On the origin of the DIII-D L-H power threshold isotope effect

Journal Article · 25 September 2023 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/acf86c · OSTI ID:2005025

Callahan, K. J. ; Schmitz, L. ; Carter, T. A. ; Belli, E. A. ; Chrystal, C. ; Haskey, S. R. ; Grierson, B. A. ; Thome, K. E. ; Smith, S. P. ; McKee, G. R. ; Staebler, G. M. ; Holland, C. ; Ashourvan, A. ; Yan, Z.

Abstract The increased low to high confinement mode (L to H-mode) power threshold $P_{\mathrm{L}\mathrm{H}}$ in DIII-D low collisionality hydrogen plasmas (compared to deuterium) is shown to result from lower impurity (carbon) content, consistent with reduced (mass-dependent) physical and chemical sputtering of graphite. Trapped gyro-Landau fluid (TGLF) quasilinear calculations and local non-linear gyrokinetic CGYRO simulations confirm stabilization of ion temperature gradient (ITG) driven turbulence by increased carbon ion dilution as the most important isotope effect. In the plasma edge, electron non-adiabaticity is also predicted to contribute to the isotope dependence of thermal transport and $P_{\mathrm{L}\mathrm{H}}$ , however its effect is subdominant compared to changes from impurity isotopic behavior. This L-H power threshold reduction with increasing carbon content at low collisionality is in stark contrast to high collisionality results, where additional impurity content appears to increase the power necessary for H-mode access.

• Sponsoring Organization: USDOE
• Grant/Contract Number: NONE; AC02-09CH11466
• OSTI ID: 2005025
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 12 Vol. 63; ISSN 0029-5515
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: IAEA
• Language: English