Effects of electron-anode interactions in applied-B ion diodes

Summary form only given. The transverse magnetic field in an applied-B ion diode is designed to minimize electron loss to the anode. However, 3-D particle-in-cell (PIC) simulations show that electron loss escalates once the ion current is sufficiently enhanced such that the ion mode instability dominates. Thus the transition from the diocotron mode to the ion mode is accompanied not only by an increase in ion beam divergence, but also by an increased flux of high-energy electrons striking the anode surface. Coupled electron-photon Monte Carlo simulations have been used in conjunction with PIC diode simulations to assess electron reflection, energy deposition leading to anode heating and thermal desorption of contaminants, enhanced ionization of desorbates due to secondary electron emission, and photon production. Electron reflection is included in the 3-D PIC simulations, and although no macroscopic diode effect is seen in the present model, the anode heating profile is affected by high-energy reflected electrons, and low-energy secondary electrons may enhance the effective electron-impact ionization cross-section by factors of 7-10 for desorbed contaminants.