DINA simulations of TCV electron cyclotron heating discharges

This paper reports on full tokamak discharge simulations in the TCV tokamak using the DINA code, of which a new open modular architecture version is presented. These new simulations include the effect of intense electron cyclotron heating, dissipated off-axis. The change in the plasma conductivity produces a time-varying plasma current profile, which in turn causes the plasma shape to relax in the almost constant vacuum quadrupole field. These simulations allow us to check on the diffusion of poloidal magnetic flux, as well as the modelling of the electron cyclotron heating. (C) 2003 Elsevier Science B.V. All rights reserved.

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Jean-Yves Favez, Jonathan Bryan Lister
2003
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https://infoscience.epfl.ch/record/120008?ln=fr

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État plasma

Tokamak

thumb|Vue intérieure du tore du Tokamak à configuration variable (TCV), dont les parois sont recouvertes de tuiles de graphite. Un tokamak est un dispositif de confinement magnétique expérimental ex

Résonance cyclotron

La résonance cyclotron électronique (ECR pour electron cyclotron resonance) est un phénomène observé aussi bien en physique des plasmas qu'en physique de la matière condensée. Un électron dans un cham

Behaviour of central plasma relaxation oscillations during localized electron cyclotron heating on the TCV tokamak

Roland Behn, Ivo Furno, Timothy Goodman, Jean-Philippe Hogge, Jean-Marc Moret, Antoine Pochelon, Holger Reimerdes, Olivier Sauter, Minh Quang Tran, Henri Weisen

During initial studies of ECRH in the TCV tokamak, non-standard central MHD activities, such as humpbacks and saturated and inverted sawteeth, have been observed while changing the heating location, the ECRH power, the plasma shape and the safety factor. For edge safety factors q(alpha) > 4.5, safety factors on-axis q(0) < 1 and small plasmas, complete sawtooth stabilization was achieved with the present 1 MW gyrotron power, and it is likely that sawtooth stabilization can be achieved for all conditions at. higher ECRH power. The conditions under which the various relaxation activities are produced or suppressed are reported, and the origins for such tron-standard behaviour are discussed.

1999

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Characterization of impurities in L- and H-modes created by divertor biasing and plasma triangularity in TdeV

A characterization of the H-mode in Tokamak de Varennes (TdeV) is presented, combining results obtained from spectroscopic measurements with observations of global plasma parameters. Controlled L- and H-modes are obtained by applying an external bias on the divertor plate and/or by varying the plasma triangularity using similar steady-state discharges with electron cyclotron resonance heating (ECRH). A qualitative study of the impurity emission asymmetries is presented and discussed by proposing a simple model which considers that the emissivity has radial and poloidal components. The poloidal velocities are small with no significant variations with respect to the plate biasing, EC power and plasma triangularity. Toroidal. rotation velocities show more consistent trends and have larger values in the H-modes with respect to the L-modes. No significant shear in the radial electric field is observed between the H- and L-modes. Differences in the electric field and in the E x B shear are observed for several discharges, but they are not consistent overall. A study on the impurity transport shows low diffusivity values in the plasma centre and high values in the edge during the H-mode. The energy confinement time decreases with the severity of the edge localized modes and, consequently, with the neutral fluxes. The presence of a toroidal torque which affects the particle transport inside the plasma plays an important role in the TdeV H-modes.

2001

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Effects of plasma shape on laser blow-off injected impurity transport in TCV

Edgar Scavino, Henri Weisen

The extreme shaping capabilities of the TCV tokamak have been used to investigate the effect of plasma geometry on the confinement of non-recycling trace impurities injected by means of the laser blow-off technique. The progression of the injected silicon in the core of TCV Ohmic limiter plasmas was followed by the 200-channel soft x-ray (SXR) photodiode array with good spatial and temporal resolution. The results show that the plasma triangularity and elongation play an important role in the impurity confinement time, tau(imp). Remarkably, the increase of elongation from kappa = 1.6 to 2.3 produces a threefold reduction of tau(imp) while the electron energy confinement time, tau(Ee), remains almost constant. tau(imp) is fairly constant in the triangularity scan for delta > 0.2, while there is a marked increase for lower values, leading to tau(imp) > 100 ms for negative triangularities. The increase of the toroidal magnetic field, B-T, from B-T = 0.92 to 1.47 T produces a decrease in the confinement time by almost a factor of 2. Simulation of the evolution of the line-integrated SXR signals, performed by the one-dimensional code STRAHL, provided both central and peripheral values of the transport coefficients together with estimates of the radial profiles. The simulations show that anomalous transport is dominant over neoclassical transport, except near the plasma centre. Interestingly, the convective velocity is positive (outwardly directed) in all limiter cases.

2003

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