Russian Gyrotrons - Achievements and Trends
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | IEEE Journal of Microwaves |
| Authors | A. G. Litvak, Г. Г. Денисов, M. Yu. Glyavin |
| Institutions | Institute of Applied Physics |
| Citations | 97 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This review details the rapid advancements and key achievements of Russian gyrotron technology developed at IAP RAS, focusing on high-power, high-frequency, and highly stable microwave sources for diverse engineering applications.
- Fusion Power Leadership: Megawatt-class, continuous-wave (CW) gyrotrons (170 GHz, 1 MW, 1000 s pulse duration) have been successfully developed and delivered for major fusion facilities (e.g., ITER), achieving total device efficiencies exceeding 50% using depressed collectors.
- THz Band Breakthrough: IAP RAS achieved world-record power levels for CW sub-THz gyrotrons (1 kW at 0.26 THz) and demonstrated pulsed operation up to 1.3 THz, addressing the critical “THz gap” problem in modern physics.
- Extreme Frequency Stability: Utilizing Phase-Lock Loop (PLL) control of the anode voltage, the frequency spectrum width was stabilized from 0.5 MHz (free-running) down to 1 Hz, corresponding to a relative stability (Af/f) of approximately 3*10-12.
- High-Efficiency Conversion: Quasi-optical mode converters were synthesized to transform complex cavity modes (e.g., TE25,10) into linearly polarized Gaussian beams with extremely high efficiency (95-97%).
- Wideband Amplification: Novel Gyro-TWTs based on Helical Corrugated Waveguides (HCW) were developed, achieving broad frequency bandwidths (up to 15%) and high pulsed output power (up to 180 kW at 35 GHz).
- Technological Applications: Gyrotrons are successfully employed in industrial complexes for microwave ceramic sintering, gas-phase deposition of isotope-pure silicon, and production of polycrystalline diamond films.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Fusion Gyrotron (ITER) | 170 | GHz | Operating frequency (TE25,10 mode) |
| Fusion Output Power (CW) | 1000 | kW | Required power for ITER ECH/CD |
| Fusion Pulse Duration | 1000 | s | Continuous-wave regime for ITER |
| Total Device Efficiency | 52-54 | % | Achieved with Single Stage Depressed Collector (SDC) |
| High Power (Pulsed) | 1.5/1.2 | MW | Achieved with 170 GHz (2 s) and 82.6 GHz (30 s) tubes |
| Record Pulsed THz Frequency | 1.3 | THz | Achieved at fundamental cyclotron resonance |
| Record Pulsed THz Power | 0.5 | kW | At 1.3 THz, 50 µs pulse duration |
| Record CW THz Power | 1 | kW | Achieved at 0.26 THz |
| CW THz Low Voltage Operation | 1.5 | kV | For spectroscopy applications (power up to 10 W) |
| Frequency Spectrum Width (Free-Running) | 0.5 | MHz | 0.263 THz gyrotron |
| Frequency Spectrum Width (Stabilized) | 1 | Hz | Achieved using Phase-Lock Loop (PLL) control |
| Relative Frequency Stability (Stabilized) | 3*10-12 | N/A | Measured over a few seconds |
| Mode Converter Efficiency | 95-97 | % | Conversion of cavity mode to Gaussian beam |
| Gyro-Klystron Pulsed Power | 700 | kW | At 35 GHz (Gain 38 dB) |
| Gyro-TWT Bandwidth | 15 | % | Achieved using Helical Corrugated Waveguide (HCW) |
Key Methodologies
Section titled “Key Methodologies”- Oversized Cavity Design: Utilization of highly oversized cavities (e.g., TE25,10 mode for 170 GHz) to manage thermal load and enable megawatt-class CW operation, coupled with efficient cooling systems.
- Energy Recovery System: Implementation of a depressed collector (SDC) to recover unspent energy from the electron beam, significantly increasing the total device efficiency (up to 57%).
- Quasi-Optical Mode Conversion: Use of synthesized three-dimensional quasi-optical converters (e.g., mirror systems) to efficiently transform the high-order operating cavity mode into a low-loss, linearly polarized Gaussian output beam.
- Frequency Control via Magnetic Field: Stepwise frequency tuning achieved by varying the main magnetic field of the superconducting magnet to selectively excite different high-order cavity modes.
- Phase-Lock Loop (PLL) Stabilization: Achieving ultra-high frequency stability (1 Hz width) by using PLL control applied to the modulating anode voltage, compensating for high-voltage power supply fluctuations.
- High Harmonic Operation (LOGs): Development of Large-Orbit Gyrotrons (LOGs) using axis-encircling electron beams to operate successfully at high cyclotron harmonics (up to the fifth), crucial for reaching THz frequencies with moderate magnetic fields.
- Helical Corrugated Waveguides (HCW): Employed in Gyro-TWTs and Gyro-BWOs to achieve strong coupling between near-cutoff and far-from-cutoff eigenmodes, resulting in an almost constant group velocity and wide frequency bandwidth.
Commercial Applications
Section titled “Commercial Applications”- Controlled Nuclear Fusion (Energy):
- Electron Cyclotron Heating (ECH) and Current Drive (CD) in large-scale facilities (ITER, DEMO, ASDEX Upgrade, EAST, KSTAR).
- Collective Thomson Scattering diagnostics for plasma parameters.
- Advanced Materials Processing:
- Microwave ceramic sintering and high-temperature material processing.
- Chemical Vapor Deposition (CVD) reactors for growing poly- and monocrystalline diamond films and plates.
- Gas-phase deposition of isotope-pure silicon with record purity.
- Scientific Spectroscopy and Diagnostics:
- High-resolution Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR)/DNP spectroscopy.
- Diagnostics of various media and gases (RAD spectroscopy).
- Creation of point sources of extreme UV radiation via terahertz discharge in gases.
- High-Power RF and Communication:
- High-power millimeter-wave radar systems.
- Deep-space and specialized satellite communication (using high-gain Gyro-Klystrons and Gyro-TWTs).
- High-speed data transmission using sub-THz sources.
- Particle Acceleration:
- High-gradient acceleration of charged particles, requiring MW-level, phase-synchronized gyrotrons.
- Ion Source Technology:
- Generation of intense beams of multicharge ions in Electron Cyclotron Resonance (ECR) ion sources.
View Original Abstract
The last decade has contributed to the rapid progress in the gyrotron development. Megawatt-class, continuous wave gyrotrons are employed as high-power millimeter (mm)-wave sources for electron cyclotron heating (ECH) and current drive in the tokamaks and stellarators. The progress in gyrotron development pushes ECH from a minor to a major heating method. Also gyrotron based technological complexes successfully applied in electron cyclotron resonance ion sources, for microwave ceramic sintering and diamond disk production. The paper describes the main features of high frequency gyrotrons. Some data about pulsed and CW tubes, working in the terahertz frequency range, are given. These gyrotrons operate (in some specific combinations) at very low voltage and beam current, demonstrate an extremely narrow frequency spectrum or wide frequency tuning. Although in comparison with the classical microwave tubes the gyrotrons are characterized by greater volume and weight due to the presence of bulky parts (such as superconducting magnets and massive collectors where the energy of the spent electron beam is dissipated) they can easily be embedded in a sophisticated laboratory equipment (e.g., spectrometers, technological systems, etc.). All these advantageous features have opened the road to many novel and prospective applications of gyrotrons.