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Recent experiments performed in JET at high level of plasma heating, in preparation of, and during the DT campaign have shown significant discrepancies between electron temperature measurements by Thomson Scattering (TS) and Electron Cyclotron Emission (ECE). In order to perform a systematic analysis of this phenomenon, a simple model of bipolar distortion of the electron distribution function has been developed, allowing analytic calculation of the EC emission and absorption coefficients. Extensive comparisons of the modelled ECE spectra (at both the 2nd and the 3rd harmonic extraordinary mode) with experimental measurements display good agreement when bulk electron distribution distortions around 1-2 times the electron thermal velocity are used and prove useful for a first level of analysis of this effect.

For high-temperature JET and TFTR discharges, electron cyclotron emission (ECE) measurements of central electron temperature were systematically found to be up to 20% higher than those taken with Thomson scattering. In recent high-performance JET discharges, central Te measurements, performed with LIDAR Thomson scattering and the X-mode ECE interferometer, have been studied in a large database, including deuterium (DD), and deuterium-tritium plasmas (DT). Discrepancies between Te measurements have been observed outside of the experimental uncertainties. ECE measurements, at high Te, have been found to be higher or lower than those of LIDAR, depending on the specific plasma scenario. In addition, discrepancies between the peaks of the second and third harmonic ranges of the ECE spectrum have been interpreted as evidence for the presence of non-Maxwellian features in the electron distribution function. These comparisons seem to suggest that such features can be found in most of the high-performance scenarios selected in this JET database.

Electron Cyclotron (EC) waves will be routinely used in future reactors not only for plasma heating and/or non-inductive current drive during the flat top but also to assist the plasma start-up phase in large tokamaks with superconductive coils. In ITER, for example, EC start-up is foreseen since first plasma operation. To limit the level of stray radiation, ECRH can be used after ohmic breakdown, as a robust solution to successfully sustain the plasma burn-through in the presence of pre-filling gas and impurity influx from the wall. On ASDEX Upgrade (AUG), a series of dedicated experiments have been performed using EC heating (X2) with a controlled Ne impurity injection in the prefill phase, to mimic non-favourable burn-through conditions such as would be expected in a discharge following a disruption event. The time for EC heating onset has been optimised to assist the early burn-through and a scan of the Ne concentration has been performed to find the threshold for successful burn-through conditions for two ECH power levels (0.7 and 1.4 MW). The toroidal magnetic field flexibility has been also documented, with the cold resonance position being shifted up to 13% in major radius to match the ITER condition. These experiments showed that optimised settings of ECH power (onset and duration of the pulse) have a key role in making feasible the early Ne burn-through (with Ne concentration up to 14% and EC power of 1.4 MW). Successful pulses will be extended to study stationarity and clean up properties. For an efficient and robust use of such a technique, it is essential to develop appropriate models capable of describing present experiments and of extrapolating (or predicting) to future scenarios. In this work, the predictive 0D model for the burn-though phase BKD0 [1] has been used to reproduce experimental results and estimate the power required for a successful burn-through as a function of the impurity concentration, finding that ECH power of 1.4 MW is required to sustain burn-through with more than 20% of Ne. The scalability of the model has been also tested on TCV [2] and its implication for ITER will be discussed.

Understanding the propagation of high power mm-wave in plasmas is of tremendous importance in the route to fusion considering their extensive use in magnetically confined fusion devices. Mm-beams, launched from the outside of the vessel must propagate through plasma edge-turbulence before reaching their target region. Until recently, the effect of edge-turbulence on the beam propagation was neglected, but it has been estimated for ITER that it could lead to significant differences in the time-averaged and instantaneous beam profiles, leading to a loss of efficiency in their use. In this paper, we present first direct experimental measurements of high power beam after propagation in simple magnetized toroidal plasmas in TCV.

The electron cyclotron (EC) system of ITER for the initial configuration is designed to provide 20MW of RF power into the plasma during 3600s and a duty cycle of up to 25% for heating and (co and counter) non-inductive current drive, also used to control the MHD plasma instabilities. The EC system is being procured by 5 domestic agencies plus the ITER Organization (IO). F4E has the largest fraction of the EC procurements, which includes 8 high voltage power supplies (HVPS), 6 gyrotrons, the ex-vessel waveguides (includes isolation valves and diamond windows) for all launchers, 4 upper launchers and the main control system. F4E is working with IO to improve the overall design of the EC system by integrating consolidated technological advances, simplifying the interfaces, and doing global engineering analysis and assessments of EC heating and current drive physics and technology capabilities. Examples are the optimization of the HVPS and gyrotron requirements and performance relative to power modulation for MHD control, common qualification programs for diamond window procurements, assessment of the EC grounding system, and the optimization of the launcher steering angles for improved EC access. Here we provide an update on the status of Europe’s contribution to the ITER EC system, and a summary of the global activities underway by F4E in collaboration with IO for the optimization of the subsystems.

Electron cyclotron waves injected from an antenna located in the upper part of the vessel will be employed in ITER to controlMHD instabilities, particularly neoclassical tearingmodes (NTMs). The derivation of the NTM stabilization criteria used up to now to guide the optimization of the launcher is reviewed in this paper and their range of validity elucidated. Possible effects leading to a deterioration of the predicted performance through a broadening of the EC deposition profile are discussed. The most detrimental effect will likely be the scattering of the EC beams from density fluctuations, resulting in a beam broadening in the 100% range. The combined impact of these effects with that of beam misalignment (with respect to the targeted surface) is discussed for a time slice of the standard Q = 10 H-mode scenario.

The current drive efficiency of the dual frequency (110 GHz and 138 GHz) ECRF system of JT-60SA is studied. The requirements for neoclassical tearing modes (NTMs) instabilities control by ECRF during the initial research phase when only part of the full system will be available are discussed.

Assistance of EC wave for plasma breakdown and current ramp up is the proposed scenario for the ITER case, characterized by low toroidal electric field. The experimental results on many tokamaks clearly indicate the capabilities of the proposed scheme to have a robust breakdown in ITER. The key aspect of this technique is the EC power required, strongly related to the absorption of the wave in the initial stage of plasma formation. This aspect is generally neglected due to the diagnostics difficulties in the plasma formation phase. As a consequence a multi-pass absorption scheme is usually considered reasonable, leading to a strong absorption after many reflections on the walls. The present study exploits the high temporal and spatial resolution of the fast scanning interferometer of FTU together with the measure of residual power obtained by a sniffer probe. The absorbed EC power is calculated considering also the polarization rotation and the subsequent mode conversion after incidence on the internal wall and compared with that derived from experimental data. The resulting EC power distribution can explain differences observed between perpendicular and oblique injection results, indicating future investigations to define ITER power requirements.

The achievable efficiency for external current drive through electron-cyclotron (EC) waves in a demonstration tokamak reactor is discussed. Two possible reactor designs, one for steady state and one for pulsed operation, are considered. It is found that for midplane injection the achievable current drive efficiency is limited by secondharmonic absorption at levels consistent with previous studies. Propagation through the second-harmonic region can be reduced by moving the launch position to the high-field side (this can be obtained by injecting the beam from an upper port in the vacuum vessel). In this case, beam tracing calculations deliver values for the EC current drive efficiency approaching those usually reported for neutral beam current drive.

The Real-Time system for the control of the magnetohydrodynamics instabilities in FTU tokamak is presented. It is based on both a-priori information derived from statistical treatment of a database and Real-Time elaboration of live diagnostics data. The analysis codes are executed in different time threads based on multi-processors machines. The actuator is the 2×0.4MW 140 GHz ECRH system equipped with the new fast quasi-optical steerable launcher.

The ITER Electron Cyclotron Equatorial Launcher is designed to be one of the heating systems to assist and sustain the development of various ITER plasma scenarios starting with the very first plasma operation. Here the capabilities for Heating and Current Drive of this system are reviewed. In particular, the optimum launching conditions are investigated for two scenarios at burn, comparing toroidal and poloidal steering options. Then, the EC capabilities are investigated for different plasma parameters corresponding to various phases of the ITER plasma discharge, from current ramp-up up to burn, and for a wide range of magnetic field, focusing in particular on the EC potential for heating and for L to H-mode assist. It is found that the EC system can contribute to a wide range of heating scenarios during the ramp-up of the magnetic field, significantly increasing the applicable range as a function of magnetic field.

The Electron Cyclotron (EC) fast launcher for real time control experiments has been installed on FTU and characterized to be fully integrated in a real-time MHD control module under development. The launcher scheme is based on a two module system, symmetric with respect to the equatorial plane of FTU, with a front steering concept and the launched beams are real-time controllable both in poloidal and toroidal directions. Specific design parameters, defined by the FTU MHD dynamics (typically island size and q profile changes), are the beam dimensions with zooming capabilities, the steering range and mirror speed with the most demanding requirement on poloidal speed of the Steering Mirror (SM) Δθ = 1° in 10 ms. A set of tests has been done to verify the system performance. High power tests of the launcher have been done on a 500 kA, 0.5·1020m−3 and 5.3 T plasma with 2·300 kW of EC power delivered to the plasma. The steering mechanism was tested under the automatic control system and showed a dynamic response in line with the requirements. Results of these tests will be presented in the paper.

Electron cyclotron resonance heating (ECRH) and electron cyclotron current drive (ECCD) are used to heat the plasma, to tailor the current profiles and to achieve different operating regimes of tokamak plasmas. Plasmas with ECRH/ECCD are characterized by non-thermal electrons, which cannot be described by a Maxwellian distribution. Non-thermal electrons are also generated during MHD activity, like sawteeth crashes. Quantifying the non-thermal electron distribution is therefore a key for understanding EC heated fusion plasmas. For this purpose a vertical electron cyclotron emission (V-ECE) diagnostic is being installed at TCV. The diagnostic layout, the calibration, the analysis technique for data interpretation, the physics potentials and limitations are discussed.

ITER is of key importance in the European fusion roadmap as it aims to prove the scientific and technological feasibility of fusion as a future energy source. The EUROfusion consortium of labs within Europe is contributing to the preparation of ITER scientific exploitation and operation and aspires to exploit ITER outcomes in view of DEMO. The paper provides an overview of the major progress obtained recently, carried out in the frame of the new (initiated in 2021) EUROfusion work-package called ' Pr eparation of I TER O peration' (PrIO). The overview paper is directly supported by the eleven EUROfusion PrIO contributions given at the 29th Fusion Energy Conference (16–21 October 2023) London, UK [www.iaea.org/events/fec2023]. The paper covers the following topics: (i) development and validation of tools in support to ITER operation (plasma breakdown/burn-through with evolving plasma volume, new infra-red synthetic diagnostic for off-line analysis and wall monitoring using Artificial Intelligence techniques, synthetic diagnostics development, development and exploitation of multi-machine databases); (ii) R&D for the radio-frequency ITER neutral beam sources leading to long duration of negative deuterium/hydrogen ions current extraction at ELISE and participation in the neutral beam test facility with progress on the ITER source SPIDER, and, the commissioning of the 1 MV high voltage accelerator (MITICA) with lessons learned for ITER; (iii) validation of neutronic tools for ITER nuclear operation following the second JET deuterium–tritium experimental campaigns carried out in 2021 and in 2023 (neutron streaming and shutdown dose rate calculation, water activation and activated corrosion products with advanced fluid dynamic simulation; irradiation of several materials under 14.1 MeV neutron flux etc). [ABSTRACT FROM AUTHOR]

The present paper is dedicated to the study of the discrepancies encountered in electron temperature (Te) measurements carried out with electron cyclotron emission (ECE) and Thomson scattering (TS) diagnostics in the core of the JET tokamak. A large database of discharges has been collected, including high-performance scenarios performed with deuterium only and deuterium–tritium mixtures. Discrepancies have been found between core Te measurements taken with an X-mode ECE interferometer (TECE) and a LIDAR TS system (TLID) for T e > 5 keV. Depending on the plasma scenario, TECE has been found to be systematically higher or lower than TLID. Discrepancies have also been observed between the peaks of the ECE spectrum in the second (X2) and third (X3) harmonic domains, even in high optical thickness conditions. These discrepancies can be interpreted as evidence of the presence of non-Maxwellian features in the electron energy distribution function (EEDF). In order to investigate the relation between the shape of the EEDF and the measured discrepancies, a model for bipolar perturbations of Maxwellian EEDF has been developed. The model allows analytical calculations of ECE absorption and emission coefficients; hence, the comparison of modeled ECE spectra with experimental data. The different experimental results observed for the various JET scenarios have been found to be qualitatively reproducible by adapting the model parameters, suggesting that bipolar distortions of the bulk EEDF could play a role in giving rise to the reported discrepancies between ECE and TS measurements. [ABSTRACT FROM AUTHOR]