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

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 & eta; (e) (& eta; (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 & nu;*(ped) < 1) under detached divertor conditions. This paves a new path toward solving the core-edge integration issue in future fusion reactors.

Automated summary

The integration of a high-performance core and a dissipative divertor, or "core-edge integration," is seen as a critical issue in designing future fusion reactors. This letter presents the first experimental evidence of electron turbulence at the DIII-D H-mode pedestal, which correlates with pedestal broadening and facilitates core-edge integration. The turbulence is enhanced by high η_e (η_e = L_n / L_T_e) due to a strong shift between density and temperature profiles associated with a closed divertor. This wide pedestal, coupled with a closed divertor, provides a solution to the core-edge integration issue in future fusion reactors.