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

TY - JOUR

T1 - On the origin of the DIII-D L-H power threshold isotope effect

AU - Callahan, K.

AU - Schmitz, L.

AU - Carter, T.

AU - Belli, E.

AU - Chrystal, C.

AU - Haskey, S.

AU - Grierson, B.

AU - Thome, K.

AU - Smith, S.

AU - McKee, G.

AU - Staebler, G.

AU - Holland, C.

AU - Ashourvan, A.

AU - Yan, Z.

N1 - Publisher Copyright: © 2023 The Author(s). Published by IOP Publishing Ltd on behalf of the IAEA. All rights reserved.

PY - 2023/12

Y1 - 2023/12

N2 - The increased low to high confinement mode (L to H-mode) power threshold P L 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 L 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.

AB - The increased low to high confinement mode (L to H-mode) power threshold P L 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 L 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.

KW - L-H transition

KW - isotope

KW - turbulence

UR - https://www.scopus.com/pages/publications/85174262944

UR - https://www.scopus.com/pages/publications/85174262944#tab=citedBy

U2 - 10.1088/1741-4326/acf86c

DO - 10.1088/1741-4326/acf86c

M3 - Article

SN - 0029-5515

VL - 63

JO - Nuclear Fusion

JF - Nuclear Fusion

IS - 12

M1 - 126009

ER -