Theory of a wideband distribution gyrotron travelling wave amplifier

We present the concept of an ultra-wideband distributed gyrotron travelling wave amplifier for millimeter and submillimeter waves. The radius of the waveguide in the interaction region is increased along the axis while the strength of the d.c. magnetic field is decreased in such a way that the wave cutoff frequency is kept nearly equal to the electron cyclotron frequency. The basic principle of operation, peak gain, and saturated efficiency are analyzed. It is shown that instantaneous bandwidth over at least two octaves is theoretically possible. Technological requirements for achieving such an amplifier are assessed, including proposed structures for distributed input wave coupling.