Photon kinetics for laser-plasma interactions

A photon kinetic formalism is employed to describe the propagation of short laser pulses in tenuous plasmas. The photon kinetic theory contains all of the ingredients necessary to describe the relativistic nonlinear optics of short laser pulses in plasmas, and the shortest time scale is determined by the local evolution of the index of refraction. We use this feature to implement a photon in cell code, in which the typical time step is much bigger than is the laser field time scale. Additional information provided by the photon kinetic framework is illustrated by one-dimensional (1-D) and two-dimensional (2-D) simulations

Influence of sideband oscillations on gyrotron efficiency

We report the observation of sideband mode effects on the efficiency of overmoded gyrotron operation. Two cavities were designed and operated which differed in the presence of sideband modes. In one version of the cavity, parasitic backward waves modes were observed and efficiencies were approximately 22% at 40 A beam current. With the use of a multi-mode self-consistent nonlinear code, a modified design was generated which eliminated the sideband modes. Experiments were conducted with this new cavity which produced efficiencies of approximately 33% at 30 A and 27% at 40 A beam current, but with a slightly higher velocity ratio than seen with the earlier cavity. An additional cavity, also with no sideband modes but with a longer cavity length and therefore higher Q obtained powers up to 1.3 MW with an efficiency of 39% at a 40 A beam current.© IEE

A laser–plasma accelerator producing monoenergetic electron beams

International audienceParticle accelerators are used in a wide variety of fields, ranging from medicine and biology to high-energy physics. The accelerating fields in conventional accelerators are limited to a few tens of MeV m^-1, owing to material breakdown at the walls of the structure. Thus, the production of energetic particle beams currently requires large-scale accelerators and expensive infrastructures. Laser–plasma accelerators have been proposed as a next generation of compact accelerators because of the huge electric fields they can sustain (>100 GeV m^-1). However, it has been difficult to use them efficiently for applications because they have produced poor-quality particle beams with large energy spreads, owing to a randomization of electrons in phase space. Here we demonstrate that this randomization can be suppressed and that the quality of the electron beams can be dramatically enhanced. Within a length of 3 mm, the laser drives a plasma bubble that traps and accelerates plasma electrons. The resulting electron beam is extremely collimated and quasi-monoenergetic, with a high charge of 0.5 nC at 170 MeV

Laser-Plasma Interactions Enabled by Emerging Technologies

An overview from the past and an outlook for the future of fundamental laser-plasma interactions research enabled by emerging laser systems