Repetitive operation of virtual cathode oscillator in an axial magnetic field

A new method for repetitive operation of a virtual cathode oscillator is developed. In this scheme, a virtual cathode oscillator in an external axial magnetic field consists of a carbon plate anode (1 mm in thickness) with a hole in the center and a knife-edged annular cathode with a diameter of D/sub c/ = 30 mm. The concept is similar to a reditron except no center part of an anode. We have observed characteristics of a repetitive-typed virtual cathode oscillator with a function of d in gap length, D/sub 0/ in a hole-diameter of an anode, and B in an axial magnetic field strength experimentally. Repetitive microwave radiations more than 450 times have been observed at D/sub 0/ = 32 mm, d = 3.8 mm and B = 0.74 T. The frequency is almost constant to about 250 shots, that is, the microwave frequency of each shot was contained in 11.8 to 12.8 GHz, however, some frequencies has been sometimes observed together in one shot after about 300 shots. The radiation of microwave has not observed rapidly after 480 operations.