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 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 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.