Secondary Ion Generation in an 18MV, 650kA Bremsstrahlung Diode

Secondary ions generated by electron impact on an anode surface is a well-known but not well-characterized phenomenon1-3. At low fluences, ions have been seen experimentally to emit at only fractions of a percent of the electron current. Conversely, when the electron energy deposition is high enough to heat a spot on the anode to 400°C, an anode plasma forms, yielding bipolar flow of ions4, Such hot-spot formation from electron beam heating can cause irreversible damage to the tantalum layer. Additionally, ions have a large impact on the diode x-ray dose pattern.