Design and Thermal Analysis of a Distributed Radiation Coupling Circuit for High Power CW Gyro-TWTs

At high average or continuous wave (CW) power operation, heavy dielectric overheating will occur in traditional dielectric-loaded (DL) gyrotron traveling wave tubes (gyro-TWTs). It will lead to dielectric outgassing and changes in dielectric properties, reducing the tube stability and amplification performance. To solve this problem, a distributed radiation coupling (DRC) circuit with lossy dielectric stepped sheets is proposed, designed, and thermally analyzed for high-power CW gyro-TWTs. It can suppress the parasitic modes by achieving sufficient radiation coupling losses. The adopted stepped sheet structure can increase the heat dissipated area of the lossy dielectric and make the power loss density distribution more uniform, thus decreasing the dielectric temperature. Multiphysics simulations show that an X-band gyro-TWT based on the DRC circuit can achieve a CW power over 100 kW from 8.8 to 10 GHz with a velocity spread of 3.26%. Compared with the traditional DL circuit, the DRC circuit increases the duty cycle of the tube from 50% to a CW state with a tolerable dielectric temperature.