21 research outputs found
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 W/cm. Several diagnostics have been
implemented (2D K imaging, K 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
International audienc
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,
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