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

Abstract

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 × 10 ²² 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. Thismore » 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 _*.« less

Authors:

Hatch, D. R.  ^[1];

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

• Search DOE PAGES for author "Maggi, C. F."
• Search DOE PAGES for ORCID "0000-0001-7208-2613"
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Perez von Thun, C.  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-1166-2179"
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Roach, C. M. ^[2]; Saarelma, S. ^[2]

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+ Show Author Affiliations

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

Publication Date:

2019-07-09

Research Org.:

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

Sponsoring Org.:

USDOE Office of Science (SC)

Contributing Org.:

JET Contributors

OSTI Identifier:

1577625

Grant/Contract Number:  

FG02-04ER54742; SC0018429

Resource Type:

Accepted Manuscript

Journal Name:

Nuclear Fusion

Additional Journal Information:

Journal Volume: 59; Journal Issue: 8; Journal ID: ISSN 0029-5515

Publisher:

IOP Science

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY