Ion thermal transport in the H-mode edge transport barrier on DIII-D

The power balance ion heat flux in the pedestal region on DIII-D increases and becomes increasingly anomalous (above conventional neoclassical) in experiments with higher temperature and lower density pedestals where the ion collisionality ( ν i *) is lowered toward values expected on ITER. Direct m...

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Bibliographic Details
Published in:Physics of plasmas 2022-01, Vol.29 (1)
Main Authors: Haskey, S. R., Ashourvan, Arash, Banerjee, S., Barada, K., Belli, E. A., Bortolon, A., Candy, J., Chen, J., Chrystal, C., Grierson, B. A., Groebner, R. J., Laggner, F. M., Knolker, M., Kramer, G. J., Major, M. R., Mckee, G., Staebler, G. M., Yan, Z., Van Zeeland, M. A.
Format: Article
Language:English
Subjects:
Backscattering
Broadband
Deuterium
Heat
Heat flux
Heat transfer
Ion temperature
Mathematical analysis
Plasma physics
Plasmas (physics)
Turbulence
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Summary:The power balance ion heat flux in the pedestal region on DIII-D increases and becomes increasingly anomalous (above conventional neoclassical) in experiments with higher temperature and lower density pedestals where the ion collisionality ( ν i *) is lowered toward values expected on ITER. Direct measurements of the main-ion temperature are shown to be essential on DIII-D when calculating the ion heat flux due to differences between the temperature of D+ and the more commonly measured C 6 + impurity ions approaching the separatrix. Neoclassical transport calculations from NEO and non-linear gyrokinetic calculations using CGYRO are consistent with these observations and show that while neoclassical transport plays an important role, the turbulent ion heat flux due to ion scale electrostatic turbulence is significant and can contribute similar or larger ion heat fluxes at lower collisionality. Beam emission spectroscopy and Doppler backscattering measurements in the steep gradient region of the H-mode pedestal reveal increased broadband, long-wavelength ion scale fluctuations for the low ν i * discharges at the radius where the non-linear CGYRO simulations were run. Taken together, increased fluctuations, power balance calculations, and gyrokinetic simulations show that the above neoclassical ion heat fluxes, including the increases at lower ν i *, are likely due to weakly suppressed ion scale electrostatic turbulence. These new results are based on world first inferred ion and electron heat fluxes in the pedestal region of deuterium plasmas using direct measurements of the deuterium temperature for power balance across ion collisionalities covering an order of magnitude from high ν i * values of 1.3 down to ITER relevant ν i * ∼ 0.1.
ISSN:1070-664X
1089-7674
DOI:10.1063/5.0072155