Core electron temperature turbulence and transport during sawtooth oscillations in the DIII-D tokamak

Abstract

Sawteeth are one of the concerning instabilities in ITER and future burning plasma experiments. Sawtooth dynamics and its interaction with broadband plasma turbulence has been a challenge for predictive simulations of core transport in future fusion devices. This study provides new observations of core turbulence behavior during sawtooth oscillations in DIII-D hydrogen L-mode neutral beam injection heated plasmas in an inner wall limited configuration. A strong correlation of electron temperature and density turbulence levels with the sawtooth oscillation phase has been observed at locations inside the Te inversion radius and/or safety factor q=1 magnetic surface. The Te turbulence amplitude in the core during the sawtooth ramp exhibits a critical Te gradient behavior inside but not near the Te inversion radius/q=1 magnetic surface. The most unstable mode calculated from the trapped gyro-landau fluid (TGLF) turbulence simulations reveal a change from low-k ion-type to low-k electron-type modes from pre- to post- sawtooth crash time periods.