2024 – Investigating the Impact of Operational Parameters on the Density Limit in Negative Triangularity Plasmas

Investigating the Impact of Operational Parameters on the Density Limit in Negative Triangularity Plasmas

2024 Research Campaign, Thrust: High Opacity and Density Operation

Purpose of Experiment

This experiment aims to explore the effects of input power, shear flows, and top triangularity on the L-mode density limit in negative triangularity (NT) plasmas using the DIII-D tokamak. The study is motivated by recent theoretical work suggesting that triangularity may influence the power dependence of the density limit in NT configurations.

Experimental Approach

The experimental approach involves systematic scans of input power (≥9 MW, 6 MW, ≤3 MW), input torque (three levels at fixed ~6 MW power), and top triangularity (-0.42 and -0.3). Density ramping will be performed during the Ip flattop phase until disruption occurs. The experiment will utilize a ‘hybrid’ NT configuration with lower single-null shaping. Analysis will focus on: 1. Power dependence of the density limit under different triangularity using power balance analysis 2. Turbulent transport and turbulence spreading near the density limit using fluctuation diagnostics 3. Edge turbulence simulations near the density limit using codes such as BOUT++ and CGYRO This research aligns with the goals of High Opacity and Density Operation Thrust and is expected to provide crucial insights into tokamak operational limits, particularly the power scaling of the density limit under varying triangularity. The findings could significantly impact future tokamak designs and operational strategies for optimized fusion energy production at high density and opacity.

Interested in a behind-the-scenes look at DIII-D? Join us for a virtual OR in-person tour during Fusion Energy Week (May 5-9)! Sign up for a tour here.

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