Intermittent fluctuations in the boundary of magnetically confined plasmas are investigated by numerical turbulence simulations of a reduced fluid model describing the evolution of the plasma density and electric drift vorticity in the two-dimensional plane perpendicular to the magnetic field. Two different cases are considered: one describing resistive drift waves in the edge region and another including only the interchange instability due to unfavorable magnetic field curvature in the scrape-off layer. Analysis of long data time series obtained by single-point recordings is compared to predictions of a stochastic model describing the plasma fluctuations as a superposition of uncorrelated pulses. For both cases investigated, the radial particle density profile in the scrape-off layer is exponential with a radially constant scale length. The probability density function for the particle density fluctuations in the far scrape-off layer has an exponential tail. Radial motion of blob-like structures leads to large-amplitude bursts with an exponential distribution of peak amplitudes and the waiting times between them. The average burst shape is well described by a two-sided exponential function. The frequency power spectral density of the particle density is simply that of the average burst shape and is the same for all radial positions in the scrape-off layer. The fluctuation statistics obtained from the numerical simulations are in excellent agreement with recent experimental measurements on magnetically confined plasmas. The statistical framework defines a new validation metric for boundary turbulence simulations.

中文翻译：

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磁化等离子体剥离层间断波动的数值湍流模拟

通过描述在垂直于磁场的二维平面中等离子体密度和电漂移涡度的演变的简化流体模型的数值湍流模拟，研究了磁约束等离子体边界中的间歇性波动。考虑了两种不同的情况：一种描述了边缘区域的电阻漂移波，另一种仅包括由于刮削层中不利的磁场曲率引起的互换不稳定性。通过单点记录获得的长数据时间序列的分析与将等离子体波动描述为不相关脉冲的叠加的随机模型的预测进行比较。对于所研究的两种情况，刮除层中的径向颗粒密度分布是指数的，具有径向恒定的尺度长度。远刮层中颗粒密度波动的概率密度函数具有指数尾部。团块状结构的径向运动导致大振幅爆发，其峰值振幅和它们之间的等待时间呈指数分布。平均突发形状由双边指数函数很好地描述。粒子密度的频率功率谱密度只是平均爆发形状的频率功率谱密度，并且对于刮除层中的所有径向位置都是相同的。从数值模拟中获得的波动统计与最近对磁约束等离子体的实验测量非常吻合。统计框架为边界湍流模拟定义了一个新的验证指标。