First results from the optimized helias Wendelstein 7-X stellarator (W7-X) have shown that core transport is no longer mostly neoclassical, as is the case in previous kinds of stellarators. Instead, power balance analysis has shown that turbulent transport poses a serious limitation to the global performance of the machine. Several studies have found this particularly relevant for ion transport, with core ion temperatures becoming clamped at relatively low values of T _i ≃ 1.7 keV, except in the few scenarios in which turbulence can be suppressed. In order to understand the precise turbulent mechanisms at play and thus design improved performance scenarios, it is important to have a clear understanding of the parametric dependencies of turbulent fluctuations, and the relation between them and turbulent transport. As a first step in this direction, in this work we use Doppler reflectometry measurements carried out during a number of relevant operational scenarios to provide a systematic characterization of ion-scale (k _⊥ ρ _i ≃ 1) density fluctuations in the core of W7-X. Then, we study the relation between fluctuation amplitude and plasma profiles and show how distinct regimes can be defined for the former, depending on normalized gradients and . Furthermore, we discuss the importance of other potentially relevant parameters such as T _e/T _i, E _r or collisionality. Comparing the different regimes, we find that turbulence amplitude depends generally on the gradient ratio η _i = , as would be expected for ITG modes, with the exception of a range of discharges, for which turbulence suppression may be better explained by an ITG to TEM transition triggered by a drop in collisionality. Finally, we show a number of scenarios under which T _i,core > 1.7 keV is achieved and how core fluctuations are suppressed in all of them, thus providing experimental evidence of microturbulence being the main responsible for the limited ion confinement in W7-X.

优化的 helias Wendelstein 7-X 仿星器 (W7-X) 的初步结果表明，核心传输不再像以前的仿星器那样主要是新古典主义的。相反，功率平衡分析表明湍流传输严重限制了机器的整体性能。几项研究发现这与离子传输特别相关，核心离子温度被限制在相对较低的T _i值≃ 1.7 keV，除了可以抑制湍流的少数场景。为了了解起作用的精确湍流机制，从而设计改进的性能场景，重要的是要清楚地了解湍流波动的参数依赖性，以及它们与湍流输运之间的关系。作为朝着这个方向迈出的第一步，在这项工作中，我们使用在许多相关操作场景中进行的多普勒反射计测量来提供W7 核心中离子尺度 ( k _⊥ ρ _i ≃ 1) 密度波动的系统表征X。然后，我们研究波动幅度和等离子体轮廓之间的关系，并展示如何根据归一化梯度为前者定义不同的状态和。此外，我们讨论了其他潜在相关参数的重要性，例如T _e / T _i、E _r或碰撞性。比较不同的状态，我们发现湍流幅度通常取决于梯度比η _i = ，正如对 ITG 模式所预期的那样，除了一系列放电，对于这些放电，ITG 到 TEM 可以更好地解释湍流抑制由碰撞下降触发的过渡。最后，我们展示了一些场景，其中T _i,core > 1.7 keV 以及如何在所有这些中抑制核心波动，从而提供了微湍流是 W7-X 中有限离子限制的主要原因的实验证据。