Detailed radiative-transfer simulations are presented for plasma that is prepared in a predominantly heliumlike ground state and then photopumped. The plasma conditions in the simulation are based on those determined in a line-coincidence experiment described in the preceding paper [C. A. Back, C. Chenais-Popovics, and R. W. Lee, Phys. Rev. A 44, 6730 (1991)]. The measured emitted flux of the resonance line of the heliumlike aluminum ion, at 7.757 Å, is used as input for the photon pump. Predictions of the fluorescence are directly compared with experimental results. The synthetic spectra are calculated, and the effect of the photopumping on the level populations and ionization balance is discussed. Also a description is included of the equivalent two-level-atom radiative-transfer scheme that is used to calculate the self-consistent solution of the level populations and the radiation field.

Aluminium wire arrays have been imploded on the 6-TW, 4-MA Double-EAGLE generator. An initial diameter of 12.5 mm and mass loading of 164 μg/cm have been identified as the optimum parameters to maximize the aluminum kilovolt K-shell yield. The implosion time of 90 ns and the initial radius of 0.625 cm correspond to an implosion kinetic energy of 19.2±3.6 keV/ion. Larger-diameter arrays have higher kinetic energies per ion but lower masses, and they produce lower kilovolt K-shell x-ray yields. Smaller-diameter arrays have kinetic energies per ion less than the minimum 12 keV required to ionize aluminum to its K shell; so these arrays produce lower K-shell yields. Time-resolved x-ray pinhole photography and time-resolved spectroscopy are utilized to determine the K-shell emitting plasmas’ sizes, temperatures, and densities as functions of time during the pinched phase. It is found that both the percentage of the mass radiating K-shell x rays and the electron temperature increase during the first 20 ns of emission. For the optimum implosion parameters, it is found that only a small percentage of the mass is radiating in the K shell and, furthermore, that the conversion of kinetic energy to kilovolt emissions alone does not account for the measured x-ray yields. The data analysis suggests that the problem of maximizing aluminum K-shell emission breaks down into two parts. On the one hand, K-shell emission is enhanced when, during the implosion phase, sufficient kinetic energy is generated to drive the aluminum plasma into the K shell on thermalization. This is in agreement with pure-kinetic-energy calculations. On the other hand, there appears to be an additional anomalous heating mechanism that scales with mass and adds to the K-shell emission during the current confinement on axis. As a result, the optimum x-ray production occurs in these experiments by maximizing the mass on axis while both achieving enough kinetic energy per ion and imploding at peak current.

The effects of a low-energy charge-exchange process between hydrogenlike ions and neutral hydrogen on x-ray spectra of He-like argon ions from the Alcator C tokamak are investigated. Dependences of charge-exchange cross sections on both the principal and angular momentum quantum numbers n and l are estimated from the observed spectra, taking cascade effects into account with the use of a collisional radiative model.

The Stark broadening of several He i lines has been measured in a pulsed arc plasma. The intensity ratio of the He i (4686 Å) and the He i (6678 Å) lines was used to estimate the electron temperature, while the electron density was independently determined from interferometry at five different wavelengths. The electron density of the plasma varies from (2.00–6.46)×${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$ and the temperature from 19 000 to 43 000 K. The results of this work are compared with the available experimental data, and all of them are used to calibrate some He ii lines, which will be used as calibration lines in future work with more complex plasmas.

We apply the approach initiated by Lanczos to compute large spectral arrays in hot plasmas. The wave functions that form the basis for the Lanczos state vectors are derived from a self-consistent ‘‘average-atom’’ model. We present calculations for a bromine plasma at low and at metallic density.

A fully spectral numerical code is used to explore the properties of voltage-driven dissipative magnetofluids inside a periodic cylinder with circular cross section. The trial functions are orthonormal eigenfunctions of the curl (Chandrasekhar-Kendall functions). Transitions are observed from axisymmetric resistive equilibria without flow to helically deformed laminar states with flow, and between pairs of helical laminar states with different pairs of poloidal and toroidal m and n numbers. States of minimum energy-dissipation rate seem to be preferred. At high values of the pinch ratio, fully developed magnetohydrodynamic turbulence is observed.

Along the auroral field lines, a fraction of the energetic electrons injected from the magnetotail is reflected by the Earth’s convergent geomagnetic field. The reflected loss-cone electrons are unstable with respect to the cyclotron maser instability, resulting in the auroral kilometric radiation. This paper investigates the kinetic friction force exerted on the energetic electrons by the enhanced radiation field. It is found that the enhanced radiation results in a deceleration of reflected electrons, thereby providing an effective resistivity. In addition, the rate of decrease (increase) of effective perpendicular (parallel) kinetic temperatures is also evaluated. The analysis is carried out over various physical parameters such as the degree of loss cone, average particle energy, and the ratio of plasma frequency to cyclotron frequency ${\mathrm{\omega }}_{\mathit{e}}^2$/${\mathrm{\Omega }}^2$.

We have formulated an effective description of surface waves propagating along the boundary between a high-temperature, high-density plasma and vacuum or a high-temperature, high-density plasma and a low-density plasma, within the framework of the anomalous skin effect. Since the anomalous skin effect is essentially collisionless, we have investigated possible collisionless dissipative mechanisms. Two mechanisms have been identified: phase breaking and capacitor heating. The possibility of exciting surface waves by an external electromagnetic wave is also discussed. We propose two types of solid planar targets that after being ionized by an intense ultrashort heating laser beam allow the excitation of surface waves by an obliquely incident p-polarized electromagnetic wave.

Line profiles for hydrogen including the case of dense plasmas are investigated on the basis of a many-particle approach. Using a Green’s-function technique, electron contributions to the shift and broadening from both separate-level and interferencelike terms are considered consistently. The theoretical approach to the line profile has been improved by including dynamic screening of collisions, contributions from Δn=0 transitions, and cross-term contributions not only to the broadening but also to the shift of the line. As an example, the line profile of ${\mathrm{H}}_{\mathrm{\alpha }}$ has been considered. An analysis of details of the second-order approximation with respect to the atom-plasma interaction is given, avoiding the no-quenching and dipole approximations. The effect of dynamic screening for high electron densities is investigated. Deviations from the linear dependence between the electron-shift contribution and the density are expected for ${\mathrm{H}}_{\mathrm{\alpha }}$ for ${\mathit{n}}_{\mathit{e}}$≥2×${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$ at temperatures of about 10 000 K.

An electron beam from a cyclotron autoresonant accelerator passing adiabatically along a down-tapered axisymmetric static magnetic field can propagate as an axis-encircling helix. This helix rotates temporally at the fundamental pump frequency of the accelerator, and varies spatially with an axial pitch that depends upon the difference between the pump frequency and the local gyrofrequency. We show that the pitch can thus be freely adjusted so as to allow both frequency and wave-number matching between the beam and a guided fast wave at each harmonic of the pump frequency. As a result, power transfer from beam to wave can occur in a process that is first order in the wave amplitude. Examples of a harmonic converter based on this concept are given for 94- and 1000-GHz sources employing magnetic fields no stronger than 10 kG. Since the electrons can maintain phase coherence during the interaction, one can speculate that the power transfer can be fairly efficient. Practical advantages of this harmonic converter for high-power applications may include alleviation of mode competition, direct output coupling, lower wall heat loading, and simpler beam collectors than for corresponding cavity gyrotron oscillators and noncryogenic magnets.

Simulations of the plasma wake-field accelerator are carried out by following the time evolution of the plasma distribution function in one dimension via the Vlasov-Maxwell equations. Simulation results are compared to numerical solutions of the nonlinear relativistic cold plasma equations and to previous theoretical estimations of trapping and thermal effects on plasma waves. It is found that highly nonlinear wakes are obtainable in the vicinity of the driving beam, where the thermal velocity spread of the plasma is reduced. In this region, wake amplitudes can significantly exceed the expectations of relativistic warm plasma models and agree closely with cold fluid theory. In all cases, however, particle trapping and thermalization due to particle scattering from the large-amplitude plasma wave reduce the wake to below the nonrelativistic wave-breaking limit after the initial accelerating peak.

A linear theory of laser heating is used to describe the coupling of optical waves to thermally induced acoustic and entropy perturbations of the medium. The analysis differs from those of previous authors in its treatment of entropy, dissipative effects, and active compensation of thermally induced laser-beam aberrations. An intuitively simple equation for the medium perturbation is derived, within the hydrodynamic approximation. The dimensionless parameters that characterize the diverse scattering regimes are discussed. The boundary-value problem is solved for specific cases of interest. Comparison with a nonlinear simulation verifies the linearized result in such cases.

An experimental investigation of entrainment and the phenomenon known as periodic pulling is described. Periodic pulling refers to the incomplete entrainment of an oscillatory nonlinear system by a periodically varying driving force. The process whereby the system’s oscillation frequency is pulled toward the driving frequency stops short of complete synchronization and is interrupted at regular intervals. In this way, periodic pulling produces pulselike amplitude and frequency modulation in the system’s oscillatory response. Associated with these combined, nonsinusoidal modulations is an asymmetric, or single-sided, spectral peak made up of spectral components at frequencies incommensurate with the undriven (spontaneous) and driving frequencies. The system being investigated uses a unijunction transistor as the nonlinear element in an electrical circuit. The behavior of the system is shown to resemble that predicted for a forced van der Pol oscillator with an adjustable nonlinear restoring force. For certain ranges of driving frequency and amplitude, when the system is not entrained to the driving force, periodic pulling is shown to alter the system’s oscillatory response significantly from that expected for conventional amplitude modulation involving two sinusoids. The essential features of the periodic pulling phenomenon are observed and compared, with good agreement, to a model.

An algorithm for the training of multilayered feedforward neural networks is presented. The strategy is very similar to the well-known tiling algorithm, yet the resulting architecture is completely different. New hidden units are added to one layer only in order to correct the errors of the previous ones; standard perceptron learning can be applied. The output of the network is given by the product of these k (±1) neurons (parity machine). In a special case with two hidden units, the capacity ${\mathrm{\alpha }}_{\mathit{c}}$ and stability of the network can be derived exactly by means of a replica-symmetric calculation. Correlations between the two sets of couplings vanish exactly. For the case of arbitrary k, estimates of ${\mathrm{\alpha }}_{\mathit{c}}$ are given. The asymptotic capacity per input neuron of a network trained according to the proposed algorithm is found to be ${\mathrm{\alpha }}_{\mathit{c}}$∼k lnk for k→∞ in the estimation. This is in agreement with recent analytic results for the algorithm-independent capacity of a parity machine.

We investigate the dynamics of large arrays of coupled phase oscillators driven by random intrinsic frequencies under a variety of coupling schemes, by computing the time-dependent cross-correlation function numerically for a two-dimensional array consisting of 128×128 oscillators as well as analytically for a simpler model. Our analysis shows that for overall equal interaction strength, a sparse-coupling scheme in which each oscillator is coupled to a small, randomly selected subset of its neighbors leads to a more rapid and robust phase locking than nearest-neighbor coupling or locally dense connection schemes.

The distribution of particle momentum in the canonical ensemble has the well-known Maxwell form. In the microcanonical ensemble this is not the case and the distribution of particle momentum has a different form that approaches the Maxwell form in the thermodynamic limit. Besides their intrinsic interest, these results could be of importance in studies of small systems, such as clusters. Exact results are illustrated for rigid rods, disks, and spheres.

An alternative class of stable multistate cellular automata (CA) is derived. They serve to significantly extend the two-state, time-irreversible CA proposed by Park, Steiglitz, and Thurston [Physica D 19, 423 (1986)]. These CA are time-reversible dynamical systems possessing an enormous array of coherent particlelike structures. The particle-interaction picture is surprisingly rich and includes particle production as well.

We find a quantitative law that describes the nature of the anomalous fluctuations in tracer concentration when diffusion occurs in a stratified medium, with drift velocities which are constant in the x direction, but vary randomly from layer to layer in the y direction. We find that the fluctuations of the tracer concentration P=P(x,t) are described by an extremely broad histogram of the form n(${\log }_{10}$P)∼A/(${\log }_{10}$P${)}^3$exp[-B/(${\log }_{10}$P${)}^2$]. Moreover, the relative fluctuations δP increase exponentially with x. Our results are supported by numerical calculations based on the method of exact enumeration.

We have analyzed the hole dynamics on a fractal lattice, and have obtained a spectral dimension (d) for the state density. This is the only independent fractal dimension needed in the discussions of the self-similar connectivity of hole motions, and the fluctuation-dissipation relationship controlling the glass relaxation and stretched exponential. The glass relaxation is a result of the local configurational rearrangements of molecular segments that is described by the hole motion. In contrast to polymeric fractals of flexible chains in solution or melt, we find that d decreases as the system is changed from linear to cross-linked polymers.

The 400 first energy levels of the quantal Sinai billiard has been calculated for different small central disk radii. The spectral rigidity over sequences of L levels, Δ${\mathrm{¯}}_3$(L), agrees with that of the Gaussian orthogonal ensemble of matrices (GOE), for L<${\mathit{L}}_{\mathit{d}}$. However, for larger intervals Δ${\mathrm{¯}}_3$ exceeds that of the GOE, and increases linearly. The value of the breakpoint ${\mathit{L}}_{\mathit{d}}$ grows with the radius, probably reflecting the increasing chaos in the classical Sinai billiard. It is suggested that in the semiclassical limit such a behavior is generic for systems with a K-mixing classical analog.