Anomalous particle pinch in tokamaks

Abstract

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, θ) plane. The polarization electric field so produced crossed with the toroidal magnetic field leads to an E × B drift of all the plasma particles, which has been shown to have a θ-averaged radially inward component (V_r) = (8/9)∈^−L/2(1¯ ∈^−L/2)^−LV_ware , where V_ware is the Ware pinch velocity (¯cE_Φ/B_θ) , and^∈ is the inverse aspect ratio. For most tokamaks < V_r > is found to be of the order of the observed inward drift ~10ms^−L.