Publications de Kurt Appert | EPFL Graph Search

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Sawtooth inversion radii and profile peaking factors of a large variety of ohmic and ECH heated L mode plasmas, including, elongations up to 2.6 and triangularities between -0.5 and 0.75, have been investigated in the TCV tokamak. In ohmic plasmas, normalized inversion radii and electron temperature profile peaking factors (corrected for sawtoothing effects) depend solely on the parameter (j)/q(0)j(0), irrespective of plasma shape. With ECH this parameter remains the main scaling parameter. Density profiles

Fully noninductive, steady-state electron cyclotron current drive (ECCD) has been demonstrated for the first time in experiments carried out in the tokamak a configuration variable (TCV) [O. Sauter , Phys. Rev. Lett. 84, 3322 (2000)]. By appropriately distributing six 0.45 MW ECCD sources over the discharge cross section, fully noninductive, stable, and stationary plasmas with I-p up to 210 kA were obtained for the full discharge duration of 1.9 s, corresponding to more than 900 energy confinement times and

Extensive simulations are performed to investigate effects of electron cyclotron instabilities on the gyrotron beam quality, using two-dimensional axisymmetric particle-in-cell (PIG) codes. Both electrostatic and electromagnetic models, as well as realistic geometries of the gyrotron, are considered. It is found that a large beam density can lead to an electrostatic-instability-induced energy spread which substantially degrades the gyrotron efficiency. (C) 1997 American institute of Physics.

We present a fully-global linear gyrokinetic simulation code (GYGLES) aimed at describing the unstable spectrum of the ion-temperature-gradient modes in toroidal geometry. We formulate the Particle-In-Cell method with finite elements defined in magnetic coordinates, which provides excellent numerical convergence properties. The poloidal mode structure corresponding to k(parallel to) = 0 is extracted without approximation from the equations, which reduces drastically the numerical resolution needed. The code

Kinetic effects such as finite ion Larmor excursions and resonant Landau interactions are studied in the toroidicity Alfven eigenmode (TAE) range of frequencies. A new Alfven mode conversion mechanism is described taking place away from the resonances through toroidal mode coupling. It generates a group of kinetic Alfven eigenmodes (KAE) in the neighbourhood of each fluid eigenmode, with wavefields that extend throughout the plasma radius and could lead to substantial a particle losses. Comparisons carried

A two-dimensional PIC code aimed at the investigation of electron-cyclotron beam instabilities in gyrotrons and their effects on the beam quality is presented. The code is based on recently developed techniques for handling charge conservation and open boundaries. It has been implemented on the massively parallel computer CRAY T3D. First results show an electromagnetic backward-wave instability periodically growing and decaying to energy levels close to those obtained from the electrostatic Bernstein wave i

The direct sparse matrix solver is based on a domain decomposition technique to achieve data and work parallelization. Geometries that have long and thin structures are specially efficiently tractable with this solver, provided that they can be decomposed mainly in one direction. Due to the separation of the algorithm into a factorization stage and a solution stage, time-dependent problems with a constant coefficient matrix are particularly well suited for this solver. The parallelization performances obtai

The present status of the theory of plasma heating by low frequency waves is reviewed from a unified point of view based on the concept of the dielectric tensor operator.

Dynamical chaos is produced by the interaction between plasma particles and two electrostatic waves. Experiments performed in a linear magnetized plasma and a ID particle-in-cell simulation agree qualitatively: above a threshold wave amplitude, ion stochastic diffusion and heating occur on a fast time scale. Self-consistency appears to limit the extent of the heating process.

We present the application of the recent physics-conforming COOL method [2,4] to the eigenvalue problem of a cylindrical waveguide filled with unmagnetized plasma. Using the Fourier transform only along the waveguide and not in poloidal direction, this is ...

Kurt Appert

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Shape dependence of sawtooth inversion radii and profile peaking factors in TCV L mode plasmas

Steady-state fully noninductive operation with electron cyclotron current drive and current profile control in the tokamak a configuration variable (TCV)

Particle-in-cell (PIC) simulations of beam instabilities in gyrotrons

Finite element approach to global gyrokinetic Particle-In-Cell simulations using magnetic coordinates

Kinetic Alfven eigenmodes in a hot tokamak plasma

Effects of electron-cyclotron instabilities on gyrotron beam quality

A direct parallel sparse matrix solver

Theory of Plasma-Heating by Low-Frequency Waves - Magnetic Pumping and Alfven Resonance Heating

Stochastic Plasma-Heating by Electrostatic-Waves - a Comparison between a Particle-in-Cell Simulation and a Laboratory Experiment

Modes of a plasma-filled waveguide determined by a numerical hp method

On resonance absorption and continuum damping (vol 5, pg 3801, 1998)

New Finite-Element Approach to Normal Mode Analysis in Magnetohydrodynamics

A Theory of Electron Tail Induced by Radio-Frequency Waves

Fusion thermonucléaire, la source d'énergie du futur

On the adiabatic interaction of coherent waves with weak turbulence in plasmas

Mode Conversion to the Kinetic Alfven-Wave in Low-Frequency Heating Experiments in the Tca Tokamak

On the Local Absorption of Linear Electromagnetic-Waves in Hot Magnetized Plasmas

Study of second stability for ITG modes

Global modes in the Alfvén wave heating scheme

Effects of magnetic field curvature on Alfvén wave heating of tokamak plasmas