Observations of the Spatial Evolution of a Potential Hump into a Strong Double Layer in a High-Voltage Straight Plasma Discharge

The propagation and spatial evolution of a potential hump generated explosively near the cathode were observed in the current-limiting phase of a high-voltage straight discharge with a preexisting hydrogen plasma. Potential profiles along the axis numerically calculated from the real-time $E$ field data demonstrate the evolution of a potential hump into a strong double layer (asymmetric electron hole) with an inverse potential jump ($\frac{e{\phi }_D}{k{T}_e}\lesssim {10}^3$) as moving toward the center of the device with a mean velocity (1.2-1.8) × ${10}^8$ cm/sec.