Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

WEST is an MA class superconducting, actively cooled, full tungsten (W) tokamak, designed to operate in long pulses up to 1000 s. In support of ITER operation and DEMO conceptual activities, key missions of WEST are: (i) qualification of high heat flux plasma-facing components in integrating both technological and physics aspects in relevant heat and particle exhaust conditions, particularly for the tungsten monoblocks foreseen in ITER divertor; (ii) integrated steady-state operation at high confinement, with a focus on power exhaust issues. During the phase 1 of operation (2017–2020), a set of actively cooled ITER-grade plasma facing unit prototypes was integrated into the inertially cooled W coated startup lower divertor. Up to 8.8 MW of RF power has been coupled to the plasma and divertor heat flux of up to 6 MW m−2 were reached. Long pulse operation was started, using the upper actively cooled divertor, with a discharge of about 1 min achieved. This paper gives an overview of the results achieved in phase 1. Perspectives for phase 2, operating with the full capability of the device with the complete ITER-grade actively cooled lower divertor, are also described

Score Following Using Spectral Analysis and Hidden Markov Models

This paper presents an approach to score following. The real-time alignment of a performance with a score is obtained through the use of a hidden Markov model. The model works on two levels. The lower level compares the features of the incoming signal with the expected ones. Groups of states of the lower level are embedded in states at the higher level, which are used to model the performance by taking into account the possible errors a performer may make. The performer's position on the score is computed through a decoding technique alternative to classic Viterbi decoding. A novel technique for the training of hidden Markov models is proposed

Score Following Using Spectral Analysis and Hidden Markov Models

This paper presents an approach to score following. The real-time alignment of a performance with a score is obtained through the use of a hidden Markov model. The model works on two levels. The lower level compares the features of the incoming signal with the expected ones. Groups of states of the lower level are embedded in states at the higher level, which are used to model the performance by taking into account the possible errors a performer may make. The performer's position on the score is computed through a decoding technique alternative to classic Viterbi decoding. A novel technique for the training of hidden Markov models is proposed

TEMPERATURE EFFECTS ON THE OPTICAL-PROPERTIES OF AMORPHOUS HYDROGENATED SILICON NITROGEN ALLOYS PREPARED BY RF SPUTTERING

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Langmuir probe measurements in the WEST tokamak

International audienc

CEA contribution to the ITER ICRH antenna design

The ITER ion-cyclotron range of frequency (ICRH) heating system is required to couple 20 MW of power in the frequency range 40-55 MHz for a large range of scenarios with Edge Localized Modes. To mitigate the associated risks, it is foreseen to design and install on ITER two port-plug antennas for a total of 20 MW coupled power on long pulse operation [1]. The CEA activity to this antenna design within the CYCLE consortium was focused on the Faraday screen design (Fig. 1) and associated radio frequency (RF) sheath modelling, the reflectometers design for edge density measurement in the antenna vicinity and a contribution to the remote handling/tooling of the antenna. This paper is an overview of each item and proposes some R&D activities on key component

Design and integration of femtosecond fiber Bragg gratings temperature probes inside actively cooled ITER-like plasma-facing components

International audienceMeasuring the temperature in plasma-facing components (PFCs) provides information both on plasma parameters in the divertor region and on the thermal stress experienced by PFCs. Fiber Bragg gratings (FBGs) are interesting candidates for this application because they are immune to electromagnetic interferences and their ability to be multiplexed allows an extended spatial coverage. Four fibers, each of them including eleven regenerated Bragg gratings, have been embedded in tungsten-coated graphite components and operated up to their signal-collapsing limit at 800°C. Extending the measurement range towards higher temperatures increases the sensitivity to plasma parameters and allows withstanding higher energy experiments. To overcome thermal limitations, the system is upgraded using femtosecond laser inscribed fibers. In addition to their outstanding thermal stability, femtosecond FBGs benefit from higher signal-to-noise ratios than regenerated FBGs. The paper addresses femtosecond FBGs design and issues relative to their integration inside the actively cooled ITER-like PFCs of the WEST tokamak. Gratings period and length is designed to increase the number of measurement spots to fourteen gratings per fiber, regularly distributed over 17cm, while ensuring robust detection even with strong thermal gradients (no overlapping or deformation of Bragg peaks). The system operates up to 1200°C with gradients reaching 200°C/mm perpendicularly and 40°C/mm in parallel to the fiber. FBGs are inserted in actively cooled ITER-like PFCs through a 2.5mm deep lateral groove localized at 5mm beneath the top of bulk tungsten mono-blocks. A PFC mock-up machined with a groove has been tested under HHF facility to assess the effect of the groove on mono-blocks thermal behavior. The test demonstrates that machined mono-blocks behave as expected from simulation and can withstand 20 MW/m 2 heat flux (i.e. 1200°C in the fiber) with 20% overheating as compared to intact mono-blocks

Status of the ITER Ion Cyclotron H&CD system

The ongoing design of the ITER Ion Cyclotron Heating and Current Drive system (20 MW, 40-55 MHz) is rendered challenging by the wide spectrum of requirements and interface constraints to which it is subject, several of which are conflicting and/or still in a high state of flux. These requirements include operation over a broad range of plasma scenarios and magnetic fields (which prompts usage of wide-band phased antenna arrays), high radio-frequency (RF) power density at the first wall (and associated operation close to voltage and current limits), resilience to ELM-induced load variations, intense thermal and mechanical loads, long pulse operation, high system availability, efficient nuclear shielding, high density of antenna services, remote-handling ability, tight installation tolerances, and nuclear safety function as tritium confinement barrier. R&D activities are ongoing or in preparation to validate critical antenna components (plasma-facing Faraday screen, RF sliding contacts, RF vacuum windows), as well as to qualify the RF power sources and the transmission and matching components. Intensive numerical modeling and experimental studies on antenna mock-ups have been conducted to validate and optimize the RF design. The paper highlights progress and outstanding issues for the various system component

Science and technology research and development in support to ITER and the Broader Approach at CEA

In parallel to the direct contribution to the procurement phase of ITER and Broader Approach, CEA has initiated research & development programmes, accompanied by experiments together with a significant modelling effort, aimed at ensuring robust operation, plasma performance, as well as mitigating the risks of the procurement phase. This overview reports the latest progress in both fusion science and technology including many areas, namely the mitigation of superconducting magnet quenches, disruption-generated runaway electrons, edge-localized modes (ELMs), the development of imaging surveillance, and heating and current drive systems for steady-state operation. The WEST (W Environment for Steady-state Tokamaks) project, turning Tore Supra into an actively cooled W-divertor platform open to the ITER partners and industries, is presented