I2-S2 · Neoclassical momentum transport and radial electric field in tokamak transport barriersNewton, Sarah1) Abstract Radial electric field shear is believed to create transport barriers in tokamak plasmas, giving improved confinement. As turbulence is suppressed in transport barriers and ion thermal transport is comparable to the neoclassical prediction, neoclassical momentum transport may govern the radial electric field. We calculate the collisional transport matrix for a low collisionality plasma with collisional impurity ions. The bulk plasma toroidal rotation velocity is taken to be subsonic, but the heavy impurities undergo poloidal redistribution due to the centrifugal force. Previously only rotation shear was considered to drive radial angular momentum transport, with a small momentum diffusivity typical of the Pfirsch-Schlüter regime. The impurities now give rise to off-diagonal terms in the transport matrix, causing the plasma to rotate spontaneously, even in the absence of momentum sources. At conventional aspect ratio, poloidal impurity redistribution is seen to increase the angular momentum flux by a factor up to e**-3/2 , making it comparable to banana regime heat transport. Radial pressure and temperature gradients are the primary driving forces of the flux.
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