Radiative instability in a diverted plasma
Bifurcations between thermal equilibria are known to occur in a radiating plasma at a constant pressure profile. For sufficiently high impurity concentrations (typically 5% for oxygen), three steady-state solutions of the heat equation are found. The lowest temperature state is always stable when the radiation loss is a function of temperature only, and not directly dependent on space. In the present study the important case is considered, where the ratio of impurity and electron density, and thereby the radiation loss, depends explicitly on space. A general stability criterion is demonstrated. It is shown that two types of radiation limit can affect the layer. One of these limits corresponds to a lack of equilibrium, while the other one is a stability loss, associated with the onset of a temperature perturbation localised in space, which leads to a transition of the plasma state towards another stable equilibrium. This last limit is due to, and depends strongly on, the impurity profile. For two configurations of interest, i.e. the axisymmetric and ergodic divertors, it is shown that the stability relative to the thermal condensation of a cold dense and radiating layer can be achieved with a large plasma power outflux.
Bibliographic Reference: Paper presented: 18th European Conference of the EPS-Plasma Physics Division, Berlin (DE), June 3-7, 1991
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Record Number: 199110364 / Last updated on: 1994-12-02
Original language: en
Available languages: en