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TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II: Difference between revisions
TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II (view source)
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'''Background''' | '''Background''' | ||
Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'' Plasma | Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence. | ||
Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>. | Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>. | ||