30 research outputs found
Dynamic convergent shock compression initiated by return current in high-intensity laser solid interactions
We investigate the dynamics of convergent shock compression in the solid wire
targets irradiated by an ultra-fast relativistic laser pulse. Our
Particle-in-Cell (PIC) simulations and coupled hydrodynamic simulations reveal
that the compression process is initiated by both magnetic pressure and surface
ablation associated with a strong transient surface return current with the
density in the order of 1e17 A/m^2 and a lifetime of 100 fs. The results show
that the dominant compression mechanism is governed by the plasma ,
i.e., the ratio of the thermal pressure to magnetic pressure. For small radii
and low atomic number Z wire targets, the magnetic pressure is the dominant
shock compression mechanism. As the target radius and atomic number Z increase,
the surface ablation pressure is the main mechanism to generate convergent
shocks based on the scaling law. Furthermore, the indirect experimental
indication of the shocked hydrogen compression is provided by measuring the
evolution of plasma expansion diameter via optical shadowgraphy. This work
could offer a novel platform to generate extremely high pressures exceeding
Gbar to study high-pressure physics using femtosecond J-level laser pulses,
offering an alternative to the nanosecond kJ laser pulse-initiated and pulse
power Z-pinch compression methods
Visualizing Ultrafast Kinetic Instabilities in Laser-Driven Solids using X-ray Scattering
Ultra-intense lasers that ionize and accelerate electrons in solids to near
the speed of light can lead to kinetic instabilities that alter the laser
absorption and subsequent electron transport, isochoric heating, and ion
acceleration. These instabilities can be difficult to characterize, but a novel
approach using X-ray scattering at keV energies allows for their visualization
with femtosecond temporal resolution on the few nanometer mesoscale. Our
experiments on laser-driven flat silicon membranes show the development of
structure with a dominant scale of ~60\unit{nm} in the plane of the laser
axis and laser polarization, and ~95\unit{nm} in the vertical direction with
a growth rate faster than . Combining the XFEL experiments
with simulations provides a complete picture of the structural evolution of
ultra-fast laser-induced instability development, indicating the excitation of
surface plasmons and the growth of a new type of filamentation instability.
These findings provide new insight into the ultra-fast instability processes in
solids under extreme conditions at the nanometer level with important
implications for inertial confinement fusion and laboratory astrophysics
Optimizing laser coupling, matter heating, and particle acceleration from solids using multiplexed ultraintense lasers
Realizing the full potential of ultrahigh-intensity lasers for particle and radiation generation will require multi-beam arrangements due to technology limitations. Here, we investigate how to optimize their coupling with solid targets. Experimentally, we show that overlapping two intense lasers in a mirror-like configuration onto a solid with a large preplasma can greatly improve the generation of hot electrons at the target front and ion acceleration at the target backside. The underlying mechanisms are analyzed through multidimensional particle-in-cell simulations, revealing that the self-induced magnetic fields driven by the two laser beams at the target front are susceptible to reconnection, which is one possible mechanism to boost electron energization. In addition, the resistive magnetic field generated during the transport of the hot electrons in the target bulk tends to improve their collimation. Our simulations also indicate that such effects can be further enhanced by overlapping more than two laser beams
High Field Suppression of Bremsstrahlung Emission in High-Intensity Laser-Plasma Interactions
This dissertation investigates the effect of macroscopic electric and magnetic fields on bremsstrahlung emission in high-intensity laser-plasma interactions, specifically in the regime of relativistic-induced transparency. The Particle-in-Cell (PIC) EPOCH simulation code has been updated to incorporate a new suppression mechanism influenced by the presence of intense electric and magnetic fields. The study compared the bremsstrahlung emissions generated under relativistic transparency conditions using three distinct models: the original bremsstrahlung model in the EPOCH code, the model modified by the magnetic suppression (MS) effect, and the newly proposed suppression model by the electric and magnetic suppression (EMS) effect.
The results demonstrated that macroscopic electric and magnetic fields have a significant effect on the decrease of bremsstrahlung photons in laser-plasma interactions. In addition, differences in electron dynamics were observed between the EPOCH and EMS models, indicating that the suppression mechanism can influence the dynamics of electron acceleration. The study provides insight into bremsstrahlung emission under extreme conditions, where energetic electrons travel through a relativistically transparent plasma while being deflected by magnetic fields with MT-level strength.
On the basis of the results, it is suggested that the implementation of conventional bremsstrahlung in PIC codes be modified to account for the discussed suppression effect