A review of the dense Z-pinch

Plasma Phys. Control. Fusion 53 (2011) 093001
Topical Review
Figure 62. Schematic of nested wire arrays with (a) low inductance and (b) high inductance
connection of the inner array. Reprinted figure with permission from [325, figure 1]. Copyright
2000 by the American Physical Society.
by radiative cooling coupled with the kinetic pressure ρVa 2 of the impinging precursor streams.
At 215 ns, figure 61 shows the structure of the ‘magnetic piston’ half-way through the implosion
phase, and consists of a large number of axisymmetric m = 0 magnetic bubbles moving towards
the axis. To the extent that it is a snowplough mechanism which requires energy loss, inelastic
collisions (excitation and ionization) will lead to XUV radiation, and this is stronger in front
of the larger bubbles that move faster. By now the wavelength of the modulations has grown
to ∼2 mm. Even with the small number of wires in this particular array the onset of global
correlation is very evident, and represents the same phenomenon as observed in high wire
number arrays. The RT structure is similar to that simulated by Peterson et al [233]. Note that
in the laboratory frame as opposed to the accelerating frame represented in theories by gravity
g, the bubbles are accelerating inward while the spike tips remain at the original wire-array
radius. These spikes form the trailing mass, clearly obvious at 245 ns in figure 61, which will
be considered in section 5.11. During the ablation and implosion phases, there appears to
be no evidence of kink and azimuthal displacement instabilities as proposed by Felber and
Rostoker [378], Marder et al [379] and Hammer and Ryutov [380] which would probably be
only slowly growing anyway. Ivanov et al [381] imaged bubble formation in 8- and 4-wire
cylindrical arrays, and employed Faraday rotation techniques to measure the magnetic field
strength. However such fields are unlikely to be characteristic of high wire-number implosions.
5.6. Nested arrays
The use of a nested, inner array has led to a significant improvement in the performance of
the wire-array Z-pinch, and was used in high performance shots [1, 2] and in recent detailed
studies [323]. It was proposed by Davis et al [60] so that, as the outer array plasma passed
through the inner array, the current would switch to the inner array, because of the high
conductivity of the inner wires and the inductive coupling between the two arrays. At this time
the driving force behind the RT growth would also transfer to the inner array which would start
to ablate and implode with initially no RT amplitude; thus at the final stagnation a much more
symmetric plasma should result.
Simulations by Chittenden et al [327] show three modes of operation as discussed in
section 5.1 while experiments on MAGPIE [325] distinguished two modes, dependent on the
fraction of total current induced in the inner array. Experiments were conducted with a 16 mm
diameter outer array and an 8 mm diameter inner array each 16×15 µm aluminium. Figure 62
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