7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Detachment and scrape-off layer radial transport characterization in Negative
Triangularity discharges in DIII-D
F. Scotti1, A. McLean1, A. Marinoni2, C. Lasnier1, D. Eldon3, C. Paz-Soldan4,
A.O. Nelson4, K. Thome3, D. Truong1, H. Wang3, M.G. Burke1, R. Wilcox5, N. Li1, J. Lore5,M. Zhao1, A. Hyatt3, T. Osborne3, T. Leonard3, M. Fenstermacher1
1
Lawrence Livermore National Laboratory, 2University of California San Diego, 3General Atomics,
4
Columbia University, 5Oak Ridge National Laboratory
e-mail (speaker): scottif@fusion.gat.com
Experiments performed during the 2023 armored negative
triangularity (NT) campaign in DIII-D simultaneously
achieved divertor detachment, an ELM-free edge, andtolerance to extrinsic impurities for divertor dissipation,demonstrating the potential for a core-edge integrated
scenario. Detachment without impurity seeding wasachieved via an increase in plasma density for the firsttime in NT discharges (triangularity dtop=dbot=-0.5).
Detachment onset conditions in the outer divertor weresustained with H-mode level confinement H98-y2~1 andnormalized pressure levels bN~2. Energy confinement
degradation (~20-30%) was observed with deeper
detachment, which correlated with the loss of the edge
electron temperature pedestal and the movement of theradiation front in contact with closed flux surfaces.
Parametric dependence of access to detachment on plasma
current Ip and power flowing into the scrape-off layer PSOL
was consistent with expectations from detachment
scalings (linear dependence on Ip and sublinear
dependence on PSOL). However, densities higher than inpositive triangularity (PT) (Greenwald fraction fGW>0.9),
were needed to achieve detachment, due to the shorter
parallel connection length and narrowing of the scrape-off
layer heat flux width at the strongest NT, approachingvalues typical of PT H-mode discharges. Impurity seedingwith nitrogen and neon reduced the detachment density up
to 30% at the expense of core dilution. Detachment onset

Figure 1. Experimental magnetic equilibria for NT
discharge with dtop=dbot=-0.5 (black) and discharge
with reduced negative triangularity dtop=dbot=-0.5(red).

density was 40% higher with ion B´ÑB drift into thedivertor compared to out of the divertor in NT (fGW~1.3vs. 0.9), while this difference is typically less than 15% in
PT. The effect of cross-field drifts on divertor profiles waslarger than observed in PT discharges due to the lower
toroidal field at the X-point in NT shapes. Discharges withlower average NT (dtop=-0.4, dbot=0.2) and longer
midplane to target parallel connection length detached at~30% lower line-averaged densities compared todischarges at the largest NT, showing that the very highdensity needed is not intrinsic to NT but due to the divertor
geometry used in these experiments. Edge fluid
simulations (UEDGE, SOLPS) quantitatively reproduce
the observed drift dependences and high densities neededfor detachment, increasing confidence in extrapolation tofuture NT divertor design.
Supported by US DOE DE-AC52-07NA27344 and DEFC02-04ER54698.

Figure 2. (top) line averaged ne (red), input power(black); (middle) normalized plasma pressure bn(black), H-mode confinement factor H98-y2 (red)and effective charge Zeff; (bottom) Te at the outerstrike point and peak heat flux (red). Detachment
onset conditions are indicated with a dashed line.