With the aim to provide more economic systems for acceleration of electrons, the possibilities of laser accelerators are discussed. The driving of electrons in laser wave fields in a longitudinal direction is based on nonlinear forces, which in simplified form cause the ponderomotion. Since the formulation of the Sessler theorem it is evident that optical signals moving with the speed of light in vacuum may not transfer energy to charged particles. A slowing down—even for a very minor difference only—does result in acceleration. Since the beat-wave accelerator using plasma led to numerous problems, a scheme is proposed that works without such dielectric effects by the superposition of laser wave fields in vacuum. Then the reduction of the signal velocity is performed by a controlled time dependence of the frequency with a phase or direction of at least one of the laser beams in interference.

The model of evaporation, motion and compression of shell laser targets in low-entropy regime is considered. The evaporation rate and accelerating pressure in spherical targets are determined in the stationary corona model. The scaling relation are obtained which make it possible to correlate laser pulse and target parameters and optimize target compression and heating for various values of laser pulse wavelengths and energy. The results of this model are compared with numerical calculation of hydrodynamic and thermal conductivity equations.

Gold cavity targets were irradiated with λ = 0.44 μm laser light at intensities ≤ 2.6 ×1013 W/cm2. The outward motion of the cavity wall was investigated by simultaneous optical and x-ray shadowgraphy. The wall motion is attributed to the pressure generated by an ablative heat wave, driven by the soft x-rays in the cavity. The observed transparency of the cavities for the x-rays used for shadowgraphy allowed the determination of the density profile of the cavity wall which decays possibly due to fragmentation.

The acceleration of electrons in a laser plasma at the densities below the critical one is investigated by a particle simulation. It is shown that the stabilization of parametric instability and limitation of the energies of the accelerated electrons take place. The structure of the plasma electron distribution function is examined.

Space observations have opened the spectral regions of X-rays and γ-rays, which are produced by plasma processes. The Plasma Universe derived from observations in these regions is drastically different from the now generally accepted ‘Visual Light Universe’ based on visual light observations alone. Historically this transition can be compared only to the transition from the the geocentric to the heliocentric cosmology.

The purpose of this paper is to discuss what criteria a cosmological theory must satisfy in order to be acceptable in the Plasma Universe.

Due to the low power density of pumping schemes for nuclear-pumped lasers prior to 1978, a method of utilizing the efficient production of narrow band fluorescence from excimers was developed. This method has since been referred to as a nuclear driven flashlamp. It is possible to achieve sufficient power densities, when combining the flashlamp with novel techniques of reactor/laser interfaces, to drive efficient, high power lasers directly with products from nuclear reactions.

Use is made of the extraordinary-mode eigenvalue equation to investigate detailed properties of the magneteron instability for relativistic nonneutral electron flow in a cylindrical high-voltage diode with cathode located at r = a and the anode located at r = b. The model is based on the cold-fluid-Maxwell equations including the full influence of self-field and cylindrical effects. The equilibrium radial electric field Er (r)êr and axial magnetic field Bz (r)êz induce an azimuthal flow of electrons with angular velocity ωb(r) = Vθb (r)/r. The stability analysis assumes flute perturbations with extraordinary-mode polarization. The equilibrium radial electric field is specified by Er (r) = const, sinh k (r − a) within the electron layer (a ≤ r ≤ rb), and emphasis is placed on calculating equilibrium and stability behavior in a parameter regime characteristic of the PBFA-II diode experiments. In particular, voltages in the range 10 MV to 14·75 MV are considered, assuming a = 12 cm, b = 15 cm, and normalized layer thickness Δb = (rb − a)/(b − a) ranging from Δb = 0·3 to Δb = 0·6. At the high voltages characteristic of PBFA-II operation, a moderately strong applied magnetic field B0 is required to assure magnetic insulation of the layer electrons from the anode. Here, B0 is the magnetic field in the vacuum region rb < r ≤ b. Correspondingly, the value of normalized density is typically small. Here, ωc0 = eB0/mc, and ωp0 is the plasma frequency at the cathode. As a general remark, for fixed values of the geometric factors Δb, b − a, etc., it is found that there is a sensitive dependence of the magnetron instability growth rate on the relativistic flow velocity as measured by , with higher values of γ(rb) favoring stronger growth. Typical maximum growth rates are in the range of a few to several percent of ωc0.

On the average, intergalactic space contains a component of gas, dust, and plasma. The numerical density of this medium depends very strongly on what the actual distance is to objects of intermediate and high redshifts. The average density could be enormously higher than currently assumed. In addition, there is the problem of how the material outside the galaxies is distributed. X-ray emission observed in clouds exterior to galaxies as well as in diffuse backgrounds in clusters of galaxies also attest to the radiation of hot plasmas between galaxies. The sizes of these X-ray emitting regions scale with their distances.

Experimental data are reported on second harmonic generation (SHG) during the interaction between a Nd laser beam (20 ns pulse-duration and peak intensity 1013 W/cm2) and a plasma of density 1019 cm−3 produced in helium. The behavior of self-focusing and the onset of steep plasma gradients under the same experimental conditions have been previously characterized by independent techniques as already reported. In the light of these former findings, the observed SH magnitude, emission pattern and time dependence are briefly discussed and compared with expectations.

The physics of muon-catalyzed fusion is summarized and discussed in the perspective of energy production by high density muon beams.

The problems of creating solid antimatter are listed and examined. Laser driven accelerators may reduce the technological and financial magnitude of the task.

A 32-year-old hypothesis of the formation of barred-spiral galaxies (Bostick 1957, 1958, 1986; Laurence, 1956) which become coherent-self-exciting homopolar generators has recently gained confirmative support from 3-D, particle-in-cell computer simulations (Nielsen et al. 1979; Buneman et al. 1980; Peratt et al. 1980, 1984, 1986). Such galaxies should be able to convert an appreciable fraction, f, of the energy from their gravitationally-collapsing plasmas to coherently-increasing magnetic energy via their coherent, self-exciting, homopolar-generator action. The following simple calculation shows that the resulting mutually-induced magnetic repulsions (Len's law) between neighboring galaxies is greater than the gravitational attractive forces between the galaxies. The observed expansion of the Universe can be thus simply accounted for without recourse to the ‘Big Bang’ hypothesis, with its unaccounted-for mysteries.

Experiments have been performed to investigate the transport and stability of microsecond-pulselength intense relativistic electron beams in the ‘ion-focused regime’ (IFR) in low-pressure neutral gas and laser-preionized channels. Beams have been generated by the Michigan Electron Long Beam Accelerator (MELBA) which operates with parameters: voltage = −0·7 to −1 MV electrically compensated for collapsing diode impedance over the first 1·5 μs, pulselength = 0·1 to 4μs limited by diode closure, and current = 0·2 to 30 kA.

Long pulse beam propagation experiments have demonstrated the following effects:

1) At pressures of 1–230 m Torr in air and helium with no laser-preionized channel:

a) the electron-beam transport efficiency peaks after times longer than the time calculated for beam-induced ionization to reach fe. = 1. Up to 100% efficient transport occurs during short spikes over a 1 m propagation distance.

b) Within 100 ns of efficient transport the propagated beam exhibits rapid beam cutoff in air and helium. This initial pulse of propagated current is followed by a series of 10 ns to 60 ns duration spikes for the remainder of the injected beam pulse. At higher gas pressures usually less current is propagated in the later peaks. At the lowest pressure for which significant current is propagated (7·6 m Torr air, 14 m Torr helium) the maximum transported current occurs in one of the later peaks.

2) In initial experiments with excimer-laser-ionized channels in diethylaniline at pressures of 3–8 × 10−4 Torr the electron-beam transport over 1·2 m is efficient (80% to 100%) for at least the first 0·5 μs and does not exhibit the erratic transport observed in the electron-beam induced channels. For fixed laser energy, a narrow pressure window exists for efficient and stable long pulse electron-beam transport. Pressures below optimal give inefficient transport while higher pressures cause ejection of the beam from the ionized channel at later times.

The typical target structure of the inertial confinement fusion by using the ion beams as the energy driver, and its optimized parameters are shown in this paper. The phenomenon occurring at the fuel implosion in the target, from which the thermonuclear fusion output energy of 2·5 GJ is released, is analyzed, and the requirements for the driver beam are summarized.

Filamentation instability for a rotating light ion beam (LIB) fusion system is investigated. Stability conditions, including the effects of fractional current neutralization, rotation of LIB and beam temperature, are derived for propagation through a background plasma. The results are illustrated by plotting stability boundaries for a rotating proton beam propagating in a plasma.

The realization of an ideal volume compression of laser-irradiated fusion pellets (by C. Yamanaka) opens the possibility for an alternative to spark ignition proposed for many years for inertial confinement fusion. A re-evaluation of the difficulties of the central spark ignition of laser driven pellets is given. The alternative volume compression theory, together with volume burn and volume ignition (discovered in 1977), have received less attention and are re-evaluated in view of the experimental verification by Yamanaka, generalized fusion gain formulas, and the variation of optimum temperatures derived at self-ignition. Reactor-level DT fusion with MJ-laser pulses and volume compression to 50 times the solid-state density are estimated. Dynamic electric fields and double layers at the surface and in the interior of plasmas result in new phenomena for the acceleration of thermal electrons to suprathermal electrons. Double layers also cause a surface tension which stabilizes against surface wave effects and Rayleigh–Taylor instabilities.

Both, in the laboratory (specifically the plasma focus) and in astrophysics, charges are accelerated in magnetically pinched current channels. The current channels are annular cylinders, defined by an electric double layer of thickness δrE and radius R due to radial polarization of the plasma. The electric field Er in the double layer and the azimuthal magnetic field Bϕ ensure drifts of charges in the axial direction, but ions do not take up the full drift velocity because their Larmor radius exceeds δrE. Magnetic pinching of the channel reduces the cross sectional area S, and an instability of drift velocity may denude a region of current channel. The inductively maintained current J then cannot be carried by free charges, even with relativistic drift velocity. A displacement current (S/4π) δEz/δt arises, Ez growing until all energy in Bϕ is transferred into Ez. During this transfer Bϕ decreases, so the pinch weakens, permitting discharge of accumulated space charge via a conduction current without reversal of J. Thereafter the cycle repeats quasi-periodically.

In astrophysics acceleration occurs in a pinched magnetic vortex tube (MVT). The difference is that now Bϕ(r, +z) = −Bϕ(r, −z) due to winding of loops of field lines. Hence J reverses across mid-pinch, which implies accumulation of space charge of one sign at mid-pinch and of opposite sign at the ends of the pinch. Now there is reversal of J when the space charge relaxes.

The experiments reported in this paper demonstrate that the PHEBUS laser facility is now currently being operated with high performances (4 TW with 250 ps pulses at 0·527 μm wavelength).

The output energy of the 2-beam PHEBUS laser system can be focused either in a small focal spot (80% of the incident energy is in a 220 μm diameter focal spot) for high intensity experiments (≥5 × 1015 W cm−2) or in very large spots (a few mm in diameter) at moderate intensities (1013 − 2·5 × 1014 W cm−2), for large scale experiments. It is shown that the spatial intensity distribution in the target plane is primarily due to intensity independent aberrations and to diffraction. Laser light absorption in plane aluminum and gold targets are interpreted in terms of inverse bremsstrahlung absorption that may account for 70 to 90% of absorbed energy. Finally, the plasma expansion is shown to be very planar and comparison with one-dimensional Lagrangian simulations gives flux limiter values of 0·03 and 0·02 respectively for Al and Au targets.