Search

Before the installation of the first ICRF launcher in WEST, dedicated RF, cold and hot leak tests have been performed in the TITAN test bed [ 1 , 2 ] (Bernard et al., 2011a,b). All the water circuits have been controlled in order to avoid any in-vessel leak. The impedance matching has been checked at low level (mW range) and the high RF voltage standoff has been validated at the nominal value of 27 kV peak. During the WEST C3a campaign, the commissioning of the first antenna has been successfully performed. About 0.6 MW of power has been coupled to the plasma, and the launcher’s load-resilience has been proved.

International audience; Plasma heating in the full Tungsten (W) Environment in Steady-state Tokamak (WEST) relies on electromagnetic waves in both Lower Hybrid (LH) and Ion Cyclotron Range of Frequencies (ICRF). The present study focuses mostly on the optimization of discharges heated with ICRF, by reporting different methods to first optimize wave coupling, optimize their absorption and reduce the impurity production. It is shown that ICRF coupling can be optimized either by moving the plasma closer to antennas, increasing the plasma density, wave frequency and LH power. We show that the absorption efficiency correlates with the hydrogen concentration with the existence of an optimum between 7 and 10% as expected for a minority heating scenario. Absolutely calibrated visible spectroscopy sightlines were used to monitor ion fluxes in different locations as part of an effort to quantitively estimate the contribution of different impurity sources to the core contamination by tungsten. It is typically found that in discharges with high total RF-power (above 5MW of LH and 3MW of ICRF), divertor and antenna limiter sources can reach similar order of magnitude during the ICRF phase.

Within the large scale fusion experimental device ITER, Ion Cyclotron Resonance Heating (ICRH) system is one of the three heating systems which will supply total heating power of 20 MW (40-55 MHz) up to one hour operation. Radio-Frequency (RF) contacts are integrated within the antennas for assembly and operation considerations, which will face extremely harsh service conditions, including neutron irradiation, heavy electrical loads (RF current reaches up to 2 kA with a linear current density of 4.8 kA/m), high thermal loads and also long-duration vacuum baking at 250°C before each experimental plasma campaign. CuCrZr and 316L steel have been shown to be proper base candidate materials for ITER RF contact louvers and conductors respectively. However, in order to limit the wear and the diffusion phenomena at the RF contact as well as to reduce the contact resistance, functional protective layers should be developed. The aim of this work is to investigate Au-Ni and Rh functional layers, electroplated on CuCrZr and 316L respectively. The efficiency of the Au-Ni/Rh coated pairs was evaluated through thermal ageing diffusion tests, using EDS cross-section mapping and XRD techniques. Wear and electrical contact performances of the Au-Ni/Rh original and thermally aged pairs have also been deeply studied on a dedicated tribometer operated at ITER relevant conditions.

The ITER Ion Cyclotron Resonance Heating (ICRH) system is designed to couple to the plasma 20 MW of RF power from two antennas in the 40-55 MHz frequency range during long pulses of up to 3600 s and under various plasma conditions with Edge Localized Modes. Radio-Frequency (RF) contacts are integrated within the ITER ICRH launcher in order to ensure the RF current continuity and ease the mechanical assembly by allowing the free thermal expansion of the Removable Vacuum Transmission Line coaxial conductors during RF operations or during 250{\textdegree}C baking phases. A material study has been carried out to determine which materials and associated coatings are relevant for RF contacts application in ITER. In parallel, RF tests have been performed with a new prototype of Multi-Contact (r) LA-CUT/0,25/0 contacts made of silver-coated CuCrZr louvers. During these tests on a RF vacuum resonator, currents between 1.2 kA and 1.3 kA peak have been reached a few tens of times in steady-state conditions without any visible damage on the louvers. A final 62MHz pulse ending in a 300s flat top at 1.9kA resulted in severe damage to the contact. In addition, a test bed which performs sliding test cycles has been built in order to reproduce the wear of the contact prototype after 30 000 sliding cycles on a 3 mm stroke at 175{\textdegree}C under vacuum. The silver coating of the louvers is removed after approximately a hundred cycles whilst, to the contrary, damage to the CuCrZr louvers is relatively low., Fusion Engineering and Design, Elsevier, A Para{\^i}tre

International audience; Three identical new WEST Ion Cyclotron Resonance Heating (ICRH) antennas have been designed, assembled then commissioned on plasma from 2013 to 2019. The WEST ICRH system is both load-resilient and compatible with long-pulse operations. The three antennas have been successfully operated together on plasma in 2019 and 2020. The load resilience capability has been demonstrated and the antenna feedback controls for phase and matching have been developed. The breakdown detection systems have been validated and successfully protected the antennas. The use of ICRH in combination with Lower Hybrid has triggered the first high confinement mode transitions identified on WEST.

This paper presents a new type of slow-wave Lower Hybrid Current Drive launcher, based on the Slotted Waveguide Antenna (SWA) concept, which is particularly attractive for the use in future magnetic fusion reactors. A low power prototype SWA has been designed for the COMPASS tokamak at IPP-Prague. The Radio-Frequency (RF) design of this low power prototype is based on hybrid electromagnetic calculations, combining Finite-Element-Method, Mode Matching and RF network computations. Two SWA prototype samples have been manufactured with different slot geometries, and they have been first measured in air. The RF design of the low power SWA prototype and its feeding circuit is discussed in this manuscript; measurements in air are also illustrated.

International audience; The paper discusses the characterization of the three high power steady-state and load-resilient ICRF launchers of WEST before their installation in the tokamak. These launchers have been characterized and validated in low-power experiments (milliwatt range) as well as in experiments at the nominal RF voltages and currents in the TITAN vacuum chamber ($\sim$30 kV and 915 A peak). The successful commissioning of two of the launchers during the WEST C3 campaign at $\sim$1 MW power level is illustrated. Manual and real-time controlled impedance-matching of the launchers are discussed, as well as the validation of their load-resilience. Furthermore, several redundant and complementary protection systems have been validated and are reviewed in the paper.

This study compares experimental observations on the two challenges of Ion Cyclotron Resonance Heating (ICRH), namely the coupling of waves to the plasma and the enhanced impurity sputtering in EAST and WEST medium size tokamaks.In WEST, Lower Hybrid (LH) power helps improving ICRH coupling. In both machines experiments reveal that fueling from the midplane not only helps to couple waves from nearby antennas like in other devices, but also has an impact on the scrape-off layer (SOL) density in regions that are not magnetically connected to the valves. Localized midplane nozzle valves allow similar (in WEST) or better (in EAST) coupling compared to poloidally distributed valves. Core density control requirements for long-pulse operation, in particular in L-mode regime, however limit the amount of gas that can be injected.During ICRH impurities can contaminate the plasma up to a level detrimental for the operation, e.g. up to 100% of ICRH power can be radiated on WEST in certain high power conditions. In WEST, tungsten (W) production measured by visible spectroscopy increases on all the observed objects during ICRH compared to a reference phase without ICRH. On some components (antenna side limiters, baffle, divertor) the rise is larger than with a similar LH power. The relative contribution of each object and physical process (RF-sheaths, fast ion ripple losses) to core contamination yet remains poorly known. Comparing antenna limiters with W-coating vs low-Z materials would help quantifying the role of these components. In EAST, the core W content, measured by EUV spectroscopy in presence of divertor sources only, is correlated with the total injected power, either from ICRH or LH. Since 2018 the LH guard limiter tiles were W-coated. Their contribution to the core W content appears more important than divertor sources when two-strap ICRH antennas magnetically connected to W components at the midplane is powered, compromising high performance operations.

International audience; In 2018, Ion Cyclotron Resonant Frequency (ICRF) waves were for the first time applied to the WEST plasmascenarios. In ICRF-only plasmas at medium density, or on top of a low level of Lower Hybrid (LH) power, the coupledICRF power increases the plasma energy content. However in discharges with large LH power at high core density, nearlyall the applied ICRF power gets radiated, mainly in the plasma bulk. Both the energy content and conducted power decrease.Two peculiarities of WEST, that may combine, are presently invoked to explain this phenomenology:1) Fast ion ripplelosses, evidenced between TF coils on the baffle, likely degrade the ICRF heating efficiency. 2) RF-enhanced W sources,evidenced on several Plasma-Facing Components (PFCs), likely over-contaminate the high-power plasmas.

WEST represents the ideal device to test a reactor relevant travelling wave array (TWA) due to its long pulse capability and full metal wall configuration. Moreover, the already installed ICRF high power launchers will allow a direct comparison between a classical in-port antenna and the TWA. The design and exploitation of a high power (2 MW) TWA mock-up to be tested in TITAN represent the first step towards its integration in WEST. This paper presents the progress in the RF characterization of this high power mock-up. An integrated modelling scheme based on the full-wave code HFSS and on Python packages for RF circuit simulations is developed and used to parametrically analyse the response of the mock-up inside TITAN. The sensitivity of the antenna to geometrical deformations, e.g. thermal dilatation or manufacturing tolerances, is analysed. The use of trimmers to compensate those deformations is discussed and results from a manufactured trimmer test-bed are presented. A diagnostic system is proposed to measure electric field and current on the straps. Aspects like sensitivity and calibration are briefly discussed. In conclusion, the next steps of the project are outlined.

Radio-frequency (RF) contacts—which are an example of electrical contacts—are commonly employed on accelerators and nuclear fusion experimental devices. RF contacts with a current load of 2 kA for steady-state operation were designed for application to the International Thermonuclear Experimental Reactor (ITER) device. In contrast to the typical working conditions of general commercial electrical contacts, those of RF contacts employed on fusion devices include high vacuum, high temperature, and neutron radiation. CuCrZr is currently of interest as a base material for the manufacture of louvers of RF contacts, which has excellent thermal and electrical properties and has low creep rate at 250 °C. In this study, a hard Au coating (Au-Ni) was electroplated on CuCrZr samples and the samples were then subjected to thermal aging treatment at 250 °C for 500 h in order to simulate the vacuum-commissioning process of the ITER. The effects of thermal aging on the hardness, elastic modulus, crystallite size, and compositions of the coating were investigated via microstructural and mechanical characterizations of the coating material. Metal atom migration in different coating layers during thermal aging was characterized and evaluated via scanning electron microscopy/energy dispersive X-ray spectroscopy observations of the cross-sectional surfaces, and the obtained results could be used to directly select the coating thickness for the final RF contact component. The contact resistance—an important parameter of the RF contact—was measured in a dedicated testbed built to simulate fusion reactor conditions between CuCrZr pins and stainless steel plates coated with Au-Ni and Rh, respectively. Radio-frequency (RF) contacts-which are an example of electrical contacts-are commonly employed on accelerators and nuclear fusion experimental devices. RF contacts with a current load of 2 kA for steady-state operation were designed for application to the International Thermonuclear Experimental Reactor (ITER) device. In contrast to the typical working conditions of general commercial electrical contacts, those of RF contacts employed on fusion devices include high vacuum, high temperature, and neutron radiation. CuCrZr is currently of interest as a base material for the manufacture of louvers of RF contacts, which has excellent thermal and electrical properties and has low creep rate at 250 {\textdegree}C. In this study, a hard Au coating (Au-Ni) was electroplated on CuCrZr samples and the samples were then subjected to thermal aging treatment at 250 {\textdegree}C for 500 h in order to simulate the vacuum-commissioning process of the ITER. The effects of thermal aging on the hardness, elastic modulus, crystallite size, and compositions of the coating were investigated via microstructural and mechanical characterizations of the coating material. Metal atom migration in different coating layers during thermal aging was characterized and evaluated via scanning electron microscopy/energy dispersive X-ray spectroscopy observations of the cross-sectional surfaces, and the obtained results could be used to directly select the coating thickness for the final RF contact component. The contact resistance-an important parameter of the RF contact-was measured in a dedicated testbed built to simulate fusion reactor conditions between CuCrZr pins and stainless steel plates coated with Au-Ni and Rh, respectively.

Embedded RF contacts are integrated within the ITER ICRH launcher to allow assembling, sliding and to lower the thermo-mechanical stress. They have to withstand a peak RF current up to 2.5 kA at 55 MHz in steady-state conditions, in the vacuum environment of themachine.The contacts have to sustain a temperature up to 250{\textdegree}Cduring several days in baking operations and have to be reliable during the whole life of the launcher without degradation. The RF contacts are critical components for the launcher performance and intensive R&D is therefore required, since no RF contactshave so far been qualified at these specifications. In order to test and validate the anticipated RF contacts in operational conditions, CEA has prepared a test platform consisting of a steady-state vacuum pumped RF resonator. In collaboration with ITER Organization and the CYCLE consortium (CYclotronCLuster for Europe), an R&D program has been conducted to develop RF contacts that meet the ITER ICRH launcher specifications. A design proposed by CYCLE consortium, using brazed lamellas supported by a spring to improve thermal exchange efficiency while guaranteeing high contact force, was tested successfully in the T-resonator up to 1.7 kA during 1200 s, but failed for larger current values due to a degradation of the contacts. Details concerning the manufacturing of the brazed contacts on its titanium holder, the RF tests results performed on the resonator and the non-destructive tests analysis of the contacts are given in this paper., Comment: Fusion Engineering and Design, Elsevier, 2015, Available online 21 April 2015

The WEST-project ( W -tungsten E nvironment in S teady-state T okamak) involves equipping Tore Supra with a full tungsten divertor, capable of withstanding heat load of 10 MW/m2 in steady-state conditions, in discharges sustained by Lower Hybrid Current Drive (LHCD). The LHCD generator, recently upgraded to deliver 9.2 MW/1000 s, is equipped with sixteen TH2103C klystrons powering two launchers. The WEST transformation involves reducing the plasma volume, thus moving the launchers ∼10 cm closer to the tokamak centre. The toroidal curvature of the launchers no longer fits the plasma curvature due to the strong magnetic field ripple effect, leading to a degradation of the LH wave coupling, especially with the Full Active Multijunction Launcher (FAM). The toroidal curvature radius of the FAM launcher mouth will therefore be reshaped from 1700 mm to 2300 mm. The machining process is described in this article. In order to improve the coupling of the LH wave, the local gas injection has been modified to help to meet the requirement of 7 MW/1000 s of LH power coupled to the plasma in the WEST scenarios. Finally, the curvature radius of the waveguide septa are rounded to minimize the excitation of suprathermal electrons near the plasma edge, which can induce high power loads on the plasma facing components.

The WEST (Tungsten (W) Environment in Steady-state Tokamak) is an upgrade of Tore-Supra (TS) which aims it into an X -point magnetic configuration tokamak equipped with an actively cooled tungsten divertor. To be a platform of ITER technologies of high heat flux components testing, three sets of Ion Cyclotron Resonant Heating (ICRH) antennas have been designed to inject 9 MW during 30 s or 3 MW during 1000 s. The antenna design is based on a load resilient prototype successfully tested in Tore Supra in 2007. In order to allow continuous-wave (CW) operations, the mechanical design of the WEST ICRH antenna is emphasized on its cooling performances by designing fully active cooling structure. Two kinds of cooling water loops are used, with temperature and pressure of 70 °C/30 bar and 25 °C/5.2 bar, respectively. The hot water loop is used for the Faraday screen (FS) and the housing box (HB), while the cold water loop is used for the straps, the matching capacitors and the impedance transformer. To enhance the heat removal ability and control the pressure drop, the cooling channels in the FS and HB are drilled directly and parallel connected as much as possible. By performing the hydraulic–thermal analysis, the lack of cooling efficiency was found in the front face of lateral collector where 1 MW/m 2 is imposed and fluid dead zones were found in some of the bars. After optimization, the cooling performance of the cooling circuit increased significantly. With a mass flow rate of 2.5 kg/s, the total pressure drop is 3.1 bar, and the peak temperatures on the FS and HB are 500 °C and 261 °C, respectively. Besides, no cavitation is found in the total cooling circuit.

29th Symposium on Fusion Technology (SOFT), Prague, CZECH REPUBLIC, SEP 05-09, 2016; International audience; One of the key missions of the Ion Cyclotron Resonant Heating (IRCH) system for WEST is to provide sufficient RF heating power in order to obtain a heat flux on the divertor target of 10 MW/m(2) during 1000 s and 20 MW/m(2) during a few tens of seconds. Based on the experience acquired in Tore Supra, the ICRH system has been upgraded for long pulse operation and Edge Localized Modes (ELM) resilience. To achieve this performance, three antennas have been designed through a European collaboration and are now under fabrication at CAS/ASIPP, at the Keye Company, Hefei, in China, within the framework of the Associated Laboratory IRFM-ASIPP. This paper describes the electrical and mechanical design of the antenna, together with the main manufacturing steps and leak test procedure used for validating the water-cooled components. Accessibility and maintenance studies on WEST have been performed with the help of virtual reality. The first ICRH antenna was delivered at Cadarache in July 2016, and is foreseen to be installed on WEST in 2017. (C) 2017 Elsevier B.V. All rights reserved.

International audience; ITER is a large scale fusion experimental device under construction in Cadarache (France) intended to prove the viability of fusion as an energy source. Ion Cyclotron Resonance Heating (ICRH) system is one of the three heating systems which will supply total heating power of 20 MW (40-55 MHz) up to one hour of operation. Radio-Frequency (RF) contacts are integrated within the antennas for assembly and operation considerations, which will face extremely harsh service conditions, including neutron irradiation, heavy electrical loads (RF current reaches up to 2 kA with a linear current density of 4.8 kA/m) and high thermal loads. Based on the thermal analysis, the contact resistance is expected to be lower than 7 mΩ to keep the maximum temperature on the louvers lower than 250°C. Few weeks of vacuum (~10$^{-5}$ Pa) baking at 250°C for outgassing is expected before each plasma experimental campaign, under which the RF contact materials' mechanical properties change and diffusion phenomena between different materials are inevitable. CuCrZr and 316L are proper base materials for ITER RF contact louvers and conductors respectively. In order to improve the RF contact's wear and corrosion resistivity as well as to reduce the contact resistance, Au-Ni and Rh functional layers could be electroplated on CuCrZr and 316L accordingly. The application of the Au-Ni/Rh coating pairs is assessed through the thermal ageing and diffusion tests. Wear and electrical contact performances of the Au-Ni/Rh pairs are deeply studied on a dedicated tribometer operated at ITER relevant conditions.

The WEST project recently launched at Cadarache consists in transforming Tore Supra in an X-point divertor configuration while extending its long pulse capability, in order to test the ITER divertor technology. The implementation of a full tungsten actively cooled divertor with plasma facing unit representative of ITER divertor targets will allow addressing risks both in terms of industrial-scale manufacturing and operation of such components. Relevant plasma scenarios are foreseen for extensive testing under high heat load in the 10–20 MW/m2 range and ITER-like fluences (1000 s pulses). Plasma facing unit monitoring and development of protection strategies will be key elements of the WEST program. WEST is scheduled to enter into operation in 2016, and will provide a key facility to prepare and be prepared for ITER.

This year Tore-Supra celebrated its 25 years of operation. During this long time, a number of technologies have been developed. First of all, it was mandatory to develop reliable superconducting magnets at ∼1.8 K, with superfluid helium as an efficient coolant. For the production of steady state discharge, three types of radio frequency (RF) additional heating systems have been developed: 1) lower hybrid current drive; 2) ion cyclotron resonance heating; and 3) electron cyclotron resonance heating. To cope with long lasting discharges (up to 380 s × 2.8 MW) and large RF additional heating power (12.3 MW × 3 s), actively cooled (AC) plasma facing components were deployed in Tore-Supra for the first time in a tokamak environment. Tore-Supra is now being modified into a D-shape axisymmetric tokamak with AC tungsten main chamber walls and a divertor, the WEST project (W-for tungsten-environment in steady-state tokamak). This new facility has the objective to offer ITER a test bed for validating the relevant AC metallic technologies in D-shape H-mode plasmas. In contrast to other metallic devices, such as JET and ASDEX Upgrade, WEST will rely only on the RF additional power systems. A set of plasma scenarios have been identified, ranging from a high total RF power scenario up to 15 MW in 30 s, to a high fluence scenario of 1000 s with up to 10 MW of injected RF power. These scenarios are able to reproduce ITER relevant conditions of steady state heat loads of 10-20 MW/m2, to test tungsten AC divertor technologies with relevant power heat fluxes and particle fluence.

After the installation and commissioning of the TITAN [1] , [2] , test facility, a key element – the T resonator – was assembled in order to facilitate testing components at high RF voltages and currents. This work is within the CEA roadmap for testing ITER ICRH components in a relevant environment. Several components of the future ITER ICRH antenna have been targeted. The embedded RF contact within the ITER ICRH antenna appeared as a critical component for antenna performance, requiring extensive R&D. Therefore, CEA has proposed and subsequently prepared a platform to test and validate the anticipated RF contact. A steady state resonator with active water cooling has been manufactured and assembled within the TITAN facility, including a hot pressurized water loop. The program consists of testing the contact at 2.25 kA and 62 MHz in steady state conditions. Sliding tests are also performed at high temperature and vacuum to understand component aging, including wear. The equipment installed is consistent with that required to test an ITER ICRH extensively.

To develop Continuous Wave (CW) high power klystrons for fusion experiments, calorimetric matched loads absorbing the RF power are necessary. To test and adjust the parameters of the new klystrons TH2103C [1] able to produce 700 kW/CW at a frequency of 3.7 GHz for upgrading the RF power available in Tore Supra LHCD transmitter, SPINNER GmbH has successfully developed, in collaboration with the CEA, and manufactured a water load capable to absorb the RF power with a Voltage Standing Wave Ratio (VSWR)

First CW test bed, devoted for ion cyclotron resonance heating (ICRH), is being built at CEA Cadarache. It has been designed for testing the ICRH antenna sub assemblies under ITER relevant conditions (vacuum, cooling and RF). This paper presents a technical overview of these facilities and discusses their future operations in the framework of the ITER ICRH European R&D program.

A new Passive Active Multijunction (PAM) Lower Hybrid heating and Current Drive (LHCD) launcher, has been successfully manufactured and tested on Tore-Supra (TS). The design and the fabrication of this new actively cooled launcher based on the PAM concept, as the present ITER LHCD design, is a major component of the TS CIMES project (Components for the Injection of Matter and Energy in Steady-state), and will play a key role in the TS near term program. To achieve 1000 s pulses with a power flux of 25 MW/m 2 the PAM launcher has been designed for steady state (CW) operation (active cooling) with the objective of coupling 2.7 MW of LHCD power to the plasma at 3.7 GHz with a parallel index N ∥ = 1.7 ± 0.2. The launcher has achieved its qualifications tests, i.e. low power Radio Frequency measurements, vacuum and hydraulic leak tests, and has been installed on Tore-Supra tokamak in September 2009. It is commissioning on plasma started a month later, quickly achieving its design performance of 2.7 MW on a 35 s pulse. After a technical description of the PAM, this paper presents an overview of the project phases (RF optimization, manufacturing and qualification) and concludes with the first experimental results of the PAM.

Using the Tore Supra infrared thermography diagnostics, a new real time feedback control has been successfully implemented to maximize additional RF power while preventing plasma facing components (PFCs) from overheating and damage. As a first step, a thermography feedback control has been used to detect and extinguish electric arcs on lower hybrid current drive (LHCD) launchers. Secondly, heating sources on PFCs have been identified highlighting the role of the power from each ion cyclotron resonance heating (ICRH) antenna and LHCD launcher and the interactions between them. A new feedback control algorithm was developed to control the additional power. The real time feedback control of PFC temperatures which makes part of an integrated feedback controller, is a reliable tool routinely used as a basic protection system. Furthermore, it has proven its capability to operate in parallel with other control schemes such as the current profile control.

Since 1999 and with the help of Institut fur Plasmaphysik (IPP) Garching, we have tested in the Tore Supra (TS) Ion Cyclotron Resonance Heating (ICRH) transmitter, arc security systems based on harmonics detection in a frequency band lower than the generator frequency. These systems have some advantages in comparison with traditional protection systems, which are based on use of a level on the V r / V f (reflected to forward voltage ratio) calculation. After some checking for adjustment, they do not use calculation, calibration with frequency or level. They can use RF signals from directional couplers or probes, so they are fully independent of the measurement systems. The detection bandwidth is independent of the antennae working frequencies. In TS the detection principle is insensitive to the cross talk between the antennae and to the antennae coupling variations. In 2001, we have built three systems based on our prototype in order to improve the protection of the three ICRH antennae Q1, Q2 and Q5. The RF principle used on TS ICRH transmitter is described. The results in the last 4 years on an ICRH transmitter module feeding a TS antenna are summarized and some examples typical signals are given.

The project of an ITER-like (IL) ion cyclotron (IC) prototype antenna was initiated in mid 2002 in Cadarache, to assess the operational characteristics of the IL scheme in a Tore Supra (TS)-sized array. The prototype was developed by modifying an existing Tore Supra resonant double loop (RDL) antenna. This strategy, chosen to reduce cost and manufacturing time, allowed the completion of the array construction at the end of 2003. The array was installed on TS in January 2004, at the beginning of the new experimental campaign. After a few comments on the design, the paper reports results on low-power characterisation, high-power commissioning and preliminary tests on TS plasmas, prior to the array dis-assembly for inspection.

Ten years after the first ion cyclotron range of frequency (ICRF) heated Tore Supra (TS) plasma shot, and as TS facility, now equipped with the new ‘CIEL’ high power handing in-vessel components (This SOFT), is progressing towards long pulse performances, the main results and experience gained from the ICRF system are reviewed. An overview of the present status of TS ICRF facility is given, with highlights on the main modifications made to the initial plant and associated results. TS ICRF system achievements are then reported from a large ICRF heated pulses database covering ten experimental campaigns (1991–2001). The main technological issues encountered, especially those relevant to next step ICRF system design, are also discussed. Finally, in view of extended pulse length performances on TS, the present limitations of the ICRF facility and future plans are outlined.

ITER-like IC antennas, fulfilling or possibly exceeding ITER requirements and designed for long pulse operation (1000 s) are currently being developed at Cadarache. As part of these developments, a project of an IC antenna prototype obtained by modifying a tore supra (TS) resonant double loop (RDL) antenna is proposed, to assess in real working conditions the performance of this scheme. After a brief comparison between the new RF circuit version and the conventional RDL circuit, which has been tested in TS for 10 years, the paper focuses on the design and manufacturing aspects of the prototype.

Three new ion cyclotron resonance heating (ICRH) launchers have been designed for the WEST project (W-Tungsten Environment in Steady-state Tokamak) in order to operate at 3 MW/launcher for 30 s and 1 MW/launcher for 1000 s on H-mode plasmas. These new launchers will be to date the first ICRH launchers to offer the unique combination of continuous-wave (CW) operation at high power and load tolerance capabilities for coupling on H-mode edge. The radio-frequency (RF) design optimization process has been carried out using full-wave electromagnetic solvers combined with electric circuit calculations. Cavity modes occurring between the launchers structures and the vacuum vessel ports have been evaluated and cleared out.

SIDON (SImulator of raDiO-frequency Networks) is an in-house developed Radio-Frequency (RF) network solver that has been implemented to cross-validate the design of WEST ICRF launchers and simulate their impedance matching algorithm while considering all mutual couplings and asymmetries. In this paper, the authors illustrate the theory of SIDON as well as results of its calculations. The authors have built time-varying plasma scenarios (a sequence of launchers front-faces L-mode and H-mode Z-matrices), where at each time step (1 millisecond here), SIDON solves the RF network. At the same time, when activated, the impedance matching algorithm controls the matching elements (vacuum capacitors) and thus their corresponding S-matrices. Typically a 1-second pulse requires around 10 seconds of computational time on a desktop computer. These tasks can be hardly handled by commercial RF software. This innovative work allows identifying strategies for the launchers future operation while insuring the limitations on the currents, voltages and electric fields, matching and Load-Resilience, as well as the required straps voltage amplitude/phase balance. In this paper, a particular attention is paid to the simulation of the launchers behavior when arcs appear at several locations of their circuits using SIDON calculator. This latter work shall confirm or identify strategies for the arc detection using various RF electrical signals. One shall note that the use of such solvers in not limited to ICRF launchers simulations but can be employed, in principle, to any linear or linearized RF problem.

International audience; The nuclear fusion research goal is to demonstrate the feasibility of fusion power for peaceful purposes. In order to achieve the conditions similar to those expected in an electricity-generating fusion power plant, plasmas with a temperature of several hundreds of millions of degrees must be generated and sustained for long periods. For this purpose, RF antennas delivering multi-megawatts of power to magnetized confined plasma are commonly used in experimental tokamaks. In the gigahertz range of frequencies, high power phased arrays known as " Lower Hybrid " (LH) antennas are used to extend the plasma duration. This paper reviews some of the technological aspects of the LH antennas used in the Tore Supra tokamak and presents the current design of a proposed 20 MW LH system for the international experiment ITER.

The WEST ICRH system has to deal with two challenging issues that no other ICRH system before ITER has faced simultaneously so far, i.e. ELMs resilience and Continuous Wave (CW) RF operation. The technical solution chosen to meet the requests imposed by the WEST scenarios is to build three new launchers based on the RF structure successfully tested in short pulses in 2007 on Tore Supra prototype launcher. This paper gives an overview of the mechanical structure of the CW ELMs resilient WEST ICRH launchers. The technical solutions chosen to drive the mechanical design are presented, in regard of the past experience on the 2007 TS prototype, together with the significant work carried out on the mechanical design to improve the launcher structure. The thermal and electro-mechanical analyses conducted and their impact on the launcher design are also presented. These three new CW ELMs resilient ICRH launchers are foreseen to be installed on WEST in 2016, and operational for the first plasmas.

International audience; With WEST (Tungsten Environment in Steady State Tokamak) (Bucalossi et al 2014 Fusion Eng. Des. 89 [http://dx.doi.org/10.1016/j.fusengdes.2014.01.062] 907?12 ), the Tore Supra facility and team expertise (Dumont et al 2014 Plasma Phys. Control. Fusion 56 [http://dx.doi.org/10.1088/0741-3335/56/7/075020] 075020 ) is used to pave the way towards ITER divertor procurement and operation. It consists in implementing a divertor configuration and installing ITER-like actively cooled tungsten monoblocks in the Tore Supra tokamak, taking full benefit of its unique long-pulse capability. WEST is a user facility platform, open to all ITER partners. This paper describes the physics basis of WEST: the estimated heat flux on the divertor target, the planned heating schemes, the expected behaviour of the L?H threshold and of the pedestal and the potential W sources. A series of operating scenarios has been modelled, showing that ITER-relevant heat fluxes on the divertor can be achieved in WEST long pulse H-mode plasmas.

The longstanding expertise of the Tore Supra team in long pulse heating and current drive with radiofrequency (RF) systems will now be exploited in the WEST device (tungsten-W Environment in Steady-state Tokamak) [1]. WEST will allow an integrated long pulse tokamak programme for testing W-divertor components at ITER-relevant heat flux (10-20 MW/m2), while treating crucial aspects for ITER-operation, such as avoidance of W-accumulation in long discharges, monitoring and control of heat fluxes on the metallic plasma facing components (PFCs) and coupling of RF waves in H-mode plasmas. Scenario modelling using the METIS-code shows that ITER-relevant heat fluxes are compatible with the sustainment of long pulse H-mode discharges, at high power (up to 15 MW / 30 s at IP = 0.8 MA) or high fluence (up to 10 MW / 1000 s at IP = 0.6 MA) [2], all based on RF heating and current drive using Ion Cyclotron Resonance Heating (ICRH) and Lower Hybrid Current Drive (LHCD). This paper gives a description of the ICRH and LH...

International audience; The design of the WEST (Tungsten-W Environment in Steady-state Tokamak) Ion cyclotron resonance heating antennas is based on a previously tested conjugate-T Resonant Double Loops prototype equipped with internal vacuum matching capacitors. The design and construction of three new WEST ICRH antennas are being carried out in close collaboration with ASIPP, within the framework of the Associated Laboratory in the fusion field between IRFM and ASIPP. The coupling performance to the plasma and the load-tolerance have been improved, while adding Continuous Wave operation capability by introducing water cooling in the entire antenna. On the generator side, the operation class of the high power tetrodes is changed from AB to B in order to allow high power operation (up to 3 MW per antenna) under higher VSWR (up to 2:1). Reliability of the generators is also improved by increasing the cavity breakdown voltage. The control and data acquisition system is also upgraded in order to resolve and react on fast events, such as ELMs. A new optical arc detection system comes in reinforcement of the V r /V f and SHAD systems.

The tokamak Tore Supra (TS) has been operated since 1988 in Cadarache Centre. With the Composants Internes et Limiteur project, it will be the only machine to be able to exploit the Advanced Tokamak Regimes in steady state operation with three heating systems ICRH, LH, ECRH. The injected RF power in the Torus is a very important parameter of the total energy balance of TS, for this reason we need the best possible knowledge of these powers. The analysis and the explanation of the different RF techniques at low power which have been used in TS on the three RF systems will be described. Principles of the different measurement systems are given. The calibration methods of these systems are discussed and the present status of the calibration uncertainties of the RF measurements is analysed. Finally, when the generators are connected to a dummy load, RF measurements are compared with the calorimetric power measurements. This study allows preparation of improvements of these systems which will be used in these next steps: Composants pour l'Injection de Matiere et d'Energie Stationnaire project (B. Beaumont, Tore Supra steady state power and particles injection: the CIMES project, in: Proceedings of the 21st SOFT, Madrid, 2000).

During the 1997 and 1998 Tore Supra shutdown, a first set of new antenna guard limiters was installed on one of the three ion cycloton resonance heating (ICRH) antennas of Tore Supra. This limiter, which was one of the main technological studies of the 1998 campaign, was widely experimented in real plasma conditions, thus allowing the validation in situ, for the first time, of the technology of active metal casting (AMC) for plasma facing components. The huge improvement in the thermal response of the new limiter generation, compared to the old one, is shown on plasma pulses made identical in terms of antenna position and injected RF power profile. By using the infrared cameras installed inside Tore Supra and viewing the antennas front, the power density fluxes received by the carbon fibre composite (CFC) surface of the limiter were evaluated by correlation with the heat load tests made on the electrons beam facility of CEA/Framatome.

Tore Supra is dedicated to long pulse operation at high power, with a record in injected energy of 1 GJ (2.8 MW × 380 s) and an achieved capability of 12 MW injected power delivered by 3 RF systems: Lower Hybrid Current Drive (LHCD), Ion Cyclotron Resonance Heating (ICRH) and Electron Cyclotron Resonance Heating (ECRH). The new WEST project (W [tungsten] Environment in Steady-state Tokamak) aims at fitting Tore Supra with an actively cooled tungsten coated wall and a bulk tungsten divertor. This new device will offer to ITER a test bed for validating the relevant technologies for actively cooled metallic components, with D-shaped H-mode plasmas. For WEST operation, different scenarii able to reproduce ITER relevant conditions in terms of steady state heat loads have been identified, ranging from a high RF power scenario (15 MW, 30 s) to a high fluence scenario (10 MW, 1000 s). This paper will focus on the evolution of the RF systems required for WEST. For the ICRH system, the main issues are its ELM resilience and its CW compatibility, three new actively cooled antennas are being designed, with the aim of reducing their sensitivity to the load variations induced by ELMs. The LH system has been recently upgraded with new klystrons and the PAM antenna, the possible reshaping of the antenna mouths is presently studied for matching with the magnetic field line in the WEST configuration. For the ECRH system, the device for the poloidal movement of the mirrors of the antenna is being changed for higher accuracy and speed.Tore Supra is dedicated to long pulse operation at high power, with a record in injected energy of 1 GJ (2.8 MW × 380 s) and an achieved capability of 12 MW injected power delivered by 3 RF systems: Lower Hybrid Current Drive (LHCD), Ion Cyclotron Resonance Heating (ICRH) and Electron Cyclotron Resonance Heating (ECRH). The new WEST project (W [tungsten] Environment in Steady-state Tokamak) aims at fitting Tore Supra with an actively cooled tungsten coated wall and a bulk tungsten divertor. This new device will offer to ITER a test bed for validating the relevant technologies for actively cooled metallic components, with D-shaped H-mode plasmas. For WEST operation, different scenarii able to reproduce ITER relevant conditions in terms of steady state heat loads have been identified, ranging from a high RF power scenario (15 MW, 30 s) to a high fluence scenario (10 MW, 1000 s). This paper will focus on the evolution of the RF systems required for WEST. For the ICRH system, the main issues are its ELM resil...

A new concept of multijunction-type antenna has been developed, the Passive Active Multijunction, which improves the cooling of the waveguides and the damping of the neutron energy (for ITER) compared to Full Active Multijunction. Due to the complexity of the structures, prototypes of the mode converters and of the Passive-Active-Multijunction launcher were fabricated and tested, in order to validate the different manufacturing processes and the manufacturer's capability to face this challenging project. This paper describes the manufacturing process, the tests of the various prototypes and the construction of the final Passive-Active-Multijunction launcher, which entered into operation in October 2009. It has been commissioned and is fully operational on the Tore-Supra tokamak, since design objectives were reached in March 2010: 2.75 MW - 78 s, power density of 25MW/m2 in active waveguides, steady-state apparent surface temperatures < 350 °C; 10 cm long distance coupling.

The main results of the Tore Supra experimental programme in the years 2007–2008 are reported. They document significant progress achieved in the domain of steady-state tokamak research, as well as in more general issues relevant for ITER and for fusion physics research. Three areas are covered: ITER relevant technology developments and tests in a real machine environment, tokamak operational issues for high power and long pulses, and fusion plasma physics. Results presented in this paper include test and validation of a new, load-resilient concept of ion cycotron resonance heating antenna and of an inspection robot operated under ultra-high vacuum and high temperature conditions; an extensive experimental campaign (5 h of plasma) aiming at deuterium inventory and carbon migration studies; real-time control of sawteeth by electron cyclotron current drive in the presence of fast ion tails; ECRH-assisted plasma start-up studies; dimensionless scalings of transport and turbulence; transport experiments using active perturbation methods; resistive and fast-particle driven MHD studies. The potential role of Tore Supra in the worldwide fusion programme before the start of ITER operation is also discussed.

A prototype of an ICRF antenna based on the load‐resilient electrical layout foreseen for ITER has been built at CEA‐Cadarache [1]. It consists of a two resonant double loop (RDL) based on the conjugate‐T concept proposed for the ITER ICRF array arranged toroidally in a close package. The antenna conditioning and commissioning have been successfully performed to validate the load resilience and the heating capability at the end of 2007. On Tore Supra despite unexciting ELMs, the load resilience studies have been conducted in L‐mode by mean of slow variations of the plasma position and fast transient variations with both pellet injection and Supersonic Molecular Beam Injection (SMBI). The capability to maintain the RF power on the ITER‐like antenna has been done successfully contrary to the classical ICRF antenna during the SMBI shots, in which the corresponding transient coupling resistance increased by a factor 3–4. In term of coupled power, a maximum power density of 6.6 MW/m2 is reached.

Since the release of the ITER ICRH system reference design report [ITER Final Design Report: DDD 5.1 –Ion Cyclotron and Current Drive System, July 2001], further design studies have been conducted. If the base of the reference design [Final Report on EFDA contract 04/1129, ITER ICRF antenna and Matching system design (Internalmatching), April 2005] is kept unchanged, several significant modifications have been proposed for a better efficiency and reliability. The increase of the poloidal order of the array and strong modifications of the matching system concept are the main changes. Technical aspects insufficiently covered in previous studies are also now worked out in detail, like the integration on a mid-plane port satisfying the constraints of the ITER environment.

The Tore Supra ICRH antennas, built in collaboration with ORNL according to the Resonant Double Loop concept, have been used for many years in various experimental schemes. In the frequency range between 35 to 80 MHg they have contributed to meet the initial aim of the Tore Supra tokamak: to operate at a plasma current up to 1.7 MA, over 30 seconds or with a heating power higher than 10 MW. Based on the experience gained, the next step, aiming at high power operation up to 25 MW with long pulse discharges (1000 s), is scheduled on Tore Supra.

On each of the Tore Supra ICRH antennas [ 1 ], 4 variable vacuum capacitors supplied by COMET * are used to match the antenna feed point impedance to the generator output impedance. On such a system, the whole transmission line is working near matched conditions, and high RF voltages are limited to the front part of the antenna. The quality, performance and reliability of the COMET capacitors, fixed or variable type, have been proved by thousands of units in operation in high power oscillators and amplifier circuits. The variable type (10 to 150 pF) fitted in Tore Supra antennas has allowed remarkable results. A record radiated power density of 1.6 kW/cm 2 , has been achieved, and RF peak voltages in excess of 40 kV are commonly used during plasma shots. However, by construction of the capacitor, a water cooled bellows on the RF current path limits the velocity of the capacitance variation. Reliable RF experiments during transients phenomena like pellet injection, monsters sawteeth or plasma displacements require the matching system to follow rapid variations of loads. Therefore, a new concept of variable vacuum capacitor allowing faster capacitance adjustment, is studied in collaboration with COMET. In this concept, the RF current flows through a sliding contact strip from PANTECHNIK + working in the sealed vacuum. The RF current path is therefore dissociated from the vacuum barrier. Sliding contacts, both in vacuum conditions and handling high RF current are not in common use in the RF field and have to be tested. This paper describes the existing variable capacitor, the new capacitor concept, the RF contact test device as well as the experimental results.

The paper gives a picture of the present status and understanding of technology and physics of Lower Hybrid Current Drive for long pulse operation in tokamaks, including the development of continuous wave (CW) high power klystrons, and its evolutions towards ITER. 3.7 GH / 700 kW CW klystrons produced in series by Thales Electron Devices are now in operation on Tore Supra. First series of eight klystrons delivered more than 4 MW to sustain non-inductive plasmas during 50 s. Moreover, a prototype of 500 kW CW klystron operating at 5 GHz developed for KSTAR by Toshiba Electron Tubes and Devices, and foreseen for ITER, is able to produce RF output powers of 300 kW / 800 s and 450 kW / 20 s on matched load. The situation on wave coupling and antennas is reported, with the latest Tore Supra results of the new CW Passive-Active Multi-junction (PAM) launcher: the antenna concept foreseen for ITER. First experiments with the PAM antenna in Tore Supra have provided extremely encouraging results in terms of power handling and coupling. Relevant ITER power density of ∼25 MW/m 2 (2.7 MW of power injected into the plasma) has been maintained over ∼80 s. In addition, LH power of 2.7 MW has been coupled at a plasma-antenna distance of 10 cm.

For a given ICRF power, the sawtooth‐free period duration increases with plama density. This trend, correlated with an increasing soft X‐ray inversion radius, clearly shows a better stabilization by hot ions at higher density. A tentative explanation is given through a full modeling of the hot ion anisotropy using a Fokker Planck code coupled with a 1/2 D power balance code simulating experimental data. A linear stability analysis of the kink/tearing m=1 mode, in terms of a MHD kinetic functional, shows that the anisotropy of the distribution function may amplify the effect of the hot ion pressure gradient. A two‐fold lengthening of the sawtooth‐free period is obtained when applying LHCD to ICRF heated plasmas. Analysis of polarimetric data shows that, instead of the continuous decrease of the central safety factor observed when using ICRF alone, the q value ‘‘freezes’’ when LHCD power exceeds 3 MW. This demonstrates a current profile control effect opening the way towards steady‐state stabilization. Work...

A new ITER-relevant lower hybrid current drive (LHCD) launcher, based on the passive-active-multijunction (PAM) concept, was brought into operation on the Tore Supra tokamak in autumn 2009. The PAM launcher concept was designed in view of ITER to allow efficient cooling of the waveguides, as required for long pulse operation. In addition, it offers low power reflection close to the cut-off density, which is very attractive for ITER, where the large distance between the plasma and the wall may bring the density in front of the launcher to low values. The first experimental campaign on Tore Supra has shown extremely encouraging results in terms of reflected power level and power handling. Power reflection coefficient −2, i.e. its design value at f = 3.7 GHz. In addition, 2.7 MW has been coupled at a plasma–launcher distance of 10 cm, with a power reflection coefficient

Travelling wave array (TWA) antennas have been proposed for the ICRH (Ion Cyclotron Resonance Heating) antennas of fusion reactors in view to decreasing the antenna voltage and associated electric field. This paper reports the progress of the design and structural analysis of an actively cooled high power TWA antenna for WEST. First, the design of a non-cooled mock-up that will be tested in the TITAN facility is presented. The main objective is to assess the voltage stand-off of the antenna at power and electric field levels relevant for future nominal operation in a fusion device. The main characteristics of the mock-up are detailed and the results from thermal and structural analysis of the mock-up tested in TITAN are presented. In the second part, the compatibility with WEST environment for an actively-cooled TWA antenna is assessed. Mechanical, electromagnetic, thermal and hydraulics constrains (.i.e VDE, plasma radiation, toroidal magnetic field ripple…) are listed in a system loads specification. A Virtual Reality analysis using IRFM tools has been performed to check compliance of the design in term of assembly inside the WEST vacuum vessel.