Experimental study of transparent TWT with the modulation of an electron beam near the cathode

Summary form only given. Currently, investigation and development of various microwave devices containing electronic flows interacting with electromagnetic fields remains one of the most important and actual problems in radiophysics. One of the central tasks is to improve the output characteristics of the vacuum sources of microwave radiation¹: power output, efficiency, increase the frequency, expand the bandwidth of generated frequencies² (or vice versa, obtaining single-frequency generation), etc. In particular, a low coefficient of performance (COP) of classic UHF amplifiers based on traveling wave tube (TWT) with a large (30-40 dB) gain associated with both long process of grouping and losses caused by the presence of the microwave absorber. TWT is a system with an increasing wave in which a signal along the high-frequency structure increases exponentially at first, and then, after reaching the nonlinear region, the growth slows down. Moreover, another gain mode may occur associated with beats wave of constant amplitude. It is interesting to study the influence of the magnitude of the input signal supplied to the cathode region of the electron gun on the efficiency of the device in the aforementioned mode. In this work we consider the experimental studies that were conducted using a transparent (without microwave absorber) TWT with helical slow-wave structure. The difference between used in experiment TWT and the standard one is that the input signal is supplied to the modulating grid positioned near the cathode. The experimental results show that the scheme with feeding the input microwave signal to the modulating grid, located near the cathode has a significant advantage, which is the high value of the gain, and efficiency of the TWT amplifier and the expansion of operating frequency band. It has been established that the maximum value of electronic efficiency for the version in which the input signal is fed to the modulating grid positi- ned near the cathode is 56% compared to 43% for option in which the input signal is fed to a retarding system Technical efficiency is 73 ÷ 75%. An increase of the bandwidth to the values Δf/f ~ 1,5 ÷ 1,7 was determined.