Chaotic transport is a subject of paramount importance in a variety of problems in plasma physics, specially those related to anomalous transport and turbulence. On the other hand, a great deal of information on chaotic transport can be obtained from simple dynamical systems like two-dimensional area-preserving (symplectic) maps, where powerful mathematical results like KAM theory are available. In this work, we review recent works on transport barriers in area-preserving maps, focusing on systems which do not obey the so-called twist property. For such systems, usual KAM theory no longer holds everywhere and novel dynamical features show up as non-resistive reconnection, shearless curves, and shearless bifurcations. After presenting some general features using a standard nontwist mapping, we consider magnetic field line maps for magnetically confined plasmas in tokamaks.

在等离子体物理中的各种问题中，特别是与异常传输和湍流有关的问题，混沌传输是最重要的主题。另一方面，可以从简单的动力学系统（如二维区域保留（渐近）映射）获得大量有关混沌传输的信息，其中可以使用像KAM理论这样的强大数学结果。在这项工作中，我们回顾了有关保留区域地图中的交通障碍的最新工作，重点是不遵守所谓扭曲特性的系统。对于这样的系统，通常的KAM理论不再处处存在，并且新颖的动力学特征显示为非电阻重新连接，无剪切曲线和无剪切分叉。在使用标准的非扭曲映射介绍了一些常规功能之后，