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Neuroimaging studies have found 'reality monitoring', our ability to distinguish internally generated experiences from those derived from the external world, to be associated with activity in the medial prefrontal cortex (mPFC) of the brain. Here we probe ...

In current-free stellarators, the parallel current density is normally too weak to drive global external kink modes. However, at finite values of beta, the bootstrap current (BC) can provide sufficient free energy to trigger this class of mode in some stellarator systems. The effect of the BC in the collisionless 1/nu regime has been investigated in several different types of stellarator reactor systems all with a volume V similar to 1000 m(3). In quasiaxisymmetric and quasihelically symmetric stellarators,

The aim of this paper is to report on recent advances made in global gyrokinetic simulations of ion temperature gradient (ITG) modes and other microinstabilities. The nonlinear development and saturation of ITG modes and the role of E x B zonal flows are studied with a global nonlinear deltaf formulation that retains parallel nonlinearity and thus allows for a check of the energy conservation property as a means of verifying the quality of the numerical simulation. Due to an optimized loading technique, the

It is now widely believed that low frequency turbulence developing from smallscale instabilities is responsible for the phenomenon of anomalous transport generally observed in magnetic confinement fusion experiments. The microinstabilities are driven by gradients of equilibrium density, ion and electron temperatures and magnetic field strength. Gyrokinetic theory is based on the Vlasov-Maxwell equations and, consistent with the ordering, averages out the fast particle gyromotion, reducing the phase space fr

Flux-driven global gyrokinetic codes are now mature enough to make predictions in terms of turbulence and transport in tokamak plasmas. Some of the recent breakthroughs of three such codes, namely GYSELA, ORB5 and XGC1, are reported and compared wherever a ...

A global nonlinear simulation code for the time evolution of ion-temperature-gradient-driven modes in theta-pinch geometry as a first approximation to the stellarator Wendelstein 7-X (W7-X) [Grieger , Proceedings of the 13th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 525] has been developed. A deltaf particle-in-cell (PIC) method is used to solve the coupled system of gyrokinetic equat

The helical distortion of a compact tokamak plasma with currents in modular Furth-Hartman type coils is investigated with respect to the impact on the magnetic field structure and to the ideal magnetohydrodynamic stability. A sequence of configurations, in which the current in the helical coils is increased up to the level of that of the main toroidal coils, is generated. The magnetic field structure acquires a ripple along the field lines when the currents in both sets of coils becomes comparable. The magn

Scientific and technical activities on JET focus on the issues likely to affect the ITER design and operation. Our understanding of the ITER reference mode of operation, the ELMy H-mode, has progressed significantly. The extrapolation of ELM size to ITER has been re-evaluated. Neoclassical tearing modes have been shown to be meta-stable in JET, and their beta limits can be raised by destabilization (modification) of sawteeth by ion cyclotron radio frequency heating (ICRH). Alpha simulation experiments with

The impact of the bootstrap current is investigated on the equilibrium properties of a two-period quasi-axisymmetric stellarator reactor with free boundary and on the corresponding ideal magnetohydrodynamic stability properties. Although the magnetic field strength B spectrum is dominated by a m/n = 1/0 component, the discrete filamentary coils trigger some small-amplitude symmetry-breaking components that can disturb,the quasi-symmetry of B. Finite beta causes the plasma column to shift outward in the abse

The pivotal role played by radial electric fields in the development of turbulence associated with anomalous transport is examined by means of global gyrokinetic simulations. It is shown that the stabilizing effect of E x B flows on ion temperature gradient (ITG) modes is quadratic in the shearing rate amplitude. For a given shearing rate it leads to an increase in the critical gradient. The electric fields (zonal flows) self-generated by ITG modes interact in a nonlinear way and it is shown that a saturate

The impact of the bootstrap current (BC) has become an important issue in the modeling of quasi-symmetric stellarator devices. Magnetohydrodynamic equilibria have been calculated with self-consistent BC in the collisionless l/nu regime for characteristic quasi-symmetric configurations: a three-period quasi-axisymmetric and a four-period quasi-helically symmetric stellarator. The relationship between magnetic geometry and BC is shown along with its effect on the equilibrium when beta is increased. The releva

An equation for the evolution of deltaf is shown to be redundant in the deltaf particle-in-cell (PIC) simulation scheme. Having eliminated this equation, an adaptive f(0) construction is shown to follow intuitively and to be straight forward to implement. (C) 2003 Elsevier B.V. All rights reserved.

Simon Allfrey

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Modulating medial prefrontal cortex activity using real-time fMRI neurofeedback: Effects on reality monitoring performance and associated functional connectivity

Bootstrap current destabilization of ideal MHD modes in three-dimensional reactor configurations

Full radius linear and nonlinear gyrokinetic simulations for tokamaks and stellarators: zonal flows, applied E x B flows, trapped electrons and finite beta

First principles based simulations of instabilities and turbulence

Predictions on heat transport and plasma rotation from global gyrokinetic simulations

Energy conservation in a nonlinear gyrokinetic particle-in-cell code for ion-temperature-gradient-driven modes in theta-pinch geometry

Effect of helical coils on the magnetic field and the stability of a compact toroidal plasma

Overview of JET results

Magnetohydrodynamic stability of free-boundary quasi-axisymmetric stellarator equilibria with finite bootstrap current

The role of radial electric fields in linear and nonlinear gyrokinetic full radius simulations

Bootstrap current and quasi-symmetry in reactor-size stellarators

Computational fusion plasma physics

A revised delta f algorithm for nonlinear PIC simulation

Computational fusion plasma physics

Effect of helical coils on the magnetic field and the stability of a compact toroidal plasma

Bootstrap current destabilisation of ideal MHD modes in 3D reactor configurations

Magneto-hydro-dynamic limits in spherical tokamaks

Role of self-generated and externally applied radial electric fields in the development of ITG driven modes, Invited Paper published in

Global nonlinear gyrokinetic simulations of ITG modes using particles in tokamak geometry

Quasiaxisymmetry in a spherical tokamak