Relevance of E x B drifts for particle and heat transport in divertors

Radial electric fields up to similar to 4 kV m(-1) are observed in the boundary between the private flux region (PFR) and the scrape-off layer (SOL) driving E X B drifts between the inner and outer targets at speeds up to 2.8 km s(-1) in the Tokamak a configuration variable divertor. The resulting E X B fluxes, located in a narrow region (Delta(rho psi) < 0.012 in normalized radius or Delta R - R-sep < 4 mm mapped to the outer midplane) are equivalent to around 20% of the total heat and particle flux to the divertor targets (inner + outer). At the peak E-r, the E X B poloidal transport is equivalent to parallel flows with M-parallel to similar to 3. In the snowflake divertor with a second X-point in the outer SOL, the drifts in the PFR-SOL boundary were equivalent to around 30% of the total heat and particle flux to the divertor targets and cover a region similar to 50% wider than in the single null (Delta(rho psi) similar to 0.018, Delta R - R-sep similar to 6 mm). The location of the PFR-SOL boundary drift shifts radially in the E-parallel to x B direction when reversing the toroidal field direction. Peaks in density and electron pressure have been identified near the primary X-point along with large gradients in density, temperature, and potential, the latter resulting in a local electric field similar to 2.7 kV m(-1) which drives a drift (1.9 km s(-1)) upwards towards the closed flux surfaces. Floating potential (V-f) magnitudes up to 75 V (similar to 2 kT(e)) were measured, indicating that V-f and parallel currents should not be neglected when estimating plasma potential.