7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Effect of density profiles on the pedestal performance

G.Q. Li1, Y.J. Yang1,2, K. Li3, T.F. Tang4, K.D. Li1, X. Lin1, K.N. Geng1, X.J. Liu1, G.S. Li1,X.X. Zhang1, X.H. Wu1,2, B. Li1,2, H.C. Fan1,2, W.J. Zhou1,21
Institute of Plasma Physics, CAS, Hefei China
2
University of Science and Technology of China, Hefei China
3
Qingdao University, Qingdao China
4
Oak Ridge Associated Universities, Oak Ridge Tennessee USAe-mail (speaker): ligq@ipp.ac.cn
The EPED model [1] (and other EPED-like models)has been validated on many tokamaks and has
successfully predicted the pedestal structure. In thestandard EPED model, the density and temperaturepedestals are assumed to have the same position andwidth. However, under some experimental conditions,such as strong gas fueling, lithium injection and impurity
seeding, the density pedestal could change its width andposition, and the pressure pedestal height and ELM
behavior also change. In this study, we developed theREPED model to study the effect of density profiles on
the pedestal performance in EAST, and then used themodel to predict the ITER pedestal performance.
EAST has some unique features that may affect thepedestal structure, such as lithium wall conditioning,
LHCD dominant heating power, full metal wall andtungsten divertor. The REPED model [2], also an
EPED-like model, has been validated with EAST
experiments. But the pedestal width coefficient G=0.12,
a little larger than the typical values in other tokamaks.
We further developed the REPED model to consider
the density pedestal and the temperature pedestal to havedifferent structures. The REPED shows that as theseparatrix density increases, the pressure pedestal heightincreases. The reason is that the higher the separatrix
density, the lower the pedestal gradient, which makes theballooning modes more stable. Our calculation also
shows that the density pedestal width can affect thepressure pedestal height. If the density pedestal width is
wider than the temperature width, the pressure pedestal
height could increase; while the narrower density
pedestal could cause the pressure pedestal height todecrease. An EAST discharge is used to validate ourmodel. In this discharge lithium injection made thedensity pedestal width wider than the temperaturepedestal width, and the experimental pressure pedestal
height agrees with the REPED prediction. Neon seeding
could further make the density pedestal even wider andthe discharge became ELM-free. In this situation, theREPED could not predict the pedestal height because thestability analysis shows that the operation point is far
away from the peeling-ballooning boundary.
The model is applied to ITER to see the effect ofdensity profiles on the ITER pedestal performance.
Figure 1 shows that if the density pedestal is 0.02 wider
than the temperature, the pressure pedestal height could
increase by 10%.
References[1] P.B. Snyder et al, Nucl. Fusion 49, 085035 (2009)[2] K. Li et al, Plasma Phys. Control. Fusion 62, 11500(2020)

Figure 1. Predicted ITER pedestal structure with density pedestal wider or narrower than temperature. (a) Density
profiles; (b) Temperature profiles; (c) Pressure profiles; (d) Current density profiles.