Operation of a high performance, harmonic-multiplying, inverted gyrotwystron

Experiment on a new type of high-power, millimeter wave amplifier, (a harmonic-multiplying, inverted gyrotwystron), are reported. Superior stability resulted from two factors: (1) interaction between a relatively low order waveguide mode (TE/sub 22/) and the beam wave at the fundamental cyclotron frequency in the traveling wave input section; (2) an internal mode filter in the highly overmoded (TE/sub 42p/), second harmonic output cavity. Bandwidth was 1.3% with saturated gain of 33 dB around 31.8 GHz. The gain-band width performance represents a significant advance for gyrotron amplifiers operating in such high order modes, and is thought to be due in part to operation of the long output cavity in several modes with different axial eigennumber (p=3, 4, 5) but with overlapping spectral regions.