A review of the dense Z-pinch

Plasma Phys. Control. Fusion 53 (2011) 093001
Topical Review
Figure 98. Schematic of a radial wire-array experiment. Currents flow radially through fine
metallic wire from an outer ring electrode to a central cylindrical electrode, producing a toroidal
magnetic field which lies below the wires. (b) The J × B force acting on the plasma ablated
from the wires produces an axially flowing precursor plasma of low magnetic Reynolds’ number.
(c) When gaps form in the wires full acceleration of the plasma with the current begins near the
central electrode, leading to the formation of a magnetic cavity, which evolves (d) into a magnetic
tower jet driven upwards by the azimuthal magnetic field [730, figure 1]. Courtesy of the Royal
Astronomical Society.
wall. This is questionable. The argument is that in the frame of the highly supersonic jet the
resistive wall will behave as a perfect conductor to magnetic perturbations. (Similar arguments
are employed for rotating plasmas in a tokamak, but here there is actually a solid conducting
wall). If the kinetic energy of the jet exceeds the magnetic energy, it can be argued that the
current driven instability will not destroy the jet, but merely lead to dissipation of the current.
Then the gross dynamics will be governed by the KH instability associated with the velocity
shear. Lucek and Bell [207] have modelled the 3D MHD evolution of a jet without a rigid wall
and find that wild kink instabilities can occur, but [208] can be stabilized by having an axial
component of magnetic field.
More needs to be done to resolve the issues. In examining data from an extra galactic radio
jet, Kronberg [725] concludes that the energy flow is dominated by the Poynting flux rather
than the kinetic energy of the jet. An estimate of the magnetic field from Faraday rotation of
3C 303 gives 3 mG (3×10 −7 T) at a distance from the jet axis of 400 pc leads to an axial current
of ∼10 18 A in a low pitch reversed field pinch configuration with β estimated as 10 −5 . In
the formation of the MHD jet the development of a ‘magnetic tower’ is postulated [727, 728].
Indeed Hartigan et al [729] argue that magnetic fields must be dominant in producing jets, even
if they later play only a minor role in bow shocks. The laboratory Z-pinch has been adapted to
model the creation of a magnetic tower by Lebedev et al [730] and modelled in 2D MHD by
Ciardi et al [731]. For this radial wire arrays were employed, rather like the spokes off a wheel,
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