Abstract
Focusing on the reactor-relevant plasma condition, where electrons and ions are expected to have a similar temperature profile, an estimate is given on the relative role of the ion temperature gradient (ITG) and trapped electron mode (TEM). A local kinetic code, which takes into account the collisional and electromagnetic effects, is utilized for the linear stability comparison between the two modes. It is shown that, when we limit our consideration to the ion-scale wavelength regime, the TEM, usually driven by the electron temperature gradient, is sub-dominant compared to the ITG in the most parameter regime, including plasma beta. The asymmetric interaction between the ITG and the TEM, in addition to the smaller fraction of trapped electrons and the collisional effect, is found to play a central role in producing this result. When we include the density gradient driven TEM, a strong interaction is also observed, with the mode being rapidly stabilized or transited to the electron temperature gradient driven TEM (ITG) as the electron (ion) temperature gradient increases. Based on these results on the linear interaction and relative role of the ITG and the two types of TEM, a brief discussion is presented on the possible evolution of temperature and density profiles in reactor-relevant conditions.
Highlights
A well-known and long-standing issue in fusion plasma research is what micro-instabilities are mainly responsible for the anomalous transport of plasma energy and particles
It is shown that, when we limit our consideration to the ion-scale wavelength regime, the trapped electron mode (TEM), usually driven by the electron temperature gradient, is sub-dominant compared to the ion temperature gradient (ITG) in the most parameter regime, including plasma beta
We have presented an estimate on the relative role of the ITG and TEM in the reactor-relevant plasma condition where ions and electrons are expected to have a similar temperature profile
Summary
A well-known and long-standing issue in fusion plasma research is what micro-instabilities are mainly responsible for the anomalous transport of plasma energy and particles. While the ITG is known to be strongly destabilized by trapped electrons, the TEM appears to be stabilized by the ion temperature gradient (this will be shown in more detail in this work) This asymmetric interaction can have a large influence on determining the relative role of the two modes. The density gradient driven TEM is rapidly stabilized or smoothly transited to the ITG when the ion and electron temperature gradients increase with a similar magnitude These results suggest that in the reactor relevant condition, the turbulent transport will be dominated by the ITG over the most parameter regime, even though it should be checked further how much the density profile is peaked from the ITG driven inward pinch and whether the density gradient driven TEM can be excited, playing a role in regulating the density and temperature profiles.
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