Patent ID: 8822912

Claim:
An ion source for use in a radiation generator comprising: a cathode to emit 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 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 electrons as they near the extractor electrode and repels the electrons on a trajectory away from the extractor electrode and toward the reflector electrode; the reflector electrode having a negative potential such that the electric field repels the electrons away from the reflector electrode and into the ionization region; at least some of the electrons, when in the ionization region, interacting with an ionizable gas to create ions.