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Experiments and simulations on the possibility of radiative contraction/collapse in the PF-1000 plasma focus

Akel M., Cikhardt J., Kubes P., Kunze H.-J., Lee S., Paduch M., Saw S. H.

Nukleonika

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2016

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Vol. 61, No. 2

145--148

EN

Experimental studies of discharges in the plasma focus facility with neon filling and respective numerical simulations employing the radiative Lee code are reported. The pinch currents exceed the Pease-Braginskii current, which indicates that radiative losses are larger than heating and that contraction of the formed plasma should occur. Both of these effects were indeed observed. Parallel numerical simulations were crucial for the identifi cation of such an effect.

2

Evolution of the small ball-like structures in the plasma focus discharge

Cikhardtova B., Kubes P., Cikhardt J., Paduch M., Zielinska E., Kravarik J., Rezac K., Kortanek J.

Nukleonika

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2016

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Vol. 61, No. 2

155--159

EN

The experiments were carried out in the PF-1000 plasma-focus device at the maximum current reaching about 2 MA, at the deuterium or neon filling and with deuterium injected from a gas-puff nozzle placed on the axis of the anode face. Ball-like structures of diameters of 1–12 mm were identifi ed in interferometric and XUV pinhole camera frames. We made the statistical description of their parameters. A lifetime of the ball- -like structures was in the range from 30 to 210 ns, and in some cases even more. These structures appeared mostly at the surface of the imploding plasma shell and they did not change their position in relation to the anode end. During the evolution of these structures, interferometric fringes were observed near the surfaces of the structures only, and their internal parts were initially chaotic (without noticeable) fringes. Subsequently the number of interferometric fringes increased (the internal ‘chaotic’ area was fi lled with fringes too) and later on it decreased. The radii of the ball-like structures were mostly increasing during their existence. The maximum electron density reached the value of 1024 to 1025 m–3. The ball-like structures decayed by absorption inside the expanded pinch column and/or gradually expired in rare plasma outside of the dense plasma column.

3

Temporal distribution of linear densities of the plasma column in a plasma focus discharge

Cikhardtova B., Kubeš P., Cikhardt J., Paduch M., Zielinska E., Kravárik J., Řezáč K., Kortanek J., Šíla O.

Nukleonika

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2015

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Vol. 60, No. 2

315--318

EN

Experiments were carried out on the PF-1000 plasma focus device, with a deuterium filling and with deuterium puffing from a gas-puff nozzle placed on the axis of the anode face. The current was reaching 2 MA. 15 interferometric frames from one shot were recorded with a Nd:YLF laser and a Mach–Zehnder interferometer, with 10–20 ns delay between the frames. As a result, the temporal and spatial distribution of the linear densities and the radial and axial velocities of the moving of plasma in the dense plasma column could be estimated.

4

MCNP calculations of neutron emission anisotropy caused by the GIT-12 hardware

Šíla O., Klír D., Řezáč K., Cikhardtova B., Cikhardt J.

Nukleonika

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2015

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Vol. 60, No. 2

323--326

EN

The MCNP6 and MCNPX calculations for the GIT-12 device in Tomsk were performed to determine the influence of the gas-puff hardware on the neutron emission anisotropy and the neutron scattering rate. A monoenergetic 2.45 MeV neutron source and F1 and F6 tallies were declared in the simulation input. A comparison between MCNP results and the measured data was made. Differences between MCNPX and MCNP6 output data were investigated. In the experiment, two nTOF scintillation detectors with the Bicron BC-408 scintillator were used to measure the neutron waveform. Four bubble BD-PND detectors were used to estimate the amount of neutrons in different places around the neutron source.

5

Electromagnetic pulses produced by expanding laser - produced Au plasma

De Marco M., Cikhardt J., Krása J., Velyhan A., Pfeifer M., Krouský E., Klír D., Řezáč D., Limpouch J., Margarone D., Ullschmied J.

Nukleonika

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2015

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Vol. 60, No. 2

239--243

EN

The interaction of an intense laser pulse with a solid target produces large number of fast free electrons. This emission gives rise to two distinct sources of the electromagnetic pulse (EMP): the pulsed return current through the holder of the target and the out flow of electrons into the vacuum. A relation between the characteristics of laser-produced plasma, the target return current and the EMP emission are presented in the case of a massive Au target irradiated with the intensity of up to 3 × 1016 W/cm2. The emission of the EMP was recorded using a 12 cm diameter Moebius loop antennas, and the target return current was measured using a new type of inductive target probe (T-probe). The simultaneous use of the inductive target probe and the Moebius loop antenna represents a new useful way of diagnosing the laser–matter interaction, which was employed to distinguish between laser-generated ion sources driven by low and high contrast laser pulses.