Impurity control by the radial electric field in a stochastic layer
The ergodic divertor allows the application of resonant magnetic perturbations which destroy the magnetic surfaces at the edge. The magnetic lines within that stochastic layer connect the confined plasma to the wall. In this paper, the possibility of impurity control by the ergodic divertor in a low collisionality regime is investigated. The friction effects are then negligible. The only possible influence on impurity ions is through the radial electric field, which appears to allow confinement of electrons in the stochastic layer. This takes place as soon as the stochasticity of the flux lines is ensured, even if the magnetic perturbation has practically no influence on the ions. It is thought that the basis of the effect is that the ions tend to be extracted outwards by the radial electric field. Effective extraction necessitates the presence of ripple modulations of the magnetic field. This mechanism leads to a flux similar to the neoclassical effect, but with a significant difference. The deleterious inward flux of impurity ions, which is proportional to the density gradient of H(+) ions, is replaced by an opposite outwards flux.
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: 199110363 / Last updated on: 1994-12-02
Original language: en
Available languages: en