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.

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Plasma diagnostics and Si etching were carried out in 13.56 MHz SF6 remote plasma generated in a hollow cathode discharge system. The plasma diagnostics were performed in the remote zone at a constant pressure of 40 Pa, at a constant applied RF power of 300 W and as a function of the SF6 flow rate (40–2000 sccm), where absolute concentrations of fluorine atoms were measured using actinometry optical emission spectroscopy; electron density, electron temperature and plasma potential were determined using single Langmuir probe, positive ion flux and negative ion fraction were determined using an electrostatic planar probe. The silicon etching process was studied at two distant values of flow rate, 80 and 1800 sccm and for three conditions of the substrate holder, namely the substrate is grounded, the substrate is negatively biased and the substrate is positively biased. The etched silicon was characterized for etch rate, optical reflectance and photoluminescence properties. It was found that the etch rate is relatively high (about 15 mg cm−2 min−1) and it is controlled mainly by the ratio of the ion flux over the reactive atomic fluorine flux, the highest etch rate was obtained at the higher flow rate (1800 sccm) and for positively biased substrate. The reflectance of the silicon surface was significantly reduced after etching and a reflectance as low as 0.2% was measured. A visible photoluminescence from the etched surface was recorded; it is centred at about 600 nm, and its intensity is inversely proportional to the measured reflectance.

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