NEWSLETTERof the International Consortium“Development of High-Power Terahertz
Science & Technology”
February 2021

№ 17

CONTENT Editorial(Page 1)

How to contribute to the Newsletter Invited papers
 Fokin A.P, Manuilov V.N., Osharin I.V., Savilov A.V. “On the applicability of absorbing rectilinear
electron beams in high-frequency gyrotrons.”(Page2)
 Bakunin V.L., Glyavin M.Yu., Novozhilova Yu.V, “Investigation of mode interaction for a gyrotron
with a dense mode spectrum.”(Page 8)
 Zuev A.S., Sedov A.S., Semenov E.S., Fokin A.P., Glyavin M.Yu., “Analysis of the possibilities tocontrol diffraction quality factors of the cavities of sub-terahertz gyrotrons.”(Page 13)
 Upcoming events (updated announcements)(Page 19)
 Special journal issues in the field of THz science(Page 22)
 List of selected recent publications, patents, and new books(Page 23)
 News from the Net(Page 34)

EDITORIAL: HOW TO CONTRIBUTE TO THE NEWSLETER
Dear Reader,
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INVITED PAPERS
On the applicability of absorbing rectilinear electron beams in high-frequency gyrotrons*

Fokin A.P, Manuilov V.N., Osharin I.V., Savilov A.V.

Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia*
Corresponding author: ap.fokin@mail.ru
Abstract. The paper presents theoretical investigation and numerical simulations of the electron-wave
interaction in a high-frequency double-beam gyrotron with an absorbing rectilinear electron beam. The
expression for the starting current in a double-beam gyrotron with one generating and one absorbing beam isderived within the model with a fixed axial field structure and the results of numerical simulations based on aself-consistent model are discussed. It has been demonstrated that the required currents of the absorbing beam
are proportional to Iradiating*L/λ, thus showing that such an approach is inefficient in the case of high-frequency,
low-power gyrotrons with long resonators.
I. Introduction
Nowadays, sources of terahertz radiation are in great demand due to a number of current and perspective
applications [1]. The gyrotrons [2,3] are the most powerful sources of continuous-wave radiation in the sub-THz to
THz frequency range, with an output power up to several hundreds of watts. Nevertheless, the operating frequency
of devices, operating at the fundamental cyclotron resonance is limited by the availability of sufficiently strongsuperconducting magnets, thus the advance to THz is inevitably tied with operation at the cyclotron harmonics.
However, such operation has several problems; the most serious one is the mode competition, especially with modes
at lower harmonics. For suppression of the parasitic modes the two groups of methods exist, namely
electrodynamical selection (irregular cavity [4], use of reflections [5], echelette systems [6], etc.) and electron
selection (using the properties of the electron beam). The second method includes selection of beam radii based on
the coupling coefficient [7], usage of axis-encircling beams in large-orbit gyrotrons [8] and systems with several
electron beams [9,10].
In this paper we investigate the efficiency of mode selection by an additional absorbing electron beam in highfrequency gyrotrons operating at high cyclotron harmonics. The concept of the gyrotron with mode selection byabsorption of the energy of the spurious modes by an additional beam was proposed by Zapevalov and Tsimring[11], and successfully tested in cm-wavelength high-power devices at the second harmonic of the cyclotron
frequency [12]. Promotion of this mode selection method to THz frequency range sources has to take into accounttheir peculiarities, such as weak electron-wave coupling, relatively low operating currents and long cavities (incontrast with high currents and short cavities in the powerful devices). Here we consider the low-power subterahertz tube with one radiating “1” and one absorbing “2” electron beams (Fig. 1). In order to ensure theconditions for cyclotron absorption, the electrons of the second beam do not rotate and have rectilinear
trajectories [11]. We consider the simple adiabatic magnetron-injection gun (MIG), so the energies of the beams
launched from cathode are the same.

Fig. 1. The scheme of the double-beam gyrotron with radiating “1” and absorbing “2” beams; 1 – cathode, 2 –modulation anode, 3 – resonator, 4 – magnet, 5 – output window
The paper is organized as follows: the general set of equations and parameters, describing the electron-wave
interaction efficiency are described in Section II. Section III is devoted to the relation of the general description withthe “classical” gyrotron theory and results of numerical simulation, as well as includes a discussion of theapplicability of absorbing beams as mode selection tools in sub-THz devices.

II. Asymptotic equations of the double-beam gyrotron
As a first step, we can get a simple analytical formula, which estimates the effect of the presence of the absorbing
rectilinear beam «2» on the starting current of a parasitic wave excited by the radiating beam «1». Since there is nointeraction of the rectilinear electron beam with modes at cyclotron harmonics [13], we will consider only modes at
the fundamental.
Evidently, the total RF wave power emitted by electrons in the double-beam system is the difference
between the power radiated by the beam “1” and the power absorbed by the beam “2”:Pe  U 0  I1 1  I 2  2  ,(1)where, U 0  mc 2 / e , I1 and I 2 are the currents of the radiating and absorbing beams respectively,  1 / 1  (v / c) 2 is the relativistic Lorentz-factor, 1 is the averaged decrease in the relativistic energy of theelectrons of the radiating beam “1”, and  2 is the averaged increase in the relativistic energy of the electrons of
the absorbing beam “2”. In the starting small-signal regime of the electron-wave interaction, the changes in theelectron energy are proportional to the squared wave amplitude a [14,15],
 1,2  a 21,2 ,where 1,2 are the normalized electron efficiencies. The power of the microwave losses in a cavity having a finite
quality factor Q is also proportional to the square of the wave amplitude:Pw  Ca 2
Here, the constant C  N s / Q includes both the norm of the operating mode Ns and the Q-factor. The starting
current of the parasitic wave, I1, is described by the energy balance condition, Pe  Pw :U 0  I11  I 22   C(2)On the other hand, the same relation describes the starting current of the parasitic mode I1 0 in the case when theabsorbing beam is absent ( I 2  0 ):U 0 I1 1  C
0(3)
Having compared equations (2) and (3), one can get the following formula describing the increase in the starting
current of the parasitic wave provided by the presence of the absorbing beam:

I1  I 2 2  1 

0
I1   I1 1 

1

.

(4)

(0)

According to this formula, a significant (𝐼1 ⁄𝐼1 ≫ 1) increase in the starting current of the parasitic wave isprovided, when the ratio between currents in the absorbing and radiating beams is as big as
I 2 1
~
.
(5)
I1 2
Let us estimate the normalized efficiencies 1,2 . We consider a gyrotron-type interaction between a particle and aquasi-critical TE wave having the transverse electric field E  a exp( it ) . Evidently, the change in the electronenergy is determined by the work of the wave on the particle, d / dt  v E . Therefore, one can get an equating
like the following [14,15]:d  a cos  .
dz ||(6)

Here,  is the factor of the electron-wave coupling determined by the transverse structure of the wave,   ,||  v ,|| / c ,  (   0 /  )t   is the resonant (slow) phase of the particle with respect to the wave,  0  eB / mc is the nonrelativistic electron cyclotron frequency, and  is the initial phase of the electron cyclotron rotation. We introduce
the transverse and axial components of the normalized electron momentum, p ,||   ,|| , and use the generalrelativistic relation: 2  1  p||2  p2 .
(7)

Having taken into account the conservation of the axial momentum, p||  const , one easily gets the equation for thetransverse momentum:dp 1
  a cos  .
dz ||(8)First, we consider an electron from the rectilinear absorbing beam “2”. Since this particle has only an axial
velocity at the input of the cavity, one should put in Eq. (8) ||   0 and   0 . The latter means that the initial(acquired at the beginning of the process of cyclotron acceleration of the electron) phase of the gyro-rotation, φ,
corresponds to the maximum of the accelerating transverse electric field of the wave. Therefore, the transverse
momentum acquired in the process of cyclotron acceleration during the motion of the particle along the cavity with2

the length L is p   aL  0 . Having taken into account Eq. (7), one obtains  2  p and, therefore, efficiency
2
of the absorbing beam is equal to: 2 L2.
(9) 2  22 a202
As for the electrons from the radiating beam “1”, they possess some initial pitch-factor (the ratio between
rotational and axial velocities)     01 ||1 0 ~ 1 . We assume that the initial energies of electrons from the bothbeams “1” and “2” are the same and, therefore,  02    01 2  ||1 0 2 . In the small-signal approximation, Eq. (6) for thechange of the particles energy from the radiating beam is transformed as follows:d  a cos  .
(10)dz
Since at the beginning of the electron-wave interaction all electrons are uniformly mixed over their initial phases in
the interval 0  0  2 , we should also describe the bunching of particles in the process of the interaction by thefollowing equation for the phase:d   0 / k (  0 /  )     ,
dz
v||
p||

(11)

where   k p|| is the factor of the inertial electron bunching. The solution of Eqs. (10) and (11) obtained in thesmall-signal approximation is well known [14,16]:a2
 1   (  )  L    ' .
0
4
2Here,  ' 

d
,
d

1

3

(12)

2

   exp(ix) dx
0is the “spectrum” of the effective high-frequency force acting on the electrons inside the cavity, and   L is theincursion of the particle phase relative to the wave for its passage through the resonator. Thus, we obtain thefollowing normalized efficiency for the radiating beam “1”:
1   2 2  L3 .
(13)
4
We should take into account also that   0.3 at the optimal phase (    ).
The small beam radius in the resonators of the THz gyrotrons complicates the development of multi-beamelectron-optical systems and limits the overall dimensions of the electron gun, which does not allow installation of
insulators between emitter rings. Due to this fact, the energies of the electrons in different beams in conventional
magnetron-injection guns are usually the same. Then, estimation (5) together with the expressions for theefficiencies for both beams with equal energies leads to the following estimation for the required ratio between
electron currents in the radiating (“1”) and absorbing (“2”) beams:
I 2 L 2  02 L
(14)~ 
  0 2 1   2 .
I1 
|| 

For typical parameters of the modern sub terahertz gyrotrons (accelerating voltage U = 20-30 kV, pitch
factors α = 1.2- 1.4) the normalized initial electron velocity can be found as  0  2U  kV  511 , so the estimate(14) gives the ratio of the currents

I 2 Lresonator~I1  parasite(15)

III. Relation with the conventional gyrotron theory
The estimates given above are based on the general theory of microwave devices operated in the regime ofinertial electron bunching with a low electron efficiency. More complex calculation of the effect of an absorbing
electron beam on the starting current in the gyrotron with equal beam energies can be done in the framework of thenonlinear gyrotron theory with the fixed axial field structure [15,17], which is applicable to the resonators with highQ-factor. The coupling factor for the electron beams with the TEm,p mode on the fundamental can be given by awell-known equation:
J m2 1  k R1,2 
e
2
1
,
(16)
G1,2  Q 3 2
Z end
2
2
2
mc  1 1 0  m, p  m J m  m, p2
 f  Z  dZ



 



0

where, Z  Hz is the normalized axial coordinate, f(Z) is the axial field profile, k   m , p R is the transverse
2 c
2
0

wavenumber and  m , p is the root of the equation J m '( )  0 corresponding to the TEm,p mode.
Following the standard procedure for derivation of the starting current in the model with a fixed field structure[15], we can get the equation for the starting current of the parasitic mode at the fundamental cyclotron resonance inpresence of an additional absorbing beam in the following form: 21 Z
1  G2 I 2 2  f  Z  eiZ dZ
0 0

2

end

I start 

Z end

d 

iZ
G1 1   f  Z  e dZ
 d  0

2

,

(17)

2  c  0  is the normalized cyclotron resonance mismatch and  c is the cutoff frequency of the 21  0 
considered parasitic mode. The resulting equation resembles the classic one for the case of a single generating beam
[15] with an addition of an energy drain by rectilinear electron beam.
The influence of the additional rectilinear electron beam on the starting currents of the parasitic modes in a 25
GHz gyrotron [12] and in a 780 GHz gyrotron [10] was investigated using both the fixed field profile model and theself-consisted gyrotron model with a non-fixed field structure [18,19]. For the equation (17), the axial profile of theparasitic modes at the fundamental resonance and their Q-factors were calculated in the cold-cavity approximation.
The powerful 25 GHz gyrotron has rather short cavity, with L   3 , so the Q-factor of the parasitic TE4,1 modeis equal to 300. The calculated dependence of starting current is presented on the Figure 2.
where  

Fig.2 Minimal starting current of TE4,1 mode in the powerful low-frequency gyrotron vs absorbing beam current forthe self-consistent model with a non-fixed field.

Due to low quality factor of the short resonator which leads to variation of axial field profile with an increase of theabsorbing beam current, the resulting dependence of the parasitic mode starting current is not linear, however,already at 5 A of the absorbing beam current the operating current of the desired second harmonic mode can beincreased more than two times. The obtained dependence is consistent with the experiments in which the TE 4,1 mode
was successfully suppressed by introducing of an absorbing beam. Since the needed absorbing beam current makes
up a small part of the total current, the decrease in total efficiency is smaller than the gain in the output power, which
proves the effectiveness of the mode selection method by an absorbing beam in the high-power gyrotrons with short
resonators.
The existing 780 GHz gyrotron, in contrast with the described above powerful gyrotron, has a resonator withL   15 and Q = 5500. In this case the axial profile of the electromagnetic field is practically undisturbed by theadditional beam, and the estimates of the starting current made by the simple formula (17) are consistent with theresults of self-consistent simulation (Fig. 3).

Fig. 3 Minimal starting current of TE1,4 mode in the terahertz gyrotron vs absorbing beam current for the model of
fixed field structure and for the self-consistent model with non-fixed field.
The calculated dependencies of TE1,4 starting current vs. magnetic field without absorbing beam (I2 = 0) and withabsorbing beam current I2 = 0.7 A are presented in Fig. 4. For considered sub-THz gyrotron with a long resonator,
the required current of the absorbing beam is greater than the current of the radiating beam, which demonstrates theinefficiency of the absorbing beam as mode selection tool in the high-frequency low-power gyrotrons.

Fig.4 Starting current of TE1,4 mode at the fundamental vs. magnetic field without absorbing beam and with anabsorbing beam current I2 = 0.7 A
IV. Conclusion
The influence of the additional rectilinear absorbing beam on the starting current of the spurious modes ingyrotrons has been investigated. The simple analytical estimates of the required I absorbing/Iradiating current ratio are
given, as well as the results of the numerical simulation. In accordance with the previous works on the powerful
gyrotrons with short resonators, the effectiveness of the absorbing beam as the mode selection tool is confirmed.

However, for the sub-THz and THz gyrotrons with weak electron-wave coupling and long cavities, the noticeable
increase of the starting currents for the spurious modes at the fundamental cyclotron harmonic occurs only for large
absorbing beam currents, proportional to Iradiating*L/λ. Therefore, for high-frequency gyrotrons, mode selection by anadditional absorbing beam seems inefficient.
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Investigation of mode interaction for a gyrotron with a dense mode spectrum
Vladimir L. Bakunin, Mikhail Yu. Glyavin, Yulia V. Novozhilova
Institute of Applied Physics RAS, Nizhny Novgorod, Russia
Abstract. Influence of the density of mode spectrum in the gyrotron cavity on the possibility of stable single
mode excitation has been investigated for high-order modes. Interaction of the operating mode with its twoneighbouring satellites symmetrically spaced in mode spectrum is analysed. Some threshold value of themode spectrum density dependent on the beam current is found.
Keywords: vacuum electronics, gyrotrons, high-power microwave generation, millimeter wave devices,
terahertz radiation

Introduction
Various applications of modern gyrotrons require high power (up to 1-2 MW) and high frequency (sub-THz to
THz band) of radiation. To fulfill these requirements and to lower thermal loading on the cavity walls, it is essential
to use high-order operating modes. However, it leads to the increase of the mode spectrum density of the cavity andstrong mode competition, resulting in the possibility of spurious modes excitation during the turn-on process of the
gyrotron. In particular, in such a cavity conditions of excitation of the triplet, formed by the operating mode with its
two neighbouring equidistant satellites, may be fulfilled. Quite a number of the early researchers investigated theauto-modulation instability (4-photon decay) of a triplet in gyrotrons with a simplified Gaussian longitudinal fieldstructure and pre-excited operating mode, not considering the question of the start-up scenario [1,2]. In several
papers, the problem of turn-on scenario and its influence on the operating regime in a multimode gyrotron isinvestigated in detail [3, 4].
The aim of this paper is to find the limiting values of the current and the mode spectrum density parameters,
where single-mode generation of the operating mode is still possible. We take into account two lateral satellites ofthe operating mode. We consider realistic field longitudinal structure in the cavity and realistic turn-on scenario,
when initial amplitudes of all the modes are equally small and the beam voltage gradually increases from the initial
to the operating value.
Model and equations
Let us consider a multimode gyrotron with a cavity similar to the one of the 170-GHz gyrotron, developed in IAP
RAS [5]. The longitudinal field structure is assumed to be fixed and is the same as the cold structure of this cavity
for the TE28,12 operating mode (Fig.1). It is assumed that the density of the mode spectrum of the cavity can bevaried by choosing different operating modes (the higher is the order of the operating mode, the denser is the
spectrum), while keeping the field structure dependence on the dimensionless longitudinal coordinate.
Self-consistent equations, describing our model at the fundamental cyclotron resonance, can be written as

dFs
I A a ex  Fs  iI
f  d
I A az 0p  exp  i s  d




a 2
dp

2
 i    p 1 p  i
 F f   exp i s  .
daz
 a az s s

(1)

(2)

Both the corresponding initial and boundary conditions for the dimensionless mode amplitudes Fs and transverse
electron momentum p are

Fs   0   Fs   , p   0   exp  i  , 0   <2 .
0(3)Here we assume that all the considered three modes have equal Q-factors and dimensionless beam parameters I.
In (1) and (2)  is the dimensionless longitudinal coordinate within the interaction space; τ is dimensionless time, is the dimensionless cyclotron frequency mismatch of the operating mode during the gyrotron turn-on process, andΔ – its value after this process. The phase mismatch between s-th mode and operating mode s   s   ms  m0 (4)contains the parameter ∆s, which characterizes the spectrum density. The tilted variables correspond to the values
that vary during the turn-on process. For more detailed descriptions of these variables see [6].

Fig. 1. Distribution of the module and field phase along the longitudinal coordinate  in the cavity of 170 GHz
TE28,12 gyrotron.
During the turn-on process the beam voltage gradually increases from its initial to the operating value. The beam
current and the dimensionless cyclotron frequency mismatch  behave in a similar way, accordingly to the typicalvolt-ampere characteristic of the diode-type gun. Guns of that type are common in the modern gyrotrons which gives
us freedom in varying of only one parameter: the beam voltage. Time-dependence of the startup scenario for I and is shown in Fig.2.

Fig. 2. Time-dependence of the cyclotron frequency mismatch  and dimensionless beam current I on thedimensionless time.

Simulations and discussion
To analyse the gyrotron regimes it is convenient to draw the starting current of the operating mode and its
satellites along with the trajectory of the turn-on process (Fig. 3). Figure 3 represent the starting currents for theoperating mode (O) and its left (L) and right (R) satellites as a function of the cyclotron frequency mismatch (which varies together with the beam voltage), for several different values of the spectrum density parameters ∆s:0.05, 0.1 and 0.2. The trajectory of the turn-on process is shown by the black solid line with an arrow. Also shown
are the boundaries of the zones of hard excitation for the operating mode and its right satellite. The areas of different
regimes of oscillation are shown on the plane of the current I and mode density ∆s parameters in Fig.4.

Fig. 3. Starting currents of the operating mode (O, red, solid), left (L, green, solid) and right (R, blue, solid)
satellites and boundaries of hard excitation zones (dashed) for spectrum density parameter ∆s = 0.05 (a), 0.1(b), 0.2 (c). Trajectories corresponding to the turn-on processes of the gyrotron with the final value of theparameter ∆= 0.4 are shown by the black lines with an arrow. The second-tier branches of the starting current
for the right satellite are also shown in (b), (c), though they are unreachable for this value of  s .
One can easily see in Fig. 3 that during the initial stage of the turn-on process the gyrotron always passes throughthe zone of a soft-self-excitation of the R-mode, which then is driven into its hard-excitation zone, giving R-mode

advantage over the other two modes. This is illustrated in the Fig.4, where one can see large domain of R. If theoperating point lies within the hard-excitation R zone (∆s is not large enough, corresponding to a very dense
spectrum), the R-mode mostly remains stable and the operating mode can’t be excited (Fig. 5a). If both ∆s and thebeam current I are large enough, one can observe excitation of the left satellite (domain L in Fig. 4; Fig. 5b) andexcitation of almost symmetrical triplet (domain T on Fig. 4; Fig. 5c). In the domain L, during the initial stage of theturn-on process the right satellite (R) is excited, then the oscillation switches to the left satellite (L) with a small
fraction of the right satellite; operating mode (O) remains almost unexcited (Fig.5b). In the domain T (Fig. 4; Fig.
5c) during the initial stage of the turn-on process the right satellite (R) is excited, then oscillation switches to thealmost symmetrical triplet of the operating mode (O) and its equidistant satellites (L,R). The possibility of excitationof the left satellite or the triplet can be explained by the fact that for these parameters (∆s and I) the right satellite
may be on the verge of its hard-excitation zone and may lose the competition during the final stage of the turn-on
process. In the regions O1 during the initial stage of the turn-on process the right satellite (R) is excited, but theoperating mode (O) wins the competition and the amplitude of the satellites become negligibly small (Fig.5d).
For every value of the beam current there is a threshold value of ∆s, which delimits domain O1 of the pureoperating mode oscillation (Fig. 5d) and domains where one of the satellites or triplet are excited (Fig. 4). The otherzone of O-oscillations O2, located between the domains L and R, is very small and to the left of O2 (with thedecrease of ∆s and corresponding densification of the spectrum) the R-domain continues.
The results of our simulations are in accordance with the results of the other researchers [2], which state that
there is a limit of the spectrum density and beyond that limit a pure operating mode oscillation becomes impossible.
Another efficient way to suppress the spurious modes excitation is frequency locking using as a driver a
monochromatic external signal [6], which doesn’t require any internal modification of the gyrotron. New techniques,developed in IAP RAS, allow very efficient injection of the external signal into the gyrotron cavity [5] and very highstability of the frequency of the driver [7].

Fig. 4. Areas of different regimes on the plane of the dimensionless beam current I and mode density parameter  s
for the chosen value of the operating mode cyclotron frequency mismatch at the end of the turn-on process  = 0.4.
Regions of the pure operating mode oscillations (O1, O2, white), triplet excitation (T, orange), left (L, green) andright (R, blue) satellite excitation; lines of the starting currents for the operating mode (red, solid), the left (green,solid) and the right (blue solid) satellites and boundary of hard excitation regions of the right satellite (blue, dashed)
are shown. Grey rectangle zone in the bottom of the plane corresponds to the absence of oscillations at any mode.
Black point corresponds to the oscillations at very-high-order operating mode TE56,24.
Results of our recent simulations show an optimistic forecast about the possibility of single-mode singlefrequency operation at the very-high-order operating mode TE56,24 with a very high spectrum density (∆s ≈0.1) [8] by
the help of the frequency locking. Considering Fig. 4, one can expect that with the use of a frequency locking, thethreshold value of  s may be significantly lowered. For example, the black point corresponding to TE56,24 moves
from the area R into the area O1. We are going to investigate the possibility of the single-mode operation in the
gyrotron with a very high spectrum density also by using the reflected signal [9, 10].

Fig. 5. Typical scenarios in the region R (a), L (b), T(c), O1(d).
Conclusion
In the modern gyrotrons with a dense mode spectrum there is a threshold value of the spectrum density
parameter, which is dependent on the beam current and delimits domains of the stable operating mode oscillationand domains of oscillation at spurious modes. For a density higher than the critical, a pure operating mode
oscillation becomes impossible at common startup scenarios. Penetration into the region of higher densities may bepossible using phase- and frequency locking by external signal or reflected signal.
References[1] Glyavin MYu, Nusinovich GS. Stability of monomode self-excited oscillations in a gyrotron with synchronousmode interaction. Soviet Journal of Communications Technology and Electronics. 1992; 37(2):29-36.
[2] Sinitsyn OV, Nusinovich GS, Antonsen TM. Stability of gyrotron operation in very high-order modes. Physics
of Plasmas. 2012; 19(063114).
[3] Nusinovich GS, Sinitsyn OV, Velikovich L, et al. Startup Scenarios in High-Power Gyrotrons. IEEE
Transactions on Plasma Science. 2004; 32(3).
[4] Nusinovich GS, Vlasov AN, Antonsen TM, et al. Excitation of parasitic modes in gyrotrons with fast voltage
rise. Physics of Plasmas; 2008; 15(103101).
[5] Chirkov AV, Denisov GG, Kuftin AN, Perspective gyrotron with mode converter for co- and counter-rotation
operating modes. Applied Physics Letters. 2015; 106(26).
[6] Bakunin VL, Denisov GG, Novozhilova YuV, et al. Mode Competition Effect on Frequency Locking of aMultimode Gyrotron by a Monochromatic External Signal. Radiophysics and Quantum Electronics. 2017; 56(89): 638-647.
[7] Fokin A, Glyavin M, Golubiatnikov G, et al. High-power sub-terahertz source with a record frequency stability
at up to 1 Hz. Scientific Reports. 2018; 8(1):1-5.
[8] Bakunin VL, Denisov GG, Novozhilova YuV. Principal Enhancement of THz-Range Gyrotron
Parameters Using Injection Locking. IEEE Electron Device Letters. 2020;41(5): 777-780.
[9] Glyavin M, Zapevalov V. Reflections Influence on the Gyrotron Oscillation Regimes. International Journal of
Infrared and Millimeter Waves. 1998; 19(11):1499-1511.
[10] Dumbrajs O, Glyavin M, Zapevalov V, et al. Influence of reflections on mode competitions in gyrotrons.
IEEE Transactions on Plasma Science. 2000; 28(3): 588-596.

Analysis of the possibilities to control diffraction quality factorsof the cavities of sub-terahertz gyrotrons
A.S. Zuev, A.S. Sedov, E.S. Semenov, A.P Fokin, M.Yu. Glyavin
Institute of Applied Physics RAS, Nizhny Novgorod, Russia
Abstract: Manufacturing of cylindrical cavities for short-wavelength gyrotrons is usually performed with amicron-scale precision. In the sub-terahertz (sub-THz) and terahertz (THz) gyrotrons, this often results in the
fabrication of slightly up-tapered cavities instead of cavities having central parts of a constant radius.
Correspondingly, the diffractive quality factors (QD-factors) of such slightly conical cavities may differ fromthose calculated for the cavities with regular central parts of a constant radius. We show that the sensitivity of
QD-factors to the cavity fabrication can be mitigated by introducing some local nonuniformities at the end of aslightly conical up-tapered section of the cavities. The proposed approach is illustrated with an example of agyrotron designed for spectroscopic applications and having an output radiation power of tens of watts at thefrequency of 0.527 THz. The paper presents some numerical modeling results, which show how the proposed
local nonuniformities reduce the sensitivity of the QD-factors on the fabrication defects.
Index Terms: gyrotron, cavity, tapering, Q-factor, efficiency, mode transformation, terahertz radiation.
1. Introduction
Nowadays, the gyrotrons [1, 2] demonstrate a record level of the continuous-wave (CW) power in the subterahertz and terahertz range [3, 4]. A number of tubes for spectroscopy, diagnostic and medical applications arecapable of generating tens [5–9] or hundreds of watts [10] at the frequencies up to 0.8 THz in the CW regime. Since
the capabilities of cryomagnets to produce strong magnetic fields are limited, for the wavelength (λ) shortening, it isnecessary to operate at higher harmonics of the gyro-frequency. As a rule, for realizing stable harmonic excitation(see, for example [11]), "long" cavities (where the length of the uniform section is about 20-30 λ) of a relatively
small radius (2-5 λ) are used. In such cavities, the processes of mode interaction are susceptible to the accuracy of
manufacturing.
Due to some limitations on the precision of manufacturing, the uniform section of the cavity can take the form of
a truncated cone (see Fig. 1a) instead of a section of a constant radius. It should be noted that the existing ultraprecision manufacturing technique permits fabricating such cavities with a 0.05-micron accuracy [12], but the
precision of conventional means used for cavity manufacturing is about 0.5-1 microns. Such accuracy strongly
affects (10-15%) the diffractive quality factor (QD-factor) of the cavity modes [13]. In the case of a cavity uptapering towards the collector, the diffraction losses increase and, correspondingly, Q D of the cavity decrease, that
leads to an increase in the starting current of the cavity modes. Since, as a rule, the sub-THz gyrotrons underconsideration operate with relatively low currents, which slightly exceed the starting current of the cylindricalcavities, this effect leads to a dramatic drop in the generated power and, in some cases, even to the absence ofgeneration. In the case of a reverse situation, where the output radius is less than the input one, Q D increases, but theoutput radiation power decreases due to an increase in the share of the Ohmic losses in the cavity walls. With anincrease in QD, this share can reach 90% that may lead to a substantial drop in the generated microwave power.
It is well known that a local non-uniformity of the cavity wall affects the QD and field distribution [14] thatmakes it possible to compensate for the change of QD caused by slight tapering of the cavity. Some studies of thiseffect in gyrotron cavities are described in [16, 17. In the present paper, we analyze requirements to the shape anddimensions of such local non-uniformities shown in Fig.1, which allow one to obtain efficient and pure mode
generation in slightly up-tapered cavities. The analysis is performed using as an example the second harmonic
gyrotron for spectroscopic applications developed at the Institute of Applied Physics of the Russian Academy of
Sciences (IAP RAS).
2. Numerical investigation of the influence of the cavity profile on the generation efficiency and mode
purityFor studying how the sensitivity of the gyrotron operation to the cavity tapering can be mitigated by the local
non-uniformities of the cavity wall, we used as an example a 0.527 THz gyrotron operating at the second harmonicof the gyro-frequency on the TE6,5 mode [18]. The operating frequency is determined by the intended application of
the tube as a radiation source for experiments on dynamic nuclear polarization (DNP) in nuclear magnetic resonance(NMR) spectrometer. The gyrotron was designed to operate with an accelerating voltage of 15 kV, an electron beam

current of 0.4 A, and a pitch factor (orbital-to-axial electron velocity ratio) of 1.2. Earlier, the electron-opticalsystem for this device was tested in a gyrotron at the fundamental resonance with an operating frequency of 0.263
THz [19]. The experimental test results of the 0.263 THz gyrotron are in agreement with the numerical simulations[5, 19] that gave us the reason to believe that the designed parameters of the electron beam are obtained. The radiusand length of the cavity section were selected to be 1.988 mm and 20 mm correspondently. The angles of the input
and output tapers are equal to 4 and 1 degree. The calculated efficiency is about 2.5%, which results in microwave
power of 150 W.

Fig. 1. Cavity with a taper (a) and with a local non-uniformity (b). The inset shows the considered non-uniformity
shapes.
Figure 2 shows the influence of the cavity tapering on the starting current and generation efficiency of the TE 6,5mode. The calculations were made using the self-consistent single-mode model described in [20]. The electron
velocity spread (the RMS value of the relative transverse velocities spread is about 10%), and the Ohmic losses (theohmic Q-factor Qohm is equal to 10460) were taken into account. As follows from Fig. 2, the efficiency dramatically
drops if the difference between the cavity radius at the input and output of the regular section exceeds 1 micron. So,
this is minimal accuracy of manufacturing for the investigated tube.

Fig. 2.The efficiency and the minimum starting current as functions of the cavity taper R.

For the first test of a 0.527 GHz gyrotron, the cavity was made using a traditional tool, namely lathe. Unfortunately,
the microwave power at the level of 5-10 watts only was obtained. This discrepancy between the theoretical andexperimental results can be explained by the influence of a possible cavity tapering of about R = 2 microns, which
dramatically reduces QD of the operating mode.
As already mentioned before, in order to minimize such effect, a local non-uniformity near the end of the regularcavity section can be used. This inhomogeneity is shown in Fig.1 and can be made with D < 0 (as described in [15])or D > 0. The introduction of a groove in the middle part of the cavity was considered for suppressing the lowfrequency oscillations at the fundamental cyclotron resonance in a gyrotron at a high cyclotron harmonic [21].
The dependence of the QD on the dimensions of the rectangular inhomogeneity (length l and depth D) ispresented in Fig. 3 for the taper with R = 2 microns. Based on the data of Fig.3, the reasonable area of
inhomogeneity dimensions, which result in high enough QD, can be defined. The several periodically located areas
with high QD at D> 0 are caused by the resonant nature of the reflection from inhomogeneity. The calculated
efficiency (for optimal frequency mismatch) is given in Fig.4. In contrast with Fig. 2, where R = 2 microns results
in a doubling of the starting current and zero efficiency, the introduction of the nonuniformity leads to an efficiency
of about 1%, which is approximately two times less than the maximum one in a gyrotron with an ideal cavity. Suchefficiency, however, takes place for a wide area of the tapering value.

Fig. 3. Isolines of the diffraction Q-factor on a logarithmic scale in the plane of the nonuniformity length l and thedepth D for the cavity with a taper with R = 2 m.

Fig. 4. Isolines of the efficiency in the plane of the non-uniformity length l and depth D for the taper ΔR = 2 μm.
The considered non-uniformity configurations are marked by asterisks.

For the gyrotrons, however, not only the efficiency is important – we must take care also about the mode purity.
The effects of mode transformation on the non-uniform section of a waveguide were analyzed based on the methodof plane cross-sections (PCS) [22, 23]. The transverse electric and magnetic fields are decomposed according to thesystem of TE and TM modes in regular reference waveguides. Since the nonuniformity under consideration has
axial symmetry, the azimuthal index m was assumed to be identical for all modes in the analysis. Figure 5 presents
the data of mode content for a rectangular inhomogeneity with the length l = 0.5 mm and the depth D = -15 microns(point 3 in figures 3 and 4).
The next step is defining the inhomogeneity size, which yields high enough efficiency and high purity of theoperating mode. The efficiency was calculated within the single-mode approximation and not include modetransformation effects. The mode conversion occurs only near the cavity output, where the interaction between theelectron beam and the parasitic modes has no strong effect on the mode excitation, so the efficiency calculations arequick and accurate enough. Figure 6 presents efficiency for different inhomogeneities marked by stars in the figures
3 and 4 as a function of the initial tapering. The use of profile No. 1 (l = 0.8 mm, D = 60 microns) results in thewidest and flat curve, but too low mode purity (82%) and efficiency. The profile No. 2 (l = 1.4 mm, D = 25 microns)
gives mode purity equal to 97%. The profile No. 3 (l = 0.5 mm, D = -15 microns) has good mode purity (94.3%) andefficiency and appears to be the most appropriate.

Fig. 5. Axial profiles of the operating TE6,5 mode and spurious modes (on the logarithmic scale), and the content of
the modes in the output wave beam.

Fig. 6. The efficiency as a function of the taper for the regular cavity and three considered inhomogeneity profiles.

The frequency tuning, necessary for spectroscopy applications, can be increased in the case of excitation ofmodes with longitudinal indexes q>1. The data of Fig.7 demonstrate that in the case of additional nonuniformity, thepositive influence on mode excitation takes place also for modes with q>1. Without non-uniformity, the efficiency
for modes with q>1 is equal to zero.
The mode purity can be increased by optimization of the inhomogeneity form. For example, the change of therectangular inhomogeneity to the 𝑠𝑖𝑛(𝑧)|𝜋0 shape or 𝑠𝑖𝑛2 (𝑧)|𝜋0 (see the inset in Fig. 1) with the same QD, mode
purity reaches 95.9% and 96.8%, respectively, in contrast with 94.5%. However, in practice, the most suitable
technology is assembling the structure as a number of cylinders. That is why in the above calculations, the shape of
the inhomogeneity was specified as a rectangular.

Fig. 7. The efficiency of mode interaction with a different number of axial variations as a function of the cavity taper
for the iris type of the nonuniformity (l = 0.5 mm, D = -15 μm).
3. Conclusion
The influence of a local inhomogeneity on the interaction efficiency and mode purity is studied for a 0.527 THz
gyrotron with a tapered cavity. Based on numerical simulation, the requirements for the optimal form of theinhomogeneity can be formulated for a wide range of initial tapering.

Acknowledgement
The authors are thankful to Prof G. Nusinovich from the Institute for Research in Electronics and Applied Physics,
University of Maryland, USA, for valuable comments and interest in this work.
References[1] V.A. Flyagin, A.V. Gaponov, M.I. Petelin, and V.K. Yulpatov, "The gyrotron," IEEE Trans. Microwave Theory
Tech., vol. 25, no 6, pp. 514-521, Jun. 1977, doi: 10.1109/TMTT.1977.1129149[2] G. Nusinovich, M. Thumm, M. Petelin. "The gyrotron at 50: Historical overview," J. Infr., Millim. THz Waves,vol. 35, no 4, pp. 325-381, Apr. 2014, doi: 10.1007/s10762-014-0050-7[3] M. Thumm, "State-of-the-art of high power gyro-devices and free electron masers," J. Infr., Millim. THz Waves,vol. 41, no. 1, pp. 1-140, Jan. 2020, doi: 10.1007/s10762-019-00631-y[4] T. Idehara, S. Sabchevski, M. Glyavin, and S. Mitsudo, "The Gyrotrons as Promising Radiation Sources for
THz Sensing and Imaging," Appl. Sci., vol. 10, no. 3, p. 980, Feb. 2020, doi: 10.3390/app10030980

[5] M. Glyavin et al. "Experimental tests of a 263 GHz gyrotron for spectroscopic applications and diagnostics ofvarious media," Rev. Sci. Instrum., vol. 86, no. 5, p. 054705, May 2015, doi: 10.1063/1.4921322[6] Т. Idehara et al., "A novel THz-band double-beam gyrotron for high-field DNP-NMR spectroscopy," Rev. Sci.
Instrum., vol. 88, no. 9, p. 094708, Sep. 2017, doi: 10.1063/1.4997994[7] R.J. Temkin, "Development of terahertz gyrotrons for spectroscopy at MIT," Terahertz Sci. Technol., vol. 7, no.
1, pp. 1-9, Mar. 2014, doi: 10.11906/TST.001-009.2014.03.01[8] M. Blank, P. Borchard, S. Cauffman, and K. Felch, "Demonstration of a 593 GHz Gyrotron for DNP," 2018
43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Nagoya, 2018, pp.
1-2, doi: 10.1109/IRMMW-THz.2018.8510010.
[9] T. Idehara and S. Sabchevski, "Development and Application of Gyrotrons at FIR UF," IEEE Trans. Plasma
Sci., vol. 46, no. 7, pp. 2452-2459, Jul. 2018, doi: 10.1109/TPS.2017.2775678[10] Yu.K. Kalynov, V.N. Manuilov, A. Sh. Fiks, and N. A. Zavolskiy, "Powerful continuous-wave sub-terahertz electron maser
operating at the 3rd cyclotron harmonic," Appl. Phys. Lett., vol. 114, no. 21, p. 213502, May 2019, doi:
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[11] M.Yu. Glyavin, A.G. Luchinin, V.N.Manuilov, G.S.Nusinovich. "Design of a subterahertz, third-harmonic,
continuous-wave gyrotron IEEE Trans. Plasma Sci., vol. 36, no. 3, pp. 591-596, (2008) DOI:
10.1109/TPS.2008.917530[12] Visit: http://www.nanotechsys.com/applications/application-reports/[13] V.E. Zapevalov and O.V. Malygin, "Diffractional quality factor of conical gyrotron resonators," (in Russian),Izv. Vyssh. Uchebn. Zaved., Radiofiz., vol. 26, no. 7, pp. 903-905, 1983.
[14] L.A. Weinstein, "Open Resonators and Open Waveguides," Golem Press, 1969[15] S.N. Vlasov, G.M. Zhislin, I.M. Orlova, M.I. Petelin, and G.G. Rogacheva, "Irregular waveguides as open
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Quant. Electron., vol. 24, no. 12, pp. 1030–1034, Dec. 1981. https://doi.org/10.1007/BF01034314[17] G.F. Brand, "Design of a new cavity for a low-power tunable gyrotron," Int. J. Infr. Millim. Waves, vol. 17, no.
4, pp. 711–719, Apr. 1996, doi: 10.1007/BF02088366[18] G.G. Denisov et al., "Design and Test of 253/527 GHz Gyrotron for Spectroscopy Applications," 2019 44th
International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Paris, France, 2019, pp.
1-3, doi: 10.1109/IRMMW-THz.2019.8874359.
[19] M. Glyavin et al., "Peculiarities of Optimizing the Subsystems of a Continuous-Wave Gyrotron with a
Generation Frequency of 0.26 THz at the Fundamental Cyclotron Resonance," Radiophys. Quant. Electron., vol.
58, no 9, pp. 649–659, Mar. 2016, doi: 10.1007/s11141-016-9637-2[20] M.A. Moiseev, L.L. Nemirovskaya, V.E. Zapevalov, and NA. Zavolsky, "Numerical simulation of modeinteraction in 170 GHz/1 MW gyrotrons for ITER," Int. J. Infr. Millim. Waves, vol. 18, no. 11, pp. 2117-2128,
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Electronics, vol. 63, no. 3, pp. 379-391, 1987, doi: 10.1080/00207218708939142

FORTHCOMING EVENTS (UPDATED ANNOUNCEMENTS)

The first International Workshop on Far-Infrared Technologies (IW-FIRT) was held in 1999 as a celebration
event for establishing FIR FU, and the second IW-FIRT was held in 2002 as a part of the Fukui University
International Congress to celebrate the 50th anniversary of our university. The third IW-FIRT was held in 2010,
eight years after the second IW-FIRT, to commemorate the 10th anniversary of the foundation of FIR UF. The
fourth, fifth, and sixth IW-FIRT were held in 2012, 2014, 2017, and 2019, successively, every few years. In
these workshops it was aimed to discuss the recent developments and future directions of far-infrared andterahertz science and technologies with a special emphasis on high power radiation sources in this frequency
region and their applications. We feel that it is the time to organize the next IW-FIRT to update our knowledge
and understanding in this rapidly developing field. Therefore, we organize the 8th International Workshop on
Far-Infrared Technologies (IW-FIRT 2021).
List of the invited speakers (in alphabetical order of family names):
Mitsuru Akaki (Kobe Univ., Japan)
Mikhail Yu. Glyavin (Institute of Applied Physics, RAS, Russia)
Masahiko Harata (Tohoku Univ., Japan)
Masaki Horitani (Saga Univ., Japan)
Iwao Hosako (NICT, Japan)
John Jelonnek (Karlsruhe Institute of Technology, Germany)
Takayasu Kawasaki (Tokyo Univ. of Science, Japan)
Setsuko Komatsu (Fukui Univ. of Technology, Japan)
Alexei Kuleshov (O. Ya. Usikov Institute for Radiophysics and Electronics of NAS of Ukraine, Ukraine)
Sergey Morozov (Institute of Applied Physics, RAS, Russia)
Yukihiro Ozaki (Kwansei Gakuin Univ., Japan)
Svilen Sabchevski (Institute of Electronics of BAS, Bulgaria)
Harumi Sato (Kobe Univ., Japan)
Hideyuki Takahashi (Kobe Univ., Japan)
Keisuke Tominaga (Kobe Univ., Japan)
Inna Tupaeva (Southern Federal Univ., Russia)
Shota Yamazaki (RIKEN, Japan)
Takeshi Yasui (Tokushima Univ., Japan)
Irina Zotova (Institute of Applied Physics, RAS, Russia)
In view of the pandemic of COVID-19 the Workshop will be held on 8 and 9 March 2021 online via
Zoom. For more detail please visit the website of the Workshop.

Announcement by the organizers: “We regret to inform you that because of the significant health risks andtransportation disruptions associated with the COVID-19 pandemic we are forced to postpone the 11th
International Workshop “Strong Microwaves and Terahertz Waves: Sources and Applications” until
summer 2021.
We will inform you about the planned dates for the Workshop as soon as they are available. Please visit thewebsite of the Workshop.
Thank you for your interest in our Workshop and hope to see all of you in Nizhny Novgorod next summer.”

The twenty-second International Vacuum Electronics Conference, IVEC 2021

The twenty-second International Vacuum Electronics Conference, IVEC 2021, organized and sponsored by theEuropean Space Agency (ESA) with the technical co-sponsorship of the IEEE Electron Devices Society (EDS).
The conference will be held virtually on 27 to 30 April 2021. For up-to-date information, please visit theconference website.

ICHPMT 2021: 15. International Conference on High Power Microwave Technologies
April 22-23, 2021 in Tokyo, JapanFor up-to-date information, please visit the conference website.

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.

CMTT 2021: 15. International Conference on Microwave and Terahertz Technology
June 03-04, 2021 in New York, United States

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

SPECIAL JOURNAL ISSUES IN THE FIELD OF THZ SCIENCESpecial Issue "Design, Technologies and Applications of High Power Vacuum Electronic Devices fromMicrowave to THz Band". For more detail, please follow the link.

Special Issue "Terahertz Optical Elements: Science and Technology". For more detail, 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 2020, i.e. after issuing the previous Newsletter#16. 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
M. Glyavin, V. Manuilov, E. Taradaev, G. Sominskii, A. Fokin, A. Sedov, “Design of a pulsed 0.5 THz
gyrotron and preliminary test of its electron gun with field emitter,” Infrared Physics & Technology, vol. 111(2020) 103480. DOI:10.1016/j.infrared.2020.103480.
http://www.sciencedirect.com/science/article/pii/S1350449520305284
R.L. Lapin, V. A. Skalyga, I.V. Izotov, S.V. Golubev, et al, “Efficiency investigation of a negative hydrogenion beam production with the use of the gasdynamic ECR plasma source,” J. Phys.: Conf. Ser., vol. 1647
(2020) 012012. DOI: 10.1088/1742-6596/1647/1/012012.
https://iopscience.iop.org/article/10.1088/1742-6596/1647/1/012012
C. Wu, I.Gr. Pagonakis, S. Illy, J. Jelonnek, “Two-dimensional leapfrog scheme for trajectories of relativistic
charged particles in static axisymmetric electric and magnetic field,” Journal of Computational Physics: X,(2020). DOI:10.1016/j.jcpx.2020.100079.
http://www.sciencedirect.com/science/article/pii/S2590055220300317
Zapevalov V.E., Zuev A.S., Kuftin A.N., “Multibarel gyrotrons,” Izv. Vuz. Radiophysics, vol. 63, n. 2 (2020)
105-114. Original in Russian: Запевалов В.Е., Зуев А.С., Куфтин А.Н., “Многоствольные
гиротроны,”Известия высших учебных заведений-Радиофизика, vol. 63, n.2 (2020) 105-114.
https://elibrary.ru/item.asp?id=44019213
Savilov A.V., "Formations of a giant “running” pulse in the process of a quasi-regular amplification of a longwave signal by a slipping electron bunch," Physics of Plasmas, vol. 27, n. 10 (2020) 104502. DOI:
10.1063/5.0023299.
https://aip.scitation.org/doi/full/10.1063/5.0023299
Z.C. Ioannidis, I. Chelis, G. Gantenbein, T. Rzesnicki, J. Jelonnek, "Experimental Classification and Enhanced
Suppression of Parasitic Oscillations in Gyrotron Beam Tunnels," in IEEE Transactions on Electron Devices,(2020). DOI: 10.1109/TED.2020.3025751.
https://ieeexplore.ieee.org/document/9240993
Movshevich B.Z., Tsvetko, A.I., Glyavi M.Y. et al. “The Fast Controller of a Gyrotron Anode Voltage,”
Instrum Exp Tech, vol. 63 (2020) 830–834. DOI:10.1134/S002044122006010X.
https://link.springer.com/article/10.1134/S002044122006010X
A. Marek et al., "Extended Feedback System for Coupled Sub-THz Gyro-Devices to Provide New Regimes ofOperation," in IEEE Transactions on Electron Devices (2020) 10.1109/TED.2020.3028531.
https://ieeexplore.ieee.org/abstract/document/9229243
A. Likhachev, S. Kishko, S. Ponomarenko, E. Khutoryan, A. Kuleshov, M. Glyavin. Y. Tatematsu, S. Mitsudo,
T. Idehara, "Low-Voltage Adiabatic Magnetron Injection Gun for 400 GHz Gyrotron," 2020 IEEE Ukrainian
Microwave Week (UkrMW), Kharkiv, Ukraine, 2020, pp. 950-953.DOI: 10.1109/UkrMW49653.2020.9252629.
https://ieeexplore.ieee.org/abstract/document/9252629

A. Maksimenko, V. Shcherbinin, V. Tkachenko, "Linear Theory of Beam-Wave Interaction in Gyrotron
Cavities with Mode Conversion," 2020 IEEE Ukrainian Microwave Week (UkrMW), Kharkiv, Ukraine, 2020,
pp. 929-932. DOI:10.1109/UkrMW49653.2020.9252719.
https://ieeexplore.ieee.org/abstract/document/9252719
A.V. Vodopyanov, V.V. Kubarev, A.V. Sidorov, O.A. Shevchenko, A.P. Veselov, Y.I. Gorbachev, S.V.
Sintsov, M.E. Viktorov, M.V. Morozkin, and M.Y. Glyavin "Continuous atmospheric pressure discharges interahertz and sub-terahertz focused beams", Proc. SPIE 11582, Fourth International Conference on Terahertz
and Microwave Radiation: Generation, Detection, and Applications, 1158210 (17 November 2020).
DOI:10.1117/12.2580544.
https://tinyurl.com/y3nyhfp4
M.M. Melnikova, N.V. Grigorieva, and N.M. Ryskin "Influence of reflected or external signal on gyrotron
operation," Proc. SPIE 11582, Fourth International Conference on Terahertz and Microwave Radiation:
Generation, Detection, and Applications, 115820M (17 November 2020). DOI:10.1117/12.2580073.
https://tinyurl.com/y6jpt6elMalkin A.M., Zheleznov I.V., Sergeev A.S., Zaslavsky V.Yu., Makhalov P.B., Ginzburg N.S., “Unified quasioptical theory of short-wavelength radiation amplification by relativistic electron beams moving near the
impedance surfaces,” Physics of Plasmas, vol. 27, n. 11 (2020) 113106. DOI: 10.1063/5.0030914.
https://aip.scitation.org/doi/full/10.1063/5.0030914
Afalla J., De Los Reyes A., Cabello N.I. et al. “A modulation-doped heterostructure-based terahertz
photoconductive antenna emitter with recessed metal contacts,” Sci Rep, vol. 10, (2020) 19926.
DOI:10.1038/s41598-020-76413-7.
https://www.nature.com/articles/s41598-020-76413-7
C.-H. Tsai, T.-H. Chang, Y. Tatemstsu, Y. Yamaguchi, et al., "Reflective Gyrotron Backward-Wave Oscillator
With Piecewise Frequency Tunability," in IEEE Transactions on Electron Devices, (2020).
DOI:10.1109/TED.2020.3036323.
https://ieeexplore.ieee.org/document/9264718
A.S. Zuev, A.S. Sedov, E.S. Semenov, A.P. Fokin and M. Y. Glyavin, "Analysis of the Possibilities to Control
Diffraction Quality Factors of the Cavities of Subterahertz Gyrotrons," in IEEE Transactions on Plasma Science,
vol. 48, n. 11 (2020) 4037-4040. DOI:10.1109/TPS.2020.3025689.
https://ieeexplore.ieee.org/document/9210040
S.S. Ponomarenko, A.A. Likhachev,V.V. Stoyanova, Y.S. Kovshov, S.A. Vlasenko, S.A. Kishko, E.M.
Khutoryan, A.N Kuleshov, "Spectral Characteristics of THz CW Clinotrons," in IEEE Transactions on Electron
Devices, vol. 67, n. 12 (2020) 5766-5770. DOI:10.1109/TED.2020.3032940.
https://ieeexplore.ieee.org/document/9248643
M. Glyavin, V. Manuilov, E. Taradaev, G. Sominskii, A. Fokin, A. Sedov, “Design of a pulsed 0.5 THz
gyrotron and preliminary test of its electron gun with field emitter,” Infrared Physics & Technology, vol. 111(2020) 103480. DOI:10.1016/j.infrared.2020.103480.
http://www.sciencedirect.com/science/article/pii/S1350449520305284
Rozental R., Samsonov S., Glyavin M., Bogdashov A., "CW Multifrequency K-Band Source Based on a
Helical-Waveguide Gyro-TWT with Delayed Feedback," in IEEE Transactions on Electron Devices, (2020).
DOI:10.1109/TED.2020.3036331.
https://ieeexplore.ieee.org/document/9263371
Krier L., Pagonakis I.Gr., Avramidis K.A., Gantenbein G., Illy, S., Jelonnek J., Jin J., Laqua H.P., Marek A.,
Moseev D., Thumm M., “Theoretical investigation on possible operation of a 140 GHz 1 MW gyrotron at 175

GHz for CTS plasma diagnostics at W7-X,” Physics of Plasmas, vol. 27, n. 11 (2020) 113107. DOI:
10.1063/5.0022151.
https://aip.scitation.org/doi/full/10.1063/5.0022151
O.I. Louksha, P.A. Trofimov, V.N. Manuilov, M.Yu. Glyavin, “Multistage Depressed Collector with Azimuthal
Magnetic Field for the DEMO Prototype Gyrotron,”Springer Proceedings in Physics, (2021). DOI:
10.1007/978-3-030-58868-7_2.
https://link.springer.com/chapter/10.1007%2F978-3-030-58868-7_2
A.A. Bogdashov and S.V. Samsonov, "Cold-Test of Transverse Input-Output Microwave Circuit Components
for a High-Power W-Band Gyro-TWT," in IEEE Electron Device Letters, (2020). DOI:
10.1109/LED.2020.3039802.
https://ieeexplore.ieee.org/abstract/document/9269425
S. Adya, S. Yuvaraj, S. Karmakar, M.V. Kartikeyan and M.K. Thumm, "Investigations on W-Band Second
Harmonic Gyrotron for 50/100-kW Operation," in IEEE Transactions on Plasma Science, doi:
10.1109/TPS.2020.3033316.
https://ieeexplore.ieee.org/abstract/document/9250691
K. Singhal, N. Gurjar, S. Jain, Vishant, A. Abhishek, A.V. Starodubov, N.M. Ryskin, et al., "Analysis of
Hollow Cathode Aperture Wall Profile on Pseudospark Discharge-Based Sheet Electron Beam Source," inIEEE Transactions on Plasma Science, (2020). DOI:10.1109/TPS.2020.3040593.
https://ieeexplore.ieee.org/document/9288708
R.A. Torgashov et al., "Investigations on High-Current-Density Sheet-Beam Driven V-Band Slow Wave
Oscillator with a Hollow Cathode," in IEEE Transactions on Plasma Science, (2020).
DOI:10.1109/TPS.2020.3040913.
https://ieeexplore.ieee.org/document/9288998
Manuilov V.N., Fedotov A.E., Zotova I.V.,. Rozental R.M, Idehara T., Mitsudo S., Glyavin M.Yu.,“Magnetron-Injection Gun with Increased Current for Frequency Tunable Medium Power Sub-THz Gyrotron,”J
Infrared Milli Terahz Waves, vol. 41 (2020) 1488–1497. DOI:10.1007/s10762-020-00746-7.
https://link.springer.com/article/10.1007/s10762-020-00746-7
N.S. Akhmadullina et al., “Plasma-chemical processes in the mixtures “metal-organic compound” and “metalinorganic salt” initiated by pulse radiation of gyrotron, J. Phys.: Conf. Ser., vol. 1686 (2020) 012012. DOI:
10.1088/1742-6596/1686/1/012012.
https://iopscience.iop.org/article/10.1088/1742-6596/1686/1/012012/meta
Artem’ev, K.V., Batanov, G.M., Berezhetskaya, N.K. et al., “Features of a Supersonic Ionization Wave in
Argon at Atmospheric Pressure in a Sub-Threshold Microwave Field,” Plasma Phys. Rep., vol. 46 (2020)
1220–1226. DOI:10.1134/S1063780X20120016.
https://link.springer.com/article/10.1134/S1063780X20120016
Z.C. Ioannidis, I. Chelis, G. Gantenbein, T. Rzesnicki and J. Jelonnek, "Experimental Classification andEnhanced Suppression of Parasitic Oscillations in Gyrotron Beam Tunnels," in IEEE Transactions on Electron
Devices, vol. 67, no. 12 (2020) 5783-5789. DOI:10.1109/TED.2020.3025751.
https://ieeexplore.ieee.org/document/9240993
I.V. Bandurkin, G.I. Kalynova, Y.K. Kalynov, I.V. Osharin, A.V. Savilov and D.Y. Shchegolkov, "ModeSelective Azimuthally Asymmetric Cavity for Terahertz Gyrotrons," in IEEE Transactions on Electron Devices,
vol. 68, n. 1 (2020) 347-352. DOI:10.1109/TED.2020.3039209.
https://ieeexplore.ieee.org/document/9286850

Oparina Yu.S., Bratman V.L., Lurie Yu., Savilov A.V., “Efficiency enhancement of THz radiation from anelectron bunch in a waveguide due to low-frequency stabilization,” Journal of Physics: Conference Series, vol.
1697 (2020) 012058. DOI: 10.1088/1742-6596/1697/1/012058.
https://iopscience.iop.org/article/10.1088/1742-6596/1697/1/012058
I.V. Bandurkin, Yu.K. Kalynov, D.D. Krygina, I.V. Osharin, A.V. Savilov, and N.A. Zavolsky "High-harmoniclarge-orbit gyrotrons for physical applications", Proc. SPIE 11582, Fourth International Conference on
Terahertz
andMicrowave
Radiation:
Generation,
Detection,andApplications,(2020).
DOI:10.1117/12.2579873.
https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11582/2579873/High-harmonic-large-orbitgyrotrons-for-physical-applications/10.1117/12.2579873.short?SSO=1
I.V. Bandurkin G.I. Kalynova, Y.K. Kalynov, I.V. Osharin, A.V. Savilov, D.Y. Shchegolkov, "Mode Selective
Azimuthally Asymmetric Cavity for Terahertz Gyrotrons," in IEEE Transactions on Electron Devices, vol. 68,
n. 1 (2020) 347-352. DOI:10.1109/TED.2020.3039209.
https://ieeexplore.ieee.org/abstract/document/9286850
Lurie Yu., Bratman V.L., “Injection of a short electron bunch into THz radiation section with an undulator andstrong guiding magnetic fields,” Physics of Plasmas,vol. 28, n. 1 (2021) 013101. DOI:10.1063/5.0030647.
https://aip.scitation.org/doi/10.1063/5.0030647
Bakunin V.L., Denisov G.G., Novozhilova, Y.V., “Influence of an External Signal with Harmonic or StepwiseModulated Parameters on the High-Power Gyrotron Operation,” Journal of Infrared, Millimeter, and Terahertz
Waves (2021). DOI:10.1007/s10762-020-00758-3.
Shcherbinin V.I., Avramidis K.A., Thumm M. et al. “Mode Discrimination by Lossy Dielectric Rods in
Cavities of Second-Harmonic Gyrotrons,” Journal of Infrared, Millimeter, and Terahertz Waves, (2021).
DOI:10.1007/s10762-020-00760-9.
https://link.springer.com/article/10.1007%2Fs10762-020-00760-9
Haas D., Thumm M., Jelonnek J., “Broadband Rotary Joint Concept for High-Power Radar Applications,”
Journal of Infrared, Millimeter, and Terahertz Waves, (2021). DOI:10.1007/s10762-020-00766-3.
https://link.springer.com/article/10.1007/s10762-020-00766-3
A.G. Litvak, G.G. Denisov and M.Y. Glyavin, "Russian Gyrotrons: Achievements and Trends," in IEEE
Journal of Microwaves, vol. 1, n. 1 (2021) 260-268. DOI:10.1109/JMW.2020.3030917.
https://ieeexplore.ieee.org/document/9318737
Ginzburg N.S., Yurovskiy L.A., Nazarovsky A.V. et al., “Generation of Terahertz Superradiance Pulses under
Stimulated Scattering of Laser Radiation by an Associated High-Current Relativistic Electron Beam,” Tech.
Phys. Lett., vol. 46 (2020) 1162–1166. DOI:10.1134/S106378502012006.
https://link.springer.com/article/10.1134/S1063785020120068
Takahashi H., Ishikawa Y., Okamoto T., Hachiya D., Dono K., Hayashi K., Asano T., Mitsudo S., Ohmichi E.,
Ohta H., “Force detection of high-frequency electron spin resonance near room temperature using high-power
millimeter-wave source gyrotron,” Applied Physics Letters, vol 118, n. 2 (2021) 022407. DOI:
10.1063/5.0036800.
https://aip.scitation.org/doi/full/10.1063/5.0036800
L. A. Yurovskiy et al., "Production of Multi-Gigawatt Sub-Nanosecond Microwave Pulses by the Method of
Chirped-Pulse-Amplification," in IEEE Electron Device Letters, (2021). DOI:10.1109/LED.2021.3053131.
https://ieeexplore.ieee.org/document/9328855

Ryskin N.M., et al., “Development of microfabricated planar slow-wave structures on dielectric substrates forminiaturized millimeter-band traveling-wave tubes,” Journal of Vacuum Science & Technology B, vol. 39, n. 1
(2021) 013204. DOI:10.1116/6.0000716.
https://avs.scitation.org/doi/10.1116/6.0000716
A.A. Dubinov, V.V. Rumyantsev, V.I. Gavrilenko, and S.V. Morozov "InP-based waveguide frequency doubler
for subterahertz-range radiation sources," Optical Engineering, vol. 60, n. 8 (2021) 082014.
DOI:10.1117/1.OE.60.8.082014.
https://tinyurl.com/y6nyvfh7
V.Y. Zaslavsky, I. Zheleznov, N. Ginzburg, I. Zotova, A. Malkin, A. Sergeev, "Frequency Multiplication in
Planar Gyrotrons as a Method for Production of High-Power Multi-THz Radiation," in IEEE Transactions on
Electron Devices, (2021). DOI:10.1109/TED.2020.3049108.
https://ieeexplore.ieee.org/document/9329150
Melnikova M.M., Tyshkun A.V., Ryskin, N.M., “Theoretical Analysis of Frequency Stabilization and Pulling
Effects in a Gyrotron with Delayed Reflection,” J Infrared, Millimeter, and Terahertz Waves (2021).
DOI:10.1007/s10762-021-00768-9.
https://link.springer.com/article/10.1007/s10762-021-00768-9
Maya Mizuno, Hideaki Kitahara, Kensuke Sasaki, Masahiko Tani, Masami Kojima, Yukihisa Suzuki, Takafumi
Tasaki, Y. Tatematsu, Masafumi Fukunari, and Kanako Wake “Dielectric property measurements of corneal
tissues for computational dosimetry of eye in terahertz band,” Biomedical Optics Express, (2021).
DOI:10.1364/BOE.412769.
https://www.osapublishing.org/boe/abstract.cfm?doi=10.1364/BOE.412769
G. Aiello, K.A. Avramidis, G. Gantenbein, J. Jelonnek, J. Jin, H.P. Laqua, A. Meier, T. Scherer, D. Strauss, M.
Thumm, “Design verification of the gyrotron diamond output window for the upgrade of the ECRH system at
W7-X,” Fusion Engineering and Design, vol. 165 (2021). DOI:10.1016/j.fusengdes.2021.112262.
http://www.sciencedirect.com/science/article/pii/S0920379621000387
B. Publications by other authors worldwide
V. Kumar, “Technology, Development Status and Applications of the Short Pulses Gyrotron Travelling Wave
Tube,” International Journal of Engineering Applied Sciences and Technology, vol. 5, n. 4 (2020) 571-578.
https://tinyurl.com/y2bfvz3o
Ohmichi E., Okamoto T., Takahashi H. et al. “Mechanically Detected Terahertz Electron Spin Resonance,”
Appl Magn Reson (2020)DOI:10.1007/s00723-020-01279-x.
https://link.springer.com/article/10.1007/s00723-020-01279-x
Rosenzweig G., Jawla S.K., Picard J.F. et al., “Phase Measurements of a 140-GHz Confocal Gyro-Amplifier,” J
Infrared, Millimeter and Terahertz Waves, (2020). DOI:10.1007/s10762-020-00751-w.
https://link.springer.com/article/10.1007/s10762-020-00751-w
Zhang Ch., Xu P., Jiang X., “Vortex electron generated by microwave photon with orbital angular momentum
in a magnetic field,” AIP Advances, vol.10, n. 10 (2020) 105230. DOI:10.1063/5.0019899.
https://aip.scitation.org/doi/full/10.1063/5.0019899
Pikin A., Pahl H., Wenander F., “Method of controlling the cyclotron motion of electron beams with anonadiabatic magnetic field,” Phys. Rev. Accel. Beams, vol.23, n. 10 (2020) 103502.
DOI:10.1103/PhysRevAccelBeams.23.103502.
https://link.aps.org/doi/10.1103/PhysRevAccelBeams.23.103502

Shah M., Patel A., Prajapati C., Sathyanarayan K., Chaudhuri P., “Thermal management and simulation studies
of a 200 ‐ kW calorimetric dummy load for HE11 mode at 42 GHz,”Heat Transfer, (2020) 1– 14.
DOI:0.1002/htj.21988.
https://onlinelibrary.wiley.com/doi/abs/10.1002/htj.21988
N. Nayek, M. K. Joshi, R. K. Sonkar, T. Tiwari, R. Bhattacharjee, "Design and Efficiency Enhancement of a
Ka-BandIndustrial
Gyrotron,"inIEEE
Transactionson
PlasmaScience,(2020).
DOI:10.1109/TPS.2020.3026696.
https://ieeexplore.ieee.org/abstract/document/9216046
D. Zhang, C. An, J. Zhang, H. Zhong, J. Gao, S. Li, "Suppression of the Parasitic Oscillations in an X-Band
Relativistic Coaxial Gyrotron Driven by an Intense Beam Current," in IEEE Transactions on Electron Devices,(2020). D)I:10.1109/TED.2020.3030560.
https://ieeexplore.ieee.org/abstract/document/9240964
H. P. Freund, R. L. Ives, W. D. Sessions, "High-Efficiency Inductive Output Tubes Using a Third Harmonic
Drive on the Grid," in IEEE Transactions on Plasma Science, (2020). DOI:10.1109/TPS.2020.3027202.
https://ieeexplore.ieee.org/abstract/document/9216509
M.V. Swati, G.S. Baghel, "Systematic Design Study of the Elliptical Sheet Beam Electron Gun for Terahertz
TWT Applications," in IEEE Transactions on Plasma Science, (2020). DOI:10.1109/TPS.2020.3027292.
https://ieeexplore.ieee.org/abstract/document/9222100
Dankov P.I., “Experimental Characterization of Positive and Negative Dielectric Constants and Artificial
Anisotropy of Meta-materials in the Microwave Range,” Journal of Physics: Conference Series, vol. 1598, n. 1
(2020) 012002. DOI: 10.1088/1742-6596/1598/1/012002.
https://iopscience.iop.org/article/10.1088/1742-6596/1598/1/012002
R. K. Singh, V. Kumar, H. Singh and A. Chandel, "Beam-Wave Interaction in a Gyro-Travelling Wave Tube
Amplifier," 2020 IEEE International Conference on Computing, Power and Communication Technologies(GUCON), Greater Noida, India, 2020, pp. 494-497. DOI: 10.1109/GUCON48875.2020.9231096.
https://ieeexplore.ieee.org/abstract/document/9231096
A. Lopez, R. Reid and J. E. Foster, "Stability Boundaries of Discharges Generated in the Focal Region of a CW
Microwave Beam," in IEEE Transactions on Plasma Science, (2020). DOI:10.1109/TPS.2020.3026244.
https://ieeexplore.ieee.org/abstract/document/9211798
Bian H.-Q., Du C.-H., Pan S., Liu P.-K., “Design and analysis of a broadband quasi-optical mode converterwith a Denisov launcher,” Hongwai Yu Haomibo Xuebao/Journal of Infrared and Millimeter Waves (Open
Access) vol. 39, n. 5 (2020) 567-575. DOI: 10.11972/j.issn.1001-9014.2020.05.006.
http://journal.sitp.ac.cn/hwyhmb/hwyhmben/ch/reader/download_pdf.aspx?file_no=2019398&year_id=2020&q
uarter_id=5&falg=1
Arzhannikov A.V., Ivanov I.A., Kalinin P.V., Kasatov A.A., Makarov M.A., Mekler K.I., Rovenskikh A.F.,
Samtsov D.A., Sandalov E.S., Sinitsky S.L., “Creation of plasma column with different density gradients togenerate terahertz radiation during beam-plasma interaction,” Journal of Physics: Conference Series, vol. 1647
(2020) 012011. DOI:10.1088/1742-6596/1647/1/012011
https://iopscience.iop.org/article/10.1088/1742-6596/1647/1/012011
Y.-h. Liu et al., "Design and Experiment on a 95-GHz 400 kW-Level Gyrotron," in IEEE Transactions on
Electron Devices, doi: 10.1109/TED.2020.3036324.
https://ieeexplore.ieee.org/abstract/document/9263332

Vishal Kesari, Sudhakar R., R. Seshadri, “Thermal management of a quasi-optical mirror in a millimetre-wave
gyrotron,” Fusion Engineering and Design, (2020) 112129. DOI:10.1016/j.fusengdes.2020.112129.
http://www.sciencedirect.com/science/article/pii/S0920379620306773
Mingyue Li, Wei Xu, Yongchao Su, “Solid-state NMR Spectroscopy in Pharmaceutical Sciences,” TrAC
Trends in Analytical Chemistry, (2020) 116152. DOI:10.1016/j.trac.2020.116152.
http://www.sciencedirect.com/science/article/pii/S0165993620303812
N. Shinohara, "Trends in Wireless Power Transfer: WPT Technology for Energy Harvesting, MllimeterWave/THz Rectennas, MIMO-WPT, and Advances in Near-Field WPT Applications," in IEEE Microwave
Magazine, vol. 22, n. 1 (2021) 46-59. DOI:10.1109/MMM.2020.3027935.
https://ieeexplore.ieee.org/abstract/document/9276646
Zhang C.X., Fu W.J., Yan Y., “Study on a gyrotron quasi-optical mode converter for terahertz imaging,”
Journal of Electromagnetic Waves, (2020). DOI:10.1080/09205071.2020.1828186.
https://www.tandfonline.com/doi/abs/10.1080/09205071.2020.1828186?journalCode=tewa20
I. Mishra, A. Bera, M.V. Kartikeyan, “Investigation of electron optical gun and beam collector for 42 GHz,
200 kW second harmonic gyrotron,” Journal of Electromagnetic Waves and Applications (2020), DOI:
10.1080/09205071.2020.1854870.
https://www.tandfonline.com/doi/abs/10.1080/09205071.2020.1854870
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Wireless Communications," in IEEE Transactions on Antennas and Propagation, (2020). DOI:
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Y. Xu et al., "Design and Experiment of a 200-kW Q-Band Gyro-TWT," in IEEE Transactions on Electron
Devices, (2020). DOI:10.1109/TED.2020.3043212.
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Siemion A., “The Magic of Optics—An Overview of Recent Advanced Terahertz Diffractive Optical Elements,”
Sensors, vol. 21, n. 1 (2020) 100. DOI: 10.3390/s21010100.
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Yurovskiy L.A., Zotova I.V., Abubakirov E.B., Rozental R.M., Sergeev A,S., Ginzburg N.S., “Generation ofultra-powerful microwave pulses in stretcher-amplifier-compressor systems,” Zhurnal Radioelektroniki Journal of Radio Electronics, n.12 (2020). DOI:10.30898/1684-1719.2020.12.21.
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Dattoli G., Di Palma E., Licciardi S., Sabia E., “Free Electron Laser High Gain Equation and Harmonic
Generation,” Applied Sciences, vol. 11, n. 1 (2020) 85. DOI:10.3390/app11010085.
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I. Lee, A. Sawant and E. Choi, "High-Directivity Orbital Angular Momentum Antenna for Millimeter-Wave
Wireless Communications," in IEEE Transactions on Antennas and Propagation, (2020). DOI:
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F. -H. Li et al., "Development of a 1-THz 4th-Harmonic Gyrotron," 2020 13th UK-Europe-China Workshop on
Millimetre-Waves and Terahertz Technologies (UCMMT), Tianjin, China, 2020, pp. 1-2, DOI:
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S.-Q. Li et al., "Terahertz harmonic gyrotron based on spoof surface plasmon," 2020 13th UK-Europe-China
Workshop on Millimetre-Waves and Terahertz Technologies (UCMMT), Tianjin, China, 2020, pp. 1-3, DOI:
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https://ieeexplore.ieee.org/abstract/document/9296010
Vishal Kesari, Sudhakar R., R. Seshadri, “Thermal management of a quasi-optical mirror in a millimetre-wave
gyrotron,” Fusion Engineering and Design, vol. 162(2021) 12129. DOI:10.1016/j.fusengdes.2020.112129.
http://www.sciencedirect.com/science/article/pii/S0920379620306773
Patel A., Bhatt P., Mahant K., Vala A. D., Chaudhari J., Mewada H., Sathyanarayan K., “Quasi-Optic Based
HE11 Miter Bend at 42 GHz for ECRH Application,” Progress In Electromagnetics Research, vol. 108 (2021)
37-48. DOI: 10.2528/PIERC20103004.
http://www.jpier.org/PIERC/pierc108/04.20103004.pdf
M. Ota, K. Kan, S. Komada, Y. Arikawa, T. Shimizu, V.K. Mag-usara, Y. Sakawa, T. Matsui, M. Nakajima,“Longitudinal and transverse spatial beam profile measurement of relativistic electron bunch by electro-optic
sampling,” Applied Physics Express, (2021). DOI:10.35848/1882-0786/abd867.
http://iopscience.iop.org/article/10.35848/1882-0786/abd867

E.F. Plinski, “Gorky’s Gyrotron Heroes,” Bulletin of the Polish Academy of Sciences: Technical Sciences, vol.
68, n. 6 (2020) 1257. DOI:10.24425/bpasts.2020.135392.
http://journals.pan.pl/dlibra/publication/135392/edition/118370/content
Lu D., Fu W., Guan X. et al. “Study on a Depressed Collector for a 75 GHz Low-Voltage Compact Gyrotron
for Industrial Application,” J Infrared Milli Terahz Waves (2021). DOI:10.1007/s10762-020-00761-8.
https://link.springer.com/article/10.1007/s10762-020-00761-8
K. Tabata, H. Britz, K. Komurasaki, R. Kawashima, H. Koizumi, “Spatial and Temporal Non-Equilibrium ofMillimeter-Wave Discharge Plasma in Microwave Rocket,” AIAA Scitech, (2021). DOI: 10.2514/6.2021-1907.
https://arc.aiaa.org/doi/abs/10.2514/6.2021-1907
Jiangtao Chen, Yu Dian Lim, Yun Zhao, Jianbiao Chen, Bingjun Yang, Zhiguo Wu, and Yan Li, “Triboelectric
Nanogenerator Driven Carbon Nanotube Cathode: A Sustainable Self-Powering Electron Source,” ACS Appl.
Electron. Mater., (2021). DOI:10.1021/acsaelm.0c01029.
https://pubs.acs.org/doi/full/10.1021/acsaelm.0c01029#
X. Liao, Z. Wu, M. Wang, Y. Pu, W. Jiang and Y. Luo, "Synthesis of Broadband Oversized Smooth-Walled
Horn for High-Power Millimeter Wave," in IEEE Transactions on Microwave Theory and Techniques, vol. 68,
n. 8 (2020) 3271-3277. DOI:10.1109/TMTT.2020.2995720.
https://ieeexplore.ieee.org/document/9106768
Yang T., Guan X., Fu W., Lu D., Yuan X., Yan Y., “Investigation on 220 GHz Taper Cascaded Over-ModeCircular Waveguide TE0n Mode Converter,” Electronics, vol. 10, n. 2 (2021) 103. DOI:
10.3390/electronics10020103.
https://www.mdpi.com/2079-9292/10/2/103/pdf
J.-F. Zhu, C.-H. Du, L.-Y. Bao, Z.-W. Zhang and P. -K. Liu, "Wideband Output Brewster Window for
Terahertz TWT Amplifiers Application," in IEEE Microwave and Wireless Components Letters, DOI:
10.1109/LMWC.2020.3045527.
https://ieeexplore.ieee.org/document/9316766
Chen ZHANG, Wei WANG, Tao SONG, Jie HUANG, Yi-Chao CAO, Di-Wei LIU, Min HU, Kai-Chun
ZHANG, Zhen-Hua WU, Ren-Bin ZHONG, Tao ZHAO, Seng GONG, Sheng-Gang LIU, “Detailed
investigations on double confocal waveguide for a gyro-TWT,” Journal of Infrared and Millimeter Waves, vol.
39, n. 5 (2020) 547.
http://www.clp.ac.cn/EN/Article/OJ11923e52f5f9ea70?type=html
Lu D., Fu W., Guan X., Yang T., Zhang Ch., Chen Chi, Han M., Yan Y., "Ultra-High Velocity Ratio in
Magnetron Injection Guns for Low-Voltage Compact Gyrotrons" Electronics 9, n. 10 (2020) 1587. DOI:
10.3390/electronics9101587.
https://www.mdpi.com/2079-9292/9/10/1587
Saifutdinov A.I., Kustova E.V., “Dynamics of plasma formation and gas heating in a focused-microwave
discharge in nitrogen,” Journal of Applied Physic, vol. 129, n. 2 (2021) 023301. DOI: 10.1063/5.0031020.
https://tinyurl.com/y5zo5gp7
Yang T., Guan X., Fu W., Lu D., Zhang C., Xie J., Yuan X., Yan Y., “ Investigation on Symmetric andAsymmetric Broadband Low-Loss W-Band Pillbox Windows,” Electronics vol. 9, n. 12 (2020) 2060.
DOI:10.3390/electronics9122060.
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Chen X., Nusinovich G.S., Dumbrajs O., et al., “Shadowing of the operating mode by sidebands in gyrotrons
with diode-type electron guns,” Physics of Plasmas, vol. 28, n. 1 (2021) 013110. DOI: 10.1063/5.0036054.

https://aip.scitation.org/doi/10.1063/5.0036054
Handong Xu, Weiye Xu, Dajun Wu, Miaohui Li, Xiaojie Wang, Liyuan Zhang, John Lohr, John Doane, James
P. Anderson, Yuri A. Gorelov, Jian Wang, Yongzhong Hou, Wusong He, Tao Zhang, “ECRH system upgrade
design using dual frequency gyrotrons for EAST,” Fusion Engineering and Design, vol. 164 (2021) 112222.
DOI:10.1016/j.fusengdes.2020.112222.
http://www.sciencedirect.com/science/article/pii/S0920379620307705
Rosenzweig G., Jawla S.K., Picard J.F, Shapiro M.A., Temkin R.J., “Phase Measurements of a 140-GHz
Confocal Gyro-Amplifier,” Journal of Infrared, Millimeter, and Terahertz Waves, vol. 42, n. 1 (2021) 29-39.
DOI:10.1007/s10762-020-00751-w.
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Wang K., Xue Q., Zhang S., Zhao D., Zhang L., “Simulation of a multistage depressed collector with secondary
electron emission for a MW-class gyrotron at 170 GHz,” AIP Advance, vol. 11, n. 1 (2021) 015233. DOI:
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Fusion Science Collaborative research on electron cyclotron heating and current drive with 28 GHz high-power
gyrotron in the QUEST spherical tokamak. Purazuma, Kaku Yugo Gakkai-Shi, 96 (6), 309-316.
https://inis.iaea.org/search/search.aspx?orig_q=RN:51119188
Kutsaev S.V., Ruelas M., Goncharik V., To H., Murokh A., “Optical Spectrometer with a Pulse-to-Pulse
Resolution for Terahertz and mm-wave Signals”, Jan 2021.
https://tinyurl.com/y339ljdw
S. -T. Han, J.R. Sirigiri, H. Khatun, V. Pathania, J. Kim, "Development of a Compact W-Band Gyrotron
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A.F. Haufler, J.H. Booske, S.C. Hagness, "Microwave Sensing for Estimating Cranberry Crop Yield: A Pilot
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C Patents
Magnetic coupler for launching and receiving electromagnetic waves and methods thereof
Inventors: Bennett, Robert (Southold, NY, US); Vannucci, Giovanni (Middletown, NJ, US); Wolniansky, Peter(Ocean Grove, NJ, US); Willis III, Thomas M. (Tinton Falls, NJ, US); Barzegar, Farhad (Branchburg, NJ, US;
Gerszberg, Irwin (Kendall Park, NJ, US); Barnickel, Donald J. (Flemington, NJ, US); Henry, Paul Shala(Holmdel, NJ, US)
US Patent: 10812123
Date of publication: 10/20/2020
https://www.freepatentsonline.com/10812123.html
Microwave generation
Inventors: Mark ISKANDER, David Rowlands
US Patent: US20200358418A1
Date of publication: 11/12/2020
https://patents.google.com/patent/US20200358418A1/en
High-frequency structure of broadband gyrotron traveling wave tube
Inventors: 罗勇赵歌歌鄢然姚叶雷王建勋刘国王丽蒲友雷蒋伟吴泽威徐勇马春光Chinese Patent: CN111755300A
Date of publication: 09/10/2020
https://patents.google.com/patent/CN111755300A/en?q=gyrotron&oq=gyrotron&sort=new&page=1
Integrated EPR NMR with frequency agile gyrotron
Inventors: Barnes, Alexander B. (St. Louis, MO, US)
United States Patent 10712298
Date of publication: 14/07/2020
https://www.freepatentsonline.com/10712298.html

NEW BOOKS
Toshitaka Idehara, Svilen Petrov Sabchevski, Mikhail Glyavin, Seitaro Mitsudo, “Studies on the Gyrotrons as
Promising Radiation Sources for THz Sensing and Imaging,” Chapter 3, pp.34-58. In: New Ideas Concerning
Science and Technology Vol. 3, (Book Publisher International 2020) Ed. Essam A. Makky.
DOI:10.9734/bpi/nicst/v3. ISBN-13 (15) 978-93-90431-48-9; ISBN-13 (15) 978-93-90431-56-4.
https://bp.bookpi.org/index.php/bpi/catalog/book/349
Anatoly Belous, Handbook of Microwave and Radar Engineering, (Springer Nature, 2021). DOI:10.1007/9783-030-58699-7. Print ISBN 978-3-030-58698-0, Online ISBN 978-3-030-58699-7.
https://link.springer.com/book/10.1007/978-3-030-58699-7.
Luis Conde, An Introduction to Plasma Physics and its Space Applications, Volume 2 Basic equations andapplications (IOP Publishing Ltd 2020). DOI:10.1088/978-0-7503-3543-0. ISBN 978-0-7503-3543-0 (ebook),
ISBN 978-0-7503-3541-6 (print). Open Access:https://iopscience.iop.org/book/978-0-7503-3543-0
Hitendra K. Malik, “Terahertz Radiation and Its Detection,” In: Laser-Matter Interaction for Radiation andEnergy (CRC Press, 2021). eBook ISBN9781315396026. DOI: 10.1201/b21799.
https://www.taylorfrancis.com/chapters/terahertz-radiation-detection-hitendra-malik/10.1201/b21799-5
Hitendra K. Malik, “THz Radiation Using Gases/Plasmas,” ibid: pp 109-146. DOI:10.1201/b21799-4.
https://www.taylorfrancis.com/chapters/thz-radiation-using-gases-plasmas-hitendra-malik/10.1201/b21799-4

NEWS FROM THE NET (OUR BROADER HORIZONS)
Inaugural Issue of new open-access journal: IEEE Journal of Microwaves

The Inaugural Issue, which includes 500+ pages of quality content covering a broad swath of the microwave
field, can be accessed from IEEE Xplore now. You also can sign up for a free print copy to be direct mailed toyou on our web site. The source of this great news - MHz to THz Community (published on 12 Jan 2021)
announces that with the release of this Inaugural Issue of the IEEE Journal of Microwaves, “we christen thefirst fully-open access technical journal focused exclusively on microwaves and spanning the entire field – fromscience to invention; from theory to applications; from astronomy, chemistry, biology and physics toengineering and technology; from nanowatt to gigawatt; and from MHz to THz. In this, and future volumes, wewill be publishing high quality technical articles covering all aspects of microwave science, technology, andapplications in sub-disciplines both within, and occasionally beyond traditional engineering. We plan tobroaden our appeal and our readership by including both overview and review articles on a wide variety of
subtopics. These will both consolidate current knowledge, making it convenient for expert referrals, and serve
as a learning tool for individuals just starting out in the microwave field.”
To access the Journal, please follow the link.
The announcement of the IEEE Journal of Microwaves reads: “Microwaves both documents and celebrates theRenaissance that we are now living through in microwave technology and applications. Microwaves’ uniquespectral region spans a wavelength range of more than six decades, from 30 meters to 30 micrometers (MHzTHz). Today, microwave devices are ubiquitous. They are literally the glue that binds our social networks.
They crop up in every corner of technology. They cross disciplines as diverse as communications and cooking,and appear in devices and instruments from the millimeter-square silicon chip to the hundred-meter-squaretokamak, at power levels from nanowatts to gigawatts. They have been undergoing continuous development foralmost one-and-one half centuries, and now they infiltrate almost every aspect of our lives – unseen, unheard,
often unnoticed. No longer! This journal is both a celebration of the successful integration of microwave
technology into our world, and a call to arms. Microwave engineering needs converts. Microwave engineering
is not dull. All the discoveries in microwave engineering were not made in the 1950’s. On the contrary, we areon a growth trajectory that surpasses anything we could have imagined even ten years ago, and this expansion
will continue well into the next decade. Over the foreseeable future, this journal will help to highlight thescience, the technology, the applications, and the accomplishments of researchers in the microwave field.
Microwaves strives to be a technical journal of the highest possible caliber, showcasing contributed andrigorously peer-reviewed papers that span the wide range of disciplines and applications that the fieldencompasses. Microwaves is also an archival teaching platform which will carry invited review articles andselected topical reports that summarize specific experimental methods, technologies, applications, andmanufacturing techniques that our renowned editors feel are essential reading for everyone in our discipline.
Microwaves will add news and opinions that are helping to shape our community and its influence on society,through contributions from both editors and authors, in order to give perspective to the science and technology
advances highlighted in the journal. Finally, Microwaves will anchor our field to the past and catapult us into
the future, with historic perspectives and biographies, and special interviews with notable scholars in several
continuously running series: Microwave Pioneers, Industry Pioneers, and Breakthroughs’ in Microwaves. The
IEEE, the Microwave Theory and Techniques Society, our contributing editors and reviewers, and especiallythis founding Editor-in-Chief, all hope that you will embrace this new model for dissemination of our collective
research work and the archiving of our accomplishments. I personally implore you to support this journal
through your contributions and your readership.
Journal of Microwaves is a model for, rather than simply a participant in, our changing future. (ISSN: 26928388, OCLC: 1163785784).”
Editor’s pick: We are glad that the Inaugural Issue of the Journal includes the following paper authored bymembers of our International Consortium:
A.G. Litvak, G.G. Denisov and M.Y. Glyavin, "Russian Gyrotrons: Achievements and Trends," in IEEE
Journal of Microwaves, vol. 1, n. 1 (2021) 260-268. DOI:10.1109/JMW.2020.3030917.
https://ieeexplore.ieee.org/document/9318737

Wakefield undulator for the generation of powerful electromagnetic radiation
Recently, Ilya Sheinman, Associate Professor of the Department of Physics of St. Petersburg Electrotechnical
University "LETI presented the project of a wakefield undulator for the generation of powerful electromagnetic
radiation in the terahertz, ultraviolet, and X-ray regions of the electromagnetic spectrum. The technology will
utilize the deviation of the particle beam from the waveguide axis, which is a negative effect in the wakefield
accelerators, arising from the interaction of the charged beam with the electromagnetic wave created by it. "Theprinciple of operation of traditional accelerators is that charged particles, moving in a circle, pass through aspecial interval in which they increase energy. Over the past 10-20 years, several fundamentally new solutions
have emerged for the design of accelerators. One of them is to place the particles in a tube filled with plasma orin a dielectric tube in a metal shell," the researcher says. "A beam of charged particles interacts with the fillingof the waveguide and creates an electromagnetic field, which is a variant of Cherenkov radiation, in which the
speed is close to the speed of light. If a small charged beam is placed in this wakefield wave, it will accelerate.
The primary beam that creates the field will lose its energy, and the secondary beam will accelerate to very highvalues."A significant disadvantage of this approach is the shift of the beam relative to the axis of the waveguide. As aresult of that, particles are attracted to the wall of a tube, which with huge energy can burn a hole in it. Ilya
Sheinman proposed to use this parasitic effect to create a wakefield undulator, a waveguide in the form of asinusoid, in which the tail of the main beam or a secondary beam of charged particles, attracted to one wall or
another, will oscillate in a transverse direction. Due to such oscillations, the electrons of the beam will movewith acceleration and generate electromagnetic waves, which is a necessary condition for creating a freeelectron laser.
Experts of the European X-Ray Free-Electron Laser Facility (European XFEL), a complex of experimental
facilities located in Hamburg, have already expressed their interest in the joint implementation of theresearcher's project.
For more information and detail, follow the source of this information on the website of ETU "LETI"

CORE: The world’s largest collection of open access research papers that offers (among
others) great collection of publications in the fields of THz science and technology that areof interest to the members of the International Consortium.
See for example the following two Editor’s picks:
Roger Lewis, “Materials for Terahertz Engineering,” In: Springer Handbook of Electronic and Photonic
Materials DOI: 10.1007/978-3-319-48933-9_55. Link to the book chapter.
Stefano Alberti, et al., “High-efficiency, long-pulse operation of MW-level dual-frequency gyrotron,
84/126GHz, for the TCV Tokamak,” DOI: 10.5445/IR/1000100042. Follow the link to the paper (post-print).

New material system to convert and generate terahertz waves
An article published recently at PhysOrg reports that a German-Spanish research team with the participation of
the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now developed a material system to generate
terahertz pulses much more effectively than before. It is based on graphene, i.e., a super-thin carbon sheet,coated with a metallic lamellar structure. Some time ago, a team of experts working on the HZDR accelerator
ELBE were able to show that graphene can act as a frequency multiplier: When the two-dimensional carbon is
irradiated with light pulses in the low terahertz frequency range, these are converted to higher frequencies. Until
now, the problem has been that extremely strong input signals, which in turn could only be produced by a fullscale particle accelerator, were required to generate such terahertz pulses efficiently. "This is obviously
impractical for future technical applications," explains the study's primary author Jan-Christoph Deinert of theInstitute of Radiation Physics at HZDR. "So, we looked for a material system that also works with a much lessviolent input, i.e., with lower field strengths." For this purpose, HZDR scientists, together with colleagues fromthe Catalan Institute of Nanoscience and Nanotechnology (ICN2), the Institute of Photonic Sciences (ICFO),
the University of Bielefeld, TU Berlin and the Mainz-based Max Planck Institute for Polymer Research, cameup with a new idea: the frequency conversion could be enhanced enormously by coating the graphene with tiny
gold lamellae, which possess a fascinating property: "They act like antennas that significantly amplify the
incoming terahertz radiation in graphene," explains project coordinator Klaas-Jan Tielrooij from ICN2. "As aresult, we get very strong fields where the graphene is exposed between the lamellae. This allows us to generate
terahertz pulses very efficiently." To test the idea, team members from ICN2 in Barcelona produced samples:First, they applied a single graphene layer to a glass carrier. On top, they vapor-deposited an ultra-thininsulating layer of aluminum oxide, followed by a lattice of gold strips. The samples were then taken to the
TELBE terahertz facility in Dresden-Rossendorf, where they were hit with light pulses in the low terahertz
range (0.3 to 0.7 THz). During this process, the experts used special detectors to analyze how effectively thegraphene coated with gold lamellae can multiply the frequency of the incident radiation.
For more details, please visit the source of this information following the link.
Journal Reference: Jan-Christoph Deinert, David Alcaraz Iranzo, Raúl Pérez, Xiaoyu Jia, Hassan A. Hafez, Igor
Ilyakov, Nilesh Awari, Min Chen, Mohammed Bawatna, Alexey N. Ponomaryov, Semyon Germanskiy, Mischa
Bonn, Frank H.L. Koppens, Dmitry Turchinovich, Michael Gensch, Sergey Kovalev, Klaas-Jan Tielrooij,“Grating-Graphene Metamaterial as a Platform for Terahertz Nonlinear Photonics,” ACS Nano, 2020; DOI:
10.1021/acsnano.0c08106.

Multiple-beam and double-mode staggered double vane travelling wave tube with ultrawide band
In a paper under the above title, published on 19 November 2020 in Scientific Reports (Open Access) the
authors present design, fabrication and cold test of an ultra-wide band travelling wave tube (TWT) with planaralignment multiple pencil beams. The fundamental double-mode of staggered double vane slow wave structure(SDV-SWS) rather than the only one mode are put forward and adopted to match with the same electron beam
to increase the bandwidth greatly. Simultaneous planar alignment multiple pencil beam tunnels are designed to
improve interaction impedance and then to enhance the output power, gain, efficiency, and growth rate. The
transmission performance of a two-stage 51-period SDV-TWT in G-band with structure attenuator between two
sections shows that it indeed has an ultra-wideband performance from 81 to 110 GHz. By using computer
numerical control machining, the SDV-SWS was manufactured and a detailed cold test was conducted. Goodagreement is found at the wide band, where S21 is above − 5 dB and S11 is below − 10 dB. 3D PIC simulations
with double-mode multiple-beam SDV-TWT within total length of 70 mm show that it can get a nearly 2120 W
peak output power, a 42.5 dB corresponding gain and a 10.7% electron efficiency at 94 GHz with a 22.1 kVbeam voltage and a 3 × 0.15 A beam current. The 3 dB bandwidth of our double-mode SDV-TWT can achieve
about 29 GHz.
Cite this article: Zhang, Z., Ruan, C., Fahad, A.K. et al. “Multiple-beam and double-mode staggered double
vane travelling wave tube with ultra-wide band,” Sci Rep 10, 20159 (2020). https://doi.org/10.1038/s41598020-77204-w.

Kenneth J Button Award for 2020
The recipient of the Button Prize for 2020 is Prof. Dr. Alfred Leitenstorfer, University of Konstanz, Germany"for establishing field-resolved technologies throughout the infrared regime and for studies of quantum
phenomena under elementary spatial-temporal confinement".