Effect of rotation on impurity density and radiated power asymmetries in NSTX and STAR

In this work, we have investigated the effect of rotation on impurity density and radiated power asymmetries for the cases of experimental NSTX plasmas and designed scenarios for the Spherical Tokamak Advanced Reactor (STAR) [1, 2]. We have investigated the 2D radiated power asymmetries using self-consistent calculations of two-dimensional electron, main ion, and impurity ion densities with rotation-induced charge separation, leading to an electrostatic potential calculated iteratively while imposing the quasi-neutrality condition [3]. In the case of NSTX, discharges with high toroidal rotation up to ~ 300 km/s have been analysed to show strong 2D asymmetry in the core radiated power for high Z impurities due to centrifugal forces. In the case of Fusion Power Plant (FPP) like devices such as STAR, rotation-induced asymmetries are found to be on the order of a few tens of percent between the low field and high field sides. Further, in this work, we also present the effect of radiative cooling rates on the radiative power density peaking off-axis for some impurities. These investigations are important to understand the effect of undesired impurities in present devices, or also to select desired noble gas impurities to purposefully radiate a large fraction of power in future devices.

References:

1] J. Menard et al., 29th IAEA Fusion Energy Conference (2023).

2] J. Berkery et al., Nucl. Fusion 64 112004 (2024).

3] K. Shah et al., Plasma Phys. Control. Fusion submitted.