Speaker
Description
The ad-hoc description of anomalous transport remains a dominant uncertainty in mean-field plasma edge modeling. In this contribution, we further develop an improved anomalous transport model based on self-consistent time-averaging of the turbulence equations, assuming electrostatic interchange turbulence [1]. This model solves an additional transport equation for the turbulent kinetic energy k, and computes anomalous diffusivities self-consistently from its solution. An analytically exact source of k inherently introduces ballooning in the model. The plasma conductivity leads to fast parallel transport of k. We further refine the model by time-averaging the nonlinear sheath conditions: electron current fluctuations, determined by electron temperature and electric potential fluctuations, impact the average fluxes through the sheath in the mean-field model.
To validate the model, we perform SOLPS-ITER simulations [2] of the TCV-X23 discharge [3] with fully extended grids [4] built with the GOAT grid generator [5]. A D-only plasma is assumed. We include drifts and use the advanced fluid neutral model [6]. We compare the performance of the new k-model with the standard approach using fixed transport coefficients.
Both models are calibrated to the experimental data through parameter optimization [7], and reproduce the midplane and target data with similar accuracy. Despite the ballooning source of k, the transport coefficients in the near SOL are fairly uniform for this case, as a result of fast parallel transport of k. The model does predict a significant increase in k, and hence perpendicular transport, towards the low-field side, qualitatively consistent with a filamentary transport picture. As a result, main chamber loads predicted by both models differ significantly, even for nearly equal upstream and target profiles.The self-consistent transport coefficient variation of the k-model leads to somewhat earlier transition into detachment in a density scan, and more rapid increase in decay lengths. We demonstrate the impact of the averaged sheath boundary conditions on target and wall fluxes.
[1] R. Coosemans et al., J. Plasma Phys. 90 (2024) 905900202.
[2] S. Wiesen et al., Journal of Nuclear Materials 463 (2015) 480–484; X. Bonnin et al., Plasma and Fusion Research, 11 (2016) 1403102.
[3] https://gitlab.eufus.psnc.pl/tsvv3/tcvx23
[4] W. Dekeyser et al., Nuclear Materials and Energy 27 (2021) 100999.
[5] S. Van den Kerkhof et al., submitted to Contrib. Plasma Phys.
[6] N. Horsten et al., Nucl. Fusion 57 (2017) 116043.
[7] S. Carli et al., Contrib. Plasma Phys. (2021)e202100184.