EFFECTS OF ELECTRON-CYCLOTRON INSTABILITIES ON GYROTRON BEAM QUALITY

A two-dimensional PIC code aimed at the investigation of electron-cycl otron beam instabilities in gyrotrons and their effects on the beam qu ality is presented. The code is based on recently developed techniques for handling charge conservation and open boundaries. It has been imp lemented on the massively parallel computer CRAY T3D. First results sh ow an electromagnetic backward-wave instability periodically growing a nd decaying to energy levels close to those obtained from the electros tatic Bernstein wave instability. On the average, the resulting beam d egradation is 3 to 4 times larger than that predicted by electrostatic models.