Particle-in-cell (PIC) methods have a long history in the study of laser-plasma interactions. Early electromagnetic codes used the Yee staggered grid for field variables combined with a leapfrog EM-field update and the Boris algorithm for particle pushing. The general properties of such schemes are well documented. Modern PIC codes tend to add to these high-order shape functions for particles, Poisson preserving field updates, collisions, ionisation, a hybrid scheme for solid density and high-field QED effects. In addition to these physics packages, the increase in computing power now allows simulations with real mass ratios, full 3D dynamics and multi-speckle interaction. This paper presents a review of the core algorithms used in current laser-plasma specific PIC codes. Also reported are estimates of self-heating rates, convergence of collisional routines and test of ionisation models which are not readily available elsewhere. Having reviewed the status of PIC algorithms we present a summary of recent applications of such codes in laser-plasma physics, concentrating on SRS, short-pulse laser-solid interactions, fast-electron transport, and QED effects.
Measurements of magnetic fields generated during ultrahigh intensity (>1019 W cm−2), short pulse (0.7–1 ps) laser–solid target interaction experiments are reported. An innovative method is used and the results are compared with particle-in-cell simulations. It is shown that polarization measurements of the self-generated harmonics of the laser can provide a convenient method for diagnosing the magnetic field—and that the experimental measurements indicate the existence of peak fields greater than 340 MG and below 460 MG at such high intensities. In particular, the observation of the X-wave cutoffs and the observed induced ellipticity of the harmonics can provide a reliable method for measuring these fields. These observations are important for evaluating the use of intense lasers in various potential applications and perhaps for understanding the complex physics of exotic astrophysical objects such as neutron stars.
Time-resolved x-ray spectra from solid targets irradiated by the VULCAN Petawatt laser focused to 1020Wcm−2 show that material at solid density is heated to temperatures above 500 eV to a depth of about 15 μm and for a duration of more than 30 ps. Modeling with the implicit hybrid plasma code LSP shows that the heating is sensitive to the laser prepulse through resistive inhibition of the laser accelerated electrons in the blow off layer.
The VULCAN ͓C. N. Danson et al., Opt. Commun. 103, 392 ͑1993͔͒ laser at the UK Central Laser Facility is being used for laboratory-based simulations of collisionless shocks. By ensuring that key dimensionless parameters in the experiments have values similar to those of supernova remnants ͑SNRs͒, the hydrodynamics and magnetic field of the experiment are scaled to those of a SNR. This makes it possible to investigate experimentally the physics of collisionless magnetized shocks in such objects. The experiments are providing data against which to test current theory. Collisionless shock formation and the interaction of two counterpropagating colliding plasmas permeated by a strong magnetic field are discussed.
The properties of high energy density plasma are under increasing scrutiny in recent years due to their importance to our understanding of stellar interiors, the cores of giant planets 1 , and the properties of hot plasma in inertial confinement fusion devices 2 . When matter is heated by X-rays, electrons in the inner shells are ionized before the valence electrons. Ionization from the inside out creates atoms or ions with empty internal electron shells, which are known as hollow atoms (or ions) 3,4,5 . Recent advances in free-electron laser (FEL) technology 6,7,8,9 have made possible the creation of condensed matter consisting predominantly of hollow atoms. In this Letter, we demonstrate that such exotic states of matter, which are very far from equilibrium, can also be formed by more conventional optical laser technology when the laser intensity approaches the radiation dominant regime 10 . Such photon-dominated systems are relevant to studies of photoionized plasmas found in active galactic nuclei and X-ray binaries 11 . Our results promote laser-produced plasma as a unique ultra-bright x-ray source for future studies of matter in extreme conditions as well as for radiography of biological systems and for material science studies 12,13,14,15 .
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