A gyrotron with a minimumQcavity

Abstract

In order to reduce the wall loading of a gyrotron cavity, a gyrotron with a minimum Q cavity is proposed and experimentally tested at 140 GHz. The minimum Q is defined as Qmin = 4π(L/λ)2, where L and λ are the effective cavity length and the wavelength. A non-linear uptaper, the radius of which gradually changes with respect to the axial direction, is used to minimize the reflection at the output taper of the open resonator. The detailed performance is investigated by means of self-consistent gyrotron theory. It is found that the electron beam significantly modifies the RF axial field profile in comparison with the cold cavity profile through the interaction between the electrons and the RF field. The maximum experimental efficiency of 37% is achieved at 150 kW and is compared with the results of self-consistent gyrotron theory. These theoretical and experimental results show the feasibility of the minimum Q cavity, especially for high power and high frequency gyrotrons.