Effects of drifts on divertor particle distribution and detachment near target plate in DIII-D

For B × ∇B drift toward the open divertor in DIII-D LSN (lower single null) plasmas, the particle flux near the inner divertor target exhibits a double-peak structure with low electron temperature. This results from the interplay between strong poloidal E_r × B flow from the outer divertor toward the inner divertor and enhanced radial E_θ × B flow at the inner target. Reversing the B_T direction reverses both flows, leading to a broad particle flux profile in the outboard SOL exhibiting a similar double-peak structure. In addition, reversing B_T facilitates the achievement of detachment near the outer strike point at lower upstream density, presumably due to the E×B drift. However, J_sat, i.e. the particle flux measured by the probe ion saturation current, remains high in the SOL, rendering it difficult to achieve fully detached plasmas. In contrast, divertor detachment with a cold and flat temperature profile and significant J_sat rollover can be achieved at both target plates with the forward Bt.

Work supported by US DOE under DE-FC02-04ER54698, DE-AC04-94AL85000.