M. Cole

Pullback transformation in gyrokinetic electromagnetic simulations

It is shown that a considerable mitigation of the cancellation problem can be achieved by a slight modification of the simulation scheme. The new scheme is verified, simulating a Toroidal Alfven Eigenmode in tokamak geometry at low perpendicular mode numbers, the so-called “MHD limit.” Also, an electromagnetic drift mode has been successfully simulated in a stellarator.

New variables for gyrokinetic electromagnetic simulations

A new approach to electromagnetic gyrokinetic simulations based on modified gyrokinetic theory is described. The method is validated using a particle-in-cell code. The Toroidal Alfven Eigenmode at low perpendicular mode numbers, the so-called “magnetohydrodynamical limit,” has been successfully simulated using this method.

Fluid electron, gyrokinetic ion simulations of linear internal kink and energetic particle modes

The internal kink mode is an important plasma instability responsible for a broad class of undesirable phenomena in tokamaks, including the sawtooth cycle and fishbones. To predict and discover ways to mitigate this behaviour in current and future devices, numerical simulations are necessary. The internal kink mode can be modelled by reduced magnetohydrodynamics (MHD). Fishbone modes are an inherently kinetic and non-linear phenomenon based on the n = 1 Energetic Particle Mode (EPM), and have been studied using hybrid codes that combine a reduced MHD bulk plasma model with a kinetic treatment of fast ions. In this work, linear simulations are presented using a hybrid model which couples a fluid treatment of electrons with a gyrokinetic treatment of both bulk and fast ions. Studies of the internal kink mode in geometry relevant to large tokamak experiments are presented and the effect of gyrokinetic ions is considered. Interaction of the kink with gyrokinetic fast ions is also considered, including the destabilisation of the linear n = 1 EPM underlying the fishbone.

Global linear gyrokinetic particle-in-cell simulations including electromagnetic effects in shaped plasmas

We give an overview of recent developments in electromagnetic simulations based on the gyrokinetic particle-in-cell codes GYGLES and EUTERPE. We present the gyrokinetic electromagnetic models implemented in the codes and discuss further improvements of the numerical algorithm, in particular the so-called pullback mitigation of the cancellation problem. The improved algorithm is employed to simulate linear electromagnetic instabilities in shaped tokamak and stellarator plasmas, which was previously impossible for the parameters considered.

A hierarchy of electromagnetic gyrokinetic and fluid hybrid models for the simulation of global modes

The goal of magnetic confinement fusion research is to produce an economically viable power reactor. This will require operation at finite plasma ?, where for instance fast particle transport by Alfv?n eigenmodes may become important. The density and energy of fast particles originating from heating and fusion will also be higher. Low frequency Alfv?nic modes can be destabilised by fast particles, with velocities comparable to the Alfv?n velocity, resulting in significant reduction of fast particle confinement. To?properly predict and manipulate this behaviour in current and future fusion devices, the numerical simulation of fast particle interaction with Alfv?n modes is necessary. Since these simulations are computationally demanding, it is desirable to use the simplest model capable of simulating a given phenomenon. Comparing a case with different physical models also permits the isolation of physics effects responsible for certain phenomena. In this paper we present a hierarchy of such numerical models and investigate their ranges of validity.

Toroidal Alfvén eigenmodes with nonlinear gyrokinetic and fluid hybrid models

Alfven eigenmodes may be important in driving fast particle transport in magnetic confinement fusion devices, with potentially deleterious results. To explain and predict this behaviour, numerical simulations are necessary. In order to predict transport, modes must be simulated through to their nonlinear saturated state. In this work, the first simulations of non-linear wave-particle interaction between an energetic particle population and a Toroidal Alfven Eigenmode are performed in which fluctuations responding self-consistently to modification of the fast particle profile are calculated with gyrokinetic treatment of all plasma species. Results from two such gyrokinetic codes are compared with new results from non-perturbative and perturbative fluid-gyrokinetic hybrid codes. There is a power-law relationship between the saturated magnetic perturbation amplitude, δB∕B0, and the linear mode growth rate, γL. All models show a transition from a higher to a lower exponent regime with increasing γL. Measured ...