Zocco Alessandro, Podavini Linda, Garcìa-Regaña José Manuel, Barnes Michael, Parra Felix I, Mishchenko A, Helander Per
Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, D-17491 Greifswald, Germany.
Università Milano Bicocca, Dipartimento di Fisica Giuseppe Occhialini, Piazza della Scienza, 3 20126 Milano, Italy.
Phys Rev E. 2022 Jul;106(1):L013202. doi: 10.1103/PhysRevE.106.L013202.
The transition from strong (fluidlike) to nearly marginal (Floquet-type) regimes of ion-temperature-gradient (ITG) driven turbulence is studied in the stellarator Wendelstein 7-X by means of numerical simulations. Close to marginality, extended (along magnetic field lines) linearly unstable modes are dominant, even in the presence of kinetic electrons, and provide a drive that results in finite turbulent transport. A total suppression of turbulence above the linear stability threshold of the ITG modes, commonly present in tokamaks and known as the "Dimits shift," is not observed. We show that this is mostly due to the peculiar radial structure of marginal turbulence, which is more localized than in the fluid case and therefore less likely to be stabilized by shearing flows.
通过数值模拟研究了在仿星器文德尔施泰因7-X中离子温度梯度（ITG）驱动湍流从强（类流体）到近边缘（弗洛凯型）状态的转变。接近边缘状态时，即使存在动力学电子，沿磁力线延伸的线性不稳定模式也占主导地位，并提供了导致有限湍流输运的驱动力。在托卡马克中普遍存在且被称为“迪米茨位移”的ITG模式线性稳定阈值以上的湍流完全抑制现象未被观察到。我们表明，这主要是由于边缘湍流独特的径向结构，它比流体情况下更局域化，因此不太可能被剪切流稳定。
