Experimental evidence of a low-dimensional attractor in the coupling of drift- and ion-sound waves

The nonlinear coupling of drift waves with sound waves is studied in a magnetized plasma. The correlation dimension of the reconstructed phase space is determined by the Grassberger–Procaccia algorithm [Physica D 9, 189 (1983)] from various time series of a single variable. In the case of distinct Fourier modes low-dimensional attractors of D2=(3.9±0.2) and D2=(4.8±0.2) appear, whereas for broadband fluctuations a dimension of D2>10 is found. Time-resolved Fourier spectra demonstrate that a four-wave interaction prevails, involving the drift wave, the sound wave, and the upper and lower sidebands of the drift wave. The number of essential modes is compared to the measured dimensions.