Observation of quasi-coherent edge fluctuations in Ohmic plasmas on NSTX

A quasi-coherent mode with frequency f = 40 kHz is observed in Ohmic plasmas in NSTX with the gas puff imaging diagnostic (GPI). This mode is located predominantly just inside the separatrix, with a maximum fluctuation amplitude similar to that of the broadband turbulence in the same frequency range. The quasi-coherent mode has a poloidal wavelength 16 cm and a poloidal velocity 49 km/s in the electron diamagnetic direction, which are similar to the characteristics expected from a linear drift-wave like mode in the edge.

在国家球形环实验装置（National Spherical Torus Experiment, NSTX）的欧姆等离子体（Ohmic plasmas）中，借助喷气成像诊断系统（gas puff imaging diagnostic, GPI）观测到频率为f=40 kHz的准相干模（quasi-coherent mode）。该准相干模主要集中在磁分界面（separatrix）内侧区域，其最大涨落振幅与同一频率区间内的宽带湍流（broadband turbulence）的最大涨落振幅相当。该准相干模的极向波长为16 cm，沿电子抗磁方向（electron diamagnetic direction）的极向速度为49 km/s，其特性与等离子体边缘线性漂移波类模（linear drift-wave like mode）的理论预期特征相符。