- Head of Laboratory Plasma Physics and Engineering in the Institute of Electronics of the Bulgarian Academy of Sciences. Scientific interests: gyro-devicesedit
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 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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In this study, the graphite/SiO2 composite performance used as an active electronic layer in an air cathode of an aluminum-air battery (Al-air battery) has been investigated. The effects of the guar gum (GG) binder content of the samples... more
In this study, the graphite/SiO2 composite performance used as an active electronic layer in an air cathode of an aluminum-air battery (Al-air battery) has been investigated. The effects of the guar gum (GG) binder content of the samples on their characteristic impedance and discharge capacity of an Al-air battery have been analyzed in the interval from 10 to 40%. The characterization of their experimental data was obtained using Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetric (CV), and Battery Testing System (BTS). It has been found that the characteristic impedance increases with increasing of the binder content. The sample with the lowest GG content provides the larger discharge capacity of the battery up to 42.54 mAh/g. This observation has been collaborated by an analysis of the CV curve, and it provides an explanation for the increase in the integrated area of the voltammetric curve by a decreased content of the GG binder. As a whole, the experimental results demonstrate that the graphite/SiO2 composite is an appropriate electronic active material for air cathodes in Al-air batteries. The obtained data can be used for an envisaged further optimization of the properties of this promising material.
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We present a precise measurement of the hyperfine structure of cesium 7 S 1 / 2 excited state by employing electromagnetically induced spectroscopy (EIS) with a cesium three-level cascade ( 6 S 1 / 2 − 6 P 3 / 2 − 7 S 1 / 2 ) atom in a... more
We present a precise measurement of the hyperfine structure of cesium 7 S 1 / 2 excited state by employing electromagnetically induced spectroscopy (EIS) with a cesium three-level cascade ( 6 S 1 / 2 − 6 P 3 / 2 − 7 S 1 / 2 ) atom in a room temperature vapor cell. A probe laser, λ p = 852 nm, was coupled to a transition | 6 S 1 / 2 ⟩ → | 6 P 3 / 2 ⟩ , related frequency locked to the resonance hyperfine transition of | 6 S 1 / 2 ⟩ → | 6 P 3 / 2 ⟩ with a Fabry–Perot (FP) cavity and an electro-optic modulator (EOM). A coupling laser, λ c = 1470 nm, drove the | 6 P 3 / 2 ⟩ → | 7 S 1 / 2 ⟩ transition with the frequency scanned over the | 6 P 3 / 2 ⟩ → | 7 S 1 / 2 ⟩ transition line. The hyperfine level interval was extracted to be 2183.61 ± 0.50 MHz by analyzing EIS spectroscopy. The optical–optical double-resonance (OODR) spectroscopy is also presented for comparison, with the corresponding value of the hyperfine level interval being 2183.48 MHz ± 0.04 MHz, and the measured hyperfine spl...
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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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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... more
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 essential tools for numerical studies, analysis, optimization and computer-aided design (CAD) of such high-performance gyrotrons operating in a CW mode and delivering output power of the order of 1-2 MW. In this report we present the current status of our simulation tools (physical models, numerical codes, pre- and post-processing programs, etc.) as well as the computational infrastructure on which they are being developed, maintained and executed.
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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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The direct transition from ortho-positronium to para-positronium with high-power sub-THz radiation has been observed with 5.1 σ significance. The observed transition rate is consistent with the theoretical calculation. A sub-THz gyrotron... more
The direct transition from ortho-positronium to para-positronium with high-power sub-THz radiation has been observed with 5.1 σ significance. The observed transition rate is consistent with the theoretical calculation. A sub-THz gyrotron is used as the light source, and a quasi-optical Fabry-Perot cavity is utilized to accumulate the radiation. This is the first observation of the positronium hyperfine splitting (Ps-HFS), which leads to the first direct measurement of Ps-HFS with a target accuracy of 100 ppm in several years.
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Abstract. The ground state hyperfine splitting of positronium,∆ HFS, is sensitive to high order corrections of QED. A new calculation up to O (α3) has revealed a 3.9 σ discrepancy between the QED prediction and the experimental results.... more
Abstract. The ground state hyperfine splitting of positronium,∆ HFS, is sensitive to high order corrections of QED. A new calculation up to O (α3) has revealed a 3.9 σ discrepancy between the QED prediction and the experimental results. This discrepancy might either be due to systematic problems in the previous experiments or to contributions beyond the Standard Model. We propose an experiment to measure∆ HFS employing new methods designed to remedy the systematic errors which may have affected the previous ...
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Special Issue Information Nowadays, the treatment of various materials with microwaves is a mature and industrially viable technology that has numerous applications due to its advantages and unique capabilities (e.g., energy efficiency,... more
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Nowadays, the treatment of various materials with microwaves is a mature and industrially viable technology that has numerous applications due to its advantages and unique capabilities (e.g., energy efficiency, precise control of the heated area, volumetric heating, etc.) compared to conventional heating. Active research in the field of microwave processing continues to be a driving force for the continuous improvement in the techniques used and their applications to novel and advanced materials.
Nowadays, the treatment of various materials with microwaves is a mature and industrially viable technology that has numerous applications due to its advantages and unique capabilities (e.g., energy efficiency, precise control of the heated area, volumetric heating, etc.) compared to conventional heating. Active research in the field of microwave processing continues to be a driving force for the continuous improvement in the techniques used and their applications to novel and advanced materials.
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The properties of electromagnetic undulators, produced by the field of a high-power microwave, are discussed. We analyze the conditions to be satisfied that allow the treatment of the emission process by relativistic charges moving... more
The properties of electromagnetic undulators, produced by the field of a high-power microwave, are discussed. We analyze the conditions to be satisfied that allow the treatment of the emission process by relativistic charges moving through it in full analogy with the case of their static counterparts. We critically review the often claimed possibility of exploiting them in programs aimed at reducing the sizes and costs of an actual free electron laser (FEL) device. We analyze several possible configurations for FELs based on powerful microwave undulators and conclude that the present level of technology, even though not yet mature, should be improved to allow a breakthrough either for low- or high-gain devices.
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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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Abstract In recent years considerable interest and attention has been focused on the theoretically appealing possibilities of increasing further both the power level and maximum frequency of radiation using new schemes of interaction in a... more
Abstract In recent years considerable interest and attention has been focused on the theoretically appealing possibilities of increasing further both the power level and maximum frequency of radiation using new schemes of interaction in a variety of gyro-devices. One promising class of such relatively new tubes is the large orbit gyrotron (LOG). Although its advantages for high harmonic operation are well known and theoretically proved not only for the relativistic range of beam energy most of the efforts so far have been concentrated on ...
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In this paper, we present the current status and both the ongoing investigation and the continuous improvements to the operational performance of a unique gyrotron, which is built using a 20 T superconducting magnet and holds a world... more
In this paper, we present the current status and both the ongoing investigation and the continuous improvements to the operational performance of a unique gyrotron, which is built using a 20 T superconducting magnet and holds a world record of 10 W THz wave generation at the highest frequency (1.08 THz) in continuous wave (CW) operation. Additionally, it has demonstrated highpurity single-mode generation on a sequence of modes that cover a wide range from sub-THz to THz frequencies at both fundamental and second-harmonic resonances of the electron cyclotron frequency. As an illustration, the measurements of the observed radiation patterns of eight output modes radiated from a currently used resonant cavity with a linear up-taper are presented and compared with the corresponding patterns simulated by scattering matrix calculations. A new design of an optimized cavity with a nonlinear up-taper, which improves further the mode purity of the generated output radiation has been proposed ...
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Fortschritte in der Formulierung eines realistischen 3D-Modells fur die Simulation von Elektronenkanonen fur Gyrotrons (Eine vorlaufige Studie) Numerische Experimente, die auf adaquaten, selbst-konsistenten physikalischen Modellen... more
Fortschritte in der Formulierung eines realistischen 3D-Modells fur die Simulation von Elektronenkanonen fur Gyrotrons (Eine vorlaufige Studie) Numerische Experimente, die auf adaquaten, selbst-konsistenten physikalischen Modellen basieren, werden in einem breiten Umfang fur das computerunterstutzte Design (CAD), die Analyse und Optimierung von elektronenoptischen Systemen von Gyrotrons eingesetzt. Ein wesentlicher Teil des benotigten physikalischen Modells ist das Emissionsmodell, d.h. die Beschreibung des vom Emitter erzeugten Strahlstroms sowie die Energieverteilung und die raumliche und winkelabhangige Verteilung der emittierten Elektronen. In dieser Arbeit prasentieren wir eine Zusammenfassung der grundlegenden Theorie, die wesentlichen Formeln und eine Diskussion der wichtigsten Faktoren fur die Inhomogenitat der Emission und der Geschwindigkeitsstreuung. Zusatzlich wird ein Uberblick uber die in verschiedenen Ray-Tracing und Particle-In-Cell (PIC) Codes eingesetzten Emissions...
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Computer aided design of powerful gyrotrons for electron cyclotron resonance heating and current drive of fusion plasmas requires adequate physical models and efficient software packages for analysis, comparison and optimization of their... more
Computer aided design of powerful gyrotrons for electron cyclotron resonance heating and current drive of fusion plasmas requires adequate physical models and efficient software packages for analysis, comparison and optimization of their electron-optical systems through numerical experiments. In this paper, we present and discuss the current status of the simulation tools available to the researchers involved in the development of multi-megawatt gyrotrons for the ITER project, review some of their recent upgrades and formulate directions for further modifications and improvements. Illustrative examples used represent results from recent numerical investigations of real constructions. Some physical problems that are outside of the capabilities of the existing computer programs and call for development of novel generation of codes are also examined. The ongoing work in this direction as well as the most characteristic features of the codes under development are briefly reviewed.
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This review paper is based on the invited talk presented by the same authors at the 8th International Workshop on Far-Infrared Technologies (IW-FIRT 2021). It overviews some well-known and novel and emerging applications of gyrotrons in... more
This review paper is based on the invited talk presented by the same authors at the 8th International Workshop on Far-Infrared Technologies (IW-FIRT 2021). It overviews some well-known and novel and emerging applications of gyrotrons in diverse scientific and technological fields and presents both the current status and the prospects of the research in such a wide area worldwide.
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In the experimental study on the frequency tuning of a double-beam gyrotron, an unexpected abrupt increase of the output power was observed for some magnetic field values corresponding to the excitation of high-order axial modes (HOAM).... more
In the experimental study on the frequency tuning of a double-beam gyrotron, an unexpected abrupt increase of the output power was observed for some magnetic field values corresponding to the excitation of high-order axial modes (HOAM). This effect can be explained through an after-cavity interaction of the spent but bunched electron beam with the neighboring transverse mode which has the same azimuthal but the next (i.e., greater by one) radial index with respect to the operating mode. The calculations show that under certain conditions the cyclotron synchronism between the electron beam and the next radial mode occurs in the extended region of an output cone, while the bunching of the spent electron beam is responsible for the excitation of this mode. The influence of some additional factors such as reflections of both modes from the output window, electron velocity spread, and magnetic field profile was studied numerically. It was shown that reflections, mode transformation, and velocity spread can enhance the effect of an abrupt power increase and reduce the starting current of the operating mode. The discovered after-cavity interaction 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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Gyrotrons are among the most powerful sources of coherent radiation that operate in CW and long pulse regimes in the sub-THz and the THz frequency ranges of the electromagnetic spectrum, i.e. between 0.3 THz and 3.0 THz (corresponding to... more
Gyrotrons are among the most powerful sources of coherent radiation that operate in CW and long pulse regimes in the sub-THz and the THz frequency ranges of the electromagnetic spectrum, i.e. between 0.3 THz and 3.0 THz (corresponding to wavelengths from 1.0 to 0.1 mm). This region, which spans between the frequency bands occupied by various electronic and photonic devices, respectively, is habitually called a THz power gap. The underlying mechanism of the operation of the gyrotron involves a formation of bunches of electrons gyrating in a helical electron beam and their synchronous interaction with a fast (i.e. having a superluminal phase velocity) electromagnetic wave, producing a bremsstrahlung radiation. In contrast to the slow-wave tubes, which utilize tiny structures with dimensions comparable to the wavelength of the radiation, the gyrotrons have a simpler resonant system (cavity resonator) with dimensions that are much greater than the wavelength. This allows much more power...
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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... 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 ...
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The gyrotrons are powerful sources of coherent radiation that can operate in both pulsed and CW (continuous wave) regimes. Their recent advancement toward higher frequencies reached the terahertz (THz) region and opened the road to many... more
The gyrotrons are powerful sources of coherent radiation that can operate in both pulsed and CW (continuous wave) regimes. Their recent advancement toward higher frequencies reached the terahertz (THz) region and opened the road to many new applications in the broad fields of high-power terahertz science and technologies. Among them are advanced spectroscopic techniques, most notably NMR-DNP (nuclear magnetic resonance with signal enhancement through dynamic nuclear polarization, ESR (electron spin resonance) spectroscopy, precise spectroscopy for measuring the HFS (hyperfine splitting) of positronium, etc. Other prominent applications include materials processing (e.g., thermal treatment as well as the sintering of advanced ceramics), remote detection of concealed radioactive materials, radars, and biological and medical research, just to name a few. Among prospective and emerging applications that utilize the gyrotrons as radiation sources are imaging and sensing for inspection an...
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In this paper we present a novel design of a quasi-optical system for conversion of gyrotron outputs into Gaussian beams. It consists of a quasi-optical antenna, focusing mirrors and a filter which removes the side lobes of the beam. The... more
In this paper we present a novel design of a quasi-optical system for conversion of gyrotron outputs into Gaussian beams. It consists of a quasi-optical antenna, focusing mirrors and a filter which removes the side lobes of the beam. The system is capable to convert three mode outputs into Gaussian beams.