MAGIC code simulation of mode locking in closed and open cavity gyrotron oscillators

Summary form only given. MAGIC has been used to simulate mode locking in a closed cavity gyrotron oscillator. Comparison is made with the results of quasi-linear theory. A cylindrical gyrotron cavity with length 12 cm and radius 0.544 cm has been simulated. The cavity supports azimuthally symmetric TE/sub 01n/ modes. The electron beam properties are 25 keV, 3.5 A, and guiding center radius 0.35 cm. The external axial magnetic field is 7.27 kG. The modulation is provided by a time-dependent electron emission axial velocity (molding the effect of a prebunching cavity). Consideration is also being given to the feasibility of mode locking open cavity (quasi-optical) gyrotrons where the empty cavity modes are nearly equally spread in frequency. The quasi-optical gyrotron has typically exhibited multimode oscillation, which will be compounded by using sheet electron beams. The present 2-D version of the quasi-optical structure is an open cavity with two mirrors separated by 30 cm. Modes oscillate along the cavity axis and sheet electron beams propagate transverse to the axis.