Experimental Observation of Nonlinear Coupling Between Rayleigh–Taylor, Kelvin–Helmholtz, and Drift-Wave Instabilities in a Magnetized Linear Plasma

We report experimental observations of independent existence, simultaneous coexistence and and nonlinear interactions among Rayleigh–Taylor (RT), Kelvin–Helmholtz (KH), and drift-wave (DW) instabilities in a cylindrical magnetized linear plasma device (IMPED). These low-frequency modes are intrinsically driven: RT by effective gravity arising from centrifugal acceleration due to poloidal flows and radial pressure gradients, KH by velocity shear, and DW by diamagnetic drift in inhomogeneous plasmas. By varying the ratio of the magnetic field in the main chamber to that in the source chamber \( (R_m = B_m / B_s) \), we independently control the density gradient scale length \( L_n \) and velocity shear scale length \( L_s \), accessing RT, KH, and DW-dominated regimes. Experimental regimes exhibiting coexistence of RT–DW, KH–DW, and RT–KH coupled-mode configurations are systematically investigated. Different Probe diagnostics reveal nonlinear spectral signatures, including frequency wavenumber triplets. Auto-bicoherence analyses confirm three-wave coupling. Elevated pressure enhances mode interactions, while higher magnetic field conditions favor the emergence of secondary low-frequency modes consistent with zonal flows and envelope modulations. These results demonstrate intrinsic mode coupling and the generation of secondary structures in a controlled linear plasma environment.