COREDIV modelling of JET ILW discharges with different impurity seeding: nitrogen, neon, argon and krypton

Abstract

Numerical simulations with the COREDIV code of JET H-mode discharges with 25 MW of auxiliary heating in the ITER-like wall (ILW) configuration with different impurity seedings – nitrogen (N), neon (Ne), argon (Ar) and krypton (Kr) – are presented. All simulations have been performed with the same transport model and input discharge parameters like auxiliary heating, volume average plasma density, confinement factor. Only the seeded impurity puff rate was changed in the calculations. It appears that for the considered heating power of 25 MW and relatively low volume electron average density <ne> = 6.2 × 1019 m−3, impurity seeding is necessary. It has been found that for every gas at the maximum level of the seeding rate, allowed by the code convergence, the power to the plate is reduced up to 2–4 MW, with electron temperature at the plate of about 2 eV, indicating semi-detached conditions in the divertor region. It should be noted, however, that in cases with low and medium Z impurity (N, Ne and Ar), tungsten radiation is a significant part of radiation losses and stays above 22–32% of the total energy losses, but for high Z impurity (Kr) it is reduced up to 10% of the total losses. The maximum of the Kr radiation is between the pedestal region and separatrix, showing that radiative mantle can be created, which might have a strong influence on the plasma parameters in the pedestal region.

Influence of impurity seeding on the plasma radiation in the EAST tokamak

“…In almost all the USN discharges, we just observe the increase of W impurity radiation in bulk plasma region, but in some cases the W accumulation in the core of plasma caused by Ne seeding will be appeared. Some modeling works on JET also expound that the W accumulation and radiation cooling in the core plasma remain a serious problem for low and medium Z impurities seeding experiments [10].…”

“…Meanwhile, some simulation works have been done to research on the radiation characteristics of different impurities seeding. In JET, the modeled radiation results by COREDIV demonstrate that tungsten (W) plays an important role on the core radiation, and its effect can be reduced by increasing the seeding impurity atomic numbers [10]. The influences of different seeded impurities on detachment and pedestal by changing the radiation local regions have been investigated using the MIST impurity transport code in Alcator C-Mod [8].…”