Abstract
This study proposes a broadband interaction structure for a fundamental harmonic TE 02 203-GHz gyrotron backward-wave oscillator (gyro-BWO). Unlike the present terahertz tunable gyrotron which achieves the tunability by interacting with a series of high order axial modes, the gyro-BWO operates with single (fundamental) axial mode in frequency tuning and has the advantage of smooth and broadband tuning. The interaction structure is designed to be low resonance for a reflective gyro-BWO (forward-wave extraction), which eliminates the major difficulty of a normal gyro-BWO, i.e. mode converter for backward-wave extraction. Numerical investigations indicate that the reflective TE 02 gyro-BWO is capable of generating a peak power of 2.8 kW corresponding to 22.6% interacting efficiency with a 3dB-tuning-bandwidth of 7.3 GHz at beam current I b =0.5 A and beam voltage V b =25 kV. For high power handling capability, the interaction structure could be scaled up and operate with TE 03 mode using same electron beam. The reflective TE 03 gyro-BWO yields a peak power of 2.5 kW and 5.7 GHz tuning bandwidth. © 2009 IEEE.