Theory of a wide-band distributed gyrotron traveling-wave amplifier

We present the concept of an ultra-wide-band distributed gyrotron traveling-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 dc 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 theoretical possible. Technological requirements for achieving such an amplifier are assessed, including proposed structures for distributed input wave coupling.