Dependence of the boundary heat flux width on core and edge profiles in Alcator C-Mod

Ballinger, S. B.; Brunner, D.; Hubbard, A. E.; Hughes, J. W.; Kuang, A. Q.; LaBombard, B.; Terry, J. L.; White, A. E.

doi:10.1088/1741-4326/ac637c

Dependence of the boundary heat flux width on core and edge profiles in Alcator C-Mod

Journal Article · Mon May 02 00:00:00 EDT 2022 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ac637c· OSTI ID:1979413

^[1]; ^[2]; Hubbard, A. E. ^[3]; ^[3]; ^[3]; ^[3]; ^[3]; White, A. E. ^[3]

MIT Plasma Science and Fusion Center, Cambridge, MA (United States); OSTI
Commonwealth Fusion Systems, Cambridge, MA (United States)
MIT Plasma Science and Fusion Center, Cambridge, MA (United States)

This work presents new evidence that the heat flux width, λ_q, in the Alcator C-Mod tokamak scales with the edge electron pressure, as observed in the ASDEX Upgrade (AUG) tokamak, but the scaling with volume-averaged pressure, $$\bar{p}$$, from the plasma stored energy, is a better predictor of λ_q in Alcator C-Mod than the edge electron pressure. These previous studies, which find that λ_q decreases with increasing plasma pressure, imply that a high performance core at high pressure will lead to challenging heat and particle exhaust due to very small λ_q. This concern has led to our significant enlargement of the C-Mod database with the electron density, temperature, and pressure profile data from the Thomson scattering and electron cyclotron emission diagnostics. Using the C-Mod database augmented with new profile data, we find that λ_q decreases with increasing edge electron pressure as $${\lambda }_{q}\propto {p}_{\mathrm{e},95}^{-0.26}$$, similar to results from AUG, and showing the strength of cross-machine comparisons. We also find that $${\lambda }_{q}\propto {p}_{\mathrm{e},\mathrm{c}\mathrm{o}\mathrm{r}\mathrm{e}}^{-0.56}$$, consistent with the original finding from C-Mod that the heat flux width scales as $${\bar{p}}^{-0.48}$$. The scalings of λ_q with separatrix pressure and gradient scale length are found to match the AUG results qualitatively. The C-Mod scalings with edge plasma quantities have more scatter than the $$\bar{p}$$ scaling, and, importantly, show different trends for H-modes relative to L- and I-mode. Furthermore, investigating the source of this discrepancy presents an opportunity for further study that may improve our ability to predict the heat flux width in different confinement scenarios in the pursuit of optimizing core-edge performance in future reactors.

View Accepted Manuscript (DOE)

Research Organization:: Massachusetts Institute of Technology (MIT), Cambridge, MA (United States)

Sponsoring Organization:: USDOE Office of Science (SC)

Grant/Contract Number:: SC0014264

OSTI ID:: 1979413

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 7 Vol. 62; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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