Photon scattering by a 4π-spherically-focused ultrastrong electromagnetic wave

The scattering of high-power probe laser pulses by tightly focused ultrastrong laser pulses has been investigated through a semiclassical approach using a perturbative method based on the Born approximation. Under a 4π-spherically-focused ultrastrong light field, the electric permittivity and magnetic permeability tensors for vacuum are calculated from the Euler-Heisenberg Lagrangian to show the nonlinear birefringent property of vacuum. And, from permittivity and permeability tensors, the scattering potential is derived for the Born approximation. The first-order solution of the Born approximation is taken as an electric field scattered from the 4π-spherically-focused laser pulse when a probe laser pulse propagates through the focused laser field. The differential cross section of the nonlinear birefringent vacuum is derived, and the number of photons scattered from the nonlinear birefringent vacuum is analyzed in the laser power range of 10-1000 PW

Forced magnetic field line reconnection in electron magnetohydrodynamics

The forced reconnection of magnetic field lines within the framework of electron magnetohydrodynamics (EMHD) has been investigated. A broad class of solutions that describe stationary reconnection have been found. The time evolution of the plasma and of the magnetic field when perturbations are imposed from the boundary of a high conductivity plasma slab are also studied. The initial magnetic field has a null surface. Following this discussion, the so-called Taylor's problem for EMHD in which the perturbations cause a change in the topology of the magnetic field has been solved. The plasma and the magnetic field are seen to evolve with the time scale of the linear tearing mode. Their time evolution is described by exponential dependences. Analytic and numerical simulation results of the nonlinear regime of forced magnetic reconnection in EMHD are also presented. Finally, the above results are compared with a case where the reconnection is mediated by dissipative electron viscosity effects. (C) 1998 American Institute of Physics

Laser-heater assisted plasma channel formation in capillary discharge waveguides

A method of creating plasma channels with controllable depth and transverse profile for the guiding of short, high power laser pulses for efficient electron acceleration is proposed. The plasma channel produced by the hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser pulse, which heats the electrons near the capillary axis. This interaction creates a deeper plasma channel within the capillary discharge that evolves on a ns-time scale, allowing laser beams with smaller spot sizes than would otherwise be possible in the unmodified capillary discharge. © 2013 American Institute of Physics

Demonstration of a high repetition rate capillary discharge waveguide

A hydrogen-filled capillary discharge waveguide operating at kHz repetition rates is presented for parameters relevant to laser plasma acceleration (LPA). The discharge current pulse was optimized for erosion mitigation with laser guiding experiments and MHD simulation. Heat flow simulations and measurements showed modest temperature rise at the capillary wall due to the average heat load at kHz repetition rates with water-cooled capillaries, which is promising for applications of LPAs such as high average power radiation sources

Radial density profile and stability of capillary discharge plasma waveguides of lengths up to 40 cm

We measured the parameter reproducibility and radial electron density profile of capillary discharge waveguides with diameters of 650 to 2 mm and lengths of 9 to 40 cm. To the best of the authors' knowledge, 40 cm is the longest discharge capillary plasma waveguide to date. This length is important for 10 GeV electron energy gain in a single laser-driven plasma wakefield acceleration stage. Evaluation of waveguide parameter variations showed that their focusing strength was stable and reproducible t

Nonuniform discharge currents in active plasma lenses

Active plasma lenses have attracted interest in novel accelerator applications due to their ability to provide large-field-gradient (short focal length), tunable, and radially symmetric focusing for charged particle beams. However, if the discharge current is not flowing uniformly as a function of radius, one can expect a radially varying field gradient as well as potential emittance degradation. We have investigated this experimentally for a 1-mm-diameter active plasma lens. The measured near-axis field gradient is approximately 35% larger than expected for a uniform current distribution, and at overfocusing currents ring-shaped electron beams are observed. These observations are explained by simulations

Radial density profile and stability of capillary discharge plasma waveguides of lengths up to 40 cm

We measured the parameter reproducibility and radial electron density profile of capillary discharge waveguides with diameters of 650 to 2 mm and lengths of 9 to 40 cm. To the best of the authors' knowledge, 40 cm is the longest discharge capillary plasma waveguide to date. This length is important for 10 GeV electron energy gain in a single laser-driven plasma wakefield acceleration stage. Evaluation of waveguide parameter variations showed that their focusing strength was stable and reproducible t

Nonuniform discharge currents in active plasma lenses

Active plasma lenses have attracted interest in novel accelerator applications due to their ability to provide large-field-gradient (short focal length), tunable, and radially symmetric focusing for charged particle beams. However, if the discharge current is not flowing uniformly as a function of radius, one can expect a radially varying field gradient as well as potential emittance degradation. We have investigated this experimentally for a 1-mm-diameter active plasma lens. The measured near-axis field gradient is approximately 35% larger than expected for a uniform current distribution, and at overfocusing currents ring-shaped electron beams are observed. These observations are explained by simulations

Cryogenically formed discharge waveguide

We describe the development and operation of a regenerative, cryogenically-formed discharge waveguide formed by freezing nitrous oxide gas onto the inner wall of a sapphire capillary. We demonstrate a technique for varying the channel diameter in situ and present guiding of low-power laser pulses through 6-cm long waveguides with channel diameters of 0.7, 0.8, and 1 mm. Measurements and simulations of the output laser fluence showed that the matched spot size could be adjusted with the thickness of the solid nitrous oxide layer

Creation of an axially uniform plasma channel in a laser-assisted capillary discharge

Dissipative capillary discharges form plasma channels which allow for high power laser guiding, enabling efficient electron acceleration in a laser wakefield accelerator. However, at the low plasma densities required to produce high-energy electrons, in order to avoid capillary wall damage, high power lasers need a tighter transverse confinement that cannot be achieved by the capillary discharge powered by Ohmic heating alone. The introduction of an additional laser for heating of the plasma leads to deeper and narrower plasma channels. Here we investigate the formation of laser-heated axially uniform plasma channels. We show that a high degree of longitudinal uniformity can be achieved despite significant evolution of the heater laser during its propagation through the channel