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首页> 外文期刊>Plasma physics and controlled fusion >Evidence for reduction of the toroidal ITG instability in the transition from saturated to improved Ohmic confinement in the tokamak TEXTOR
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Evidence for reduction of the toroidal ITG instability in the transition from saturated to improved Ohmic confinement in the tokamak TEXTOR

机译：降低托卡马克TEXTOR从饱和到改善的欧姆约束的过渡过程中环形ITG不稳定性的证据

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摘要

In high density Ohmically heated discharges in the tokamak TEXTOR a transition from the saturated Ohmic confinement (SOC) to the improved Ohmic confinement (IOC) was observed triggered by a sudden reduction of the external gas flow. The SOC-IOC transition was investigated regarding the influence of the toroidal ITG instability driven by the ion temperature gradient (ITG). The ion temperature profiles were measured with high radial resolution by means of charge-exchange recombination spectroscopy (CXRS) with a high-energetic diagnostic hydrogen beam recently installed at TEXTOR. On the basis of the measured ion temperature distributions the eta(i) parameter (ratio of the density and ion temperature decay lengths) and the growth rate of the toroidal ITG instability were calculated. After the SOC-IOC transition eta(i) drops and lies in a noticeably smaller radial region over the threshold for the toroidal ITG. In consequence of it, the IOC regime is characterized by a clear reduction of the ITG growth rate gamma(ITG) which was calculated including finite Larmor radius effects. The steepening of the plasma density profile after the decrease of the external gas flow is the main reason for the reduction of the ITG growth rate and the subsequent confinement transition to the IOC regime. [References: 22]
机译：在托卡马克TEXTOR中的高密度欧姆加热放电中，观察到外部气流的突然减少触发了从饱和欧姆限制（SOC）到改进的欧姆限制（IOC）的转变。针对由离子温度梯度（ITG）驱动的环形ITG不稳定性的影响，研究了SOC-IOC跃迁。离子温度曲线是通过电荷交换复合光谱法（CXRS）和最近安装在TEXTOR上的高能诊断氢束以高径向分辨率进行测量的。根据测得的离子温度分布，计算eta（i）参数（密度与离子温度衰减长度之比）和环形ITG不稳定性的增长率。在SOC-IOC过渡之后，eta（i）下降并位于环形ITG阈值之上的明显较小的径向区域中。因此，IOC机制的特征在于ITG增长率gamma（ITG）的明显降低，而该系数的计算包括有限的拉莫尔半径效应。外部气流减少后等离子体密度分布曲线的陡峭，是导致ITG增长率降低以及随后向IOC模式过渡的主要原因。 [参考：22]

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