Dynamics of the inboard scrape-off layer in ASDEX Upgrade

We present our studies of the inboard scrape-off layer (SOL) at ASDEX Upgrade under various magnetic configurations and the dynamics of the high-density region near the inboard plasma edge [1]. We investigate hollow density profiles at the inboard midplane SOL using multiple diagnostics and a novel interpretation of reflectometry data based on the spectral signature of the beat signal [2]. We also examine the magnetic configuration's role in shaping the inboard SOL profile, particularly as the plasma nears a double-null configuration typical of many reactor designs [3]. Our findings reveal a narrowing of the inboard SOL profile, driven by magnetic disconnection from the outboard SOL. These findings highlight the significance of magnetic topology and parallel heat conduction in determining inboard SOL properties. Steep density gradients exist at the secondary separatrix in the midplane and divertor regions caused by the inboard high-density region. Near double-null, a significant reduction in conducted heat to the inboard SOL results in decreased electron and neutral density in the inboard divertor. Lastly, we demonstrate that unfavorable field configurations significantly suppress the high-density region and use these scenarios to measure the edge density decay length at the inboard and outboard midplane, consistently finding a larger outboard decay length, corroborating the expected ballooning nature of radial transport in tokamaks.