NEWSLETTERof the International Consortium“Development of High-Power Terahertz
Science & Technology”
February 2022

№ 20

CONTENT Editorial(Page 1)

How to contribute to the Newsletter Invited papers• M. Glyavin, A. Gashturi, A. Malkin, I. Zheleznov, Y.Tatematsu, I. Zotova, “Investigation of Mode
Interaction in Harmonic Sub-THz Gyrotron"(Page 2)
• G.G. Denisov, I.V. Zotova, I.V. Zheleznov, A.M. Malkin, E.S. Semenov, M.Yu. Glyavin, “The
Concept of Phase-Locking of Second-Harmonic Gyrotrons for Providing MW-Level Output Power”(Page 7)
 Forthcoming events(Page 15)
 List of selected recent publications and new books(Page 18)
 News from the Net(Page 27)

EDITORIAL: HOW TO CONTRIBUTE TO THE NEWSLETER
Dear Reader,
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Please submit your contributions to the Newsletter as well as requests for information to:Professor Masahiko Tani
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the International Consortium
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Editor of the website and the Newsletter
Institute of Electronics of the Bulgarian
Academy of Sciencessabch@ie.bas.bg

INVITED PAPERS
Investigation of Mode Interaction in Harmonic Sub-THz Gyrotron
M. Glyavin1, A. Gashturi1, A. Malkin1, I. Zheleznov1, Y.Tatematsu2 and I. Zotova1
1

2

Institute of Applied Physics RAS, Nizhny Novgorod, Russia
Research Center for Development of Far-Infrared Region, University of Fukui, Japanglyavin@ipfran.ru
Abstract

Within the frame of a non-stationary self-consistent model, we have investigated the regimes ofsimultaneous oscillations at two different modes, which are resonant with the first and second
cyclotron harmonics of electron oscillations, respectively. Simulations were carried out forparameters of a sub-THz gyrotron developed at FIR UF (Fukui, Japan). It was shown that thehard self-excitation at the second cyclotron harmonic is possible in the presence of generation
at the first one. Simulations also predict the possibility of simultaneous generation at two
harmonics in the excitation zone of the second harmonic modes at relatively high beam currents.
Furthermore, it was demonstrated that in this case, the axial structure of the generated field canvary in the process of nonlinear interaction.

The gyrotron has established itself as one of the most efficient high-power generators of microwave andmillimeter waves. The most powerful gyrotrons reach 1–2 MW power in long-pulsed and continuous-wave
regimes. Such gyrotrons operate at the fundamental cyclotron harmonic. In order to advance into thesubmillimeter-wave band under conditions of a limited magnetic field, it becomes imperative to generateradiation at the second (or higher) harmonic of the gyrofrequency. However, operation at cyclotron harmonics
complicates the problem of mode selectivity in gyrotron cavities. This problem becomes severe with anincrease in the radiation frequency when the mode spectrum becomes denser. In this case, the rotating electron
beam, which represents a nonlinear medium, can interact with several modes at different cyclotron harmonics[1, 2] that may lead to their simultaneous excitation [3-6].
This article is devoted to simulations of mode interaction for the parameters of the sub-terahertz multifrequency FU CW GVII gyrotron [7], which was recently developed at FIR UF (University of Fukui, Japan).
The gyrotron should operate at frequencies from 274 to 422 GHz (9 fixed modes) at the second harmonic of the
gyrofrequency. At the same time, the differences between the observed regimes and regimes predicted in
calculations were found in experiments. In particular, simultaneous excitation of two modes at the first and thesecond cyclotron harmonics took place in the area of parameters where the observation of single-mode secondharmonic generation was expected. Figure 1 shows one of such regimes when, instead of one Gaussian beamcorresponding to the excitation of the TE5,5 mode at the frequency of 353 GHz, two wave-beams were recorded.
One of such beams corresponds to expectations, but the second corresponds to the TE0,3 mode generated withhigh efficiency at the first cyclotron harmonic. This discrepancy was most likely caused by the use of a modelwith a fixed axial field structure for preliminary calculations of the indicated gyrotron. Note that the importanceof self-consistent modification of the axial profile of the excited field for mode competition at the front of beam
voltage was pointed out in [8] for the case of fundamental-harmonic gyrotrons. Here we extend this approach tothe case of interaction of modes excited at different harmonics.
Further, we study in detail the generation regimes of the FU CW GVII gyrotron within the framework of
the more complicated model with a self-consistent field structure. First, the performed simulation demonstrates
the impossibility of selective excitation of the TE5,5 mode in the calculated zone with the maximum efficiency.
Second, the simultaneous excitation at two cyclotron harmonics is predicted with an increase in the beam
current when a change in the axial structure of the field in the process of nonlinear interaction becomes
essential.

Fig. 1. Calculated (left) and measured (right) distribution of the output wave-beams of the FU CW GVII gyrotron
at 353 GHz for the case of calculated excitation of the TE5,5 mode at the second cyclotron harmonic. The mode
TE0,3 is excited at the fundamental resonance.

We will consider the interaction regimes in the gyrotron based on the self-consistent multimode model[9], which has already demonstrated its effectiveness in comparison with experimental data. This model isbased on the following system of equations (cf. [10,11]):i∂ 2 an
∂Z 2

2p 2p

+ sn

∂an
I
i m −s ϕ=+ isn ( dn ( Z ) − χ∆ n ) an i n ∫ ∫ p sn e ( n n ) d θ0 d ϕ,2
∂τ
4p 0 0()( )sn −1 −i ( m − s ) ϕ
∂p
∂p
2
n n .
+ χ −1 + ip p − 1 = i ∑ an p*
e
∂Z
∂τ
n

(1)

with the non-reflection boundary conditions in the following form (cf. [10]):τ −i ( dn ( 0 ) −χ∆ n )( τ−τ′ )1ean ( τ, 0 ) −∫ipsn 0an ( τ, L ) +τ − τ′
τ −iχ∆ n ( τ−τ′ )1e∫ipsn 0τ − τ′∂an ( τ′, 0 )d τ′ =0 ,∂Z∂an ( τ′, L )d τ′ =0 ,∂Z

where L is the normalized length of the interaction space with the physical length l .

(2a)

(2b)

Simulations were carried out for parameters close to the experimental data [7]: operating frequency of
353 GHz; accelerating voltage of 14.4 kV; electrons pitch-factor of 1.7; radius and length of the regular part of
the gyrotron cavity of 2.78 and 20 mm, respectively; injection radius of 1.2 mm. Interaction of the abovementioned pair of modes, namely, co-rotating with electrons TE0,3 mode at the first cyclotron harmonic andcounter-rotating TE5,5 mode at the second harmonic, were taken into account. Note that we considered the caseof non-degenerate modes with m2 ≠ m1s ; thus, observed regimes do not include the effect of frequency
multiplication.
Figure 2 shows zones of generation regimes of the gyrotron under study in the plane of parameters“beam current versus magnetic field”, temporal evolutions of the mode's amplitude and the axial field structures
established in the steady-state generation are shown in Fig. 3.

Fig. 2. Zones of different generation regimes for competition of TE5,5 (second harmonic) and TE0,3 (firstharmonic) modes.

In the case of the second harmonic mode, this mode has one axial variation, when the magnetic field isin the range of 6.45-6.49 T, and two axial variations (as will be shown later) when the magnetic field is in therange of 6.50-6.52 T. The parasitic mode at the fundamental has one axial variation when the magnetic field
varies from 6.38 T to 6.43 T that follows by the zone with two variations when the magnetic field varies from
6.43 T to 6.49 T and so on.
The simulations also predict the occurrence of small zones where these modes at both harmonics coexist
at high currents. These zones contain points 3 and 5 shown in Fig. 2. As shown in Fig. 3, at the point 3 thesecond harmonic mode has one axial variation that agrees with its axial structure in the solo self-excitation
regime at low currents. Correspondingly, at the point 5 this mode has only one axial variation in the presence ofthe competitor, instead of two variations in the solo regime. Such coexistence - excitation of the second
harmonic simultaneously with the first one - was not found in the previous studies of harmonic gyrotrons.

a)b)Fig. 3. Establishment of steady-state regimes for the selected cases shown in Fig.2 (a) with an estimate of thepowers of the generated modes, and their axial HF field structures (b). Blue and red lines correspond to the first
and the second harmonics, respectively.

The experimental situation described in [7] corresponds (for the operating current of 0.3 A) to the point
2 in Fig. 2. This point lies in the region of hard self-excitation for the second harmonic mode. For realizing
efficient oscillations in this zone, when just only this mode is considered, it is necessary to vary gyrotron
parameters in such a way that, first, the oscillations are excited in the zone of soft self-excitation (where thebeam current exceeds the start current) and, then, this gyrotron is driven in the zone of hard excitation. If weconsider the excitation of two modes just at this point, we find that, first, the mode at the fundamental is excited
and, then, this mode induces excitation of the second harmonic mode. In simulations, output power at bothmodes is close. Decreasing the power of second harmonic generation obtained in the experiments (see Fig.1)
may be explained by higher ohmic losses for higher frequency and the axial mode with one variation.
In the present study, the self-consistent non-stationary theory was used, which takes into account theevolution of axial structures of modes under the beam influence. By using this theory it was possible to find thezones of the coexistence of modes at two different cyclotron harmonics. This fact indicates that such a theory
should be used for accurate predicting the generation regimes in harmonic gyrotrons.
The authors are grateful to Prof. G.S. Nusinovich for his interest in this work, stimulating discussions,and numerous valuable comments.
References[1] V.E. Zapevalov, G.S. Korablev, and Sh.Ye. Tsimring, Radio Eng. Electron. Phys., vol. 22, n. 8 (1977) 86-94.
[2] V.E. Zapevalov, I.G. Zarnitsyna, and G.S. Nusinovich, Radiophys Quantum Electron, vol. 22 (1979) 254–258.
DOI:10.1007/BF01034911.
[3] V.L. Bratman, A.E. Fedotov, and T. Idehara, Int. J. Infrared Milli. Waves, vol. 22 (2001) 1409.
[4] G.S. Nusinovich, IEEE Transactions on Plasma Science, vol. 27, n. 2(1999) 313-326. DOI:10.1109/27.772257.
[5] A.P. Gashturi, G.S. Nusinovich, I.V. Zotova, E.S. Semenov, S.P. Sabchevski, and M.Yu. Glyavin, Physics ofPlasmas, vol. 27 (2020) 063304. DOI10.1063/5.0010593.
[6] Yu.K. Kalynov, I.V. Osharin and A.V. Savilov, IEEE Transactions on Electron Devices 67, 3795 (2020);
doi:10.1109/TED.2020.3009617.
[7] Y. Tatematsu, Y. Yamaguchi, M. Fukunari, et al., Journal of Infrared, Millimeter, and Terahertz Waves, vol. 41(2020) 576–589. DOI:10.1007/s10762-020-00681-7.
[8] E.M. Khutoryan1, G.S. Nusinovich, and O.V. Sinitsyn, Physics of Plasmas, vol. 21 (2014) 093114. DOI:
10.1063/1.4896709.
[9] M. Glyavin, I. Zotova, R. Rozental, A. Malkin, A. Sergeev, A. Fokin, V. Rumyantsev, and S. Morozov, Journalof Infrared, Millimeter, and Terahertz Waves, vol. 41 (2020) 1245. DOI:10.1007/s10762-020-00726-x.
[10] N.S. Ginzburg, G.S. Nusinovich, and N.A. Zavolsky, International Journal of Electronics, vol. 61, n. 6 (1986)
881-894. DOI:10.1080/00207218608920927 .
[11] N.A. Zavol'skii, and G.S. Nusinovich, Radiophys Quantum Electron, vol. 33 (1990) 627–632.
DOI:10.1007/BF01048496.

More detail in: Glyavin M., Gashturi A., Malkin A. et al. “Investigation of Mode Interaction in Harmonic SubTHz Gyrotron,” Journal of Infrared, Millimeter, and Terahertz Waves, vol.
DOI:10.1007/s10762-021-00818-2.

42 (2021) 843–850.

The Concept of Phase-Locking of Second-Harmonic Gyrotrons for Providing MW-Level
Output Power
G.G. Denisov, I.V. Zotova, I.V. Zheleznov, A.M. Malkin, E.S. Semenov, M.Yu. Glyavin
Institute of Applied Physics of the Russian Academy of Sciences, 603950, Nizhny Novgorod, Russia

Abstract: We propose the method of providing MW-level output power in CW or long-pulse
second-harmonic (SH) gyrotrons using phase-locking by a weak external monochromatic
signal. Typically, the power of harmonic gyrotrons is hindered due to excitation of spurious
fundamental-harmonic modes at the front of the accelerating voltage and the beam current.
Injection of a seeding signal at the operating SH mode (priming) can suppress the spurious
generation during the start-up process. Within the frame of a self-consistent multi-mode
model, we demonstrate the applicability of this approach to provide ~1 MW radiation in a
230 GHz SH gyrotron with the high order TE34,14 operating mode which is standardly
unattainable for harmonic operation.
At present, the gyrotrons are the most powerful sources of coherent millimeter and sub-millimeter waves
capable of operating in long-pulse and continuous wave (CW) regimes with megawatt power levels. The
important application of high-power gyrotrons is plasma heating and current drive in controlled thermonuclear
fusion installations. Such systems typically use gyrotrons of the short-wavelength part of the millimeter range(the generation frequency of 110-170 GHz) operating at the first (fundamental) cyclotron harmonic. The
modern challenge in the development of high-power gyrotrons is associated with a significant increase in theiroperating frequency, which is in demand, for example, in next generation of tokamaks with a strong magnetic
field planned for construction. Some progress in these studies was achieved recently in fundamental-harmonic(FH) gyrotrons. However, presently, this progress is restrained by the problem of creating strong magnetic
fields in volumes, sufficient for installing high-power gyrotrons equipped with a large-diameter cathode.
Undoubtedly, it is attractive to use generation at the second cyclotron harmonic for increasing thefrequency, which provides proportional reduction of the guiding magnetic field. According to the theoreticalconsiderations, the maximum electron efficiency of second-harmonic (SH) gyrotrons in the single-mode
approximation is close to that of gyrotrons based on the fundamental cyclotron resonance. However, the output
power of experimentally implemented high-frequency SH gyrotrons does not exceed several tens of kilowatts
with efficiency restricted by 20%. The main problem that hinders obtaining a high power of SH radiation iscompetition with modes excited by the beam at the fundamental resonance. Moreover, spurious FH modes canbe excited at the smooth front of the accelerating voltage and the beam current and, then, continue to exist in
the steady-state regime suppressing the operating SH mode.
It should be noted that there are some approaches to solving the described problem aimed at increasing thestarting currents of parasitic FH modes, as well as selecting the gyrotron start-up scenario for earlier excitationof the operating SH mode. However, these methods were mainly considered for sufficiently low transverse

modes. At the same time, for high-power high-frequency generation, operation at high-order transverse modes
is needed for reducing the Ohmic load. Note that the requirement for high power in CW or long pulse regimes
makes it highly undesirable electrodynamics selection methods using irregularities in the gyrotron cavity.
Simultaneously, electronic selection methods based on axis-encircling or additional absorbing electron beams
contradict the requirement for high efficiency.
At the same time, the well-known and currently actively investigated method of spurious modes
suppression for fundamental-harmonic gyrotrons is associated with locking by an external weak
monochromatic signal with the frequency and structure of the operating mode. In the start-up process, such asignal can provide priming the desired mode and helps this mode to suppress the competitors. Moreover,according to recent studies, frequency-locking also provides a noticeable increase in efficiency, radiation power,
and improvement of generation stability of fundamental-harmonic gyrotrons. This paper proposes applying thismethod to second-harmonic sub-THz gyrotrons to provide single-mode single-frequency generation withmegawatt-level output power. This way does not require any essential modification of the device or acomplicated start-up scenario. Note, however, that the situation with the 2nd harmonic priming is complicatedby the inherent for such gyrotrons nonlinear effect, when the excited harmonic facilitates the excitation ofparasitic modes at the fundamental frequency. Nevertheless, for considered area of parameters this effect was
not observed; thus, as will be shown below, weak external signal may provide priming of the desired mode, andits oscillations will remain stable with respect to all possible competitors.
In this paper, we describe the basic multi-mode model of electron-wave interaction, taking into account thestart-up process and priming by an external signal. Since the quality factors of high-power gyrotrons’ cavities
are fairly low, the model with the self-consistent axial profile of the RF field is used in contrast with previous
considerations. Then, as an example of applicability of the proposed approach, we consider a possibility of
megawatt-level second-harmonic generation in a 230-GHz gyrotron with the TE34,14 operating mode.
Theoretical analysis presented further is based on the model of low-Q cavity gyrotrons with nonfixed axial
mode structures. Such gyrotron can be described by the following self-consistent system of partial differential
equations, which describes competition of many transverse modes excited at different cyclotron harmonics (cf.
[1]):
i

∂ 2 an
∂Z

2

+ sn

∂an
+ ( ie n ( Z ) + i∆ n + ρn ) an =∂τa a n I 2p 2pi m −s ϕ= i I ⊥ n ∫ ∫ p sn e ( n n ) d θ0 d ϕ,a|| 4p2s

0 02( p − 1) =a

2∂p a ⊥+ip∂p g+∂Z 4a� ∂τ

2

�

s −2

( )

sn −1 −i ( m − s )ϕann n
= i ∑ ⊥ an p*
e
.
a
a
g �
n

(1)
Here p is the complex transverse momentum of electrons normalized to its absolute value at the entrance ofinteraction space, Z =β⊥2 ωg z / 2cβ|| and t = β⊥4 ωg t / 8β||2 are dimensionless axial coordinate and time,

s −4

an

eAn
snsn b⊥nme cωg 2 sn −1 sn ! g

J mn − sn ( n n Rb ) is the normalized amplitude of the n-th mode ТЕmn ,qn excited at thecyclotron harmonic with number sn at the frequency ωcn ≈ sn ωg where ωg is the relativistic gyrofrequency inthe operating point chosen as the reference frequency, β⊥ =V⊥ / c and β|| =V|| / c are normalized electrons
velocities, g =β⊥ / β|| is the pitch-factor, γ ≈ 1 + eU / me c 2 is the relativistic factor, U is the accelerating voltage inthe operating point (at the end of the start-up process),2( s − 4 )I n = 64neI b bb
|| ⊥
γ
me c3

 s sn 
sn3  n 
 sn
 2 sn ! 

2

(

2
n R
Jm
−s ( n b )nn

n n2 − mn2) J m2 ( nn )nis the normalized current parameter, Ib is the operating electron current, Rb is the injection radius, J mn ( x) is theBessel function of the first order, mn is the azimuthal index of the n-th mode, n n is its eigenvalue,(

2 −4
ρn= sn2 4β||0β⊥0 Qnohm is the parameter of Ohmic losses, Qnohm= Rd n−1 1 − mn2 n −n 2

) is the Ohmic Q-factor, dn is thefrequency-dependent skin depth. The function εn ( Z ) = 8β||2 sn2 (ωcn − ωcn ( Z )) / ωcn β⊥4 describes the variation of the cutoff frequency ωcn ( Z ) =n n c / R( Z ) along z-axis, R ( Z ) is the profile of the smoothly tapered gyrotron cavity, ωcn isthe cut-off frequency in its regular part.
Unlike [1], the gyrotron start-up is taken into account in Eqs.(1) by slow variation of electron beam
parameters (energy, current, axial and transverse velocities) in the process of the accelerating voltage rising
U (τ) :=αγγ (U ( τ ) )γ=, α I ( τ)Ib (U ( τ ) )Ib,b|| (U ( τ ) )b⊥ (U ( τ ) )=α|| ( τ )=, α⊥ ( τ)
,
bb
⊥
||

(2)

The function ∆ n (τ) = 8β||2 sn2 ( sn ωg α −g1 − ωcn ) / ωcn β⊥4 describes start-up variation of the cyclotron resonance detuning.
For diode-type magnetron-injection guns, the temporal dependence of the pitch-factor and the currentvoltage characteristic taking into account the Schottky effect are given by relations [2]:g (U ( τ ) ) =g

U ( τ)(

1+ g

Ib (U ( τ ) ) =
Ib e

B

2

)

U − g 2U ( τ )( U− U).

,

(3)

(4)

Equations (3),(4) allow us to calculate the functions (2) introduced above. The coefficient В in (4) is foundbased on experimental current-voltage characteristics of modern high-power gyrotrons (see, for example, [3]).
The equations (1) have to be supplemented by proper boundary conditions. For the equations of motion,
we apply standard conditions corresponding to electrons uniformly distributed over the cyclotron rotation
phases at the entrance of the interaction space: p( Z = 0) = eiθ0 , θ0 ∈ [0, 2p) . Note, that we consider here interaction

with a thin electron beam without velocity spread. For modes' amplitudes, boundary conditions are written in
the form:an ( τ, 0 ) −1τ −iΦ n ( τ,τ′,0 )

∫
iπs
n 0

an ( τ, L ) +eτ − τ′1∂an ( τ′, 0 )∂Zτ −iF n ( τ,τ′, L )

∫
iπs
n 0

e

d τ′ =0 ,∂an ( τ′, L )τ − τ′= 2dn, N F0 e

∂Z

(5a)

d τ′ =,(5b)iΩn τ+iF n ( τ,0, L )where δn, N is the Kronecker delta, L =β⊥2 0 ωH lz / 2β||0 c is the normalized length of the gyrotron cavity with theτ′, Z ) sn−1 ∫ ( ∆ n ( τ′′ ) +ε n ( Z ) − isn )d τ′′ , F0 and Ω n = 8β||2 sn (ω0 − ωcn ) / ωcn β⊥4 are the normalized
physical length lz , Φ n ( τ, τ=τ′amplitude and the frequency of the external monochromatic signal. In order to write the boundary condition
Eq.(5b) at the gyrotron output (see [4] for details), we assume that the transverse structure and direction ofrotation of the external signal are the same as that of the operating mode with n = N . For high-power gyrotrons
it can be realized based on a novel quasi-optical convertor proposed in [5]. Note that some modifications of
Eq.5b (compared to the form obtained in [4]) are caused by the fact that the gyrofrequency changes during the
gyrotron start-up.
Based on the developed model, we performed simulations of a high-power second-harmonic gyrotron with
an operating frequency of 230 GHz. With the megawatt power level in mind, the fairly high transverse mode
TE34,14 was chosen as the operating one to provide an acceptable Ohmic load. In the simulation, it was assumed
that the gyrotron cavity was made of copper, taking into account the possible surface roughness (i.e., the valueof the skin depth was taken twice as much as that given by the known formula d n = ( 2π )−1 cλ n σ , whereσ = 5 ⋅1017 is the copper conductivity).

The optimized profile of the gyrotron cavity with the radius of the regular part of 18.34 mm and the lengthof 12 mm is shown in Fig.1a. Figure 1b demonstrates the extremely dense spectrum of competing modes near
the operating frequency. Note that for the injection radius of 7.17 mm (which corresponds to the maximum of
the coupling coefficient for the operating SH mode), there are several dangerous competitors at the fundamental
resonance, including modes of the equidistant spectrum TE±15,8, TE±16,8 with higher coupling coefficients andthe nearest in the magnetic field modes TE18,7 and TE±6,12.
Note that the length of the regular part of the gyrotron cavity was significantly shortened in comparison
with the value optimal for achieving the maximum SH efficiency; thus, diffractive Q-factor of the desired mode
was of 2500. It was done in order to decrease the diffraction Q-factors of competing FH modes and,accordingly, to increase their starting currents [6]. Nevertheless, for the accelerating voltage of 100 kV and thepitch-factor of 1.3, the generation zone of the operating SH mode is almost completely overlapped by zones ofcompeting FH modes (Fig.2); thus, selective gyrotron excitation with high power at the second harmonic in thefree-running regime is not possible. However, as shown below, efficient excitation of the second harmonic with
sufficiently high efficiency and power can be provided in the regime of frequency-locking by a weak externalsignal.
22

R(z), mm

(a)
20

18

16

Coupling coeff., a.u.

0

16

8

z, mm

3 TE
-15,8

(b)

TE15,82

24

32

TE16,8TE6,12 TE-13,9TE-16,8TE-4,13TE-2,14
TE-6,12TE4,13TE0,14TE34,14TE2,14
TE35,14
TE-29,16TE-30,16

TE18,7TE8,11
TE-31,15

1
0
114

115
116
s
Cutoff frequencies/ n, GHz

117

Fig.1 (a) The optimized cavity profile of the simulated 230-GHz gyrotron. (b) Normalized coupling coefficients of
the operating and competing modes (modes spectrum) for the injection radius of 7.17 mm. Blue and red lines
correspond to FH modes of direct and opposite rotation. Differently rotating SH modes are marked by green andorange lines, respectively. Black lines show modes which are not important for competition.

For further simulations, the operating current was chosen equal to 50 A, since for this value, the megawatt
level of SH generation can be reached at the TE34,14 mode. The simplest start-up scenario with a linear voltage
rise in time from 75 to 100 kV was considered (Fig.3). Note here, that in practice, the voltage rise time in longpulse gyrotrons is on the order of milliseconds. However, a typical cavity fill time is on the order ofnanoseconds. Therefore, the choice of 300 ns for describing the start-up scenario looks like a reasonable scale,
which is fast enough for saving the time of simulations and, at the same time, sufficiently slow for studying thephysics of nonlinear processes.
In the free-running regime, the TE16,8 fundamental-harmonic mode (blue line in Fig.3) is the first which is
excited on the rising front of the accelerating voltage, suppresses all other competitors, and continues to exist ina steady-state generation regime (Fig.4) with an output power of about 1.1 MW. As a result, transverse
efficiency η⊥ =1 − ( 2p )−1 p 2

θ0

is 35%; total efficiency is 22% taking into account the Ohmic losses. Untypical

low FH efficiency is explained by using the shortened cavity.

Fig.2 Excitation zones for competing modes: the operating voltage U =100 kV, the pitch-factor g = 1.3 . The
operating point with the maximum efficiency is marked by the green star (the guiding magnetic field of 4.76 T).

Fig.3 Modes’ excitation zones depending on the accelerating voltage for the guiding magnetic field of 4.76 T. Blackline shows the current-voltage characteristics in the start-up process. The operating point with maximum efficiency
is marked by the green star|an|, a.u.

1
0.001

( s =1)
TE16,8

1E-06

(a)

1E-09
1E-12

0

200

400

600

t, ns
0.4

η

┴

0.3

( s =1)
TE16,8

0.2

(b)

0.1
0

0

200

400

600

t, ns
Fig.4. Results of simulations for the free-running (autonomous) regime. Temporal dependences of amplitudes ofcompeting modes (a) and the transverse efficiency (b) are shown. The start-up process ends at 300 ns

The situation is principally different in the frequency-locking regime. In simulations, we use the externalsignal with a power of 50 kW (about 5% of the desired output level of 1 MW), which for the given frequency
can be generated by a FH gyrotron [7]. Such signal provides priming the desirable SH mode TE34,14 (Fig.5),
which, as a result, wins in the competition. The zone of efficient priming corresponds to hard self-excitation at
the second harmonic (Fig.2). Note, that in the operating point, the gyrotron should remain locked by theexternal signal the switching off of which leads to the excitation of the parasitic FH TE-15,8 mode.
According to simulations, the output power of second harmonic generation reaches 0.95 MW (total efficiency is~20%); the Ohmic loads on the cavity walls is of ~2.5 кВт/см2 which is still acceptable for water cooling.

|an|, a.u.

1
( s = 2)0.001

( s =1) TE
TE16,8
34,14

1E-06

( s =1)
TE18,7

1E-09
1E-12

0

200

(a)

400

600

t, ns
0.4

η

┴

0.3
( s = 2)
TE34,14

0.2
0.1
0

0

200

(b)
400

600

t, ns
Fig.5. Results of simulations for the frequency-locking regime. Temporal dependences of amplitudes ofcompeting modes (a) and the transverse efficiency (b) are shown. The start-up process ends at 300 ns.

50
15.7%

f0 fcold, MHz

40

30

13.5%

17.3%
16.6%

20

12 MHzoperating
point

10

18.2%
19%

0
4.75

4.76

4.77
4.78
B0, T

4.79

4.8

Fig.6. Frequency-locking band vs. guiding magnetic field. The output efficiency at the boundaries of the band ismarked.

In Fig.6, the dependence of frequency-locking bandwidth on the guiding magnetic field is shown. For theoperating point, the frequency-locking bandwidth is about 10 MHz. This value can be doubled when the current
is reduced to 45 A. However, in this case, the generation efficiency decreases to 16%, and the power,
respectively, is 0.7 MW.
Note that the calculated bandwidth value is limited by competition with FH modes and, as a result, it is
two times smaller than that 20 MHz given by the well-known Adler formula. Moreover, this zone is at least
twice as narrow as compared with the simulations at a given voltage, i.e., not taking into account the gyrotron
start-up.
Thus, with a specific example, we have shown that the locking a gyrotron with an external monochromatic
signal makes it possible to provide selective excitation of second-harmonic generation at the very high-ordertransverse mode (much higher than in the currently known record experiments [10]). In such a way, it ispossible to significantly increase in SH gyrotrons output power. However, the efficiency of SH generation
remains strongly limited by competition with fundamental-harmonic modes. Nevertheless, the proposed method
may ultimately allow gyrotrons to move at a high-power level to a range of higher frequencies based on
existing superconducting magnets.
Refreences[1] M. Glyavin, I. Zotova, R. Rozental, A. Malkin, A. Sergeev, A. Fokin, V. Rumyantsev, and S. Morozov, “Investigationof the frequency double-multiplication effect in a sub-THz gyrotron,” J Infrared Milli Terahz Waves, vol. 41(2020) 12451251. DOI: 10.1007/s10762-020-00726-x.
[2] M.Yu. Glyavin, and V.N. Manuilov, “Synthesis of current-voltage characteristics of 670 GHz gyrotron magnetron
injection gun and calculation of the parameters of a helical electron beam at the leading edge of a high-voltage pulse”,
Journal of Infrared, Millimeter, and Terahertz Waves, vol. 34, n. 2 (2013) 119-126. DOI: 10.1007/s10762-012-9953-3.

[3] M.Yu. Glyavin, A.L. Goldenberg, A.N. Kuftin, V.K. Lygin, A.S. Postnikova, and V.E. Zapevalov, “Experimental
studies of gyrotron electron beam systems,” IEEE Transactions on Plasma Science, vol. 279, n. 2 (1999) 474-483. DOI:
10.1109/27.772276.
[4] N.S. Ginzburg, A.S. Sergeev, and I.V. Zotova, “Time-domain self-consistent theory of frequency-locking regimes ingyrotrons with low-Q resonators,” Physics of Plasmas, vol. 22 (2015) 033101. DOI: 10.1063/1.4913672.
[5] A.V. Chirkov, G.G. Denisov, and A.N. Kuftin, “Perspective gyrotron with mode converter for co- and counterrotation operating modes,” Appl. Phys. Lett., vol. 106 (2015) 263501. DOI: 10.1063/1.4923269.
[6] V.E. Zapevalov, S.A. Malygin, and S.E. Tsimring, “High-power gyrotron at second harmonic of cyclotron frequency,”
Radiophys. Quantum Electron., vol. 36 (1993) 346-353. DOI: 10.1007/BF01038234.
[7] G.G. Denisov, M.Yu. Glyavin, A.P. Fokin, A.N. Kuftin, A.I. Tsvetkov, A.S. Sedov, E.A. Soluyanova, M.I. Bakulin,
E.V. Sokolov, E.M. Tai, M.V. Morozkin, M.D. Proyavin, and V.E. Zapevalov, “First experimental tests of powerful 250
GHz gyrotron for future fusion research and collective Thomson scattering diagnostics,” Review of Scientific Instruments,
vol. 89 (2018) 084702. DOI: 10.1063/1.5040242.

More detail in: G. G. Denisov et al., "Phase-Locking of Second-Harmonic Gyrotrons for Providing MW-Level
Output Power," in IEEE Transactions on Electron Devices, vol. 69, n. 2 (2022) 754-758. DOI:
10.1109/TED.2021.3134187.

FORTHCOMING EVENTSThe Organizing Committee of the 47th International Conference on Infrared, Millimeter, and Terahertz Waves(IRMMW-THz 2022) has announced Call for Abstracts. The message of the Conference Chair reads:“Following two consecutive years of Covid-triggered online-only venues, we are extremely pleased to be able
to plan a hybrid event in 2022 from 28th August to 2nd September to take place in Delft, Netherlands on thecampus of the Technical University of Delft (www.tudelft.nl).
The in-person conference will be held at the upscale and modern Aula Conference Center(https://www.tudelft.nl/en/about-tu-delft/our-campus/conferences-and-events), centrally located on the Delft
University of Technology campus and only a 10-minute walk from the historic Delft city center. The Aula
Center has excellent facilities with an auditorium for the Plenary sessions that can accommodate up to 1100
people and many in-center breakout rooms for our smaller technical sessions. It also has wonderful poster
presentation and exhibition space. We plan to have a live exhibition, where you can meet our sponsors and talkwith our exhibitors in person. The online portion of the conference will take place using the Whova platform(as in Chengdu), where you can attend all the technical sessions and also gather information about our sponsors
and exhibitors.
Our abstract submission process officially opens on 1st February 2022 at: https://www.irmmwthz2022.tudelft.nl/abstract.html. All the relevant conference information and the detailed abstract submission
guidelines are already posted on the conference website (http://www.irmmw-thz2022.org).
The deadline for your abstract submission is 25thMarch 2022.”

The Twenty-Third International Vacuum Electronics Conference (IVEC) will be held in Monterey, California,
on April 25-29, 2022. This year the conference will be a hybrid event under the sponsorship of the IEEE
Electron Devices Society (EDS). The in-person meeting will be held at the Marriott Conference Center. The
hybrid event will permit remote attendance and conference presentations as well. For detail information about
the event, please visit the website of the conference.

The International Research Conference is a federated organization dedicated to bringing together a significant
number of diverse scholarly events for presentation within the conference program. Events will run over a spanof time during the conference depending on the number and length of the presentations. With its high quality, it
provides an exceptional value for students, academics and industry researchers.
International Conference on Terahertz Science, Technology and Applications aims to bring together leading
academic scientists, researchers and research scholars to exchange and share their experiences and research
results on all aspects of Terahertz Science, Technology and Applications. It also provides a premierinterdisciplinary platform for researchers, practitioners and educators to present and discuss the most recent
innovations, trends, and concerns as well as practical challenges encountered and solutions adopted in the fieldsof Terahertz Science, Technology and Applications.
For more information, please follow the link.

International Conference on Terahertz Science aims to bring together leading academic scientists, researchers
and research scholars to exchange and share their experiences and research results on all aspects of Terahertz
Science. It also provides a premier interdisciplinary platform for researchers, practitioners and educators topresent and discuss the most recent innovations, trends, and concerns as well as practical challenges
encountered and solutions adopted in the fields of Terahertz Science.
For more information, please follow the link.

International Conference on Terahertz Radiation Sources for Imaging and Sensing aims to bring together
leading academic scientists, researchers and research scholars to exchange and share their experiences andresearch results on all aspects of Terahertz Radiation Sources for Imaging and Sensing. It also provides apremier interdisciplinary platform for researchers, practitioners and educators to present and discuss the mostrecent innovations, trends, and concerns as well as practical challenges encountered and solutions adopted in
the fields of Terahertz Radiation Sources for Imaging and Sensing.
For more information, please follow the link.

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 October 2021, i.e. after issuing the previous Newsletter#19. 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
N. Kumar, A. Abhishek, Vishant, K. Singhal, N. Gurjar, S. Jain, A.V. Starodubov, N.M. Ryskin,“Pseudospark-Driven High-Current Miniaturized Voltage-Tunable Sheet-Electron-Beam Source," in IEEE
Transactions on Electron Devices, (2021). DOI:10.1109/TED.2021.3119555.
https://ieeexplore.ieee.org/document/958531
S.V. Samsonov, G.G. Denisov, A.A. Bogdashov, I.G. Gachev, "Cyclotron Resonance Maser with Zigzag
Quasi-Optical Transmission Line: Concept and Modeling," in IEEE Transactions on Electron Devices, vol. 68,
n. 11 (2021) 5846-5850. DOI:10.1109/TED.2021.3114141.
https://ieeexplore.ieee.org/document/9552432
A.B. Adilova, M.I. Balakin, S.A. Gerasimova, N.M. Ryskin, "Bifurcation analysis of multistability ofsynchronous states in the system of two delay-coupled oscillators," Chaos, vol. 31 (2021) 113103.
DOI:10.1063/5.0065670.
https://aip.scitation.org/doi/10.1063/5.0065670
Omrani A,, Yadav R., Link G., Lähivaara T., Vauhkonen M.,, Jelonnek J., "An Electromagnetic Time-Reversal
Imaging Algorithm for Moisture Detection in Polymer Foam in an Industrial Microwave Drying System,"Sensors, vol. 21, n. 21 (2021) 7409. DOI:10.3390/s21217409.
https://www.mdpi.com/1424-8220/21/21/7409
Yuriy K. Kalynov, Andrey V. Savilov, and Eugeny S. Semenov, "Parasitic excitation of fundamental-cyclotronharmonic waves in high-harmonic gyrotrons," Physics of Plasmas, vol. 28 (2021) 113105. DOI:
10.1063/5.0071351.
https://aip.scitation.org/doi/10.1063/5.0071351
Vakhin A.V., Khelkhal M.A., Tajik A., Ignashev N.E., Krapivnitskaya T.O., Peskov N.Y., Glyavin M.Y.,
Bulanova S.A., Slavkina O.V., Schekoldin K.A., “Microwave Radiation Impact on Heavy Oil Upgrading from
Carbonate Deposits in the Presence of Nano-Sized Magnetite,” Processes, vol. 9. n. 11 (2021).
DOI:10.3390/pr9112021.
https://www.mdpi.com/2227-9717/9/11/2021
Hosseini M., Kaasinen A., Aliyari Shoorehdeli M., Link G., Lähivaara T., Vauhkonen M., “System
Identification of Conveyor Belt Microwave Drying Process of Polymer Foams Using Electrical Capacitance
Tomography,” Sensors, vol. 21, n. 21 (2021) 7170. DOI:10.3390/s21217170.
https://www.mdpi.com/1424-8220/21/21/7170
Manfred Thumm, “State-of-the-Art of High-Power Gyro-Devices. Update of Experimental Results 2021,” KITSCIENTIFIC REPORTS 7761 (20210. DOI: DOI 10.5445/KSP/1000136043. ISSN 1869-9669.
https://library.oapen.org/bitstream/handle/20.500.12657/51438/KIT-SR_7761.pdf?sequence=1
C. Wu, G. Aiello, K.A. Avramidis, A. Bruschi, et al. “Basic design considerations for a frequency step-tunable
electron cyclotron wave system to suppress NTMs in DEMO,” Fusion Engineering and Design, vol. 173 (2021)
112931. DOI:10.1016/j.fusengdes.2021.112931.

https://www.sciencedirect.com/science/article/pii/S0920379621007079
Krasilnikov A.V., Konovalov S.V., Bondarchuk E.N. et al. “Tokamak with Reactor Technologies (TRT):
Concept, Missions, Key Distinctive Features and Expected Characteristics,” Plasma Phys. Rep., vol. 47 (2021)
1092–1106. DOI:10.1134/S1063780X21110192.
https://link.springer.com/article/10.1134%2FS1063780X21110192
Belousov V.I., Denisov G.G., Shmelev M.Y., “System of Electron Cyclotron Heating at the TRTTokamak,”Plasma Phys. Rep., vol. 47 (2021) 1158–1168. DOI:10.1134/S1063780X21110143.
https://link.springer.com/article/10.1134%2FS1063780X21110143
V.N. Manuilov, M.V. Morozkin, “Suppression of parasitic secondary emission in a magnetron-injection gun ofa 24-GHz technological gyrotron,” Results in Physics, vol. 31 (2021) 105034. DOI:10.1016/j.rinp.2021.105034.
https://www.sciencedirect.com/science/article/pii/S2211379721010275
Ginzburg N.S., Samsonov S.V., Denisov G.G., Vilkov M.N., Zotova I.V., Bogdashov A.A., Gachev I.G.,
Sergeev A.S., Rozental R.M., “Ka-Band 100-kW Subnanosecond Pulse Generator Mode-Locked by aNonlinear Cyclotron Resonance Absorber,” Physical Review Applied, vol. 16, n. 5 (2021) 054045. DOI:
10.1103/PhysRevApplied.16.054045.
https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.16.054045
A.G. Luchinin, V.A. Malyshev, E.A. Kopelovich, K.F. Burdonov, M.E. Gushchin, M.V. Morozkin, M.D.
Proyavin, R.M. Rozental, A.A. Soloviev, M.V. Starodubtsev, A.P. Fokin, J. Fuchs, and M.Yu. Glyavin, "Pulsed
magnetic field generation system for laser-plasma research", Review of Scientific Instruments, vol. 92, (2021)
123506. DOI:10.1063/5.0035302.
https://aip.scitation.org/doi/10.1063/5.0035302
Savoldi, Laura, Konstantinos A. Avramidis, Ferran Albajar, Stefano Alberti, Alberto Leggieri, and Francisco
Sanchez.. "A Validation Roadmap of Multi-Physics Simulators of the Resonator of MW-Class CW Gyrotrons
for Fusion Applications," Energies, vol 14, n. 23 (2021). DOI:10.3390/en14238027.
https://www.mdpi.com/1996-1073/14/23/8027
A. Likhachev, Yu. Kovshov, S. Kishko, S. Ponomarenko, S. Vlasenko, A. Ivanov, A. Kuleshov , "Supply
voltage control for guaranteed performance of compact terahertz vacuum electron devices", Review of
Scientific Instruments, vol. 92 (2021) 124704. DOI:10.1063/5.0070533.
https://aip.scitation.org/doi/10.1063/5.0070533
N.A. Zavol’Sky, V.E. Zapevalov, M.A. Moiseev, “Numerical Modeling of the Processes of Electron-Wave
Interaction in the Cavities of High-Power Gyrotrons with a Frequency of 300 GHz,” Radiophysics andQuantum Electronics, (2021) 1-12. DOI: 10.1007/s11141-021-10121-8.
https://link.springer.com/article/10.1007%2Fs11141-021-10121-8
M.L. Kulygin, I.A. Litovsky, A.V. Chirkov, I.N. Shevelev, G.I. Kalynova, M.Y. Shmelev, "Terahertz Active
Nanosecond Gigawatt Compressor Thermal Feasibility," 2021 IEEE International Conference on Microwaves,
Antennas, Communications and Electronic Systems (COMCAS), 2021, pp. 99-102. DOI:
10.1109/COMCAS52219.2021.9629071.
https://ieeexplore.ieee.org/abstract/document/9629071
M.L. Kulygin, D.Y. Schegolkov, V.I. Belousov, A.V. Chirkov, I.N. Shevelev, I.A. Litovsky, "Nanosecond
Gigawatt Compressor Excitation Dynamics," 2021 IEEE International Conference on Microwaves, Antennas,
Communications and Electronic Systems (COMCAS), 2021, pp. 473-476. DOI:10.1109/
COMCAS52219.2021.9629100.
https://ieeexplore.ieee.org/abstract/document/9629100

Rozental R.M., Samsonov S.V., Bogdashov A.A. et al. “Multifrequency Radiation at the Kilowatt Power Levelin a Continuous Helical Gyroresonance K-Band Backward Wave Oscillator with External Reflections,” Tech.
Phys. Lett. (2021). DOI:10.1134/S1063785021030299.
https://link.springer.com/article/10.1134%2FS1063785021030299
Tsvetkov A.I., Vodopyanov A.V., Mansfel’d D.A. et al., “Preparation of a Highly Dispersed Powder of Tin
Monoxide by the Evaporation/Condensation Method under Heating with Focused Radiation of a Subterahertz
Gyrotron,” Tech. Phys. Lett. (2021). DOI:10.1134/S1063785021030147.
https://link.springer.com/article/10.1134%2FS1063785021030147
Ruess, Tobias, Gantenbein, Gerd, Ioannidis, Zisis, Rzesnicki, Tomasz, Wagner, Dietmar, Thumm, Manfred andJelonnek, John. "Frequency and mode measurement techniques for megawatt-class gyrotrons" tm - Technisches
Messen, (2021). DOI:10.1515/teme-2021-0039.
https://www.degruyter.com/document/doi/10.1515/teme-2021-0039/html
I.V. Bandurkin, Y.K. Kalynov, A.V. Savilov, "Single-Cavity Gyromultipliers with Asymmetric Electron
Beams," in IEEE Transactions on Electron Devices, (2021). DOI:10.1109/TED.2021.3130856.
https://ieeexplore.ieee.org/abstract/document/9642401
Tsvetkov A.I., Vodopyanov A.V., Mansfel’d D.A. et al. “Preparation of a Highly Dispersed Powder of Tin
Monoxide by the Evaporation/Condensation Method under Heating with Focused Radiation of a Subterahertz
Gyrotron,” Tech. Phys. Lett. (2021). DOI:10.1134/S1063785021030147.
https://link.springer.com/article/10.1134/S1063785021030147
Barabin, S.V., Kropachev, G.N., Lukashin, A.Y. et al. “Еmittance Measurements of a Gasdynamic Electron
Cyclotron Resonant Ion Source,”Tech. Phys. Lett. (2021). DOI:10.1134/S1063785021050199.
https://link.springer.com/article/10.1134/S1063785021050199
G.G. Denisov et al., "Phase-Locking of Second-Harmonic Gyrotrons for Providing MW-Level Output Power,"in IEEE Transactions on Electron Devices, (2021). DOI:10.1109/TED.2021.3134187.
https://ieeexplore.ieee.org/document/9656818
Sidorov A.V., Veselov A.P., Razin S.V., Barmashova T.V., et al. “Gas discharge sustained by powerful THz
and sub-THz gyrotrons in the mixtures of noble gases with nitrogen,” Journal of Physics: Conference Series,
vol. 2103 (2021) 012211. DOI:10.1088/1742-6596/2103/1/012211.
https://iopscience.iop.org/article/10.1088/1742-6596/2103/1/012211
N.S. Ginzburg, A.M. Malkin, V.Y. Zaslavsky, A.E. Fedotov, A.S. Sergeev, "Relativistic Sub-THz SurfaceWave Sheet-Beam Amplifier With Transverse Energy Input and Output," in IEEE Transactions on Electron
Devices, (2021). DOI: 10.1109/TED.2021.3134197.
https://ieeexplore.ieee.org/document/9659820
Tsvetkov A.I., Mansfeld D.A., Vodopyanov A.V. et al. “Experimental Evaluation of the Temperature
Dependence of the Absorption of Metal Oxide Powders Heated by a 527-GHz Gyrotron Radiation,” Tech. Phys.
Lett. (2021). DOI:10.1134/S1063785021080277.
https://link.springer.com/article/10.1134/S1063785021080277
I.A. Navrotsky, N.M. Ryskin, "Electron-Optic System with High Compression of a Multiple Elliptic Electron
Beam for a Miniaturized THz-band Vacuum Electron Device," in IEEE Access, (2021). DOI:
10.1109/ACCESS.2021.3138963.
https://ieeexplore.ieee.org/document/9663398
Zuev A.S., Fokin A.P., Ananichev A.A. et al. Realization of an Octave Frequency Step-Tuning of Sub-terahertz
Gyrotron for Advanced Fusion Research. J Infrared Milli Terahz Waves (2021). DOI:10.1007/s10762-02100832-4.

https://link.springer.com/article/10.1007%2Fs10762-021-00832-4
M.M. Melnikova, N. M. Ryskin, "Influence of reflections on mode-competition processes in a high-power
multimode gyrotron," Physics of Plasmas, vol. 29 (2022) 013104. DOI:10.1063/5.0071210.
https://aip.scitation.org/doi/10.1063/5.0071210
Denisov G., Kuftin A., ManuilovV., Chirkov A., Popov L., Zapevalov V., Zuev A., Sedov A., Zheleznov I.,
Glyavin M, “Concept design of the megawatt power level gyrotron stabilized by a low-power signal for DEMO
project,” Nuclear Fusion, (2022). DOI: 10.1088/1741-4326/ac4946.
https://iopscience.iop.org/article/10.1088/1741-4326/ac4946
S. Adya, S. Yuvaraj, M. Rawat, M. V. Kartikeyan, M.K. Thumm, "Investigations on RF Behavior of a V-Band
Second Harmonic Gyrotron for 100/200 kW Operation," in IEEE Transactions on Plasma Science, (2022).
DOI:10.1109/TPS.2022.3140350.
https://ieeexplore.ieee.org/document/9681477
Zapevalov V.E., Zuev A.S., Parshin V.V., Semenov E.S., Serov E.A., “Reduction of Ohmic Losses in theCavities of Low-Power Terahertz Gyrotrons,” Radiophys Quantum El (2022). DOI:10.1007/s11141-02110127-2.
https://link.springer.com/article/10.1007%2Fs11141-021-10127-2
Rozental R.M., Samsonov S.V., Bogdashov A.A. et al. “Multifrequency Radiation at the Kilowatt Power Levelin a Continuous Helical Gyroresonance K-Band Backward Wave Oscillator with External Reflections,” Tech.
Phys. Lett. (2021). DOI:10.1134/S1063785021030299.
https://link.springer.com/article/10.1134%2FS1063785021030299
Manuilov V.N., Zaslavsky V.Y., Kuftin A.N. et al. “Optimization of the Magnetron-Injection Gun for a HighPower Planar Millimeter-Wave Gyrotron,” Radiophys Quantum El., (2022). DOI:10.1007/s11141-021-10126-3.
https://link.springer.com/article/10.1007%2Fs11141-021-10126-3
S. Ponomarenko, S. Kishko, A. Likhachev, E. Khutoryan, A. Kuleshov, “Electromagnetic sources for THz
imaging and DNP NMR spectroscopy,” In: Electromagnetic Waves and Antennas for Biomedical Applications,2021. DOI: 10.1049/PBHE033E_ch3.
https://digital-library.theiet.org/content/books/10.1049/pbhe033e_ch3
M.S. Gitlin, S.A. Bulanova, A.P. Fokin, M.Yu. Glyavin, et al., "Imaging of a High-Power Millimeter Wave
Beam Using a Millimeter Wave-Induced Gas Breakdown Initiated by a Metal-Dielectric Screen," in IEEE
Transactions on Plasma Science, (2022). DOI:10.1109/TPS.2022.3142902.
https://ieeexplore.ieee.org/document/9694494
I.V. Bandurkin et al., "Frequency-Tunable Second Harmonic Gyrotron with Selective Cavity: Design and
Simulations," in IEEE Transactions on Electron Devices, (2022). DOI:10.1109/TED.2022.3142657.
https://ieeexplore.ieee.org/document/9693990
Novak E., Samsonov S., Savilov A., “Klystron-like Cyclotron Amplification of a Transversely Propagating
Wave by a Spatially Developed Electron Beam,” Electronics, vol. 11, n.3 (2022) 323. DOI:
10.3390/electronics11030323.
https://www.mdpi.com/2079-9292/11/3/323
M.S. Gitlin et al., "Imaging of a High-Power Millimeter Wave Beam Using a Millimeter Wave-Induced Gas
Breakdown Initiated by a Metal-Dielectric Screen," in IEEE Transactions on Plasma Science, (2022). DOI:
10.1109/TPS.2022.3142902.
https://ieeexplore.ieee.org/document/9694494

V.E. Zapevalov, A.S. Zuev, O.P. Plankin, E.S. Semenov, "New Gyrotron Concept: Multi-barrel Gyrotron,"2021 Photonics & Electromagnetics Research Symposium (PIERS), (2021) 1527-1530. DOI:
10.1109/PIERS53385.2021.9695109.
https://ieeexplore.ieee.org/abstract/document/9695109
A.S. Zuev, A.P. Fokin, A.A. Ananichev, A.N. Kuftin, V.E. Zapevalov, M.Y. Glyavin, "Broadband Frequency
Tuning in a Powerful Gyrotron for Fusion," 2021 Photonics & Electromagnetics Research Symposium (PIERS),
2021, pp. 1605-1607. DOI:10.1109/PIERS53385.2021.9695026.
https://ieeexplore.ieee.org/abstract/document/9695026
I.V. Bandurkin et al., "400-GHz Frequency-tunable Second-harmonic Gyrotron with Irregular Cavity," 2021
Photonics & Electromagnetics Research Symposium (PIERS), 2021, pp. 1060-1065. DOI:
10.1109/PIERS53385.2021.9694686.
https://ieeexplore.ieee.org/abstract/document/9694686
S.V. Samsonov, G.G. Denisov, A.A. Bogdashov, I.G. Gachev, "Gyro-TWT and Gyro-BWO with a Microwave
Circuit in the Form of Zigzag Quasi-optical Transmission Line," 2021 Photonics & Electromagnetics Research
Symposium (PIERS), 2021, pp. 2790-2799. DOI: 10.1109/PIERS53385.2021.9695051.
https://ieeexplore.ieee.org/abstract/document/9695051
Y.K. Kalynov, G.I. Kalynova, I.V. Osharin, A.V. Savilov, D.Y. Shchegolkov, "Terahertz Gyrotrons with
Azimuthally-asymmetric Cavities," 2021 Photonics & Electromagnetics Research Symposium (PIERS), 2021,
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NEW BOOKS“High Power Microwave Sources and Technologies Using Metamaterials,” John W. Luginsland (Editor), Jason
A. Marshall (Editor), Arje Nachman (Editor), Edl Schamiloglu (Editor). ISBN: 978-1-119-38444-1 December
2021 Wiley-IEEE Press 320 Pages.
https://www.wiley.com/en-us/High+Power+Microwave+Sources+and+Technologies+Using+Metamaterials-p9781119384441“THz Communications: Paving the Way Towards Wireless Tbps,” Editors Thomas Kürner, Daniel M.
Mittleman Tadao Nagatsuma. Series Title: Springer Series in Optical Sciences Series. DOI:10.1007/978-3-03073738-2.
https://link.springer.com/book/10.1007/978-3-030-73738-2#about

Khanna, Vinod Kumar, “Solid-state devices and vacuum tubes, Practical Terahertz Electronics: Devices andApplications, Volume 1 (2021) IOP Publishing. DOI:10.1088/978-0-7503-3171-5.
https://iopscience.iop.org/book/978-0-7503-3171-5/chapter/bk978-0-7503-3171-5ch8
Lulu Wang (Editor), “Electromagnetic Waves and Antennas for Biomedical Applications.” (Healthcare
Technologies, 2021). DOI: 10.1049/PBHE033E. ISBN: 9781839531675, e-ISBN: 9781839531682 (338 pages).
https://digital-library.theiet.org/content/books/he/pbhe033e“Electromagnetic Vortices: Wave Phenomena and Engineering Applications,” Editors: Zhi Hao Jiang, Douglas
H. Werner. First published:19 November 2021, Wiley). Print ISBN:9781119662822 |Online
ISBN:9781119662945 |DOI:10.1002/9781119662945.
https://onlinelibrary.wiley.com/doi/book/10.1002/9781119662945

NEWS FROM THE NET (OUR BROADER HORIZONS)Japan seeks nuclear fusion reactor prototype by midcentury
On 9 Jan 2022 NikkeiAsia reported “Japan aims to hammer out its very first research and development strategy
for nuclear fusion by summer, Nikkei has learned, with the goal of achieving a prototype reactor by around2050”. In another report, it has been announced that Kyoto Fusioneering (KF), the first fusion energy startup in
Asia and Japan, has raised 1.33 billion yen (US$ 11.7 million) in its latest round of funding. In particular, KF
will use funds for the concentrated development of its plant engineering technologies for plasma heating(gyrotrons) and heat extraction (blankets), which are required for fusion reactor projects currently underdevelopment worldwide. The company can also accelerate its global expansion to recruit talented engineers andbusiness professionals globally, whilst at the same time furthering its reach by leveraging existing industrial
capabilities unique to Japan.

A leap forward for terahertz lasers
In a recent report by Leah Burrows it is announced that researchers have taken a major step towards bringing
terahertz frequencies out of their hard-to-reach region of the electromagnetic spectrum and into everyday
applications. In a new paper, the researchers demonstrate a first-of-its-kind terahertz laser that is compact,
operates at room temperature and can produce 120 individual frequencies spanning the 0.25 - 1.3 THz, far morerange than previous terahertz sources. The laser could be used in a range of applications, such as skin and breast
cancer imaging, drug detection, airport security and ultrahigh-capacity optical wireless links. The research,
conducted by a team from at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS),
in collaboration with the DEVCOM Army Research Lab and DRS Daylight Solutions, is published in APL
Photonics (Open Access). “This is a leap-ahead technology for generating terahertz radiation,” said Federico
Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow inElectrical Engineering at SEAS and senior author of the paper. “Thanks to its compactness, efficiency, widetuning range, and room temperature operation, this laser has the potential to become a key technology to bridge
the terahertz gap for applications in imaging, security, or communications.” This radiation source is a quantum
cascade laser-pumped molecular laser (QPML) tunable over 1 THz spanning the range from 0.25 to 1.3 THz.
The authors of the paper say “Thanks to its large permanent dipole moment and large rotational constants,
methyl fluoride (CH3F) as a QPML gain medium combines a lower threshold, larger power efficiency, and awider tuning range than other molecules. These key features of the CH3F QPML, operated in a compact cavity
at room temperature, pave the way to a versatile THz source to bridge the THz gap”. For further reading on this
topic see the report “Terahertz Lasers Are About to Have a Moment”, published by Payal Dhar in IEEE
Spectrum.

Physicist Solves Century Old Problem of Radiation Reaction
On its website, the Lancaster University announces: “A Lancaster physicist has proposed a radical solution to
the question of how a charged particle, such as an electron, responds to its own electromagnetic field. This
question has challenged physicists for over 100 years but mathematical physicist Dr. Jonathan Gratus has
suggested an alternative approach - published in the Journal of Physics A- with controversial implications.” Theauthor claims: “In this letter we have presented the case why Maxwell–Lorentz without self-interaction is thebest model for the dynamics of charged particles. It has many advantages.” The history of attempts to calculate
this radiation reaction (also known as radiation damping) date back to Lorentz in 1892. Major contributions
were then made by many well-known physicists including Plank, Abraham, von Laue, Born, Schott, Pauli,
Dirac, and Landau. Active research continues to this day with many articles published every year.
Reference: “Maxwell–Lorentz without self-interactions: conservation of energy and momentum” by Jonathan
Gratus, 21 January 2022, Journal of Physics A Mathematical and Theoretical. DOI: 10.1088/1751-8121/ac48ee.
(Open Access)Slow waves on long helices
In a recent paper, the authors report: “Slowing light in a non-dispersive and controllable fashion opens the door
to many new phenomena in photonics. As such, many schemes have been put forward to decrease the velocity
of light, most of which are limited in bandwidth or incur high losses. In this paper we show that a long metallic
helix supports a low-loss, broadband slow wave with a mode index that can be controlled via geometricaldesign. For one particular geometry, we characterize the dispersion of the mode, finding a relatively constantmode index of ∼ 45 between 10 and 30 GHz. We compare our experimental results to both a geometrical modeland full numerical simulation to quantify and understand the limitations in bandwidth. We find that the
bandwidth of the region of linear dispersion is associated with the degree of hybridisation between the fields ofa helical mode that travels around the helical wire and an axial mode that disperses along the light line. Finally,
we discuss approaches to broaden the frequency range of near-constant mode index: we find that placing astraight wire along the axis of the helix suppresses the interaction between the axial and high index modes
supported by the helix, leading to both an increase in bandwidth and a more linear dispersion.”
Reference: Barr, L.E., Ward, G.P., Hibbins, A.P. et al. Slow waves on long helices. Sci Rep 12, 1902 (2022).
DOI:0.1038/s41598-022-05345-1. (Open Access)

When Light Loses Symmetry, It Can Hold Particles
A post at PhysOrg presents a paper devoted to optical trapping. The annotation says: “Optical tweezers use lightto immobilize microscopic particles as small as a single atom in 3D space. The basic principle behind opticaltweezers is the momentum transfer between light and the object being held. Analogous to the water pushing ona dam that blocks the stream, light pushes onto and attracts objects that make the light bend. This so-called
optical force can be designed to point to a certain point in space, where a particle will be held. In fact, theoptical trapping technique has so far won two Nobel Prizes, one in 1997 for holding and cooling down single
atoms, a second in 2018 for offering biologists a tool to study single biomolecules such as DNA and proteins.
Researchers led by Prof. Yuanjie Pang at Huazhong University of Science and Technology (HUST), China, areinterested in the use of fiber optical tweezers, where light and particles are manipulated at the tip of an opticalfiber. This technique eliminates the requirement of conventional, bulky, optical accessories such as microscopes,
lenses and mirrors. Their idea is to start with a perfectly annular symmetric light mode that can only betransmitted in the optical fiber and will not leak into the surrounding space through the fiber tip, and have aparticle to break the mode symmetry and thereby scatter light into the space. This way, by changing thesymmetry and the momentum of the light, the particle receives a reactive force that holds it at the fiber tip. heresearchers predict potential applications such as performing an in-vivo single bioparticle-manipulating
experiment by using the fiber optical tweezers as an endoscope in the interior of a living animal.
Reference: Lou, Y., Ning, X., Wu, B. et al. Optical trapping using transverse electromagnetic (TEM)-like modein a coaxial nanowaveguide. Front. Optoelectron. 14, 399–406 (2021). DOI:10.1007/s12200-021-1134-3.