An ion source for use in a particle accelerator includes at least one cathode. The at least one cathode has an array of nano-sized projections and an array of gates adjacent the array of nano-sized projections. The array of nano-sized projections and the array of gates have a first voltage difference such that an electric field in the cathode causes electrons to be emitted from the array of nano-sized projections and accelerated downstream. There is a ion source electrode downstream of the at least one cathode, and the at least one cathode and the ion source electrode have the same voltage applied such that the electrons enter the space encompassed by the ion source electrode, some of the electrons as they travel within the ion source electrode striking an ionizable gas to create ions.