Nonlinear coherent dense plasma structures—‘blobs’—that form in the turbulent edge plasma of a tokamak play an important role in the anomalous nature of the plasma transport in that region. A plasma blob is normally formed when another kind of coherent structure—a radially elongated streamer structure—breaks due to differential stretching in the radial and poloidal directions. We investigate the nature of such a blob formation in the scrape-off layer region by taking into account electron temperature effects. It is found that the shear related to the poloidal gradient of the poloidal electric field plays a major role. A blob is predicted to form when this shear exceeds the interchange mode growth rate within the radially elongated region. Our theoretical estimate of this extended criterion for blob formation is validated from three-dimensional numerical simulation results using the BOUT++ framework and could be useful in the interpretation of blob formation in the presence of finite electron temperature gradient that is applicable in the H and L mode discharges.

在托卡马克湍流边缘等离子体中形成的非线性相干致密等离子体结构——“团块”——在该区域等离子体传输的异常性质中起着重要作用。当另一种相干结构——径向拉长的拖缆结构——由于径向和极向方向的不同拉伸而破裂时，通常会形成等离子体团。我们通过考虑电子温度效应来研究刮削层区域中这种斑点形成的性质。发现与极向电场的极向梯度相关的剪切起主要作用。当这种剪切超过径向拉长区域内的交换模式增长率时，预计会形成斑点。