Search Results (4 total)

We present 2D simulations of both beam-driven and laser-driven plasma wakefield accelerators, using the object-oriented particle-in-cell code XOOPIC, which is time explicit, fully electromagnetic, and capable of running on massively parallel supercomputers. Simulations of laser-driven wakefields with low \(∼10¹⁶ W/cm²\) and high \(∼10¹⁸ W/cm²\) peak intensity laser pulses are conducted in slab geometry, showing agreement with theory and fluid simulations. Simulations of the E-157 beam wakefield experiment at the Stanford Linear Accelerator Center, in which a 30 GeV electron beam passes through 1 m of preionized lithium plasma, are conducted in cylindrical geometry, obtaining good agreement with previous work. We briefly describe some of the more significant modifications to XOOPIC required by this work, and summarize the issues relevant to modeling relativistic electron-neutral collisions in a particle-in-cell code.

The power exchange between crossed laser beams made possible by an ion-acoustic wave is studied, as is the associated frequency cascade. The beam evolution is found to depend sensitively on whether the beams are monochromatic or multichromatic initially, and whether their intersection region lies partially or completely within the plasma.

The evolution of the stimulated Raman scattering (SRS) instability in time and two spatial dimensions is studied analytically for initial and boundary conditions representative of a laser pulse convecting into fresh plasma. For most scattering angles, SRS saturates due to the lateral convection of the Stokes wave. The steady-state amplitude profiles of the Stokes and Langmuir waves are highly two dimensional.

The evolution of the stimulated Brillouin scattering (SBS) instability in time and two spatial dimensions is studied analytically. An exact solution of the linearized equations governing SBS in a finite homogeneous plasma shows that this two-dimensional instability usually saturates because of the convection of the ion-acoustic wave, regardless of whether the associated one-dimensional interaction is convectively or absolutely unstable. The steady-state intensity profile of the Stokes light wave is often highly two dimensional.