Study of the plasma edge turbulence in tokamaks
The plasma edge in tokamaks is known to be very turbulent. The non linear stability of a test mode is investigated in the presence of an helical potential perturbation, i.e. a "pump mode", which simulates the plasma turbulence. The particle trajectories in this perturbed equilibrium are derived using an Hamiltonian formalism. The electrons appear to have trapped trajectories in the potential well of the pump mode, while the ions experience a large convective motion. These two effects have a large influence on the test mode stability. First, non linearly trapped electrons supply an energy source for the test mode. Second, the ion convective motion introduces a radial scale of the test mode larger than the ion Larmor radius, in agreement with experimental data. These two phenomena allow a bifurcation in the turbulence level and provide, therefore, an explanation for the L-H transition.
Bibliographic Reference: Report: EUR-CEA-FC-1386 EN (1990) 14 pp.
Availability: Available from CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR)
Record Number: 199011157 / Last updated on: 1994-12-01
Original language: en
Available languages: en