Influence of Trapped Thermal Particles on Internal Kink Modes in High-Temperature Tokamaks

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ELMy H-mode experiments at JET in 2000/mid-2002 have focused on discharges with normalized parameters for plasma density, energy confinement and beta similar to those of the ITER Q(DT) = 10 reference regime (n/n(GW) similar to 0.85, H-98(y,H-2) similar to 1, beta(N) similar to 1.8). ELMy H-mode plasmas have been realized reaching or even exceeding those parameters in steady-state conditions (up to similar to5 s or 12tau(epsilon)) in a reproducible way and only limited by the duration of the additional heati

A variety of techniques are being tested on ASDEX Upgrade for avoiding or reducing the divertor energy load caused by ELMs. Quiescent H-mode operation has been improved by operation with recently boronized vessel walls. Z(eff) values in QH-modes are now similar to2.5, comparable with those found in ELMy H-modes of similar density. Type It ELM operation has been generated in discharges with ICRF additional heating alone, thus demonstrating its compatibility with reactor-relevant low core momentum and particl

Electromagnetic microinstabilities in tokamak plasmas are studied by means of a linear global eigenvalue numerical code. Ion dynamics is described by the gyrokinetic equation, so that finite ion Larmor radius effects are taken into account to all orders. Nonadiabatic electrons are included in the model, with passing particles described by the drift-kinetic equation and trapped particles through the bounce averaged drift-kinetic equation. A large aspect ratio plasma with circular shifted surfaces is consider

With the very high electron cyclotron (EC) wave power density achieved in the TCV tokamak, more than 20 MW m(-3), quasilinear modelling predicts an electron cyclotron current drive (ECCD) efficiency well in excess to the experimental value, by up to a factor of 10. Experimentally, radial transport of suprathermal electrons consistent with a diffusion coefficient larger than 1.5 m(2) s(-1) has been observed. This implies that the radial transport time is of the same order as the electron deflection time, sug

The dependence of the measured damping rate upon the neutral beam heating power (P-NBI) and plasma beta has been experimentally investigated for n = 1 toroidal Alfven eigenmodes (TAEs) in JET limiter plasmas with a monotonic safety factor profile and low edge magnetic shear. The mode frequency is observed to decrease with increasing beta, as predicted by various theoretical models. For low P-NBI < 3 MW, a single n = 1 TAE splits into two modes closely spaced around the expected TAE frequency, and the mode d

During high recycling conditions and divertor detachment in the TCV tokamak, divertor target Langmuir probes never measure electron temperatures much below similar to5 eV. Code simulations using B2-EIRENE of these plasmas indicate that Te approximate to 1 eV. This inconsistency has also been seen in other tokamaks. In this paper, the influence on a theoretical Langmuir probe VI-characteristic of a strong T-e gradient parallel to the magnetic field is examined by using B2-EIRENE simulated T-e and n(e) profil

Gyrotrons at high frequency with high-output power are mainly developed for microwave heating and current drive in plasmas for thermonuclear fusion. For the stellarator Wendelstein 7-X, now under construction at IPP Greifswald, Germany, a 10-MW electron-cyclotron-resonance-heating (ECRH) system is foreseen. A 1-MW 140-GHz gyrotron with synthetic diamond window for continuous wave operation and with a single stage depressed collector for energy recovery and improvement of efficiency has been designed, constr

In this PhD thesis we deal with two mathematical problems arising from quantum mechanics. We consider a spinless non relativistic quantum particle whose configuration space is a two dimensional surface S. We also suppose that the particle feels the effect of an homogeneous magnetic field perpendicular to the surface S. In the first case S = R × SL1, the infinite cylinder of circumference L, corresponding to periodic boundary conditions, while in the second one S = R2. In both cases the particle feels the ef

A scheme is proposed for calcg. electrostatic potential (ESP) derived charges from mixed quantum mechanics/ mol. mechanics (QM/MM) mol. dynamics simulations. These charges are fitted to the electrostatic field due to the quantum charge d. evaluated on the MM atoms close to the QM system and are restrained to the corresponding Hirshfeld value by a quadratic penalty function. The D-RESP charges estd. by this procedure reproduce the field due to the charge d. polarized by the environment and can be obtained as

Current profile tailoring by electron cyclotron heating (ECH) and current drive (ECCD) is used to improve central electron energy confinement in the TCV tokamak. Counter-ECCD on axis alone achieves this goal in a transient manner only. A stable scenario is obtained by a two-step sequence of err-axis ECH, which stabilizes magnetohydrodynamics modes, and on-axis counter-ECCD, which generates a flat or inverted current profile. This high-confinement regime, with central temperatures up to 9 keV (at a. normaliz

In the TCV tokamak the sawtooth period and the sawtooth amplitude are observed to depend strongly on the shape of the poloidal plasma cross section. Systematic scans of plasma elongation and triangularity show small sawteeth with short periods at high elongation or low and negative triangularity, and large sawteeth with long periods at low elongation or high triangularity. Additional central electron cyclotron heating power further amplifies the shape dependence of the sawtooth properties. The sawtooth peri

Recent stability results of external kink modes and vertical modes in compact stellarators are presented. The vertical mode is found to be stabilized by externally generated poloidal flux. A simple stability criterion is derived in the limit of large aspect ratio and constant current density. For a wall at infinite distance from the plasma, the amount of external flux needed for stabilization is given by F-i = (kappa(2) - kappa)/(kappa(2) + 1), where kappa is the axisymmetric elongation and F-i is the fract

Influence of Trapped Thermal Particles on Internal Kink Modes in High-Temperature Tokamaks

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Towards the realization on JET of an integrated H-mode scenario for ITER

ITER-relevant H-mode physics at ASDEX upgrade

Global-gyrokinetic study of finite beta effects on linear microinstabilities

Modelling of the electron cyclotron current drive experiments in the TCV tokamak

Measurement of the damping rate of n=1 toroidal Alfven eigenmodes as a function of the neutral beam heating power and plasma beta on JET

Predicted effects of parallel temperature gradients on the overestimation of TCV divertor target Langmuir probe T-e measurements

Advanced high-power gyrotrons

Aspects of two dimensional magnetic Schrödinger operatorsquantum hall systems and magnetic Stark resonances

D-RESP: Dynamically Generated Electrostatic Potential Derived Charges from Quantum Mechanics/Molecular Mechanics Simulations

Long-pulse improved central electron confinement in the TCV tokamak with electron cyclotron heating and current drive

Effect of triangular and elongated plasma shape on the sawtooth stability

Magnetohydrodynamics stability of compact stellarators