First experimental tests of a new small angle slot divertor on DIII-D. (9th July 2019)

• Record Type: Journal Article
• Authors: Guo, H.Y.; Wang, H.Q.; Watkins, J.G.; Casali, L.; Covele, B.; Moser, A.L.; Osborne, T.; Samuell, C.M.; Shafer, M.W.; Stangeby, P.C.; Thomas, D.M.; Boedo, J.; Buttery, R.J.; Groebner, R.; Hill, D.N.; Holland, L.; Hyatt, A.W.; Jaervinen, A.E.; Kellman, A.; Lao, L.L.; Lasnier, C.J.; Leonard, A.W.; Murphy, C.; Ren, J.; Sang, C.F.; Sontag, A.C.; Taylor, T.S.
• Other Names: collab.
• Is Part Of: Nuclear fusion. Volume 59:Number 8(2019:Aug.)
• Publication Date: 2019-07-09
• Subjects: advanced divertor -- plasma-material interactions -- tokamak -- DIII-D; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/1741-4326/ab26ee
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: A new small angle slot (SAS) divertor concept has been developed to enhance neutral cooling across the divertor target by coupling a closed slot structure with appropriate target shaping. Initial tests on DIII-D find a strong interplay between such anticipated 'SAS' effects and cross-field drifts, favouring operation with the ion B × ∇ B drift away from the X -point, as currently employed for advanced tokamaks. This offers the following key improvements relative to DIII-D's open lower divertor or partially-closed upper divertor: (i) SAS allows for transition to low temperature moderately detached divertor conditions with T e ≲ 10 eV at very low main plasma densities, lower than are usually attainable at all in DIII-D high confinement (H-mode) plasmas as used in these tests; (ii) Pedestal performance and core confinement are significantly improved with SAS. The final confinement collapse associated with the onset of X -point MARFE (multifaceted asymmetric radiation from the edge) following deep detachment occurs at significantly higher pedestal densities, thus widening the window of H-mode operation compatible with a dissipative divertor. For operation with the ion B × ∇ B drift toward the X -point, the divertor plasma transitions to a bifurcative detached state at much higher densities, similar to other divertor configurations in DIII-D. These results highlight the strong interplay between divertor closure and drifts, and point to an interesting divertor optimization path to explore that offers potential for future fusion reactors.