Wilfred Anthony Cooper

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The ideal magnetohydrodynamic stability properties of a three-field period stellarator with quasiaxial symmetry features proposed by Garabedian and Ku [Phys. Plasmas 6, 645 (1999)] are investigated. The stability limit imposed by local ballooning and Mercier modes allows beta similar to 5.3% to be achieved by tailoring the pressure profile. For this system, the global external kink modes are shown to be stable. To demonstrate this, a sequence of configurations has been developed that varies from the referen

Free boundary three-dimensional anisotropic pressure magnetohydrodynamic equilibria with nested magnetic flux surfaces are computed through the minimisation of the plasma energy functional

W={\int}_{V}{d^3}x\left[{B^2}/(2\mu_0)+p_{||}/(\Gamma-1)\right]

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Fixed boundary three-dimensional anisotropic pressure equilibria are computed that are consistent with a family of distribution functions that load particles preferentially towards v parallel to similar or equal to v and model the effects of balanced tange ...

The recent revival of interest in the application of the ''ballooning formaiism'' to low-frequency plasma instabilities has prompted a comparison of the Wentzel-Kramers-Brillouin (WKB) ballooning approximation with an (in principle) exact normal mode calculation for a three-dimensional plasma equilibrium. Semiclassical quantization, using the ideal magnetohydrodynamic (MHD) ballooning eigenvalue to provide a local dispersion relation, is applied to a ten-field period stellarator test case. Excellent qualita

An approximation to a quasi-omnigenous structure of the magnetic field strength has been numerically obtained by optimization of the magnetic configuration of a conventional heliotron/torsatron. This configuration shows very good collisionless confinement of the guiding centre orbits of fusion alpha-particles for values of up to 0.05.

Fast particles in fusion plasmas may drive Alfven modes unstable leading to fluctuations of the internal electromagnetic fields and potential loss of particles. Such instabilities can have an impact on the performance and the wall-load of machines with bur ...

The ideal magnetohydrodynamic stability with respect to localized ballooning modes and the Mercier criterion of a quasihelically symmetric stellarator configuration is investigated. Configurations with an enhanced magnetic mirror and a deeper magnetic well that can be achieved by energizing a set of auxiliary coils have also been analyzed. In all cases, the Mercier criterion imposes a slightly stricter beta limit than the ballooning modes. Using relatively broad pressure profiles, the Mercier criterion yiel

We investigate the redistribution of the neutral beam driven current in the presence of small scale turbulence in the ITER steady-state scenario. Gyrokinetic simulations show that anomalous transport of beam ions can be larger than collisional estimates. The impact on the beam driven current in ITER is studied with a single particle following code. The results indicate that the current driven by the 1MeV neutral beam injection is not significantly redistributed by the microturbulent fields. The numerical in

Using a generalized anisotropic tokamak equilibrium and an exact guiding centre drift formulation, the effect of parallel and perpendicular anisotropy on the toroidal precession drift is investigated. Signiﬁcant differences between parallel and perpendicul ...

A new solver for Maxwell's equations in three-dimensional (3D) plasma configurations is presented. The new code LEMan (Low-frequency ElectroMagnetic wave propagation) determines a global solution of the wave equation in a realistic stellarator geometry at ...

Key physics issues in the design of a high-beta quasi-axisymmetric stellarator configuration are discussed. The goal of the design study is a compact stellarator configuration with aspect ratio comparable to that of tokamaks and good transport and stability properties. Quasi-axisymmetry has been used to provide good drift trajectories. Ballooning stabilization has been accomplished by strong axisymmetric shaping, yielding a stellarator configuration whose core is in the second stability regime for balloonin

The three-dimensional VMEC equilibrium solver has been adapted to numerically investigate the approximate toroidal rotation model we have derived. We concentrate our applications on the simulation of JET snakes and MAST long-lived modes under free boundary ...

The local three-dimensional (3-D) ideal magnetohydrodynamic (MHD) stability properties of a 12-field period torsatron device of moderate aspect ratio are investigated as a function of an externally applied quadrupole magnetic field. It is demonstrated that with a parabolic pressure profile the volume-averaged beta limit due to the ballooning instabilities decreases from beta congruent-to 2% to beta congruent-to 1.5% as the current I(mid) in the quadrupole field coils normalized to that in the main helical c

The magnetic topology and particle drift orbits are analysed in a monotonic q profile and in a reversed shear TEXTOR equilibrium that is subject to a magnetic perturbation driven by the Dynamic Ergodic Divertor (DED). The main results prove that there exists a transport barrier for magnetic field lines and for circulating particles in the reversed shear case when the DED is applied. This transport barrier occurs near the surface of minimum q value where the KAM theory may be invalid. Moreover, it should be

The relaxation of the constraint of periodicity imposed by the external confining magnetic field coils in a nominally 4-field period Helias Advanced Stellarator configuration produces weak periodicity-breaking deformations of the plasma. The corrugations a ...

The global ideal magnetohydrodynamic (MHD) stability of plasmas with a prescribed helical boundary deformation and nonvanishing toroidal current is investigated with respect to the (m,n) external modes with n = 1,2,3, and m = n + 1. L = 2, 3 and mixtures (of both) configurations were studied by systematically varying parameters such as the aspect ratio, the number of equilibrium field periods, the toroidal current density, and the pressure profiles. The study focuses mainly on the q < 2 area. It is shown th

Finite toroidal plasma current reduces the magnitude of the normal magnetic field line curvature near midvolume in a quasiaxisymmetric stellarator. This improves the ideal ballooning stability conditions. Near the edge of the plasma, a hollow toroidal current profile deteriorates the ballooning stability properties by enhancing the normal curvature, while a parabolic current profile improves this stability because the normal curvature decreases. The magnetic field line bending term can also impact the stabi

A drift-magnetohydrodynamic theory is applied to a background anisotropic pressure equilibrium state to generate a drift corrected ballooning mode equation. The ratio of the mode frequency to the hot particle drift frequency constitutes the critical expans ...

A new three-dimensional code, VENUS+delta f, for neoclassical transport calculations in nonaxisymmetric toroidal systems is presented. Numerical drift orbits from the original VENUS code and the delta f method developed for tokamak transport calculations a ...

Recent progress in the Large Helical Device (LHD) experiment during the last 2 yr is reviewed. The LHD has been extending its operational regime toward fusion-relevant conditions while taking advantage of the net-current-free heliotron concept employing a superconducting coil system. Heating capability has exceeded 10 MW, and the central ion and electron temperatures have reached 7 and 10 keV respectively. The maximum values of beta and pulse length have been extended to 3.2% and 150 s, respectively. Severa

Wilfred Anthony Cooper

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Stability of a compact three-period stellarator with quasiaxial symmetry features

Three-dimensional anisotropic pressure free boundary equilibria

Three-dimensional anisotropic pressure equilibria that model balanced tangential neutral beam injection effects

Spectrum of ballooning instabilities in a stellarator

A new class of quasi-omnigenous configurations

Benchmark of gyrokinetic, kinetic MHD and gyrofluid codes for the linear calculation of fast particle driven TAE dynamics

Local ideal magnetohydrodynamic stability of a quasihelically symmetric stellarator

Numerical modelling of the electromagnetic turbulent transport of energetic ions in burning plasmas

Impact of pressure anisotropy on tokamak equilibria and the toroidal magnetic precession

A full-wave solver of the Maxwell's equations in 3D cold plasmas

Physics design of a high-beta quasi-axisymmetric stellarator

Free boundary equilibrium in 3D tokamaks with toroidal rotation

Effect of Quadrupole Fields on Local 3-Dimensional (3-D) Ideal Magnetohydrodynamic (Mhd) Stability in Torsatrons

Magnetic topology and guiding centre drift orbits in a reversed shear tokamak

Stellarator nonlinearly saturated periodicity-breaking ideal magnetohydrodynamic equilibrium states

External kinks in plasmas with helical boundary deformation and net toroidal current

Effect of toroidal current and profile on ballooning instability mechanisms in a quasiaxisymmetric stellarator

Drift stabilization of ballooning modes in an inward-Shifted LHD configuration

Venus plus delta f: A bootstrap current calculation module for 3-D configurations

Review on the progress of the LHD experiment