Effect of preionization on the axial run-down velocity, focus amplitude and current sheath formation in 3.3 kJ small He plasma

The sheath dynamics is an important parameter in dense plasma focus. In this paper, the effect of preionization on sheath dynamics, pinching and its filamentary structure is studied by measuring the axial run-down velocity and its confinement time. A discharge is produced in a 3.3 kJ pure He plasma. The Rogowski and high-voltage signals reveal the formation of an axisymmetric parabolic current sheath, high focusing amplitude during collapse phase with preionization source. The working pressure effect on sheath dynamics and spatial evolution is also studied. The enlarge and symmetric pinhole images with preionization support and conform with the results obtained.