Plasma Science: From Fundamental Research to Technological Applications (1995)
Chapter: Stochastic Effects
Coherent Structures and Vortex Dynamics
The progress made during the past decade in studies of single-component plasmas has created a number of important scientific and technological opportunities. The ability to confine and manipulate pure electron plasmas and to create near-equilibrium states opens up unique opportunities to study transport in plasmas and fluids. The equations that govern two-dimensional flows in these plasmas are identical to the equations that govern two-dimensional flows in inviscid incompressible fluids. Exploiting this analogy, researchers have now conducted successful studies of vortex merger in electron plasmas, and the opportunity now exists to study important phenomena in fluid mechanics, such as the relaxation of two-dimensional turbulence (see Plate 2), the interaction of vortices with turbulence and shear flows, and turbulent transport.
Transport Processes
On longer time scales, the transport of particles due to like-particle collisions is only partially understood. In principle, this is a more difficult problem than the interaction of two-dimensional vortices because three-dimensional effects may be important, as well as the combined effects of single-particle and collective interactions. These effects are related to fundamental issues in kinetic theory and transport processes in neutral plasmas, but they can be isolated and studied more easily in single-component plasmas because of the unusually long confinement times.
Confinement Properties in Nonaxisymmetric Geometries
Recently, magnetized, single-component electron plasmas have been created that are not symmetric in the plane perpendicular to the confining magnetic field. (See Figure 2.2.) These plasmas were found to have surprisingly long confinement times. It does not appear that these long-lived, asymmetric states can be explained by the simplest models of good confinement of single-component plasmas with cylindrical symmetry, which indicates that the fundamental principles of single-component plasma confinement are not fully understood.
Stochastic Effects
In complex magnetic field geometries, the combined influence of the applied field configuration and the self-electric and self-magnetic fields of the nonneutral electron or ion beam can significantly affect individual particle motion and beam dynamics. For example, this can occur in the periodic wiggler field in free-electron lasers or in the periodic quadrupole focusing field in induction accelerators, particularly at sufficiently high beam intensities. Although the
