Motivation

Over the past three decades, understanding the role of spatially inhomogeneous flows arising from E x B drifts in the plasma has become an issue of critical importance for the plasma physics and fusion science communities. In systems as diverse as solar atmospheres to planetary magnetospheres to fusion energy experiments, inhomogeneities in plasma flows are important mechanisms that influence the stability of the plasma.

The impact of spatially sheared flows on the plasma can be observed in a variety of settings:

• In toroidal fusion energy experiments, a strongly sheared poloidal flow is a feature that is associated with the transition to enhanced confinement regimes - so called H-modes. Accompanying this transition is a general reduction in low frequency plasma instabilities.
  
  
• In the space plasma environment, a similar physical mechanism of sheared flow is responsible for generating ion acoustic, ion cyclotron and lower hybrid type instabilities. These instabilities have been proposed as mechanisms for enhanced particle heating and transport in the ionosphere.
  
  
• In laboratory experiments, it is found that the instabilities are tied to the magnitude and directionality of the radial electric field.
  
  

These different effects which seem to arise from the velocity inhomogeneity suggests that there is a continuum of phenomena, dependent upon the plasma parameters and boundary conditions, that can arise in a plasma with sheared flows.