Time-Varying Inductance of the Plasma Sheet in the PF1000 Plasma-Focus Device

The time-varying inductance Lp(t) of the system formed by the coaxial electrodes and the current sheet (CS) in plasma focus (PF) discharges was calculated for the first time by Mather and Bottoms [1] on a 13-kJ PF device in Los Alamos using measured values of V(t) , the voltage at the breach end of the electrodes, and dI/dt, the time derivative of the current circulating through the system. Recently, the same method was applied to assess Lp(t) in devices of lower energy [2]–[4]. This physical magnitude was also used for estimating other relevant parameters, like the voltage drop over the pinch column [5], [6]. The purpose of this paper is to extend this procedure to the high-energy device PF1000, operated by the International Center for Dense Magnetized Plasmas (ICDMP) from Warsaw, Poland, using measurements performed during an experimental campaign conducted in 2013. High-energy devices as PF1000, besides having much larger capacitor banks, also has larger electrodes, which leads to larger gun inductances and consequently higher voltage drops in the pinch. Hence, the goal of the present study is to validate the application of the mentioned technique in large PF devices and also to produce additional information, namely, the behavior of the voltage drop over the pinch plasma column.Fil: Bruzzone, Horacio Abel. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Acuña, Hugo Néstor. Universidad Nacional de Mar del Plata; ArgentinaFil: Barbaglia, Mario Oscar. Universidad Nacional del Centro de la Provincia de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Milanese, Maria Magdalena. Universidad Nacional del Centro de la Provincia de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Miklaszewski, Ryszard. Institute of Plasma Physics and Laser Microfusion; PoloniaFil: Paduch, Marian. Institute of Plasma Physics and Laser Microfusion; PoloniaFil: Zielinska, Ewa. Institute of Plasma Physics and Laser Microfusion; PoloniaFil: Clausse, Alejandro. Comision Nacional de Energía Atómica; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Studies of plasma interactions with tungsten targets in PF-1000U facility

This paper presents results of experimental studies of tungsten samples of 99.95% purity, which were irradiated by intense plasma-ion streams. The behaviour of tungsten, and particularly its structural change induced by high plasma loads, is of great importance for fusion technology. The reported measurements were performed within a modified PF-1000U plasma-focus facility operated at the IFPiLM in Warsaw, Poland. The working gas was pure deuterium. In order to determine the main plasma parameters and to study the behaviour of impurities at different instants of the plasma discharge, the optical emission spectroscopy was used. The dependence of plasma parameters on the initial charging voltage (16, 19 and 21 kV) was studied. Detailed optical measurements were performed during interactions of a plasma stream with the tungsten samples placed at the z-axis of the facility, at a distance of 6 cm from the electrode outlets. The recorded spectra showed distinct WI and WII spectral lines. Investigation of a target surface morphology, after its irradiation by intense plasma streams, was performed by means of an optical microscope. The observations revealed that some amounts of the electrodes material (mainly copper) were deposited upon the irradiated sample surface. In all the cases, melted zones were observed upon the irradiated target surface, and in experiments performed at the highest charging voltage there were formed some cracks

Study of tungsten surface interaction with plasma streams at DPF-1000U

In this note experimental studies of tungsten (W) samples irradiated by intense plasma-ion streams are reported. Measurements were performed using the modified plasma focus device DPF-1000U equipped with an axial gas-puffing system. The main diagnostic tool was a Mechelle®900 optical spectrometer. The electron density of a freely propagating plasma stream (i.e., the plasma stream observed without any target inside the vacuum chamber) was estimated on the basis of the half-width of the Dβ spectral line, taking into account the linear Stark effect. For a freely propagating plasma stream the maximum electron density amounted to about 1.3 × 1017 cm−3 and was reached during the maximum plasma compression. The plasma electron density depends on the initial conditions of the experiments. It was thus important to determine first the plasma flow characteristics before attempting any target irradiation. These data were needed for comparison with plasma characteristics after an irradiation of the investigated target. In fact, spectroscopic measurements performed during interactions of plasma streams with the investigated W samples showed many WI and WII spectral lines. The surface erosion was determined from mass losses of the irradiated samples. Changes on the surfaces of the irradiated samples were also investigated with an optical microscope and some sputtering and melting zones were observed

Update on the Scientific Status of the Plasma Focus

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