  In this work, we study the impact of aspect ratio A = R0 /r (the ratio of
major radius R0 to minor radius r) on the confinement benefits of Negative
Triangularity (NT) plasma shaping. We use high-fidelity flux tube gyrokinetic
GENE simulations and consider several different scenarios: four of them
inspired by TCV experimental data, a scenario inspired by DIII-D experimental
data and a scenario expected in the new SMART spherical tokamak. The present
study reveals a surprising and non-trivial dependence. NT improves confinement
at any value of A for ITG turbulence, while for TEM turbulence confinement is
improved only in the case of large and conventional aspect ratios.
Additionally, through a detailed study of a large aspect ratio case with pure
ITG drive, we develop an intuitive physical picture that explains the
beneficial effect of NT at large and conventional aspect ratios. This picture
does not hold in TEM-dominated regimes, where a complex synergistic effect of
many factors is found. Finally, we performed the first linear gyrokinetic
simulations of SMART, finding that both NT and PT scenarios are dominated by
micro-tearing-mode (MTM) turbulence and that NT is more susceptible to MTMs at
tight aspect ratio. However, we found that a regime where ITG dominates in
SMART can be found, and in this regime NT is more linearly stable.
