ACADEMICIAN EMIL DJAKOV INSTITUTE OF ELECTRONICS
BULGARIAN ACADEMY OF SCIENCES

72, Tzarigradsko chaussee blvd, 1784-Sofia, Bulgaria


 

  

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 SELECTED  PROJECTS   PROJECTS  2012  OTHER ONGOING PROJECTS       

    

    

SELECTED PROJECTS

    

EC-Project EURATOM of FP7

Contract No FU07-CT-2007-00059/Fusion CSA/EURATOM
MODELING AND SIMULATION OF GYROTRONS FOR ITER

S. Sabchevski1, M. Damyanova1, I. Zhelyazkov2, P. Dankov2, P. Malinov2,
E. Balabanova1, E. Vasileva1 and R. Enikov1

1Emil Djakov Institute of Electronics,
Bulgarian Academy of Sciences, 72 Tsarigradsko Chaussee, 1784 Sofia, Bulgaria,
Association EURATOM-INRNE
2Faculty of Physics, St. Kliment Ohridski University of Sofia,
5 James Bourchier Blvd., 1164 Sofia, Bulgaria
Association EURATOM-INRNE

Motivation, scope and main activities of the project
High-power gyrotrons with megawatt output power and frequencies ranging from 77 to 170 GHz are necessary for electron cyclotron resonance heating (ECRH), electron cyclotron current drive (ECCD) and ECH-assisted start-up of magnetically confined plasmas in various reactors for controlled thermonuclear fusion (tokamaks and stellarators), as well as for plasma control and stabilization (e.g., NTM suppression and MHD control). The gyrotrons are used also for plasma diagnostics based on collective Thomson scattering (CTS). Typical tubes that illustrate the state-of-the-art in the development of gyrotrons for fusion are: megawatt-class CW gyrotrons with frequencies of 77 GHz for LHD, 110 GHz for JT-60SA and DIII-D, 140 GHz for W7-X, 170 GHz for ITER developed in EU, Japan, Russia, and US.

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3D FEMTOSECOND LASER MICROPROCESSING OF BIOMATERIALS
FOR APPLICATION IN MEDICINE

Project DMU 03/15 funded by the Bulgarian National Science Fund
Project coordinator: Dr. Albena Daskalova
Project period: 2011 - 2014

Laboratory of Biophotonics, Group Leader Prof. L. Avramov

Acad. Emil Djakov Institute of Electronics, Bulgarian Academy of Sciences,
72 Tsaridradsko Chaussee, 1784 Sofia, Bulgaria

Project goals

The principal goal of the regenerative medicine is to promote tissue regeneration and healing after injury or disease that can be achieved through a delivery of cells and/or factors in tissue engineered scaffolds designed to provide a biomimetic microenvironment conducive to cell adhesion, proliferation, differentiation, and host tissue integration. Scaffolds constructed from biocompatible polymers (gelatin, collagen and their blends) have been developed for the needs of skin tissue replacement. The main demands to engineered scaffolds are: biocompatibility, biodegradability, high surface area for cell attachment, and a good mechanical integrity suitable for treatment handling. The surface topography has been shown to be a key issue in cell proliferation. The scaffold design should mimic the in vivo tissue microarchitecture and the cellular microenvironment. The biomaterials' microstructure and mechanical properties influence the scaffold bioactivity.

The goal of the present project was to demonstrate the effectiveness of applying femtosecond laser pulses to the modification of surfaces of natural biopolymers gelatin, collagen and collagen-elastin thin films and the formation of micro and nanoscale structures, as well as to study the dependence of the thin-film structure evolution on the laser parameters.

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LIGHT-INDUCED ATOMIC DESORPTION (LIAD)
FOR ALL-OPTICAL CONTROL OF LIGHT

M Taslakov, S Tsvetkov and S Gateva

E. Djakov Institute of Electronics, Bulgarian Academy of Sciences,
72 Tsarigradsko Chaussee, 1784 Sofia, Bulgaria

Introduction

The light-induced atomic desorption (LIAD) is a non-thermal process whereby atoms adsorbed at a surface are released under illumination. LIAD was reported for the first time by Gozzini et al., has been subsequently investigated extensively both experimentally and theoretically and has found various applications vapor density stabilization, magneto-optical trap (MOT) loading, surface nanostructuring etc.. However, there are still several aspects of the LIAD dynamics that remain unexplained and questions that are open - for example, the question on whether there is a common mechanism underlying all LIAD observations [8]. LIAD is influenced by many parameters, among which are the cell dimensions and geometry, the wavelength of the illuminating light, the atomic species, the cell's history, the stem-opening area, etc. The models of LIAD are taking into account different processes for description of the LIAD dynamics. Reducing the factors influencing LIAD will assist in gaining a better understanding of these processes and their dynamics.

Under this project, a special system for homogeneous illumination of the cell was developed. The Rb D2 line absorption spectra in uncoated and coated cells were compared without illumination, with one-side illumination and with homogeneous illumination. The transmission was measured as a function of the illumination intensity and the tuning direction. The dynamics of the LIAD in an uncoated cell was analyzed. The results demonstrated the potential of the system for development of new optoelectronic elements, LIAD-loaded atomic devices and their miniaturization, new methods for surface and coating diagnostics, and analysis of the quality of vacuum cells.

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VELOCITY DISTRIBUTION OF ALKALI ATOMS
IN MICROMETRIC THIN CELLS

Project DMU 02/17 funded by the Bulgarian National Science Fund
Project coordinator: Dr. Petko Todorov
Project period: 2009 - 2013

P Todorov1, N Petrov1, I Maurin2, S Saltiel2,3 and D Bloch2

Partners

1Institute of Electronics, BAS,
72, Tsarigradsko Chaussee blvd., 1784 Sofia, Bulgaria
2Laboratoire de Physique des Lasers, Universite Paris 13, Sorbonne Paris-Cite,
UMR 7538 du CNRS, 99 Avenue J.-B. Clement, F-93430 Villetaneuse, France
3Faculty of Physics, University of Sofia,
5, J. Bourchier Blvd., 1164 Sofia, Bulgaria

Introduction

When one considers a gas at thermal equilibrium on the basis of the kinetic theory of gasses as a part of thermodynamics, it is natural that one should assume that the particles' velocity distribution is Maxwellian, and also that the velocity vector distribution is isotropic. These two points may not be perfectly equivalent, as the anisotropic shape of the container may induce anisotropy in the vector distribution. The kinetic theory only considers ideal containers, i.e. ideal surfaces at the boundary of the gas region. It is by a flux equilibrium between atoms incoming to and departing from the surface that one derives the Knudsen law for a rarefied gas ("molecular regime"), namely, a "cosθ" probability for a departing atom direction, with being the angle between the departing atom trajectory and the normal to the surface. This "cosθ" law is well-known, but has no connection with the microscopic description. It cannot be applied to accommodation effects (surface and gas at different temperatures, as often occurs in aeronautical studies), nor can it be used in a detailed study of the atomic desorption from a well-characterized surface; nevertheless, it remains widely adopted when various averagings have to be introduced in the modeling. The tradition for using such a "cosθ" model is so strong that detailed desorption studies performed under high vacuum, rather than in a thermal gas surrounding, often describe the angular behavior along a "cosθ" expansion, i.e. a f(θ) law as f(θ) = ∑nan(cosθ)n.

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ROOM-TEMPERATURE MULTIFERROICS BASED ON Y-TYPE HEXAFERRITES

Contract DNTS/SLOVENIA 01/4 /2011 financed by the Bulgarian National Science Fund
Project coordinator S. Kolev

S Kolev, T Koutzarova, Ch Ghelev and I Bliznakova

E. Djakov Institute of Electronics, Bulgarian Academy of Sciences,
72 Tsarigradsko Chaussee, 1784 Sofia, Bulgaria

In view of implementing the project's tasks, we developed two "soft chemistry"-based methodologies for preparing complex oxides, such as Ba2Mg2Fe12O22 and Ba1.5Sr0.5Zn2Fe12O22, namely, sonochemical synthesis and sol-gel auto-combustion.

The sonochemical synthesis of complex oxides consists in the co-precipitation of metal cations in the presence of a high-power ultrasound field. We will present below a brief description of the technology developed. The process of preparing a precursor for the synthesis of Y-type hexaferrites has to do with the co-precipitation of Ba2+, Mg2+ and Fe3+ or Ba2+, Sr2+, Zn2+ and Fe3+ cations by NaOH. The process takes place under the influence of a high-power ultrasound pulse. We determined the metal cations' concentration and ratios needed for the co-precipitation to occur, together with the ultrasound pulse power and duration. We further studied the effect of the temperature in the 1080 − 1170 °C range, as well as of the time of synthesis, on the phase content of the hexaferrite studied.

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