93 research outputs found
Study of the effect of lattice structure on the transport of MA fast electron currents at the PHELIX laser facility
Collisionless Shock Acceleration of protons in a plasma slab produced in a gas jet by the collision of two laser-driven hydrodynamic shockwaves
We recently proposed a new technique of plasma tailoring by laser-driven
hydrodynamic shockwaves generated on both sides of a gas jet [J.-R. Marqu\`es
et al., Phys. Plasmas 28, 023103 (2021)]. In the continuation of this numerical
work, we studied experimentally the influence of the tailoring on proton
acceleration driven by a high-intensity picosecond-laser, in three cases:
without tailoring, by tailoring only the entrance side of the ps-laser, or both
sides of the gas jet. Without tailoring the acceleration is transverse to the
laser axis, with a low-energy exponential spectrum, produced by Coulomb
explosion. When the front side of the gas jet is tailored, a forward
acceleration appears, that is significantly enhanced when both the front and
back sides of the plasma are tailored. This forward acceleration produces
higher energy protons, with a peaked spectrum, and is in good agreement with
the mechanism of Collisionless Shock Acceleration (CSA). The spatio-temporal
evolution of the plasma profile was characterized by optical shadowgraphy of a
probe beam. The refraction and absorption of this beam was simulated by
post-processing 3D hydrodynamic simulations of the plasma tailoring. Comparison
with the experimental results allowed to estimate the thickness and
near-critical density of the plasma slab produced by tailoring both sides of
the gas jet. These parameters are in good agreement with those required for
CSA
Optimization of plasma mirror reflectivity and optical quality using double laser pulses
We measure a record 962.5 % specularly reflected energy fraction from an interaction with a plasma mirror surface preionised by a controlled prepulse and find that the optical quality is dependent on the inter pulse time delay. Simulations show that the main pulse reflected energy is a strong function of plasma density scale length, which increases with the time delay and reaches a peak reflectivity for a scale length of 0.3 m, which is achieved here for a pulse separation time of 3 ps. It is found that the incident laser quasi near field intensity distribution leads to nonuniformities in this plasma expansion and consequent critical surface position distribution. The plasma mirror optical quality is found to be governed by the resultant perturbations in the critical surface position, which become larger with inter pulse time delay
Role of lattice structure and low temperature resistivity on fast electron beam filamentation in carbon
The influence of low temperature (eV to tens-of-eV) electrical resistivity on the onset of the filamentation instability in fast-electron transport is investigated in targets comprising of layers of ordered (diamond) and disordered (vitreous) carbon. It is shown experimentally and numerically that the thickness of the disordered carbon layer influences the degree of filamentation of the fast-electron beam. Strong filamentation is produced if the thickness is of the order of 60 μm or greater, for an electron distribution driven by a sub-picosecond, mid-1020 Wcm-2 laser pulse. It is shown that the position of the vitreous carbon layer relative to the fast-electron source (where the beam current density and background temperature are highest) does not have a strong effect because the resistive filamentation growth rate is high in disordered carbon over a wide range of temperatures up to the Spitzer regime
X-ray phase-contrast imaging for laser-induced shock waves
X-ray phase-contrast imaging (XPCI) is a versatile technique with applications in many fields, including fundamental physics, biology and medicine. Where X-ray absorption radiography requires high density ratios for effective imaging, the image contrast for XPCI is a function of the density gradient. In this letter, we apply XPCI to the study of laser-driven shock waves. Our experiment was conducted at the Petawatt High-Energy Laser for Heavy Ion EXperiments (PHELIX) at GSI. Two laser beams were used: one to launch a shock wave and the other to generate an X-ray source for phase-contrast imaging. Our results suggest that this technique is suitable for the study of warm dense matter (WDM), inertial confinement fusion (ICF) and laboratory astrophysics
Measurement of the angle, temperature and flux of fast electrons emitted from intense laser-solid interactions
High-intensity laser-solid interactions generate relativistic electrons, as well as high-energy (multi-MeV) ions and X-rays. The directionality, spectra and total number of electrons that escape atarget-foil is dependent on the absorption, transport and rear-side sheath conditions. Measuring the electrons escaping the target will aid in improving our understanding of these absorption processes and the rear-surface sheath fields that retard the escaping electrons and accelerate ions via the target normal sheath acceleration (TNSA) mechanism. A comprehensive Geant4 study was performed to help analyse measurements made with a wrap-around diagnostic that surrounds the target and uses differential filtering with a FUJI-film image plate detector. The contribution of secondary sources such as X-rays and protons to the measured signal have been taken into account to aid in the retrieval of the electron signal. Angular and spectral data from a high-intensity laser-solid interaction are presented and accompanied by simulations. The total number of emitted electrons has been measured as 2.6 × 1013 with an estimated total energy of 12 ± 1 J from a 100 mu;m Cu target with140 J of incident laser energy during a 4 × 1020 W cm-2 interaction
Propagation-based imaging phase-contrast enhanced imaging setup for single shot acquisition using laser-generated X-ray sources
The development of new diagnostics is important to improve the interpretation of experiments. Often well-known physical processes and techniques originally developed in unrelated fields of science can be applied to a different area with a significant impact on the quality of the produced data. X-ray phase-contrast imaging (XPCI) is one techniques which has found many applications in biology and medicine. This is due to its capability to emphasise the presence of strong density variations normally oriented with respect to the X-ray propagation direction. With the availability of short energetic X-ray pulses XPCI extends to time-resolved pump-probe measurements of laser-matter interaction where strong density gradient are also present. In this work we present the setup for XPCI tested at the laser PHELiX at GSI in Germany
Directed fast electron beams in ultraintense picosecond laser irradiated solid targets
We report on fast electron transport and emission patterns from solid targets irradiated by s-polarized, relativistically intense, picosecond laser pulses. A beam of multi-MeV electrons is found to be transported along the target surface in the laser polarization direction. The spatial-intensity and energy distributions of this beam are compared with the beam produced along the laser propagation axis. It is shown that even for peak laser intensities an order of magnitude higher than the relativistic threshold; laser polarization still plays an important role in electron energy transport. Results from 3D particle-in-cell simulations confirm the findings. The characterization of directional beam emission is important for applications requiring efficient energy transfer, including secondary photon and ion source development
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