Publications de René Chavan | EPFL Graph Search

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Analysis of magnetic fluctuations is important for understanding the magneto-hydrodynamic (MHD) properties of fusion plasmas. These properties affect nearly all aspects of behaviour of magnetic confinement, and thus are of interest in topics ranging from global plasma stability, control, and disruption avoidance, to more subtle areas such as MHD spectroscopy. Mode number analysis is generally accomplished by interpreting signals from a finite number of Mirnov coils, which typically are unevenly spaced in th

Magnetic diagnostics for the new generation fusion reactor “ITER” are required to be extremely reliable since they provide measurements essential for reactor operation and protection, plasma control and for measurement of several parameters fundamental to ...

The high-frequency (HF) magnetic sensors for ITER are currently based on a conventional, Mirnov-type, pick-up coil, with an effective area in the range 0.03

The M1 mirrors are part of the in -vessel quasi -optical Electron Cyclotron beam propagation system of the DEMO nuclear fusion reactor. These four mirrors are all non -movable and with a plane reflecting surface. Based on their functionality they are divid ...

For future divertor studies on TCV measurements of electron temperature and density and their spatial gradients along open flux surfaces will be of major interest. A Thomson scattering system is proposed for this purpose, which takes advantage of the good access via horizontal ports on three vertical levels. The modular design of the existing Thomson scattering diagnostic on TCV offers the possibility to modify it for simultaneous measurements in the main plasma and in the divertor region using the same las

Four of the 16 ITER upper port plugs will be devoted to electron cyclotron resonance heating (ECRH) in order to control the magneto-hydrodynamic (MHD) instabilities. In order to achieve the stabilisation of the neoclassical tearing modes (NTM) and sawtooth oscillation, a deposition of a very localized and peaked current density profile over a broad poloidal steering range is required. In the present optical configuration eight 2MW mm-wave beams enter each of the four upper launchers (UL) through waveguides

A core density fluctuation imaging diagnostic is being developed for the TCV tokamak, employing a 7 cm wide CO2 laser beam transmitted through the plasma in a near-toroidal direction. The proposed system employs the phase contrast method and can resolve wa ...

Many future fusion devices will rely heavily, if not solely, on electron cyclotron (EC) heating subsystems to provide bulk heating, instability control (neoclassical tearing mode (NTM) stabilization), and thermal instability control. Efficient use of the i ...

This paper presents experimental results on the accessibility and the properties of plasmas with improved confinement in TCV. First, the H-mode threshold power is measured in Ohmic plasmas. Above an Ohmic threshold density, the threshold power increases with the density. A lower threshold density is found when additional electron cyclotron heating (ECH) is applied. At these low densities, the threshold power increases dramatically with decreasing density. Only a small fraction of the wide operational domain

On the Tokamak a Configuration Variable (TCV), electron internal transport barriers (eITBs) can be formed during a gradual evolution from a centrally peaked to a hollow current profile while all external actuators are held constant. The formation occurs ra ...

Experiments with high-power electron cyclotron heating (ECH) and current drive (ECCD) in the TCV tokamak are discussed. Power up to 2.7 MW from six gyrotrons is delivered to the tokamak at the second-harmonic frequency (82.7 GHz) in X-mode. The power is transmitted to the plasma by six independent launchers, each equipped with steerable mirrors that allow a wide variety of injection angles in both the poloidal and toroidal directions. Fully non-inductive operation of the tokamak has been achieved in steady

The ITER high-frequency (HF) magnetic sensor is currently intended to be a conventional, Mirnov-type, pickup coil, designed to provide measurements of magnetic instabilities with magnitude as low as |dB|~10e-4G at the position of the sensors and up to freq ...

The EU DEMO Tokamak is foreseen to be equipped with an electron cyclotron (EC) system for plasma heating, magnetohydrodynamic (MHD) control, and thermal instability suppression. Up to six launchers will be installed into equatorial ports with the aim to in ...

Each of the four ITER Electron Cyclotron Heating Upper Launcher (ECHUL) features eight transmission lines (TLs) that are used to inject 170-GHz microwave power into the plasma at a level of up to 1.31 MW (at the TL diamond window) per line. The millimeter ...

The physics of tokamak plasmas, in which electrons are heated by electron cyclotron heating (ECH) and whose current is driven by electron cyclotron current drive (ECCD), is investigated in this paper together with applications on tokamak A configuration variable (TCV) using modifications of the pressure and current profiles to improve the operational regimes. In order to explain the experimentally determined current drive efficiency and hard x-ray and electron cyclotron emission measurements, it is shown th

The ITER ECRH system consists of 24 gyrotrons with up to 24 MW installed millimeter wave heating power at 170 GHz, power supplies, control system, transmission lines, one Equatorial and the four Upper Launchers. With its high frequency and small beam focus ...

The Closure Plate Sub-Plate (CPSP), which defines the border between ex-vessel and in-vessel components of the Electron Cyclotron Upper Launcher (EC UL), bundles the waveguides into a sub-assembly which can be manipulated separately from the UL Port Plug ( ...

The mm-wave power exiting the eight In-Vessel waveguides inside the ITER Electron Cyclotron Upper Launcher is reflected by three fixed mirror sets and finally aimed by two independent steering mirrors to specific plasma locations. A design solution for bot ...

The large variety of plasma shapes produced in the TCV tokamak places unique demands on the plasma facing surfaces. In particular, the central column graphite armour tiles are solicited during the creation of all TCV plasmas and function as power handling surfaces for both limited and diverted discharges. The higher power flux densities accompanying the addition of electron cyclotron heating systems have necessitated a new, optimized, design for these tiles. The optimization process and the subsequent new t

The TCV tokamak offers outstanding variability of the plasma shape. Using x-ray tomography, the shape of the inner flux surfaces of a poloidal cross section of the plasma can be reconstructed, including fast variations due to MHD activity. Both the hardware and the software of the 200 channel system developed for TCV are described. A new 'dynamical' calibration takes actual plasma parameters into account to determine the spectrum-dependent detector efficiency, resulting in an enhanced quality of reconstruct

René Chavan

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Astrophysics and Fusion Plasmas: application of the SparSpec algorithm to the data analysis and design of the ITER high-frequency Mirnov coil diagnostic system

3D Thermal and CFD Simulations of the Divertor Magnetic Coils for ITER

Prototyping Conventionally Wound High-Frequency Magnetic Sensors for ITER

Pre-conceptual design of the fixed mirrors for the DEMO Electron Cyclotron Heating antenna

A Thomson scattering diagnostic for measurements in the divertor region of TCV

Design and manufacturing of the ITER ECRH Upper launcher mirrors

Design of a tangential phase contrast imaging diagnostic for the TCV tokamak

High power mm-wave loss measurements of ITER ex-vessel waveguide components at the FALCON test facility at the Swiss Plasma Center

Accessibility and properties of ELMy H-mode and ITB plasmas in TCV

Safety factor profile requirements for electron ITB formation in TCV

High-power ECH and fully non-inductive operation with ECCD in the TCV tokamak

Prototyping a High-Frequency Inductive Magnetic Sensor Using the Nonconventional, Low-Temperature Co-Fired Ceramic Technology for Use in ITER

Design Progress of Structural Components of the EU DEMO EC Equatorial Launcher

Design and Thermal-Structural Analyses of Ancillary Components for the Optical Steering Mirror (M4) for the ITER ECH Upper Launcher

ECH physics and new operational regimes on TCV

Nearing final design of the ITER EC H&CD Upper Launcher

Design status of the double Closure Plate Sub-Plate concept for the ITER Electron Cyclotron Upper Launcher

Electromagnetic and mechanical analyses of the ITER electron cyclotron Upper launcher steering M4 mirrors for the vertical displacement event

The design of central column protection tiles for the TCV tokamak

X-ray tomography on the TCV tokamak