C. Darbos

THE EC H&CD TRANSMISSION LINE FOR ITER

Abstract The transmission line (TL) subsystem associated with the ITER electron cyclotron heating and current drive system has reached the conceptual design maturity. At this stage the responsibility of finalizing the design has been transferred from the ITER Organization to the U.S. Domestic Agency. The purpose of the TL is to transmit the microwaves generated by the 170-GHz gyrotrons installed in the radio-frequency building to the launchers located in one equatorial and four upper tokamak ports. Each TL consists of evacuated HE11 waveguides, direct-current breaks, power monitors, mitre bends, polarizers, switches, loads, and pumping sections and will have a typical length that ranges from 100 to 160 m. Overall transmission efficiency could be as high as 92% depending on the specific path between a given gyrotron and launcher. All components are required to be 2-MW compatible, and their layout and organization have been optimized for simplifying the maintenance accessibility and monitoring the primary tritium barrier integrity. Two different TL layouts are at the moment under study, to accommodate the two alternative options for the European sources: four 2-MW units or eight 1-MW units. In this paper the actual design is presented and the technical requirements are discussed.

The targeted heating and current drive applications for the ITER electron cyclotron system

A 24 MW Electron Cyclotron (EC) system operating at 170 GHz and 3600 s pulse length is to be installed on ITER. The EC plant shall deliver 20 MW of this power to the plasma for Heating and Current Drive (H&CD) applications. The EC system is designed for plasma initiation, central heating, current drive, current profile tailoring, and Magneto-hydrodynamic control (in particular, sawteeth and Neo-classical Tearing Mode) in the flat-top phase of the plasma. A preliminary design review was performed in 2012, which identified a need for extended application of the EC system to the plasma ramp-up, flattop, and ramp down phases of ITER plasma pulse. The various functionalities are prioritized based on those applications, which can be uniquely addressed with the EC system in contrast to other H&CD systems. An initial attempt has been developed at prioritizing the allocated H&CD applications for the three scenarios envisioned: ELMy H-mode (15 MA), Hybrid (∼12 MA), and Advanced (∼9 MA) scenarios. This leads to the ...

Study of the ITER Stray Magnetic Field Effect on the EU 170-GHz 2-MW Coaxial Cavity Gyrotron

In this paper, the effect of the ITER stray magnetic field (SMF) on the operation of the European gyrotron has been studied. The SMFs include the magnetic field generated by neighboring gyrotrons, the ITER tokamak, and also the field perturbations caused by the ferromagnetic structural materials used in the ECRH building.The 3-D self-consistent electrostatic code ARIADNE has been used for the evaluation of the SMF effect on the electron beam in the cavity and the collector region. It is shown that the beam parameters at the cavity of the gyrotron are not significantly affected by the SMF. On the other hand, the magnetic field lines in the collector region are significantly deformed in the presence of the SMF. A part of the electron beam is guided to the inappropriately cooled part of the collector surface, while the electron beam power is distributed in a significantly smaller area of the collector walls. In addition, the use of an advanced transverse sweeping system is proposed which would allow to compensate the SMF and to improve the collector operation.

Development of high power gyrotron for ITER application

Recent progress on the development of a high power 170 GHz gyrotron obtained in Japan Atomic Energy Agency (JAEA) is presented. Firstly, the repetitive operation of 800 kW/600 s with an interval of 20–30 min was performed. The electrical efficiency was 52–57% with the depressed collector. The 72 shots of 88 shots was very stable 600 s oscillation. No damage was found on the gyrotron by this test. Secondly, 5 kHz-full power modulation was demonstrated at CW mode. For this purpose, a full beam current modulation was realized by switching the anode voltage to minimized the collector heat load. Thirdly, in the dual frequency gyrotron development, the 1.3 MW oscillations at 170 GHz and 136.8 GHz were successfully demonstrated by changing the cavity field and the anode voltage keeping other parameters constant.

The 118-GHz electron cyclotron heating system on Tore Supra

Abstract An electron cyclotron resonance heating (ECRH) system capable of delivering 2.4 MW cw has been designed to be built at Commissariat à l’Energie Atomique, Cadarache, for the Tore Supra (TS) experiment, to provide plasma heating and current drive by electron cyclotron resonance interaction. The planned system was composed of a generator using six gyrotrons 500 kW for 5 s or 400 kW cw working at 118 GHz. Six transmission lines made of corrugated waveguide, 63.5-mm diameter, carry the HE11 mode to one antenna composed of six fixed mirrors and three independently movable mirrors for the adjustment of the injection angles of the rf beams. The antenna was built and installed in TS, and all transmission line components ordered and installed between the gyrotron locations and the antenna. In the same way, the required six oil tanks, the six cryomagnets, and the six modulating anode devices were designed and manufactured. In parallel, after demonstration in the factory of proper operation of the prototype gyrotron, the manufacture of a first so-called series gyrotron was made. But this gyrotron experienced hard limitations (overheating inducing prohibited outgassing, parasitic oscillations) during the long-pulse tests in Cadarache, and the achieved performance was 300 kW for 110 s. A new study was then carried out in collaboration with Thales Electron Devices, the EURATOM-CEA Association, and the EURATOM-Confédération Suisse Association to understand and overcome the limitations, which led to the construction of a new modified gyrotron. During the tests in factory of this new gyrotron, the output beam showed two peaks, a pattern never predicted by simulations. The gyrotron was nevertheless transferred to Cadarache for long-pulse testing, but an arc on the windows definitely stopped the tests. To understand the cause of the observed two peaks, various low-level tests were then performed on a model of the mode converter with different shapes for the launcher, but without real improvement. Besides measurements, the use of a new software, Surf3D, based on integral equations and providing a complete three-dimensional modeling, showed that the problem mainly comes from the third mirror, whose curvature is too high and consequently not well taken into account by the calculation. These technological problems have seriously delayed the development of the gyrotrons; as a consequence, only two tubes (intermediate developments) are presently available on TS to inject 700 kW in 5-s pulses. In spite of this relatively low power, the localized absorption property of electron cyclotron waves has been used on TS in a wide variety of experiments, such as stabilization and control of the sawtooth period, perturbative transport studies by ECRH modulations, and ECRH-assisted plasma start-up.

ITER project and RF systems

ITER is an international project supported by seven partners: China, Europe, India, Japan, Korea, Russian Federation and USA. Formally established in 2006, construction has started in France, more precisely in Provence. General progress of the project is presented followed by a focus on the RF systems which will provide 40 MW into the plasma, based on systems around 50 MHz and 170 GHz. These systems are using high power grid tubes, gyrotrons, and the latest power supplies technology to feed kilometres of transmission lines connected to specific antennas located at a few centimeters from the hot burning plasma.

The Engineering Analysis in Support of the ITER Electron Cyclotron Heating and Current Drive Transmission Lines

Abstract An engineering study has been performed on the ITER electron cyclotron transmission lines with the aim of optimizing its conceptual design. The support types and optimum spacing, cooling, vacuum, seismic, and gravitational effects were reviewed. For the vacuum system it was shown that two pumps per line, with a capacity of 50 l/s, are sufficient. It was explained that the temperature variation inside the building is the predominant factor that influences the thermal expansion of the lines. The support strategy is one of minimizing the number of constraints. Variation in support interspacing reduces the degree of harmonic disturbances. The section of transmission line inside the ITER port cell was identified as critical with regards to occurrence of deformation and stresses. Potential solutions are described. The use of seismic breaks is discussed in light of the differences in foundation and structure of the ITER tokamak building and assembly hall. It is proposed that this interface be studied in more detail, after more data is available on the behavior of these buildings. The geometry of individual supports should be simple, with the fewest possible adjustments. The supports are designed to allow small movements of the waveguide to compensate for the thermal expansion or contraction. The transmission line system can be made for optimum alignment during nominal operating temperatures by prestressing during installation.

Status of the ITER electron cyclotron H&CD system

This paper presents the status of the design and the integration of the 20 MW EC H&CD system under development for the ITER Tokamak. Progress includes agreement on the first set of procurement arrangements (EC Transmission Line and the RF building housing both IC and EC systems), advancing the design of all components to either the conceptual or preliminary design stage, optimization of gyrotrons performances and finalization of launchers design.