2025 – Particle and impurity transport in negative triangularity discharges

Particle and impurity transport in negative triangularity discharges

2025 Research Campaign, Negative Triangularity

Purpose of Experiment

The purpose of this experiment is systematics validation of particle transport models in negative triangularity discharges. Negative triangularity prevents L-H transition and allows to access plasma parameters which would not be accessible in either L or H mode positive triangularity plasmas. In addition, elm free edge will reduce uncertainty in the inference of the particle and impurity transport coefficients from experimental data and thus enables a more stringent tests of the gyrokinetics models. Due to a missing edge transport barrier, the core impurity confinement is dominated by a turbulent transport and we might be able to observe a weaker parameter dependencies of turbulent transport which are hidden by a parameter dependence of ELMs and pedestal in the H-mode.

Experimental Approach

This experiment will perform several parameter scans – torque, electron/ion power, collisionality and upper triangularity. These parameters should have the strongest impact on the turbulent impurity transport. In addition, charge and mass dependence of impurity transport will be investigated by comparing transport coefficients for D, He, B, C, F, Ne, Ar, Ca and W. These impurities will be injected by DIII-D gas puff system, impurity powder dropper and laser blow off system. Impurity density will be inferred from spectroscopic charge exchange measurements and Soft-X ray measurements. The inferred transport coefficients will be later compared with nonlinear gyrokinetics modeling using PORTALS and neoclassical model NEO.

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