Influence of the electron velocity spread and the beam width on the efficiency and mode competition in the high-power pulsed gyrotron for 300 GHz band collective Thomson scattering diagnostics in the large helical device

Abstract

We present results of a theoretical study of influence of the electron velocity spread and the radial width on the efficiency and mode competition in a 300-kW, 300-GHz gyrotron operating in the TE22,2 mode. This gyrotron was developed for application to collective Thomson scattering diagnostics in the large helical device and 300-kW level high power single TE22,2 mode oscillation has been demonstrated [Yamaguchi et al., J. Instrum. 10, c10002 (2015)]. Effects of a finite voltage rise time corresponding to the real power supply of this gyrotron are also considered. Simulations tracking eight competing modes show that the electron velocity spread and the finite beam width influence not only the efficiency of the gyrotron operation but also the mode competition scenario during the startup phase. A combination of the finite rise time with the electron velocity spread or the finite beam width affects the mode competition scenario. The simulation calculation reproduces the experimental observation of high power single mode oscillation of the TE22,2 mode as the design mode. This gives a theoretical basis of the experimentally obtained high power oscillation with the design mode in a real gyrotron and moreover shows a high power oscillation regime of the design mode.

The influences of beam quality and Ohmic loss on the beam-wave interaction in a 420 GHz second-harmonic complex-cavity gyrotron

“…Generally, there are three main factors to influence the beam-wave interaction in gyrotrons, the first one is the beam quality such as the finite beam width and electron velocity spread, the second is the Ohmic loss in the cavity wall and the third is the reflections from the transmission lines and window. As reported in [17][18][19][20][21][22][23][24][25][26], many works have been done to discuss the influences of these factors, it is shown that these factors not only deteriorate the gyrotron efficiency but also influence the mode competition. Since these works are basically aimed at the cylindrical and coaxial cavity resonators, thus we will extend these investigations to the complex-cavity gyrotron operating at THz frequency band.…”

Возбуждение Высоких Циклотронных Гармоник В Сильноточном Релятивистском Гиротроне В Режиме Умножения Частоты

“…Используя разложение J ′ s (χ) ≈ sχ s −1 /2 s s!, электронноволновое взаимодействие с учетом разброса по скоростям можно описать следующей системой уравнений (ср. с [11]):…”

Excitation of high cyclotron harmonics in a high-current relativistic gyrotron in the frequency multiplication regime

“…, where A n (z , t) is the slowly varying complex amplitude of the n-th mode, function E n ⊥ (r) describes the mode radial structure, ϕ is the azimuthal angle, ω 0 H = eH 0 /m e cγ 0 is the unexcited gyrofrequency (gyrofrequency at the entrance to the interaction space). Using expansion J ′ s (χ) ≈ sχ s −1 /2 s s!, the electron−wave interaction may be described, with accounting for the velocity dispersion, by the following set of equations (compare with [11]):…”