Investigation on misalignment tolerances of 240-GHz DEMO gyrotrons

Considering the design goals and technological constraints for DEMO gyrotrons, conceptual design and tolerance analyses of a 236 GHz 1 MW conventional, hollow-cavity gyrotron and of a 237.5 GHz 2 MW coaxial-cavity gyrotron are ongoing at KIT. At such high power and frequency, very high order operating modes (eigenvalues > 100) are necessary to keep cavity wall loading at 2 kW/cm². Both the small wavelength and the high eigenvalue make the gyrotrons susceptible to misalignment of electron beam and - if present - coaxial insert. For the hollow-cavity gyrotron, the influence of the off-axis electron beam on gyrotron operation has been very accurately investigated in interaction simulations with realistic beam parameters. For the coaxial-cavity gyrotron, the influence of insert misalignment on modes and on an aligned electron beam has been studied.