Emilia Balabanova

Bulgarian Academy of Sciences | BAS

Gyrotrons are the most powerful sources of CW coherent radiation in the sub-THz and THz frequency bands. In recent years, they have demonstrated a remarkable potential for bridging the so-called THz-gap in the electromagnetic spectrum and opened the road to many novel applications of the terahertz waves. Among them are various advanced spectroscopi...

As the most powerful CW sources of coherent radiation in the sub-terahertz to terahertz frequency range the gyrotrons have demonstrated a remarkable potential for numerous novel and prospective applications in the fundamental physical research and the technologies. Among them are powerful gyrotrons for electron cyclotron resonance heating (ECRH) an...

Powerful gyrotrons are necessary as sources of strong microwaves for electron cyclotron resonance heating (ECRH) and electron cyclotron current drive (ECCD) of magnetically confined plasmas in various reactors (most notably ITER) for controlled thermonuclear fusion. Adequate physical models and efficient problem-oriented software packages are essen...

Gyrotrons are the most powerful sources of coherent CW (continuous wave) radiation in the frequency range situated between the long-wavelength edge of the infrared light (far-infrared region) and the microwaves, i.e., in the region of the electromagnetic spectrum which is usually called the THz-gap (or T-gap), since the output power of other device...

Fitting formulae are presented for the calculation of the second interaction virial coefficients, mixture viscosities and binary diffusion coefficients for CF4/O2 and SF6/O2 gas mixtures in the temperature range between 200 K and 1000 K. The data recommended are obtained from the isotropic (n-6) Lennard-Jones intermolecular interaction potentials o...

A temperature-dependent effective intermolecular interaction potential is applied to describe the interaction between two nitrogen fluoride (NF3) molecules in gas phase. To this end, a spherically-symmetric (n-6) Lennard-Jones temperature-dependent potential (LJTDP) is used. The (n-6) LJTDP takes into account the influence of vibrational excitation...

A great number of problem-oriented software packages (e.g., DAPHNE, ESRAY, GYROSIM, just to name a few) are used for computer-aided design (CAD) and optimization of high-power gyrotrons for fusion research (most notably for ECRH and ECCD). In them, adequate self-consistent physical models formulated in a two-dimensional space (2D) are implemented....

In the present work the influence of nanopowders TiN, TiCN in the electron beam surface alloying of low carbon steel samples is investigated. It is found that the use of nanoparticles leads to changes in the microstructure of the electron beam treated zones, as well as to increase of microhardness and wear resistance of nanomodified samples.

In this review paper devoted to the 50th anniversary of the Institute of Electronics of the Bulgarian Academy of Sciences, we present the main research topics and the most significant scientific achievements of the laboratory Plasma Physics and Engineering that illustrate its history and present as well as provide a basis for its further developmen...

The paper proposes a technique to weld T-joints from carbon steel using a paste containing diamond nanoparticles of 3 nm in average diameter. Welding is carried out by gas metal arc welding method with argon gas (MAG method). The welding beads are made using a current of 60 A, a voltage of 20V, a welding speed of 35 mm/min and 20 l/ min shielding g...

Modelling and simulation are essential tools for computer-aided design (CAD), analysis and optimization of high-power gyrotrons used as radiation sources for electron cyclotron resonance heating (ECRH) and current drive (ECCD) of magnetically confined plasmas in the thermonuclear reactor ITER. In this communication, we present the current status of...

We studied the applicability of the spherically-symmetric (n-6) Lennard-Jones temperature dependent potential (LJTDP) for describing the binary interactions between O2 molecules in the temperature range between 200 K and 1300 K for pressures below 0.1 MPa. We observed a reasonable agreement between the thermophysical properties calculated using the...

In the lecture two items are discussed: i) the processes leading to nanostructured materials – nano- powders or layers production; ii) the analysis of nanocomposites TEM micrographs. The processes that are considered are carried out in thermal plasma setups. They related to the production of some ceramic materials such as Si-oxide, -nitride, -carb...

TEM micrographs can be used to compute fractal dimensions of 3-dimensional objects. In order to covert the fractal dimension of TEM micrograph to the 3-dimensional fractal dimension, a modified sphere method was developed. Using this method, fractal dimensions of some nanosized silica powders were computed.

The thermal plasma is a partially ionized gas, that is characterized by high enthalpy i.e. very high temperature (thousands, K). This makes the thermal plasma a perfect agent for manufacturing any type of substances, but it is especially effective for high boiling temperature substances. The main processes, carried out in the thermal plasma setups,...

The La-manganites with perovskite (P) structure are considered as favorite cathode materials for SOFC because of their high electric conductivity, good chemical stability and thermal expansion compatibility with the electrolyte solid layer. The present work shows the possibility of Sr doped P structures production under different initial conditions...

The presented work summarises our results concerning the modelling of silica vapour-to- silica nanoparticles generation in both forms - non-aggregated and aggregated, realised in a thermal arc plasma set up. It is shown that some operating parameters, such as initial temperature of the vapour and the vapour supersaturtion, play important role in th...

The fluid-dynamics approximation is used to present the flow dynamics in a non-isothermal aerosol reactor for silica nanoparticle production. Two flows are mixed in the reactor. One of them is plasma gas and raw substance vapour, the other is cooling gas. Different types of mixing are considered and their influence on the temperature variation in t...

The mechanism of silica nanoparticle generation by high-temperature (flame and thermal arc plasma) methods is studied by modelling. Processes responsible for particle formation and growth are considered. Parameters such as temperature, characteristic coagulation and coalescence time and residence time-influencing particle structure are investigated...

The production of ultrafine powder by mixing cooling gas (oxygen) and hot gas (plasma gas and silica vapour) in a flow reactor is considered. A simple one-dimensional model is developed to study the influence of the mixing on the particle growth mechanism. Two functions, one for the variation of the cooling gas concentration along the reactor lengt...

Ultrafine (nanometric) silica powders have many technological applications as thixotropic agents and thermal insulators. These applications require the study of the powder characteristics, such as the particle size distribution function (PSDF), mean particle size, and specific surface area. In the present study, a thermal arc plasma method for ultr...

The mechanism of ultrafine SiO2 particle production under thermal arc plasma conditions is studied by modelling. Two cases of the process are considered in the model: (i) when it is determined as a pure free-molecular coagulation; (ii) when the coagulation is influenced by the interparticle forces. The Hamaker formula is used to present the van der...

The production of ultrafine silica particles is examined by modelling the processes in a flow plasma reactor. The model is based on the authors' experimental data on silica sand processing by use of thermal arc plasma. The free-molecular coagulation is assumed to be the dominant process for particle growth. This is carried out at fast cooling of th...

Systematic calculations of maximum inversion were performed for iodine photodissociation laser in dependence on the mixture composition. The flash-lamp radiation was modelled as emanating from an optically thin Xe plasma. Duration of the pumping pulse is about 300 s. The sensitivity of the model to the values of kinetic constants was also tested.

Experimental results of the synthesis of ultrafine powders (UFP) under conditions which characterize quasi-equilibrium, as well as non-equilibrium low temperature plasma (LTP), are summarized. The basic steps involved in the plasmachemical processes for producing UFP are considered. The process of powder vaporization is limiting, determining the ch...

The kinetics of iodine laser amplifiers is examined by solving the time evolution equations of chemical kinetics during optical pumping. The pumping radiation intensity is modelled by a black body of the temperature varying in time (corresponding to the flash lamp pulse). A brief comparison is made of pumping effects by long and short light pulses....