抄録
A large orbit gyrotron (LOG) operating at higher harmonics of electron cyclotron frequency has been constructed by use of a permanent magnet system whose intensity is around 1 T. The operation test was already performed successfully up to the fourth harmonic. The operation efficiency was extremely high even at the third and the fourth harmonics, because of high efficient interaction between beam electron and high frequency electric field in LOG. The test results of the LOG are summarized.
