Up-down symmetry breaking in global tokamak edge simulations

In global tokamak edge simulations, plasma density and temperature are found to be poloidally asymmetric despite the (nearly) symmetric geometry and boundary conditions. In particular, in the closed flux region, the ion temperature tends to be higher at the bottom, that is, in the direction of the ion drift, due to the action of the binormal component of the ion heat flux. The plasma density exhibits similar asymmetric pattern but with opposite polarity; it is higher on top, meaning in the direction of the electron drift. The ion temperature up-down symmetry breaking was accounted for in neoclassical transport, and through the force-balance constraint these effects further cause the density to be up-down asymmetric. Analytic estimates of the asymmetry on plasma profiles are given, and its impact on flows and turbulence are also discussed.