Anomalous particle pinch in tokamaks

An anomalous particle pinch in tokamaks has been known to exist since the T-3 tokamak. However, it is now known to occur in almost all tokamaks. No satisfactory explanation has been reported for it so far. A theory is given here for an understanding of this pinch based on an idea given earlier by the author. The induction electric field polarizes the trapped particles, producing a polarization charge density in the (r, theta) plane. The polarization electric field so produced crossed with the toroidal magnetic field leads to an E x B drift of all the plasma particles, which has been shown to have a theta-averaged radially inward component (V-r) = (8/9)epsilon(-1/2)(1 - epsilon(1/2))(-1) V-Ware, where V-Ware is the Ware pinch velocity (-cE(phi)/B-theta), and E is the inverse aspect ratio. For most tokamaks < V-r > is found to be of the order of the observed inward drift similar to 10 ms(-1).