A method of generating flat-top waveform in the time-domain based on stimulated Brillouin scattering (SBS) using medium with short phonon lifetime is proposed. In theory, the transmitted pulse is simulated in the case of several media with different phonon lifetime. In experiment, FC-72 and HT-270, which differ significantly in the phonon lifetime, are exploited in the experiment. Both the theoretical and experimental results indicate that, when choosing medium with short phonon lifetime, the top is almost a platform, while there is a peak in the front and a platform thereafter when choosing medium with long phonon lifetime.

The Low Temperatures Laboratory of CEA/Grenoble (France) is involved in the development of cryogenic systems for inertial fusion since a ten of years. A conceptual design for the cryogenic infrastructure of the Laser MegaJoule (LMJ) facility has been proposed. Several prototypes have been designed, built and tested like for example the 1500 bars cryo compressor for the targets filling, the target positioner and the thermal shroud remover.

The HIPER project will necessitate the development of such equipments. The main difference is that this time, the cryogenic targets are direct drive targets. The first phase of HIPER experiments is a single shot period. Based on the experience gained the last years, not only by our laboratory but also by Omega and G.A teams, we could design the new HIPER equipments for this phase.

Some experimental results obtained with the prototypes of the LMJ cryogenic system are given and a first conceptual design for the HIPER single shot cryogenic system is shown.

We describe a direct model for simulation of relativistic electrons acceleration with a given electromagnetic field which is determined by wave packet parameters. The multimode time-spatial structure of a focused Nd-laser beam with stochastic phase disturbances of each spectral component is taken into account as a source of random forces. Electron energies of more than 10 MeV are obtained even at moderate flux densities of 1016 W/cm2. The developed numerical code makes it possible to obtain a quantitative energy distribution function in relation to both field intensity and the temporal bell-shape of the laser pulse. The efficient heating of electrons can be triggered in the presence of a counter propagating wave being reflected from the critical plasma area with a different reflection coefficient. The heating mechanism occurs with a delay relative to the beginning of the pulse when the laser fields exceed some threshold amplitudes. The qualitative comparison of simulation results with the experimental data is given as evidence that this mechanism is reasonable.

New results obtained in experiments on laser irradiation (I = 5 × 1013 W/cm2, λ = 1.054 µm) of low-density (2–10 mg/cm3) porous materials (agar, triacetate cellulose, and foam polysterene) are presented and discussed from the standpoint of optimum porous material utilization in target designs for inertial confinement fusion. The influence of low-density material microstructure of irradiated samples on the absorption of laser radiation and the energy transfer processes was investigated using X-ray and optical diagnostic methods with high temporal and spatial resolution.

For operation of an ion source in an intense ion beam diode, it is desirable to form a localized and robust source of high purity. A cryogenically operated ion source has great promise, since the ions are formed from a condensed high-purity gas, which has been confined to a relatively thin ice layer on the anode surface. Previous experiments have established the principles of operation of such an ion source, but have been limited in repetitive duration due to the use of short-lived liquid He cooling of the anode surface. We detail here the successful development of a “Cryo-Diode” in which the cooling was achieved with a closed-cycle cryo-pump. This results in an ion source design that can potentially be operated for an indefinite duration. Time-of-flight measurements with Faraday cups indicate that the resultant ion beam is of high-purity, and composed of singly charged ions formed out of the gas frozen out on the anode surface.

Angular distributions of currents and velocities (energies) of ions produced at various target irradiation angles and laser intensities ranged from 1010 W/cm2 to 1017 W/cm2 were analyzed. It was confirmed that for low laser intensities the ion current distributions are always peaked along the target normal. However, at laser intensities comparable to or higher than 1014 W/cm2, the preferred direction of ion emission strongly depends on the irradiation geometry (laser focus setting, the irradiation angle), and can be off the target normal. This is very likely caused by the non-linear interaction of the laser beam with produced plasma, in particular, by the action of ponderomotive forces and the laser beam self-focusing.

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.

The KrF laser has been considered as an inertial fusion driver alternative to diode-pumped lasers. The possibilities of KrF lasers for fast ignition is supported by their short wavelength and the corresponding larger penetration depth together with the possible use of the same amplifiers for fusion driver and fast ignitor. It is shown that in the case of a fusion test facility both the energy and the intensity requirements can be fulfilled. A fast ignitor using 20 ps KrF pulses requires beam smoothing techniques after angular multiplexing due to the coherence of the beam. A multiple beam fast ignitor is suggested as an alternative in which a high number of beams of 1 ps duration are separately focused on the fuel after polarization demultiplexing. This arrangement allows even the pulse-forming of the ignitor.

This paper describes a fast multi-channel radiation pyrometer that was developed for warm dense-matter experiments with intense heavy ion beams at the Gesellschaft für Schwerionenforschung mbH (GSI). The pyrometer is capable of measuring brightness temperatures from 2000 K to 50,000 K, at six wavelengths in the visible and near-infrared parts of the spectrum, with 5 ns temporal resolution, and several micrometers spatial resolution. The pyrometer's spectral discrimination technique is based on interference filters, which also act as mirrors to allow for simultaneous spectral discrimination of the same ray at multiple wavelengths.

The properties of beams of high energy protons accelerated during ultraintense, picosecond laser-irradiation of thin foil targets are investigated as a function of preplasma expansion at the target front surface. Significant enhancement in the maximum proton energy and laser-to-proton energy conversion efficiency is observed at optimum preplasma density gradients, due to self-focusing of the incident laser pulse. For very long preplasma expansion, the propagating laser pulse is observed to filament, resulting in highly uniform proton beams, but with reduced flux and maximum energy.

A scheme is proposed for the acceleration of electrons generated during the ionization of a gas by two laser pulses. The electrons created from the ionization of neutral atoms near the rising edge of the pulse do not gain sufficient energy. If a prepulse is used before the main pulse then the prepulse removes electrons from the outer shells, and the main laser pulse interacts with the electrons in the inner shells of high atomic number gases, such as krypton and argon. The electrons are generated close to the peak of the main laser pulse and gain energy in GeV with a small spread in the energy and low emittance angle.

This paper reports on the properties of a supershort avalanche electron beam generated in the air or other gases under atmospheric pressure and gives the analysis of a generation mechanism of supershort avalanche electron beam, as well as methods of such electron beams registration. It is reported that in the air under the pressure of 1 atm, a supershort (<100 ps) avalanche electron beam is formed in the solid angle more than 2π steradian. The electron beam has been obtained behind a 45 µm thick Al-Be foil in SF6 and Xe under the pressure of 2 atm, and in He, under the pressure of about 15 atm. It is shown that in SF6 under the high pressure (>1 atm) duration (full width at half maximum) of supershort avalanche electron beam pulse is about 150 ps.

This paper presents a review of physical principles, design, and performances of plasma-cathode direct current (dc) electron beam guns operated in so called fore-vacuum pressure (1–15 Pa). That operation pressure range was not reached before for any kind of electron sources. A number of unique parameters of the e-beam were obtained, such as electron energy (up to 25 kV), dc beam current (up 0.5 A), and total beam power (up to 7 kW). For electron beam generation at these relatively high pressures, the following special features are important: high probability of electrical breakdown within the accelerating gap, a strong influence of back-streaming ions on both the emission electrode and the emitting plasma, generation of secondary plasma in the beam propagation region, and intense beam-plasma interactions that lead in turn to broadening of the beam energy spectrum and beam defocusing. Yet other unique peculiarities can occur for the case of ribbon electron beams, having to do with local maxima in the lateral beam current density distribution. The construction details of several plasma-cathode electron sources and some specific applications are also presented.

Laser produced ion beams have a large divergence angle and a wide energy spread. To our knowledge, this is the first demonstration of collimation and monochromatisation of laser accelerated proton beams, using a permanent quadrupole magnet lens system. It acts as a tunable band pass filter by collimating or focusing the protons with the same energy. Because it gathers nearly the whole proton emission, a strong enhancement of the beam density appears. For the collimated beam, an increase of the proton density in the (3.7 ± 0.3) MeV energy band up to a factor of ~30, from possible 40, relative to the non-collimated beam is demonstrated. With the help of this simple, reliable, and well established technique new perspectives will be opened for science and technology, monoenergetic ion beams can be attained in any lab, where a source of laser accelerated ions exist. This finding enables to apply afterward well known beam steering techniques to the formed ion beam, which are applied in conventional accelerators to manipulate the beam parameters or to transport the beams and make them use in many application.

This report addresses the physical concept and the results of mathematical modeling of cryogenic layer degrading caused by its radiation heating during direct drive target injection into the reaction chamber. Special attention is paid to the influence of a solid layer structure on the roughening of the layer surface that is of critical importance for the development of target injection scenario.

Inverse Compton scattering is a promising method to implement a high brightness, ultra-short, energy tunable X-ray source at accelerator facilities. We have developed an inverse Compton backscattering X-ray source driven by the multi-10 TW laser installed at Daresbury. Hard X-rays, with spectral peaks ranging from 15 to 30 keV, depending on the scattering geometry, will be generated through the interaction of laser pulses with electron bunches delivered by the energy recovery linac machine, initially known as energy recovery linac prototype and subsequently renamed accelerators and lasers in combined experiments. X-ray pulses containing 9 × 107 photons per pulse will be created from head-on collisions, with a pulse duration comparable to the incoming electron bunch length. For transverse collisions 8 × 106 photons per pulse will be generated, where the laser pulse transit time defines the X-ray pulse duration. The peak spectral brightness is predicted to be ~1021 photons/(s mm2 mrad2 0.1% Δλ/λ).

An experimental study on the angular distribution and conversion of multi-keV X-ray sources produced from 2 ns-duration 527nm laser irradiated thick-foil targets on Shenguang II laser facility (SG-II) is reported. The angular distributions measured in front of the targets can be fitted with the function of f(θ) = α+ (1−α)cosβθ (θ is the viewing angle relative to the target normal), where α = 0.41 ± 0.014, β = 0.77 ± 0.04 for Ti K-shell X-ray sources (~4.75 keV for Ti K-shell), and α = 0.085 ± 0.06, β = 0.59 ± 0.07 for Ag/Pd/Mo L-shell X-ray sources (2–2.8 keV for Mo L-shell, 2.8–3.5 keV for Pd L-shell, and 3–3.8 keV for Ag L-shell). The isotropy of the angular distribution of L-shell emission is worse than that of the K-shell emission at larger viewing angle (>70°), due to its larger optical depth (stronger self-absorption) in the cold plasma side lobe surrounding the central emission region, and in the central hot plasma region (emission region). There is no observable difference in the angular distributions of the L-shell X-ray emission among Ag, Pd, and Mo. The conversion efficiency of Ag/Pd/Mo L-shell X-ray sources is higher than that of the Ti K-shell X-ray sources, but the gain relative to the K-shell emission is not as high as that by using short pulse lasers. The conversion efficiency of the L-shell X-ray sources decreases with increasing atomic numbers (or X-ray photon energy), similar to the behavior of the K-shell X-ray source.

A time-dependent solution for neutral-plasma isothermal expansions into a vacuum in a special-transformation coordinate system is obtained. In this new coordinate system, the special self-similar solutions of it were given by Huang and co-workers (Appl. Phys. Lett. 92, 031501). Combining the time-dependent solution and the quasi-linear increase of the electron density due to the hot-electron recirculation, an analytic model is proposed to reveal the influence of the hot-electron recirculation on the increase of electric field and on the acceleration of ions of different masses and charges.