Equilibrium and Stability
If we look only at the motions of individual particles, it would be easy to design a magnetic field which will confine a collisionless plasma. We need only make sure that the lines of force do not hit the vacuum wall and arrange the symmetry of the system in such a way that all the particle drifts v E , v ∇ B , and so forth are parallel to the walls. From a macroscopic fluid viewpoint, however, it is not easy to see whether a plasma will be confined in a magnetic field designed to contain individual particles. No matter how the external fields are arranged, the plasma can generate internal fields which affect its motion. For instance, charge bunching can create E fields which can cause × drifts to the wall. Currents in the plasma can generate B fields which cause grad- drifts outward.