An explanation of the L to H mode transition induced by applied radial voltageFunded under: FP2-FUSION 10C
The response of the edge plasma to an applied voltage is analysed. When the anomalous transport is ambipolar, the radial current is determined by neoclassical fluxes. An equation is given for the neoclassical radial current which is valid across the transition between the plateau and the collisional viscous regimes. The same current can be driven by two different electric fields, E(1) or E(2), allowing an equilibrium field profile, where E changes abruptly from E(1) to E(2) at some intermediate radius, while maintaining current continuity. It is shown unambiguously that a continuous electric field profile becomes unstable when the applied voltage exceeds a critical value, the instability being driven by negative incremental resistivity. The profile then bifurcates to one with discontinuous electric field. Quantitative comparisons are made with TEXTOR results, and the predictions found to be in qualitative agreement with measurement. The implications for spontaneous L-H transitions are discussed.
Bibliographic Reference: Report: JET-P(93)07 EN (1993) 39 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199310602 / Last updated on: 1994-11-29
Original language: en
Available languages: en