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

100%

Ladygina M. S., Skladnik-Sadowska E., Zaloga D. R., Malinowski K., Sadowski M. J., Kubkowska M., Kowalska-Strzeciwilk E., Paduch M., Zielinska E., Miklaszewski R., Garkusha I. E., Gribkov V. A.

issue 2

293-296

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.

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

86%

Surała W., Sadowski M. J., Paduch M., Zielinska E., Tomaszewski K.

issue 2

303-308

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 μm or 200–300 μm in diameter and coated with filters of 500 μm Al foil and 10 μm 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 filters 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 confirmed the appearance of a filamentary fine structure in the PF discharges. In the past years the formation of such filaments 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.

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2 Nukleonika

2 2015

2 Paduch M.

2 Sadowski M. J.

2 Zielinska E.

1 Garkusha I. E.

1 Gribkov V. A.

1 Kowalska-Strzeciwilk E.

1 Kubkowska M.

1 Ladygina M. S.

1 Malinowski K.

1 Miklaszewski R.

1 Skladnik-Sadowska E.

1 Surała W.

1 Tomaszewski K.

1 Zaloga D. R.

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

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