P2-28: Modeling of beam generation in IOT electron guns

The computational capabilities needed for practical IOT/MBIOT design will be discussed. These were evaluated using a combination of analysis and test simulations employing static and fully electromagnetic codes. The presentation will focus on the most difficult aspect: simulation of beam formation in the cathode-grid region. It will be shown that electron transit delay in the cathode-grid gap causes inherent asymmetries in beam properties: pulse shape, secondary emission, etc. Acceleration across the anode - cathode gap exacerbates these differences because the pulse head and tail experience dissimilar space charge effects. Thus IOT beam formation is fundamentally time dependent (i.e. non-harmonic) and requires, at minimum, electrostatic particle-in-cell techniques for accurate simulation.