Emission Gating of Sheet Electron Beam for High-Power Gridless Inductive Output Tube

The gridless inductive output tube (IOT) is a versatile variant of the conventional IOT. It primarily offers high-power operation in the MW-range, and a compact, flexible design. The electron beam is density-modulated at the cathode to achieve bunching with a non-intercepting anode. This paper presents an analysis on the emission gating of a sheet electron beam designed for a high-power gridless IOT. Here, the focusing electrode is utilized for this modulation by applying a potential difference, relative to the cathode. The field intensity required for emission is calculated using a modified Fowler-Norheim equation, which accounts for the transition into the space-charge limited regime, and compensates for the geometric effects of the emission surface. The beam voltage is 80 kV, beam current is 36.5A, and perveance is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.6 \times 10^{-6}\mathrm{A}/\mathrm{V}^{3/2}$</tex>. The beam is confined with a magnetic field of 0.7 T. The compressed beam dimensions are <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.54\ \text{mm} \times 37.6\ \text{mm}$</tex>. The simulated current density at the cathode is 20.27 A/ cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with a peak electric field of the order of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10^{6}\mathrm{V}/\mathrm{m}$</tex>. The simulation results show agreement with the Fowler-Nordheim model for the electric field intensity required to operate this beam.