In one embodiment, an X-ray tube includes an electron beam source including a primary cathode configured to emit an electron beam and an anode assembly including an anode configured to receive the electron beam and to emit X-rays when impacted by the electron beam. The X-ray tube also includes an enclosure, at least the primary cathode and the anode being disposed in the enclosure, and a secondary cathode disposed in the enclosure and configured to emit electrons to impact the anode for degassing the enclosure.