Investigation of the hollow beam structure on optical transition radiaton
The features of studying the structure of a dense annular beam with OTR from metal targets at electron energy ≤ 50 keV are described. The image of the cross section of the annular beam with sub-millimeter wall thickness is obtained.
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| Дата: | 2004 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2004
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| Цитувати: | Investigation of the hollow beam structure on optical transition radiaton / M.I. Ayzatsky, V.A. Kushnir, V.V. Mytrochenko, A. Opanasenko, V. Zhiglo, // Вопросы атомной науки и техники. — 2004. — № 2. — С. 123-125. — Бібліогр.: 6 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-793652025-02-09T20:36:13Z Investigation of the hollow beam structure on optical transition radiaton Дослідження структури кільцевого пучка за перехідним оптичним випромінюванням Исследование структуры кольцевого пучка по переходному оптическому излучению Ayzatsky, M.I. Kushnir, V.A. Mytrochenko, V.V. Opanasenko, A. Zhiglo, V. Элементы ускорителей The features of studying the structure of a dense annular beam with OTR from metal targets at electron energy ≤ 50 keV are described. The image of the cross section of the annular beam with sub-millimeter wall thickness is obtained. Описані особливості дослідження структури щільного кільцевого пучка за допомогою перехідного оптичного випромінювання з металевих мішеней при енергії електронів до 50 кеВ. Одержано зображення поперечного перерізу кільцевого пучка з товщиною стінки менше міліметра. Описаны особенности исследования структуры плотного кольцевого пучка электронов с помощью переходного оптического излучения из металлических мишеней при энергии электронов до 50 кэВ. Получено изображение поперечного сечения кольцевого пучка с толщиной стенки меньше миллиметра. Authors express gratitude to the employees of the R&D "Accelerator" for the help in experiment. 2004 Article Investigation of the hollow beam structure on optical transition radiaton / M.I. Ayzatsky, V.A. Kushnir, V.V. Mytrochenko, A. Opanasenko, V. Zhiglo, // Вопросы атомной науки и техники. — 2004. — № 2. — С. 123-125. — Бібліогр.: 6 назв. — англ. 1562-6016 PACS: 29.25.BX, 41.75.FR https://nasplib.isofts.kiev.ua/handle/123456789/79365 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Элементы ускорителей Элементы ускорителей |
| spellingShingle |
Элементы ускорителей Элементы ускорителей Ayzatsky, M.I. Kushnir, V.A. Mytrochenko, V.V. Opanasenko, A. Zhiglo, V. Investigation of the hollow beam structure on optical transition radiaton Вопросы атомной науки и техники |
| description |
The features of studying the structure of a dense annular beam with OTR from metal targets at electron energy ≤ 50 keV are described. The image of the cross section of the annular beam with sub-millimeter wall thickness is
obtained. |
| format |
Article |
| author |
Ayzatsky, M.I. Kushnir, V.A. Mytrochenko, V.V. Opanasenko, A. Zhiglo, V. |
| author_facet |
Ayzatsky, M.I. Kushnir, V.A. Mytrochenko, V.V. Opanasenko, A. Zhiglo, V. |
| author_sort |
Ayzatsky, M.I. |
| title |
Investigation of the hollow beam structure on optical transition radiaton |
| title_short |
Investigation of the hollow beam structure on optical transition radiaton |
| title_full |
Investigation of the hollow beam structure on optical transition radiaton |
| title_fullStr |
Investigation of the hollow beam structure on optical transition radiaton |
| title_full_unstemmed |
Investigation of the hollow beam structure on optical transition radiaton |
| title_sort |
investigation of the hollow beam structure on optical transition radiaton |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2004 |
| topic_facet |
Элементы ускорителей |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/79365 |
| citation_txt |
Investigation of the hollow beam structure on optical transition radiaton / M.I. Ayzatsky, V.A. Kushnir, V.V. Mytrochenko, A. Opanasenko, V. Zhiglo, // Вопросы атомной науки и техники. — 2004. — № 2. — С. 123-125. — Бібліогр.: 6 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
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| fulltext |
INVESTIGATION OF THE HOLLOW BEAM STRUCTURE
ON OPTICAL TRANSITION RADIATON
M.I. Ayzatsky, V.A. Kushnir, V.V. Mytrochenko, A. Opanasenko, V. Zhiglo
National Science Center "Kharkov Institute of Physics & Technology", Kharkiv 61108
E-mail: zhiglo@kipt.kharkov.ua
The features of studying the structure of a dense annular beam with OTR from metal targets at electron ener-
gy ≤ 50 keV are described. The image of the cross section of the annular beam with sub-millimeter wall thickness is
obtained.
PACS: 29.25.BX, 41.75.FR
1. INTRODUCTION
One of directions in development of powerful RF
sources is the development of cluster klystrons with the
annular structure of a beam [1]. Experimental study of
the stability and formation of such beams requires spa-
tial resolution of measurement of their structure less
than 0.01 mm. This requirement, at a beam power densi-
ty of about 1010 W/m2, makes usage of a conventional
probe or scintillator techniques rather complicated. Op-
tical transient radiation (OTR) from thick cooled targets
is alternative technique in this case. However, till now
OTR diagnostics was utilized, basically, for relativistic
beams under small thermal loads of targets. Application
of this technique for diagnostics of low-energy electron
beams, that began recently [2], still requires extensive
researches.
The present work describes features of studying the
structure of a dense annular beam with OTR from metal
targets at electron energy ≤50 keV. Possibility of OTR
registration in this case is limited by the two main fac-
tors. Firstly, a solenoid, which is needed to transport the
beam, limits an aperture of the optical system. Second-
ly, because of low energy of particles the total power of
the beam is dissipated in a thin surface layer of a target
that causes its thermal erosion. Necessity of carrying out
researches of transversal structure of an annular beam
arose in the context of development of a X-band cluster
klystron with an anode voltage of 50 kV [3].
2. THEORY
It is convenient to analyze a transversal structure of
a beam in the plane, which is perpendicular to the direc-
tion of beam propagation. Therefore orientation of a tar-
get was chosen perpendicularly to the beam. Further,
beams with a longitudinal energy, which essentially ex-
ceeds transverse one, will be considered. In this case it
is possible to take into account only normal incident an-
gle of electrons on the target.
Using the spectral density of the radiation energy of
a charge е crossing a boundary of a metal on a normal
[4], the OTR brightness emitted by the electron beam
with the pulse current density j is defined as:
( )
2
1/ 2
22 1/ 2
sin cos( )
cos 11 cos
ejB
c
β θ ε θθ ω
π ε θβ θ
й щ
= ∆Чк ъ
+−к ъл ы
(1)
where β = v/c is the relative velocity of an electron, θ is
the observation angle, δΩ is the solid angle in the direc-
tion of observation, ω is the circular frequency of radiat-
ed waves, ε is the relative dielectric permeability of the
metal, ∆ω = 2.018×1015 Hz is the visible part of a spec-
trum.
Proceeding from the above-mentioned goal of a
practical application of the OTR technique, we will con-
sider the radiation of an annular beam with the energy
of 50 keV, the external radius of 4 mm, the wall thick-
ness of 1 mm and the current of 10 A (j=45 A/cm2). For
this case the dependence (1) is shown in Fig.1.
0
10000
20000
30000
40000
50000
60000
0 10 20 30 40 50 60 70 80 90
Angle of observation in degrees
B
ri
g
h
tn
e
s
s
i
n
c
d
/m
2
Fig.1. The dependence of radiation brightness on the
angle of observation
This dependence can be used for calculation of an
exposition at photographing. However, for the visual re-
search of pulse beams, the correction is required. It is
connected with the inertia of visual sensation which dis-
appears gradually during a relaxation time τ
f = 0.05...0.2 s depending on the brightness. At the peri-
od of pulse repetition T << τf, the brightness of obser-
vation B(T, τ) slightly differs from its average value [5].
It can be shown that for our experimental conditions
(pulse duration of 4∙10-6 s and repetition period of 0.1 s)
the brightness of observation is 1.38∙10–4 times of that
value from (1).
3. ANALYSIS OF OPTICAL SYSTEM
As follows from Fig. 1, the maximum of radiation is
at θm = 73°. Capture of such an angle by the optical sys-
tem, without significant aberrations is impossible [5].
Therefore, the optical system directed at an angle θ ≈ θm
usually sees only a limited area around of the maximum
of radiation. Such a scheme is shown in Fig.2. In this
case the position of the target is inclined relatively to the
optical axis that causes known difficulties during trans-
fer of the three-dimensional image because of a limited
depth of focus and perspective distortions. Therefore,
the small angle θ is preferable.
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 2.
Series: Nuclear Physics Investigations (43), p.123-125. 123
mailto:zhiglo@kipt.kharkov.ua
Y
θ
U
Y
y R
f f x x0
e-
γ
θ
mirror
target
lens
θ1
θ2
photo plate
1 2
Y΄
Fig. 2. The scheme of registering OTR
The condition of sharpness of the image is given:
1tg(U)
2tg( )
Y
Yθ
∆
Ј Ч , (2)
where Y is the beam radius on the target, Y∆ is the
needed linear resolution, U is the aperture angle.
A high resolution can be obtained at a large θ only
for small U as it follows from Eq. (2). For ∆Y/Y = 0.01
and θ0 = 30°, U = 0.009°. This limitation of the system
optical power can be removed by arrangement of a re-
gistering photoplate in the plane of the image 1, as it is
shown in Fig. 2. To estimate a gain in sensitivity of
measurements, we will define luminosity of the images
in planes 1 and 2 taking into account (2) and definition:
2
0 0
1 ( , , )sin( )
U
E B u u d du
M
π
θ ϕ ϕ= т т , (3)
where u is the aperture angle of the ray, φ is the azimuth
of the ray, M is the magnification of the subject area. If
the optical axis coincides with the direction of observa-
tion then B(u,θ,φ) = B(ζ), where
cos(ζ) = cos(u) cos(θ) + cos(φ)sin(u) sin(θ).
The relation of E1/E2 at K = 3 and A = 1/5.6 is given
in Fig.3.
0
50
100
150
200
250
300
350
0 10 20 30 40 50 60
Angle of observation in degrees
E 1
/E
2
Fig.3. The simulated relation of the image luminosities
in planes 1 and 2 (see Fig.2)
Let us analyze the relationship connecting A, K and
U. The aperture angle U in Eq. (3) has the limitation
caused by the non-uniform brightness of the target
which is connected with the different angles of observa-
tion θ1, θ, θ2 of the various points on the target (see
Fig.2). Let d denotes a distance from the objective to the
target, then
1
2t ( ) t ( )
cos( )
Yg g
d
θ θ
θ
= ± . (4)
From Eq. (4) and Eq. (1) it is possible to show that
ΔB/B < 0.1 at d > 300 mm for Y = 5mm and θ = 30˚. Us-
ing the relations AK/(K+1) = R/d and R ≤ D/4, where D
is the vacuum chamber diameter, which limits transver-
sal dimension of the optical system, we obtain:
A ≤ D(K+1)/(4Kd) . (5)
The depth of focus at visual researches does not limit A,
due to focusing.
The reason of perspective distortion is dependence
K(x) = -f/x. Its value is estimated as:
0 0
sinK Y
K x
θ∆ = . (6)
Here K0 = K(x0), ΔK = K(x) - K(x0). For technical rea-
sons: f ≥ 4R [5], and R ≤ 0.25D. Therefore,
0
0 sin
K DK
K Y θ
∆
Ј Ч . (7)
It is necessary to note that the value D is less than the
diameter of the solenoid.
As follows from Eq. (4) and Eq. (7), the reduction of
the luminosity error and of the beam cross-section error
requires the reduction of θ that results in reduction of
the brightness and, hence, of the current measurement
threshold of the beam. From Eqs. (5), (7) one can see,
that small optical magnifications are necessary for re-
ducing the distortions of the image and increasing its lu-
minosity.
4. EXPERIMENTAL SETUP AND RESULTS
The special device (see Fig.4) was created for the vi-
sual examination of the electron beam generated by the
magnetron gun [3] with the error ∆Y = 0.1 mm.
Fig.4. Experimental setup: 1 - block of objective, ocular
and mirror, 2 - output window, 3 - mirror, 4 - target
The diameter D was of 140 mm. The radius of the
output optical window of 22 mm limited the optical
aperture. The distance between the target and the object-
ive d was of 548 mm. As basic elements of the optical
system the objective with the resolution in the focal
plane of 1/30 mm, A = 1/9, f = 105 mm and the ocular
with foc = 17.8 mm and θ = 30° were chosen. The calcu-
lated values were the following: K = 0.28,
ΔY = ΔY′/K = 0.12 mm, ΔY/Y = 0.024, the subjective
magnification G = f/foc = 5.9, the diameter of the output
iris δ = 2R/G = 4 mm, tg(U) = 23.3/548 = 0.024. At the
given D, from Eq. (5) it follows A = ½. It is much more
than the chosen A = 1/9. Reducing of A does not cause,
however, the loss of luminosity of the retina, but only
limits the allowable subjective magnification [5]. Such
system is inefficient at photographing because of the
loss of light exposure E ~ A2. The condition (2) was sat-
isfied, therefore, focusing was not required. As follows
from Eq. (6), ΔK/K0 is 0.15 that exceeds the required
value 0.1. As d > 300 mm, the error in the luminosity of
124
the target is less than 10%. To the obtained linear resol-
ution ΔY = 0.12 mm corresponding is the angle of view
2.7′ (at G =5.9), that is higher then the eye resolution,
but lower than the recommended value 4′ [5]. Such a
choice of G is made to preserve the subjective bright-
ness of an image.
For specified δ = 4 mm the calculated subjective lu-
minosity is 0.12 lx, that is 30% of the normal light ex-
posure of a retina [5].
The experiments have shown that a beam with the
current 10 A is easily observed. However, at decreasing
the beam current and energy down to 2 A and 25 keV,
respectively, the luminosity of the image and the resolu-
tion is deficient for correct measurements. It corre-
sponds to j = 9 A/cm2 and the beam power density of
2.2∙105 W/cm2. In this case, the calculated light expo-
sure of a retina is 5% of normal. We can state that the
above-specified beam parameters correspond to the sen-
sitivity of the device. The view of this beam in the ocu-
lar is shown in Fig.5. This image was obtained with the
digital camera and numerically corrected on the angle
θ = 30º. The elliptic form of the beam is caused by the
conditions of its formation [3].
The visual examination of the titanic and silver tar-
gets showed that the beam forms a mark with the sur-
face roughness sizes of 0.02...0.05 mm.
5. DISCUSSION
The sensitivity of the created installation is limited
by the aperture of an eye, therefore it is maximal for vi-
sual researches. The detailed description of the image
structure requires a brightness which is on the order of
magnitude greater, than the sensitivity. Therefore for the
visual OTR - diagnostics at the beam energy 50 keV the
limit of the beam density is about 45 A/cm2.
The spatial resolution is limited by dimensions of
the solenoid (see (7)), or by sizes of the free space need-
ed to contain the optical system, that can be much less
than the solenoid diameter. The obtained resolution of
0.12 mm can be improved, as follows from the technical
capabilities of solenoids, up to 0.03 mm. The threshold
power density of 2.2∙105 W/cm2 exceeds the evaporation
limit ~ 1∙105 W/cm2. Therefore, finally, the linear reso-
lution is limited by the sizes of surface protrusions
0.02...0.05 mm. As a probable decision, of interest is the
graphite target [2], though the carrying of carbon in vac-
uum requires study in this case.
Authors express gratitude to the employees of the
R&D "Accelerator" for the help in experiment.
REFERENCES
1. R.B. Palmer, R. Miller. A cluster klystron.
SLAC-PUB-4706, Sept. 1988.
2. C. Bal, E. Bravin, E. Chevallay et al. OTR from
non-relativistic electrons. CERN-AB-2003-062
BDI.
3. N.I. Ayzatsky, V.N. Boriskin, A.N. Dovbya et
al. Generation of Electron Beam in a Multicath-
ode Secondary-Emission Source // Technical
Physics, 2003, v.48, No.2, p.245–249.
4. V.L. Ginsburg, V.N. Cytovich. Transition Ra-
diation and Scattering. M.: Nauka, 1984, p.360.
5. B. Tudorovskiy. Theory of optical devices. M.,
1952, v.2, p.567.
6. V.K. Popov. Approximate calculation of modes
of a pulse beam-processing of materials // Elec-
tr. tekhnika. Ser: Electonika SVCh, 1967, v.1,
p.122–130.
ИССЛЕДОВАНИЕ СТРУКТУРЫ КОЛЬЦЕВОГО ПУЧКА
ПО ПЕРЕХОДНОМУ ОПТИЧЕСКОМУ ИЗЛУЧЕНИЮ
Н.И. Айзацкий, В.Ф. Жигло, В.А. Кушнир, В.В. Митроченко, А. Опанасенко
Описаны особенности исследования структуры плотного кольцевого пучка электронов с помощью пере-
ходного оптического излучения из металлических мишеней при энергии электронов до 50 кэВ. Получено
изображение поперечного сечения кольцевого пучка с толщиной стенки меньше миллиметра.
ДОСЛІДЖЕННЯ СТРУКТУРИ КІЛЬЦЕВОГО ПУЧКА
ЗА ПЕРЕХІДНИМ ОПТИЧНИМ ВИПРОМІНЮВАННЯМ
М.І Айзацький, В.Ф. Жигло, В.А. Кушнир, В.В. Митроченко, А. Опанасенко
Описані особливості дослідження структури щільного кільцевого пучка за допомогою перехідного
оптичного випромінювання з металевих мішеней при енергії електронів до 50 кеВ. Одержано зображення
поперечного перерізу кільцевого пучка з товщиною стінки менше міліметра.
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 2.
Series: Nuclear Physics Investigations (43), p.123-125. 125
National Science Center "Kharkov Institute of Physics & Technology", Kharkiv 61108
E-mail: zhiglo@kipt.kharkov.ua
1. INTRODUCTION
2. THEORY
3. ANALYSIS of OPTICAL SYSTEM
4. EXPERIMENTAL SETUP and RESULTS
5. DISCUSSION
REFERENCES
ДОСЛІДЖЕННЯ СТРУКТУРИ КІЛЬЦЕВОГО ПУЧКА
ЗА ПЕРЕХІДНИМ ОПТИЧНИМ ВИПРОМІНЮВАННЯМ
|