title: Start-up scenario in gyrotrons with a nonstationary microwave-field structure.
abstract: Megawatt class gyrotrons operate in very high-order modes. Therefore, control of a gyrotron oscillator's start-up is important for excitation of the desired mode in the presence of the many undesired modes. Analysis of such scenario using the self-consistent code MAGY [M. Botton, IEEE Trans. Plasma Sci. 26, 882 (1998)10.1109/27.700860] reveals that during start-up not only mode amplitudes vary in time, but also their axial structure can be time dependent. Simulations done for a 1.5 MW gyrotron show that the excitation of a single operating mode can exhibit a sort of intermittency when, first, it is excited as a mode whose axial structure extends outside the interaction cavity, then it ceases and then reappears as a mode mostly localized in the cavity. This phenomenon makes it necessary to analyze start-up scenarios in such gyrotrons with the use of codes that account for the possible evolution of field profiles.
authors.affiliation: IREAP, University of Maryland, College Park, Maryland 20742-3511, USA.
authors.forename: G S
authors.initials: GS
authors.lastname: Nusinovich
authors.forename: M
authors.initials: M
authors.lastname: Yeddulla
authors.forename: T M
authors.initials: TM
authors.lastname: Antonsen
authors.forename: A N
authors.initials: AN
authors.lastname: Vlasov