Disentangling Core and Edge Mechanisms of the Density Limit in DIII-D Negative Triangularity Plasmas
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arXiv
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| Format: | Preprint |
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2025
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| author | Hong, R. Diamond, P. H. Sauter, O. Chen, J. Khabanov, F. Li, Z. Liu, D. Marinoni, A. McKee, G. R. Rhodes, T. L. Scotti, F. Thome, K. E. Tynan, G. R. Van Zeeland, M. A. Yan, Z. Zeng, L. Team, the DIII-D NT |
| author_facet | Hong, R. Diamond, P. H. Sauter, O. Chen, J. Khabanov, F. Li, Z. Liu, D. Marinoni, A. McKee, G. R. Rhodes, T. L. Scotti, F. Thome, K. E. Tynan, G. R. Van Zeeland, M. A. Yan, Z. Zeng, L. Team, the DIII-D NT |
| contents | The density limit is investigated in the DIII-D negative triangularity (NT) plasmas which lack a standard H-mode edge. We find the limit may not be a singular disruptive boundary but a multifaceted density saturation phenomenon governed by distinct core and edge transport mechanisms. Sustained, non-disruptive operation is achieved at densities up to 1.8 times the Greenwald limit ($n_\mathrm{G}$) until the termination of auxiliary heating. Systematic power scans reveal distinct power scalings for the core ($n_e \propto P_\mathrm{SOL}^{0.27\pm0.03}$) and edge ($n_e \propto P_\mathrm{SOL}^{0.42\pm0.04}$) density limits. The edge density saturation is triggered abruptly by the onset of a non-disruptive, high-field side radiative instability that clamps the edge density below $n_\mathrm{G}$. In contrast, the core density continues to rise until it saturates, a state characterized by substantially enhanced core turbulence. Core transport evolves from a diffusive to an intermittent, avalanche-like state, as indicated by heavy-tailed probability density functions (kurtosis $\approx 6$), elevated Hurst exponents, and a $1/f$-type power spectrum. These findings suggest that the density limit in the low-confinement regime is determined by a combination of edge radiative instabilities and core turbulent transport. This distinction provides separate targets for control strategies aimed at extending the operational space of future fusion devices. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_02773 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Disentangling Core and Edge Mechanisms of the Density Limit in DIII-D Negative Triangularity Plasmas Hong, R. Diamond, P. H. Sauter, O. Chen, J. Khabanov, F. Li, Z. Liu, D. Marinoni, A. McKee, G. R. Rhodes, T. L. Scotti, F. Thome, K. E. Tynan, G. R. Van Zeeland, M. A. Yan, Z. Zeng, L. Team, the DIII-D NT Plasma Physics The density limit is investigated in the DIII-D negative triangularity (NT) plasmas which lack a standard H-mode edge. We find the limit may not be a singular disruptive boundary but a multifaceted density saturation phenomenon governed by distinct core and edge transport mechanisms. Sustained, non-disruptive operation is achieved at densities up to 1.8 times the Greenwald limit ($n_\mathrm{G}$) until the termination of auxiliary heating. Systematic power scans reveal distinct power scalings for the core ($n_e \propto P_\mathrm{SOL}^{0.27\pm0.03}$) and edge ($n_e \propto P_\mathrm{SOL}^{0.42\pm0.04}$) density limits. The edge density saturation is triggered abruptly by the onset of a non-disruptive, high-field side radiative instability that clamps the edge density below $n_\mathrm{G}$. In contrast, the core density continues to rise until it saturates, a state characterized by substantially enhanced core turbulence. Core transport evolves from a diffusive to an intermittent, avalanche-like state, as indicated by heavy-tailed probability density functions (kurtosis $\approx 6$), elevated Hurst exponents, and a $1/f$-type power spectrum. These findings suggest that the density limit in the low-confinement regime is determined by a combination of edge radiative instabilities and core turbulent transport. This distinction provides separate targets for control strategies aimed at extending the operational space of future fusion devices. |
| title | Disentangling Core and Edge Mechanisms of the Density Limit in DIII-D Negative Triangularity Plasmas |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2504.02773 |