A MECHANICALLY TUNABLE MAGNETRON INJECTION GUN

The magnetron injection gun (MIG) has been the predominant choice as t he electron-beam generator in gyrodevices and it can be tuned by exter nally installed magnetic-field trim coils. The double-anode MIG, tradi tionally employed in most experiments, has the intermediate anode as a n internal tuning mechanism. The single-anode design, on the other han d, is simpler to construct but lacks an internal beam tuning mechanism . The current paper describes a method to allow mechanical tuning of t he MIG, Since the tip of the cathode is located in the region of the h ighest electric-field gradient, its extension and retraction relative to the rest of the cathode assembly provide an effective means for loc al electric-field profile modification and, therefore, a tuning mechan ism for the electron-beam property and quality. It is demonstrated, in computer simulations and experimental tests, that the tuning mechanis m adds a useful degree of freedom to the single-anode MIG for beam opt imization. This method may also be applied to the double-anode design. (C) 1997 American Institute of Physics.