Divertor detachment in negative-delta configurations in the TCV tokamak

Experimental observations on TCV and DIII-D have shown that negative triangularity (δ) discharges may have H-mode grade confinement in L-Mode operation, which opens the possibility for high confinement reactors side-stepping the challenges associated with H-mode such as ELMs, narrow scrape-off layer widths, and density control. To ensure safe power exhaust, partially or fully detached divertor operation will still be required. In this work, we investigate detachment on TCV in ohmic L-Mode δ<0 configurations and compare it to matched ohmic L-Mode δ>0 cases. Preliminary results indicate that detachment is generally harder to reach in negative δ, where sufficient cooling (< 5eV) of the outer target is achieved only with high levels of N₂ seeding, and generally comes at the price of degraded core confinement. This behavior is currently ascribed to a connection length reduction at δ<0, resulting in a larger fraction of the exhaust power being diverted towards the outer target compared to δ>0.