Laser Plasma Laboratory Research Articles

Radiation from particles moving in small-scale magnetic fields created in solid-density laser-plasma laboratory experiments

Plasmas created by high-intensity lasers are often subject to the formation of kinetic-streaming instabilities, such as the Weibel instability, which lead to the spontaneous generation of high-amplitude, tangled magnetic fields. These fields typically exist on small spatial scales, i.e., “sub-Larmor scales.” Radiation from charged particles moving through small-scale electromagnetic (EM) turbulence has spectral characteristics distinct from both synchrotron and cyclotron radiation, and it carries valuable information on the statistical properties of the EM field structure and evolution. Consequently, this radiation from laser-produced plasmas may offer insight into the underlying electromagnetic turbulence. Here, we investigate the prospects for, and demonstrate the feasibility of, such direct radiative diagnostics for mildly relativistic, solid-density laser plasmas produced in lab experiments.

Electromagnetic field generation in the downstream of electrostatic shocks due to electron trapping.

A new magnetic field generation mechanism in electrostatic shocks is found, which can produce fields with magnetic energy density as high as 0.01 of the kinetic energy density of the flows on time scales ∼10(4)ωpe-1. Electron trapping during the shock formation process creates a strong temperature anisotropy in the distribution function, giving rise to the pure Weibel instability. The generated magnetic field is well confined to the downstream region of the electrostatic shock. The shock formation process is not modified, and the features of the shock front responsible for ion acceleration, which are currently probed in laser-plasma laboratory experiments, are maintained. However, such a strong magnetic field determines the particle trajectories downstream and has the potential to modify the signatures of the collisionless shock.

Three-Dimensional Relativistic Particle-in-Cell Hybrid Code Based on an Exponential Integrator

In this paper, we present a new 3-D full electromagnetic relativistic hybrid plasma code, the hybrid virtual laser plasma laboratory. The full kinetic particle-in-cell method is used to simulate low-density hot plasmas while the hydrodynamic model applies to the high-density cold background plasma. To simulate the linear electromagnetic response of the high-density plasma, we use a newly developed form of an exponential integrator method. It allows us to simulate plasmas of arbitrary densities using large time steps. The model reproduces the plasma dispersion and gives the correct spatial scales like the plasma skin depth even for large grid cell sizes. We test the hybrid model validity by applying it to some physical examples.

Geometric effects on EUV emissions in spherical and planar targets

We explored the radiation hydrodynamics of tin microsphere targets exposed to 1-μm, 8-ns laser pulses, and compared them with thick planar targets. Previous research [1] has shown that the conversion efficiency of laser light to in-band emissions around 13.5 nm is lower in microsphere targets. Our work was designed to elucidate the reasons for this drop in emission. Differences in plasma expansion, laser absorption and atomic emissions were measured in the UCSD Laser Plasma Laboratory and modeled using the 2D radiation hydrodynamic code h2d. Experimental data are compared with modeling and differences between emissions in planar and spherical targets explained.

One-dimensional electromagnetic relativistic PIC-hydrodynamic hybrid simulation code H-VLPL (hybrid virtual laser plasma lab)

In this paper we present a new one-dimensional full electromagnetic relativistic hybrid plasma model. The full kinetic particle-in-cell (PIC) and hydrodynamic model have been combined in the single hybrid plasma code H-VLPL (hybrid virtual laser plasma laboratory). The semi-implicit algorithm allows to simulate plasmas of arbitrary densities via automatic reduction of the highest plasma frequencies down to the numerically stable range. At the same time, the model keeps the correct spatial scales like the plasma skin depth. We discuss the numerically efficient implementation of this model. Further, we carefully test the hybrid model validity by applying it to a series of physical examples. The new mathematical method allows to overcome the typical time step restrictions of explicit PIC codes.

Relativistic laser–plasma bubbles: new sources of energetic particles and x-rays

Using direct three-dimensional particle-in-cell (PIC) simulations we study the acceleration of electrons and ions in laser–plasma. The PIC simulations allow us to understand the results of actual experiments better, and to look beyond the presently available technology and model for laser parameters that will be obtained in the nearest future. The code VLPL (Virtual Laser-Plasma Laboratory) has been further developed and now it can model the x-ray emission by relativistic electrons in the synchrotron regime. It appears that the strongly non-linear plasma wave excited by a short laser pulse works as a compact high-brightness source of x-ray radiation. We have also checked the possibility of proton trapping in the non-linear plasma wave and find that this is already possible at intensities around 1022 W cm−2.

Physics of ultra-intense laser-plasma interaction

The fast-ignition scheme in ICF has instigated research in a new area of laser-plasma interaction physics. This is due to the high laser-pulse intensities involved. At power densities of 1018 W cm-2, the physics becomes essentially kinetic in nature and highly nonlinear and hence requires special tools for its adequate description. Particle-in-cell (PIC) codes meet this challenge. Simulations obtained with the first three-dimensional PIC code VLPL (virtual laser plasma laboratory) developed at MPQ are presented for a broad variety of irradiation and plasma conditions. Particular attention is paid to a detailed comparison of numerical and experimental results and to the mechanism which accelerates the electrons to relativistic energies.

Relativistic laser-plasma interaction by multi-dimensional particle-in-cell simulations

Interaction of relativistically strong laser pulses with plasmas is investigated by a multi-dimensional particle-in-cell (PIC) code VLPL (Virtual Laser Plasma Laboratory) [Bull. Am. Phys. Soc. 41, 1502 (1996)]. Acceleration of background electrons to multi-MeV energies, generation of 100 MG magnetic fields, and dynamics of ion channel boring are studied. It is shown that direct v×B push by the laser pulse in the presence of an azimuthal dc magnetic field effectively accelerates background plasma electrons to energies significantly higher than the ponderomotive potential. The authors call this novel effect “B-loop” acceleration mechanism. It is dominant in near-critical plasma, or when plasma waves disappear due to wavebreaking. Laser channeling in under- and overdense plasmas is also studied. Energy spectra of the accelerated electrons and ions and the laser energy conversion efficiency at the critical surface are presented. It is shown that the accelerated electrons propagate in the form of magnetized jets. This physics is crucial for the fast ignitor concept in inertial confinement fusion.