Dependence of the L-Mode scrape-off layer power fall-off length on the upper triangularity in TCV

This paper reports on experimental observations on TCV with a scan in upper triangularity delta(up), including negative triangularity, focusing on the power fall-off length lambda(q) in L-Mode. The upper triangularity is scanned from -0.28 to 0.47. Smaller lambda(out)(q) is measured at the outer divertor target for decreasing delta(up) together with higher edge temperature T-e,T-edge leading to increased confinement. This effect is observed for both magnetic drift directions for discharges in deuterium and helium. In helium larger lambda(q) values are observed compared to deuterium. The power fall-off length at the inner divertor target lambda(in)(q) has a non-monotonic behaviour with changing triangularity. The largest values are around delta(up) = 0. The ratio lambda(in)(q)/lambda(out)(q) increases for decreasing delta(up) for positive triangularity and is approximately constant for negative triangularity. lambda(out)(q) is compared to available scaling laws. Partial agreement is only observed for a scaling law containing a proxy for T-e,T-edge at ASDEX Upgrade (Sieglin 2016 Plasma Phys. Control. Fusion 58 055015). Extending this scaling to TCV and using T-e,T-edge at rho(pol) = 0.95 suggests that lambda(out)(q) is independent of machine size lambda(L-Mode)(q) (mm)= 165.B-pol(T)(-0.66). A(u)(-0.15). T-e,T-edge(eV)(-0.93). R(m)(-0.03). Possible explanations for smaller lambda(out)(q) for decreasing delta(up) is a reduction in turbulence or a direct effect of increasing T-e,T-edge.