Design of micrograting structures for laser acceleration of electrons

Preliminary modeling of micrograting structures indicates that gratings can be designed to support the pi -mode for acceleration of beta equivalent to 1 electrons. Two structures were originally proposed for laser acceleration experiments, the collonade and foxhole microgratings. Initially, freespace boundaries were included in the x planes at +or-10 mu m to simulate the original designs of the collonade and foxhole gratings. The collonade structure did not exhibit radiation at the desired frequency. Varying the angle of the collonades had only a slight effect on the location of the peak frequency, but no angle resulted in the desired resonant frequency. Simulations of the foxhole indicated that a width of 10.5 mu m resulted in a cavity mode being excited in this region. This mode has a zero crossing at x=0 which is undesirable since it provides no acceleration along the axis of the grating. By reducing the height of the foxhole structure to 4.1 mu m, and putting metallic walls in the x planes spaced at the width of the structure, resonance was obtained.<>