Longitudinal space charge debunching and compensation in high-frequency accelerators

Space charge debunching is a major issue for future high-gradient, high-frequency accelerator techniques. Space charge will set limits on the maximum six-dimensional phase space density obtainable in optical or plasma based accelerators. These accelerators will have short microbunches a fraction of an optical wavelength, in which space charge debunching is unmitigated by two-dimensional effects. The element of an accelerator system most vulnerable to space charge is the drift space between the prebuncher and the acceleration sections. A self-consistent model coupling the energy and phase modulation in the drift space is developed. It is shown that both space charge effects and coherent energy spread can be offset by adjusting the prebuncher and beam optics parameters. In the accelerator sections, the large relativistically corrected inertia together with two-dimensional effects combine to make space charge debunching unimportant. The analytical results compare well with PARMELA code simulations.