Kinetic instability in inductively oscillatory plasma equilibrium.

A uniform in space, oscillatory in time plasma equilibrium sustained by a time-dependent current density is analytically and numerically studied resorting to particle-in-cell simulations. The dispersion relation is derived from the Vlasov equation for oscillating equilibrium distribution functions, and used to demonstrate that the plasma has an infinite number of unstable kinetic modes. This instability represents a kinetic mechanism for the decay of the initial mode of infinite wavelength (or equivalently null wave number), for which no classical wave breaking or Landau damping exists.

High-order harmonic generation in an electron-positron-ion plasma.

The laser interaction with an electron-positron-ion mixed plasma is studied from the perspective of the associated high-order harmonic generation. For an idealized mixed plasma which is assumed with a sharp plasma-vacuum interface and uniform density distribution, when it is irradiated by a weakly relativistic laser pulse, well-defined signals at harmonics of the plasma frequency in the harmonic spectrum are observed. These characteristic signals are attributed to the inverse two-plasmon decay of the counterpropagating monochromatic plasma waves which are excited by the energetic electrons and the positron beam accelerated by the laser.

Plasma Wakes Driven by Photon Bursts via Compton Scattering.

Photon bursts with a wavelength smaller than the plasma interparticle distance can drive plasma wakes via Compton scattering. We investigate this fundamental process analytically and numerically for different photon frequencies, photon flux, and plasma magnetization. Our results show that Langmuir and extraordinary modes are driven efficiently when the photon energy density lies above a certain threshold.

Prospect of Studying Nonperturbative QED with Beam-Beam Collisions.

We demonstrate the experimental feasibility of probing the fully nonperturbative regime of quantum electrodynamics with a 100 GeV-class particle collider. By using tightly compressed and focused electron beams, beamstrahlung radiation losses can be mitigated, allowing the particles to experience extreme electromagnetic fields. Three-dimensional particle-in-cell simulations confirm the viability of this approach.

Seeded QED cascades in counterpropagating laser pulses.

The growth rates of seeded QED cascades in counterpropagating lasers are calculated with first-principles two- and three-dimensional QED-PIC (particle-in-cell) simulations. The dependence of the growth rate on the laser polarization and intensity is compared with analytical models that support the findings of the simulations. The models provide insight regarding the qualitative trend of the cascade growth when the intensity of the laser field is varied.

Transverse electron-scale instability in relativistic shear flows.

Electron-scale surface waves are shown to be unstable in the transverse plane of a sheared flow in an initially unmagnetized collisionless plasma, not captured by (magneto)hydrodynamics. It is found that these unstable modes have a higher growth rate than the closely related electron-scale Kelvin-Helmholtz instability in relativistic shears. Multidimensional particle-in-cell simulations verify the analytic results and further reveal the emergence of mushroomlike electron density structures in the nonlinear phase of the instability, similar to those observed in the Rayleigh Taylor instability despite the great disparity in scales and different underlying physics.

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.

dc-Magnetic-field generation in unmagnetized shear flows.

The generation of dc magnetic fields in unmagnetized electron-ion shear flows is shown to be associated to either initial thermal effects or the onset of electron-scale shear instabilities, in particular the cold Kelvin-Helmholtz instability. This mechanism, intrinsic to shear gradients on the electron scale, is described through a kinetic model that predicts the growth and the saturation of the dc field in both scenarios. The theoretical results are confirmed by multidimensional particle-in-cell simulations, demonstrating the formation of long-lived magnetic fields (t~100's ω(pi)(-1)) along the full longitudinal extent of the shear layer, with a typical transverse width of √[γ(0)]c/ω(pe), reaching magnitudes eB(dc)/m(e)cω(pe)~β(0)√[γ(0)] for an initial sharp shear.

Transverse plasma-wave localization in multiple dimensions.

Plasma-wave behavior in multiple dimensions is studied using two- and three-dimensional particle-in-cell simulations. We find that large-amplitude waves with kλ(D)≳0.2, where k is the wave number of the wave and λ(D) is the Debye length, localize in the transverse direction around their axis due to nonlinear, local damping caused by transiting particles.

Time and space resolved interferometry for laser-generated fast electron measurements.

A technique developed to measure in time and space the dynamics of the electron populations resulting from the irradiation of thin solids by ultraintense lasers is presented. It is a phase reflectometry technique that uses an optical probe beam reflecting off the target rear surface. The phase of the probe beam is sensitive to both laser-produced fast electrons of low-density streaming into vacuum and warm solid density electrons that are heated by the fast electrons.

Propagation and damping of nonlinear plasma wave packets.

Nonlinear electron plasma wave packets are shown to locally damp at the rear of the packet. Resonant particles enter the back of the packet and linearly damp the first few wavelengths, thereby carrying energy away from the back edge and eventually eroding the packet. This process could significantly affect the recurrence and long-time behavior of stimulated Raman scattering because it is predicted that a nonlinear packet will erode away before it travels a speckle length.

Rarefaction acceleration and kinetic effects in thin-foil expansion into a vacuum.

The collisionless expansion into a vacuum of a thin plasma foil adiabatically cooling down is studied with a particular emphasis on the evolution of the electron distribution function. It is shown that during the expansion the bulk of the distribution function evolves towards a top-hat distribution. As a result, while the electrons globally lose energy in favor of the ions, the rarefaction wave accelerates until it reaches the center of the foil.

Hot and cold electron dynamics following high-intensity laser matter interaction.

The characteristics of fast electrons laser accelerated from solids and expanding into a vacuum from the rear target surface have been measured via optical probe reflectometry. This allows access to the time- and space-resolved dynamics of the fast electron density and temperature and of the energy partition into bulk (cold) electrons. In particular, it is found that the density of the hot electrons on the target rear surface is bell shaped, and that their mean energy at the same location is radially homogeneous and decreases with the target thickness.

Electron kinetic effects in plasma expansion and ion acceleration.

The one-dimensional expansion of a plasma slab is studied using a kinetic description of the electrons based on an adiabatic invariant. The distribution function of the electrons is determined at any time and any position. Solution of the Poisson equation then enables us to determine the electric potential and the ion acceleration.

Laser-foil acceleration of high-energy protons in small-scale plasma gradients.

Proton beams laser accelerated from thin foils are studied for various plasma gradients on the foil rear surface. The beam maximum energy and spectral slope reduce with the gradient scale length, in good agreement with numerical simulations. The results also show that the jxB mechanism determines the temperature of the electrons driving the ion expansion.

Dynamics of electric fields driving the laser acceleration of multi-MeV protons.

The acceleration of multi-MeV protons from the rear surface of thin solid foils irradiated by an intense (approximately 10(18) W/cm2) and short (approximately 1.5 ps) laser pulse has been investigated using transverse proton probing. The structure of the electric field driving the expansion of the proton beam has been resolved with high spatial and temporal resolution.