Speaker – Dr István Cziegler -University of York
Turbulence and Confinement in Magnetic Fusion
The performance of magnetic confinement fusion devices, such as tokamaks, is strongly influenced
by the effectiveness of the magnetic field in holding heat and mass inside the plasma volume and
away from solid walls. Research over the past 70 years has shown that turbulent transport across
the confining magnetic field is the dominant process setting the gradients of all important
thermodynamic quantities. Recent advances have revealed the key role which the formation and
interaction of turbulent structures can play in generating plasma phases with often counter-intuitive
phenomena, such as transport barriers or spontaneous rotation. The latter makes it clear that
plasma flows can interact with turbulent fluctuations, leading to changes in the quality of global
confinement. The most characteristic feature of all turbulent flows is spectral transfer, i.e. spreading
fluctuation power over a wide range of physical scales.
Zonal flows constitute a special case in the field of flow–turbulence interactions, since the mutual
effects of turbulence and large-scale flows are of similar magnitude. In most turbulence simulations
the plasma is observed to generate its own radially varying flow. Through spectral transfer, these
flows can provide a transport-free reservoir of energy for turbulence that is thus benign to
confinement. The exploration of the role of such nonlinear behaviour is at the forefront of present
day studies in the theory and experiments of magnetic confinement research.