire ‘cold-start’ 2D simulations showed a
persistent core surrounded by a m = 0 unstable coronal plasma in the r–z plane, showing
excellent agreement with coronal measurements in experiments by Beg et al [254]. Expansion
rates and coronal plasma formation have recently been studied by Shelkovenko et al [337].
A paper by Yu et al [338] shows that radiation transport is greater than thermal transport
in most of the dense plasma surrounding the wire core. Yu employs r-ϑ simulations of a wire
in an array to obtain the mass ablation rate in an asymptotic steady state, using a single-group
radiation diffusion model. To gain physical insight and to obtain analytic scaling laws Yu
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