Density peaking and particle transport in negative triangularity discharges on DIII-D

Electron transport in negative triangularity (NT) discharges was found to be an order of magnitude lower than for comparable positive triangularity discharges using gas puff modulation technique to separate the convective and diffusive components. Similar to positive triangularity plasmas, core density peaking increases with decreasing collisionality [1]. A dimensionless collisionality scan demonstrated that [GM1] the electron density peaking expressed as ne_0.4/ne_0.8 increased from 1.1 to 1.3 when the collisionality decreased by a factor 4. Gas puff modulations were applied to disentangle the contributions from Neutral Beam Injection (NBI) core fueling versus an inward pinch in setting the core density profile [2]. Transport analysis using the Aurora framework, shows particle transport values (for both D and V), at least an order of magnitude lower when compared to positive triangularity for the plasma core. Counter to previous dimensionless collisionality analysis of particle transport, the increase in peaking in NT is due to additional core NBI fueling, not an increase in |V/D| [2].

References

[1] C. Angioni, et al. PRL 90, 20 (2003), 205003.

[2] S. Mordijck et al. Nuclear Fusion 60, 6 (2020), 066019.