Gyro-devices and their applications

Gyro-oscillators (gyrotrons) are mainly used as high power millimeter wave sources for electron cyclotron resonance heating (ECRH), current drive (ECCD), stability control and active diagnostics of magnetically confined fusion plasmas. The maximum pulse length of commercially available 140 GHz, megawatt-class gyrotrons is 30 min (CPI and European KIT-CRPP-TED collaboration), at 44% efficiency. The Japan 170 GHz ITER gyrotron achieved 1 MW, 800 s at 55% efficiency and holds the energy world record of 2.88 GJ (0.8 MW, 60 min) and the efficiency record of 57% for tubes with an output power of more than 0.5 MW. The Russian 170 GHz ITER gyrotron achieved 1 MW (0.8 MW) with a pulse duration of 570 s (1000 s) at 53% (55%) efficiency. All these gyrotrons are equipped with synthetic diamond output windows and single-stage depressed collectors for energy recovery. Operation at the 1^st and the 2^nd harmonic of the EC frequency enables gyrotrons to act as high-power step-tunable mm- and sub-mm wave sources up to the THz frequency range for plasma diagnostics, high-frequency broadband electron paramagnetic resonance (EPR) and dynamic nuclear polarization-nuclear magnetic resonance (DNP-NMR) spectroscopy as well as for medical therapy. Gyrotrons have also been successfully used in materials processing, plasma chemistry and ECR multicharged heavy ion sources. Such technological applications require tubes with the following parameters: f ≥ 24 GHz, P_out = 4-50 kW, CW, η>;30%. The development of various types of high average power Ka- and W-band gyro-amplifiers allows high resolution ranging and imaging in atmospheric and planetary science. The present paper gives a short review of the state-of-the-art and future prospects of gyro-devices and their applications.