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

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-fre-quency gyrotrons; coaxial-cavity multi-megawatt gyrotrons; complex two-section stepped cavity gyrotrons; gyrotrons for technological and spectroscopy applica-tions; 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 oscil-lators (“gyromonotrons or just gyrotrons”) are mainly used as high-power millim-eter-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. ... mehrMegawatt-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-sta-bilized 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 dura-tion 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 param-eters: 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, gyrot-wystrons, and gyro-TWTs are 10 kW, 5 kW, and 20 kW, respectively.