Gyrokinetic modelling of light to heavy impurity transport in tokamaks

Abstract

Impurity transport is numerically investigated for different types of impurity, such as helium (He), argon (Ar), and tungsten (W). Both turbulent and neoclassical transports are treated self-consistently using the full-f gyrokinetic software GYSELA. For a light impurity (He), the transport is mainly controlled by turbulence, while neoclassical transport is found to be dominant in the case of a heavy impurity (W). The impact of a poloidal asymmetry of the impurity density is also studied in detail and it is found to be strong in case of a high charge impurity, due to its Boltzmann-type response. Such strong asymmetry might lead to a core accumulation of heavy impurities by reducing the thermal screening factor of neoclassical transport. The two main contributions to neoclassical transport—Pfirsch–Schlüter (PS) flux and banana–plateau (BP) flux—are also studied. Depending on their mass (A) and charge (Z), the magnitudes of each flux are determined accordingly. Tungsten shows a strong PS flux compared to the other impurities, while BP flux is dominant in the case of argon. An analytical model including the effect of poloidal asymmetry is compared with the numerical simulation and a good agreement is found between them.

Effects of alpha particles on the transport of helium ash driven by collisionless trapped electron mode turbulence

“…The experiments on TFTR tokamak show that except the very central region, the transport level of helium ash in D-T plasmas is much higher than the prediction from neoclassical theory [13]. Moreover, both the experiments by external puffing or injecting helium impurity [14][15][16][17][18] and the fullf gyrokinetic simulation by GYSELA code [19] show that the transport level of helium impurity is anomalous. This phenomenon of anomalous transport is generally believed to be induced by the micro-turbulence [20].…”

Transport barrier in 5D gyrokinetic flux-driven simulations

“…The next step with this study is to inject impurities, like helium and tungsten, in the same manner as Lim [66], and observe the effect of those barriers on the impurity heat and particle transport with similar parameters in GYSELA.…”

Effect of toroidal rotation on impurity transport in tokamak improved confinement

“…Neoclassical transport coefficients for impurities are calculated by introducing geometrical factors (P A and P B ) into NCLASS in order to consider the poloidal asymmetry due to the toroidal rotation. The impurity flux is expressed in the following form [11,[41][42][43][44][45],…”