Wilfred Anthony Cooper

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

We present SCENIC simulations of a W7X 4He plasma with 1% H minority and with an antenna model close to the design foreseen for the W7X ICRF antenna [1, 2]. A high mirror and a standard equilibrium are considered. The injected wave frequency is fixed at 33.8 MHz and 39.6MHz respectively and only fundamental minority heating is considered. Included in this calculation is a new realistic model of the antenna, where it is found that the localization of the antenna geometry tends to break the five-fold periodic

The impact of equilibrium helical flows on the stability properties of low shear tokamak plasmas is assessed. The corrections due to such helical flow to the equilibrium profiles (mass density, pressure, Shafranov shift, magnetic fluxes) are computed by mi ...

For self-consistent ICRF heating simulations, four codes have been coupled: VMEC[1] provides a fully shaped, anisotropic 3D MHD equilibrium (bi- Maxwellian distribution function), transferred to Boozer coordinates by TERPSICHORE[2]. The full-wave code LEMan[3,4] provides the IC wave field, power deposition and wave numbers (new anisotropic dielectric tensor and upshifted k). Finally, VENUS[5,6] computes the evolution of the distribution function due to ICRF heating and Coulomb collisions on the background t

The TERPSICHORE three-dimensional linear ideal magnetohydrodynamic (MHD) stability code [Theory of Fusion Plasmas, Proceedings of the Joint Varenna-Lausanne International Workshop, Chexbres, Switzerland, 1988 (Editrice Compositori, Bologna, Italy, 1989), p. 93; Controlled Fusion and Plasma Heating, Proceedings of the 17th European Conference, Amsterdam, The Netherlands (European Physical Society, Petit-Lancy, Switzerland, 1990), Vol. 14B, Part II, p. 931; Theory of Fusion Plasmas, Proceedings of the Joint V

The compact conventional six-period torsatron L-V with an aspect ratio of A = 3 has been considered as a starting point for further computational optimization of the collisionless confinement of the guiding center orbits of fusion a particles. The configurations obtained possess improved neoclassical transport together with an equilibrium beta limit at a level of approximate to 10%. The optimization of magnetohydrodynamic (MHD) stability and the coil design are underway. (C) 2003 MAIK "Nauka/Interper

A fully kinetic assessment of the stability properties of toroidal drift modes has been obtained for a case for the Large Helical Device [A. Iiyoshi et al., Nucl. Fusion 39, 1245 (1999)]. This calculation retains the important effects in the linearized gyrokinetic equation, using the lowest-order "ballooning representation" for high toroidal mode number instabilities in the electrostatic limit. Results for toroidal drift waves destabilized by trapped particle dynamics and ion temperature gradients are prese

A low aspect ratio stellarator CHS-qa with a quasi-axisymmetric configuration has been designed at NIFS, whose main objective is the experimental study of confinement improvement. The high beta equilibrium was obtained with the HINT code which does not require the assumption of nested magnetic surfaces. The equilibria with bootstrap current were calculated using the SPBSC code and their global MHD stability was evaluated with the TERPSICHORE code. The boundary structure of the magnetic field was examined to

Strategies for the improvement of quasiaxisymmetric stellarator configurations are explored. Calculations of equilibrium flux surfaces for candidate configurations are also presented. One optimization strategy is found to generate configurations with improved neoclassical confinement, simpler coils with lower current density, and improved flux surface quality relative to previous designs. The flux surface calculations find significant differences in the extent of islands and stochastic regions between candi

Minority ion cyclotron resonance heating is studied using the self-consistent numerical model SCENIC. This model includes 3D geometries with full shaping and anisotropic pressure effects, warm contributions to the dielectric tensor and full orbit effects. ...

Kinked saturated m = 1 helical structures are frequently observed in tokamak hybrid plasmas and in reversed field pinches (RFP). These modes occur when an extremum in the safety factor is close to, but necessarily resonant with, a low order rational (typic ...

This work shows a self-consistent numerical model of ion cyclotron resonant heating (ICRH) in a plasma of arbitrary (2D or 3D) geometry. Effects of anisotropy and full shaping on both MHD equilibrium and the dielectric tensor are explored. In particular, it is shown that the dielectric tensor becomes dependent on poloidal angle. Also, the anisotropic effects dominate the dielectric tensor. Using single particle simulations it is demonstrated that anisotropy develops due to ICRH. The changing of the equilibr

The characteristics of magnetohydrodynamics (MHD) stability of plasmas with the internal diffusion barrier (IDB) are intensively studied in the Large Helical Device (LHD) experiment. These plasma are produced by the rapid fueling into the core region with ...

Ballooning theory is an asymptotic method for treating modes with short wavelength across the magnetic field lines but essentially no phase variation along the lines. The latter constraint leads to problems with maintaining the physically required poloidal and toroidal periodicity, which can be solved in various ways. In this paper we review the approach of Dewar and Glasser, which applies to general three-dimensional equilibria, and also review some recent applications of the formalism to a heliotron/torsa

A fully kinetic assessment of the stability properties of toroidal drift modes has been obtained for nonaxisymmetric (stellarator) geometry, in the electrostatic limit. This calculation is a comprehensive solution of the linearized gyrokinetic equation, using the lowest-order "ballooning representation" for high toroidal mode number instabilities, with a model collision operator. Results for toroidal drift waves destabilized by temperature gradients and/or trapped particle dynamics are presented, using thre

An analysis of kinetic ballooning modes is presented, ray trajectories for the inward shifted Large Helical Device configuration at modest $$ and with an anisotropic pressure profile due to the hot particles are evaluated and an estimate of the margi ...

Kinetic effects have been implemented in the three-dimensional full-wave code LEMan. These allow modeling Landau damping as well as the Kinetic Alfvén Wave (KAW). Special attention has been taken on the exact computation of the parallel wave vector as it c ...

The ideal magnetohydrodynamic (MHD) stability of the National Compact Stellarator Experiment (NCSX) is extensively analyzed using the most advanced three-dimensional MHD codes. It is shown that the NCSX is stable to finite-n MHD modes, including the vertic ...

Numerical computations of ITER equilibria in the hybrid scenario using a three-dimensional (3D) magnetohydrodynamic equilibrium code with nested magnetic flux surfaces demonstrate the formation of internal 3D helical cores similar to saturated ideal intern ...

Non-axisymmetric free-boundary equilibrium computations are shown to represent nonlinearly saturated external kink modes and external kink-like sidebands coupled to pressure-driven infernal modes. In this study of edge harmonic oscillations associated with ...

An analysis of edge localised mode-free (quiescent) H-mode discharges exhibiting edge harmonic magnetoydrodynamic activity in the JET-carbon wall machine is presented. It is observed that the otherwise quiescent pulses with multiple-n harmonic oscillations ...

Wilfred Anthony Cooper

Chat with Graph Search

Applications of the SCENIC code package to the minority ion-cyclotron heating in Wendelstein 7-X plasmas

Helical equilibrium magnetohydrodynamic flow effects on the stability properties of low-n ideal external-infernal modes in weak shear tokamak configurations

Self-consistent ICRF simulations in fully shaped anisotropic plasmas

Fully 3-Dimensional Ideal Magnetohydrodynamic Stability Analysis of Low-N Modes and Mercier Modes in Stellarators

Compact torsatron with improved alpha-particle confinement

Drift mode calculations for the Large Helical Device

Confinement characteristics of the quasi-axisymmetric stellarator CHS-qa

Recent advances in the design of quasiaxisymmetric stellarator plasma configurations

Ion cyclotron resonance heating with consistent finite orbit widths and anisotropic equilibria

Ideal saturated MHD helical structures in axisymmetric hybrid plasmas

Monte Carlo ICRH simulations in fully shaped anisotropic plasmas

MHD Stability Analysis of IDB Plasma in LHD

Calculation of global modes via ballooning formalisms

Drift mode calculations in nonaxisymmetric geometry

Diamagnetic drift stabilized ballooning modes in a 3D heliotron

Convolution and iterative methods applied to low frequency waves in 3D configurations

Ideal magnetohydrodynamic stability of the NCSX

Helical ITER hybrid scenario equilibria

Current and pressure gradient triggering and nonlinear saturation of low-n edge harmonic oscillations in tokamaks

Understanding JET-C quiescent phases with edge harmonic magnetohydrodynamic activity and comparison with behaviour under ITER-like wall conditioning