Direct measurement of the electron turbulence-broadening edge transport barrier to facilitate core–edge integration in tokamak fusion plasmas

• Published in: Nuclear fusion Vol. 63; no. 8; pp. 84002 - 84008
• Main Authors: Wang, H.Q., Hong, R., Jian, X., Rhodes, T.L., Guo, H.Y., Leonard, A.W., Ma, X., Watkins, J.G., Ren, J., Grierson, B.A., Shafer, M.W, Scotti, F., Osborne, T.H., Thomas, D.M., Yan, Z.
• Format: Journal Article
• Language: English
• Published: IAEA IOP Publishing 01.08.2023
• Subjects: H-mode pedestal; tokamak; turbulence
• ISSN: 0029-5515; 1741-4326
• DOI: 10.1088/1741-4326/acdfe2

Abstract The integration of a high-performance core and a dissipative divertor, or the so-called ‘core–edge integration,’ has been widely identified as a critical gap in the design of future fusion reactors. In this letter, we report, for the first time, direct experimental evidence of electron turbulence at the DIII-D H-mode pedestal that correlates with the broadening of the pedestal and thus facilitates core–edge integration. In agreement with gyrokinetic simulations, this electron turbulence is enhanced by high η e ( η e = L n / L T e , where L n is the density scale length and L T e is the electron temperature scale length), which is due to a strong shift between the density and temperature pedestal profiles associated with a closed divertor. The modeled turbulence drives significant heat transport with a lower pressure gradient that may broaden the pedestal to a greater degree than the empirical and theoretically predicted pedestal width scalings. Such a wide pedestal, coupled with a closed divertor, enables us to achieve a good core–edge scenario that integrates a high-temperature low-collisionality pedestal (pedestal top temperature T e,ped > 0.8 keV and a pedestal top collisionality ν * ped < 1) under detached divertor conditions. This paves a new path toward solving the core–edge integration issue in future fusion reactors.