NEWSLETTERof the International Consortium“Development of High-Power Terahertz
Science & Technology”
June 2021№ 18

CONTENT Editorial(Page 1)

How to contribute to the Newsletter Invited papers• A.P. Fokin, A.A. Bogdashov, Yu.V. Novozhilova, V.L. Bakunin, V.V. Parshin, M.Yu. Glyavin“Experimental Demonstration of Gyrotron Frequency Stabilization by Resonant Reflection.”(Page2)• A.P. Fokin, V.L. Bakunin, M.Yu. Glyavin, and G. S. Nusinovich, “Automodulation instability ingyrotrons operating at the second cyclotron harmonic.”(Page 6)
 Personalia:• Academician A. Gaponov-Grekhov at 95(Page 10)
• Professor G. Denisov at 65(Page 11)
 Upcoming events(Page 12)
 List of selected recent publications, and new books(Page 12) News from the Net(Page 22)

EDITORIAL: HOW TO CONTRIBUTE TO THE NEWSLETER
Dear Reader,
We are inviting contributions to the following rubrics:• Research highlights (annotations) presenting the projects pursued by the members of the Consortium.
• Short regular and invited papers.
• Proposals for collaborative research work.
• News from the participating institutions.
• Information about conferences, symposia, workshops, seminars.
• Programs and frameworks for an exchange of visits and mobility of researchers. Job opportunities(especially for young researchers, e.g. postdoctoral positions, specializations, internships).
• Annotations of books, conference proceedings, software and internet resources. Additions to the list of
the recent scientific publications and conference reports at the website of the Consortium(http://fir.ufukui.ac.jp/Website_Consortium/publist.html ).
• Information and announcements about awards and nominations.
• Short presentations of laboratories and research groups belonging to the participating institutions.
Please submit your contributions to the Newsletter as well as requests for information to:Professor Masahiko Tani
Director of FIR UF – Facilitator of
the International Consortium
FIR UFtani@fir.u-fukui.ac.jp

Dr. Svilen Sabchevski
Editor of the website and the Newsletter
Institute of Electronics of the Bulgarian
Academy of Sciencessabch@ie.bas.bg

INVITED PAPERS
Experimental Demonstration of Gyrotron Frequency Stabilization
by Resonant Reflection
A.P. Fokin*, A.A. Bogdashov, Yu.V. Novozhilova, V.L. Bakunin, V.V. Parshin, M.Yu. Glyavin
Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia*
Corresponding author: ap.fokin@mail.ru
Currently, gyrotrons are among the most popular and promising sources of microwave radiation for various
applications such as plasma heating and diagnostics, spectroscopy of various media, and technologicalprocesses. Therefore, their spectral characteristics are of great interest to the community, and the gyrotron
frequency tuning and stabilization are actively investigated. Many studies considered active frequency
manipulation by variation of the electron beam parameters, as well as phase locking by the external signal andchanging the spectral characteristics of the radiation (spectrum control), in particular, frequency stabilization by
the wave reflected from the nonresonant load. Each of the methods has its advantages and limitations. The
active frequency manipulation provides the best stability and control but has speed limitations. The phaselocking requires the external stabilized source with the power of several percent of the gyrotron, and the use ofreflection from nonresonant load requires a long delay line.
The method of frequency stabilization and spectrum control using the high-Q loads is free of the listed
restrictions. This method is well known and is used in numerous applications, such as the feeding of microtron
and linear accelerators by magnetrons in microwave electronics or stabilization of laser frequency. The theoryof gyrotron frequency stabilization by the external high-resonant load was developed in [1-3]. This reportpresents experimental results and simulation of frequency stabilization of gyrotron by the signal reflected fromthe resonant (high-Q) load.
The influence of the narrow-band signal reflected from the resonator with high quality factor Q can beconsidered as the frequency locking by an external quasi-monochromatic signal. The radiation frequency of the
gyrotron with a variation of its parameters, for example, the magnetic field, can be kept in a narrow frequency
band of the external resonator fres Qres . For this, the phase of the reflected wave must be optimal, and themagnetic field must vary in such an interval, that the corresponding radiation frequency of the free-runningf
R f
Qgyrotron remains close to the frequency of the external resonator res within a locking bandwidth 0 res dif .
Q
Q
Here res is the quality factor of the resonant reflector, dif is diffraction Q-factor of the gyrotron cavity, R0 is
maximal value of the reflection coefficient. Dependence of the reflection coefficient (amplitude-wise) on the=
R R0 (1 + iξ ) =ξ 2Qres ( f rad − f res ) f res f radfrequency for the resonant reflector is, where,being the gyrotron
radiation frequency. Using the theory of the gyrotron with resonant reflections, one can obtain the relationshipbetween magnetic field B and the gyrotron radiation frequency:
B= B +( )(( frad 0 )′ B

frad − frad 0 B + fres K cos ψ − ξ sin ψ)G,where f rad 0 ( B ) is the free-running gyrotron radiation frequency corresponding to the value of the magnetic
field B in the absence of an external resonator;( frad 0 )′ B ≈ const is the derivative of the free-running radiation

frequency over B within the interval of the magnetic field, where f rad 0 ( B ) is close to=K

1 + q R0 Qres Qdif

where

2

td

=
ψ 2π f res td + arctg (1 q )is the stabilization coefficient,is the delay time andq = Re [ χ ′A ] Im [ χ ′A ]

;

χ ′A

(

G Qres 1 + ξ
f res=,

2).

is the phase of the reflected signal,is the derivative of the electron beam complex

susceptibility over field amplitude for free-running gyrotron. Within the magnetic field interval, where f rad 0 ( B )fis close to res , we can consider the q and K constant.
This expression was derived using a single-mode model of the gyrotron with the fixed field stricture; theelectron beam was considered ideal (i.e., without velocity and position spread). For the considered lowfrequency setup, the frequency separation of the neighbor modes is sufficient, and the Q factor of the gyrotron
resonator is relatively big, which allows us to make the estimations using the simple approach. Using the real
gyrotron and reflector parameters, we can get the dependence of the frequency on the magnetic field. An
example of such a curve for the parameters of the experiment (K = 4 and favorable ψ = 3π/2) is presented inFig. 1.

Fig. 1. Theoretical dependence of the gyrotron frequency on the magnetic field for the phase of the reflectedsignal ψ = 3π/2 and stabilization coefficient K = 4, which corresponds to the parameters of the experiment. The
dashed line represents the free-running gyrotron; the solid line is the gyrotron with the resonance reflector.
A gyrotron with an output frequency of 28 GHz and power up to 15 kW, operating at the second cyclotron
harmonic at the ТЕ02 mode, was used for theoretical estimations as well as experimental tests. The gyrotron
has a cylindrical cavity with linear input and output tapers with a total quality factor Q0 of ~3400. The gyrotron
has a direct output at the TE0,2 mode in a cylindrical waveguide with a diameter of 32 mm.
The resonant reflections were provided by the quasi-optical resonator with two spherical mirrors. The mirror
diameter was 120 mm, curvature radius - 390 mm, the distance between the mirrors was about 240 mm, andwas fine-tuned by a micrometric adjustment screw. Since the gyrotron has the direct output of the radiation, theset of waveguide converters from TE0,2 mode of the gyrotron resonator to the Gaussian beam (TE0,2 – TE0,1– TE1,1 – TEM0,0) was installed after the output window of the gyrotron. The gyrotron and resonator’scoupling was done using the polyethylene terephthalate (PET) film with 180 μm thickness, installed at the 45degree angle to the wave propagation direction (Fig. 2). The resulting measured quality factor of the quasiR = 10%
2

optical resonator was about 30 000, and the power reflection coefficient was. The scheme of theexperiment is presented in Fig. 2; the measured reflection coefficient for different mirror separations is shownin Fig. 3.

Fig. 2. The layout of the experiment: 1 – gyrotron; 2 – waveguide mode converter; 3 – quasi-optical resonator;
4 – PET film; 5 – dummy load.

Fig. 3. Measured frequency dependence of the reflection coefficient |S11| of the quasi-optical resonator fordifferent mirror separations. It is important that tuning of the resonant frequency within a gyrotron operation
band (27.95-28.1 GHz) does not change the maximal reflection coefficient.
In order to limit the heating of the PET film in the quasi-optical resonator, the gyrotron was operated in the
low-power regime, with accelerating voltage U0 = 16 kV, beam current 0.45 A, and maximum output power
1.8 kW. The frequency of the resonator was tuned to the value inside the gyrotron frequency tuning band by
adjustment of the mirror separation, the exact resonant frequency was fres = 28.0501 GHz. The spectral
characteristics of the gyrotron radiation were measured using an Agilent N9010A spectrum analyzer. The
gyrotron was turned on at a high magnetic field in the region of soft TE0,2 mode excitation, and then themagnetic field B was decreased in small steps. For each magnetic field, the gyrotron radiation spectrum wasrecorded and then combined to present the dependence of the radiation frequency and spectrum width on themagnetic field. Obtained combined spectra are presented in Fig 4 for the free-running gyrotron and the gyrotron
with the quasi-optical resonator in the output transmission line.

Fig. 4. Combined spectra of gyrotron radiation for a set of magnetic fields for the free-running gyrotron (a) andthe gyrotron with a resonant reflector (b).

Obtained data clearly demonstrates the effect of frequency stabilization by reflections of the gyrotron output
signal from a resonant reflector. When the gyrotron frequency lies within the external resonator’s frequencylocking band, and the reflected signal phase is optimized, the gyrotron frequency’s sensitivity to technicalparameters’ variations is significantly reduced. The df/dB is reduced by approximately ten times, from 7 GHz/T
to 0.8 GHz/T (Fig. 4), and the sensitivity to the variation of the accelerating voltage df/dU0 is reduced from
3.5 MHz/kV to 0.6 MHz/kV (which is demonstrated by the spectrum width). A comparison of the spectrums at
the same magnetic field for the free-running gyrotron and the gyrotron with the resonant reflector is presented
in Fig. 5.
The possibility of frequency stabilization in the locking band of the resonant reflector, with reducing thesensitivity both to the magnetic field and accelerating voltage variation up to ten times, has been demonstrated.
Obtained experimental data is in agreement with theoretical predictions.

Fig. 5. The spectrum of the free-running gyrotron (blue) and the gyrotron with the resonant reflector (red) forthe case of operation within the locking band (B = 0.5167 T).
To advance the considered method of frequency stabilization by reflections from the resonant load to thehigh power gyrotrons, it is possible to use, for example, the travelling-wave resonator with the corrugatedmirror as the coupling element. It is also possible to use the same scheme with the quasi-optical resonator, butwith the water-cooled diamond disc as the coupler (similar to the output windows of the MW-class gyrotrons).
References[1] M.Y. Glyavin, G.G. Denisov, M.L. Kulygin, and Y. V. Novozhilova, “Stabilization of gyrotron frequency
by reflection from nonresonant and resonant loads,” Tech. Phys. Lett., vol. 41, no. 7, pp. 628–631, Jul. 2015,
doi: 10.1134/S106378501507007X.
[2] Y.V. Novozhilova and A. S. Ishenko, “Analytical Theory of an RF Generator Phase-Locked by the
Resonant Load with Delayed Reflection,” J. Infrared, Millimeter, Terahertz Waves, vol. 32, no. 12, pp. 1394–
1406, Dec. 2011, doi: 10.1007/s10762-011-9828-z.
[3] I.V. Zotova, G.G. Denisov, N.S. Ginzburg, A.S. Sergeev, and R.M. Rozental, “Time-domain theory of lowQ gyrotrons with frequency-dependent reflections of output radiation,” Phys. Plasmas, vol. 25, no. 1, p. 013104,
Jan. 2018, doi: 10.1063/1.5008666.
For more detail, please access the original publication:
A.P. Fokin, A.A. Bogdashov, Yu.V. Novozhilova, V.L. Bakunin, V.V. Parshin, M.Yu. Glyavin,“Experimental Demonstration of Gyrotron Frequency Stabilization by Resonant Reflection,” IEEE
Electron Device Letters, (2021) DOI: 10.1109/LED.2021.3083641.

Automodulation instability in gyrotrons operating at the second cyclotron harmonic
A. P. Fokin1, V. L. Bakunin1, M. Yu. Glyavin1 and G. S. Nusinovich2
12Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, 603950, Russia
Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 207423511, USA
I.

Introduction
Gyrotron operation at cyclotron harmonics in existing cryomagnets is very attractive because it allows
increasing the operating frequency proportionally to the harmonic number ns > 1 . As any source of high-powerelectromagnetic (EM) radiation driven by an electron beam, high-power gyrotrons operate in high-order modesof microwave circuits serving as an interaction space. Therefore, as a rule, in addition to the desired mode, anelectron beam can resonantly interact with some parasitic modes having the frequencies close to the electron
cyclotron frequency or its harmonics. Competition between such modes was, first, studied for the case of pairwise interaction, when only one parasitic mode competes with the desired one. Then, the demands for further
increasing the gyrotron power resulted in operating in higher-order modes where the mode spectrum is denser.
In general, the choice of operating modes was always a challenge. Initially, in the 1960s-1970s, the symmetricTEm,p-modes with azimuthal indices m = 0 were used in gyrotrons operating at the fundamental cyclotron
resonance. Such modes were especially attractive for high-frequency (sub-terahertz and terahertz) gyrotrons
because they have lower ohmic losses than azimuthally rotating ones. However, later this development was
stopped because of severe competition between the TE0,p- modes and the TE2,p- modes with close frequencies,
with the latter being stronger coupled to electron beams. As a result, the gyrotron development was switchedtoward operating in azimuthally rotating TEm,p-modes with azimuthal indices m ≠ 0 .
Recently, it was shown [1] that in harmonic gyrotrons operating in symmetric modes with azimuthal
indices m = 0 , the electron beam coupling to the competing modes with m=2 can be much weaker. So, a stable
operation at cyclotron harmonics can be realized even in the case of high-order symmetric modes. This sort ofoperation is very attractive because it allows the development of high-power gyrotrons with an acceptable levelof ohmic loss density at higher frequencies (sub-terahertz and THz frequency range).
In [1], it was shown that a high-order symmetric mode operating at the second cyclotron harmonic could
be selectively excited in spite of the presence of parasitic modes at the fundamental in the resonator spectrum.
However, the stability was analyzed in [1] for the pair-wise interaction, i.e., when only one parasitic mode at
the fundamental has a frequency close to one half of the operating mode's frequency. The multimode dynamics
is frequently investigated in powerful gyrotrons operating in high-order modes at the fundamental, while thenumber of studies of harmonic gyrotrons is relatively small.
In general, for gyrotrons operating at harmonics, the automodulation (or sideband) instability is causedby the parametric interaction between the desired mode at the second harmonic (either rotating with m ≠ 0 orsymmetric with m = 0 ), and a pair of parasitic waves at the fundamental is very important. The conditions forthe parametric coupling of such modes can be formulated as conditions for the frequencies and azimuthal
indices of these modes asω,Q
m1 + m3 =m2 .

ω1 + ω3 − ω2 ≤

(1)

(2)
In (1)-(2), the index '2' designates the desired mode at the second cyclotron harmonic, and '1' and '3' designate
two modes at the fundamental. Equations (1) and (2) are analogous to the photon energy and angularmomentum conservation law in nonlinear optics. From Eq. (2), it follows that in the case of a symmetricharmonic mode ( m2 = 0 ) it should be m3 = −m1 . This condition means that the pair of parasitic modes can beformed by a single TEm,p-mode with two polarizations, i.e., by two waves with the same absolute value of theazimuthal index, which are co- and counter-rotating with electrons azimuthally. When the condition (1) is not
valid, we should expect a more straightforward case of pair-wise interaction, in which the phase difference
between the modes with well-separated frequencies varies much faster than the mode amplitudes do. Therefore,we can average equations for the mode amplitudes over the fast beating of the phase difference of these threemodes. As a result, the equations for mode amplitudes become independent on the phase relations.
Our present study aims to analyze the role, which the pair of parasitic modes at the fundamental can playin the stability of oscillations in second harmonic gyrotrons. Theoretical estimation and numerical modeling are
based on the well-known model with a fixed longitudinal mode structure [2].
Some possible detunings of operation (second harmonic) and parasitic (fundamental one) modes areillustrated by Fig. 1.

Fig. 1 Operating mode at the second cyclotron harmonic ( ω2 ) and the pair of modes at the fundamental for thecase of non-symmetric (a) and symmetric (b) operating mode.
To further investigate the conditions for automodulation instability in a gyrotron operating at the second
cyclotron harmonic, we performed a numerical simulation of the multimode processes in the cold-cavity
approximation (i.e. ignoring effect of an electron beam on the axial structure of the resonator field). For
minimizing the number of parameters characterizing the gyrotron operation, we assumed that the axial structure{of the resonator field could be described by the Gaussian distribution f =(ς ) exp − ( 2ς / ς out )2}.

Prior to analyzing stability of single-mode oscillations at the second harmonic, we should describe thestationary operation in this mode. To achieve the maximum efficiency of the operating mode at the second
harmonic, the normalized length of the interaction space was chosen equal to ς out = 7.5 . In Fig. 2, the lines of
equal orbital efficiencies are shown in the plane of the beam current parameter Iˆ = I Q and the cyclotron222

resonance mismatch; the dashed line represents the starting current. These results show that the maximum
efficiency corresponds to the normalized current parameter close to Iˆ2 = 0.5 and the optimal value of thecyclotron mismatch of ∆ =0.57 . This optimal point lies in the region of hard self-excitation. For getting there, agyrotron should be driven by a proper start-up scenario, which implies either tuning of the guiding magnetic
field or the variation of the beam and mod-anode voltages during the voltage rise.
Next, we use the electron motion calculated at the first step to solve the perturbation equations and thendefine the region of instability in the parameter space, and the stability criteria. When the normalized
parameters of the operating mode are fixed, it is necessary to determine the region of its instability in the planeof detunings of two parasitic modes at the fundamental. In our simulations, the quality factors of both sidebands
were considered equal, and their ratio to the Q-factor of the operating mode: Q±1 = Q2 4 . The coupling
coefficients G±1 G2 = 4 , which give us the normalized currents for the satellites I ±1 = I 2 β ⊥2 . For the gyrotron
with the operating mode Q-factor Q2 = 1000 , accelerating voltage 100 kV, and beam pitch-factor 1.2, the limits
4
for the mode mismatches are given as follows: ∆1 + ∆ −1 ≤ 2 ≈ 0.025 .
β ⊥ Q2The zone of the automodulation instability is shown in Fig. 3 in the plane of the left and right sidebands'mismatches with the central mode. The zone of the automodulation instability is shown in Fig. 3 in the plane of
the left and right sidebands' mismatches with the central mode.

Fig. 2. Contours of equal orbital efficiencies and the start current (dashed line)

Fig. 3. The zone of the instability of the second harmonic mode.
The difference in the gyrotron operation within the zone of the instability and outside of it was verified
by self-consistent simulations of the basic set of equations. Results are shown in Fig. 4.
As seen in Fig. 4a, when the detunings are equal to ∆1 = 0.42, ∆ −1 = −0.4 (this point lies outside of theinstability zone shown in Fig. 3), the oscillations of the operating mode are unperturbed. However, when the
detunings are equal to ∆1 = 0.82, ∆ −1 = −0.8 (this choice of detunings gives us the point inside the instability
zone in Fig. 3), the amplitude of the operating mode is decreased, and the excitation of both sidebands isobserved.
The study described above presents the simple theory of parametric interaction of a second harmonicmode with sidebands at the fundamental in gyrotrons. This theory allows calculating the zones of stable singlemode oscillations and helps to select gyrotron parameters for a reliable, stable generation. This theory can be
modified to account for the spread in electron beam velocities and guiding center radii and consider theinteraction with the modes at the fundamental with several axial variations of the field. Such considerations canlead to the expansion of the zone of instability and softening of the mode density criteria.
The gyrotron operation, when parameters are chosen inside the calculated zone of instability and outsideof it, is illustrated by consideration of some examples. It is shown, however, that for typical parameters of themodern gyrotrons (Q close to 1000, accelerating voltage less than 100 kV, and beam pitch-factors 1.2-1.5), therequirements to the mode density (the indices of the operating mode) for occurring such automodulation
instability significantly exceed the typical values of mode indices even of the most powerful gyrotrons.

Fig. 4. Time-dependent amplitudes of the operating mode and the satellites outside of the region of instability(a) and inside it (b).
References:[1] A.P. Fokin, V.L. Bakunin, M.Yu. Glyavin, G.S. Nusinovich, “Automodulation instability in gyrotrons
operating at the second cyclotron harmonic,” Physics of Plasmas, vol. 28 (2021) 043303. DOI:
10.1063/5.0046914[2] M.A. Moiseev and G.S. Nusinovich, "Concerning the theory of multimode oscillation in agyromonotron," Radiophys. Quantum Electron., vol. 17, no. 11 (1974) 1305–1311.
DOI:10.1007/BF01042032.
For more detail, please see the original paper:
A.P.Fokin, V.L. Bakunin, M.Yu. Glyavin, G.S. Nusinovich, “Automodulation instability in gyrotrons
operating at the second cyclotron harmonic. Physics of Plasmas, vol. 28 (2021) 043303. DOI:
10.1063/5.0046914

PERSONALIA
Academician Andrei Viktorovich Gaponov-Grekhov at 95

The great Russian physicist Andrey Viktorovich Gaponov-Grekhov, an Academician of the Russian
Academy of Sciences was born on 7 June 1926 in Moscow. He is well-known as the founder of the Institute ofApplied Physics of the RAS and its first director (1976-2003).
A. Gaponov-Grekhov graduated from Gorky University (now Lobachevsky State University of Nizhni
Nogrorod) in 1949. In the same year he entered the postgraduate course to the academician A. A. Andronov. He
offered him a topic for his Ph.D. thesis on the general theory of electromechanical systems and in 1955 at the
Leningrad Polytechnic Institute he defended his thesis "Electromechanical systems with sliding contacts and the
dynamic theory of electrical machines". For the importance of this work, the applicant was immediately
awarded the degree of Doctor of Physical and Mathematical Sciences. After completing his postgraduate
studies, A.V. Gaponov-Grekhov worked as a teacher at the Gorky Polytechnic Institute (1952-1955), and after
receiving his doctorate until 1977 he worked at the State Institute of Physics and Technology (Gorky ResearchInstitute of Physics and Technology, now NIPTI), while remaining a professor at the Polytechnic Institute. On
June 26, 1964, he was elected a Corresponding Member of the USSR Academy of Sciences in the Departmentof General and Applied Physics (Radio Engineering and Electronics), and on November 26, 1968 - an
Academician. Since 1966, he worked as Deputy Director of NIRFI, in 1976 he headed the Institute of Applied
Physics of the Academy of Sciences of the USSR and directed it until 2003. In 1989-1991 he was elected a
deputy of the Supreme Soviet of the USSR. In 2003–2015, he was the scientific director of the IAP RAS, at thepresent time he is an advisor to the RAS.
Academician Gaponov-Grekhov is an author of fundamental works in the field of electrodynamics,
plasma physics, physical electronics, the electrodynamics of a nonlinear medium, and the theory of distributed
nonlinear systems. He has conducted theoretical and experimental research on induced cyclotron radiation,
which allowed the development of masers on electron cyclotron resonance (State Prize of the USSR,

1967) and most notably the gyrotron. His remarkable achievements as a scientist and longstanding leader of
the Institute of Applied Physics of the Russian Academy of Sciences (IAP-RAS) in Nizhni Novgorod have beenrecognized by many highest national and international awards and prizes. Among them are Lomonosov GrandGold Medal, Hero of Socialist Labor, Order of Merit to the Fatherland, Order of Lenin, Order of the October
Revolution, State Prize of the USSR, State Prize of the Russian Federation, and many others.

Professor Grigory Gennadievich Denisov at 65

Grigory Gennadievich Denisov was born on April 30, 1956 in the city of Gorky, now Nizhny
Novgorod).
After graduating from the Faculty of Radio Physics of the Gorky State University in 1978, he worked at
the Institute of Applied Physics of the Russian Academy of Sciences, first as an intern researcher, thensuccessively as a junior researcher, associate professor, head of laboratory, and head of department. In 1985,
under the leadership of Academician A.V. Gaponov-Grekhov, he defended his Ph.D. thesis "Relativistic
electron microwave oscillators of the millimeter-wavelength range with highly selective electrodynamic
systems", and in 2002 his doctoral thesis "Formation, transformation and transmission of radiation in oversize
electrodynamic systems". In 2011, he was elected a Corresponding Member of the Russian Academy of
Sciences. Since 2012, he has been the Head of the Plasma Physics and High-Power Electronics Division and
Deputy Director for Science at the Institute. Since 11 Jun 2019 he is a Director of IAP-RAS.
Over the years he has become widely known in Russia and abroad for his theoretical and experimental
work on electrodynamics of multimode systems and high-power electronics. He is the author of more than 300
scientific papers, 6 author’s certificates, and patents (Hirsch index 36, the number of citations is more than5000).
In these areas, G. Denisov performed basic works: fundamentally new methods for diagnostics andtransformation of the spatial structures of high-power wave beams were proposed and developed and new typesof high-power electronic microwave devices were proposed and implemented. Works by G. Denisov
determined the successful development of new highly demanded microwave devices with record-breaking
parameters, including megawatt gyrotrons for controlled thermonuclear fusion facilities, millimeter-wave gyroTWT with a wide band of amplified frequencies, and free-electron masers. The results of his work are also very
important in the development of promising facilities for the study of new methods of microwave processing ofmaterials to create new sources of multiply charged ions for growing diamond films by CVD technology.
G. Denisov was awarded the Lenin Komsomol Prize for achievements in science (1986), the D. Rose
International Prize for achievements in fusion technology (1997), the State Prize of the Russian Federation forachievements in science and technology (2003), Prize of the Government of the Russian Federation for thedevelopment of industrial production of megawatt gyrotrons for controlled thermonuclear fusion facilities(2011).
G.G. Denisov is a member of the Scientific Council of the IAP RAS, a member of the IAP RAS
dissertation council, the chairman of the expert council of Gycom Ltd, a member of the ITER Scientific andTechnical Coordination Council under the State Atomic Energy Corporation “Rosatom”, and a member of theexpert council of the Ministry of Education and Science. For many years, he has also been conducting teaching
work (now as a professor) at the Nizhny Novgorod State University. He prepared a large number of highly
qualified specialists in the field of radio physics and high-power electronics, of which seven defended their PhD
thesis and one, a doctoral thesis. G. Denisov is the head of the scientific school “Generation, amplification,transformation, and transportation of high-power microwave and terahertz radiation for the purpose of its use inphysical and technological research”, which combines about 40 scientists, including 8 doctors 14 candidates ofscience. The school has repeatedly received grants under the program of the President of the Russian Federation
on state support of the leading scientific schools.
As a Director of IAP-RAS, Professor G. Denisov actively supports the collaboration of the International
Consortium “Development of High-Power THz Science and Technology”.

FORTHCOMING EVENTS (UPDATED ANNOUNCEMENTS)

46th International Conference on Infrared, Millimeter and Terahertz Waves
Date: Aug 29 –Sep 3 2021
VENUE: INTERCONTINENTAL CENTURY CITY，CHENGDU，SICHUAN，CHINA P. R.

For up-to-date information, please visit the conference website.

LIST OF SELECTED RECENT PUBLICATIONS
Bibliography and links to selected recent publications on topics related to the research field of theInternational Consortium and published after February 2021, i.e. after issuing the previous Newsletter#17. This cumulative list is in chronological order as collected from various bibliographical and alert
services
A. Publications by authors from the institutions participating in the International Consortium
Bakunin V.L., Denisov G.G., Novozhilova Y.V., “Influence of an External Signal with Harmonic or tepwiseModulated Parameters on the High-Power Gyrotron Operation,” J Infrared, Millimeter, and Terahertz Waves,vol. 42(2021) 117–129. DOI:10.1007/s10762-020-00758-3.
https://link.springer.com/article/10.1007/s10762-020-00758-3

Y. Y. Danilov et al., "Slit-Type Cavities for Cyclotron Resonance Masers Operating at TM Modes," in IEEE
Transactions on Electron Devices, (2021). DOI:10.1109/TED.2021.3055162.
https://ieeexplore.ieee.org/document/9351704
T. Kawasaki, Y. Yamaguchi, T. Ueda, Y. Ishikawa, T. Yaji, T. Ohta, K. Tsukiyama, T. Idehara, M. Saiki, and
M. Tani, "Irradiation effect of a submillimeter wave from 420 GHz gyrotron on amyloid peptides in vitro,"
Biomedical optics express, 11.9 (2020) 5341-5351. DOI: 10.1364/BOE.395218.
https://www.osapublishing.org/boe/fulltext.cfm?uri=boe-11-9-5341&id=437734
T.I. Tkachova1, V.I. Shcherbinin, V.I. Tkachenko, Z.C. Ioannidis, M. Thumm, J. Jelonnek, “Starting currents
of modes in cylindrical cavities with mode-converting corrugations for second-harmonic gyrotrons.” J Infrared,
Millimeter, and Terahertz Waves, vol. 42 (2021) 260–274. DOI:10.1007/s10762-021-00772-z.
https://link.springer.com/article/10.1007/s10762-021-00772-z
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He T., Wang S., Wang Z., Shao W., Xu D., Li X., Gong, Y., “Electron-optical system for dual radial sheet
beams for Ka-band cascaded angular log-periodic strip-line traveling wave tube,” AIP Advances, vol. 11, n. 3
(2021) 035325. DOI:10.1063/5.0037161.
https://aip.scitation.org/doi/full/10.1063/5.0037161
V. Kesari, R. Seshadri, "RF and Thermo-Mechanical Examinations of Output Windows for W-Band Gyrotron,"in IEEE Transactions on Electron Devices, (2021). DOI:10.1109/TED.2021.3053227.
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S. Yajima, K. Kajiwara, M. Isozaki, N. Kobayashi, R. Ikeda, T. Kobayashi, T. Shinya, H. Yamazaki, K.
Takahashi, “Estimation of RF power absorption and stray distribution at plasma breakdown based on the designof ITER ECH&CD equatorial launcher,” Fusion Engineering and Design, vol. 170 (2021) 112470.
DOI:10.1016/j.fusengdes.2021.112470.
https://www.sciencedirect.com/science/article/pii/S0920379621002465
L. Hu et al., "Development of a 28-GHz/50-kW/30-s Gyrotron System for Fusion Application," IEEE
Transactions on Plasma Science, (2021). DOI:10.1109/TPS.2021.3066553.
https://ieeexplore.ieee.org/document/9387773

S. Kaboli, "A Microscopic Assessment About the Fracture of Alumina in the Pillbox-Type RF Window ofHigh-Power Electron Tubes," IEEE Transactions on Plasma Science, (2021) DOI:10.1109/TPS.2021.3064570.
https://ieeexplore.ieee.org/abstract/document/9382211
O. Chellaï, S. Alberti, I. Furno, T.P Goodman, et al, “Millimeter-wave beam scattering and induced broadening
by plasma turbulence in the TCV tokamak,” Nuclear Fusion (2021). DOI: 0.1088/1741-4326/abf43f.
https://iopscience.iop.org/article/10.1088/1741-4326/abf43f
Badodi N.; Cammi A., Leggieri A., Sanchez F., Savoldi L., “A New Lumped Approach for the Simulation of
the Magnetron Injection Gun for MegaWatt-Class EU Gyrotrons,” Energies, vol. 14 (2021) 14, 2068.
DOI:/10.3390/en14082068.
https://www.mdpi.com/1996-1073/14/8/2068
X. Wang, D. Gao, Y. Wang, F. Zhang, "Novel double-band input coupler for gyroklystron and gyro-TWT,"AIP Advances, vol. 11(2021) 045019. DOI:10.1063/5.0049068.
https://aip.scitation.org/doi/full/10.1063/5.0049068
S. Yajima, T. Kobayashi, K. Kajiwara, R. Ikeda, K. Takahashi, “Development of a new analytic method formiter bend polarizer on ECW transmission line,” Fusion Engineering and Design, vol. 17 (2021) 112487.
DOI:10.1016/j.fusengdes.2021.112487.
https://www.sciencedirect.com/science/article/pii/S0920379621002635
C.-L. Hung, Y.-S. Yeh, T.-H. Chang, "Linear and Nonlinear Characteristics of a Low-Voltage Gyrotron
Backward-Wave Oscillator in the Subterahertz Range," in IEEE Transactions on Plasma Science, (2021).
DOI:10.1109/TPS.2021.3072243.
https://ieeexplore.ieee.org/abstract/document/9410456
Karthikeyan M.P., Samanta D., Banerjee A., Roy A., Inokawa H. (2021) “Design and Development of
Terahertz Medical Screening Devices.” In: Chakraborty M., Jha R.K., Balas V.E., Sur S.N., Kandar D. (eds)
Trends in Wireless Communication and Information Security. Lecture Notes in Electrical Engineering, vol. 740.
Springer, Singapore. DOI:10.1007/978-981-33-6393-9_40.
https://link.springer.com/chapter/10.1007%2F978-981-33-6393-9_40
Kutsaev S.V., “Electron bunchers for industrial RF linear accelerators: theory and design guide,” Eur. Phys. J.
Plus, vol. 136(2021) 446. DOI:10.1140/epjp/s13360-021-01312-3.
https://link.springer.com/article/10.1140/epjp/s13360-021-01312-3
G. Shu et al., "Design and Microfabrication of an Interaction Circuit for a 0.3THz Sheet Beam Extended
Interaction Oscillator with Multiple-Mode Operation," IEEE Transactions on Terahertz Science andTechnology, (2021). DOI:10.1109/TTHZ.2021.3076696.
https://ieeexplore.ieee.org/document/9419764
S. Karmakar, J.C. Mudiganti, “Design of the interaction cavity for a 110-GHz, 1.5-MW Gyrotron,“ Journal of
Electromagnetic Waves and Applications, (2021). DOI:10.1080/09205071.2021.1918265.
https://www.tandfonline.com/doi/abs/10.1080/09205071.2021.1918265?journalCode=tewa20
G. Shu, G. Liu, Z. Qian and W. He, "Design, Microfabrication, and Characterization of a Subterahertz-Band
High-Order Overmoded Double-Staggered Grating Waveguide for Multiple-Sheet Electron Beam Devices," inIEEE Transactions on Electron Devices, (2021). DOI:10.1109/TED.2021.3075417.
https://ieeexplore.ieee.org/document/9424188
V. Kesari, R. Seshadri, "RF and Thermo-Mechanical Examinations of Output Windows for W-Band Gyrotron,"
IEEE Transactions on Electron Devices, vol. 68, no. 4 (2021) 1899-1904. DOI: 10.1109/TED.2021.3053227.
https://ieeexplore.ieee.org/document/9380568

C.-L. Hung, Y.-S. Yeh, T.-H. Chang, "Linear and Nonlinear Characteristics of a Low-Voltage Gyrotron
Backward-Wave Oscillator in the Subterahertz Range," in IEEE Transactions on Plasma Science, vol. 49, no. 5(2021) 1557-1563. DOI:10.1109/TPS.2021.3072243.
https://ieeexplore.ieee.org/document/9410456
A.M. Cook et al., "A High-Current-Density Electron Beam for Millimeter-Wave Amplifiers," IEEE
Transactions on Electron Devices, (2021). DOI:10.1109/TED.2021.3075191.
https://ieeexplore.ieee.org/document/9428003
D. Li et al., "Investigation of Oversized Circular Waveguides With Deformed Cross Section for Gradual TE₀₁
Mode Bends," in IEEE Transactions on Microwave Theory and Techniques, (2021). DOI:
10.1109/TMTT.2021.3072379.
https://ieeexplore.ieee.org/abstract/document/9426928
Wenjie Fu, Shijie Hu, Chaoyang Zhang, Xiaotong Guan, and Yang Yan, "Compact quasi-optical mode
converter based on anisotropic metasurfaces," Opt. Express, vol. 29 (2021) 16205-16213.
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Y. Jiang et al., "Demonstration of a 220-GHz Continuous Wave Traveling Wave Tube," IEEE Transactions on
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Z. Wang, J. Zhang, X. Sun, P. Wang, H. Xiao, T. Ding, J. Xie, X. Han , "Fully redundant auxiliary system for
gyrotron-based terahertz sources in long-term operation", Review of Scientific Instruments, vol. 92 (2021)
054711. DOI:10.1063/5.0050044.
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Annenkov V., Berendeev E., Volchok E., Timofeev I., “Particle-in-Cell Simulations of High-Power THz
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NEW BOOKS
Georg Gaertner, Wolfram Knapp, Richard G. Forbes (Eds.), “Modern Developments in Vacuum Electron
Sources,” Physics and Astronomy, (Springer Nature Switzerland AG 2020). DOI:10.1007/978-3-030-47291-7.
Print ISBN 978-3-030-47290-0, Online ISBN 978-3-030-47291-7.
https://link.springer.com/book/10.1007%2F978-3-030-47291-7#about
Gaertner G. (2020) History of Vacuum Electronics and Vacuum Electron Sources and Future Development
Trends. In: Gaertner G., Knapp W., Forbes R.G. (eds) Modern Developments in Vacuum Electron Sources.
Topics in Applied Physics, vol 135. Springer, Cham. DOI:10.1007/978-3-030-47291-7_1. Print ISBN 978-3030-47290-0, Online ISBN 978-3-030-47291-7.
https://link.springer.com/chapter/10.1007/978-3-030-47291-7_1
Sebastian Ruess, “Pushing the KIT 2 MW Coaxial-Cavity Short-Pulse Gyrotron Towards a DEMO Relevant
Design,” (KIT Scientific Publishing, 2021, Karlsruhe). DOI:10.5445/KSP/1000117846. ISBN 9783731510246.
https://library.oapen.org/handle/20.500.12657/46721
S Chatterjee, “Sources and Security Issues in Terahertz Technologies,” In Advanced Materials for Future
Terahertz Devices, Circuits and Systems, Editors: Acharyya, Aritra, Das, Palash (Eds.) In Lecture Notes inElectrical Engineering, vol. 727 (Springer, 2021). eBook ISBN 978-981-334-489-1. DOI:10.1007/978-981-334489-1. Hardcover ISBN 978-981-334-488-4.
https://www.springer.com/gp/book/9789813344884
Malik H.K. (2021). Laser-Matter Interaction for Radiation and Energy (1st ed.). CRC Press.
DOI:10.1201/b21799. eBook ISBN9781315396026.
https://tinyurl.com/s6hwyzdt
Advanced Materials for Future Terahertz Devices, Circuits and Systems Editors: Acharyya, Aritra, Das, Palash(Eds.), eSpringer Singapore, 2021. Book ISBN 978-981-334-489-1. DOI:10.1007/978-981-33-4489-1.
Hardcover ISBN 978-981-334-488-4.
https://www.springer.com/gp/book/9789813344884
Mauro Fernandes Pereira, “Terahertz (THz), Mid Infrared (MIR) and Near Infrared (NIR) Technologies forProtection of Critical Infrastructures Against Explosives and CBRN,” Springer Nature (2021). ISBN
9402420827, 9789402420821.
https://link.springer.com/book/10.1007/978-94-024-2082-1
Malhotra, Isha, and Ghanshyam Singh. "Terahertz Antenna Technology for Imaging and Sensing
Applications," (Springer Nature). DOI: 10.1007/978-3-030-68960-5. Hardcover ISBN 978-3-030-68959-9;
Softcover ISBN 978-3-030-68962-9; eBook ISBN 978-3-030-68960-5.
https://link.springer.com/book/10.1007%2F978-3-030-68960-5
Asim Ray (Ed.), “Oxide Electronics,” (2021 John Wiley & Sons, Ltd.). Print ISBN:9781119529477; Online
ISBN:9781119529538. |DOI:10.1002/9781119529538.
https://onlinelibrary.wiley.com/doi/book/10.1002/9781119529538
L. Li, J. Cheng, W. Qiuliang, "Research on Solenoidal Permanent Magnet for Guiding and Focusing Annular
Electron Beams," IEEE Transactions on Plasma Science, (2021). DOI:10.1109/TPS.2021.3082540.
https://ieeexplore.ieee.org/abstract/document/9447174

NEWS FROM THE NET (OUR BROADER HORIZONS)
Ultrahigh-sensitivity molecular spectroscopy in the subterahertz range has become a reality
On 11 March 2021 the website Scientific Russia announces that the Institute of Applied Physics of the Russian
Academy of Sciences (IAP RAS) has created a subterahertz molecular spectrometer with a record sensitivity
for this frequency range (the ability to detect extremely low absorption) 1.3 × 10–11 cm – 1. The spectrometer
combines two unique technologies created at the IAP RAS: a gyrotron, a source of powerful radiation, and aradioacoustic molecular absorption detector.
For more detail on the developed spectrometer please access the publication: G.Yu. Golubyatnikov, M.A.
Koshelev, A.I. Tsvetkov, A.P. Fokin, M.Yu. Glyavin, M.Yu. Tretyakov, “Sub-Terahertz High-Sensitivity HighResolution Molecular Spectroscopy with a Gyrotron,” IEEE Trans. on Terahertz Sci. Technol., vol. 10, n. 5(2020) 502–512. DOI:10.1109/TTHZ.2020.2984459.
Polymer film protects from electromagnetic radiation, signal interference
In her post, Holly Ober announces a breakthrough report published in Advanced Materials—“ElectricallyInsulating Flexible Films with Quasi-1D van der Waals Fillers as Efficient Electromagnetic Shields in the GHz
and Sub-THz Frequency Bands, by Zahra Barani, et al. It describes a flexible film using a quasi-onedimensional nanomaterial filler that combines excellent electromagnetic shielding with ease of manufacture.
“These novel films are promising for high-frequency communication technologies, which require
electromagnetic interference shielding films that are flexible, lightweight, corrosion-resistant, inexpensive, andelectrically insulating,” said senior author Alexander A. Balandin, a distinguished professor of electrical andcomputer engineering at UC Riverside’s Marlan and Rosemary Bourns College of Engineering. “They couple
strongly to high-frequency radiofrequency radiation while remaining electrically insulating in direct current
measurements.”
IEEE Vacuum Electronics Young Scientist Award 2021
Chao-Hai Du was awarded for publishing a monograph related to gyro-TWTs theory and engineering,
improving the theory for modeling dielectric-loaded gyro-TWTs, proposing a solution to realize high current
axis-encircling electron beams for harmonic gyrotron application, and proposing innovative schemes fordeveloping frequency-tunable THz gyrotrons.
https://vacuumelectronics.org/ivec_award/chao-hai_du.html
A fast and accurate way to optimize fusion energy devices
On 19 April 2021, the Princeton Plasma Physics Laboratory (PPL) reports on a fast and accurate way to
optimize fusion energy devices. A model once thought to be nearly impossible for quickly and accurately
designing radio frequency (RF) waves needed to fire up doughnut-shaped tokamak fusion facilities has beendeveloped by a graduate student at PPPL. The student, Nick Lopez, has innovated a fast and accurate way to
calculate the energy and path of RF waves that are distorted by roadblocks called “caustics” that make thebehavior of the waves highly complex. The report cites Lopez who says “Caustics are extraordinarily difficult
to describe mathematically in order to simulate — and we need to be able to simulate them to optimize thedelivery of RF waves,” said Lopez, whose findings are reported in a paper in the Journal of Optics. “The trick is
to simulate caustics accurately and we’ve now found a way to do that.”
For more detail, please follow the link to the paper: N.A. Lopez and I.Y. Dodin, “Metaplectic geometrical
optics for modeling caustics in uniform and non-uniform media,” J. Opt., vol. 23 (2021) 025601. DOI:
10.1088/2040-8986/abd1ce.

OAM Light for Communications
In the June 2021 issue of Optics&Photonics News Alan Eli Willner overviews the possibility to boost thecapacity and performance of the optical communication system using light carrying orbital angular momentum.
This topic is attracting attention among the gyrotron community since the gyrotrons are natural sources of wave
beams with OAM. See for example: M. Thumm, “Gyro-devices – natural sources of high-power high-orderangular momentum millimeter-wave beams,” Terahertz Science and Technology, vol. 13, no. 1 (2020) 1 – 21.
DOI: 10.1051/tst/2020131001. (Open Access).