Evaluation of tungsten influx rate using line emissions from W$^{5+}$ ions in EAST Tokamak

• Main Authors: Zhang, Fengling, Mitnik, Darío, Zhang, Ling, Bao, Runjia, Zhang, Wenming, Cheng, Yunxin, Hu, Ailan, Morita, Shigeru, Ding, Xiaobin, Jie, Yinxian, Liu, Haiqing
• Format: Journal Article
• Language: English
• Published: 03-10-2024
• Subjects: Physics - Plasma Physics
• DOI: 10.48550/arxiv.2410.02669

The S/XB ratios (ionization per emitted photon) allow one to relate
spectroscopic emissivity measurements to the impurity influx from a localized
source. In this work, we determine the tungsten influx by examining two
dominant EUV (Extreme Ultraviolet) line emissions at 382.13 \AA and 394.07 \AA,
corresponding to the $4f 14 5f \rightarrow 4f 14 5d$ radiative transitions of
the W$^{5+}$ ion. The ground configuration of W$^{5+}$ consists of the ground
level and a metastable level, with the latter having a higher population than
the ground state. Therefore, a simple approach assuming that the transitions
are independent, i.e., only populated by a unique level source, requires
correction. To address this, we have developed a fully collisional-radiative
modeling in which 430 levels contribute to the ionization. We have utilized
three advanced computational codes -- HULLAC (Hebrew University - Lawrence
Livermore Atomic Code), AS (AutoStructure), and FAC (Flexible Atomic Code) --
for the atomic structure calculations. These codes provide the necessary
information such as wavelengths, collisional and radiative transition rate
coefficients. The FAC code was also used to calculate the direct
electron-impact ionization under the distorted-wave approximation. We also
included contributions to total ionization from excitation-autoionization
processes up to $n = 15$ manifolds from the distorted-wave calculations.
Subsequently, we used these results to ascertain the tungsten impurity influx
in a dedicated discharge of the EAST tokamak, which operates with full tungsten
divertors. In our findings, we observed that for the density range relevant to
the edge region of a tokamak reactor, the S/XB ratios are almost independent of
electron density but exhibit significant variation with electron temperature.