Neutron fluxes of up to 7 × 10 7 neutrons/sr were measured when planar deuterated targets were irradiated with 1.3 ps FWHM (full width at half maximum) laser pulses at a wavelength of 1054 nm and focused intensities up to 10 19 W cm −2 . The neutron energy spectra are consistent with an angularly dispersed beam target interaction, whereas a thermonuclear source is considered unlikely.

The paper presents a comparison of the main characteristics and experimental results obtained in plasma focus (PF) experiments in the POSEIDON 500 kJ facility in Stuttgart and the PF-360 kJ device in Świerk. Parameters of various electrodes and insulators are given, and studies on the evolution of the discharges are summarized. Selected data on X-ray, ion and neutron emission are given. Also presented are recent experimental results — a maximum neutron yield of up to 2.5 × 1011 for 500 kJ/80 kV runs with a new ceramic insulator in POSEIDON and an average neutron yield of 1.2 × 1011 for operation at 171 kJ/36 kV in PF-360. Particular attention is paid to the neutron scaling and the saturation effects observed at higher energy and current levels. Proposals are made for new experimental studies which can facilitate further progress in PF research.

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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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The total current I total waveform in a plasma focus discharge is the most commonly measured quantity, contrasting with the difficult measurement of I pinch . However, yield laws should be scaled to focus pinch current I pinch rather than the peak I total . This paper describes how I pinch may be computed from the I total trace by fitting a computed current trace to the measured current trace using the Lee model. The method is applied to an experiment in which both the I total trace and the plasma sheath current trace were measured. The result shows good agreement between the values of computed and measured I pinch .

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The energy and mass analysis of ions emitted from a 50-kJ, 18-kV, plasma focus machine was performed with a Thomson analyzer. Energy distribution functions offast deuterons (E>350 keV) and those of impurity ions have been determined. The energy distributions of the 0, N, and C impurity ions in different ionization states have similar character. They usually increase exponentially and after reaching the maximum at E /Z;:::: 1.0 Me V they decrease exponentially to E /Z;:::: 1.8 MeV. For deuterons at lower operating pressures (Po<2 mbar) the energy distribution measured decreases exponentially from 0.35 to about 3.0 MeV. In some cases, independent of the operating pressure, the maximum energies of the distribution extend to 0.5-1.5 MeV only. With an argon admixture (up to 4.5%) Ar+ -Ar7+ ions of energy from 0.5 to 14 MeV are produced.