Application of a laser differential interferometer to plasma focus

A laser differential interferometer, a modification of an ordinary Schlieren system, is used to study the evolution of plasma sheath structure and the influence of X-ray emission in a plasma focus, and is found to give good results. From the interferograms it is clear that the filling pressure affects not only the propagation velocity of the plasma sheath, but also its structure, and the different structure of plasma above the anode in turn influences X-ray emission. Whilst the pinched plasma gives higher X-ray yield in a low filling pressure, the turbulent plasma with a protrusion above the plasma layer in a high filling pressure leads to low or no X-ray emission. A high density volume emerges from the target of anode at about t=200 ns, well after the focus is over, which may be the metallic vapour released from the target due to an intense electron beam bombardment. From an experimental point of view it appears that the differential interferometer is simpler to use than other interferometers and has proved to be very useful in the diagnostics of plasma focus.