Cyclotron-resonance maser in a periodically loaded quadrupole transmission line

A cyclotron-resonance maser (CRM) is implemented in a periodic quadrupole waveguide. The device oscillates at the fundamental and high harmonics of the cyclotron frequency. This CRM employs a tenuous low-energy electron beam (∼10 keV, 0.2 A). The periodic structure consists of an array of disks along the quadrupole transmission line, hence it combines both azimuthal and axial periodicities. This waveguide responds as a band-pass filter (BPF) with uniformly spaced passbands. The CRM is tuned to operate when the cyclotron harmonic frequencies coincide with the waveguide passbands. Microwave emission is observed at the first passband (∼2.4 GHz), and simultaneously at the second and third harmonics in the corresponding BPF passbands (∼4.9 and ∼7.4 GHz, respectively). A polarized detector reveals the circular polarization of the em wave inside the tube. The results of this experiment may lead to the development of novel CRM harmonic generators and CRM arrays.