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Nonlinear Neoclassical Transport in Toroidal Edge Plasmas
Author(s) -
Fülöp T.,
Helander P.
Publication year - 2002
Publication title -
contributions to plasma physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.531
H-Index - 47
eISSN - 1521-3986
pISSN - 0863-1042
DOI - 10.1002/1521-3986(200204)42:2/4<339::aid-ctpp339>3.0.co;2-h
Subject(s) - tokamak , plasma , ion , impurity , physics , pedestal , toroid , pressure gradient , nonlinear system , flux (metallurgy) , atomic physics , condensed matter physics , enhanced data rates for gsm evolution , heat flux , materials science , mechanics , nuclear physics , heat transfer , quantum mechanics , telecommunications , archaeology , computer science , metallurgy , history
Edge plasma processes play a critical role for the global confinement of the plasma in a tokamak. In the edge region, where impurity ions are abundant and the temperature and density gradients are large, the assumptions of standard neoclassical theory break down. This paper reviews recent extensions of neoclassical theory to treat this problem, in particular our own work, which focuses on the nonlinear aspects of transport in a plasma with heavy impurity ions. In this theory, the pressure and temperature gradients are allowed to be steeper than in conventional theory neoclassical theory, so that the friction force between the bulk ions and heavy impurities is comparable to the parallel impurity pressure gradient. The impurity ions are then found to undergo a spontaneous rearrangement on each flux surface. This reduces their parallel friction with the bulk ions and causes the neoclassical ion flux to become a non‐monotonic function of the gradients for plasma parameters typical of the tokamak edge. Thus, the neoclassical confinement is improved in regions where the gradients are large, such as in the edge pedestal.