Transport Processes

Abstract

The first and most fundamental problem in thermonuclear fusion research is to heat a plasma to the ignition temperature and to confine such a plasma such that the product of the plasma density n and the confinement time τ satisfies the Lawson criterion (9.1.12). For magnetic confinement, the confinement time τ is determined by the transport process. It is a simple problem if the magnetic field is straight and the particles can be transported across the magnetic field only by collisions. However, if one wants to confine a plasma in a reasonably sized vessel such that the MHD equilibrium and stability are guaranteed, one inevitably has to use a curved magnetic field geometry, as explained in Chap. 9, so that the transport processes have to be treated in a complex configuration such as in tokamaks. The problem then becomes extremely complicated, partly due to the geometrical effects on the particle orbits and more seriously due to electromagnetic fluctuations that result from microscopic instabilities. In this chapter, we first describe in Sects. 13.1–3 the geometrical effects, considering only the collisional displacement of the particle orbits across magnetic surfaces. We then briefly describe the so-called anomalous transport due to electromagnetic fluctuations in Sect. 13.4–6. At present, the physical mechanism of the anomalous transport as observed in tokamaks and other advanced devices is not well understood, but remarkable progress has been seen in recent years. These developments are beyond the scope of the present book. Several recent seminal papers are cited, however [13.1–4].