Investigation Of A Ku-band Foil-less Radial Transit-time Oscillator With Low Guiding Magnetic Field

In the late 30 years, with the development of pulse power technology and relative demands, high power microwave technology(HPMT) has developed a lot. The HPM sources have obtained gigawatts level output power at middle-low bands, such as P、L、C、X band. However, at relatively high bands(such as Ku-band), output power is limited to hundreds of megawatts owing to the decrement of dimensions and power capacity. Due to the virtues, such as simple structure, pure frequency spectrum and high power, the transit-time HPM sources have been gaining great graces by researchers. Traditional axial transit-time HPM sources mostly have a high-impedance(~100 ?), which limits the electron beam input power. The research on low-impedance devices mainly focuses on the coaxial and radial structures. Otherwise, the beam-wave interaction efficiency of coaxial devices remains low, about 10%, at X and Ku band at present. Meanwhile, for the radial devices, there are usually metallic foils in them, which is noxious for the long-pulse and repetitive operation. High power, high frequency band, long-pulse and repetitive operation are developing trends of HPM sources in the future. Based on it, a Ku-band foil-less radial transit-time oscillator(RTTO) with low confining magnetic field is presented in this paper, and some detailed research has been done as follows:Firstly, the space-charge limiting current of the radial structure is deduced and calculated, which proves the advantage that the space-charge effect is weak in such a structure. The working mode is turned out radial TM01 mode through numerical simulations. Based on the small-signal theory, the electron beam conductance is calculated in 0 mode, π/2 mode andπmode, respectively. Theπ/2 mode is selected as the operating vertical mode.Secondly, the presented HPM source is studied by PIC particle simulations widely. Corresponding results indicate that, with an input electron beam of 300 kV voltage and 18.3 kA current, a microwave of 2.2 GW and 14.26 GHz is obtained in such a device. The power exchange efficiency is 40%, and the external confining magnetic field is 0.6 T. The influence factors on the output performance are also analyzed. Moreover, the interference of angular non-uniform modes is proved vanished through 3D PIC particle simulations. In addition, some preliminary research on the Ku-band radial klystron amplifier(RKA) is done, and some results are presented. With the electron beam excitement of 300 kV voltage and 10 kA current, a microwave of 990 MW and 14.2 GHz is obtained. The gain is 43.7 dB, and energy efficiency is about 33%.Lastly, relative engineering designs of the presented device are done, making preparations for experiments. Furthermore, radial confining magnetic field coils, which can be employed in radial HPM sources, is proposed to generate a uniform magnetic field along the radial. Solenoid inductance parameters, number of required capacitor groups and length of the electromagnetism line are calculated. With a current of 722 A in the electromagnetism line, a radial magnetic field of 0.6 T can be obtained. What′s more, the microwave extraction components, such as radial-line wave-port, supporting bars structure and mode transform device, are designed by electromagnetism simulation Microsoft. The energy conversion efficiency exceeds 99% in such components, which transform the mode from TEM to TM01. Besides, the maximal RF field strength in these components is estimated under the poured power of 2.2 GW.