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The wire-array z-pinch has in a very short time achieved remarkable performance as a powerful (>200?TW), pulsed soft x-ray source of high efficiency (~15%) and of great relevance to inertial confinement fusion. The underlying physics involves the transformation of wire cores to a plasma corona, the occurrence of uncorrelated axial instabilities, inward flowing low magnetic Reynolds number jets, sometimes an accumulated stable and dynamically confined precursor column, an almost constant velocity implosion when gaps occur in the wire cores and finally at stagnation a fast-rising soft x-ray pulse of typically 5?ns FWHM. Nested arrays improve the performance and can operate in several modes. Three hohlraum designs have been tested; one of these, the dynamic hohlraum, has achieved a radiation temperature of ~230?eV and has compressed a capsule from 2 to ~0.8?mm diameter with a neutron yield of > 1010thermal DD neutrons. Lower mass stainless steel wire arrays are used for K?radiation sources. Generally implosions lead to more energy radiated than the implosive kinetic energy, and this is hypothesized as being due to ion viscous heating, as fast-growing short wavelength nonlinear MHD instabilities are dissipated; record ion temperatures of 200-300?keV are predicted and have been measured for the stainless steel array on Zat Sandia.

A review of recent experiments on the MAGPIE generator (1?MA, 250?ns) aimed at studying the implosion dynamics of wire array Z-pinches is presented. The first phase of implosion is dominated by the gradual ablation of stationary wire cores and gradual redistribution of the array mass by the precursor plasma flow. It is found that the rate of wire ablation depends on the magnitude of the global (collective) magnetic field of the array, and increases with the field. The existence of the modulation of the ablation rate along the wires leads to the presence of a 'trailing' mass left behind by the imploding current sheath. The trailing mass provides an alternative path for the current, reducing the force available for compression of the pinch at stagnation. The observed dependence of the ablation rate on inter-wire separation suggests an explanation for the existence of the optimal wire number maximizing the x-ray power. Axially resolved spectroscopy shows the presence of the x-ray 'bright' spots (< 150?µm) emitting intense continuum radiation.

Progress in understanding the physics of dynamic-hohlraums is reviewed for a system capable of generating 13?TW of axial radiation for high temperature (>200?eV) radiation-flow experiments and ICF capsule implosions.

Proton imaging is a recently proposed technique for diagnosis of dense plasmas, which favourably exploits the properties of protons produced by high-intensity laser-matter interaction. The technique allows the distribution of electric fields in plasmas and around laser-irradiated targets to be explored for the first time with high temporal and spatial resolution. This leads to the possibility of investigating as yet unexplored physical issues. In particular we will present measurements of transient electric fields in laser-plasmas and around laser-irradiated targets under various interaction conditions. Complex electric field structures have been observed in long-scale laser-produced plasmas, while global target charge-up and growth of electromagnetic instabilities have been detected following ultraintense interactions with solid targets.

The modified Fokker–Planck collision operator for partially degenerate electrons was derived in an earlier paper [J. Plasma Phys. 58, 577 (1997)]. This is now employed to study linear electron transport for a partially degenerate, magnetized plasma. Because polynomial expansions can yield incorrect transport coefficients owing to lack of resolution of the small fraction of low-energy unmagnetized electrons, a numerical discrete-ordinate scheme is employed. The inclusion of electron–electron collisions advances the model beyond that of Lee and More, and in the classical limit agrees with the results of Epperlein and Haines.

The problem of producing the hard X-ray burst at the onset of solar flares may be thought of in terms of the problem of producing the non-thermal electrons which emit the X-rays via bremsstrahlung. Electron acceleration to relativistic energies without similar ion acceleration is difficult to achieve, even in an ad hoc theoretical model. Yet from global energetic considerations, it is not feasible to accelerate the electrons as a minor constituent of the total energetic particle population. Therefore, it is necessary to invoke a more sophisticated process for the electron acceleration. In this paper we describe a mechanism for achieving this via an initial acceleration of a neutralized ion beam. When such a beam impacts the chromosphere, the electrons start to scatter while the ions continue downwards, rapidly setting up an electric field which is either cancelled by the inflow of background chromospheric electrons or results in the runaway acceleration of beam electrons. In the former case the result is simply heating, whereas in the latter case much of the ion kinetic energy is transferred into electron kinetic energy. The final electron energy may be similar to the typical energy of the ions. The electrons that are accelerated are those in the neutral beam that experience an electric field greater than the critical Dreicer field. Thus there will be a low-energy cut-off to the electron spectrum which overcomes the well-known energetics problem at low energies with certain other spectral forms.

The quantum Boltzmann collision operator is expanded to yield a degenerate form of the Fokker–Planck collision operator. This is analysed using Rosenbluth potentials to give a degenerate analogue of the Shkarofsky operator. The distribution function is then expanded about an equilibrium Fermi–Dirac distribution function using a tensor perturbation formulation to give a zeroth-order and a first-order collision operator. These equations are shown to satisfy the relevant conservation equations. It is shown that the distribution function relaxes to a Fermi–Dirac form through electron–electron collisions.

The main part of this paper surveys the mechanisms that can lead to rotation of plasma in an electrodeless discharge (commonly called a theta pinch) and in a mirror machine. Eight proposed mechanisms are examined, of which two are found to be incorrect in some way. Another mechanism, in which the reaction is purely electromagnetic, applies only to the tenuous plasma of a mirror machine. The remaining five theories apply to the highly compressed plasma of a theta pinch. These all rely fundamentally on the large difference in mass between an ion and an electron, i.e. either on Hall currents or the correction for finite ion Larmor radius in the stress tensor. The mechanisms which incorporate the Hall effect cause an equal and opposite mechanical reaction either on the wall (Roberts and Taylor), or on external conductors (Haines), or on the plasma at each end of the discharge axis (Bostick). The mechanisms which use the collisionless stress tensor predict either radial division into oppositely rotating plasma (Velikhov) or a transfer of angular momentum to the walls by collisions during the initial stage of physical contact (Haines). This last theory is new and arose as a result of a critical examination of an earlier theory (Jensen and Voorhies).Experimental evidence for rotation has been confined mainly to high speed photographic techniques, and methods of obtaining a more definite measurement of the rotation and its origin are suggested.The paper distinguishes carefully between the angular motions associated with the centre of mass, the guiding centres and the diamagnetic current, and also considers the stability of a rotating plasma including the Hall effect and the collisionless stress tensor.