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A 140-GHz, 1.5-MW, [TE.sub.28,16]-coaxial cavity gyrotton with a dual rf beam output has been designed, built, and tested. For the first time, the generated rf power has been split into two parts and coupled out through two rf output windows in order to reduce the power loading in the windows. The quasioptical output system is based on a two-step mode conversion scheme. First, the cavity mode [TE.sub.-28,16] is converted into its degenerate whispering gallery mode [TE.sub.+76,2] using a rippled-wall mode converter. Then, this mode is transformed into two TEMo0 output wave beams. A maximum rf output power of about 950 kW with an output efficiency of 20% has been measured. According to numerical calculations, an rf power above 1.5 MW is expected to be generated in the cavity. Even if all losses are taken into account, a discrepancy between experiment and calculations remains. The power deficit seems to be partly caused by the influence of the stray radiation captured inside the tube. However, the two main reasons are probably an incomplete mode conversion from [TE.sub.-28,16] to [TE.sub.+76,2] and a large energy spread of the electron beam due to trapped electrons. An increased amount of captured stray radiation resulted in a reduced stability of operation. A single-stage depressed collector was used successfully, increasing the rf output efficiency from 20% to 29%. Index Terms - Coaxial gyrotron, dual rf beam.

The design of a 1.5-MW, 140-GHz, [TE.sub.28,16]-coaxial cavity gyrotron is presented and results of experimental operation are given. A cavity with a cylindrical outer wall and a radially tapered inner rod with longitudinal corrugations was used. A maximum output power of 1.17 MW has been measured in the design mode with an efficiency of 27.2%. Single-mode operation has been found over a wide range of operating parameters. The experimental values agree well with the results of multimode calculations. Frequency-step tuning has been performed between 115.6 and 164.2 GHz. In particular, an output power of 0.9 MW has been measured in the [TE.sub.25,14] mode at 123.0 GHz and 1.16 MW in the [TE.sub.32,18] mode at 158.9 GHz. At frequencies with strong window reflections the parameter range for which stable operation is possible is reduced significantly. In order to obtain results relevant for a technical realization of a continuously operated gyrotron, a tube with a radial radio frequency (rf)-beam output through two output windows and a single-stage depressed collector has been designed and is under fabrication. A two-step mode conversion scheme - [TE.sub.-28,16] to [TE.sub.+76,2] to [TEM.sub.00] - which generates two narrowly directed (60 [degrees] at the launcher) output wavebeams has been chosen for the a quasioptical (q.o.) mode converter system. A conversion efficiency of 94% is expected. Index Terms - Coaxial cavity gyrotron, frequency tunability, magnetron injection gun.

Summarizes the main results of experimental testing of the 140 GHz/ 1.5 MW coaxial gyrotron. Design parameters of the 140 GHz/ 1.5 MW coaxial gyrotron; Experimental study of the gyrotron with the diode type inverse electron gun; Electron beam energy recovery, frequency step tuning and output power modulation.

Describes the design, manufacture and testing of a 50 A electron gun with a beam power of 4.5 MW for a 1.5 MW, 140 GHz coaxial gyrotron. Measurement of the beam properties using scaled-down parameters; Experimental values of the velocity ratio.

A general method is developed for the analysis of mode competition in a gyrotron with tapered external magnetic field. Exploratory calculations show strong dependence of the operating regime of a gyrotron on tapering of the magnetic field. Detailed results are presented for the gyrotron operating at the Kernforschungszentrum Karlsruhe with frequency 150 GHz in the TE[sub 03] mode. [ABSTRACT FROM AUTHOR]