Experimental study of fast-ion confinement in NT versus PT shaped plasmas in the TCV tokamak*

Negative triangularity (NT) shaped plasmas in tokamaks exhibit improved confinement compared to positive triangularity (PT) shaped plasmas in L-mode, likely due to reduced microturbulence. Notably, NT plasmas achieve this enhanced confinement without ELMs, an instability in H-mode plasmas that future fusion reactors cannot tolerate, making NT plasmas attractive for future reactors. However, experimental studies on fast ion confinement in NT plasmas are limited, with only one systematic study on the DIII-D tokamak published.

The TCV tokamak has led investigations into NT shaped plasmas, demonstrating improved confinement properties. With its flexible shaping capabilities and recent upgrades to the neutral beam injection system and fast-ion loss detector diagnostic, TCV can now systematically investigate fast ion confinement in NT plasmas. Experiments have been conducted to compare fast-ion confinement in NT and mirrored PT plasmas. Results from these experiments will be presented, comparing fast-ion confinement in MHD quiescent plasmas with neoclassical modeling using the TRANSP and ASCOT codes. Preliminary findings reveal comparable fast-ion confinement between NT and PT configurations. Additionally, insights into mode properties and associated fast-ion transport in MHD active plasmas will be discussed, enhancing our understanding of plasma confinement in NT-shaped tokamaks.