Abstract
Coaxial cavities are the main interaction structures of high-power high-frequency gyrotrons at present. With the increase of operating frequency and output power, ohmic loss becomes to be a vital issue needed to be analyzed compulsorily for coaxial-cavity gyrotron. It would lead to operating frequency shift and efficiency decline. In addition, the long pulse operation would be deteriorated to a large extent as a consequence of rather severe ohmic losses. Therefore, it is of great meaning to analyze the ohmic losses of coaxial cavity more accurately. In this paper, a new method is introduced to analyze the influence of the ohmic losses on coaxial cavities and TE34,11 mode operating at 170 GHz is taken as an example to compare this method with other two methods. The results show that this method can be used to analyze the coaxial cavity with higher accuracy and fewer restrictions.
Highlights
Driven by applications such as controlled thermonuclear fusion, gyrotron oscillators are developing towards higher frequency and higher power
Only the ohmic losses on the outer wall is considered, and the influence of ohmic losses on interaction and the ohmic loss density can be calculated by beam-wave interaction equations (Eqs (40) ∼ (42)), the expression of longitudinal wave number in hollow cavity with lossy wall (Eq (33)), and the expression of ohmic loss density distribution (Eq (34) and Eq (35))
The expression of the longitudinal wave number in coaxial cavities with lossy walls is derived by perturbation of boundary conditions, and based on this expression a new method to analyze the influence of the ohmic losses on coaxial cavities is introduced
Summary
Driven by applications such as controlled thermonuclear fusion, gyrotron oscillators are developing towards higher frequency and higher power. One is to estimate the output power and efficiency by ignoring the effect of the ohmic losses on the beamwave interaction and using the ideal result.4–6 Another is ignoring the ohmic losses on the surface of insert and analyzing the influence of the ohmic losses on outer conductor by using the formulas of hollow cavity.. Another is ignoring the ohmic losses on the surface of insert and analyzing the influence of the ohmic losses on outer conductor by using the formulas of hollow cavity.7,8 These two methods cannot analyze the impact of the ohmic losses on the beam-wave interaction accurately. A more accurate method to analyze the ohmic losses in coaxial cavities is introduced This method is based on the technique called perturbation of boundary conditions and the selfconsistent nonlinear beam-wave interaction equations.
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