Predictive modeling of pedestal structure in KSTAR using EPED model

Abstract

A predictive calculation is given for the structure of edge pedestal in the H-mode plasma of the KSTAR (Korea Superconducting Tokamak Advanced Research) device using the EPED model. Particularly, the dependence of pedestal width and height on various plasma parameters is studied in detail. The two codes, ELITE and HELENA, are utilized for the stability analysis of the peeling-ballooning and kinetic ballooning modes, respectively. Summarizing the main results, the pedestal slope and height have a strong dependence on plasma current, rapidly increasing with it, while the pedestal width is almost independent of it. The plasma density or collisionality gives initially a mild stabilization, increasing the pedestal slope and height, but above some threshold value its effect turns to a destabilization, reducing the pedestal width and height. Among several plasma shape parameters, the triangularity gives the most dominant effect, rapidly increasing the pedestal width and height, while the effect of elongation and squareness appears to be relatively weak. Implication of these edge results, particularly in relation to the global plasma performance, is discussed. V C 2013 AIP Publishing LLC. [http://dx.

Physics-based integrated modeling of the energy confinement time scaling laws for the H- and L-modes in the KSTAR-type tokamak model

“…The scaling factor can be obtained from figure 8(a), with the estimated value found to be about 0.04 and 0.03 at P in ~ 5.0 MW and 10.0 MW, respectively. Note that the magnitude is very small, almost near zero, which is similar to that obtained in [22] using the EPED-like model, where the pedestal slope is calculated more directly. As discussed in [22], this weak B T dependence may be explained if we note that in the wellknown ballooning driving force term,…”

“…Note that the magnitude is very small, almost near zero, which is similar to that obtained in [22] using the EPED-like model, where the pedestal slope is calculated more directly. As discussed in [22], this weak B T dependence may be explained if we note that in the wellknown ballooning driving force term,…”

“…One thing to note here is that this result was obtained in the relatively low density regime of N b < 0.5 n G , where n G is the Greenwald density [31]. As shown in [22], this pedestal dependence on density can be changed substantially in the higher density regime. While this regime is not considered here, it would be important to check further in the future with the empirical scaling law itself.…”

“…Let us now consider the scaling factor, c 1 , coming from the pedestal boundary. In this case it is first noted that several works [7,22,26,27] have already been conducted using the EPED1 or EPED model, with some comparison with experimental data, showing that the I P dependence of the pedestal pressure is relatively strong. It has, however, been found that the exact scaling factor still has some variation depending on the used method or model, and also the core-edge coupling effect was treated approximately in most of these works.…”

“…Also, as mentioned earlier, we solve only the temperature profile equation, while a prescribed profile is used for the density. Finally, it is noted that in this work our study will be limited to a relatively narrow parameter regime, particularly taking the KSTAR-type medium-size tokamak [22] as the reference model, where the parameter values are given as major radius (R) = 1.74 m, minor radius (a) = 0.48 m, plasma current (I P ) = 1.0 MA, toroidal field (B T ) = 1.96 T, elongation (κ) = 1.8 and triangularity (δ) = 0.6.…”