The gyro oscillators or simply gyrotrons are used in a variety of applications where high electromagnetic power is required at millimeter/submillimeter wave frequencies. The research on the gyrotron microwave tube was initiated by the demand of high power, high frequency electromagnetic wave source in the magnetically confined plasma fusion application. Since the initial phase of gyrotron development, new thrust areas have been explored by the several research groups. The gyrotron shows several unique advantages as a high power source compare to the other millimeter/submillimeter wave sources either semiconductor based devices or vacuum based tube devices. At present gyrotron is used successfully in the field of plasma heating, plasma diagnosis, medical spectroscopy, material processing, whether monitoring etc. discussed in detail in this article. Several new fields of technology like security, metal joining, planetary defense etc. are under exploration for the futuristic use of gyrotron. In this review article, the applications of gyrotron, various issues remained in the further modification of the device, global scenario of the gyrotron development are discussed in detail.

A Review on the Applications of High Power, High Frequency Microwave Source: Gyrotron

https://pure.mpg.de/pubman/item/item_2573928_5/component/file_2574793/Poli_TORBEAM.pdf

TORBEAM 2.0, a paraxial beam tracing code for electron-cyclotron beams in fusion plasmas for extended physics applications

Sawtooth control using electron cyclotron current drive (ECCD) has been demonstrated in ITER-like plasmas with a large fast ion fraction, wide q = 1 radius and long uncontrolled sawtooth period in DIII-D. The sawtooth period is minimized when the ECCD resonance is just inside the q = 1 surface. Sawtooth destabilization using driven current inside q = 1 avoids the triggering of performance-degrading neoclassical tearing modes (NTMs), even at much higher pressure than required in the ITER baseline scenario. Operation at βN = 3 without 3/2 or 2/1 NTMs has been achieved in ITER demonstration plasmas when sawtooth control is applied using only modest ECCD power. Numerical modelling qualitatively confirms that the achieved driven current changes the local magnetic shear sufficiently to compensate for the stabilizing influence of the energetic particles in the plasma core.

/pdf/sawtooth-control-using-electron-cyclotron-current-drive-in-1pk932hwab.pdf

Sawtooth control using electron cyclotron current drive in ITER demonstration plasmas in DIII-D

Enhancement of the output power per gyrotron has been planned in the Large Helical Device (LHD). Three 77-GHz gyrotrons with an output power of more than 1 MW have been operated. In addition, a high power gyrotron with the frequency of 154 GHz (1 MW/5 s, 0.5 MW/CW) was newly installed in 2012, and the total injection power of Electron cyclotron resonance heating (ECRH) reached 4.6 MW. The operational regime of ECRH plasma on the LHD has been extended due to the upgraded ECRH system such as the central electron temperature of 13.5 keV with the line-averaged electron density ne_fir = 1 × 1019 m−3. The electron thermal confinement clearly improved inside the electron internal transport barrier, and the electron thermal diffusivity reached neoclassical level. The global energy confinement time increased with increase of ne_fir. The plasma stored energy of 530 kJ with ne_fir = 3.2 × 1019 m−3, which is 1.7 times larger than the previous record in the ECRH plasma in the LHD, has been successfully achieved.

Extension of high Te regime with upgraded electron cyclotron resonance heating system in the Large Helical Device

During the first hundred milliseconds, the frequency and RF output power of long pulse operating gyrotrons undergo deterministic variation. This well-known behavior is caused by the thermal expansion of the cavity and internal electrostatic processes related to the ionization of residual gas. A macroscopic analytical investigation of the gas conditions in modern gyrotrons indicates that ionization processes are unlikely to influence the overall internal gas pressure. In combination with electrostatic potential considerations, it was found that the beam depression voltage is not fully neutralized; in the case of W7-X gyrotrons, a maximum value of about 60 % neutralization is expected, in conflict with the common assumption of full neutralization in steady state. Using experimentally measured frequency shifts and the Evridiki gyrotron interaction simulation code, a fitting process was employed to further investigate these effects. The results are in very good agreement with the theoretical predictions and allow a separation of the time constants of the two processes causing the frequency tuning.

Frequency-Based Investigation of Charge Neutralization Processes and Thermal Cavity Expansion in Gyrotrons

Since the end of EDA, the design of the Electron Cyclotron Heating and Current Drive (ECH&CD) system has been modified to respond to progress in physics understanding and change of interface conditions. Nominal RF power of 20 MW is shared by four upper launchers or one equatorial launcher RF beams are steered by front steering mirrors providing wide sweeping angle for the RF beam. DC high voltage power supply may be composed of IGBT pulse step modulators because of high frequency modulation and design flexibility to three different types of 170 GHz gyrotrons provided by three parties. The RF power from the 170 GHz gyrotron is transmitted to the launcher by 63.5 mmφ corrugated waveguide line and remotely switched by a waveguide switch between the upper launcher and the equatorial launcher. The ECH&CD system has also a start‐up sub‐system for assist of initial discharge composed of three 127.5 GHz gyrotrons and a dedicated DC high voltage power supply. Three of transmission lines are shared between 170 GHz gyrotron and 127.5 GHz gyrotron so as to inject RF beam for the start‐up through the equatorial launcher. R&Ds of components for high power long pulse and mirror steering mechanism have been on‐going in the parties to establish a reliable ITER ECH&CD system.

/pdf/design-of-electron-cyclotron-heating-and-current-drive-3s1vrhv4ev.pdf

Design of Electron Cyclotron Heating and Current Drive System of ITER

Note: Proceedings 4th Int. Workshop on Strong Microwaves in Plasmas, Nizhny Novogord, Russia, August 1999 (Invited paper), Vol. 1, ISBN 5-8048-0007-8, 114 - 133 (2000) Reference CRPP-CONF-2000-033 Record created on 2008-05-13, modified on 2017-05-12

Recent results in ECH and ECCD experiments in the TCV tokamak

Keywords: LRP 735 ; JET Reference CRPP-REPORT-2002-014 Record created on 2008-04-18, modified on 2017-05-12

General description of the evacuated wave-guide transmission line for the JET-EP ECRH project

Keywords: LRP 719 ; JET Reference CRPP-REPORT-2002-015 Record created on 2008-04-18, modified on 2017-05-12

CRPP's evacuated waveguide proposal for JET-EP ECRH transmission line

The EU will be providing the largest contribution to the ITER electron cyclotron (EC) heating and current drive (H&CD) system (20 MW, CW at 170 GHz). The contribution includes one third of the H&CD gyrotrons, their associated power supplies and four upper port launcher antennas. In all areas of participation, the EU EC partnership (coordinated by the European Fusion Development Agreement) aims toward advancing the technology, while staying within a specified cost envelope. This is portrayed in the co-axial gyrotron development that offers the potential to double the output power per source (2.0 MW), increasing the delivered power for a fixed number of auxiliary systems. The EU partnerships also attempt to increase performance for the entire EC system, in particular the launching antennas. The proposed front steering launcher design offers greater control of MHD activity than the previous remote steering design and opens up the possibility of an enhanced performance UL. The EC physics requirements are repartitioned between the upper and equatorial launchers for a synergetic balance, which increases the EC physics capabilities while relaxing some of the engineering requirements.

/pdf/eu-developments-of-the-iter-ecrh-system-45tnnsi4jq.pdf

EU developments of the ITER ECRH system

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