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1

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

Ladygina M. S., Skladnik-Sadowska E., Zaloga D. R., Sadowski M. J., Kubkowska M., Kowalska-Strzeciwilk E., Krawczyk N., Paduch M., Miklaszewski R., Garkusha I. E.

Nukleonika

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2016

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Vol. 61, No. 2

149--153

EN

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 modifi ed 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.

2

Comparison of silicon drift detectors made by Amptek and PNDetectors in application to the PHA system for W7-X

Krawczyk N., Kaczmarczyk J., Kubkowska M., Ryć L.

Nukleonika

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2016

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Vol. 61, No. 4

409--412

EN

The paper presents comparison of two silicon drift detectors (SDD), one made by Amptek, USA, and the second one by PNDetector, Germany, which are considered for a soft X-ray diagnostic system for W7-X. The sensitive area of the first one is 7 mm2 × 450 m and the second one is 10 mm2 × 450 m. The first detector is cooled by a double-stage Peltier element, while the second detector is cooled by single-stage Peltier element. Each one is equipped with a field-effect transistor (FET). In the detector from Amptek, the FET is mounted separately, while in the detector from PNDetector, the FET is integrated on the chip. The nominal energy resolution given by the producers of the fi rst and the second one is 136 eV@5.9 keV (at –50°C) and 132 eV@5.9 keV (at –20°C), respectively. Owing to many advantages, the investigated detectors are good candidates for soft X-ray measurements in magnetic confi nement devices. They are suitable for soft X-ray diagnostics, like the pulse height analysis (PHA) system for the stellarator Wendelstein 7-X, which has been developed and manufactured at the Institute of Plasma Physics and Laser Microfusion (IPPLM), Warsaw, in collaboration with the Max Planck Institute for Plasma Physics (IPP), Greifswald. The diagnostic is important for the measurements of plasma electron temperature, impurities content, and possible suprathermal tails in the spectra. In order to choose the best type of detector, analysis of technical parameters and laboratory tests were done. Detailed studies show that the most suitable detector for the PHA diagnostics is the PNDetector.

3

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

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.

Nukleonika

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2015

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Vol. 60, No. 2

293--296

EN

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.

4

Comparison of optical spectra recorded during DPF-1000U plasma experiments with gas-puffing

Zaloga D. R., Skladnik-Sadowska E., Kubkowska M., Ladygina M. S., Malinowski K., Kwiatkowski R., Sadowski M. J., Paduch M., Zielinska E., Makhlaj V. A.

Nukleonika

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2015

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Vol. 60, No. 2

309--314

EN

The results are presented of the optical spectra measurements for free plasma streams generated with the use of the modifi ed DPF-1000U machine. This facility was recently equipped with a gas injection system (the so-called gas-puff) placed on the symmetry axis behind the central opening in the inner electrode. The DPF-1000U experimental chamber was fi lled up with pure deuterium at the initial pressure of 1.6 or 2.4 mbar. Additionally, when the use was made of the gas-puff system about 1 cm3 of pure deuterium was injected at the pressure of 2 bars. The gas injection was initiated 1.5 or 2 ms before the triggering of the main discharge. The investigated plasma discharges were powered from a condenser bank charged initially to 23 kV (corresponding to the energy of 352 kJ), and the maximum discharge current amounted to about 1.8 MA. In order to investigate properties of a dense plasma column formed during DPF-1000U discharges the use was made of the optical emission spectroscopy. The optical spectra were recorded along the line of sight perpendicular to the vacuum chamber, using a Mechelle®900 spectrometer. The recent analysis of all the recorded spectra made it possible to compare the temporal changes in the electron density of a freely propagating plasma stream for discharges without and with the gas-puffing. Using this data an appropriate mode of operation of the DPF-1000U facility could be determined.

5

Overview of the application of laser - based techniques in plasma - wall interaction research program at IFPiLM

Kubkowska M., Gąsior P., Czarnecka A., Rosiński M., Wołowski J.

Nukleonika

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2012

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Vol. 57, No. 2

163-166

EN

The purpose of this paper is to give an overview of the progress in the application of the laser-based techniques which has been achieved in the research in the field of plasma-wall interaction (PWI) at the Division of Laser-Produced Plasmas (DLPP), Institute of Plasma Physics and Laser Microfusion (IFPiLM, Warsaw, Poland) since 2005. The evolution of the experimental set-up which started in a simple configuration for the laser ablative co-deposit removal is presented with stress on the milestones which led to subsequent modifications, namely installation of laser induced breakdown spectroscopy (LIBS), fast HR (high resolution) CCDs, pulsed fiber-laser and the common triggering system.

6

Optical emission spectroscopy of plasma streams in PF-1000 experiments

Jakubowska K., Kubkowska M., Skladnik-Sadowska E., Malinowski K., Marchenko A. K., Paduch M., Sadowski M. J., Scholz M.

Nukleonika

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2011

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Vol. 56, No. 2

125-129

EN

The optical spectroscopy in the visible range was used to determine properties of the dense magnetized plasma generated in the PF-1000, a 1 MJ plasma focus device operating in the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw, Poland. The experiments were performed in a vacuum chamber pumped out to the basic pressure of 2 x 10.5 hPa. The initial pressure of the pure deuterium filling was 2.9 hPa, while that of the deuterium--argon mixture was 1.07 hPa of D2 and 0.13 hPa of Ar. The deuterium-plasma emission contained the Balmer series (Dalfa, Dbeta and Dgamma) and a few distinct copper (Cu I) lines originating from the inner electrode material. The emission of the deuterium-argon plasma was rich in Ar II lines. The electron density (ne), averaged over line of sight, of order of 1016 cm.3 was calculated on the basis of the Dalfa and Dbeta emission only, because the D�ż line was strongly self-absorbed. A group of the Ar II spectral lines was used to estimate the excitation temperature (Texc = 3 eV) by means of a Boltzmann plot. Additionally, the temporal evolution of the electron density was determined on basis of the Stark broadening of the Dalfa and Dgamma lines.