I-Mode Exhaust Experiments on ASDEX Upgrade

Experiments conducted on ASDEX Upgrade (AUG) investigating the compatibility of dissipative divertors with high performance I-modes show plasmas exhibit a prompt, I/L back-transition prior to significant reductions in divertor heat flux when seeding nitrogen into the private flux region. The I-mode regime is currently being explored as a candidate reactor scenario, leveraging its demonstrated access to enhanced energy confinement, H$_{\mathrm{98}}$ \textgreater 1.0, while maintaining L-mode-like impurity confinement and avoiding large ELMs. Recently published attempts to integrate I-mode with detached divertor operation on Alcator C-Mod are introduced to give context to new AUG experiments at 1.0 MA, 2.5 T, with densities of 4-5e19 m$^{\mathrm{-3}}$. In AUG, ECH heating of \textasciitilde 2.2 MW is used to enter into a stationary I-mode, reaching pedestal-top T$_{\mathrm{e}}$ \textasciitilde 900 eV. Private flux N$_{\mathrm{2}}$ seeding at rate necessary to cause reductions in divertor heat flux, 3.0-6.0e21 el/s, results in an I/L back-transition within 1-2