A review of the dense Z-pinch

Plasma Phys. Control. Fusion 53 (2011) 093001
Topical Review
Division of the American Physical Society as well as the series of International Conferences
on Dense Z-pinches, and represent a marked shift of interest back to perhaps the oldest topic
in plasma physics. At the 2005 European Physical Society Conference on Plasma Physics, the
opening Alfvén Prize lecture and the following plenary lecture were devoted to the remarkable
achievements of wire-array Z-pinches.
The new growth in Z-pinch research was already occurring from 1975 from smaller and
pioneering research at Imperial College, Ecole Polytechnique, the universities of Düsseldorf
and Stuttgart in Europe, Los Alamos National Laboratory, the Naval Research Laboratory
at Washington, the Air Force Research Laboratory at Albuquerque, Physics International and
Maxwell Laboratories in the US, and the Russian laboratories at Troitzk and Tomsk, plus many
other smaller groups.
One stimulus for this growth was the technological development of pulsed power at AWE
(Aldermaston) pioneered by Martin and his team [6], and further developed in the national
laboratories in the US and USSR in the 1970s. This would allow the coupling of 1–100 TW
of power in typically a 100 ns pulse to a Z-pinch load.
Whilst a major purpose of such experiments in the US national laboratories was the
development of an intense pulsed x-ray source, the availability of megampère and megavolt
power sources led the more academic scientific world to study also the subjects of radiative
collapse and high power-density controlled fusion, together with the possibility of stabilizing
by finite ion Larmor radius and sheared flow. This was the main original motivation behind the
DZP project at Imperial College which led to the construction of the MAGPIE (Mega Ampère
Generator for Plasma Implosion Experiments) facility (2.4 MV, 2 MA, 150 ns) in 1989 [7]. It
was opened formally in April 1993 at the 3rd International DZP Conference in London by
J C Martin and by Drs R S Pease and S I Braginskii, the two independent discoverers in 1957
of a so-called limiting current (known as the Pease–Braginskii current), when bremsstrahlung
losses balance Joule heating [8, 9].
In addition to the availability of technology was the theoretical realization that under
the conditions for fusion or for radiative collapse [10], the ion Larmor radius would be a
significant fraction of the pinch radius, and enhanced stability might occur [11–13]; this
enhanced stability has only recently been established experimentally [14]. Under radiative
collapse conditions, a one-dimensional simulation [15] predicts the occurrence for 1 ps of a
density of 10 5 ×solid hydrogen limited only by degeneracy pressure and opacity. However, this
again assumes stability, which experimentally was found not to occur when employing frozen
deuterium fibres as initial conditions. (More recently it has been shown that ion-viscous heating
associated with the nonlinear development of short wavelength m = 0 MHD modes would
in any case prevent radiative collapse at high currents. Indeed this heating mechanism has
produced record temperatures of 200–300 keV in stainless-steel wire arrays. See section 5.8.)
Meanwhile with the spectacular results of short, high power x-ray pulses coming from wire
implosions at Sandia, the MAGPIE generator was switched to study this subject in 1998. The
physical processes could be explored in detail using the many diagnostics, laser probing and
x-ray and optical, streak and framing cameras, which have easy access to the wire arrays.
Z-pinches have also been studied at CERN for use as a magnetic lens for focussing high
energy charged particle beams [16]. Rocca et al employed the Z-pinch as a compact table-top
x-ray laser in a capillary configuration [17]. Z-pinches can be used as a source of x-rays or
neutrons for diagnostic purposes. In laser-plasma Z-pinch-like phenomena also occur due to
∇T ×∇n generation of azimuthal magnetic fields [18], while fields of opposite sign also arise
in the fast-ignitor concept [19].
In this review we will cover all the basic physics of the Z-pinch especially its susceptibility
to instabilities, and its applications.
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