Development of a High-Power W-band Gyrotron Oscillator

Abstract

This thesis reports the design and experimental demonstration of a high power W-band gyrotron oscillator. This gyrotron is the first gyrotron developed in Korea. Two type gyrotrons are developed such as a short-pulse gyrotron of 20 microseconds and long-pulse gyrotron of 3 seconds. The gyrotron is composed of a diode type electron gun operating at 40 kV, an interaction cavity generating a TE 6,2 mode, a mode converter for producing a pure Gaussian-like output beam, a output window to pass the beam with minimum loss, and a collector for a dissipation of electron energy. These critical components of the short-pulse gyrotron such as a diode type electron gun, internal quasi-optical mode converter, and an interaction cavity have been designed using CST Particle Studio, EGUN code, LOT, Surf 3D, and ANSYS. Designed components are cold tested its performance. We introduce the proposed new cold test method for a performance evaluation of the mode converter. We will show that this method using a simple, non-rotating, higher order mode generator is an easy and efficient method for verifying the performance of quasi-optical mode converter. The component design procedure is detailed here. The performance of the short-pulse gyrotron was tested experimentally. The output power, the operating frequency and the output beam pattern was evaluated. The maximum power of 60 kW with the operating frequency of 95.2 GHz was achieved with an efficiency of 23%. We introduce that a newly proposed method for measuring the output power of the gyrotron. This method based on Friis transmission formula is a calibration-free method and available in real time. To use this method, the directivity of the gyrotron must be defined and calculated. Besides, the output beam pattern of the gyrotron must be well-focused Gaussian-like beam. Presented here are the detailed the directivity calculation procedure of the gyrotron and experimental results. The output beam pattern is measured in various methods and analyzed. The results of the output power, the operating frequency and the beam pattern show a good agreement between the simulation and experimental results. The experimental results are presented in this thesis in detail. In addition, a superconducting magnet and a collector are designed for a CW gyrotron. Other components such as the electron gun, the internal mode converter and the interaction cavity were used in commonly. However, the cooling system was applied to the interaction cavity and the output window due to the pulse width. The CW gyrotron operation was achieved during 3 seconds without any arcing. The CW gyrotron produced about output power of 26kW with 95.1 GHz at a beam voltage of 38kV and a beam current of 3A, corresponding to an efficiency of about 23%.