Experimental study on low-velocity-spread axis-encircling electron gun for harmonic gyrotrons

The annular Pierce-type electron gun was fabricated and used as a source of axis-encircling electron beam. Initial canonical angular momentum spreads at the cathode and the crossing of the electron beam with the magnetic fluxline before the magnetic cusp are considered. It means that there will be a small orbit gyration of electrons before the magnetic cusp even though the cyclotron frequency and Larmor radius are small.