- Institute of Electronics of the
Bulgarian Academy of Sciences
72 Tzarigradsko Shose Blvd.
1784 Sofia, BULGARIA - +359 02 979 5922
Dr. Svilen Sabchevski
Bulgarian Academy of Sciences, Institute of Electronics, Department Member
- Computational Physics, Electromagnetism, Electron Optics, Modelling and Simulation of Electron Devices, Terahertz Waves, Millimeter Waves, and 26 moreFar Infrared Physics, Electron Beam Technologies, Physics of Intense Charged Particle Beams, ITER Project, Charged Particle Optics, Gyrotrons, Sub-millimeter Waves, Design of Electronics, THz Genration, Public Health, Theoretical Physics, Optics, Electron Microscopy, Meshless Methods, Electromagnetic Fields, Electromagnetic Radiation, Computational Electromagnetics, Microwave and Millimetre Wave Radar and Imaging, Electromagnetic Fields and Microwave Techniques, Plasma Physics, RF and Microwave Systems, Numerical Simulations, Microwave/ mmW/ Sub-mmW/ Thz Imaging, Electromagnetics, Plasma, and Electron beam weldingedit
- Professional Interests: Computational Physics; Modelling and Simulation of Electron Devices; Electron Optics; Phys... moreProfessional Interests:
Computational Physics; Modelling and Simulation of Electron Devices; Electron Optics; Physics of Intense Charged Particle Beams; Electron Beam Technologies; Computational Electro Magnetics; Microwave Radiation Sources; High Frequency Gyrotrons; Powerful Gyrotrons; Quasioptical Systems; Infrared, Millimeter and Terahertz Wavesedit
Nowadays, gyrotrons are used in numerous and diverse fields of research and technology. Their most prominent application is to electron cyclotron resonance plasma heating and current drive-in reactors for controlled thermonuclear fusion.... more
Nowadays, gyrotrons are used in numerous and diverse fields of research and technology. Their most prominent application is to electron cyclotron resonance plasma heating and current drive-in reactors for controlled thermonuclear fusion. Another matured field is the thermal microwave treatment of materials in industrial-grade gyrotron-based technological systems. The unique spectral properties of gyrotron radiation, frequency tunability, and the possibility for precise control and modulation of both the output power and frequency have made the gyrotrons attractive and appropriate radiation sources for various novel advanced spectroscopic techniques. Among them are ESR (electron spin resonance), NMR-DNP (nuclear magnetic resonance with a signal enhancement through dynamic nuclear polarization), XDMR (X-ray detected magnetic resonance), acoustic molecular spectroscopy, as well as high-precision spectroscopy for measuring the SFS (super-fine splitting of the energy levels of positroniu...
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In this investigation, manganese has been produced from medium grade manganese ore from Karangnunggal mine (West Java, Indonesia). The effects of keeping it at a temperature of 1200°C in methane gas on the structural properties have been... more
In this investigation, manganese has been produced from medium grade manganese ore from Karangnunggal mine (West Java, Indonesia). The effects of keeping it at a temperature of 1200°C in methane gas on the structural properties have been studied. The material’s properties have been characterized on the basis of the experimental data obtained using X-ray fluorescence (XRF), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Fourier Transform Infrared (FTIR) spectroscopy. It has been found that MnO2 is reduced to hausmannite (Mn3O4), manganosite (MnO) and manganese carbide (Mn7C3). An increase of the keeping time up to 45 minutes during the sintering process leads to an increase of the MnO concentration, while at 90 minutes, the concentration decreases. The analysis based on the interpretation of both XRD patterns and FTIR spectrum allows one to explain the blockage in the particle surface of the ore by an increase of the carbon deposition.
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抄録 The electron cyclotron autoresonance is of both theoretical and practical interest for acceleration of charged particles and for generation of microwave radiation in various gyro-devices. In this paper a unified approach is applied to... more
抄録 The electron cyclotron autoresonance is of both theoretical and practical interest for acceleration of charged particles and for generation of microwave radiation in various gyro-devices. In this paper a unified approach is applied to the analysis of the interaction of electrons with electromagnetic waves with different characteristic impedance. In contrast to the previous works that consider only plane transverse waves and TE modes our analysis is applied also to TM modes. An approximate constant of motion (adiabatic invariant) is ...
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Synopsis Positronium is an ideal system for the research of the QED. The hyperfine splitting of positronium (Ps-HFS) is sensitive to the new physics beyond the Standard Model via a vacuum oscillation. Previous experimental results of the... more
Synopsis Positronium is an ideal system for the research of the QED. The hyperfine splitting of positronium (Ps-HFS) is sensitive to the new physics beyond the Standard Model via a vacuum oscillation. Previous experimental results of the Ps-HFS show 3.5 σ discrepancy from the QED calculation, and it might be caused by uncertainties of the indirect method with static magnetic field and a few GHz RF. We developed a new direct measurement system of the Ps-HFS without static magnetic field, using a sub-THz gyrotron and a quasi-optical ...
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In this study, the calcium carbonate from onyx stone used as a pore-forming agent in the ceramic membrane of kaolin, zeolite, and silica xerogel composites were investigated. Four different membrane samples were prepared with varying onyx... more
In this study, the calcium carbonate from onyx stone used as a pore-forming agent in the ceramic membrane of kaolin, zeolite, and silica xerogel composites were investigated. Four different membrane samples were prepared with varying onyx stone content from 5 wt.% to 30 wt.% into composite and then the prepared samples were sintered at 1200C. The structural properties of the prepared sample was investigated in detail using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), and N2 adsorption-desorption isotherms. The removal performance of the membrane was successfully tested during coconut sap treatment. It has been found that the prepared samples have a porous structure made up of interconnected pores and their volume fraction depends on onyx stone content. The sample with the onyx stone content of 30 wt.% provides the largest volume fraction of homogeneously interconnected pores and its presence demontrates the largest valu...
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An unexpected abrupt increase of the output power at magnetic field values corresponding to the excitation of high-order axial modes (HOAM) was observed experimentally and is explained theoretically through an after-cavity interaction of... more
An unexpected abrupt increase of the output power at magnetic field values corresponding to the excitation of high-order axial modes (HOAM) was observed experimentally and is explained theoretically through an after-cavity interaction of the bunched electron beam with the next radial mode. The calculations showed that under certain conditions this effect can be either useful for a power increase at the HOAM operation of the frequency-tunable gyrotron or harmful for high cyclotron harmonic operation due to an expansion of the zone of fundamental cyclotron resonance mode excitation.
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Abstract Coherent sources of radiation in the sub-terahertz and the terahertz frequency range are in great demand for various spectroscopic studies (eg electron spin resonance spectroscopy, DNP/NMR spectroscopy etc.). The required levels... more
Abstract Coherent sources of radiation in the sub-terahertz and the terahertz frequency range are in great demand for various spectroscopic studies (eg electron spin resonance spectroscopy, DNP/NMR spectroscopy etc.). The required levels of the output power as well as the needed specific spectral characteristics make the gyrotrons the most promising and high-performance devices for such applications. Recently, an initial design of a versatile second harmonic gyrotron utilizing a compact cryo-free 8 T superconducting magnet has ...
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Gyrotrons are used as high-power sources of coherent radiation operating in pulsed and CW regimes in many scientific and technological fields. In this paper, we discuss two of their numerous applications. The first one is in... more
Gyrotrons are used as high-power sources of coherent radiation operating in pulsed and CW regimes in many scientific and technological fields. In this paper, we discuss two of their numerous applications. The first one is in gyrotron-powered electromagnetic wigglers and undulators. The second one is for driving high-gradient accelerating structures in compact particle accelerators. The comparison, between the requirements imposed by these two concepts on the radiation sources on one hand and the output parameters of the currently available high-performance gyrotrons on the other hand, show that they match each other to a high degree. We consider this as a manifestation of the feasibility and potential of these concepts. It is believed that after the first successful proof-of-principle experiments they will find more wide usage in the advanced FEL and particle accelerators.
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In this feasibility study a novel prospective electrode material for electric double layer capacitors (EDLC) has been investigated. This promising material is activated carbon (AC) film produced using sago waste as a precursor. Important... more
In this feasibility study a novel prospective electrode material for electric double layer capacitors (EDLC) has been investigated. This promising material is activated carbon (AC) film produced using sago waste as a precursor. Important parameters of the technological process are the KOH to charcoal ratio and the content of the polytetrafluoroethylene (PTFE) binder. The influence of these parameters on the microtexture and pore structure and on the electrochemical characteristics of the AC films has been studied in detail. The measured specific surface area (SSA) of the samples is in the range from 212 to 1498 m2/g. It has been found that the presence of micropores increases the specific capacity while the presence of the mesopores acts in the opposite direction, because these mesopores are too wide in diameter for aqueous electrolyte. The specific capacitance of the studied samples has been found to be in the range from 16 to 64 F/g.
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In this paper, we present the preliminary results of an ongoing experimental study of a novel double-beam gyrotron, which has been designed to operate in CW regime on the second harmonic of the cyclotron resonance with a frequency of 0.79... more
In this paper, we present the preliminary results of an ongoing experimental study of a novel double-beam gyrotron, which has been designed to operate in CW regime on the second harmonic of the cyclotron resonance with a frequency of 0.79 THz. A number of fundamental and second harmonic modes can be excited in the frequency range 0.3–0.8 THz. The observed output power levels of the order of several tens watt are available at the second harmonic of cyclotron resonance for application of this tube as a powerful radiation source for a high-field 1.2 GHz, proton DNP-NMR spectroscopy.
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Simulation tools for computer-aided design and numerical investigations of high-power gyrotrons
A gyrotron with an axis-encircling electron beam is useful for high frequency operation, because the higher beam,efficiency is kept even at hgh harmonic of electron cyclotron resonance. We have designed and constructed such a gyrotron... more
A gyrotron with an axis-encircling electron beam is useful for
high frequency operation, because the higher beam,efficiency
is kept even at hgh harmonic of electron cyclotron resonance.
We have designed and constructed such a gyrotron with a permanent
magnet. The gyrotron has already succeeded in the
operations at the third harmonic and the fourth harmonic
resonance. The frequencies are 84.88 GHz and 112.8 GHz,
respectively. Operation Favity modes are TC311an d TE
The magnet system consists of the main permanent magnet
and additional coils for controlling the field intensities at cavity
and electron gun regions. The magnetic field at the cavity
region can be varied from 0.97 T to 1.18 T. At the optimum
condition of the magnetic field intensity, the output powers
at the thmd harmonic operation is 1.2 kW. The operation is
pulsed, the pulse length is 1 mz and the repetition frequency
is 1 Hz. The beam energy and current are 40 kV and A.
Starting current, beam efficiency and emission pattern also
have been measured. In this paper, the operation results of
the gyrotrou and comparison with the computer simulation
results are described.
high frequency operation, because the higher beam,efficiency
is kept even at hgh harmonic of electron cyclotron resonance.
We have designed and constructed such a gyrotron with a permanent
magnet. The gyrotron has already succeeded in the
operations at the third harmonic and the fourth harmonic
resonance. The frequencies are 84.88 GHz and 112.8 GHz,
respectively. Operation Favity modes are TC311an d TE
The magnet system consists of the main permanent magnet
and additional coils for controlling the field intensities at cavity
and electron gun regions. The magnetic field at the cavity
region can be varied from 0.97 T to 1.18 T. At the optimum
condition of the magnetic field intensity, the output powers
at the thmd harmonic operation is 1.2 kW. The operation is
pulsed, the pulse length is 1 mz and the repetition frequency
is 1 Hz. The beam energy and current are 40 kV and A.
Starting current, beam efficiency and emission pattern also
have been measured. In this paper, the operation results of
the gyrotrou and comparison with the computer simulation
results are described.
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Simulation tools for computer-aided design and numerical investigations of high-power gyrotrons
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In this paper, we present results of a hyperthermia treatment of malignant tumors using a gyrotron as a radiation source for heating of the cancerous tissue. They clearly demonstrate the efficiency of the irradiation by sub-THz waves,... more
In this paper, we present results of a hyperthermia treatment of malignant tumors using a gyrotron as a radiation source for heating of the cancerous tissue. They clearly demonstrate the efficiency of the irradiation by sub-THz waves, which leads to steady decrease of the volume of the tumor and finally to its disappearance. A combination of hyperthermia and photodynamic therapy (PDT) that utilizes a novel multifunctional photosensitizer has also been explored. In the latter case, the results are even more convincing and promising. In particular, while after a hyperthermia treatment sometimes a regrowth of the tumor is being observed, in the case of combined hyperthermia and PDT such regrowth has never been noticed. Another combined therapy is based on a preheating of the tumor by gyrotron radiation to temperatures lower than the hyperthermia temperature of 43 °C and followed then by PDT. The results show that such combination significantly increases the efficiency of the treatment. We consider this phenomenon as a synergy effect since it is absent when hyperthermia and PDT are applied separately, and manifests itself only when both methods are combined.
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ABSTRACT In this study, we investigate mullite containing ceramics prepared from alumina (α-Al2O3) and silica xerogel converted from sago waste ash. The silica xerogel was ground and then mixed with a varying content of α-Al2O3. The... more
ABSTRACT In this study, we investigate mullite containing ceramics prepared from alumina (α-Al2O3) and silica xerogel converted from sago waste ash. The silica xerogel was ground and then mixed with a varying content of α-Al2O3. The measurements were performed on cylindrical samples sintered at temperatures ranging from 900 °C to 1700 °C. In order to understand the mullitization process and structure formation a series of analyses were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermo-gravimetric analysis (TGA) and a differential scanning calorimetry (DSC). The results show that the mullite phase can be formed at a temperature as low as 1100 °C. It was found that a complete mullitization takes place for the composition of 40 mol% α-Al2O3 sintered at 1600 °C.
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Abstract A versatile and compact sub-THz second harmonic gyrotron with output parameters suitable for various spectroscopic studies is under development now at FIR FU Research Center. Here we present and discuss the results of the initial... more
Abstract A versatile and compact sub-THz second harmonic gyrotron with output parameters suitable for various spectroscopic studies is under development now at FIR FU Research Center. Here we present and discuss the results of the initial computer-aided design (CAD) of this novel prospective member of the Gyrotron FU CW series.
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Positronium is an ideal system for the research of Quantum Electrodynamics (QED), especially for QED in bound state. The discrepancy of 3.9σ was found recently between the measured HFS values and the QED prediction of O(α3). It might be... more
Positronium is an ideal system for the research of Quantum Electrodynamics (QED), especially for QED in bound state. The discrepancy of 3.9σ was found recently between the measured HFS values and the QED prediction of O(α3). It might be due to the contribution of unknown new physics or systematic problems in the all previous measurements. We propose a new method to measure HFS directly and precisely. A gyrotron, a novel sub-THz light source is adopted with a Fabry-Pérot cavity with high finesse and an efficient transportation system in order to obtain sufficient radiation power at 203 GHz. The present status of the optimization studies and the current design of the experiment are described.
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In this paper we review our approach and the physical models developed over the years for investigation of the space-charge compensation in intense technological electron beams and its influence on the beam propagation. We discuss a... more
In this paper we review our approach and the physical models developed over the years for investigation of the space-charge compensation in intense technological electron beams and its influence on the beam propagation. We discuss a detailed classification of the electron beams under the presence of space-charge neutralization. Results of numerical experiments, illustrating different aspects of the developed models and computer codes, are presented and discussed.