Secondary Ion Emission Modeling in a Planar Bremsstrahlung Diode Operated Above 10MV

In the HERMES-III accelerator at Sandia National Laboratories, a high energy, high current electron beam is generated and directed through an anode converter to produce intense radiation output. The impacting electrons also liberate secondary ions which is a known, but not well understood, phenomenon [1] . Secondary ions are emitted with a yield f ≈ 0.01 ⁓ 0.09 to the incident electrons [2] . The heavier ion species accelerate slowly into the diode, neutralizing the electrons from the cathode, thus increasing the diode current. The increased self-magnetic force of the beam current radially tightens beam footprint on the converter surface. The higher energy density can cause a positive feedback problem, severely narrowing the beam and affecting machine performance.