ITER Electron Cyclotron Heating Research Articles

Progress in the ITER electron cyclotron heating and current drive system design

An electron cyclotron system is one of the four auxiliary plasma heating systems to be installed on the ITER tokamak. The ITER EC system consists of 24 gyrotrons with associated 12 high voltage power supplies, a set of evacuated transmission lines and two types of launchers. The whole system is designed to inject 20MW of microwave power at 170GHz into the plasma. The primary functions of the system include plasma start-up, central heating and current drive, and magneto-hydrodynamic instabilities control. The design takes present day technology and extends towards high power CW operation, which represents a large step forward as compared to the present state of the art. The ITER EC system will be a stepping stone to future EC systems for DEMO and beyond.The EC system is faced with significant challenges, which not only includes an advanced microwave system for plasma heating and current drive applications but also has to comply with stringent requirements associated with nuclear safety as ITER became the first fusion device licensed as basic nuclear installations as of 9 November 2012.Since conceptual design of the EC system established in 2007, the EC system has progressed to a preliminary design stage in 2012, and is now moving forward towards a final design. The majority of the subsystems have completed the detailed design and now advancing towards the final design completion.

Assessment of the ITER EC Upper Launcher Performance

The 24 MW ITER Electron Cyclotron (EC) Heating and Current Drive (HC) system, operating at 170 GHz, consists of one Equatorial (EL) and four Upper Launchers (UL). The main task of the UL will be the control of Magneto-Hydrodynamic (MHD) activity such as Neoclassical Tearing Modes (NTMs) at the q=3/2 and q=2 surfaces, but it will also be needed for current profile tailoring in advanced scenarios and to assist plasma break-down and L-to H-mode transition. Moreover, it is required to be effective both when ITER will operate at nominal and reduced magnetic field magnitude. Here the performance of the UL is assessed through the study of the full temporal evolution of different scenarios, including the reference ITER 15MA H-mode plasma, a half-field case at 2.65T, and a steady state scenario. The ECCD efficiency has been evaluated for a wide range of injection angles, deriving the optimal angles and the power required for NTMs stabilization, as well as the steering range necessary to reach the rational surfaces during all the phases of the discharge. The steering sensitivity to shifts of the target or aiming errors has been estimated too. The result is an assessment of the UL design requirements to achieve the desired functionalities, which, together with the engineering limits, will be used to drive the optimization and finalization of the UL design.

Optimization of the ITER electron cyclotron equatorial launcher for improved heating and current drive functional capabilities

The design of the ITER Electron Cyclotron Heating and Current Drive (EC H&CD) system has evolved in the last years both in goals and functionalities by considering an expanded range of applications. A large effort has been devoted to a better integration of the equatorial and the upper launchers, both from the point of view of the performance and of the design impact on the engineering constraints. However, from the analysis of the ECCD performance in two references H-mode scenarios at burn (the inductive H-mode and the advanced non-inductive scenario), it was clear that the EC power deposition was not optimal for steady-state applications in the plasma region around mid radius. An optimization study of the equatorial launcher is presented here aiming at removing this limitation of the EC system capabilities. Changing the steering of the equatorial launcher from toroidal to poloidal ensures EC power deposition out to the normalized toroidal radius ρ ≈ 0.6, and nearly doubles the EC driven current around mid radius, without significant performance degradation in the core plasma region. In addition to the improved performance, the proposed design change is able to relax some engineering design constraints on both launchers.

Prototyping of the Blanket Shield Module for the ITER EC H&CD Upper launcher

The design of the ITER Electron Cyclotron Heating and Current Drive (ECH&CD) Upper launcher is recently in the first of two final design phases. The first phase deals with the finalization of all FCS (First Confinement System) components as well as with specific design progress for the remaining In-vessel components.The most outstanding structural In-vessel component of an ECH&CD Upper launcher is the Blanket Shield Module (BSM) with the First Wall Panel (FWP). Both of them form the plasma facing part of the launcher, which has to meet strong demands on dissipation of nuclear heat loads and mechanical rigidity. Nuclear heat loads from 3MW/m3 at the First Wall Panel’ surface, decaying down to a tenth in a distance of 0.5m behind of it will affect the BSM and the FWP. Additional heating of maximum 0.5MW/m2 due to plasma radiation must be dissipated from the FWP.To guarantee save and homogenous removal of such extensive heat loads, the BSM is designed as a welded steel-case with specific cooling channels inside its wall structure. Attached to its face side is the FWP with a high-power cooling structure.Based on computational analysis the optimum cooling channel geometry has been investigated. Specific pre-prototype tests have been made and associated assembly parameters have been determined in order to identify optimum manufacturing processes and joining techniques, which guarantee a robust design with maximum geometrical accuracy.This paper describes the design, manufacturing and testing of a full-size mock-up of the BSM. The study was carried out in an industrial cooperation with MAN Diesel and Turbo SE.

ITER ECH&CD Upper Launcher: Design options and Remote Handling issues of the waveguide assembly

The ITER Electron Cyclotron Heating and Current Drive Upper Launcher, developed by the ECHUL-CA Consortium of Euratom Associations (CRPP, CNR, ITER-NL, IPF, IPP, KIT and Politecnico di Milano), is presently in its final design phase.The study presented here deals with design options and Remote Handling issues related to the waveguide assembly, an ensemble of mm-wave transmission line components mounted on a vacuum flange. This flange is part of the primary vacuum boundary of the ITER vessel. This paper describes the preliminary assessment of the RH compatibility of the sub-assembly, and a conceptual description of the maintenance actions to be performed on it.A comparison between two possible configurations for the tapers is reported: a waveguide integrated design, in which tapers are integral part of the in-plug waveguide, and an auxiliary shield integrated design, in which the tapers are integrated into the Auxiliary Shield.An important aspect in the design is to ensure the Remote Handling compatibility. Due to lack of space and limited dexterity of the slave manipulator, the general approach in defining the maintenance strategy is to avoid breaking the interfaces of the different components of the assembly, and to extract it from the Upper Port Plug as a single entity. An assessment on possible replacement procedure and the required tools are presented here.

The ITER EC H&CD Upper Launcher: Analysis of vertical Remote Handling applied to the BSM maintenance

This paper deals with Remote Handling activities foreseen on the Blanket Shield Module, the plasma facing component of the ITER Electron Cyclotron Heating and Current Drive Upper Launcher. The maintenance configuration considered here is the Vertical Remote Handling, meaning gravity acting along the launcher radial axis. The plant, where the maintenance under consideration is occurring, is the Hot Cell Facility Work Cell.The study here reported has been carried out within the presently ongoing EFDA Goal Oriented Training program on Remote Handling (GOT-RH), which aims to support ITER activities. This document and its contents have to be considered as part of a more vast RAMI analysis to be developed within the GOT-RH, which aims to maximize the Electron Cyclotron Heating and Current Drive system availability.The Baseline CAD model of the Electron Cyclotron Heating and Current Drive Upper Launcher is currently in its preliminary design phase and does not provide enough details for developing a fully detailed maintenance strategy. Therefore, through a System Engineering approach, a set of assumptions was conceived on the launcher structure, as a basis for development of a Remote Handling strategy. Moreover, to compare different design solutions related to the possibility of integrating a quasi-optical component into the Blanket Shield Module, a Trade-Off was made, and its contents are shown here.The outcome of this System Engineering approach has been formalized into Task Definition Forms whose contents are reported here. The Remote Handling strategy presented in this work will be tested in the near future both through Virtual Reality simulations and through prototype experiments.

High power millimeter wave experiment of torus diamond window prototype for ITER EC H&CD system

The design of the torus diamond window for the ITER electron cyclotron heating and current drive (EC H&CD) system has advanced considering a reliable and manufacturable structure. The diamond window prototype was fabricated based on the design and the high power experiment was carried out to verify the millimeter wave transmission capability. Transmission of 740kW-100s was demonstrated and no significant temperature increase of the window structure and no damage on the diamond disk were obtained. The temperature saturation of the cooling water for the window was observed and loss tangent of 7.8×10−6, which was the lowest value that we had ever obtained at JAEA, was evaluated. This result indicates that the diamond window design is feasible and promising the high power more than 1MW transmission.

High Performance Parallel Monte Carlo Transport Computations for ITER Fusion Neutronics Applications

Large scale neutronics calculations for radiation safety and machine reliability are required to support design activities for the ITER fusion reactor which is currently in phase of construction. Its large size and complexity of diagnostics, control and heating systems and ports, and also channel penetrations inside the thick blanket shielding surrounding the 14 MeV D-T neutron source are essential challenges for neutronics calculations. In the ITER tokamak geometry, the Monte Carlo (MC) method is the preferred one for radiation transport calculations. Due to the independence of particle histories, their tracks can be processed in parallel. Parallel computations on high performance cluster computers substantially increase number of sampled particles and therefore allow reaching the desired statistical precision of the MC results using the MCNP5 code. The MCNP5 parallel performance was assessed on the HPC-FF supercomputer. Use of CAD-based approach with high spatial resolution improves systematic adequacy of the MC geometry modeling. These achievements are demonstrated on radiation transport calculations for designing the Blanket Shield Module and Auxiliary Shield of the ITER Electron Cyclotron Heating (ECH) upper launcher. The spatial distributions of nuclear heating were analysed by using the graphical representation of the MCNP5 mesh-tally results in 2D and 3D plots.

High power millimeter wave experiment of ITER relevant electron cyclotron heating and current drive system

High power, long pulse millimeter (mm) wave experiments of the RF test stand (RFTS) of Japan Atomic Energy Agency (JAEA) were performed. The system consists of a 1 MW/170 GHz gyrotron, a long and short distance transmission line (TL), and an equatorial launcher (EL) mock-up. The RFTS has an ITER-relevant configuration, i.e., consisted by a 1 MW-170 GHz gyrotron, a mm wave TL, and an EL mock-up. The TL is composed of a matching optics unit, evacuated circular corrugated waveguides, 6-miter bends, an in-line waveguide switch, and an isolation valve. The EL-mock-up is fabricated according to the current design of the ITER launcher. The Gaussian-like beam radiation with the steering capability of 20°-40° from the EL mock-up was also successfully proved. The high power, long pulse power transmission test was conducted with the metallic load replaced by the EL mock-up, and the transmission of 1 MW/800 s and 0.5 MW/1000 s was successfully demonstrated with no arcing and no damages. The transmission efficiency of the TL was 96%. The results prove the feasibility of the ITER electron cyclotron heating and current drive system.

The EC H&CD Transmission Line for ITER

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

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.

Loss Estimate for ITER ECH Transmission Line Including Multimode Propagation

The ITER electron cyclotron heating (ECH) transmission lines (TLs) are 63.5-mm-diam corrugated waveguides that will each carry 1 MW of power at 170 GHz. The TL is defined here as the corrugated waveguide system connecting the gyrotron mirror optics unit (MOU) to the entrance of the ECH launcher and includes miter bends and other corrugated waveguide components. The losses on the ITER TL have been calculated for four possible cases corresponding to having HE11 mode purity at the input of the TL of 100, 97, 90, and 80%. The losses due to coupling, ohmic, and mode conversion loss are evaluated in detail using a numerical code and analytical approaches. Estimates of the calorimetric loss on the line show that the output power is reduced by about 5, ±1% because of ohmic loss in each of the four cases. Estimates of the mode conversion loss show that the fraction of output power in the HE11 mode is ~3% smaller than the fraction of input power in the HE11 mode. High output mode purity therefore can be achieved only with significantly higher input mode purity. Combining both ohmic and mode conversion loss, the efficiency of the TL from the gyrotron MOU to the ECH launcher can be roughly estimated in theory as 92% times the fraction of input power in the HE11 mode.

Progress on the ITER Upper Launcher Millimeter-Wave Design and Testing

The aim of the ITER electron cyclotron heating and current drive upper launcher (UL) is to control magnetohydrodynamic activity in the plasma, in particular neoclassical tearing modes, requiring a narrow and peaked deposition of the radio-frequency (rf) power.The millimeter-wave (mm-wave) system of the UL is optimized to ensure that the eight rf beams are all focused to a small beam width at the resonance location. The present design uses two mitre bends per beam and a focusing mirror for each set of four beams, orientating each set onto a single steering mirror (SM) to inject it into the plasma. The SM is rotated using a frictionless and backlash free pneumo-mechanical system. A first prototype of the SM has been constructed to demonstrate the manufacturability and the actuation principle and to develop an adequate control strategy.A test program has been developed to ensure the integrity of the launcher from the pre-build-to-print design phase (research and development) up to the tests after maintenance.This paper presents a general overview of the system, a description of the progress in the mm-wave optical layout, low-power tests, alignment specifications of the mm-wave components, and SM capabilities to meet the ITER requirements.

Design of a high power millimeter wave launcher for EC H&CD system on ITER

An optimization procedure of the quasi-optical system for a millimeter wave launcher is developed for the ITER electron cyclotron heating and current drive (EC H&CD) launcher. In the launcher, the radiated RF beams from eight corrugated waveguides are reflected sequentially by two mirrors and injected into a plasma through a small aperture in the blanket shield module on the top of the launcher. Using a steepest decent method, the heat load on the mirrors is successfully reduced to the acceptable level by flattening the RF power profile on the mirrors keeping the scattering of the RF power to a minimum from the mirrors. It is found that 20 MW injection will be acceptable even when the resistivity of 2.64 × 10 −8 Ωm for the surface of the mirror (dispersion strengthened copper, 151 °C assumed) is increased by a factor of ∼10 with a contamination.

Steady-state operation of 170 GHz–1 MW gyrotron for ITER

A 170 GHz gyrotron has been developed at JAEA, which has achieved operation of 1 MW/800 s and up to 55% efficiency. This is the first demonstration of a gyrotron achieving and even exceeding the ITER operating requirements of 1 MW/500 s and 50% efficiency. In addition the gyrotron demonstrated operation for 1 h with an output power of 0.6 MW. The oscillation was stable with all cooling water temperatures and vacuum pressure reaching equilibrium conditions during the pulse length at either power level. The successful operation was aided by a very low level of stray radiation (∼2% of the output power), which contributed to fast conditioning and stable operation. The output power from the gyrotron was coupled into an ITER sized corrugated waveguide (ϕ = 63.5 mm) via a matching optics unit with a total of 0.97 MW transmitted to the dummy load after two miter bends and ∼7 m of a waveguide without any trouble. These results give an encouraging outlook for the success of the ITER electron cyclotron heating and current drive system.

Detailed Beam-Pattern Calculations for the ITER Electron Cyclotron Heating and Current Drive Upper Launcher

Electron cyclotron resonance heating (ECRH) and electron cyclotron current drive systems in fusion-grade devices meet the severe requirements (in terms of high power handling capability, extended steering range, and room availability) that guide the design of complex multiple-mirror quasi-optical launchers. A valuable step in this process is a beam-pattern calculation in vacuum including relevant electromagnetic effects not easily included in analytical evaluations. In fact, the analytical approach is a means to study the design layout at a first order and is able to derive the relevant quantities as a function of the steering angle and of the beam path in a form suitable to interface with most of the currently available beam-tracing codes. On the other hand, electromagnetic calculations using physical optics tools provide a complete description of the resulting full beam pattern, including the effects of aberration, beam truncation, thermal deformation of the mirrors, and the surrounding structures. Moreover, numerical calculation with reliable and benchmarked codes is a very efficient way to test subsequent updates of a given launcher model, once the basic geometry has been implemented. In this paper, we discuss in particular the application of the GRASP® code to the case of the remote steering option for the ITER ECRH upper launcher.

Critical Design Issues of the ITER ECH Front Steering Upper Launcher

The front steering (FS) launcher is one of two concepts that have been considered for the ITER electron cyclotron heating upper launcher by the European Union. During the development of a detailed conceptual design, the team involved with the FS launcher project listed all of the critical issues associated with installing an FS launcher in the ITER upper port, and then work was concentrated on providing a solution to each of the critical design issues. A similar procedure was performed for the alternative launcher option (remote steering launcher). These actions helped the ITER International Team evaluate the two systems and then choose a final optimum launcher. This evaluation occurred at the end of 2005, with both systems having equivalent reliability, but the FS offered significant enhancement in the physics performance. These differences led ITER-IT to select the FS launcher as the reference design. The goal of this paper is to provide a generalized review of the critical design issues and their solutions as they pertain to the FS launcher. In addition, the overall design and performance of the FS launcher is given along with a brief description of an extended performance launcher design that relaxes the engineering constraints, while increasing the physics capabilities.

Electrical Powering Concept for ITER Electron Cyclotron Radio-Frequency Sources

The ITER electron cyclotron heating (ECH) baseline scheme (2001) is composed of 24 gyrotrons, each generating 1 MW of radio-frequency power at 170 GHz in addition to 3 gyrotrons (1 MW) at 120 GHz for breakdown assist. Considering an efficiency of ≥45%, which can be achieved with the depressed-collector–type gyrotron (CPD), the amount of electrical power would be in the range of 55 MW. This paper has two purposes. First, it presents requirements that will be imposed on the electrical power supplies with regard to the updated physics needs for ITER presently being discussed. Demanding parameters (like modulation capability, transient margin, and fault clearing) will be described. In this context, the consequences of those new requirements on the technical choices and the impact on the complexity of the power supplies will be discussed. Second, two possible schemes for the ITER reference power supply design for the ECH system will be compared. The advantages (and respective disadvantages) of each solution will be highlighted taking care of the requirements previously presented. In conclusion, a proposal is presented for a revised ECH power supply structure.

Transmission Line Technology for Electron Cyclotron Heating

We briefly review the history of transmission line technology for electron cyclotron heating (ECH) applications and then survey the major developments over the past few years. These developments are grouped by function. Papers in this special issue are highlighted. We concentrate on the transmission from a matching optics unit near a gyrotron microwave source to the location of a vacuum window near the plasma, without review of window and launcher technology. Prospects for components handling more than 1-MW continuous wave are reviewed. While both waveguide and free-space propagation are considered, a greater emphasis is placed on corrugated waveguide components in preparation for the ITER ECH system.

EU developments of the ITER ECRH system

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.