TJ-II: impact of impurities on turbulence: Difference between revisions

In the context of analytical theory, the stabilizing role of impurities on Ion-Temperature-Gradient (ITG) driven instability has been known for decades, see e.g. <ref>R. R. Domínguez and M. N. Rosenbluth, Nuclear Fusion '''29''' 844 (1989).</ref>, where the derived linear dispersion relation shows that the increase of the impurity concentration has a positive impact on the critical gradient of the toroidal ITG mode and its growth rate. Numerically, and on a quasi-linear fashion, in  <ref>R. R. Domínguez and G. M. Staebler, Nuclear Fusion '''33''' 51 (1993).</ref> the benign impact of increasing the effective charge, $Z_{\text{eff}}$, on ITG stability is demonstrated, albeit for the simplified slab geometry, at the time that the impact is found deleterious for Trapped Electron Modes (TEMs). The interest in these early works and on the question itself about the active role of impurities on the overall turbulence behavior has been brought to the front line of stellarator research by recent experiments in W7-X  <ref>R. Lunsford ''et al'' Phys. Plasmas '''28''' 082506 (2021) </ref>. In the reported experimental conclusions, it is highlighted an increase of up to a 30% in the central ion temperature follows the injection of non-trace amounts of Boron. Given the evidence