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 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.

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.

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.

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 self-radiation characteristics of plasma created under the effect of a powerful laser radiation on a target are considered. The radiation in the spectral range from 1 to 1300 Å is calculated in coherent assumption for given gas-dynamic fields corresponding to various phases of laser target explosion. The source function was determined in accordance with a plasma radiation-collision model with the assumption of its transparency. Calculations show that the contribution of line radiation to the total flux may be from 20 to 60%. Mainly, this paper considers radiation transfer. The effect of self-radiation on level populations and frequency redistribution at resonance scattering is taken into account. The resonance scattering is predominant in the coronal plasma. Exit of photons from deeper layers of the target in comparison with the coherent case increases. Macroscopic plasma motion leading to spectral line shift is taken into consideration in the calculations. Output radiation spectral intensity distribution in oxygen and silicon H-like ions resonance lines has been determined. Spectral line profiles calculated with account of basic broadening mechanisms were used.

Radiation characteristics of laser targets are studied in the soft X-ray region where photorecombination, bremsstrahlung and transitions in the discrete spectrum are the basic mechanisms of spectrum formation. The impact-radiational model is employed to describe the states of the laser target plasma. Characteristics obtained from the solution of the kinetic problem are used to compute absorption and emission coefficients. To set the time scale for a given field of gas-dynamic parameters, the transfer equation is solved and detailed information is obtained on the spectral composition of the outgoing radiation and its temporal evolution. Effective emission temperatures and radiation losses are determined. Integral radiation parameters are compared which have been derived from the solution of the transfer equation employing a volume luminescence approximation.

Taking into account the emission and absorption of resonance radiation in a recombining laser-produced plasma of intermediate density, the system of rate equations for the population densities coupled with the radiative transfer equation is approximately treated. In the case of spatially varying absorption we derive an approximate form of the rate equation determining the population density of the upper resonance level. By applying this relation to an axially symmetric plasma a simple formula that describes the effect of radiation reabsorption on the spatial behaviour of the population density is obtained.

The paper demonstrates the possibility of the current increase in laser plasma by more than one order at the preaction of low-energy pulse on the target. The conversion effectivity of 0·32% is obtained at the intensity of the principal pulse of a CO2 laser equal to 4 × 109 W/cm2 and at the residual gas pressure of 10−5 torr.

Focusing processes of a rotating and propagating light ion beam in the drift region are studied numerically by using a 2-dimensional hybrid (particle–fluid) code. An intense ion beam with the current density of 8 kA/cm2 and the total current of 2·5 MA, which is extracted from the diode with the applied voltage of 5·6 MV, is injected into the drift region filled with a low-density plasma. When a radial magnetic field is applied to the neighborhood of entrance, the beam ions start to rotate in the azimuthal direction owing to the Lorentz force. When the pressure of the background plasma is chosen such as the density of the beam becomes comparable with that of the background plasma in the vicinity of the focal spot, the current-neutralization fraction decreases and large self-magnetic fields are induced. The beam is confined by the fields within a small radius, even after passing the focal spot. Because the angular momentum of the beam is conserved, the beam rotation velocity increases up to the same order of the propagation one at a few mm radius. This rotation motion induces the azimuthal magnetic field and stabilizes the beam propagation. In the case where the plasma pressure was 3·0 Torr and the 0·2-Tesla radial magnetic field was applied over the distance of 2·0 cm near the entrance, the maximum beam intensity of 108TW/cm2 in the axial direction was obtained and the half width at half maximum (HWHM) of the focused profile was 3·5 mm.

Recent advances in X-ray laser research have significantly increased the possibilities for X-ray laser applications. In this paper, we report the first demonstration of pointing and focusing of a soft X-ray laser beam. A LLNL selenium soft X-ray laser at 206 and 209 Å was used in these experiments. Two state of the art 76 mm diameter multilayer mirrors were used to collimate and refocus the laser onto a set of cross hairs which were constructed from 100 μm diameter wires. The cross hairs were located 4.6 m from the X-ray laser source. Results show that the laser can be pointed to within 75 μrad and focused to a 235 μm diameter spot. It is expected that eventually spot sizes near 100 μm and flux levels of 100J/cm2 at X-ray irradiances up to 1012W/cm2 can be provided to a remote application, using a similar beam relaying system.

The following errors were found in the article “Nuclear Driven Flashlamps”, by M. A. Prelas, F. P. Boody, G. H. Miley and J. F. Kunze, Lasers and Particle Beams, 6(1), 25 (1988):

Error 1 Page 29, Paragraph 2, Line 14—

Error 2 Page 35, Equations on page should be

Error 3 Page 37, Table 5, the bottom of Table 5 should read

* experimental data

Error 4 Page 44, Equations 19 and 20 should be

Error 5 Page 44, Equation 21 should be

Error 6 Page 44, Equation 26 should be

Error 7 Page 50, Equation 36 should be

Error 8 Page 55, Section 6. Production Chemicals should be

6.1 Production of Chemicals

Error 9 Page 56, Equation 38 should be

Error 10 Page 56, Section 6.2, paragraph 3, line 5, eg should be

Eg