Observation of Collisionless Electrostatic Shocks

Large-amplitude ion-acoustic waves ($\frac{e\varphi }{k{T}_e}\lesssim 0.3$) are excited in the University of California, Los Angeles double-plasma device by the interpenetration of two plasmas with high electron-to-ion temperature ratios ($6<\mathrm{}\frac{T_e}{T_i}<20\mathrm{}$). A compressional wave with a ramp shape is found to steepen in a fashion consistent with the classical overtaking predicted by the usual Riemann invariants. This steepening continues until dispersive short scale ($k\approx \frac{1}{2}{k}_{\mathrm{D}}$) oscillations develop at the front. Ions streaming in front of the shock are also observed.