Impact of Cross-field Drifts on Detachment in DIII-D

Simulations of DIII-D plasmas have revealed the strong role of \textbf{E}$\times$\textbf{B}-drifts in the low field side (LFS) detachment structure. High confinement modes (H-mode) with the $\nabla$B-drift towards the X-point (fwd B$_T$) enter detachment at 20\% higher upstream density, n$_{e,sep}$, than plasmas with the $\nabla$B-drift away from the X-point (rev B$_T$). In contrast, low confinement modes (L-mode) enter detachment at 10\% lower n$_{e,sep}$ in fwd B$_T$. Despite this, both L- and H-modes detached plasmas show strong target flux, J$_{SAT}$, reduction with increasing n$_{e,sep}$ in fwd B$_T$, while only a modest reduction occurs in rev B$_T$. In fwd B$_T$ H-mode, a step-wise transition from attached to strongly detached conditions is observed with increasing ne,sep. UEDGE simulations indicate that the strong poloidal \textbf{E}$\times$\textbf{B}-drift in the private flux region in H-mode drives the difference for the detachment onset relative to L-mode. In fwd B$_T$, the dependence of this poloidal \textbf{E}$\times$\textbf{B}-drift on the divertor conditions can reinforce the plasma into either attached or strongly detached state. In rev B$_T$, radial \textbf{E}$\times$\textbf{B}-drift depletes strike-line n$_e$, limiting the degree of detachment.