The review addresses transitions into regimes with improved confinement. The E x B paradigm is tested on the example of L-H transitions. It is demonstrated that L-H transitions may emerge either due to an amplification of the diamagnetic drift term caused by enhanced pressure gradient or due to an increase poloidal rotation velocity at the separatrix. In general, it is asserted that the emergence and dynamics of transitions is very sensitive to fine details of prelude plasma profiles. The L-H transition occurs provided the ambipolar electric field changes dramatically within a few centimeters. The dynamics of interest consists of threshold conditions for barrier formation, barrier propagation speed, and profile steepening rates, barrier limits and mechanisms for their relaxation and termination.
Astrophysics and Space Science
- Pub Date: