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 sa tisfactory explanation has been reported for it so far. A theory is given h ere for an understanding of this pinch based on an idea given earlier by th e author. The induction electric field polarizes the trapped particles, pro ducing a polarization charge density in the (r, theta) plane. The polarizat ion electric field so produced crossed with the toroidal magnetic field lea ds to an E x B drift of all the plasma particles, which has been shown to h ave 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(p hi)/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).