MEGAWATT MICROWAVE POWER

Manfred Thumm

Forschungszentrum Karlsruhe, Association Euratom-FZK,

Institut fuer Hochleistungsimpuls- und Mikrowellentechnik,

P.O.Box 3640, 76021 Karlsruhe, Germany

and Universitaet Karlsruhe, Institut fuer Hoechstfrequenztechnik und Elektronik,
Kaiserstr. 12, 76131 Karlsruhe, Germany

manfred.thumm@ihm.fzk.de

Gyrotron oscillators (gyromonotrons) are mainly used as high power millimeter wave sources for electron cyclotron resonance heating (ECRH), electron cyclotron current drive (ECCD), stability control and diagnostics of magnetically confined plasmas for generation of energy by controlled thermonuclear fusion. The maximum pulse length of commercially available 140 GHz, megawatt-class gyrotrons employing synthetic diamond output windows is 30 minutes (CPI and European FZK-CRPP-CEA-TED collaboration). The world record parameters of the European 140 GHz gyrotron are: 0.92 MW output power at 30 min. pulse duration, 97.5% Gaussian mode purity and almost 45% efficiency, employing a single-stage depressed collector for energy recovery. A maximum output power of 1.2 MW in 4.1 s pulses was generated with the JAEA-TOSHIBA 110 GHz gyrotron. The Japan 170 GHz ITER gyrotron holds the energy world record of 2.16 GJ (0.6 MW, 60 min.) for tubes with an output power of more than 0.5 MW. The Russian 170 GHz ITER gyrotron (IAP-GYCOM) achieved 0.64 MW with a pulse duration of almost 300 s. The state-of-the art of industrial megawatt-class longpulse fusion gyrotrons (³140 GHz) is summarized in the table. Diagnostic gyrotrons deliver P_out = 40 kW with t = 40 ms at frequencies up to 650 GHz (h ³ 4%). Gyrotron oscillators have also been successfully used in materials processing. Such technological applications require gyrotrons with the following parameters: f ³ 24 GHz, P_out = 4-50 kW, CW, h ³ 30%. This paper gives an update of the experimental achievements related to the development of high power gyrotron oscillators for long pulse or CW operation and pulsed gyrotrons for plasma diagnostics. In addition, this work gives a short overview of the present development status of coaxial-cavity multi-megawatt gyrotrons, gyrotrons for technological and spectroscopy applications, gyroklystrons, gyro-TWT amplifiers, gyrotwystron ampli-fiers, gyro-BWOs, and of dielectric vacuum windows for such high-power sources.

Table 1: State-of-the-art of industrial megawatt-class longpulse fusion gyrotrons
(f ³ 140 GHz) with TEM₀₀-output