Numerical simulations of a new, compact, millimeter wave gyrotron trav
eling-wave-tube amplifier is reported. Rf amplification takes place in
a periodic coupled double-ridged cavity circuit employed with an axis
-encircling electron beam, 2.7 dB/cm linear axial gain at 32 GHz and 1
.4% efficiency are observed, Avoidance of spontaneous oscillations req
uires precise specification of the magnetic field.