History, Present State-of-the-Art and Future of Gyrotrons

Manfred Thumm

Forschungszentrum Karlsruhe, Association EURATOM-FZK,

Institut für Hochleistungsimpuls- und Mikrowellentechnik (IHM), D-76021 Karlsruhe, Germany, und
Universität Karlsruhe, Institut für Hochfrequenztechnik und Elektronik (IHE), D-76131 Karlsruhe, Germany







Gyrotron oscillators (gyro-monotrons) are mainly used as high power millimeter wave sources for electron cyclotron resonance heating (ECRH), current drive (ECCD), stability control and diagnostics of magnetically confined thermonuclear fusion plasmas. The maximum pulse length of commercially available 140 GHz, megawatt-class gyrotrons employing synthetic diamond output windows is 30 min (CPI and European FZK-CRPP-CEA-TED collaboration), at 45% efficiency, employing a single-stage depressed collector for energy recovery. The prototype of the Japan 170 GHz ITER gyrotron holds the energy world record of 2.88 GJ (0.8 MW, 60 min.) and the efficiency record of 55% at 1 MW, 800 s for tubes with an output power of more than 0.5 MW. The Russian 170 GHz ITER prototype tube achieved 0.83 MW with a pulse duration of 203 s. Russian sub-millimeter wave and THz gyrotrons for plasma diagnostics or spectroscopy applications deliver Pout = 40 kW with t = 40 µs at frequencies up to 650 GHz (h > 4%), Pout = 1.6 kW at 1.0 THz (h = 2.2%) and Pout = 0.5 kW at 1.3 THz (h = 0.7%). Gyrotron oscillators have also been successfully used in materials processing and ECR multi-charged heavy ion sources. Such technological applications require gyrotrons with the following parameters: f > 24 GHz , Pout = 4-50 kW, CW, h > 30%. This seminar talk gives a short review of the history of gyrotrons, an update of the present experimental achievements and an outlook into future developments of multi-megawatt coaxial-cavity gyrotrons, frequency-step tunable gyrotrons and gyrotrons for specific technological and spectroscopic applications.