Abstract
Electromagnetic gyrokinetic simulations ofelectron-temperature-gradient-driven modes on electrongyroradius scales are performed in the geometry ofan advanced stellarator fusion experiment, Wendelstein 7-AS.Based on linear simulations, a criticalelectron-temperature-gradient formula is established which happens to agree quitewell with a previously derived formula for tokamaks in theappropriate limit. Nonlinear simulations are used to study theturbulence and transport characteristics which are dominated bythe presence of high-amplitude radially elongated vortices or`streamers'. The role of Debye shielding effects is alsoexamined.
Highlights
It has long been known that the cross-field particle and heat transport in magnetically confined fusion plasmas generally exceeds predictions based on collision-induced processes by up to two orders of magnitude
Whereas edge turbulence seems to be mainly driven by electromagnetic ion-temperature-gradient (ITG) modes, drift Alfven waves, and ballooning modes [2, 3], core turbulence is believed to be caused by electrostatic ITG modes and trapped electron modes [4]
Our result is in good agreement with the tokamak formula, equations (1) and (2), a result which is consistent with recent work by Jost et al [18] who performed global linear gyrokinetic simulations of ITG modes with adiabatic electrons in the core of quasi-symmetric stellarators, showing that ITG modes are not significantly affected by local magnetic shear
Summary
It has long been known that the cross-field particle and heat transport in magnetically confined fusion plasmas generally exceeds predictions based on collision-induced processes by up to two orders of magnitude. There is strong experimental evidence that these anomalous losses can generally be attributed to various kinds of fine-scale turbulence (at perpendicular spatial scales somewhat larger than the ion gyroradius) driven by density and/or temperature gradients [1]. For several reasons it is useful to distinguish between edge and core turbulence where the edge region is mainly characterized by much shorter length scales of the density and temperature profiles, Le⊥dge ∼ 1 cm versus Lc⊥ore ∼ 1 m. Whereas edge turbulence seems to be mainly driven by electromagnetic ion-temperature-gradient (ITG) modes, drift Alfven waves (electromagnetic electron drift waves), and ballooning modes [2, 3], core turbulence is believed to be caused by electrostatic ITG modes and trapped electron modes [4]. High-performance plasma discharges with internal transport barriers
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