High-Resolution Simulations of Plasma Interactions with Ultra-Short Electromagnetic Pulses

Summary form only given. We report results from two types of high-resolution particle-in-cell (PIC) simulations: (i) wake-driven electron acceleration by intense ultra short laser pulses, and (ii) generation of high-power electromagnetic radiation by free-electron laser (FEL) amplifiers. Large-scale full PIC simulations play a crucial role in the modeling of electronic devices, laser-plasma interactions and magnetic reconnection. Inadequate spatial resolution of experimental features (beam and laser pulse shapes, plasma and device boundaries, discontinuities, etc.) may give rise to unacceptable errors in critical simulation results. On the other hand, uniform fine resolution is often prohibitive. We show that a consistent extension of structured adaptive mesh refinement (SAMR) to electromagnetic PIC models is made possible through recent advances in computational technologies. Our simulations of the propagation of ultra-short (100 TW, 20 fs) laser pulses in underdense plasmas and concomitant generation of high-energy electrons (up to 60 MeV) indicate that the use of inadequate resolution and/or certain standard subgridding algorithms may result in significantly modifying the plasma response in such simulations, which leads to errors in the longitudinal wake field and the electron energy spectrum. Likewise, low-resolution simulations of the resonant interaction of relativistic electron beams with magnetic field wigglers tend to underestimate the amount of radiated electromagnetic power. The novel adaptive mesh capabilities are being implemented in a new 3D EM-PIC code, EMPOWER (ElectroMagnetic Particle Operation With Extended Resolution), which is targeted towards laser-plasma interaction and microwave source applications.