Rotating motion of a propagating LIB is analyzed in order to suppress the mixed mode of the Kelvin-Helmholtz instability, the tearing instability and the sausage instability by the action of a self-induced magnetic field in the axial direction. The beams are assumed to be charge-neutralized but not current-neutralized. The steady-state solutions of a propagating LIB with rotation are first obtained numerically. Through the dispersion relation with respect to the ikonal type of perturbations, which are added to the steady-state solutions, the growth rates of instabilities appearing in an LIB are obtained. It is concluded that if the mean rotating velocity of an LIB is comparable to the propagation velocity, in other words, if the induced magnetic field intensity in the axial direction is comparable to the magnetic field intensity in the azimuthal direction, the instability disappears in the propagating ion beam.

The first experimental study of the propagation of electrons created by an intense laser in shock-compressed matter has been performed with the VULCAN laser facility at the Rutherford Appleton Laboratory, to investigate one of the fundamental phases of the fast ignitor concept for inertial confinement fusion. Plastic plane targets were irradiated on one side with two pulsed laser beams, each with I ≈ 1014 W/cm2, t ≈ 2 ns, E ≈ 80 J per pulse, to generate a planar shock wave; on the opposite side of the target, a chirped pulse amplification (CPA) laser beam (I ≈ 1016 W/cm2, t ≈ 3 ps, E ≈ 10 J) was focused to generate the fast electrons. The results show an increase of hot electron penetration in compressed matter with respect to an ordinary one. Experimental results have been analyzed with computer simulations.

Absorption of electrical energy provided to a metal wire in an exploding wire system is thought to be terminated or greatly diminished when the plasma is formed, after the joule heating of the metallic wire by the electrical current. Accordingly, it is common to account for the electrical energy delivered to the wire that the integration of current and voltage signals is halted when the voltage peak changes its slope. Usually, this moment is synchronized with the plasma appearance, as detected by optical sensors. In this work, experimental evidence of a two-step electrical energy absorption in an exploding wire surrounded by atmospheric air is presented. During the first step of the energy absorption the plasma is not formed, indicating that the delivered energy is not enough for ionizing the wire, giving place to a dark pause that lasts until a second energy absorption produces a plasma. The delay between the two steps can reach ≈2.2 µs for copper wires of 50 µm diameter charged at an initial voltage of 10 kV. Experimental investigation of variation of the delay between the two steps with different metals, charging voltages, and wire diameters are presented. A relation of the current density with the initial kinetic energy of the plasma and the electrical current rate is devised as a possible explanation of the observed phenomena.

In this paper, a scheme of compound optical limiting based on nonlinear material dissolved into Brillouin medium is proposed. Both nonlinear material and Brillouin medium used as the solvent play roles of optical limiting, so the proposed optical limiting scheme presents a lower output clamp value and flatter output energy compared with the single stimulated Brillouin scattering (SBS). Compound optical limiting of F16PCCu/acetone is prepared and output energy characteristic based on it is studied in this paper. Both the theoretical and experimental results indicate that the output clamp value and output energy based on the compound method is lower and flatter than that based on single SBS optical limiting. Some properties of the compound optical limiting, such as limiting energy range, limiting waveband, response speed, limiting threshold and damage threshold, also are analyzed and discussed in the later part of this paper.

A study of the space-time structure of the light reflected when a plastic target (CH)n is irradiated at a maximum power of 1012 watt/cm2 by a Nd glass laser pulse of nanosecond duration is described. The reflected light has been used for time integrated spot imaging, whereas the time dependence of the reflected power at different angles has been studied by optical guides of different length coupled with a single fast photodiode. It has been found that: 1) the spot images are formed by a high contrast stationary speckle pattern, indicating the presence of a random phase mixing in the back-scattered light; 2) the interaction is characterized by a high reflection in the initial stages (t ≤ 0·3 ns) followed by almost complete absorption.

The energy balance of the p-11B fusion scenario with compensation of the transfer of kinetic energy of protons and alpha particles to the gas medium by the electric field is considered. It is shown that such scenario cannot provide the use of p-11B fusion reaction for power production due to the very low ratio of the energy release of the fusion reaction to the energy necessary for compensation. The upper boundary of this ratio is about $2\times {10}^{-3}$.

In inertial confinement fusion experiments that involve short-laser pulses such as fast ignition (FI), diagnosis of neutrons is usually very challenging because high-intensity γ rays generated by short-laser pulses would mask the much weaker neutron signal. In this paper, fast-response scintillators with low afterglow and gated microchannel plate photomultiplier tubes are combined to build neutron time-of-flight (nTOF) spectrometers for such experiments. Direct-drive implosion experiments of deuterium-gas-filled capsules were performed at the Shenguang-II Upgrade (SG-II-UP) laser facility to study the compressed fuel areal density (〈ρR〉) and evaluate the performance of such nTOF diagnostics. Two newly developed quenched liquid scintillator detectors and a gated ultrafast plastic scintillator detector were used to measure the secondary DT neutrons and primary DD neutrons, respectively. The secondary neutron signals were clearly discriminated from the γ rays from (n, γ) reactions, and the compressed fuel areal density obtained with the yield-ratio method agrees well with the simulations. Additionally, a small scintillator decay tail and a clear DD neutron signal were observed in an integrated FI experiment as a result of the low afterglow of the oxygen-quenched liquid scintillator.

Two series of experiments on laser irradiation of the different thickness Al-foils were made using laser facilities “GARPUN” and “PICO” (Lebedev Physical Institute, Moscow). “GARPUN” is the KrF-laser with pulse energy Elas ≈ 100 J and pulse duration τ ≈ 100 ns. “PICO” is a Nd-laser facility. The laser energy is Elas1 ≈ 20 J and τ ≈ 3–4 ns in a single beam. The burn through time (tb) of different thickness foils was studied. We have varied the foil thickness: d = 20–500 μm for “GARPUN” facility experiments, and d = 3–12 μm for the case of “PICO” experiments. It was discovered that the rates of the foil burn through are much higher than those obtained in (Dahmani et al., 1991a,b). The experimental data were analyzed with the help of 2D numerical simulations, using the 2D Euler code “NUTCY.” Good agreement was obtained between numerical and experimental results. In the first case the rate of foil “enlightment” is defined by transversal displacement of matter (“drilling effect”). With allowance for the effect of “hot spots formations” it was possible to explain the burn through of thick foils and low laser energy at the rear side of films in “PICO” facility experiments (“microdrilling effect”). The methods of the diminishing of the influence of microdrilling effect (or “imprint” effect) on the nonuniformity of ablation pressure are discussed.

A new design for heavy-ion beam driven ramp wave loading experiments is suggested and analyzed. The proposed setup utilizes the long stopping ranges and the variable focal spot geometry of the high-energy uranium beams available at the GSI Helmholtzzentrum für Schwerionenforschung and Facility for Antiproton and Ion Research accelerator centers in Darmstadt, Germany. The release wave created by ion beams can be utilized to create a planar ramp loading of various samples. In such experiments, the predicted high pressure amplitudes (up to 10 Mbar) and short timescales of compression (<10 ns) will allow to test the time-dependent material deformation at unprecedented extreme conditions.

To understand in detail what happens with an imploding wire array would require one to account for many different processes beginning with the wire explosion and ending with the Rayleigh–Taylor instabilities. Haines (1998) has performed a heuristic analysis of the multiwire array implosion and suggested that the dynamics and behavior of the wire array pinch be divided into four distinct phases. These phases are as follows: the electrical explosion of an individual wire (Phase 1), merging of the wire plasmas and the current shell formation (Phase 2), running-in of the wire array (Phase 3), and the stagnation of the pinch at the axis (Phase 4).

Experimental study of the radiation scattered at the laser heating of low-density foam targets and transmitted through the targets is presented. The scattered and transmitted radiations were investigated using spectrometers and streak cameras providing spatial, angular, spectral and temporal resolutions that enabled us to study the dynamics of the process of burning-through of the thick foam targets, the velocities of the plasma critical density motion as well as mass velocity of the plasma.

Non-local thermodynamic equilibrium radiative transfer calculations have been performed to predict emission spectra from plasma heated by intense proton beams. Multilevel, steady-state atomic rate equations were solved self-consistently with the radiation field to determine excitation and ionization populations. Ion beam effects were, included in the rate equations. Proton-impact ionization cross sections were calculated using a plane wave Born approximation model with Hartree-Fock wave functions for the electrons. We examined the dependence of emission spectra on the temperature and thickness of the plasma. In addition, Kα satellite line spectra were computed to assess its potential as a temperature diagnostic. Calculated Kα spectral results are compared with recent Particle Beam Fusion Accelerator II experimental data.

A kinetic model of electron cascade growth in the electromagnetic field of a focused intense laser pulse as used for laser spark generation in gases has been numerically implemented in Visual C code. The effects considered comprise Drude absorption, diffusive kinetic and inelastic losses as well as (three-particle) electron recombination. The objectives were to illustrate the dynamic process of gas ionization, and to clarify the pressure dependence of known breakdown thresholds within a range of about 2 × 104 to 2 × 106 Pa of initial pressure. Two-dimensional (cylindric coordinates) simulations of the optical breakdown in nitrogen were conducted on a commercial PC, using constant values for the collision cross section (2 × 10−19 m2), prevalent electronic excitation states (~4.8 eV), and a laser wavelength of 1064 nm. A certain aerosol concentration on the order of 3 ppb was assumed in order to provide initial electrons for cascade growth. Exemplary results with laser pulse energy of 26 mJ, pulse duration of 14 ns and an 18 µm focal spot size illustrate the dynamic process of ionization within a very short time period of less than 0.5 ns. The kinetic energy of the electrons is found to increase sharply up to more than 100,000 K on breakdown. A series of simulations considered the minimum pulse energy of breakdown (MPE) under variation of initial pressure. Identical laser parameters as in experiments conducted previously were used and the results are in excellent agreement with respect to curve shapes, i.e., MPE ~1/p0.4 in the first experiment and MPE ~1/p0.3 in the second one. The absolute values lie within a factor of two, which is explained by model abstraction and input data uncertainties.

This paper discusses the principles of reduction of quantum noise in optical radiation. The dynamics of photon number fluctuations in direct and cascade two-photon processes is investigated. The paper considers the cases of absorption and emission for the fields originally prepared in coherent and thermal states. It is shown that photon antibunching and bunching should occur for the passed radiation. The photon antibunching effect is only in definite time intervals of field interaction with resonance absorbing or emitting systems.

The possible cases of accumulation of photon antibunching effects are considered.

The effect of long scale-length irradiation non-uniformities on the implosion of two different directly driven, gas filled shells (representative of large families of laser fusion targets) is studied by means of 2-D numerical fluid simulations. Quantitative results are given for parameters measuring the shell deformation and the azimuthal variation of the (density × radius) product (<ρR) as functions of the wavelength and of the amplitude of the irradiation non-uniformity. The reflection of the imploding shock wave is also qualitatively illustrated.

The paper reviews a number of X-ray streak cameras developed at AWRE. These cameras are used to provide temporal and one-dimensional spatial or spectral information on X-rays emitted from laser produced plasmas. Two of these cameras have been designed to be combined with other diagnostic instrumentation; one with a Wolter X-ray microscope (×22 magnification) and the other with a Bragg diffraction crystal spectrometer. This latter instrument provides a few eV spectral resolution and ∼15 ps temporal resolution; a typical experimental application at the AWRE HELEN laser facility will be described. The paper describes the circuitry of the bipolar avalanche transistor ramp generator used to drive the streak plates of the cameras. Improvements to this include: (a) increasing the fastest streak rate to ∼10 ps mm−1 by a distributed capacitance network across each of the bipolar stacks of transistors, and (b) reducing the trigger jitter to approximately ±10 ps by the use of a new mix of transistors in the stack and a Raytheon RS 3500 avalanche transistor. Additional improvements have now been added. These include a ‘half-scan’ user facility to aid initial camera timing and direct switching to select the sweep rate of the camera.

The Pseudospark is an axially symmetric, high-voltage gas discharge operating at pressures below 100 Pa. It is capable of producing pinched high current ion beams. Streak camera photographs of the operation of this discharge reveal that a pinch with a diameter of ∼1 mm occurs in the diode. The beam then expands to about 1 to 10 mm in a distance of 12 cm. The beam-target interaction shows a UV-emitting plasma corresponding to protons with a main energy of 100 keV and a current density of about 16 kA/cm2. Initial theoretical results for the pseudospark are given.

Modeling plus simulations using the one-dimensional Lagrangian radiation-hydrodynamics code HYADES are compared with data from classical and ablative Rayleigh–Taylor experiments conducted on the Nova laser. Comparisons between the experiments and modeling for both the gross hydrodynamic motion and the perturbation evolution are made and show good agreement. A third order perturbation analysis is applied to demonstrate the onset of nonlinearity. A simple, physically intuitive saturation model is used to describe the growth further into the nonlinear regime. Finally, we present the first comparison of the Betti ablation front theory with indirect-drive RT data and obtain good agreement.

In this study, ion acceleration from thin planar diamond-like carbon (DLC) and polystyrene (PS) foils irradiated by ultraintense (a0 = 200) and ultrashort (15 fs) laser pulses is investigated numerically. The effects of target composition and thickness on the acceleration of protons and carbon ions are reported by 1D3V particle-in-cell simulation code and compared with the analytical models of ion acceleration. In the analytical formalism, the acceleration criterion of ions with different charge-to-mass ratio (q/m) is obtained. This criterion is related to the potential difference through the electrostatic shock distortion and its velocity. According to this result, charged particles with large q/m ratio have a good chance to accelerate in front of the electrostatic shock field. It is shown that mono-energetic proton bunch with energies >1.5 GeV is produced by 20 nm DLC foil supported by 10 nm hydrogen layer. Finally nanometer PS foil is examined and 2.33 Gev protons with ~1.5% energy spread are obtained for 50 nm thickness.