Frequency-Tunable CW Gyro-BWO With a Helically ... - IEEE Xplore

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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 32, NO. 3, JUNE 2004

Frequency-Tunable CW Gyro-BWO With a Helically Rippled Operating Waveguide Sergey V. Samsonov, Gregory G. Denisov, Vladimir L. Bratman, Alexander A. Bogdashov, Mikhail Yu. Glyavin, Alexei G. Luchinin, Vladimir K. Lygin, and Manfred K. Thumm, Fellow, IEEE

Abstract—Operation of a continuous wave gyrotron backward-wave oscillator (gyro-BWO) with a helically rippled operating waveguide has been experimentally studied. The gyro-BWO exploits a dc oil-cooled magnet with magnetic field up to 0.5 T and utilizes a weakly relativistic (20 keV) electron beam produced by a magnetron injection gun. Stable generation at the second cyclotron harmonic with a maximum power of 7 kW and an efficiency of 15% at a frequency of 24.7 GHz was achieved. Smooth oscillation frequency tuning by varying the magnetic field was measured to be as wide as 5% at the half-power level. The first gyro-BWO operation with a single-stage energy recovery system was realized. The use of a depressed collector provided an efficiency increase up to 23% and an opportunity for reduction of the main power supply voltage down to 10 kV. Index Terms—Continuous wave (CW) high-power microwave device, cyclotron-resonance maser, gyrotron backward-wave oscillator (gyro-BWO), smooth-frequency tuning.

I. INTRODUCTION

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HE GYROTRON backward-wave oscillator (gyro-BWO) is known as a source of frequency-tunable high-power coherent radiation, which is attractive for a number of applications. It is based on the resonant cyclotron interaction of electrons gyrating in the external magnetic field with an oppositely traveling electromagnetic wave (Fig. 1). Being a variety of the cyclotron-resonance masers (CRMs), the gyro-BWO has advantages over the slow-wave electron devices in higher power capabilities, especially at millimeter and submillimeter waves. On the other hand, a gyro-device operating with a traveling-wave and a nonresonant-microwave structure can provide a broadband smooth frequency tuning by variation of the magnetic field or the electron beam energy. The gyro-BWO operation has been theoretically analyzed in detail (see, e.g., [1]–[4]) and successfully realized in a number of experiments [5]–[7]. In the experimental studies at the Naval Research Laboratory [5] and the National Tsing Hua University [6], pulsed Ka-band gyro-BWO operation at the fundamental cyclotron harmonic and fundamental mode of a smooth cylindrical waveguide was demonstrated with Manuscript received November 11, 2003; revised December 27, 2003. This work was supported in part by Gycom, Ltd. (Nizhny Novgorod, Russia) and in part by the Russian Foundation for Basic Research under Grant 01-02-16780. S. V. Samsonov, G. G. Denisov, V. L. Bratman, A. A. Bogdashov, M. Yu. Glyavin, A. G. Luchinin, and V. K. Lygin are with the Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950, Russia (e-mail: [email protected]). M. K. Thumm is with the Forschungszentrum Karlsruhe, Association EURATOM-FZK, Institut für Hochleistungsimpuls- und Mikrowellentechnik, D-76021 Karlsruhe, Germany. Digital Object Identifier 10.1109/TPS.2004.828871

Fig. 1. Dispersion diagram of a gyro-BWO with a cylindrical waveguide.

voltage- and magnetic-frequency tuning of up to 5% and 13%, respectively, a very high efficiency (for BWO) of nearly 20% and a pulsed power up to 100 kW. The use of a novel microwave system in the form of a helically corrugated waveguide [8], [9] opens up new potentials of the gyro-BWO and allows realization of a high-power continuous wave (CW) device attractive for applications. Under certain parameters, a helical corrugation of the inner surface of an oversized circular waveguide provides dispersion of a circularly polarized eigenmode which is favorable for realization of traveling-wave gyro-devices, such as gyro-TWT and gyro-BWO [9]–[12]. The main attractive property of the mentioned-above eigenwave dispersion is its sufficiently large group velocity at zero axial wavenumber, which ensures a broadband operation with minimum negative impact of electron velocity spread. In the course of the experiments on the helical-waveguide gyro-TWT performed at the Institute of Applied Physics, the gyro-BWO operation was also studied [10]–[12], which was simplified by the fact that switching between TWT and BWO modes required just the change of polarity of the guiding magnetic field. In these proof-of-principle experiments stable and reliable Ka-band gyro-BWO operation at the second cyclotron harmonic was demonstrated with maximum output power of about 1 MW, efficiency of 10%, frequency tuning band of 15% for a 20-ns 300-keV electron beam [11] and 10-kW power, 5% efficiency, 10% tuning for a 10- s 45-keV electron beam [10], [12]. Analysis of the gyro-BWO capabilities showed that this device may be attractive for a number of technological applications, for which CW kilowatt-power gyrotrons are actively used [13]. This was the motivation to start a project aimed at realizing a CW tunable gyro-BWO with a power of several kilowatts at a frequency of about 24 GHz [12]. In initial experiments, a pulsed prototype of the gyro-BWO was tested which stably oscillated at the second cyclotron harmonic producing about 8-kW peak power and 6% frequency tuning for a 22-kV, 8-A electron

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SAMSONOV et al.: FREQUENCY-TUNABLE CW GYRO-BWO WITH A HELICALLY RIPPLED OPERATING WAVEGUIDE

Fig. 2. Schematic dispersion diagram for a gyro-TWT (a) and a gyro-BWO (b) with a helically rippled waveguide.

Fig. 3. Schematic view of principal elements of the helical-waveguide gyro-BWO: an axis-encircling electron beam and a waveguide with 3-fold helical corrugation.

beam. The main reason for the pulsed operation was a 15-kW limit of the average electron beam power accepted by the collector. A modified version of the gyro-BWO included a longer interaction circuit, a larger-diameter collector (correspondingly, a larger solenoid), and a dc break permitting the depressed collector realization. The setup details and results of the experiment are discussed in this paper. II. SPECIFIC FEATURES OF THE HELICAL-WAVEGUIDE GYRO-DEVICES The advantage in using a helically corrugated waveguide for gyrotron-type devices is based on the fact that gyrating electrons can excite a mode of a circular waveguide with selective direction of its azimuthal rotation. This effect is especially pronounced for an axis-encircling electron beam that resonantly exmodes with azimuthal indices equal cites only corotating TE . The helical symto the cyclotron harmonic number, metry allows transformation of a selected rotation direction to a selected axial direction (codirected or counterdirected with respect to electrons’ axial velocity). In particular, in the experiments on helical-waveguide gyro-devices [12] electrons selectively interact with a near to cutoff TE mode at the second cyclotron harmonic. This circularly polarized partial mode of a circular waveguide is resonantly coupled with a counter-romode on a three-fold helical corrugation resulting tating TE in appearance of an eigenwave with large group velocity at zero axial wavenumber (Figs. 2 and 3). The surface of an operating waveguide with a three-fold sinusoidal helical corrugation can be represented in cylindrical coordinates , , as follows: (1)

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where is the mean radius of the waveguide, and are the amplitude and the axial number of the corrugation, respectively, and is the corrugation period. This corrugation pronear-cutoff mode and the vides effective coupling of the traveling mode if the ripple period is chosen so that the , where is the axial Bragg condition is satisfied: mode at the cutoff frequency of the wavenumber of the mode. The resonant coupling of the waves corresponds to the intersection of their dispersion curves or, more exactly for the considered situation, the intersection occurs between the TE mode and the first (or minus first) spatial harmonic of the TE mode (Fig. 2). Let us note that the operating eigenwave group velocity in the frequency region of interest can be controlled within a sufficiently wide range by varying either the corrugation amplitude or the period. This fact is especially important for a gyro-TWT, where the equality of the wave group velocity and the axial electron velocity ensures the most broadband operation. For a gyro-BWO, the starting current and the frequency-tuning band are generally increasing functions of the wave-group velocity. On the other hand, if the interaction length is too long, then the velocity spread can be the major factor limiting the tuning band. Therefore, by compromising the tuning band, efficient helical-waveguide gyro-BWO operation can be provided for a very wide range of operating parameters such as beam current, voltage, frequency range, etc. Using the configuration discussed above the mode of operation can be switched between the gyro-TWT and the gyro-BWO by merely changing the polarity of the magnetic field, which has been performed in the proof-of-principle experiments [10]–[12].

III. EXPERIMENTAL DESIGN AND SETUP Specific features of the CW helical-waveguide gyro-BWO as compared to our previous experiments were the use of a magnetron-injection gun (MIG) typical for conventional gyrotrons and a low-voltage (20 kV) electron beam. It should be noted that an electron beam produced by a MIG is not an axis-encircling beam which may affect the selectivity of the configuration discussed in Section II. Namely, a possibility of the spurious mode excitation at the second cyclotron harmonic appears also in the regime of the gyro-BWO [Fig. 4(b)]. Correspondingly, the MIG was designed to produce an electron beam with a radius of about 1.5 mm [Fig. 4(a)], at which the starting current of the parasitic gyro-BWO oscillations slightly exceeded that of the operating mode. It should also be noted that because of the considerably larger axial wavenumber, the starting current of the spurious mode increases by a higher factor with an increase of electron-velocity spread. The parameters of a helically rippled waveguide were initially optimized on the basis of a simplified one-dimensional (1-D) model [9] for an efficient and broadband gyro-BWO operation with a 20 kV/2 A electron beam. The simulations showed a possibility to achieve a maximum efficiency of 16% and a frequency-tuning band of up to 7% (Fig. 5) for an electron beam with a pitch-factor of 1.7 and a perpendicular velocity spread of 25% (rms value of the spread is about 8%). The computations

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Fig. 5. Simulated tuning characteristic of the gyro-BWO: power (squares) and frequency (circles) as functions of magnetic field (the dashed line corresponds to doubled cyclotron frequency).

Fig. 4. Waveguide and electron beam (a) cross sections and (b) dispersion diagram for the CW gyro-BWO (the dashed lines correspond to the partial modes; the dotted line corresponds to the calculated dispersion of the operating mode).

also predicted the possibility of nearly two times efficiency enhancement due to energy recovery by a single-stage depressed collector. Three helically rippled waveguides differing by the length and the corrugation period were made at the Forschungszentrum (Karlsruhe, Germany). The measured wave dispersions were in a good agreement with theoretically predicted curves (Fig. 4) (see [9] for details of the methods used for the dispersion measurement and calculation). The operating helical waveguide was tapered at both ends where the amplitude of the corrugations decreased linearly to meet a circular waveguide with mean di. At these tapers the operating eigenmode was almost ameter totally converted into a circularly polarized TE mode because the operating frequency range was below the cutoff frequency of the TE mode of the smooth waveguide. For a CW-operated gyro-BWO, the parameters of the waveguide were the mm, corrugation amplitude following: mean radius mm, corrugation period mm, length of the mm, section with constant corrugation amplitude mm each. lengths of the tapers In the gyro-BWO, the operating mode propagating toward the cathode was transformed into the TE mode at the upstream taper, reflected by the so-called resonant reflector [14], then traveled along the waveguide without resonant interaction with the electron beam, passed through a dc break, a collector and a half-wavelength output window (Fig. 6) before absorption in a dummy load being simultaneously a calorimeter for RF power measurement. The resonant reflector was a simple

rectangular groove where the TM mode was trapped near its cutoff. In spite of its resonant principle of operation, the groove parameters can be chosen so that it effectively reflects the TE mode in a sufficiently broad-frequency band. The resonant reflector used reflected more than 95% of the power within the frequency range from 22 to 26 GHz. As compared to an equivalent cutoff reflector, it has 33% larger minimal diameter, thus simplifying the electron-beam transport. A dc break insulating the collector inevitably led to a gap (which was 4 mm in length) for the TE output mode propagation. Without special measures this gap would result in irradiative losses of about 10% in power and a rather high reflection. This problem was effectively solved by implementing a specially designed set of conical sections (Fig. 6), which produced a mixture of modes with sufficiently small near-the-wall RF field in the region of the gap and converted this mixture back to the TE mode. According to numerical simulations this set reduced the irradiative losses down to the value of less than 1%, while keeping the power content of 90–97% of the TE mode at the output (the remaining output power radiated through the window in higher-order modes) for frequencies between 23 and 26 GHz. The dc insulation of the collector and also the anode allowed separate measurements of the electron currents to the anode, the tube body and the collector, as well as application of various energy recovery schemes.

IV. EXPERIMENTAL RESULTS The experiments demonstrated the selective second harmonic operation of the gyro-BWO at the desired mode for the designed values of the magnetic field, beam voltage and current in the CW (several hours) regime. No oscillations were observed at the spurious gyro-BWO mode discussed above. The main output characteristic of this device is the oscillation frequency and power as a function of the applied magnetic field. The measured maximum output power, frequency range, and tuning band (Fig. 7) were in reasonable agreement with the design. The frequency was measured by means of a resonant wavelength-meter with a relative accuracy of 0.1%. Rather large variations in the output power (oscillating behavior of power versus field) can be explained by the improperly matched output window. The window was typical for technological gyrotrons and represented a single


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Fig. 6. A schematic view of the CW gyro-BWO: 1 – cathode; 2 – anode; 3 – gun coil; 4 – main coil; 5 – collector coil; 6 – output window; 7 – resonant reflector; 8 – operating waveguide; 9 – collector insulator.

Fig. 7. Measured oscillation power (squares) and frequency (circles) as functions of magnetic field for the beam voltage of 20 kV and total beam current of 2 A (the dashed line corresponds to doubled cyclotron frequency).

BN half-wavelength disc for which the minimum reflection occurred at the frequency of 23.3 GHz. For the gyro-BWO oscillation frequencies of 24–26 GHz, the window reflected 2–8% of power, which resulted in appearance of a standing wave between the upstream reflector and the window, similarly to excitation of a low- two-mirror resonator. Because of the excitation of such longitudinal modes, the measured frequency tuning was not perfectly smooth (see Fig. 7). It should also be noted that for each experimental point, the gun coil current that controlled the electron pitch-factor was slightly optimized for maximum output power. In some cases, it resulted in considerably large anode current (up to 0.2–0.3 A) that was evidently caused by reflection of some electrons with too large initial pitch-factor from a magnetic mirror. The tuning characteristic of the gyro-BWO can be smoothed by the use of a broadband multiple-disc low-reflection window whose operation has been successfully tested in gyro-TWT experiments [12], [15]. Along with the magnetic tuning, the frequency tuning by voltage was also checked and was measured to be about 0.15 GHz at the half-power level.

Fig. 8. Maximum efficiency (squares) and power (circles) of the gyro-BWO.

The maximum beam current emitted by the cathode in the CW regime amounted to 2.35 A. At this current, the maximum measured power was as high as 7 kW (Fig. 8). For the beam current in the range of 1.75–2.35 A, the gyro-BWO efficiency calculated as the ratio between the output power and the product of cathode voltage and total gun current was about 15%. In these regimes, the measured anode current that did not participate in the electron-wave interaction amounted to 0.25 A. Correspondingly, the electron efficiency was about 17% that is close to the value predicted for a rather high electron pitch factor of 1.7–1.8. The presence of the significant reflection of electrons allowed estimation of the actual perpendicular velocity spread which was determined to be as large as 20–30% (7–10% rms). At a beam current of 2 A, gyro-BWO operation was tested in the regime with a single-stage energy recovery (depressed collector). In this proof-of-principle experiment the retarding collector voltage was simply applied by means of collector connection to the ground through a set of various resistors. When the collector potential increased from zero to almost 10 kV, the tube efficiency grew from 15% to 23%. That was accompanied by the monotonous increase in the body current from 10 mA to 23

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Fig. 9. Results of the energy recovery experiment for the main power supply voltage of 20 kV and current of 2 A.

mA and the drop of the output power from 6 to 4.5 kW (Fig. 9). The operation at several different values of the magnetic field, i.e., the tuning ability, was checked at the depressed collector voltage of 7.5 kV. The measured power differed from that with the grounded collector by less than 10%. Along with a substantial increase in the device efficiency, the use of the depressed collector allows reduction of the voltage of the main power supply down to almost 10 kV, which makes the gyro-BWO significantly more attractive for technological applications.

[8] G. G. Denisov and S. J. Cook, “New microwave system for gyro-TWT,” in Dig. 21th Int. Conf. Infrared Millimeter Waves, Berlin, Germany, 1996, p. AT2. [9] G. G. Denisov, V. L. Bratman, A. D. R. Phelps, and S. V. Samsonov, “Gyro-TWT with a helical operating waveguide: New possibilities to enhance efficiency and frequency bandwidth,” IEEE Trans. Plasma Sci., vol. 26, pp. 508–518, June 1998. [10] S. V. Samsonov, V. L. Bratman, G. G. Denisov, N. G. Kolganov, V. N. Manuilov, M. M. Ofitserov, A. B. Volkov, A. W. Cross, W. He, A. D. R. Phelps, K. Ronald, C. G. Whyte, and A. R. Young, “Frequency-broadband gyro-devices operating with eigenwaves of helically grooved waveguides,” in Proc. 12th Symp. High-Current Electronics, G. Mesyats, B. Kovalchuk, and G. Remnev, Eds., Tomsk, Russia, 2000, pp. 403–407. [11] V. L. Bratman, G. G. Denisov, V. N. Manuilov, S. V. Samsonov, and A. B. Volkov, “Development of helical-waveguide gyro-devices based on low-energy electron beams,” in Dig. 26th Int. Conf. Infrared Millimeter Waves, O. Portugall and J. Leotin, Eds., Toulouse, France, 2001, pp. 5–105. [12] V. L. Bratman, A. W. Cross, G. G. Denisov, M. Y. Glyavin, W. He, A. G. Luchinin, V. K. Lygin, V. N. Manuilov, A. D. R. Phelps, S. V. Samsonov, M. Thumm, and A. B. Volkov, “Broadband gyro-TWT’s and gyro-BWO’s with helically rippled waveguides,” in Proc. 5th Int. Workshop Strong Microwaves in Plasmas, A. G. Litvak, Ed., Nizhny Novgorod, Russia, 2002, pp. 46–57. [13] Y. Bykov, A. Eremeev, M. Glyavin, V. Kholoptsev, A. Luchinin, I. Plotnikov, G. Denisov, A. Bogdashev, G. Kalynova, V. Semenov, and N. Zharova, “24–84 GHz gyrotron systems for technological microwave applications,” IEEE Trans. Plasma Sci., vol. 32, pp. 67–72, Feb. 2004. [14] G. G. Denisov, D. A. Lukovnikov, and S. V. Samsonov, “Resonant reflectors for free electron masers,” Int. J. Infrared Millimeter Waves, vol. 16, no. 4, pp. 745–752, 1995. [15] D. E. Pershing, K. T. Nguyen, J. P. Calame, B. G. Danly, and B. LeKa band gyro-TWT amplifier with vush, “Implementation of a TE distributed loss,” in Dig. 27th Int. Conf. Infrared Millimeter Waves, R. Temkin, Ed., San Diego, CA, 2002, pp. 199–200.

V. CONCLUSION A frequency-tunable gyro-BWO with a helically rippled operating waveguide was designed and operated at the second cyclotron harmonic in the CW regime. Its operation was tested under parameters typical for technological gyrotrons, and comparable output power and efficiency were achieved with an important extra capability of the smooth frequency tuning. The frequency tuning band can be widened up to 8%–10% by enhancing the electron-beam quality and using a helical waveguide providing higher operating eigenwave group velocity, while the use of a broadband low-reflection output window can result in a smoother tuning characteristic. REFERENCES [1] V. K. Yulpatov, “Nonlinear theory of interaction between a periodic electron beam and an electromagnetic wave,” Radiophys. Quantum Electron., vol. 10, pp. 471–476, 1967. [2] N. S. Ginzburg, I. G. Zarnitsyna, and G. S. Nusinovich, “Theory of relativistic cyclotron autoresonance maser with an opposite wave,” Radio Eng. Electron. Phys., vol. 24, no. 6, pp. 113–118, 1979. [3] A. K. Ganguly and S. Ahn, “Nonlinear analysis of the gyro-BWO in three dimensions,” Int. J. Electron., vol. 67, no. 2, pp. 261–276, 1989. [4] G. S. Nusinovich and O. Dumbrajs, “Theory of gyro-backward wave oscillator with tapered magnetic field and waveguide cross section,” IEEE Trans. Plasma Sci., vol. 24, pp. 620–629, June 1996. [5] S. Y. Park, R. H. Kyser, C. M. Armstrong, R. K. Parker, and V. L. Granatstein, “Experimental study of a Ka-band gyrotron backward-wave oscillator,” IEEE Trans. Plasma Sci., vol. 18, pp. 321–325, June 1990. [6] C. S. Kou, S. G. Chen, L. R. Barnett, H. Y. Chen, and K. R. Chu, “Experimental study of an injection-locked gyrotron backward-wave oscillator,” Phys. Rev. Lett., vol. 70, pp. 924–927, 1993. [7] T. A. Spencer, R. M. Gilgenbach, and J. J. Choi, “Gyrotron-backward-wave-oscillator experiments utilizing a high current, high voltage, microsecond electron accelerator,” J. Appl. Phys., vol. 72, no. 4, pp. 1221–1224, 1992.

Sergey V. Samsonov was born in Arzamas-16, Gorky Region, USSR, in 1966. He received the M.S. degree with honors from the Advanced School of General and Applied Physics, Nizhny Novgorod State University, Nizhny Novgorod, Russia, in 1989 and the Ph.D. degree in physics from the Institute of Applied Physics (IAP), Russian Academy of Sciences, Nizhny Novgorod, Russia, in 1996. He is currently a Senior Scientist at the IAP, Russian Academy of Sciences. His research interests include both theoretical and experimental study of high-power electron devices, in particular, cyclotron resonance masers. Dr. Samsonov was awarded the Medal and Prize of the Russian Academy of Sciences for Young Scientists in 2000.

Gregory G. Denisov was born in Gorky, USSR (now Nizhny Novgorod, Russia), in 1956. He received the M.S. degree in radiophysics from Gorky State University, Gorky, USSR, in 1978 and the Ph.D. degree and the Doctor of Science degree from the Institute of Applied Physics (IAP), Academy of Sciences of the USSR (now the Russian Academy of Sciences), Nizhny Novgorod, Russia, in 1985 and 2002, respectively. His current position is the Head of the Gyrotron Division, IAP, Russian Academy of Sciences. His main research interests include relativistic microwave oscillators and amplifiers (e.g., free-electron masers and cyclotron-autoresonance masers), transmission lines and antenna systems for high power microwave radiation, methods for measurement and control of wave-beam parameters, powerful microwave sources for ECRH systems in fusion installations (gyrotrons), and technological setups. Dr. Denisov was awarded the Excellence in Fusion Engineering Prize from Fusion Power Associates in 1996.


Vladimir L. Bratman was born in Chirchik, Uzbekistan (formerly the USSR), in 1945. He received the M.S. and Ph.D. degrees in physics from Gorky State University, Gorky, USSR, in 1967 and 1977, respectively, and the Doctor of Science degree from the Tomsk Institute of High-Current Electronics, Tomsk, Russia, in 1992. From 1970 to 1974, he was a Member of the Technical Staff at the Gorky Research Institute “Salyut,” Gorky, USSR. He joined the Gorky Radio Physical Research Institute in 1974 and the Institute of Applied Physics of the Russian Academy of Sciences in 1977. Since 1985, he is Head of the Short-Wavelength Relativistic Devices Group. In 1992, he became a Professor in the Advanced School of General and Applied Physics, Nizhny Novgorod State University, Nizhny Novgorod, Russia. The title Soros Professor was conferred on V. L. Bratman in 1998 and 2000. V. L. Bratman was a Visiting Professor in several research institutions and participated in a number of international projects (Brazil, The Netherlands, Israel, UK, Japan, and Italy). His current research interests include high-power radiation from cyclotron-resonance masers (including gyrotrons and cyclotron-autoresonance masers) and from free-electron lasers, as well as the development of powerful sources of millimeter- and submillimeter-wave-radiation for plasma diagnostics and ECRH. Prof. Bratman was a Member of the Editorial Board of the Collected Papers “Relativistic HF Electronics” (1979–1992). He is now a Member of the Editorial Board of Radiophysics and Quantum Electronics.

Alexander A. Bogdashov was born in Dzerzhinsk, Gorky region, USSR, in 1970. He received the M.S. degree in physics from the Advanced School of General and Applied Physics, Nizhny Novgorod State University, Nizhny Novgorod, Russia, in 1993. He is currently working toward the Ph.D. degree at the Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. His research interest is concentrated on the computational electrodynamics and its applications for high-power electronics (waveguide mode converters design and optimization, quasi-optical mirror and antenna synthesis, notch filters, and microwave transmission lines). Mr. Bogdashov was awarded the Medal and Prize of the Russian Academy of Sciences for Young Scientists in 2003.

Mikhail Yu. Glyavin was born in Nizhny Novgorod (former Gorky), Russia, on February 14, 1965. He received the degree in microwave electronics and the Ph.D. degree in physics from the Gorky Politechnical Institute, Gorky, U.S.S.R., in 1988 and 2000, respectively. Since 1988, he has been working at the Institute of Applied Physics of the Academy of Sciences of the U.S.S.R. (from 1991—Russian Academy of Sciences), where he is engaged in the development of high-power gyrotrons for nuclear fusion. His dissertation was focused on studies of gyrotrons and more specifically on methods for increasing the efficiency. From 1999 to 2002, he was a Visiting Researcher at the FIR FU Center, Fukui, Japan. His research interests are in the field of the theoretical and experimental investigations of various gyro-device, including gyrotrons and their application to materials processing.

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Alexey G. Luchinin was born in 1945. He received the M.S. degree in radiophysics from Lobachevsky State University, Gorky, USSR in 1968 and the Ph.D. degree in physics from the Institute of Applied Physics (IAP), Russian Academy of Sciences, Nizhny Novgorod, in 1985. Since 1977, he has been working at the IAP. He has more than 50 publications on the theoretical and experimental topics. His research interests include development of high-efficiency, powerful sources of microwave radiation, in particular, gyrotrons for nuclear fusion and technological applications.

Vladimir K. Lygin was born in 1945. He received the M.S. degree in radiophysics and the Ph.D. degree in physics from Lobachevsky State University, Gorky, USSR, in 1968 and 1982, respectively. From 1968 to 1977, he was with Lobachevsky State University, and since 1977, he has been with the Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, where he is engaged in gyrotron development. He has authored more than 50 publications on the theoretical and experimental topics. His research is concentrated on the methods for simulations of helical electron beams and the design of particular electron guns for gyrotrons.

Manfred K. Thumm (SM’94–F’02) was born in Magdeburg, Germany, on August 5, 1943. He received the Dipl. Phys. and Dr.rer.nat. degrees in physics from the University of Tübingen, Tübingen,, Germany, in 1972 and 1976, respectively. At the University of Tübingen, he was involved in the investigation of spin-dependent nuclear forces in inelastic neutron scattering. From 1972 to 1975, he was Doctoral Fellow of the “Studienstiftung des Deutschen Volkes.” In 1976, he joined the Institute for Plasma Research of the Electrical Engineering Department, University of Stuttgart, Stuttgart, Germany, where he worked on RF production, RF heating, and diagnostics of toroidal pinch plasmas for thermonuclear fusion research. From 1982 to 1990, his research activities were mainly devoted to electromagnetic theory and verifying experiments in the areas of components development for the transmission of very high-power millimeter waves through overmoded waveguides and of antenna structures for RF plasma heating with microwaves. In June 1990, he became a Full Professor at the Institute for Microwaves and Electronics, University of Karlsruhe, Karlsruhe, Germany, and Head of the Gyrotron Development and Microwave Technology Division in the Institute for Technical Physics of the Research Center Karlsruhe (Forschungszentrum Karlsruhe/FZK). Since April 1999, he has been the Director of the Institute for Pulsed Power and Microwave Technology of the FZK, where his current research projects are the development of high-power gyrotrons, dielectric vacuum windows, transmission lines, and antennas for nuclear fusion plasma heating and industrial materials processing. He has authored/coauthored two books, seven book chapters, 122 research papers in scientific journals, and 530 conference proceedings articles. He holds ten patents on active and passive microwave devices. Dr. Thumm is vice chairman of Chapter 8.6 (Vacuum Electronics and Displays) of the Information Technical Society (ITE) in German VDE and a member of the German Physical Society (DPG). He has been awarded with the Kenneth John Button Medal and Prize 2000 in recognition of outstanding contributions to the research in the field of millimeter wave and infrared physics. In 2002, he was awarded the title of Honorary Doctor, presented by the St. Petersburg State Technical University, for his contributions to the development and application of electron beam devices.