H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
H01J25/50—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field
H01J25/52—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field with an electron space having a shape that does not prevent any electron from moving completely around the cathode or guide electrode
H01J25/58—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field with an electron space having a shape that does not prevent any electron from moving completely around the cathode or guide electrode having a number of resonators; having a composite resonator, e.g. a helix