Detailed Design of a 1 THz CW Gyrotron (Gyrotron FU CW III) Using a 20 T Superconducting Magnet

摘要

The gyrotron is an important and promising high power stable THz radiation source in future for development of high power THz research and technology. Recently, a gyrotron in FIR FU with a 21 T pulse magnet achieved breakthrough of 1 THz [1]. For many applications, however, CW radiation sources are needed. In order to meet this requirement and to expand the application of our devices to new fields of research and technology, we have started the development of novel series, namely Gyrotron FU CW Series. The third member of this new line of tubes is Gyrotron FU CW III with frequency of 1 THz and expected output power 100 watt. The design and simulation result of this gyrotron will be presented. The gyrotron consists of a 20 T superconducting magnet, a demountable gyrotron tube, a triode-type magnetron injection gun, and a sapphire output window. Additional coils are installed surrounding the electron gun centered at the emitter to adjust the beam radius and beam quality at the cavity region. The cavity is a simple cylindrical one whose diameter and length are 3.9 mm and 10 mm. A cross-sectional view of the gyrotron system is shown in Fig. 1. There are two pumping bores. The first one is located near the electron gun to assure the vacuum condition inside the tube. The second one is placed after the collector in order to keep the vacuum despite the out-gassing from the electron collector as well as the resonator. The total length of tube including the collector is 2.5 m. Sets of two stages for horizontal adjustment are located at both the top and the bottom part of the cryostat and are used to align the gyrotron tube with respect to the magnetic field of the superconducting magnet, thereby aligning the axis of the electron beam. The gyrotron tube is demountable which enables to change some parts of it. The water jacket with a constant flow rate is installed surrounding the whole gyrotron tube, including the collector, to maintain the tube temperature at a permissible level for stable operation of the gyrotron.