Particle-in-cell simulation of dielectric wall accelerators

Computer simulations of dielectric wall accelerators using state-of-the-art multi-dimensional particle-in-cell (PIC) codes were carried out. Specifically, the cylindrical waveguide is lined with a dielectric with permittivity of 3.75 and its inner radius is 0.57cm. The temporal shape of the driving electron beam has a double-triangle profile with different amplitudes in beam current and its total pulse length is chosen to be 4 ps. The total charge of the drive beam is 5 nC. We used the two dimensional PIC code Merlin in cylindrical geometry to simulate self-consistently the electron beam propagation and the excitation of the wakefield in the dielectric wall waveguide. The initial choice of the beam energy is 100 MeV. Our simulations show a strong coherent excitation of the wakefield at the fundamental mode of 300 GHz with a peak longitudinal electric field amplitude of 117 MV/m. Higher order modes are also observed in our simulations. The longitudinal decelerating electric field at the beam position is 17.5 MV/m resulting in a transformer ratio of 6.7 which agrees very well with the 1-D theoretical value of 6.6. However, our simulations show the amplitude of the longitudinal electric field having a radial gradient in contrast to being constant predicted by the 1-D analytic theory in the ultra-relativistic limit. The effects of beam energy and emittance have also been studied. We further perform 3-D simulations using the LSP code to investigate effects due to azimuthal asymmetry. Detail comparison between 1-D analytic theory with 2-D and 3-D simulations using different beam parameters will be presented.