Numerical study of the effects of the magnetic axis misalignment in the EU coaxial cavity gyrotron for ITER

Summary form only given. The axis of symmetry of the magnetic field is not always ideally aligned to the mechanical axis of the gyrotron, mainly for two reasons: (i) misalignment of the coils in the magnet and (ii) mechanical inaccuracies on the gun and cavity position. In this work, the effects of the magnetic field misalignment are numerically studied for the coaxial cavity EU gyrotron¹ for ITER. First, the degradation of the electron beam is calculated using the three-dimensional, electrostatic, self-consistent code ARIADNE² for several cases of misalignment, shifting and tilting the mechanical axis to the magnetic axis. Second, the effects of the degraded beam on the output power, the electronic efficiency and the mode competition are studied using the multi-mode interaction code EURIDICE³. The goal of this work is to estimate the acceptable tolerances in the misalignment for efficient gyrotron operation.