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

TJ-II: impact of impurities on turbulence (view source)

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Jose.regana

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-== Experimental campaign ==
-Spring 2022
-== Proposal title ==
-'''Impact of impurities on turbulent transport'''
-== Name and affiliation of proponent ==
-[https://orcid.org/0000-0001-7632-3357  García-Regaña, J. M.], [https://orcid.org/0000-0003-1717-3509  Baciero, A.], [https://orcid.org/0000-0000-0000-0000  Calvo, I.], [https://orcid.org/0000-0000-0000-0000  Carralero D.], [https://orcid.org/0000-0000-0000-0000  Estrada T.], [https://orcid.org/0000-0000-0000-0000  González-Jerez A.], [https://orcid.org/0000-0003-4236-7727  López-Miranda, B.], Medina, F., [https://orcid.org/0000-0002-5881-1442  McCarthy K. J.], [https://orcid.org/0000-0001-7521-4503  Ochando, M. A.], [https://orcid.org/0000-0000-0000-0000  Thienpondt, H.], [https://orcid.org/0000-0001-8510-1422  Velasco, J. L.], and the TJ-II team,
-Laboratorio Nacional de Fusion, CIEMAT (Spain)
-== Details of contact person at LNF ==
-jose.regana@ciemat.es
 == Description of the activity ==
 '''Motivation.'''
-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
+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 approaching the problem quasi-linearly, in  <ref>R. R. Domínguez and G. M. Staebler, Nuclear Fusion '''33''' 51 (1993).</ref> the benign impact of increasing the effective charge, <math>Z_{\text{eff}}</math>, on ITG stability is demonstrated, albeit for the simplified slab geometry. In contrast to this, in the work just cited, at the time that the impact is found beneficial for the stability of the ITG mode, it is found deleterious for Trapped Electron Modes (TEMs). In addition, in
+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 W7-X experiments <ref>R. Lunsford ''et al'' Phys. Plasmas '''28''' 082506 (2021) </ref>. In the cited work, the conclusions highlight the increase of up to a 30% in the central ion temperature that follows after the injection of non-trace amounts of Boron. Given the limitations found in W7-X to achieve high core ion temperature <ref>M. N. A. Beurskens ''et al''., Nuclear Fusion '''61''' 116072 (2021)</ref>, with the exception of scenarios with reduced turbulence where W7-X, the motivation to study systematically the means to reduce the turbulence ion heat transport is strongly motivated. In contrast with the afore-mentioned analytical and numerical works, that employ approximations of different kind or consider simplified geometries, the possibility to study the problem numerically in all its complexity is at hand. Multi-species gyrokinetic simulations with the codes stella<ref>M. Barnes ''et al''., J. Comp. Phys '''391''' 365 (2019)</ref>, have just become affordable recently and, indeed, have been reported in the stellarator literature for the first time in <ref>J. M. García-Regaña ''et al''., J. Plasma Phys. '''87'''(1) 855870103 (2021)</ref>.
 ''' Proposal '''