Electron Cyclotron Wave System Research Articles

Basic design considerations for a frequency step-tunable electron cyclotron wave system to suppress NTMs in DEMO

An Electron Cyclotron Wave (ECW) system will be used in the European DEMO for the stabilization of Neoclassical Tearing Modes (NTMs). In order to avoid movable mirrors in the harsh environment close to the plasma and to simplify the NTM launcher integration, the tuning of the ECW deposition location can be achieved by launching frequency-tunable ECWs from fixed mirrors while the frequency is tuned in discrete steps of 2–3GHz. An overview of the frequency step-tunable ECW system for NTM stabilization is presented. The design considerations are discussed based on the current DEMO baseline parameters and the status of technologies. A simulation of NTM stabilization with an idealized frequency tunable ECW system on an analytical NTM model is shown. The simulation takes into account a realistic tuning speed based on the present technology and considers the current NTM launcher configurations in DEMO. A simple sweeping strategy is adapted for the control of frequency. Various uncertainties, which will affect the feasibility, need to be further investigated.

Numerical analysis of the optimized performance of the electron cyclotron wave system in a HL-2M tokamak**Project supported by the National Natural Science Foundation of China (Grant Nos. 11375085, 11405082, 11505092, 11475083, and 11375053), the National Magnetic Confinement Fusion Science Program of China (Grant Nos. 2013GB104004, 2013GB111000, 2014GB107000, and 2014GB108002), and the Natural Science Foundation of Hunan Province, China (Grant No.

The capabilities of current drive, neoclassical tearing mode (NTM) stabilization, and sawtooth control are analyzed for the electron–cyclotron wave (ECW) system in a HL-2M tokamak. Better performance of the upper launcher is demonstrated in comparison with that of a dropped upper launcher, in terms of JEC/Jbs for NTM stabilization and IECCD/(Δρtor)2 for sawtooth control. 1-MW ECW power is enough for the 3/2 NTM stabilization, and 1.8-MW ECW power is required to suppress 2/1 NTM in a single null divertor equilibrium with 1.2-MA toroidal current with the upper launcher. Optimization simulation of electron–cyclotron current drive (ECCD) is carried out for three mirrors in an equatorial port, indicating that the middle mirror has a good performance compared with the top and bottom mirrors. The results for balanced co- and counter-ECCD in an equatorial port are also presented.

Conceptual design of CFETR electron cyclotron wave system

China Fusion Engineering Test Reactor (CFETR) is a test tokamak which is built for magnetically confined fusion plasma experiments. The electron cyclotron (EC) wave system of CFETR is designed to inject 20MW RF power into the plasma for heating and current drive (H&CD) applications. The EC wave system consists of RF sources, twenty transmission lines (TLs) and one equatorial launcher. RF sources contain twenty gyrotrons with the output power 1MW. There are series of microwave components distributed along the TL and the percentage of power losses of each TL is about 8.7%. In the equatorial launcher, five RF beams are injected into one focusing mirror and then reflected to the plasma via one injection mirror. The focusing mirror is spherical to focus Gaussian beam and the injection mirror which is flat can steer in the toroidal direction. After optic calculation and optimization, all the quasi-optical parameters for launcher design are given. Combining with the thermal stress analysis, the chosen inner diameter of water channel of injection mirror is 12mm and the suggested water velocity is 3m/s.

Optimization simulations of electron cyclotron wave heating and current drive in experimental advanced superconducting tokamak

A large number of simulations of electron cyclotron heating and current drive (ECCD) were carried out using TORAY before the installation of an electron cyclotron wave system with a maximum of 4 MW power and 140 GHz frequency on the experimental advanced superconducting tokamak (EAST). The findings that the range of allowable launch angles is about 50° poloidal and about 60° toroidal, when all the plasma areas of interest are covered, determine the allowable steering angles of the launch mirror under a power deposition rate not less than 0.98. The variable range of the integrated driven current is larger at a radius of 0.5a–0.6a than at other radii. The best scheme for core localized heating is a launch from Z = 30 cm (the vertical mirror position). From an analysis of the optimum figures of merit of the ECCD, it is found that a launch from Z = 30 cm is the best for the suppression of neoclassical tearing modes.

Physics analysis of the ITER ECW system for optimized performance

A predictive analysis of the capabilities of the ITER electron cyclotron wave system is presented in this work. Modifications of both the upper launcher and the equatorial launcher aimed at increasing the potentialities of the system are identified and discussed. A modification of the upper launcher has already been incorporated in the updated front steering design called the extended physics launcher. By adopting different deposition ranges for the upper and lower steering mirrors, this design offers the flexibility to drive current from the radial region required for the stabilization of neoclassical tearing modes (NTM) up to that required for sawtooth control, allowing a synergy with the equatorial launcher. Here a comparison of the performance of the new design of the upper launcher with those of a dropped upper launcher is performed, showing that better performance for both NTM stabilization and sawtooth control may be obtained by lowering the upper port location. An analysis of the EC current driven by the equatorial launcher is also presented, showing that adding to the present design the possibility to drive counter-current in addition to the existing co-current capability would increase the flexibility of the system. The behaviour of all launchers at reduced magnetic fields is also discussed.

Installation and commisionning of the EU test facility for ITER gyrotrons

In the frame of the EU program on the ITER electron cyclotron wave (ECW) system, the development of a 170 GHz, 2 MW CW coaxial gyrotron with depressed collector (C-GT170) has been launched during the Sixth Framework Program (2003–2006) in the European Technology Workplan. Such development relies on the availability of a test facility (TF) capable of providing both the energy sources and sinks required by this new electron tube (electrical energy, cooling capacity), and allowing the control and acquisition of a large range of signals used to understand and improve the gyrotron behaviour. The TF will be used, in a later stage, for the component test of the ITER ECW system. This paper will report on the design, installation and commissioning of the TF in Lausanne.

Neutronics analysis of the ECW launching system in the ITER upper port

Abstract This paper is devoted to the neutronics analysis of the electron cyclotron wave (ECW) launching system installed in the ITER upper port. The launcher design developed by FOM Rijnhuizen with a twisted arrangement of straight waveguides was selected to facilitate the maintenance of the ECW system by avoiding mitre bends. Two types of ECW launcher designs were considered in this paper: limited and full focusing. Three dimensional MCNP models of the ECW launchers were developed with high accuracy directly from the CAD geometry models by means of an interface programme. A shielding analysis was performed to estimate the length and thickness required for the shield around the waveguides. A two-step method making use of surface sources and point detectors was applied in the neutron streaming calculations in order to estimate the radiation load on the CVD diamond window. The neutron and gamma fluxes, the nuclear heat density, and the helium production were calculated. The results show that the design limits both for the limited and the full focusing ECW models are met.

Megawatt Gyrotrons for ECR Heating and Current-Drive Systems in Controlled-Fusion Facilities

We discuss the results and main trends in developing megawatt gyrotrons used as microwave sources for electron-cyclotron wave systems in controlled-fusion facilities. Such systems require gyrotrons with power no less than 1 MW operable during a time of about 1000 s in the frequency range 110–170 GHz. We also highlight the main design principles of such gyrotrons and the most striking aspects and prospects of their development in the last years.

Design study of a test stand for ITER gyrotron

In the frame of development of the ITER electron cyclotron wave (ECW) system, a two MW CW coaxial cavity gyrotron will be developed during the Sixth Framework Program (2003–2006). Such development relies on the availability of a test stand capable of providing the electrical energy and cooling capacity. This test stand will possibly be used, in a later stage, for the component test of the ITER ECW system. This paper will first present the main parameters of this new coaxial gyrotron. Then we describe the test stand itself, including the general requirements for testing and evaluating the behaviour of the RF source and then a description of the electrical system design. Compared to the ITER reference design, the test stand emphasises the requirement of flexibility, which is necessary during the development of the gyrotron. The additional electrical equipment is included in the overview of the electrical system. The cooling system will be an important part of the design study. Indeed, the design efficiency of such a depressed collector gyrotron is ≈50%, implying >4 MW of continuous heat dissipation and evacuation by the cooling equipment. The specifications of the cooling system must also comply with ITER reference design values.

Neoclassical tearing mode stabilization by ECCD in ITER

A dynamic model, based on a 3-D Fokker-Planck code coupled to the island evolution equations, is used to evaluate the feasibility of active control of Neoclassical Tearing modes by Electron Cyclotron Current Drive (ECCD) in International Thermonuclear Experimental Reactor (ITER). The parameters of the present version of ITER, i.e., RTO/RC ITER (IAM option) are used. Both m = 3, n = 2 and m = 2, n = 1 modes are considered. It is shown that an Electron Cyclotron wave system at 140 GHz, with toroidally steerable antennas, can stabilize both modes simultaneously if a power ⩾30 MW is available.

Pre- and post-irradiation studies on mm-wave losses in reference window materials for electron cyclotron wave systems

Dielectric materials for transmission windows in electron cyclotron (EC) wave systems are studied for the radiation effects on their dielectric properties (permittivity, loss tangent). Based on comparative neutron irradiation experiments performed at cryogenic and reactor pool temperatures, it is shown here that fast neutron fluences up to at least 2–4 × 10 20 n/m 2 ( E > 0.1 MeV) do not critically affect the mm-wave losses in HEMEX grade sapphire, the reference material for the cryogenically cooled high power EC window. Fast neutron (10 20 n/m 2) and electron (5 × 10 −6 dpa) irradiations on specially developed CVD diamond grades for conventionally cooled windows demonstrate acceptable mm-wave loss levels, whereas loss at lower frequencies can be significantly affected. In-beam measurements under X-ray irradiation show no additional loss terms in sapphire and CVD diamond, at least up to 0.45 Gy/s. Dielectric data obtained for synthetic quartz indicate that the observed changes due to neutron damage are not severe for fast neutron fluences at least up to 10 22 n/m 2.

Dielectric measurements on sapphire for electron cyclotron wave systems

Three different grades of sapphire have been investigated in the unirradiated state at 25–300 K and 145 GHz. The initial T 2 dependence of dielectric loss was found to become steeper below 150 K, reaching exponents around 4 at 70 K. In the HEMEX grade, the loss starts to level off to constant values below about 100 K. A specimen subjected to the RIED effect under electron irradiation showed a similar behaviour but reaching higher constant loss levels. Fast neutron irradiations were performed in the fluence ranges of 10 20–300 K were observed in HEMEX grades irradiated up significant property changes in the dielectric properties at 70–300 K were observed in HEMEX grades irradiated up to 10 21 n/m 2. The use of the present data base for the assessment of tolerable fluence levels for a cryogenically-cooled torus window in electron cyclotron wave systems is discussed.