We report the experimental observation of highly nonlinear coherent structures in a linear magnetized plasma characterized by a strong background density gradient and significant $\mathbf{E}\times \mathbf{B}$ velocity shear under high ion-neutral collisionality. These structures, identified as drift acoustic waves, exhibit large normalized density fluctuations reaching amplitudes of up to $\sim 10\%$ and show periodic sawtoothlike waveforms. These observed waveforms are well described by cnoidal functions, corresponding to stationary nonlinear wave trains. Cnoidal waves are exact solutions of Korteweg–de Vries-type equations, alongside the more commonly studied soliton solutions. To the best of our knowledge, this work presents the first controlled experimental observation of cnoidal wave trains in a highly collisional magnetized plasma through systematic variation of profile gradients. These findings provide important new insights into the nonlinear evolution and saturation of drift acoustic waves in inhomogeneous, sheared, and collisional magnetized plasmas.

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• Nonlinear phenomena in plasmas
• Plasma instabilities