Single-module analysis and experimental scale model testing indicate that a new design of the pulse-forming and transformer sections of the Particle Beam Fusion Accelerator II (PBFA II) will improve the energy transport efficiency of this machine by greater than 50%. However, these results have not considered multimodule, cross-coupling effects. This paper presents an approximate analysis of these cross-coupling effects, predicts problems that will occur, and indicates how to overcome them. Although this analysis is directed specifically at PBFA II, the techniques presented apply to the design of pulsed power machines with open-transmission lines whenever abrupt junctions occur.

Coherent X rays can be produced by Compton scattering of laser light on a relativistic electron beam, whose current is periodically modulated by the same laser radiation in a suitable miniundulator. If electron and laser photon energy are properly matched, the modulated electron beam acts as a moving diffraction grating and the X rays show a high degree of coherence. A practical implementation of this scheme is shown.

The development of hydrodynamic instability in laser targets is studied by means of the 2D numerical code “ATLANT.” At the linear stage, perturbations grow as At the nonlinear stage, the growth rate of Rayleigh-Taylor instability is reduced and new harmonics are generated. The effect of the nonuniformity of laser irradiation has been investigated for long- and shortwave perturbations. The growth rate of short-wave perturbations may be effectively decreased by means of symmetrical prepulses.

The hydrodynamic efficiency of conversion of the energy of fast charged particles into the kinetic energy of the bulk motion of plane-parallel shells is investigated in the framework of two simple models–one based on the stepwise density profile and the other employing a self-similar solution. The analytical estimates obtained are substantiated with ID hydrodynamic calculations. In case of spherical shells, the three key dimensionless parameters determining the values of the hydrodynamic efficiency are pointed out; the dependence of the hydrodynamic efficiency on these parameters has been explored numerically. The effects of a nonuniform energy deposition (increasing by the end of the fast particle ranges) and of a nonuniform absorber composition are also discussed.

Coupling of the core with the surrounding corona of hot electrons produced around the plasma critical surface in a spherically symmetric laser-imploded Z-layered plasma target has been analyzed. Considering that the energy equipartition exists between the cold electrons of the core and the hot coronal electrons in the core–corona overlapping region, the analytic expression for core–corona coupling has been derived. The efficiency of heat transfer from the hot corona to the cold core depends on the laser wavelength, mean electron temperature in the ablation region, and the width of the Z-layer in the plasma pellet. Numerical results indicate that short wavelength lasers are favorable for efficient heating of the core by the surrounding hot corona. The core-corona coupling increases primarily with the mean electron temperature up to a certain extent and beyond that further laser flux transfer to the hot corona results in decoupling of the core from the corona. The presence of Z-layer is likely to reduce the electron mean free path in the ablation region and affects the laser wavelength scaling of the core-corona coupling. It is also found to have positive influence on the maximum coupling efficiency of the core with the hot corona.

The interaction of externally injected charged particles (electrons) with plasma waves moving with a phase velocity that is very close to the speed of light is examined. Such plasma waves form the basis of at least three collective accelerator schemes: the plasma beat wave accelerator (PBWA), the plasma wake-field accelerator (PWFA), and the laser wake-field accelerator (LWFA). First, the electron trapping threshold, energy gain and acceleration length are examined using a 1-D model. This model elucidates how the final energies of the injected test electrons depend upon their injection and extraction phases and phase slippage. Phase energy diagrams are shown to be extremely useful in visualizing wave-particle interactions in 1-D. Second, we examine, using a two-dimensional model, the effects of radial electric fields on focusing or defocusing the injected particles depending upon their radial positions and phases in the relativistically moving potential well. Finally, we extend the model to 3-D so that the effect of injected particles' emittance on the acceleration process may be determined. This simple 3-D model will be extremely useful in predicting the electron energy spectra of several current experiments designed to demonstrate ultrahigh gradient acceleration of externally injected test particles by relativistic plasma waves.

Kinematical relations of nonlinear interaction of laser beams with free charged particles are analyzed. General expressions are found for the number of scattered photons as a function of the number of simultaneously absorbed and/or emitted photons and the kinetic parameters of the charged particle-photon system. The results are applied to the processes of particle acceleration by lasers, frequency conversion, solitonic propagation, and others.

By using a linear analysis, a new type of thermal self-focusing instability without inverse bremsstrahlung absorption is analyzed. In the model it is assumed that part of the light is absorbed only at the critical surface and that the heat conduction is restricted to a layer on the target. Perturbations with wavelengths comparable to target radius are studied.

The parameters of self-generated electron beams have been measured and correlated to the dynamics of a 60 kV, 28 kJ plasma focus. The electron beam emission occurs in two periods: the first corresponds to the initial formation and disruption of the pinched plasma and terminates with the disruption of the plasma column, and the second period occurs after the breaking up of the focus plasma. The first period is characterized by high-energy electron beams, whereas in the second period the electron beams have lower average energies but higher currents. A relativistic electron beam is found to occur around the time of first compression, when the plasma is observed to be macroscopically stable, in contrast to measurements obtained from machines with similar energies but operating at lower voltages. The plasma X-ray emission is observed to be closely related to the electron beam characteristics. Possible mechanisms for the formation of the electron beams observed are discussed.

A method for the compression of magnetic flux inside a cylindrical liner imploded by laser beams is analyzed using a thin shell model. Simple scaling relations are derived for a number of key parameters. The potential of this scheme, as a fast-rising magnetic pulse generator, is explored based on the scalings obtained.

A self-similar analysis of supersonic compression of a “screw-pinch” plasma is carried out that generalizes earlier analyses of pure θ-pinch and Z-pinch implosions. Solutions are found for various implosion modes. It is shown that the screw-pinch plasma implosion differs qualitatively from θ-pinch and Z-pinch implosions.

Calculations of the electron impact excitation cross sections and deposition efficiencies for singly ionized argon with electrons of energies up to and including relativistic values have been made using the first Born approximation and the generalized oscillator formalism. Deposition efficiencies for fast electrons were generated from the Peterson and Green integral equation. Cross sections and efficiencies were produced for 29 transitions from the ground state configuration of Arii to excited energy levels with (Ne)3s23p44s and (Ne)3s23p43d configurations and for 40 transitions between excited energy levels from 4s and 3d to 4p orbitals. Efficiencies are constant for electron energies above 1 keV to 10 MeV. Electrons ejected from inner shells contribute up to 12% of the efficiency of the transition for electrons above 10 keV.

A model of an electron beam interacting with neutral argon was developed by solving the chemical kinetic rate equations for the time-dependent populations of ground and excited levels of Arl and Aril as well as the populations of electron energy groups. Intensities of spectral lines were calculated, from predicted population densities and Einstein coefficients, and compared to experimental results.

The thermal plasma is generated during the beam pulse and persists for some time after the pulse is terminated. Low energy levels of Arii with a 4s or 4p valence electron have similar time profiles to the plasma density. However, high energy levels of Aril with a 4p′ or 4p′ valence electron have similar temporal profiles as the beam current. They are populated predominantly by direct ionization and exceed levels populated by thermal electrons. The 4p′ levels decay rapidly to 4s′ levels, which have very high beam deposition efficiencies for being pumped back to the 4p′ levels. In this way, certain transitions such as 4s′–4p′ in ArII are pumped directly by the electron beam. Without direct ionization, these transitions would be negligible compared to those transitions which have lower energy levels.