Design of the ITER 170 GHz gyrotron gun

The optimized design of the ITER 2 MW, 170 GHz, CW, coaxial cavity gyrotron gun is presented. Simulations show that a good beam quality can be attained (pitch-ratio spread /spl delta//spl alpha/ of /spl sim/1.9%, electron beam thickness in the cavity of /spl sim/0.45 mm) and confirm previous results that the lowest /spl delta//spl alpha/ values are achieved at an intermediate type of the electron flow. Adjusting the currents through the gun coils results in considerable variation of the beam pitch-ratio /spl alpha/. This can compensate the deviations of /spl alpha/ from its specified value of 1.3 for changes in magnetic field and axial alignment.