Intense light-ion beam (LIB) propagation through a plasma channel is numerically investigated by using a two-dimensional simulation code. Analyses are given for the LIB propagation which couples with the motion of the channel plasma. Although the electron back current neutralizes the LIB current under typical beam and channel plasma conditions, the Lorentz force of the electron back current expands the LIB radially. The expansion of the LIB depends strongly on the density of the channel plasma. A strong current of the order of 1 MA is shown to propagate stably in an argon plasma channel.

The symmetry of heavy ion driven inertial confinement fusion targets is investigated with a two-dimensional Eulerian hydrodynamic code. The importance of the beam geometry is studied. The HIBALL design in its present form seems to inhibit a spherical implosion of the target. It is shown that the beam angle in the HIBALL geometry should be about 35 degrees.

By employing analytic solutions for the electromagnetic field at resonance absorption, first derived by Denisov, the total nonlinear force, in the plane of incidence has been evaluated. This 2-D force results in a conical type emission towards the vacuum and into the plasma which depends critically on the collision frequency and the density scale length. It is found that, for neodynium glass laser intensities of 1014 W/cm2, keV ions can be produced by nonlinear force acceleration. The analysis is limited by the following requirements: the dielectric constant varies linearly with distance, the angle of incidence is not too small and most importantly self consistent and transient wave processes occur at a later time and are neglected.

A simple model is presented for the thermodynamic and hydrodynamic behaviour of solid targets heated by intense charged particle beams. The model gives the temperature and pressure generated by the beam and allows a direct comparison with the pressure generated by laser beams. The model is in good agreement with a coupled thermodynamic hydrodynamic computer simulation.

Numerical simulations and analyses are given for the implosion of a hollow shell target driven by proton beams. The target consists of three layers of Pb, Al and DT. The Pb and Al layers play roles of a tamper and a pusher, respectively. The main part of the beam energy is deposited in the Al layer. But the process of deposition depends strongly on the distribution of incident angles and particle energies. As the Al layer is heated by proton beams, the layer expands and pushes the DT layer toward the target centre. This type of implosion motion is examined by using a similarity solution for the slab model. To obtain an optimum velocity for the DT implosion, the optimum target size and optimum layer thicknesses are determined. The Rayleigh–Taylor instability, accompanied by the implosion motion is investigated, and the implosion is found to be stable with respect to the chosen target structure. The effects of inhomogeneities on implosion are shown to be severe. The initial fluctuation of the temperature or the density in the Al layer must be less than 3% and the maximum amplitude of the ripples on the initial boundary surface should be less than 3 μm with a view to achieving a high target gain.

A photolithographic process to fabricate the transition metal targets used in X-ray laser experiments is described.

Strong ion coupling effects could play an important role in laser–and particle beam–compressed ICF layered targets. Some light is shed on these effects by examining structure and pair correlation functions calculated from some of the well known strongly coupled plasma approximation schemes.

The effect of small-scale wavefront perturbations on laser radiation is investigated at flux densities close to maximum. The model and calculated results for the effect of the degree of radiation coherence on the laser radiation brightness as functions of flux density and length and shape of the active medium are presented. For the restricted coherence of the laser radiation, the rate of small-scale perturbation growth is shown to decrease in theactive medium. The principal optical scheme of a laser for fusion experiments, with the maximum radiation brightness, is given as an example.

The one-dimensional Lagrangian code MEDUSA has been adapted to model the pressure of laser photons and the transfer of laser light momentum to underdense plasma investigated using the modified code. It is shown for lasers of wavelength ≃ 1μm that the plasma electron density needs to be close to the critical density (1021cm−3) and that the laser intensity needs to be greater than ∼1016Wcm−2 for significant laser momentum transfer to plasma. It was found that small plasmas (scale-length = 1 μm) result in the best ‘signature’ of laser light momentum transfer to plasma (more enhanced expansion velocities) but that the largest momentum transfer is for the largest plasmas considered (scale-length = 100 μm). The formation of suitable underdense plasmas for momentum transfer by a laser pre-pulse onto a foil target is investigated using a two-dimensional Eulerian code.

The change of the energetic quantum levels of electrons in atoms or ions within plasma due to the electrostatic energy of the Debye sphere, is discussed on the basis of an electrostatic quantum model which permits an immediate, and therefore an integrated, inclusion of the Debye screening. The resulting Debye field leads to an alternative (temperature dependent) formulation of the Inglis-Teller Stark merging of spectral lines. In the new model the drowning of lines gives values closer to the Inglis-Teller limit than values given by the quantum approximation of the hydrogenic model. The straightforward calculation of the polarization shift based on the new model is closest to the experimental values and is between the very low values given by the semiclassical approach and the too high values given by the quantum approach of the hydrogenic effective charge model.

While the action of electrostatic double layers in the periphery of an expanding laser produced plasma has been discussed and treated many years ago, some new aspects pioneered recently by Alfvén in the theory of cosmic plasmas, indicate the possibility of a new treatment. The thermally produced electrostatic double layer which has been re-derived for a homogeneous plasma shows that a strong upshift of ion energies (by the mass ratio) is possible, in agreement with experiments. The number of accelerated ions is many orders of magnitude smaller than observed at keV and MeV energies. The nonlinear force acceleration could explain the number and energy of the observed fast ions. It is shown, however, that electrostatic double layers can be generated which should produce super-fast ions. This paper presents a derivation of the spread double layers in the case of inhomogeneous plasmas. It is concluded that the hydrodynamically expected multi GeV heavy ions for 10TW laser pulses (generated by relativistic self-focussing and nonlinear forces) should produce super-fast ions up to the TeV range. Further conclusions are drawn from the electrostatically measured upshifted (by 300 keV) DT fusion alphas from laser compressed plasma. An analysis of alpha spectra attempts to distinguish between different models of the stopping power in the plasmas. The analysis preliminarily arrives at a preference for the collective model.

Inertial Confinement Fusion (ICF) research has been extensively advanced with the increase of the focusable power on target by the development of glass laser technology and its higher harmonic generation (Yamanaka & Kato et al. 1981) and by CO2 lasers (Yamanaka & Nakai et al. 1981) which cover the wavelength range from 10 μm to 0·25 μm and power densities up to 1017 W/cm2. With improved understanding of the implosion in the fuel pellet, breakeven conditions, or ignition, are expected to be achieved within the 1980's with the construction of lasers in the region of 100 kJ and 100 TW output power.

The expansion of laser-produced plasmas in two-dimensions is examined analytically using an asymptotic (time→∞) isothermal self-similar model. The ion emission velocity and energy spectra are calculated and expressions given for the number and energy of expanding ions as a function of angle to the target. By relating the total ion kinetic energy of expansion to the temperature of the initial plasma, it is shown that ion probe signals give a measure of the initial plasma temperature. The model is extended to a plasma with two initial temperatures (a ‘hot’ component and a ‘cold’ component) and it is shown that the ion energy spectra here can be used to deduce the initial temperatures of the ‘hot’ and ‘cold’ ions and the relative number of the ‘hot’ ions to the ‘cold’ ions. The results are used to interpret data from an array of ion probes (at different angles to the target) for a plasma produced by irradiating a 25 μm thick nickel foil with a ∼20 ρs neodymium laser pulse.

It is shown that appropriate conditions for DL formation may be created in laser produced plasma. In particular, a ‘feedback’ mechanism is suggested:

Wave instabilities → absorption of laser energy → inward heat flux → DL formation → heat flux inhibition → wave instabilities

Plasma-target potentials and plasma-currents, produced by Nd. laser intensities (IL) between 1012 to 1015 W/cm2, were measured in situ. These measurements seem to be the first direct evidence of DLs in laser produced plasma. Electric fields of EDL ∼ 5 × 105 to 5 × 106 Volts/cm and widths of 10 to 100 Debye lengths are estimated for the DL.

Scaling laws are derived for the measured extremum potentials (V) and currents (I): . Two different slopes were obtained experimentally, one slope equal to α = β = 1·0 for IL < 1014 W/cm2 and another of α = β = 0·4 for IL > 1014 W/cm2. These data are explained for temperature scaling law for the low irradiance and for the high irradiance. While the first scaling law is consistent with inverse bremsstrahlung absorption, the second scaling necessitates other absorption processes. Potential and current probes are suggested as useful devices in detecting wave plasma instabilities.

A theory based on the field and non-linearity expansions interms of Laguerre-Gauss functions is presented. The theoryi useful when very fast self focusing occurs, as in the case of relativistic self focusing. Results for self trapping with a saturable non-linearity are closer to the numerical results than those obtained by any other theory.

The generation of high-energy-density plasmas by the electromagnetic implosion of cylindrical foils (i.e., imploding plasma shells or hollow z-pinches) has been explored analytically and through numerical simulation. These theoretical investigations have been performed for a variety of foil initial conditions (radius, height, and foil mass) for both capacitive and inductive pulsed power systems. The development of the theoretical modeling techniques is presented, covering both circuit models and plasma load models. The circuit models include simple single loop capacitive and multiple loop inductive systems. These circuits are coupled to the imploding plasma loads whose response has been studied by models ranging from simple time varying inductances to complex two-dimensional magnetohydrodynamic numerical simulations. Results from a series of configurations are given, showing the development of modelling techniques used to study the dynamics of the plasma implosion process and the role of instabilities. Interaction between analytic techniques and detailed numerical simulation has led to improvement in all theoretical modeling techniques presently used to study the implosion process. Comparisons of implosion times, shell structure, instability growth rates, and thermalization times have shown good agreement between analytic/heuristic techniques and more detailed two dimensional magnetohydrodynamic simulations. These in turn have provided excellent agreement with experimental results for both capacitor and inductor pulse power systems.

A model of laser interaction with a preformed target plasma is developed for the conditions of so called stimulated Brillouin backscattering (SBS) model experiments and its applicability is demonstrated by various tests. Most of the features can be understood from analytical approximations. A consequence of irradiation by a narrow beam, typical of model experiments, is the stabilization of electron temperature at low values. Another consequence equally unexpected is the SBS threshold dependence on beam radius and the particular power law dependence on plasma density. On the basis of this model the wide scatter of the SBS threshold between model experiments can be explained. It is also demonstrated that, for the conditions of these model experiments, classical Spitzer heat conduction suffices.

A hydrodynamic description is used to derive a nonlinear wave equation in the geometry of the capacitor model. For a streaming cold plasma the equation can be solved analytically. For the warm plasma case numerical results of high amplitude waves and wave breaking are presented. Flat minima and peaked maxima of the electron density and the oscillatory velocity are the most characteristic features of highly nonlinear electron waves. Their Bohm–Gross dispersion relation is modified by self-interaction of the fundamental mode.

A one-dimensional, time-dependent fluid code is presented that numerically solves the hydrodynamic equations together with the wave equation for a picosecond pulse laser heated plasma. The laser light absorption by classical inverse bremsstrahlung and the ponderomotive force are evaluated self-consistently from the computed electromagnetic field quantities. At oblique incidence of p-polarized 1·054 μm laser radiation the resonant electric field is saturated by plasma wave convection through the nonlinear density profile steepening prior to wave breaking.