Theory of high-harmonic gyrotron oscillators with slotted cross-section structure

A linear-theory analysis of gyrotron oscillators with slotted cross section is used to calculate the net change in beam energy [δγ]/sub tophio/. In the authors new formalism, geometric factors are clearly distinguished from the geometry-independent harmonic resonance terms which are due to the fundamental electron cyclotron maser and peniotron interactions. This separation of the interaction terms from the geometric factors greatly simplifies the physical analysis, and leads to a very compact form for [δγ]/sub tophio/. The theory is applied to slotted rectangular oscillators (which have not previously been treated) and to slotted cylindrical oscillators to show that a unified expression can be obtained for the start oscillation condition. In sample applications of our theory, it is demonstrated that slots lower the start oscillation condition in both cylindrical and rectangular geometries, and can lead to a decrease in this condition as harmonic number is increased in the rectangular geometry. The use of these slotted devices thus appears quite attractive in the millimeter-wave regime. The authors also find that the peniotron interaction, which is easily identified in our formalism, may be very strong in slotted cavities