4 research outputs found
Two-fluid and magnetohydrodynamic modelling of magnetic reconnection in the MAST spherical tokamak and the solar corona
Twisted magnetic flux ropes are ubiquitous in space and laboratory plasmas,
and the merging of such flux ropes through magnetic reconnection is an
important mechanism for restructuring magnetic fields and releasing free
magnetic energy. The merging-compression scenario is one possible start up
scheme for spherical tokamaks, which has been used on the Mega Amp Spherical
Tokamak MAST. Two current-carrying plasma rings, or flux ropes, approach each
other through the mutual attraction of their like currents, and merge, through
magnetic reconnection, into a single plasma torus, with substantial plasma
heating. 2D resistive MHD and Hall MHD simulations of this process are
reported, and new results for the temperature distribution of ions and
electrons are presented. A model of the based on relaxation theory is also
described, which is now extended to tight aspect ratio geometry. This model
allows prediction of the final merged state and the heating. The implications
of the relaxation model for heating of the solar corona are also discussed, and
a model of the merger of two or more twisted coronal flux ropes is presented,
allowing for different senses of twist
Two-fluid and magnetohydrodynamic modelling of magnetic reconnection in the MAST spherical tokamak and the solar corona
Overview of recent physics results from MAST
New results from MAST are presented that focus on validating models in order to extrapolate to future devices. Measurements during start-up experiments have shown how the bulk ion temperature rise scales with the square of the reconnecting field. During the current ramp up models are not able to correctly predict the current diffusion. Experiments have been performed looking at edge and core turbulence. At the edge detailed studies have revealed how filament characteristic are responsible for determining the near and far SOL density profiles. In the core the intrinsic rotation and electron scale turbulence have been measured. The role that the fast ion gradient has on redistributing fast ions through fishbone modes has led to a redesign of the neutral beam injector on MAST Upgrade. In H-mode the turbulence at the pedestal top has been shown to be consistent with being due to electron temperature gradient modes. A reconnection process appears to occur during ELMs and the number of filaments released determines the power profile at the divertor. Resonant magnetic perturbations can mitigate ELMs provided the edge peeling response is maximised and the core kink response minimised. The mitigation of intrinsic error fields with toroidal mode number n>1 has been shown to be important for plasma performance