The Effect of Drifts on the DIII-D Boundary Plasma PDF Download

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Languages : en
Pages : 8

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Book Description
The effect of ExB and diamagnetic drifts on the boundary plasma of a diverted tokamak is examined by comparing simulations obtained from the 2D fluid code UEDGE with data from the DIII-D tokamak. The effect of drifts on a single null L-mode configuration is determined by comparing the measurements with two simulations which are identical except that only one includes drifts. The dominant effect is seen on the high B-field side of the divertor where the plasma density is a factor of two higher when drifts are included. This effect occurs because a radial electric field associated with steep electron temperature radial gradients along the separatrix between the X-point and strike points drives a poloidal flow from the outer to inner divertor in the private region. The higher density yields higher radiation power, moving line radiation zones further off the divertor plate. The simulated profiles of both D{sub {alpha}} and CIII radiation obtained with drift effects included are more consistent with measurements. The drifts also affect the in/out asymmetry of both divertor heating power and divertor ion flux. The effect of drifts on the up/down asymmetry of double null plasma configurations is also considered, although not in as much detail. The up/down asymmetry of the divertor heat flux which is measured in double null plasmas on DIII-D is consistent with that obtained in UEDGE simulations which include the effect of drifts. Drift effects can be important in determining the profile of divertor heating powers, and the distribution of recycling neutrals, and therefore should be included in the design of divertor structures for future fusion devices.