Observability and controllability of plasma instabilities

Although the questions of whether all the dynamical states are accessible (''observability'') and amenable to control (''controllability'') play central roles in control science and engineering, these have been completely ignored in the literature of control of plasma instabilities. These problems are discussed and the general conclusion is that any plasma instability of discrete spectrum is completely observable and controllable with a few, but, most often, a single pair of, suitably located point sensor and suppressor.