Patent ID: 8779351

Claim:
An ion source for use in a radiation generator comprising: a cathode to emit primary electrons; a cathode grid downstream of the cathode; a reflector electrode downstream of the cathode grid; a reflector grid radially inward of the reflector electrode; and an extractor electrode downstream of the reflector electrode, the extractor electrode and cathode grid defining an ionization region therebetween; the cathode and the cathode grid having a first voltage difference such that a resultant electric field in the ion source accelerates the primary electrons through the cathode grid and into the ionization region on a trajectory toward the extractor electrode; the reflector grid and the extractor electrode having a second voltage difference less than the first voltage difference such that the electric field slows the primary electrons as they near the extractor electrode and repels the primary electrons on a trajectory away from the extractor electrode and toward the reflector electrode; the cathode and reflector electrode having a third voltage difference less than the first voltage difference such that some of the primary electrons are attracted to and strike the reflector electrode, creating secondary electrons having an electron energy less than the primary electrons; the reflector grid having a positive potential with respect to the reflector electrode such that the electric field attracts the primary and secondary electrons away from the reflector electrode and into the ionization region; at least some of the primary or secondary electrons, when in the ionization region, interacting with an ionizable gas to create ions.