Direct gyrokinetic comparison of pedestal transport in JET with carbon and ITER-like walls

Hatch, D. R.; Kotschenreuther, M.; Mahajan, S. M.; Merlo, G.; Field, A. R.; Giroud, C.; Hillesheim, J. C.; Maggi, C. F.; Perez von Thun, C.; Roach, C. M.; Saarelma, S.

doi:10.1088/1741-4326/ab25bd

Title: Direct gyrokinetic comparison of pedestal transport in JET with carbon and ITER-like walls

Journal Article · 08 July 2019 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/ab25bd · OSTI ID:1577625

^[1]; Kotschenreuther, M. ^[1]; Mahajan, S. M. ^[1]; Merlo, G. ^[1]; Field, A. R. ^[2]; Giroud, C. ^[2]; Hillesheim, J. C. ^[2];

^[2];

^[3]; Roach, C. M. ^[2]; Saarelma, S. ^[2]

Univ. of Texas, Austin, TX (United States)
Culham Science Centre, Abingdon (United Kingdom). Culham Centre for Fusion Energy (CCFE)
Forschungszentrum Juelich (Germany)

Our work compares the gyrokinetic instabilities and transport in two representative JET pedestals, one (pulse 78697) from the JET configuration with a carbon wall (C) and another (pulse 92432) from after the installation of JET's ITER-like Wall (ILW). The discharges were selected for a comparison of JET-ILW and JET-C discharges with good confinement at high current (3 MA, corresponding also to low ρ_*) and retain the distinguishing features of JET-C and JET-ILW, notably, decreased pedestal top temperature for JET-ILW. A comparison of the profiles and heating power reveals a stark qualitative difference between the discharges: the JET-ILW pulse (92432) requires twice the heating power, at a gas rate of 1.9 × 10²² e s^-1, to sustain roughly half the temperature gradient of the JET-C pulse (78697), operated at zero gas rate. This points to heat transport as a central component of the dynamics limiting the JET-ILW pedestal and reinforces the following emerging JET-ILW pedestal transport paradigm, which is proposed for further examination by both theory and experiment. ILW conditions modify the density pedestal in ways that decrease the normalized pedestal density gradient a/L n , normally via an outward shift in relation to the temperature pedestal. This is attributable to some combination of direct metal wall effects and the need for increased fueling to mitigate tungsten contamination. The modification to the density profile increases η=L_n/L_γ, thereby producing more robust ion temperature gradient (ITG) and electron temperature gradient driven instability. The decreased pedestal gradients for JET-ILW (92432) also result in a strongly reduced E × B shear rate, further enhancing the ion scale turbulence. Collectively, these effects limit the pedestal temperature and demand more heating power to achieve good pedestal performance. Our simulations, consistent with basic theoretical arguments, find higher ITG turbulence, stronger stiffness, and higher pedestal transport in the ILW plasma at lower ρ_*.

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Research Organization:: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); Univ. of Texas, Austin, TX (United States)

Sponsoring Organization:: USDOE Office of Science (SC)

Contributing Organization:: JET Contributors

Grant/Contract Number:: FG02-04ER54742; SC0018429

OSTI ID:: 1577625

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 8 Vol. 59; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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Microtearing modes as the source of magnetic fluctuations in the JET pedestal Hatch, D. R.; Kotschenreuther, M.; Mahajan, S. M. Nuclear Fusion, Vol. 61, Issue 3 https://doi.org/10.1088/1741-4326/abd21a	journal	February 2021
Isotope dependence of the type I ELMy H-mode pedestal in JET-ILW hydrogen and deuterium plasmas Horvath, L.; Maggi, C. F.; Chankin, A. Nuclear Fusion, Vol. 61, Issue 4 https://doi.org/10.1088/1741-4326/abdd77	journal	March 2021
Overview of the JET preparation for deuterium–tritium operation with the ITER like-wall Joffrin, E.; Abduallev, S.; Abhangi, M. Nuclear Fusion, Vol. 59, Issue 11 https://doi.org/10.1088/1741-4326/ab2276	journal	August 2019
Overview of the JET preparation for deuterium–tritium operation with the ITER like-wall Joffrin, E.; Abduallev, S.; Abhangi, M. Karlsruhe https://doi.org/10.5445/ir/1000098397	text	January 2019

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