Papers by Dr. Svilen Sabchevski
Photonics
Nowadays, gyrotrons are used in numerous and diverse fields of research and technology. Their mos... 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...
IOP Conference Series: Materials Science and Engineering, 2019
A novel type of ceramic porcelain insulator material was produced by mixing kaolin with zeolite. ... more A novel type of ceramic porcelain insulator material was produced by mixing kaolin with zeolite. The composition was prepared by adding a controllable amount of kaolin ranging from 30 wt% to 100 wt% into the zeolite. Then a series of samples were sintered at 1200 o C. The influence of the composition on the structural properties was studied in detail using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). The results show that the microstructure of porcelain body is characterized by the presence of elongated mullite grains. It was found also that the decrease of the kaolin content in the porcelain body leads to a decrease in the crystalline phase of mullite. The analysis of the structural properties of such ceramics indicates that zeolite could not be recommended as an appropriate material for manufacturing of high-voltage ceramic porcelain insulators by mixing it with kaolin.
International Journal of Materials Science and Engineering, 2018
In this paper, we present and discuss experimental results from a microwave sintering of a mullit... more In this paper, we present and discuss experimental results from a microwave sintering of a mullite ceramic, produced from a mixture of alumina and silica xerogel extracted from a sago waste ash. The composition has been prepared by adding 60 %wt amount of alumina into the silica xerogel. As a radiation source for the microwave heating, a 28 GHz wave gyrotron has been used. The influence of the sintering temperature on the structural properties was studied in detail. It has been found that the mixture crystallizes completely as a single mullite phase at a temperature of 1600°C after heating for 10 min at a temperature rate of 45oC/min. Most importantly, such result cannot be achieved by conventional heating. The results that have been obtained in this study allow one to conclude that the microwave sintering of using a 28 GHz gyrotron is an appropriate technological process for the production of mullite ceramics and is characterized by several advantages such as shorter times of the thermal cycle, lower sintering temperatures and higher quality of the final product.
Reduction behavior of medium grade manganese ore from Karangnunggal during a sintering process in methane gas
IOP Conference Series: Materials Science and Engineering, 2019
In this investigation, manganese has been produced from medium grade manganese ore from Karangnun... 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.
Modeling and simulation of gyrotrons (平成 14 年度 福井大学遠赤外領域開発研究センター 研究成果報告書)--(1 遠赤外光源及び伝送技術の開発)
The Progress in the Studies of Mode Interaction in Gyrotrons
Journal of Infrared, Millimeter, and Terahertz Waves, 2022
平成14年度福井大学遠赤外領域開発研究センター研究成果報告書;6ジャイロトロンによる高品質セラミックス焼結 Microwave heating of boron carbide rods
遠赤外領域開発研究, 2002
On the Theory of Cyclotron Autoresonance (平成15年度 福井大学遠赤外領域開発研究センター 研究成果報告書) -- (1 遠赤外光源の開発)
遠赤外領域開発研究 : 福井大学遠赤外領域開発研究センター研究成果報告書, 2003
抄録 The electron cyclotron autoresonance is of both theoretical and practical interest for acceler... 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 ...
The first direct measurement of the hyperfine splitting in positronium
Journal of Physics: Conference Series, 2009
Synopsis Positronium is an ideal system for the research of the QED. The hyperfine splitting of p... 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 ...
Applied sciences, Oct 13, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
１テスラ永久磁石を用いたLarge Orbit Gyrotron II
International Journal of Engineering, 2022
In this study, the calcium carbonate from onyx stone used as a pore-forming agent in the ceramic ... 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...
EC-Project EURATOM of FP7 Contract No FU07-CT-2007-00059/Fusion CSA/EURATOM MODELING AND SIMULATION OF GYROTRONS FOR ITER (Annual Report 2011)
Plasma additional heating and Tokamak engineering issues
High Frequency Sources of Coherent Radiation for Fusion Plasmas, 2021
Undulator based free electron laser
High Frequency Sources of Coherent Radiation for Fusion Plasmas, 2021
International Journal of Technology, 2017
This investigation presents the synthesis procedure and the results of an investigation of the cr... more This investigation presents the synthesis procedure and the results of an investigation of the crystallite growth of TiO 2 and the formation of Si-O-Ti bonds in novel silica xerogel (SiO 2) glass ceramic produced from an amorphous SX derived from sago waste ash. The composition had been prepared by adding various amounts of TiO 2 , from 20 wt% to 80 wt%, into the amorphous SiO 2 , and then a series of samples were sintered at 1200°C for 2 hours. The influence of the content of TiO 2 and the sintering temperature on the properties of TiO 2 , namely crystallite size and formation of Si-O-Ti bonds, has been studied in detail. The properties of the produced ceramics have been characterized on the basis of the experimental data obtained using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. It has been found that an addition of SiO 2 confers an appreciable effect on the quantity of Si-O-Ti bonds. The interpretation of the XRD pattern allows one to explain the increase in the crystallite size of rutile TiO 2 by a decreased quantity of Si-O-Ti bonds.
Physics of Plasmas, 2020
The investigation of interaction between modes resonant with electrons at different cyclotron har... more The investigation of interaction between modes resonant with electrons at different cyclotron harmonics is presented. The study is focused on mode interaction in the region of currents lower than the start current of the parasitic mode at the fundamental. In this region, the excitation of such parasitic modes is possible due to nonlinear excitation of them by the harmonic modes only. It is shown that, when the beam current increases, various oscillation regimes replace each other: when the current exceeds the start current of the harmonic mode only slightly, the single-frequency oscillations of this mode are stable. At higher currents, due to nonlinear excitation, the oscillations of both modes with constant amplitudes are possible. Then, this regime is replaced by the auto-modulation of two modes with periodically varying mode amplitudes. Finally, at even higher currents, the parasitic mode at the fundamental suppresses the parental second harmonic mode. The role of two saturation mechanisms (the orbital phase bunching and the depletion of the free rotational energy in the process of beam-wave interaction) in the nonlinear excitation of parasitic modes at the fundamental is analyzed. The parallels between this set of events and events that take place in the prey-predator theory are discussed.
Influence of the Aftercavity Interaction on the Output Power of a Gyrotron Operating at a High-Order Axial Mode
2021 22nd International Vacuum Electronics Conference (IVEC), 2021
An unexpected abrupt increase of the output power at magnetic field values corresponding to the e... 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.
25aB-8 Gyrotron FU V Aの開発
arXiv: High Energy Physics - Experiment, Jul 6, 2010
Hyperfine splitting of positronium is an important parameter for particle physics. This paper giv... more Hyperfine splitting of positronium is an important parameter for particle physics. This paper gives experimental techniques and results of R&D studies of our experiment to observe direct hyperfine transition of ortho-positronium to parapositronium.
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Papers by Dr. Svilen Sabchevski