A. Blagoev

Sofia University "St. Kliment Ohridski", Scientific Research Department, Faculty Member

Followers

Following

Co-authors

Public Views

Interests

Uploads

Papers by A. Blagoev

A modelling of the breakdown phase in the plasma focus discharge

Plasma Physics and Controlled Fusion, 2009

ABSTRACT The breakdown phase in the plasma focus (PF) discharge is modelled by the Monte Carlo-pa... more

Bootstrap and jackknife solving of linear equation system for experimental data processing

Effect of oscillations of the plasma potential on the measurement of the electron energy distribution function by probe current modulation

ABSTRACT

Measurements of the Basic Characteristics of the Dense Plasma Focus Device

In the experiments with the 3 kJ plasma focus device at the Sofia University are measured the bas... more In the experiments with the 3 kJ plasma focus device at the Sofia University are measured the basic characteristics, namely the discharge current, the current derivative, the soft X-ray and the hard X-ray emission from the plasma. The average dose of the X-Ray emission is a few tenth of Sv per shot. A study of the influence of soft X-rays upon biologic objects has been started. PACS codes: 52.70.La, 87.53.-j 1 Basic Measurements with the Plasma Focus Device 1.1 Experimental setup In the Faculty of Physics at the University of Sofia a Mather’s type dense plasma focus device (DPF) is in regular operation from about one and a half year. In the experiments with this device it is possible to obtain the quantitative results of the typical processes in a small DPF machines. As every usual DPF, it consists of a capacitor bank, fast switch and vacuum chamber, containing the electrode system. The capacitor bank has capacitance of 20 μF, with the maximal DC voltage of 40 kV. The insulator is m...

Download

Spectroscopic Investigation of Time Evolution of Laser-Produced Tungsten Plasma

The paper reports on optical emission spectroscopic studies of tungsten plasma generated using 10... more The paper reports on optical emission spectroscopic studies of tungsten plasma generated using 1064 nm, 3.5 ns pulses from a Nd:YAG laser. The spectra emitted from the p lasma plume were characterized by means of an optical spectrometer Mechelle5000 in the wavelength range of 200-900 nm and were recorded by an iCCD. The vacuum chamber was also equipped with ion diagnostics, namely an ion collector (Faraday cup) and an electrostatic ion energy analyzer with a windowless electron multiplier to observe time-of-flight spectra of emitted ions. The experimental work was devoted to investigations of time evolution of the optical spectrum of tungsten plasma. To observe spectra emitted by expanding plasma the triggering delay of the photomultiplier was being changed in the range from 0 to 500 ns from the laser shot. The acquisition time was 100 ns. In the observed wavelength range the emission spectra consisted mainly of W I and W II lines; however, the ratio of intensity of lines of differe...

Study of the breakdown in a Plasma Focus like device

ABSTRACT Earlier investigations of breakdown in a Plasma Focus like device [3] show some differen... more ABSTRACT Earlier investigations of breakdown in a Plasma Focus like device [3] show some differences between experimental data and modelling results. One of these is the earlier start time of breakdown predicted by the model. In present work we will focus our attention on initiation of the ionization processes in this device and we will explain the reason for the simulated earlier breakdown.

24pXQ-9 DIFFUSION AND DEPOPULATION OF THE METASTABLE : Cd 5^3P_0,2 STATES IN Cd-Ne AFTRGLOW PLASMA

Influence of hydrogen on the sputtered atoms’ transport in a cylindrical hollow cathode

Vacuum, 2000

ABSTRACT A pulsed hollow cathode discharge in Ar and Ne is used to investigate the temporal evolu... more ABSTRACT A pulsed hollow cathode discharge in Ar and Ne is used to investigate the temporal evolution of sputtered Mg density in the afterglow phase. A diffusion model of this transport is assumed, including the process of reflection by the wall (Chantry PJ, Phelps AV, Shultz GJ. Phys Rev 1966;152:81–9 [1]; Rusinov IM, Paeva GW, Blagoev AB. J Phys D: Appl Phys 1997;30:1878–84 [2]; Suzuki S. Itoh H, Ikuta N, Sekizawa H. J Phys D: Appl Phys 1992;25:1568–74 [4]; Stewart IM. J Phys D: Appl Phys 1994;27:1487–91 [5]. Decays of ground-state Mg atom densities are recorded using an optical absorption technique. The observed decay rates reveal an essential temporal dependence. This behavior is supposed to be due to changes in the wall loss probability with time during the afterglow. The influence of adsorbed hydrogen on the properties of the wall surface is investigated. Suppression of Mg atoms sputtering and change in the wall sticking probability value for these atoms is observed in the presence of hydrogen.

Determination of the diffusion coefficient of Mg atoms in 3He at ambient temperatures

Vacuum, 2004

ABSTRACT The diffusive transport of sputtered ground-state Mg atoms in 3He gas at ambient tempera... more ABSTRACT The diffusive transport of sputtered ground-state Mg atoms in 3He gas at ambient temperatures has been investigated by using a pulse-periodic gas discharge in a 0.3m in length and 27mm in diameter cylindrical hollow cathode. Mg atoms are sputtered from the cathode surface during the pulse. An optical-absorption technique with temporal resolution is applied to record the decay curves of the ground-state Mg atom density in the afterglow phase, involving absorption of the resonance Mg I 2852 line. The experimental loss rates obtained for various buffer gas pressures at temperature T=295K are used to derive the diffusion coefficient in the bulk (D0=390 (+60/−50)cm2s−1, for 133Pa pressure) and the sticking probability of the Mg atoms to the wall surface (S=0.1–1). The diffusion coefficient value is compared with some theoretical results.

Diffusion model of the transport of sputtered metal atoms in a cylindrical vessel

Vacuum, 2002

ABSTRACT Measurement of the diffusion loss rate of metal atoms sputtered by a pulsed gas discharg... more ABSTRACT Measurement of the diffusion loss rate of metal atoms sputtered by a pulsed gas discharge in a vessel represents a convenient method for determination of the diffusion coefficient of metal atoms in gases (J. Phys. D 30 (1997) 1878). This measurement should be combined with an appropriate diffusion model, which takes into account the experimental geometry and the interactions of the diffusing particles with the walls of the container. The effect of the latter is usually accounted for through the boundary condition used. In this work we consider a boundary condition based on a thermodynamic approach. The obtained diffusion model for cylindrical geometry is compared with experimental results for the diffusion of ground-state Mg atoms in Kr, as well as with some other model solutions.

Irradiation of samples for fusion prospective materials by the plasma focus device of Sofia University

Physica Scripta, 2014

This paper presents the first results for irradiation of tungsten, molybdenum and stainless steel... more This paper presents the first results for irradiation of tungsten, molybdenum and stainless steel samples with the 4 kJ plasma focus (PF) device at the University of Sofia. The samples were placed 4 cm above the anode of the PF machine and were exposed to a considerable number of shots. The working gas was deuterium with the pressure adjusted in the range of 1–3.3 mbar. Thus, the plasma streams and the fast-ion beam, which appear after the pinch phase, impinge the samples. The interaction of the pinch products with the targets causes substantial surface damage to the specimens. A mesh of partially melted cracks and re-crystallized regions are revealed on this surface and various chemical compounds are also present.

Studies of Diffusion Losses in Gaseous Media Using a Boundary Condition of the Third Kind

Japanese Journal of Applied Physics, 2000

ABSTRACT The application of two approaches for the simultaneous measurement of diffusion and refl... more ABSTRACT The application of two approaches for the simultaneous measurement of diffusion and reflection coefficients of particles in gaseous media is carried out using one and the same data set. Both approaches are based on the analysis of the effective lifetimes of particles measured under different experimental conditions and implement a boundary condition of the third kind. The experimental data used are those of Mg atoms diffusing in neon and argon. These were obtained by a pulsed afterglow technique using a hollow cathode gas discharge. The results obtained after processing the data by the two methods are found to show good agreement.

Beam Non-Uniformity Smoothing Using Density Valley Formed by Heavy Ion Beam Deposition in Inertial Confinement Fusion Fuel Pellet

Japanese Journal of Applied Physics, 2001

ABSTRACT We study the beam nonuniformity smoothing effect of radiation transport in the density v... more ABSTRACT We study the beam nonuniformity smoothing effect of radiation transport in the density valley formed by an ion-beam deposition in a heavy ion-beam inertial confinement fusion pellet by numerical simulations. The simulation results show that the radiation energy is confined in the density valley, and the beam nonuniformity can be smoothed out by the radiation transport along the density valley. In addition, an estimation for the Rayleigh-Taylor instability during the implosion phase is also presented.

Absolute calibration of arbitrary total cross sections for electron impact excitation of Xe metastable states in the near-threshold region

Journal of Physics B Atomic Molecular and Optical Physics

A comparison of the arbitrary cross sections for electron impact excitation of Xe metastable stat... more A comparison of the arbitrary cross sections for electron impact excitation of Xe metastable states obtained by Buckmann et al. (1983) with the afterglow results for quenching rate constants makes the calibration in absolute units of the excitation cross section possible. It is also shown that the resonance capture of the thermal electron by the metastable atom in a temporary negative ion state, followed by a decay to the ground state is an essential mechanism for de-excitation of the rare gas metastables. This quenching channel prevails over the conventional channel with a 1/V energy dependence for the Xe metastable atoms. The relation to a similar model for a decay of excimer molecules, is discussed.

Hybrid nuclear reactors

Detection of neutral tungsten by laser-induced fluorescence

Absolute calibration of arbitrary total cross sections for electron impact excitation of Xe metastable states in the near-threshold region

Journal of Physics B: Atomic and Molecular Physics, 1984

ABSTRACT A comparison of the arbitrary cross sections for electron impact excitation of Xe metast... more ABSTRACT A comparison of the arbitrary cross sections for electron impact excitation of Xe metastable states obtained by Buckmann et al. (1983) with the afterglow results for quenching rate constants makes the calibration in absolute units of the excitation cross section possible. It is also shown that the resonance capture of the thermal electron by the metastable atom in a temporary negative ion state, followed by a decay to the ground state is an essential mechanism for de-excitation of the rare gas metastables. This quenching channel prevails over the conventional channel with a 1/V energy dependence for the Xe metastable atoms. The relation to a similar model for a decay of excimer molecules, is discussed.

Influence of the amplitude of the superimposed potential oscillations on probe measurements of the electron distribution function

Sputtered Atoms Transport in a Cyllindrical Hollow Cathode

A pulsed hollow cathode discharge in Ar and Ne is used to investigate the temporal evolution of s... more A pulsed hollow cathode discharge in Ar and Ne is used to investigate the temporal evolution of sputtered Mg density in the afterglow phase. A diffusion model of this transport is assumed, including the process of reflection by the wall through a boundary condition of the third kind.(S. Suzuki, H. Itoh, N. Ikuta, and H Sekizawa J. Phys. D: Appl.

Spectroscopic Investigation of Time Evolution of Laser-Produced Tungsten Plasma

The paper reports on optical emission spectroscopic studies of tungsten plasma generated using 10... more The paper reports on optical emission spectroscopic studies of tungsten plasma generated using 1064 nm, 3.5 ns pulses from a Nd:YAG laser. The spectra emitted from the plasma plume were characterized by means of an optical spectrometer Mechelle5000 in the wavelength range of 200-900 nm and were recorded by an iCCD. The vacuum chamber was also equipped with ion diagnostics, namely an ion collector (Faraday cup) and an electrostatic ion energy analyzer with a windowless electron multiplier to observe time-of-flight spectra of emitted ions. The experimental work was devoted to investigations of time evolution of the optical spectrum of tungsten plasma. To observe spectra emitted by expanding plasma the triggering delay of the photomultiplier was being changed in the range from 0 to 500 ns from the laser shot. The acquisition time was 100 ns. In the observed wavelength range the emission spectra consisted mainly of W I and W II lines; however, the ratio of intensity of lines of different charge states depended on the observation time. The average electron temperature during plasma expansion was estimated as 1.5 eV and electron density as 5.5×10 17 cm-3. A signal from the ion collector made it possible to estimate the average energy of tungsten ions as the laser beam. In the spectra collected by the ion energy analyzer tungsten ions up to 4+ ion charge were observed.

Download

A. Blagoev

Uploads

Papers by A. Blagoev

Log In