State-of-the-art of high power gyro-devices and free electron masers. Update 2008

Abstract

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 megawatt-class 140 GHz gyrotron are: 0.92 MW output power at 30 min. pulse duration, 97.5% Gaussian mode purity and 44% 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 2.88 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 gyrotron achieved 0.83 MW with a pulse duration of almost 203 s. Russian gyrotrons for plasma diagnostics or spectroscopy applications deliver Pout = 40 kW with τ = 40 μs at frequencies up to 650 GHz (η > 4%), P out = 1.5 kW at 1 THz (η = 2.2%), and P out = 0.5 kW at 1.3 THz (η = 0.7%). Gyrotron oscillators have also been successfully used in materials processing. Such technological applications require gyrotrons with the following parameters: f > 24 GHz , Pout = 4-50 kW, CW, η > 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, relativistic gyrotrons, quasi-optical gyrotrons, fast-and slow-wave cyclotron autoresonance masers (CARMs), gyroklystrons, gyro-TWT amplifiers, gyrotwystron amplifiers, gyro-BWO's, gyropeniotrons, magnicons, gyroharmonic converters, free electron masers (FEMs) and of vacuum windows for such high-power mm-wave sources. The highest CW powers produced by gyroklystrons and FEMs are, respectively, 10 kW (94 GHz) and 36 W (15 GHz). The IR FEL at the Thomas Jefferson National Accelerator Facility in the USA obtained a record average power of 14.2 kW at a wavelength of 1.6 μm. The THz FEL (NOVEL) at the Budker Institute of Nuclear Physics in Russia obtained a maximum average power of 0.5 kW in the wavelength range 110-240 μm (2.73-1.25 THz).