[en] Generation of ultra-intense laser pulses is very important for a number of scientific and technical applications, such as the fast ignition (FI) scheme for in the inertial confinement fusion (ICF), the plasma accelerators, etc. The chirped pulse amplification is the actual technique to reach maximum peak power at a given energy. The pulse energy is then limited by the thermal damage of compression gratings, which for multi-kJ applications have to be very large and extremely expensive. There is another idea, which is based on non-linear pulse energy conversion. It does not require the pulse stretching or compression but considers the stimulated Brillouin and/or Raman scattering (SBS/SRS) in plasma. The use of plasma releases the problem of thermal and optical damage of the active media, but requires an efficient control of the dynamics of the stimulated scattering. We develop a model of a pulsating regime of the backward SBS at high laser intensities. This regime corresponds to the strong coupling between the scattered and ion acoustic wave and allows one to consider the pulse durations shorter than the ion acoustic wave period. The results of the theoretical model are compared with the 2D electromagnetic paraxial code and the full PIC 1D code. We explore the optical conditions for generating ultrahigh laser peak power. By using a gas jet or exploding foil plasma of 10% of the critical density, one may expect to achieve an efficient compression of a 1 ns 40 KJ laser pulse down to a few ps at the length of a few mm. We will present the analysis how the plasma density and flow velocity, the noise level and the profile of the Stokes prepulse affect the pulse compression characteristics and the conversion efficiency. (Author)

[en] Recent experiments demonstrate an efficient acceleration of protons and heavier ion species in the interaction of relativistically intense laser pulses with thin solid foils. These energetic particles are originating from the target surface where the density gradient is extremely steep and the electrostatic field attains to very large values. However the details of the acceleration mechanisms are not well understood. In this talk I will discuss the physical processes, which take place in plasma set in expansion by a minority of highly energetic electrons. The expansion is in a form of a collisionless, electrostatic shock waver, its position and amplitude control the number and the energy spectrum of accelerated protons. the energy re partition between the protons and other ion species depends strongly on the target composition, the hot electron spectrum, and the shock wave structure. Simple analytical models will be compared with the hybrid numerical simulations where the ions are described kinetically and the electrons assure the charge neutralization and with the PIC simulations where all species are treated kinetically. (Author)

[en] Experiments have been conducted at the LULI (Laboratoire pour l'Utilisation des Lasers Intenses) multibeam laser facility to study in detail stimulated Brillouin (SBS) and Raman (SRS) scattering from an intense (mean average intensity up to 10¹⁴W/cm²) long (600 ps full width at half-maximum) laser beam interacting with thin exploded plastic foils. The plasmas are well characterized and the vacuum laser intensity distribution is well known due to using either random phase plates or polarization smoothing. Direct and simultaneous Thomson scattering measurements of the associated plasma waves allow us to obtain detailed information about the SBS and SRS temporal evolution and spatial localization. These data are being used to benchmark a statistical model of SBS and SRS from self-focused speckles. The results of this comparison will be presented in a companion paper. The analysis shows that both SBS and SRS are originated from self-focused speckles and reveals that plasma heating has an important effect on speckle self-focusing

No abstract available

[en] New laser facilities able to deliver either ultra high energy short pulses or ultra high intensity pulses are being constructed and will open new and exciting opportunities for laser ion acceleration. The interaction of a high intensity short pulse with underdense, near-critical and overdense targets has been studied using 2D Particle-In-Cell simulations in these regimes. In the ultra high energy regime, proton beams with maximum energies of hundreds of MeV and a high number of high energy protons could be accelerated using thin solid foils or low density targets. In the ultra high intensity regime, radiation losses will start affecting laser ion acceleration using thin overdense targets for intensities higher than 10²² W/cm², and produce very energetic ions. (authors)

[en] We present a detailed study of the properties of electron beam injected and trapped in an high intensity optical lattice. By using the hydrodynamic and kinetic approaches, we identified the beam trapping conditions, the high-frequency longitudinal beam Eigenmodes and their dependence on the electron angular and energy spread. The coupling of these beam Eigenmodes to the laser waves is also considered. This corresponds to the convective parametric instability: a stimulated scattering of two laser beams creating the optical lattice on the trapped electron beam mode. The amplification coefficients for the up-scattered Raman modes propagating parallel to the electron beam are calculated and their dependence on the beam characteristics is analyzed. (authors)

[en] Laser-driven fast electron beams generated in planar foils or double cone targets have been characterized by means of two-dimensional particle-in-cell simulations. The laser beam focusing by the cone walls reduces the fast electron beam radius and increases the electron mean kinetic energy. Nevertheless, the beam divergence is high in both types of targets and can be split into two components: the dispersion angle and the radial velocity. The fast electron energy spectrum presents a power law profile. The effects of the fast electron source characteristics on the energy deposition in an 'ideal' precompressed inertial fusion target have been analysed. The radial velocity component of the fast electron beam significantly increases the energy required for ignition while the electron power law spectrum increases it slightly when compared with the standard exponential one.

[en] Shock ignition is an inertial confinement fusion scheme where the ignition conditions are achieved in two steps. First, the DT shell is compressed at a low implosion velocity creating a central core at a low temperature and a high density. Then, a strong spherical converging shock is launched before the fuel stagnation time. It increases the central pressure and ignites the core. It is shown in this paper that this latter phase can be described analytically by using a self-similar solution to the equations of ideal hydrodynamics. A high and uniformly distributed pressure in the hot spot can be created thus providing favorable conditions for ignition. Analytic ignition criteria are obtained that relate the areal density of the compressed core with the shock velocity. The conclusions of the analytical model are confirmed in full hydrodynamic simulations.

[en] Collision detection of a large number N of particles can be challenging. Directly testing N particles for collisions among each other leads to N-2 queries. Especially in scenarios, where fast, densely packed particles interact, challenges arise for classical methods like Particle-in-Cell or Monte-Carlo. Modern collision detection methods utilising bounding volume hierarchies are suitable to overcome these challenges and allow a detailed analysis of the interaction of large number of particles. This approach is applied to the analysis of the collision of two photon beams leading to the creation of electron-positron pairs. (authors)

[en] The propagation through an insulator of a high-current monoenergetic fast electron beam is investigated in a one-dimensional model. The target ionization provides the charge and current neutralization and enables the beam propagation. The ionization process consists of two stages: (i) the self-consistent electric field ionization of atoms in the beam front and (ii) the collisional ionization of atoms by the return current in the beam body. The ionization in the beam front defines the propagation velocity. The charge neutralization quickly suppresses the electric field behind the beam front and the plasma heating by the return current supports the collisional ionization in the beam body. This constitutes the main mechanism of the energy loss for high beam densities