Publications de Jan Vaclavik | EPFL Graph Search

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Strong electric fields generate an ExB rotation of the equilibrium plasma. Experiments have shown that this effect could lower the anomalous transport in tokamaks. The study of the effect of these flows on the linear stability of ion temperature gradient (ITG) modes has therefore been undertaken. The question is addressed solving the spectrum of the gyrokinetic equation in the full two-dimensional poloidal plane for a large aspect ratio tokamak with concentric circular magnetic surfaces. Results show a stro

The modelling of Alfvenic instabilities is discussed from the point of view of mode-conversion, showing how the development of the theory affects the predictions as the limitations of the models are gradually relaxed. Conventional tokamak plasmas are relatively well understood and are used for the case of a kinetic Alfven eigenmode (AE) to assess the resonant wave-particle interactions along the magnetic field. The large safety factor in the core of deeply reversed shear plasmas and the low magnetic field o

The effects of applied radial electric fields on the stability of ion temperature gradient (ITG) modes and trapped particle modes are investigated with a full radius gyrokinetic formulation in both axisymmetric and helically symmetric configurations. The validity of a simplified stabilization criterion often applied to experimental analysis (the shearing rate larger than the linear growth rate) is examined for various profiles of ExB flows using an expression for the shearing rate derived for arbitrary quas

In the scope of the study of low-frequency electrostatic microinstabilities in tokamak plasmas, attention has been focused on the effect of trapped ions. The ballooning transform has been applied to the gyrokinetic equation, for the case of a large aspect ratio plasma with circular magnetic surfaces. A new eigenvalue code has been developed to solve the resulting integral equation, for the case of adiabatic electrons and full ion dynamics, thus taking into account both circulating and trapped ions. The goal

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 semi-Lagrangian code for the solution of the electrostatic drift-kinetic equations in straight cylinder configuration is presented. The code, CYGNE, is part of a project with the long term aim of studying microturbulence in fusion devices. The code has been constructed in such a way as to preserve a good control of the constants of motion, possessed by the drift-kinetic equations, until the nonlinear saturation of the ion-temperature-gadient modes occurs. Studies of convergence with phase space resolution

The global stability of toroidicity induced Alfven eigenmodes (TAEs) in the presence of fast ions in realistic tokamak fusion-grade plasmas is analysed with a global, perturbative approach. Volume averaged fast particle betas for marginal stability are obtained and analysed for a wide range of plasma parameters such as the fast ion radial density profile width, the ratio of birth velocity to the Alfven velocity on axis and the bulk plasma bets. There is evidence of different stability behaviour of two types

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.

Relying on the good agreement observed between the gyrokinetic PENN model and the low toroidal mode number n damping measurements from JET, the stability of Alfven eigenmodes (AEs) is predicted for reactor relevant conditions. Full non-local wave-particle power transfers are computed between global wavefields and alpha particles in an ITER reference equilibrium, showing that low-n eigenmodes (n similar or equal to 2) are strongly damped and intermediate-n eigenmodes (n similar or equal to 12) with a global

Alfven eigenmodes (AEs) with intermediate toroidal mode numbers are modelled using the global gyrokinetic PENN code to determine the stability of high performance tokamak discharges in the presence of energetic particles. A large plasma pressure and a weak magnetic shear in the core give rise to radially extended kinetic AEs, which are stabilized by the high shear at the edge of a divertor (X point) configuration. Large values for the safety factor and the ion Larmor radius in reversed shear operation may h

A common feature of the Vlasov equation is that it develops fine-scale filamentation as time evolves, as observed, for example, in global nonlinear simulations of the ion-temperature-gradient instability. From a numerical point of view, it is not trivial t ...

Considering the spectral problem of microinstabilities in a curved system, methods for solving the global gyrokinetic equation are presented for the simple case of a cylindrical plasma. They prove to be efficient for computing the full unstable spectrum of ion temperature gradient (ITG) type modes and have shown to be applicable to the two-dimensional integral equation of tokamak configurations. (C) 1998 American Institute of Physics.

The spectrum of n = 0 Alfven modes is calculated analytically and numerically in cylindrical and toroidal geometries. It includes global Alfven eigenmodes (GAEs) and surface modes (SMs) of the fast magnetoacoustic wave. These modes are not induced by toroidicity. The n = 0 GAEs owe their existence to shear. The frequency spacing between different radial and poloidal modes and the correlation of eigenfrequencies with changes in the edge density are examined and found to be in complete agreement with experime

Tokamaks with large pressure gradients (alpha(max)) formed in regions of weak magnetic shear are shown to be susceptible to novel, low-n, global, kinetic, electromagnetic modes with a toroidal mode number n in the range 2

Jan Vaclavik

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Effect of E x B flows on global linear ion temperature gradient modes

Gyrokinetic modelling of macro-instabilities in high performance tokamak plasmas

Radial electric fields and global electrostatic microinstabilities in tokamaks and stellarators

Applicability of the ballooning transform to trapped ion modes

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

Kinetic Alfven eigenmodes in a hot tokamak plasma

A semi-Lagrangian code for nonlinear global simulations of electrostatic drift-kinetic ITG modes

Global Marginal Stability of Taes in the Presence of Fast Ions

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

Global Alfven eigenmode stability in thermonuclear tokamak plasmas

Stability of Alfven eigenmodes in optimized tokamaks

Fine-scale structures and negative-density regions: Comparison of numerical methods for solving the advection equation

Global approach to the spectral problem of microinstabilities in a cylindrical plasma using a gyrokinetic model

Alfven frequency modes and global Alfven eigenmodes

Global gyrokinetic stability of pressure-gradient-driven electromagnetic modes in tokamaks with regions of low shear

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

Quasilinear theory of uniformly magnetized inhomogeneous plasmas

A Theory of Electron Tail Induced by Radio-Frequency Waves

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

Ion and electron temperature ratio and magnetic shear effects on electromagnetic instabilities