Main research experiences:

Edge Localized Modes

In both experiment and theory it has been found that a high pedestal height is required for the next step fusion devices.  However the formation of Edge Localized modes (ELM) in a tokamak plasma limits the pedestal height decreaseing the level of confinement and have a risk of damaging components in the tokamak chamber.  However ELM events also have a benifical effect in that they clean the plasma through increased transport of impurities.  Therefore conditions that give a decent pedestal height but with torable ELM events is preferable.  Thus a high understanding of the Physics behind ELMs is crucial.

1) Modeling of Edge Localized Modes using a Taylor Relaxation Model Initialised by a current density driven external Peeling Mode.

The Taylor Relaxation model says that an ELM event could be caused by a Taylor relaxation initialised by an external Peeling mode driven by the high current density gradients found in the pedestal of a H-mode plasma.  This relaxation would act from the plasma edge working inwards towards the core leaving a Taylor relaxed state in it's wake.  In a simple geometry the relaxed state can be see as a flattened toroidal current density which would have a further destabalising effect on the plasma.  However a negative skin current is created at the same time, by a discontinuity in the poloidal magnetic field at the plasma edge. This has an opposing stabalising effect.  By caculating when these two effects balance, using the minimum potential energy in the plasma, we can gain predictions for the radial extent of the Taylor relaxation needed to bring the plasma to a stable state.  This then leads to approximations of ELM widths, mode numbers and ELM frequencies.

Recent results from JET have shown a multiple resonance occuring within the dependence of ELM frequency on the edge saftey factor when a low n Resonant Magnetic Perturbation field is applied.  The Taylor relaxation model explains this occurance through a detailed structure in the term describing the distance between a radial position and the resonant surface where n = mq.  This structure can only be seen when the edge current density is low.  Thus one explanation for the experimental results is then that when RMP is applied the edge current density is decreased.

2) The Explosive Nature of Edge Localized Modes

A widely used and accepted model for the larger type I ELMs is the non-linear Ballooning model. This is based around the Ballooning equation which includes the effects of magnetic     field line curvature, magnetic shear, toroidal symmetry and gravity. Through this equation we can predict the stability of the plasma and determine the behavior of the plasma along the field  lines. One interesting result from this model is the prediction that ELM events will be seen as filaments aligned with the magnetic field lines with a radially explosive nature.   

More recently the model showed theoretically that the direction of the ELM event depends on     the current density. This cannot be seen experimentally as a filament going towards the core    would have no visible effect.  This could contribute to explanations of different sizes of ELMs.