Experimentally-based ExB drifts in the DIII-D divertor and SOL calculated from integration of Ohm's law using Thomson scattering measurements of T e and n e

摘要

The 2D spatial distributions of cross field drift velocities are calculated from 2D Thomson scattering measurements of T e and n e in the divertor and SOL of DIII-D. In contrast with the method that has been used on DIII-D where the 2D distribution of plasma potential V plasma is obtained from measurements of the probe floating potential of reciprocating probes, the present method does not require insertion of a probe into the plasma and can therefore be used in high power discharges. The 2D spatial distribution of V plasma is calculated from Ohm's Law for the parallel electric field E || along each flux tube, E ∥ ( s ∥ ) = ? 1.71 d T e / d s ∥ ? ( T e / n e ) d n e / d s ∥ , where the Thomson scattering values of T e and n e are used. To within a constant of integration, V plasma is obtained by integrating E || along the flux-tubes (field lines); the constant is obtained for each flux tube using the sheath drop at the target calculated from the characteristic of Langmuir probes built into the divertor tiles. The 2D distributions of E radial = ? d V p / d s radial , E poloidal = ? d V p / d s poloidal , v ExB poloidal = E radial / B and v ExB radial = E poloidal / B are then calculated as well as the particle drift flux densities Γ ExB poloidal = nv ExB poloidal and Γ ExB radial = nv ExB radial for electrons, fuel ions and impurity ions, using the appropriate values of particle density, n.