als Vortrag :

Gyro-Devices

M. Thumm

Forschungszentrum Karlsruhe, Association Euratom-FZK, IHM,
Postfach 3640, D-76021 Karlsruhe, Germany
and Universität Karlsruhe, Institut für Höchstfrequenztechnik und Elektronik,
Kaiserstr. 12, D-76128 Karlsruhe, Germany

Gyro-devices are microwave vacuum electron tubes based on the Electron Cyclotron Maser (ECM) instability. The free energy is the rotational energy of weakly relativistic electrons
(1 < g £ 1.2) in a longitudinal magnetic cavity field. In contrast to klystrons the interaction circuit is a high-order-mode cavity allowing higher power at higher frequencies.

At present 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 0.5-1.0 MW gyrotrons is 5 s at 110 GHz and 10 s at 140 GHz and 170 GHz, with efficiencies slightly above 30%. The energy world record of 90 MJ (0.64 MW at 140 s pulse length and 140 GHz) has been achieved by the European FZK-CRPP-TED-CEA collaboration. Total efficiencies around 50 % have been obtained using single-stage depressed collectors. Diagnostic gyrotrons deliver P_out = 40 kW with t = 40 ms at frequencies up to 650 GHz (h > 4%). Gyrotron oscillators have also been successfully used in materials processing. Such technological applications require gyrotrons with the following parameters: f > 24 GHz , P_out = 10-50 kW, CW, h > 30%. This paper introduces into the principles of gyro-devices and reports about the experimental achievements related to the development of high power gyrotron oscillators for long pulse or CW operation and pulsed diagnostic gyrotrons. In addition, this lecture gives a short overview of the present development status of coaxial cavity gyrotrons, gyrotrons for technological applications, relativistic gyrotrons, quasi-optical gyrotrons, cyclotron autoresonance masers (CARMs), gyroklystrons, gyro-TWT amplifiers, gyrotwystron amplifiers, gyro-BWO's and of vacuum windows for such high-power mm-wave sources. The highest CW powers produced by gyrotron oscillators and gyroklystrons are 340 kW (28 GHz) and 10 kW (94 GHz).

Gyrotron oscillators also are successfully utilized in materials processing (e.g. advanced ceramic sintering, surface hardening or dielectric coating of metals and alloys) as well as in plasma chemistry [1-3,52-55]. The use of gyrotrons for such technological applications appears to be of interest if one can realize a relatively simple, low cost device which is easy in service (such as a magnetron). Gyrotrons with low magnetic field (operated at the 2nd harmonic of the electron cyclotron frequency), low anode voltage, high efficiency and long lifetime are under development. Mitsubishi in Japan and Gycom in Russia are employing permanent magnet systems
[56-60]. The state-of-the-art in this area of industrial gyrotrons is summarized in Table XVII.

The next generation of high-energy physics accelerators and the next frontier in understanding of elementary particles is based on the supercollider. For normal-conducting linear electron-positron colliders that will reach center-of-mass energies of > 1 TeV it is thought that sources at 17 to 35 GHz with P_out = 300 MW, t = 0.2 ms and characteristics that will allow approximately 1000 pulses per second will be necessary as drivers [61-63]. These must be phase-coherent devices, which can be either amplifiers or phase locked oscillators. Such generators are also required for super-range high-resolution radar and atmospheric sensing [64-67]. Therefore this lecture gives an overview of the present development status of relativistic gyrotrons (Tables XVIII and XIX), cyclotron autoresonance masers (CARM) (Table XXI), gyroklystrons (Table XXII and XXIII), gyrotron travelling wave tube amplifiers (Gyro-TWT) (Table XXIV and XXV) and gyrotwystrons (Table XXVI) for such purposes as well as of broadband gyrotron backward wave oscillators (Gyro-BWO) (Table XXVII) for use as drivers for FEM amplifiers.