Recent measurements of soft X-ray emission from the DPF-1000U facility

Abstract

Abstract. Soft X-ray imaging is a very useful diagnostic technique in plasma-focus (PF) experiments. This paper reports results of four experimental sessions which were carried out at the DPF-1000U plasma-focus facility in 2013 and 2014. Over 200 discharges were performed at various experimental conditions. Measurements were taken using two X-ray pinhole cameras with a line of sight perpendicular to the z-axis, at different azimuthal angles (about 20° and 200°), and looking towards the centre of the PF-pinch column. They were equipped with diaphragms 1000 m or 200-300 m in diameter and coated with fi lters of 500 m Al foil and 10 m Be foil, respectively. Data on the neutron emission were collected with silver activation counters. For time-resolved measurements the use was made of four PIN diodes equipped with various fi lters and oriented towards the centre of the PF-column, in the direction perpendicular to the electrode axis. The recorded X-ray images revealed that when the additional gas-puff system is activated during the discharge, the stability of the discharge is improved. The data collected in these experiments confi rmed the appearance of a fi lamentary fi ne structure in the PF discharges. In the past years the formation of such fi laments was observed in many Z-pinch type experiments. Some of the recorded X-ray images have also revealed the appearance of the so-called hot--spots, i.e. small plasma regions of a very intense X-ray emission. Such a phenomenon was observed before in many PF experiments, e.g. in the MAJA-PF device, but it has not been investigated so far in a large facility such as the DPF-1000U. The time-resolved measurements provided the evidence of a time lapse between the X-ray emission from plasma regions located at different distance from the anode surface. The formation of distinct 'hot-spots' in different instants of the DPF-1000U discharge was also observed.

Update on the Scientific Status of the Plasma Focus

“…Recently, experiments performed with the PF-1000 facility in Warsaw, Poland, have also confirmed the formation of super-dense plasma micro-regions in discharges performed with a high-Z gas admixture. In some cases PF discharges carried out with the D2 filling and puffing have also shown distinct hot-spots [161], as shown in Figure 23. Detailed studies of PF-1000 discharges, as performed with pinhole cameras and filtered PIN-diodes [162], showed that a local electron temperature can reach even 7.5 keV, as shown in Figure 24.…”

“…Recently, experiments performed with the PF-1000 facility in Warsaw, Poland, have also confirmed the formation of super-dense plasma micro-regions in discharges performed with a high-Z gas admixture. In some cases PF discharges carried out with the D 2 filling and puffing have also shown distinct hot-spots [161], as shown in Figure 23.…”

Measurements of fast electron beams and soft X-ray emission from plasma-focus experiments

“…It should also be noted that in different measuring channels, there were also recorded some narrow spikes corresponding to mono-energetic electron microbeams. The appearance of such microbeams could be explained by the acceleration of some electrons within tiny plasma diodes (formed probably near hot-spots), as described in our earlier papers [12,13] and in the introduction.…”