The effects of field reversal on the W7-AS island divertor at low densities

For the W7-AS divertor configuration with the present inboard plates deeply cutting the magnetic islands, asymmetries in the distributions of density, particle and energy flows in the island scrape-off layer have been observed. The asymmetries are reversed as the B-field is reversed. After examining the classical drifts, we conclude that the asymmetries are driven by drifts arising from a radial temperature gradient in the islands. The effects of this drift are investigated by a simple one-dimensional model and fully three-dimensional simulations with the EMC3 code. Calculations are compared to measurements.