Impact of nitrogen seeding on detachment and Scrape-off Layer properties in type-I ELMy H-mode TCV plasmas

Seeded impurities are essential to achieve divertor detachment, thereby mitigating the Scrape-off Layer (SOL) heat and particle exhaust in tokamak devices. Nonetheless, knowledge of their effect on SOL transport mechanisms is currently limited, complicating extrapolation to next step fusion reactors. To this end, a dataset of N₂-seeded type-I ELMy H-mode TCV plasmas in either low density, high input power (low collisionality, -ν^*) or medium-high density, lower power (high-ν^*) regimes has been assembled and is presented in this work. The D₂ gas fuelling and N₂ injection rates have been varied independently to disentangle their effects on SOL profiles. Both scenarios have been successfully detached with N₂ seeding, albeit only in between ELMs. A sustained higher core radiation and an increase in effective ion charge Z_eff in the confined region suggest core impurity accumulation during and after N₂ injection. At high-ν^*, seeding N₂ at zero D₂ rate does not yield any clear change in either the near SOL density gradient lengths and far SOL shoulder amplitude, or on the edge electron temperature profile. At low-ν^*, increasing the D₂ gas rate without seeding results in a progressive flattening of the SOL density profile. On the other hand, it is observed that seeding N₂ at low-ν^* has a more pronounced effect compared to high-ν^*, leading to cooling of the edge pedestal and overall steepening of the density profile, in terms of a decrease in the near SOL decay length and a distinct reduction in the far SOL shoulder.