The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space
The longitudinal dynamic effect on the diocotron wave evolution was clarified. The main features of the plasma particles trapping and confining during the ‘hot’ electron beam propagation through the space of drift were studied.
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2012
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| Назва видання: | Вопросы атомной науки и техники |
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| Цитувати: | The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space / M.I. Tarasov, I.K. Tarasov, D.A. Sitnikov // Вопросы атомной науки и техники. — 2012. — № 6. — С. 90-92. — Бібліогр.: 3 назв. — англ. |
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irk-123456789-1091112016-11-21T03:02:42Z The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space Tarasov, M.I. Tarasov, I.K. Sitnikov, D.A. Фундаментальная физика плазмы The longitudinal dynamic effect on the diocotron wave evolution was clarified. The main features of the plasma particles trapping and confining during the ‘hot’ electron beam propagation through the space of drift were studied. Определена роль продольной динамики в эволюции диокотронной волны. Также были изучены основные особенности захвата и удержания частиц при прохождении «горячего» электронного потока в пространстве дрейфа. Вивчено роль поздовжньої динаміки в еволюції діокотронної хвилі. Досліджено ключові особливості захоплення та утримання частинок при проходженні «гарячого» електронного потоку в просторі дрейфу. 2012 Article The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space / M.I. Tarasov, I.K. Tarasov, D.A. Sitnikov // Вопросы атомной науки и техники. — 2012. — № 6. — С. 90-92. — Бібліогр.: 3 назв. — англ. 1562-6016 PACS: 52.27.Jt http://dspace.nbuv.gov.ua/handle/123456789/109111 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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English |
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Фундаментальная физика плазмы Фундаментальная физика плазмы |
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Фундаментальная физика плазмы Фундаментальная физика плазмы Tarasov, M.I. Tarasov, I.K. Sitnikov, D.A. The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space Вопросы атомной науки и техники |
| description |
The longitudinal dynamic effect on the diocotron wave evolution was clarified. The main features of the plasma particles trapping and confining during the ‘hot’ electron beam propagation through the space of drift were studied. |
| format |
Article |
| author |
Tarasov, M.I. Tarasov, I.K. Sitnikov, D.A. |
| author_facet |
Tarasov, M.I. Tarasov, I.K. Sitnikov, D.A. |
| author_sort |
Tarasov, M.I. |
| title |
The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space |
| title_short |
The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space |
| title_full |
The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space |
| title_fullStr |
The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space |
| title_full_unstemmed |
The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space |
| title_sort |
dynamics of 3d diocotron wave during the “hot“ electron flow propagation in the drift space |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2012 |
| topic_facet |
Фундаментальная физика плазмы |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/109111 |
| citation_txt |
The dynamics of 3D diocotron wave during the “hot“ electron flow propagation in the drift space / M.I. Tarasov, I.K. Tarasov, D.A. Sitnikov // Вопросы атомной науки и техники. — 2012. — № 6. — С. 90-92. — Бібліогр.: 3 назв. — англ. |
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Вопросы атомной науки и техники |
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| fulltext |
90 ISSN 1562-6016. ВАНТ. 2012. №6(82)
THE DYNAMICS OF 3D DIOCOTRON WAVE DURING THE “HOT“ ELECTRON
FLOW PROPAGATION IN THE DRIFT SPACE
M.I. Tarasov, I.K. Tarasov, D.A. Sitnikov
Institute of Plasma Physics National Science Center “Kharkov Institute of Physics and
Technology”, Kharkov, Ukraine
E-mail: itarasov@ipp.kharkov.ua
The longitudinal dynamic effect on the diocotron wave evolution was clarified. The main features of the plasma
particles trapping and confining during the ‘hot’ electron beam propagation through the space of drift were studied.
PACS: 52.27.Jt
INTRODUCTION
A huge amount of publications were dedicated to
charged particles confinement in a cylindrical Penning
trap. Such systems allowed to observe and to study a
number of interesting effects in the plasma column
dynamics. Unfortunately Penning traps weren’t so
useful in studying the effects developed during the
charged particles flow propagation along the magnetic
field axis. For these investigations we have used a
cylindrical setup without the axial confining field. In
our case the width of the flow particles distribution by
longitudinal velocities is close by its magnitude to the
average longitudinal velocity. The experimental results
have shown the diocotron instability development [1].
The diocotron waves had pronounced azimuthal and
longitudinal components. It was also detected that the
instability development is localized in the potential dip
which is created by the flow particles spatial charge.
1. EXPERIMENTAL SETUP
The electron flow passed through the cylindrical drift
tube in longitudinal magnetic field (H = 890…2100 Oe)
from the indirectly heated injector cathode to the
particles collector (Fig. 1). The injection was carried out
by applying a negative potential pulse (injection pulse)
to the cathode.
Injection pulse
Entrance grid Exit grid
Capacity
probe
Capacity
probe
Electrostatic
Langmuir
probe
Vacuum
chamber
Particles
collector
Magnetic
field coils
Fig. 1. The schematic of experimental setup
The flow current is measured by metal grid installed
at the drift tube entrance and particles collector placed
at the system end. The diocotron oscillations are studied
by a couple of capacitive probes and mobile Langmuir
probe. The entrance diafragm was present only during
the experiments with the hollow cylyndrical electron
flow.
2. EXPERIMENTAL RESULTS
In both types of the flow radial profile (cylindrical
and tubular) the generation of low-frequency diocotron
oscillations was observed.
The width of the electron distribution by longitudinal
motion energies was equal by the order of magnitude to
the average kinetic energy of the flow longitudinal
motion. The distribution had two maxima corresponded
to electron energy Ee ≈ 15 eV and Ee ≈ 30 eV.
The spatial distribution of electrostatic potential also
exhibited two maxima under condition of high enough
injection current. In the case of tubular profile the
potential measurements were averaged by duration of
the injection pulse. The electron flow was shaped as a
hollow tube. The measurements of the flow current
distribution have shown formation of so called ‘reverse
flow’ at both external and internal edges of the electron
tube (Fig.2).
0.6 1.2 1.8 2.4-0.6-1.2-1.8-2.4
I (A.U.)
20
40
direct flow
reverse flow reverse flow
direct flow
r (cm)
Thus one could conclude that the particles at the flow
edges have the lowest energies of the longitudinal
motion. So the potential barrier formed at the electron
tube edges. Such a barrier creates a reflecting
electrostatic potential which decelerates the flow
particles and finally forms the reflected ‘reverse flow’.
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.80.0
I
(2
m
A
)
π
t (ms)
Fig. 3. The dynamics of diocotron oscillations observed
by the capacity probes
Fig. 2. The flow intensity radial
ISSN 1562-6016. ВАНТ. 2012. №6(82) 91
The potential barrier obviously formed as the result
of influence of the electron tube spatial charge electric
field on the slowest part of the flow particles.
So called diocotron oscillations represent an
azimuthal motion of non-symmetric bunch (or bunches)
of the flow electrons shifted from the system axis
(Fig. 3). The generation of diocotron waves was
observed during the pulse of the flow injection. The
waves frequency was in the range f = 10…50 kHz.
After the flow injection breakdown some sort of
damping diocotron wave was observed. Such waves
were named ‘residual’. Their frequency was relatively
low (f = 1…10 kHz). It is also useful to note that the
injection breakdown is followed by a jump-like change
of the wave amplitude.
The experiments with the cylindrical electron flow
were carried out on the same experimental setup that
was used earlier to study the dynamics of tubular flow.
The only difference between these two experiments was
absence of the entrance diaphragm which cut off the
central part of the flow.
The main purpose of this experiment was to observe a
more pronounced non-linear dynamics of the diocotron
waves.
Fig. 5. The effect of short additional beam injection
The development of such non-linear effects was
stimulated by the presence of additional space charge in
the central part of the flow. Also one of the key issues
was to find out the connection between the longitudinal
dynamics of the flow and diocotron waves behaviour.
The experiments with cylindrical (non-tubular) flow
exhibited strong nonlinear effects. In particular a
pronounced amplitude modulation of the diocotron
oscillations was observed during the flow injection
(Fig. 4). The modulation depth and frequency increased
together with the magnetic field intensity. For H =
980 Oe, for example, fMOD ≈ 2…3 kHz. The residual
diocotron waves were also observed in this regime. The
growth of the magnetic field intensity here leads to
decrease of the damping rate of residual waves.
In our earlier papers we presented the results of
experiments carried out with additional beam injection
after the main injection pulse breakdown [2,3]. It was
shown that such injection may turn back the damping
process and provide the wave “pumping” or echo-like
effect.
Another interesting effect is jumpwise changing of
the residual wave amplitude observed after a ‘short’
additional beam injection during the residual wave
damping (Fig. 5).
The effect of additional injection in this case
depends on the polarity of the oscillations half-period in
which it was carried out. Assuming that the geometry of
both main and additional injected flows (beams) is
similar we conclude that this effect is caused by the
longitudinal dynamics of the diocotron waves.
To explore the main features of axial dynamics of
the diocotron waves the probe measurements in the
different points of the drift tube were carried out.
Fig. 6. Longitudinal distribution of electroctatic
potential in the drift tube (a) and the self-consistent trap
oscillstions (b)
Fig. 4. The dinamics of diocotron oscillations during the cylindrical beam propagation through the drift
chamber for high (a) and low (b) magnetic field intensitie
92 ISSN 1562-6016. ВАНТ. 2012. №6(82)
The probes were separated in the axial direction.
Both the averaged longitudinal potential distribution and
the potential fluctuations in different points of the drift
chamber were studied. It was shown that the potential
distribution form depends strongly on the injection
parameters and time (Fig. 6.).
0,0000 0,0005 0,0010 0,0015
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
I C
O
LL
, I
G
R
(A
.U
.)
t (s)
Entrance grid Uaccel = 27 V
Collector H = 980 Oe
IHEAT = 1.8 A
Fig. 7. The flow current on the collector and entrance
grid electrodes
In particular, the configuration with two space
charge potential barriers is not stable. Actially the
longitudinal distribution of the electrostatic potential
“oscillates” with some small enough frequency (f ≈ 3
kHz). It is also remarkable that the potential oscillations
in the points corresponding to the mentioned above
potential barriers are counter-phased. Such dynamics
may cause the separation of the electrons trapped
between the potential barriers by their longitudinal
velocities. The oscillations of the potential dip walls
cause the fast particles ejection along the magnetic field
axis. Thus the most high-energetic particles leave the
self-consistent confining configuration formed by the
flow particles space charge. This suggestion is
supported by the results of electron current
measurements on the system collector and entrance grid.
The current curves exhibit a number of spike-like
oscillations which frequency corresponds to the
frequency of the potential barrier oscillations and the
amplitude modulation frequency of the diocotron
oscillations (Fig.7).
CONCLUSIONS
A number of conclusions were made from the given
experimental results.
In the case of homogeneous electron flow profile
the diocotron oscillations pattern has a pronounced
stochastic nature.
The diocotron wave has a pronounced three
dimentional dynamics (proved by the experiments with
an additional beam injection).
In both cylindrical and tubular flows the excitation
of diocotron wave was followed by development of
modulation instability.
The diocotron instability is localized in the spatial
area in which the self-consistent electron trap is formed
The self-consistent electron trap is formed by a pair
of potential barriers which oscillate in opposite phases
The frequency of barrier oscillations is close to
modulation frequency of the diocotron oscillations and
to the frequency of the flow particles ejection from the
self-consistent trap
REFERENCES
1. R.W. Gould. Electron Tube and Microwave
Laboratory: California Institute of Technology,
Technical Report .1955, № 3
2. I.K. Tarasov, M.I. Tarasov // Ukrainian Journal of
Physics 2008, v.53, № 4, p.339-344.
3. M.I. Tarasov, I.K. Tarasov, D.A Sitnikov //
International Conference and School on Plasma
Physics and Controlled Fusion and 4-th Alushta
International Workshop on the Role of Electric Fields
in Plasma Confinement in Stellarators and Tokamaks,
Alushta (Crimea), Ukraine, September 13-18, 2010,
Book of Abstracts, p. 93.
Article received 23.10.12
ТРЕХМЕРНАЯ ДИНАМИКА ДИОКОТРОННОЙ ВОЛНЫ В ПРОЦЕССЕ ПРОХОЖДЕНИЯ
«ГОРЯЧЕГО» ПОТОКА ЭЛЕКТРОНОВ В ПРОСТРАНСТВЕ ДРЕЙФА
М.И. Тарасов, И.К. Тарасов, Д.А. Ситников
Определена роль продольной динамики в эволюции диокотронной волны. Также были изучены основные
особенности захвата и удержания частиц при прохождении «горячего» электронного потока в пространстве
дрейфа.
ТРИВИМІРНА ДИНАМІКА ДІОКОТРОННОЇ ХВИЛІ В ПРОЦЕСІ ПРОХОДЖЕННЯ
«ГАРЯЧОГО» ПОТОКУ ЕЛЕКТРОНІВ У ПРОСТОРІ ДРЕЙФУ
М.І. Тарасов, І.К. Тарасов, Д.А. Сітнiков
Вивчено роль поздовжньої динаміки в еволюції діокотронної хвилі. Досліджено ключові особливості
захоплення та утримання частинок при проходженні «гарячого» електронного потоку в просторі дрейфу.
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