Parameter dependencies of the separatrix density in low triangularity L-mode and H-mode JET-ILW plasmas. (1st March 2023)

• Record Type: Journal Article
• Authors: Lomanowski, B.; Rubino, G.; Uccello, A.; Dunne, M.; Vianello, N.; Aleiferis, S.; Canik, J.; Carvalho, I.; Corrigan, G.; Frassinetti, L.; Frigione, D.; Garzotti, L.; Groth, M.; Meigs, A.; Maslov, M.; von Thun, C. Perez; Rimini, F.; Schneider, P.A.; Sergienko, G.; Simpson, J.; Van Eester, D.
• Is Part Of: Nuclear fusion. Volume 63:Number 3(2023)
• Publication Date: 2023-03-01
• Subjects: separatrix density -- divertor and main chamber recycling -- two point model -- SOL-pedestal-core integration; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/1741-4326/aca9de
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: The midplane electron separatrix density, n e, sep, in JET-ILW L-mode and H-mode low triangularity deuterium fuelled plasmas exhibits a strong explicit dependence on the averaged outer divertor target electron temperature, n e, sep ∼ T e, ot −1/2 . This dependence is reproduced by analytic reversed two point model (rev-2PM), and arises from parallel pressure balance, as well as the ratio of the power and momentum volumetric loss factors, (1 − f cooling )/(1 − f mom-loss ). Quantifying the influence of the (1 − f cooling ) and (1 − f mom-loss ) loss factors on n e, sep has been enabled by measurement estimates of these quantities from L-mode density (fueling) ramps in the outer horizontal, VH(C), and vertical target, VV, divertor configurations. Rev-2PM n e, sep estimates from the extended H-mode and more limited L-mode datasets are recovered to within ±25% of the measurements, with a scaling factor applied to account for use of T e, ot, an averaged quantity, rather than flux tube resolved target values. Both the (1 − f cooling ) and (1 − f mom-loss ) trends and recovery of n e, sep using the rev-2PM formatting are reproduced in EDGE2D-EIRENE L-mode-like and H-mode-like density scan simulations. The general lack of a divertor configuration effect in the JET-ILW n e, sep trends can be attributed to a significant influence of main chamber recycling, which has been shown in the EDGE2D-EIRENE results to moderate n e, sep with respect to changes in divertor neutral leakage imposed by changes in the divertor configuration. The unified n e, sep vs T e, ot trends can, however, be broken if large modifications to the divertor geometry (e.g. complete removal of the outer divertor baffle structure) are introduced in the model. The more pronounced high-field side high density region formation in the VH(C) configuration with reduced clearance to the separatrix does not appear to have a significant influence on the outer midplane separatrix and pedestal parameters when mapped to T e, ot, although conditions at the inner midplane could not be assessed.