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The experimental and theoretical investigations of damage development and distribution in double-forged tungsten under plasma irradiation-initiated extreme heat loads

Väli B., Laas T., Paju J., Shirokova V., Paduch M., Gribkov V. A., Demina E. V., Pimenov V. N., Makhlaj V. A., Antonov M.

Nukleonika

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2016

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Vol. 61, No. 2

169--177

EN

The influence of extreme heat loads, as produced by a multiple pulses of non-homogeneous flow of slow plasma (0.1–1 keV) and fast ions (100 keV), on double-forged tungsten (DFW) was investigated. For generation of deuterium plasma and fast deuterons, plasma-focus devices PF-12 and PF-1000 are used. Depending on devices and conditions, the power flux density of plasma varied in a range of 107–1010 W/cm2 with pulse duration of 50–100 ns. Power flux density of fast ions was 1010–1012 W/cm2 at the pulse duration of 10–50 ns. To achieve the combined effect of different kind of plasmas, the samples were later irradiated with hydrogen plasma (105 W/cm2, 0.25 ms) by a QSPA Kh-50 plasma generator. Surface modification was analysed by scanning electron microscopy (SEM) and microroughness measurements. For estimation of damages in the bulk of material, an electrical conductivity method was used. Investigations showed that irradiation of DFW with multiple plasma pulses generated a mesh of micro- and macrocracks due to high heat load. A comparison with single forged tungsten (W) and tungsten doped with 1% lanthanum-oxide (WL10) reveals the better crack-resistance of DFW. Also, sizes of cells formed between the cracks on the DFW’s surface were larger than in cases of W or WL10. Measurements of electrical conductivity indicated a layer of decreased conductivity, which reached up to 500 µm. It depended mainly on values of power flux density of fast ions, but not on the number of pulses. Thus, it may be concluded that bulk defects (weakening bonds between grains and crystals, dislocations, point-defects) were generated due to mechanical shock wave, which was generated by the fast ions flux. Damages and erosion of materials under different combined radiation conditions have also been discussed.

2

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.

3

Irradiation of austenitic steel 10Cr12Mn14Ni4AlMo and titanium alloy Ti-Al-V by pulsed streams of fast nitrogen ions and plasma in a dense plasma focus

Gribkov V. A., Pimenov V. N., Roschupkin V. V., Maslyaev S. A., Demina E. V., Lyakhovitsky M. M., Dubrovsky A. V., Sasinovskaya

Nukleonika

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2012

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Vol. 57, No. 2

291-295

EN

Austenitic steel 10Cr12Mn14Ni4AlMo and Ti-4Al-3V alloy were irradiated with nanosecond pulsed nitrogen ion and plasma streams in plasma focus devices. The two different modes of the treatment were applied: high power density (greater-than or equal to 10 8 W/cm2) irradiation with melting of the surface layer and irradiation with power density similar to 10 7 W/cm2 below the melting threshold. Structure and phase changes as well as the mechanisms of modification and hardening of the surface layers of the steel and titanium alloy upon applied irradiation are discussed.

4

Damage and modification of materials produced by pulsed ion and plasma streams in Dense Plasma Focus device

Pimenov V. N., Demina E. V., Ivanov L. I., Gribkov V. A., Dubrovsky A. V., Ugaste U., Laas T., Scholz M., Miklaszewski R., Kolman B., Tartari A.

Nukleonika

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2008

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Vol. 53, No. 3

111-121

EN

The Dense Plasma Focus (DPF) devices PF-1000, PF-6 and PF-5M working with different gases and in dissimilar irradiation modes were used to carry out experimental investigations of irradiation of a number of materials by powerful pulsed ion and high-temperature plasma streams. The materials under test were designed for application in structural and functional components of thermonuclear fusion devices with magnetic (MPC) and inertial (IPC) plasma confinement, as well as for working chambers of plasma and accelerator devices. The main features of the materials are low-activation and radiation-resistant properties. On the basis of the investigations a significant progress was achieved in understanding of dynamics of high-energy nano- and micro-second pulsed streams in DPF from one side as well as on the mechanisms of their influence upon materials under irradiation from the other one. We demonstrated that this approach can be useful for certain tests of plasma-facing materials (e.g. W for MPC and stainless steels for IPC) and of structural (construction) elements of the above-mentioned devices subjected to pulsed high-energy radiation streams. The results obtained suggest also that DPF devices can be used in new pulse technologies for material treatment by means of powerful nanosecond and microsecond pulses of plasma and ion streams.

5

Preliminary study on X-ray source from Plasma Focus device for fast radiography

Da Re A., Mezzetti F., Tartari A., Verri G., Rapezzi L., Gribkov V. A.

Nukleonika

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2001

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Vol. 46, suppl. 1

123--125

EN

Plasma derived flash X-ray sources may find potential applications in medicine and industry. Notwithstanding, as is the case of Plasma Focus (PF) devices, their characterisation in term of photon energy, temporal and spatial beam stability is far to be considered satisfactory. In this work, a radiographic approach, which avoids the effects caused by the intrinsic instability of the pinch output of a PF machine, is proposed and an attenuation curve can be attained even in presence of Xray emission instability. Using two radiographic films for each shot exposition symmetrically positioned and collimated to the pinch region the mean energy of the photons in the X-ray beam are evaluated. The X-ray emission symmetry from the pinch region was then utilised to control the validity of the proposed methodology.

6

Experimental study of a powerful energy flow effect on materials in PF-1000 installation

Borowiecki M., De Chiara P., Dubrovsky A. V., Dyomina E. V., Gribkov V. A., Ivanov L. I., Maslyaev S. A., Mezzetti F., Miklaszewski R., Pimenov V. N., Pizzo L., Scholz M., Szydlowski A., Ugaste Y. E., Volobuev I. V.

Nukleonika

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2001

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Vol. 46, suppl. 1

117--122

EN

The report describes some of the results obtained in an experimental study of the impact of a powerful plasma stream and a fast ion beam generated in a PF-1000 device on different materials perspective for the use in radiation loaded parts of pulsed plasma installations. Investigations were done during and after the interaction processes. It is shown that in case of irradiation of samples only by high power flux density plasma streams the effect of detachment still preserved. At the same time a low power flux density high-energy ion beam plays an important role in the process of saturation of the irradiated material by hydrogen.

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An internal standard for Fast Neutron Activation Analysis spectra obtained by means of Plasma Focus devices

Verri G., Tartari A., Rapezzi L., Mezzetti F., Gribkov V. A., Da Re A.

Nukleonika

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2001

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Vol. 46, suppl. 1

103--105

EN

The behaviour of Pb activation peaks, which appear in an X-ray spectrum of Fast Neutron Activation Analysis (FNAA) performed by means of a Plasma Focus (PF) neutron source and an NaI scintillator counter, has been studied. The PF device generates neutron bursts of different intensities. To know the exact neutron flux illuminating a sample during PF discharges an external neutron counter is usually used. The nature and behaviour of the indicated peaks suggest that one could use one of them as an internal standard for neutron production measurement instead of an external counter. This technique allows more reliable and accurate determinations of the presence of various elements.

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0.2-kJ and 2-kJ high rep rate Dense Plasma foci : their design, technology, and applications

Dubrovsky A. V., Gribkov V. A., Ivanov Y. P., Lee P., Lee S., Liu M., Samarin V. A.

Nukleonika

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2001

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Vol. 46, suppl. 1

107--111

EN

The paper presents various designs of several medium and small size Dense Plasma Focus (DPF) chambers intended for numerous applications, a description of technologies used in these facilities, and some results reached with these devices by using a number of diagnostic techniques. In present experiments the DP foci have been used mainly as an X-ray source. We discuss here how it is possible to satisfy absolutely new and very strict demands on the construction and technology for the devices to be eventually applied in science and industry. Between these characteristics there are a high repetition rate (typically 1…15 Hz) and a long lifetime (over 1 million shots). Their switching elements, a collector and chambers must withstand a high quasi-continuous heat load (up to 100 kW). High energy density in the central part of the chamber anode and the necessity to provide a channel for radiation extraction demanded a special construction and specific materials implementation in this region. Their X-ray spectrum should be tuned. They have to operate with different working gases and preferably in a wide range of pressures. All these points are discussed in this report. Capabilities of the described techniques are illustrated by results of the recent experimental studies carried out with facilities located at the Nanyang Technological University (NX1) as well as at the Lebedev Physical Institute (PF-0.2).