New trends in gyrotron development

Abstract

Gyro-devices provide the highest CW or average power of microwaves in centimeter, millimeter and submillimeter wavelength ranges and therefore they are very attractive as microwave sources for many of applications such as plasma fusion, radiolocation, ion sources, telecommunication, technology, spectroscopy and some other. In last years an essential progress in the device development was demonstrated. The paper presents State-of the Art in the device development, new demands in the parameters enhancement and possible ways to achieve the goals. Gyro-Devices. State-of-the ArtGyrotrons for plasma fusion installations usually operate at frequencies 40-170 GHz [1][2][3][4][5][6]. Requested output power of the tubes is about 1 MW and pulse duration is between seconds and thousands seconds (depending on plasma machine parameters). In ITER installation there will be 24 of 170 GHz gyrotron systems with 1 MW microwave power each. ITER requirements include also high efficiency of the gyrotrons over 50%, possibility of power modulation with frequency up to 5 kHz, compatibility of the gyrotron complex with ITER control system. In May, 2015 a Russian Prototype of ITER Gyrotron System was completed and its operation was demonstrated [2][3][4][5]. The system includes gyrotron oscillator, liquid-free superconducting magnet, supplementary magnets, several electric power supplies, cooling systems control and protection systems, and other auxiliary units. The gyrotron system shows reliable operation with required parameters. In October, 2015 Final Design Review Procedure for the gyrotron system was successfully passed and in 2016 fabrication of the first serial gyrotron system was completed. Megawatt power at very long pulses (300-1000 s) was also demonstrated with gyrotron at 140 GHz frequency for electron-cyclotron systems of EAST (China) and KSTAR (Korea) superconducting tokamaks. Megawatt power gyrotrons with moderate pulse duration from 2 to 10 seconds were developed for TCV, HL-2A, and ASDEX Upgrade tokamaks.There are successful developments of megawatt gyrotrons [1, 6] by European team including industrial company Thales, by CPI (USA), by Japanese cooperation of QST/Toshiba and Tsukuba University. The point worth mentioning is that the new stellarator W7-X is equipped now with 9 gyrotrons capable to operate at 140 GHz frequency and power of 0.8-1.0 MW in 1800 second pulses.Gyro-amplifiers are intrinsically more difficult in realization because of multi-mode microwave systems, but in recent years there is a remarkable progress in their development. At IAP/GYCOM we are developing an original concept of a gyro-TWT that is based on the use of a helically corrugated waveguide that radically changes the dispersion of the modes of a circular waveguide. The operating mode has sufficiently high and almost constant group velocity at zero axial wavenumber which enables broadband operation of the helical-waveguide gyro-TWT with minimum sensitivity to electron velocity spread. A number of experiments have proved the main theoret...

Frontiers in the Application of RF Vacuum Electronics

“…The gyrotron device [ 92 ], [ 93 ] has been the primary source concept for EC HCD applications to date, providing unit powers up to ~1 MW in the range of 30–170 GHz for pulse lengths up to 1000 s [ 94 ], [ 95 ], [ 96 ]. Several cylindrical cavity designs have yielded multifrequency sources with similar output performance [ 97 ], [ 98 ], [ 99 ] and higher unit powers ~1.5 MW, albeit at shorter pulse lengths [ 100 ].…”

High-power gyrotrons for electron cyclotron heating and current drive

“…At IAP Nizhny Novgorod there are new developments in phase locking megawatt-class gyro-oscillators [143][144][145]. Starting from a 1.5 MW, 170 GHz, TE 28,12 -mode tube with 2.5 s pulse length, 49% efficiency (with SDC) and 97% Gaussian-beam output, a gyrotron operating efficiently in modes of both rotations was developed and tested in proof-of-principle experiments.…”