Besides strong geodesic acoustic mode (GAM) activity, turbulence in the I-mode confinement regime of ASDEX Upgrade exhibits two prominent features, the weakly coherent mode (WCM) and strongly intermittent solitary density perturbations. The nonlinear interaction between these structures is studied in detail by means of a conditional averaged wavelet-bicoherence analysis. The wavelet analysis reveals that these density perturbations are at the WCM frequency. The GAM is coupled to all frequency scales of the velocity fluctuations via a modulational instability. The WCM shows coupling to higher frequencies prior to the bursts, indicating a process resembling wave-steepening. A possible mechanism for the generation of such solitary density perturbations by a Korteweg–de Vries-like nonlinearity is discussed.

除了强测地线声模式 (GAM) 活动外，ASDEX 升级的 I 模式限制机制中的湍流表现出两个突出特征，弱相干模式 (WCM) 和强间歇性孤立密度扰动。通过条件平均小波双相干分析详细研究了这些结构之间的非线性相互作用。小波分析表明这些密度扰动处于 WCM 频率。GAM 通过调制不稳定性耦合到速度波动的所有频率尺度。WCM 显示在爆发之前耦合到更高的频率，表明一个类似于波陡化的过程。讨论了由类 Korteweg-de Vries 非线性产生这种孤立密度扰动的可能机制。