State-of-the-Art of High-Power Gyro-Devices: 2025 Update of Experimental Results

Abstract

This report presents an update of the experimental achievements published in the review “State-of-the-Art of High-Power Gyro-Devices and Free Electron Masers,” Journal of Infrared, Millimeter, and Terahertz Waves, 41, No. 1, pp 1–140 (2020) related to the development of gyro-devices (Tables 2–34). Emphasis is on high-power gyrotron oscillators for long-pulse or continuous wave (CW) operation and pulsed gyrotrons for many other applications. In addition, this work gives a short update on the present development status of frequency step-tunable and multi-frequency gyrotrons; coaxial-cavity multi-megawatt gyrotrons; complex two-section stepped cavity gyrotrons; gyrotrons for technological and spectroscopy applications; relativistic gyrotrons; large orbit gyrotrons (LOGs); quasi-optical gyrotrons; fast- and slow-wave cyclotron autoresonance masers (CARMs); gyroklystron, gyro-TWT, and gyrotwystron amplifiers; gyro-harmonic converters; gyro-BWOs; and dielectric vacuum windows for such high-power mm-wave sources. Gyrotron oscillators (“gyromonotrons or just gyrotrons”) are mainly used as high-power millimeter-wave sources for electron cyclotron heating (ECH), electron cyclotron current drive (ECCD), stability control, and diagnostics of magnetically confined plasmas for clean generation of energy by controlled thermonuclear fusion. Megawatt-class gyrotrons employ synthetic-diamond output windows and single-stage depressed collectors (SDCs) for electron energy recovery. The maximum pulse length of the 140 GHz, 1.3 MW IPP-KIT-THALES gyrotron is 3 min (1.2 MW/6 min) at 97.5% Gaussian output mode purity and 47% efficiency. The 1 MW version of this tube operates at pulse lengths up to 30 min, and PLL-frequency stabilization has been demonstrated. The first Japan QST-CANON 170 GHz ITER gyrotron prototype achieved 1 MW, 800 s at 55% efficiency and holds the energy world record of 2.88 GJ (0.8 MW, 60 min, 57%). The Russian 170 GHz ITER gyrotron obtained 0.99 (1.2) MW with a pulse duration of 1000 (100) s and 57 (53)% efficiency. First frequency-injection-locked operation of a very high-order-mode Russian 170 GHz-1 MW gyrotron (IAP) has been demonstrated in short pulses using a PLL-frequency-stabilized 20 kW gyrotron master oscillator. A Russian short-pulse 74.2 GHz, 100 kW gyrotron (SPbSTU) with 4-stage depressed collector achieved an efficiency of 72%. The prototype tube of the KIT 2 MW, 170 GHz coaxial-cavity gyrotron (pulse duration 50 ms) achieved in 1 ms pulses the record power of 2.2 MW at 48% efficiency and 96% Gaussian mode purity and was operated at pulse lengths up to 50 ms. High-power CW gyrotron oscillators have also been successfully used in materials processing. Such technological applications require tubes with the following parameters: f ≥ 24 GHz, Pout = 4–50 kW, CW, η ≥ 30%. Gyrotrons with pulsed magnet for various short-pulse applications deliver Pout = 210 kW with τ = 20 µs at frequencies up to 670 GHz (η ≅ 20%), Pout = 5.3 kW at 1 THz (η = 6.1%), and Pout = 0.5 kW at 1.3 THz (η = 0.6%). The average powers produced by 94 GHz gyroklystrons, gyrotwystrons, and gyro-TWTs are 10 kW, 5 kW, and 20 kW, respectively.