This paper is a sequel to the 1998 review paper “Scientific status of the Dense Plasma Focus” with 16 authors belonging to 16 nations, whose initiative led to the establishment of the International Center for Dense Magnetized Plasmas (ICDMP) in the year 2000. Its focus is on understanding the principal defining characteristic features of the plasma focus in the light of the developments that have taken place in the last 20 years, in terms of new facilities, diagnostics, models, and insights. Although it is too soon to proclaim with certainty what the plasma focus phenomenon is, the results available to date conclusively indicate what it is demonstrably not. The review looks at the experimental data, cross-correlated across multiple diagnostics and multiple devices, to delineate the contours of an emerging narrative that is fascinatingly different from the standard narrative, which has guided the consensus in the plasma focus community for several decades, without invalidating it. It raises a question mark over the Fundamental Premise of Controlled Fusion Research, namely, that any fusion reaction having the character of a beam-target process must necessarily be more inefficient than a thermonuclear process with a confined thermal plasma at a suitably high temperature. Open questions that need attention of researchers are highlighted. A future course of action is suggested that individual plasma focus laboratories could adopt in order to positively influence the future growth of research in this field, to the general benefit of not only the controlled fusion research community but also the world at large.

The results of studies of the plasma-current sheath structure on the PF-1000 facility in the stage close to the instant of pinch formation are presented. The measurements were performed using various modifications of the calibrated magnetic probes. Studies of the influence of the probe shape and dimensions on the measurements accuracy were done. The current flowing in the converging sheath at a distance of 40 mm from the axis of the facility electrodes was measured. In the optimal operating modes, this current is equal to the total discharge current, which indicates the high efficiency of current transportation toward the axis. In such shots a compact high-quality sheath forms with shock wave in front of the magnetic piston. It is shown that the neutron yield depends on the current compressed onto the axis. This dependence agrees well with the known scaling, Y n ∼ I 4 . The use of the total discharge current in constructing the current scaling, especially for facilities with a large stored energy, is unjustified.

The magnetic field distribution substantially affects mechanisms for the generation of radiation in Z-pinches. Investigation of the axial component of the magnetic field is one of the important problems in plasma focus studies. The measurements of the Bz-component of the magnetic field on the PF-1000 facility were done with the multichannel absolutely calibrated probe both at the stage of plasma-current sheath radial compression and in the dense-pinch stage. In the compression stage, the axial component of the magnetic field reaches several kG that comprises ∼ 10% of the azimuthal component. The presence of the Bz field is a powerful argument in favor of the existence of closed magnetic configurations, which play an important role in the generation of neutrons.