In the magnicon RF amplifier, the drive and gain cavities are cylindrical deflection cavities which operate in a rotating TMiio-rnode and spin up an electron beam to high transverse momentum. As a result of the rotating-mode interaction, the electron beam entry point into the output cavity rotates about the axis at the drive frequency. The gyrotron-Iike output cavity can be operated at in times the drive frequency by using a mode with an azimuthal index of m., as this mode rotates at /;; '' times its RF frequency, thus maintaining synchronism with the electron beam. Previous frequency-multiplying magnicons have used m -2; in this paper it is shown that magnicons with m = 4 may be practical, provided one also operates the output cavity at the m/2 harmonic of the cyclotron frequency. Operation at higher harmonics lowers the frequency of the deflection cavities allowing lower RF fields, reducing cavity breakdown problems; lower magnetic fields, reducing magnet cost and complexity; and a larger electron beam, relaxing beam quality constraints. On the other hand, higher order azimuthal-index magnicon modes interacting at higher order cyclotron interactions are subject to competition with nonsynchronous (gyrotron) modes and are more sensitive to electron beam scanning angle spread. A time-dependent multimode gyrotron code has been modified to examine competition in the output cavity between the phasesynchronous operating mode and other nonsynchronous modes which interact via the conventional gyrotron interaction. Calculations have been carried out for fourth-harmonic magnicons with TM.no and TE n mode output cavities and include the effects of mode competition with nonsynchronous modes as well as a spread in entry-point angles of the scanning electron beam.
ASJC Scopus subject areas
- Nuclear and High Energy Physics
- Condensed Matter Physics