Prompt core confinement improvement across the L-H transition in DIII-D: Profile stiffness, turbulence dynamics, and isotope effect

We elaborate on the nature of the prompt core confinement improvement observed at the L-H transition in DIII-D, which is a long-standing issue unsolved for more than two decades and can impact future fusion reactor performance. Dynamic transport analysis suggests the essential role of the profile stiffness for understanding the mechanism of the prompt core confinement improvement. Beam emission spectroscopy shows that transport reduction at the core cannot be explained only by the ion scale turbulence density fluctuation suppression. Properties of nonlocal confinement improvement across the L-H transition are experimentally assessed in hydrogen (H) and deuterium (D) plasmas. Prompt core confinement improvement is found to be more rapid in the lighter hydrogen isotope.

Automated summary

This paper elaborates on the unresolved issue of the prompt core confinement improvement observed at the L-H transition in DIII-D, which can have implications for future fusion reactor performance. The role of profile stiffness in understanding the mechanism of this improvement is emphasized through dynamic transport analysis, while beam emission spectroscopy reveals that ion scale turbulence density fluctuation suppression alone cannot explain the transport reduction at the core. Experimental assessments of nonlocal confinement improvement across the L-H transition are conducted in hydrogen (H) and deuterium (D) plasmas, with findings indicating a more rapid prompt core confinement improvement in the lighter hydrogen isotope.