Laser-driven fast electron dynamics in gaseous media under the influence of large electric fields

We present the results of experiments performed at the LULI laboratory, using the 100 TW laser facility, on the study of the propagation of fast electrons in gas targets. The implemented diagnostics included chirped shadowgraphy and proton imaging. Proton images showed the presence of very large fields in the gas (produced by charge separation). In turn, these imply a strong inhibition of propagation, and a slowing down of the fast electron cloud as it penetrates in the gas. Indeed chirped shadowgraphy images show a reduction in time of the velocity of the electron cloud from the initial value, of the order of a fraction of c, over a time scale of a few picoseconds. © 2009 American Institute of Physics

Study of the propagation of ultra-intense laser-produced fast electrons in gas jets

We present the results of some recent experiments performed at the LULI laboratory using the 100 TW laser facility concerning the study of the propagation of fast electrons in gas targets. Novel diagnostics have been implemented including chirped shadowgraphy and proton radiography. Proton radiography images did show the presence of very strong fields in the gas probably produced by charge separation. In turn, these imply a slowing down of the fast electron cloud as it penetrates in the gas, and a strong inhibition of propagation. Indeed chirped shadowgraphy images show a strong reduction of the electron cloud velocity from the initial value close to a fraction of c

Behaviour of fast electron transport in solid targets

One of the main issues of the fast ignitor scheme is the role of fast electron transport in the solid fuel heating. Recent experiments used a new target scheme based on the use of cone to guide the PW laser and enhance the electron production. In this context it is fundamental to understand the physics underlying this new target scheme. We report here recent and preliminary results of ultra-intense laser pulse interaction with three layer targets in presence of the cone or without. Experiments have been performed at LULI with the 100 TW laser facility, at intensities up to 3 10$^{19}$ W/cm$^{2}$. Several diagnostics have been implemented (2D K$\alpha$ imaging, K$\alpha$ spectroscopy and rear side imaging, protons emission) to quantify the cone effect

Unraveling resistive versus collisional contributions to relativistic electron beam stopping power in cold-solid and in warm-dense plasmas

We present results on laser-driven relativistic electron beam propagation through aluminum samples, which are either solid and cold or compressed and heated by laser-induced shock. A full numerical description of fast electron generation and transport is found to reproduce the experimental absolute Kα yield and spot size measurements for varying target thicknesses, and to sequentially quantify the collisional and resistive electron stopping powers. The results demonstrate that both stopping mechanisms are enhanced in compressed Al samples and are attributed to the increase in the medium density and resistivity, respectively. For the achieved time- and space-averaged electronic current density, ⟨jh⟩∼8×1010 A/cm2 in the samples, the collisional and resistive stopping powers in warm and compressed Al are estimated to be 1.5 keV/μm and 0.8 keV/μm , respectively. By contrast, for cold and solid Al, the corresponding estimated values are 1.1 keV/μm and 0.6 keV/μm . Prospective numerical simulations involving higher jh show that the resistive stopping power can reach the same level as the collisional one. In addition to the effects of compression, the effect of the transient behavior of the resistivity of Al during relativistic electron beam transport becomes progressively more dominant, and for a significantly high current density, jh∼1012 A/cm2 , cancels the difference in the electron resistive stopping power (or the total stopping power in units of areal density) between solid and compressed samples. Analytical calculations extend the analysis up to jh=1014 A/cm2 (representative of the full-scale fast ignition scenario of inertial confinement fusion), where a very rapid transition to the Spitzer resistivity regime saturates the resistive stopping power, averaged over the electron beam duration, to values of ∼1 keV/μm

Study of the propagation of ultra-intense laser-produced fast electrons in gas jets

We present the results of some recent experiments performed at the LULI laboratory using the 100 TW laser facility concerning the study of the propagation of fast electrons in gas targets. Novel diagnostics have been implemented including chirped shadowgraphy and proton radiography. Proton radiography images did show the presence of very strong fields in the gas probably produced by charge separation. In turn, these imply a slowing down of the fast electron cloud as it penetrates in the gas, and a strong inhibition of propagation. Indeed chirped shadowgraphy images show a strong reduction of the electron cloud velocity from the initial value close to a fraction of c

X-ray absorption radiography for high pressure shock wave studies

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Transient development of SRS and SBS in ps-time scale by using sub-ps Thomson diagnostic

The control of parametric instabilities in large plasmas remains a challenge for the ICF program. Clearly, kinetic effects play an important role in the saturation mechanisms. Sub-picosecond Thomson analysis associated with short pulse interaction permits to explore these topics. A set of experiments have been performed in preformed, He plasmas using the 100-TW laser facility at LULI. The spectra of the electrostatic waves driven by stimulated Raman and Brillouin backscatterings generated in the 1.5 ps, ${\rm \omega}$ laser interaction have been measured with 0.3 ps time-resolution by using a short Thomson probe. Additionally, space-resolved and k-resolved spectra have been obtained. The experiments show that the fastest instability -B-SRS- first develops in the rising part of the pump. The B-SBS-driven IAW grows more slowly. B-SRS then abruptly vanishes around the maximum of the pump, while the IAW can be detected tens of picoseconds after the pump, allowing direct measurement of the IAW damping. The EPW k-spectra show that the EPW dispersion relation significantly deviates from the standard one. They exhibit a k-feature which could be related to the presence of a hot electron population produced in the B-SRS saturation process