High beta poloidal with ITB scenario development in neg-D plasmas

2023 Research Campaign, Thrust: Negative Triangularity

Purpose of Experiment

The purpose of this experiment is to develop high poloidal beta (βΡ) scenario with large radius ITB in negative triangularity (NT) plasmas on DIII-D. By doing so, the advantages of the two may be integrated together. NT configuration provides high βΡ plasma a non-ELMing edge, while high βΡ scenario gives NT plasma an advanced tokamak (AT) core with ITB at large radius, further enhancing energy confinement quality (H98y2) in NT plasmas. From physics point of view, this experiment will apply α-stabilization effect, which is confirmed in DIII-D high βΡ experiments with positive triangularity, on NT plasma for strong turbulence suppression and develop ITB at large radius. Therefore, successful execution of this experiment will show an AT path towards fusion energy with excellent core-edge integration, high H98y2 at low rotation, high βΝ, no ELMs, detached divertor, etc. This experiment has a secondary goal on understanding transport properties of ITB plasma at different neutral beam injection (NBI) torque and comparing with gyrokinetic modeling results by GTC code.

Experimental Approach

This experiment will adapt plasma waveforms from a previous successful high βΡ discharge at low plasma current (~ 0.6 MA). Off-axis current drive is preferred. It will help create a low magnetic shear detour around the instability mountain at large radius [Wang, Nature Communications 2021]. This an important approach to access ITB regime. Due to different plasma shape, it may be necessary to make certain changes in the early heating power and timing, gas puffing rate and timing, etc. High field side deuterium gas puffing and pellet injection are preferred to improve fueling efficiency. They may also help on ITB development according to gyrokinetic theory analysis [Kotschenreuther, 61st Annual Meeting of the American Physics Society Division of Plasma Physics 2019]. Counter-beams are preferred in order to accommodate the requirement of torque scan in a wide range. Different plasma current flattop ranging from 0.5 to 0.8 MA may be considered, depending on the progress of experiment.

See more details, including project leads, at U.S. Department of Energy, Office of Scientific and Technical Information (OSTI).