| dc.description |
A tokamak is never exactly axisymmetric, either because of field errors or because the magnetic field is intentionally perturbed–something that is becoming increasingly popular for controlling the plasma edge. Conversely, a stellarator generally lacks symmetry but may be `quasisymmetric', meaning that the strength (but not the direction) of the magnetic field possesses a symmetry. An exactly quasisymmetric stellarator has many properties that are identical to those of a corresponding tokamak. It is thus important to understand how the physics of plasma confinement depends on the symmetry properties of the magnetic field.This issue of Plasma Physics and Controlled Fusion contains a cluster of nine articles addressing various such issues, including MHD equilibrium, rotation, Alfvénic instabilities, and edge physics. Very interesting and relevant questions are discussed, such as: When do magnetic islands form in a stellarator? How do Alfvén eigenmodes in tokamaks and stellarators compare? How do their divertors compare? To what extent can a stellarator plasma rotate? How does this rotation affect the turbulence? Can a tokamak magnetic equilibrium bifurcate into one resembling a stellarator?I hope that stellarator and tokamak physicists alike will find these papers useful, and that they will help to spread awareness and understanding of these issues across the plasma physics community. |
