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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. [ABSTRACT FROM AUTHOR]

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 1022W/cm², and produce very energetic ions. [ABSTRACT FROM AUTHOR]

We present an overview of the interpretation of laser plasma interaction (LPI) experiments carried out on the LIL facility. These multikilojoule experiments have been done using underdense foam targets at 0.351 µm laser light leading to high temperature and large plasmas. We discuss the interpretation using our different numerical tools: hydrodynamics simulations carried out with the code FCI2 to characterize the plasma, linear gain estimates with the postprocessor Piranah and paraxial simulations with the code HERA. [ABSTRACT FROM AUTHOR]

Shock Ignition is considered as a relatively robust and efficient approach to inertial confinement fusion. A strong converging shock, which is used to ignite the fuel, is launched by a high power laser pulse with intensity in the range of 1015 - 1016 W/cm² (at the wavelength of 351 nm). In the lower end of this intensity range the interaction is dominated by collisions while the parametric instabilities are playing a secondary role. This is manifested in a relatively weak reflectivity and efficient electron heating. The interaction is dominated by collective effects at the upper edge of the intensity range. The stimulated Brillouin and Raman scattering (SBS and SRS respectively) take place in a less dense plasma and cavitation provides an efficient collisionless absorption mechanism. The transition from collisional to collisionless absorption in laser plasma interactions at higher intensities is studied here with the help of large scale one-dimensional Particle-in-Cell (PIC) simulations. The relation between the collisional and collisionless processes is manifested in the energy spectrum of electrons transporting the absorbed laser energy and in the spectrum of the reflected laser light. [ABSTRACT FROM AUTHOR]

In the shock ignition scheme, the ICF target is first compressed with a long (nanosecond) pulse before creating a convergent shock with a short (~100 ps) pulse to ignite thermonuclear reactions. This short pulse is typically (~2.1010-1016 W/cm²) above LPI (Laser Plasma Instabilities) thresholds. The plasma is in a regime where the electron temperature is expected to be very high (2-4 keV) and the laser coupling to the plasma is not well understood. Emulating LPI in the corona requires large and hot plasmas produced by high-energy lasers. We conducted experiments on the LIL (Ligne d'Integration Laser, 10 kJ at 3ω) and the LULI2000 (0.4 kJ at 2ω) facilities, to approach these conditions and study absorption and LPI produced by a high intensity beam in preformed plasmas. After introducing the main risks associated with the short pulse propagation, we present the latest experiment we conducted on LPI in relevant conditions for shock ignition. [ABSTRACT FROM AUTHOR]

Laser-plasma interaction is investigated for conditions relevant for the shock-ignition (SI) scheme of inertial confinement fusion using two-dimensional particle-in-cell (PIC) simulations of an intense laser beam propagating in a hot, large-scale, non-uniform plasma. The temporal evolution and interdependence of Raman- (SRS), and Brillouin- (SBS), side/backscattering as well as Two-Plasmon-Decay (TPD) are studied. TPD is developing in concomitance with SRS creating a broad spectrum of plasma waves near the quarter-critical density. They are rapidly saturated due to plasma cavitation within a few picoseconds. The hot electron spectrum created by SRS and TPD is relatively soft, limited to energies below one hundred keV. [ABSTRACT FROM AUTHOR]

Shock ignition of DT capsules involves two major steps. First, the fuel is assembled by means of a low velocity conventional implosion. At stagnation, the central core has a temperature lower than the one needed for ignition. Then a second, strong spherical converging shock, launched from a high intensity laser spike, arrives to the core. This shock crosses the core, rebounds at the target center and increases the central pressure to the ignition conditions. In this work we consider this latter phase by using the Guderley self-similar solution for converging flows. Our model accounts for the fusion reaction energy deposition, thermal and radiation losses thus describing the basic physics of hot spot ignition. The ignition criterion derived from the analytical model is successfully compared with full scale hydrodynamic simulations. [ABSTRACT FROM AUTHOR]

Radiation losses of electrons in intense laser fields constitute a process of major importance when considering laser-matter interaction at ultra-high intensities. Radiation losses can strongly modify the electron (and in turn ion) dynamics, and are associated with intense and directional emission of high energy photons. Accounting for such effects is therefore necessary for adequate modeling of electron and ion acceleration and creation of secondary photon sources at the forthcoming ultra-high power laser facilities. To account for radiation losses, the radiation friction force was introduced in the particle-in-cell code PICLS using a renormalized Lorentz-Abraham-Dirac model. A study of the effect of radiation friction on ultra high intensity laser ion acceleration with thin targets is presented and shows the importance of radiation losses for intensities higher than 1022 W/cm2. For ultra thin targets radiation losses can even improve laser ion acceleration. The regime of low density targets has also been investigated. It is shown that this regime of laser ion acceleration is still very efficient at ultra high intensities but that radiation losses are always detrimental to laser ion acceleration in this regime. [ABSTRACT FROM AUTHOR]

Ultra-short laser pulse interaction with a micro-structured surface of a melted metal is a promising source of hard X-ray radiation. Micro-structuring is achieved by a weak prepulse which produces narrow high density micro-jets. Interaction of the main laser pulse with such jets is shown to be a 100 times more efficient X-ray source than ordinary metal targets. This paper presents the results of optical and x-ray studies of laser-plasma interaction physics under such conditions supported by numerical simulations of fast electron generation. [ABSTRACT FROM AUTHOR]