Wilfred Anthony Cooper

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Concerns about the flexibility and robustness of a compact quasiaxial stellarator design are addressed by studying the effects of varied pressure and rotational transform profiles on expected performance. For thirty, related, fully three-dimensional configurations the global, ideal magnetohydrodynamic (MHD) stability and energetic particle transport are evaluated. It is found that tokamak intuition is relevant to understanding the magnetohydrodynamic stability, with pressure gradient driving terms and shear

The topological features of a stochastic magnetic field are investigated by the tracing of magnetic field lines. The first method consists of direct integration of the field line equations. An alternative approach is to invoke the incompressibility of the magnetic field in order to formulate a Hamiltonian description of the magnetic field lines. The third and last approach involves building a canonical map that models the magnetic topology. These three different methods are applied to the TEXTOR tokamak dev

First global linear study of electrostatic drift waves in two realistic quasisymmetric configurations, namely the Quasi-Axially symmetric Stellarator with three fields periods (QAS3) [P. Garabian and L. P. Ku, Phys. Plasma 6, 645 (1999)] and the Helically Symmetric eXperiment (HSX) [F. S. B. Anderson , Trans. Fusion Technol. 27, 273 (1995)], are presented. Effects of the shape of the plasma on the growth rate and frequency of the ion temperature gradient (ITG) driven mode are investigated by varying the qua

The high-beta capability of the spherical tokamak, coupled with a suite of world-leading diagnostics on MAST, has facilitated significant improvements in the understanding of performance-limiting core instabilities in high performance plasmas. For instance ...

DIII-D research is addressing critical challenges in preparation for ITER and the next generation of fusion devices through focusing on plasma physics fundamentals that underpin key fusion goals, understanding the interaction of disparate core and boundary ...

The GENE/GIST code package is developed for the investigation of plasma microturbulence, suitable for both stellarator and tokamak configurations. The geometry module is able to process typical equilibrium files and create the interface for the gyrokinetic ...

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

Fully kinetic assessments of the stability properties of toroidal drift modes have been obtained for cases for the large helical device (LHD). This calculation employs the comprehensive linear microinstability code FULL, as recently extended for nonaxisymmetric systems. The code 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. These effects include trapped particles

A reduced scalar magnetohydrodynamic (MHD) description for linear perturbations of arbitrary aspect-ratio, fully three-dimensional plasma configurations is derived for perturbations with short scale-length perpendicular to the magnetic field. The application of the scalar wave equation to ballooning modes is presented. It is shown that coexistence of toroidally extended and toroidally localized unstable ideal hydromagnetic ballooning modes occurs in an interchange-unstable equilibrium case modelling the Lar

Electromagnetic wave propagation in the Alfven frequency range in two-dimensional (2-D) and three-dimensional (3-D) plasma configurations is investigated by using a recently developed full-wave code, LEMan. The code solves the Maxwell equation globally in a fully 3-D numerical equilibrium geometry with nested magnetic surfaces and implements a cold plasma model with finite electron mass. Energy balance is used for the self-consistency and convergence checks. The code is applied for several 2-D systems and a

Magnetohydrodynamic equilibrium states with a three-dimensional helical core are computed to model the MAST spherical tokamak and the RFX-mod reversed field pinch. The boundary is fixed as axisymmetric. The MAST equilibrium state has the appearance of an i ...

Neoclassical transport and a particle confinement are analysed for three 3-D reactor designs-the QAS3, the ST/sphellamak hybrid and the sphellamak-using the VENUS code. It is observed that neither the QAS3 nor the ST/sphellamak is truly aquasi-axisymmetric configuration. Thus the transport is governed by the helical deformation of the magnetic Field strength, and these configurations do not effectively confine the trapped a particles. On the other hand, the sphellamak is a nearly isodynamic structure in the

The possibility of fulfilling the condition of poloidal closure of the contours of the second adiabatic invariant for all reflected particles is studied for systems with poloidally closed contours of the magnetic field B on the magnetic surfaces through computational stellarator optimization. It is shown that by adjusting the geometry this is possible in a major fraction of the plasma volume. The most salient characteristic (as compared to previous quasi-isodynamic configurations) is a magnetic axis whose c

The highest volume averaged beta values beta (t) of 2.2% at B-t = 0.75 T (gas puff) and 2.4% at D-t = 1.3 T (pellet) in helical devices have been achieved in LHD. The beta (t) dependence of MHD activities has been investigated in NBI plasmas. The n/m = 1/2 mode, excited in the core region, and the t = 1 resonant modes, in the peripheral region, have been observed. Both of the fluctuation amplitudes increase with beta (t) and pressure gradient. The strong n/m = 1/2 mode, which affects the plasma profile., ha

A particular configuration of the LHD stellarator with an unusually flat pressure profile has been chosen to be a test case for comparison of the MHD stability property predictions of different three-dimensional and averaged codes for the purpose of code comparison and validation. In particular, two relatively localized instabilities, the fastest growing modes with toroidal mode numbers n = 2 and n = 3, were studied using several different codes, with the good agreement that has been found providing justifi

The linear equation for ideal magnetohydrodynamic ballooning modes in three-dimensional configurations is derived in the coordinate system that is optimal for the representation of the equilibrium state. The magnetic field lines in this coordinate system, however, are not straight. The form of the Mercier criterion that is currently in use is recovered from the asymptotic analysis of the ballooning equation. To determine the parallel-current density, a magnetic differential equation expressed in the optimal

A Hamiltonian formulation of the relativistic guiding center drifts is extended to anisotropic pressure plasmas. The magnetic coordinates devised by Boozer are adapted to the anisotropic pressure model and retain canonical properties for two-dimensional an ...

Magnetohydrodynamic (MHD) equilibrium states with a three-dimensional helical core that display the characteristics of a saturated ideal internal kink mode are computed to model snake structures that have been observed in the JET tokamak [A.~Weller et al. ...

W7X stellarator 3D equilibrium has been computed with the equilibrium code ANIMEC (Anisotropic Neumann Inverse Moments Equilibrium Code). This equilibrium was used to model ICRH minority heating in 4He(H) plasma with the 3D full-wave code LEMan (Low frequency ElectroMagnetic wave propagation). The coupled power spatial distribution is shown for different resonance positions within the range of frequencies foreseen for the ICRH antenna. It is found that for the high mirror equilibrium examined, the antenna f

We describe a few relevant aspects of the new plasma physics stability code, TERPSICHORE, which breaks new ground both in plasma theory and in its algorithmic implementation. We chose a highly accurate discrete mathematical representation which led to the choice of algorithms that matched the vector-parallel architecture of the Cray Y-MP and Cray-2 supercomputers quite well. The resulting code runs at Gflop/s speeds, which translates into a very high efficiency. This means we can perform very extensive stud

Wilfred Anthony Cooper

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Robustness and flexibility in compact quasiaxial stellarators: Global ideal magnetohydrodynamic stability and energetic particle transport

Mapping of a stochastic magnetic field in toroidal systems

Global linear gyrokinetic simulations in quasi-symmetric configurations

Macroscopic Stability of High Beta MAST plasmas

DIII-D research towards establishing the scientific basis for future fusion reactors

A geometry interface for gyrokinetic microturbulence investigations in toroidal configurations

Magnetohydrodynamics stability of compact stellarators

Microinstability studies for the large helical device

Quasi-two-dimensional waves in three-dimensional magnetic confinement systems

Three-dimensional full-wave propagation code for cold plasma

Magnetohydrodynamic properties of nominally axisymmetric systems with 3D helical core

Neoclassical transport and alpha particle confinement in novel 3-D reactor systems

Improved alpha-particle confinement in stellarators with poloidally closed contours of the magnetic field strength

MHD characteristics in the high beta regime of the Large Helical Device

Comparison of the calculations of the stability properties of a specific stellarator equilibrium with different MHD stability codes

Local three-dimensional MHD stability in equilibrium optimized coordinates

Relativistic Hamiltonian guiding center drift formalism in anisotropic pressure magnetic coordinates

JET Snake Magnetohydrodynamic Equilibria

Modeling of ion-cyclotron resonant heating in Wendelstein 7-X equilibrium

The Terpsichore Code for the Stability Analysis of Magnetically Confined Fusion Plasmas