Comprehensive Design and Whole-Cavity Simulation of a Multibeam Inductive Output Tube Using a 3rd Harmonic Drive on the Grid

We discuss the design and whole-cavity simulation of a multibeam inductive output tube (MBIOT) that uses a third harmonic component to the drive voltage on the grid. High-efficiency IOTs are characterized by efficiencies of 70%–75%. However, efficiencies greater than 80% would substantially reduce the operating costs of next-generation accelerators. To achieve this, we consider the addition of a third harmonic component to the drive signal on the grid. We consider an eight-beam MBIOT with a 700 MHz resonant cavity using a voltage of 35 kV and an average current of 7.25 A yielding a perveance of about
$1.1 ~\mu \text{P}$
. We simulate this using the NEMESIS simulation code which has been extended using a 3-D Poisson solver based on the Petsc package from Argonne National Laboratory. The effect of the third harmonic is greatest when the third harmonic phase is shifted by
$\pi $
radians with respect to the fundamental drive and with third harmonic powers greater than about 50% that of the fundamental. We show that efficiencies approaching 82% are possible. Designs for the MBIOT input coupler, grids, and output cavity have been developed based on these simulations and will be discussed.