Oscillatory and wave activity in the runaway electrons flow
The presence of the accelerated particles flow (the flow of runaway electrons) in the plasma confinement volume may case a number of different instabilities. In this work we investigate the spectrum of fluctuations in a flow of charged particles to identify the oscillatory and wave processes obser...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2016
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irk-123456789-1152322017-03-31T03:02:25Z Oscillatory and wave activity in the runaway electrons flow Tarasov, I.K. Tarasov, M.I. Sitnikov, D.A. Olshansky, V.V. Lystopad, V.M. Lymar, N.V. Gnidenko, M.V. Magnetic confinement The presence of the accelerated particles flow (the flow of runaway electrons) in the plasma confinement volume may case a number of different instabilities. In this work we investigate the spectrum of fluctuations in a flow of charged particles to identify the oscillatory and wave processes observed. Besides, we pay special attention to the interaction between the flow particles and plasma fluctuations. The main evidence of such interaction is the presence of modulation in the particles flow with the corresponding characteristic modulation frequency. Namely, the modulation frequency in such cases corresponds to the frequency of characteristic oscillations of the discharge plasma. Basing on this, we carried out the experimental investigations of spectrum of oscillations observed in the circuits of edge electrostatic probes during the microwave pumping pulse and also on the back edge of the magnetic field pulse. Присутствие в объёме удержания плазмы потока ускоренных электронов (убегающих электронов) может приводить к раскачке разного рода неустойчивостей. В данной работе речь идёт об исследовании спектра флуктуаций в потоке, а также идентификации наблюдаемых колебательных и волновых процессов. Кроме того, уделено особое внимание взаимодействию частиц потока с флуктуациями плазмы. В качестве основного признака такого взаимодействия можно рассматривать наличие в потоке убегающих электронов модуляции с частотами, соответствующими характерным частотам волновых процессов в плазме разряда. Основываясь на этих соображениях, были проведены исследования спектра колебаний тока в цепи периферийных электростатических зондов как во время импульса ВЧ-накачки, так и на заднем фронте импульса магнитного поля. Присутність в обсязі утримання плазми потоку прискорених електронів (втікаючих електронів) може призводити до розгойдування різного роду нестiйкостей. У даній роботі мова йде про дослідження спектра флуктуацій в потоці, а також ідентифікації спостережуваних коливальних і хвильових процесів. Крім того, приділено особливу увагу взаємодії часток потоку з флуктуаціями плазми. В якості основної ознаки такої взаємодії можна розглядати наявність в потоці втікаючих електронів модуляції з частотами, відповідними характерним частотам хвильових процесів у плазмі розряду. Грунтуючись на цих міркуваннях, були проведені дослідження спектра коливань струму в ланцюзі периферійних електростатичних зондів як під час імпульсу ВЧ-накачки, так і на задньому фронті імпульсу магнітного поля. 2016 Article Oscillatory and wave activity in the runaway electrons flow / I.K. Tarasov, M.I. Tarasov, D.A. Sitnikov, V.V. Olshansky, V.M. Lystopad, N.V. Lymar, M.V. Gnidenko // Вопросы атомной науки и техники. — 2016. — № 6. — С. 29-32. — Бібліогр.: 8 назв. — англ. 1562-6016 PACS: 52.59.Rz, 52.70.Nc, 52.70.La http://dspace.nbuv.gov.ua/handle/123456789/115232 en Вопросы атомной науки и техники 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 |
Magnetic confinement Magnetic confinement |
| spellingShingle |
Magnetic confinement Magnetic confinement Tarasov, I.K. Tarasov, M.I. Sitnikov, D.A. Olshansky, V.V. Lystopad, V.M. Lymar, N.V. Gnidenko, M.V. Oscillatory and wave activity in the runaway electrons flow Вопросы атомной науки и техники |
| description |
The presence of the accelerated particles flow (the flow of runaway electrons) in the plasma confinement volume
may case a number of different instabilities. In this work we investigate the spectrum of fluctuations in a flow of
charged particles to identify the oscillatory and wave processes observed. Besides, we pay special attention to the
interaction between the flow particles and plasma fluctuations. The main evidence of such interaction is the presence
of modulation in the particles flow with the corresponding characteristic modulation frequency. Namely, the
modulation frequency in such cases corresponds to the frequency of characteristic oscillations of the discharge
plasma. Basing on this, we carried out the experimental investigations of spectrum of oscillations observed in the
circuits of edge electrostatic probes during the microwave pumping pulse and also on the back edge of the magnetic
field pulse. |
| format |
Article |
| author |
Tarasov, I.K. Tarasov, M.I. Sitnikov, D.A. Olshansky, V.V. Lystopad, V.M. Lymar, N.V. Gnidenko, M.V. |
| author_facet |
Tarasov, I.K. Tarasov, M.I. Sitnikov, D.A. Olshansky, V.V. Lystopad, V.M. Lymar, N.V. Gnidenko, M.V. |
| author_sort |
Tarasov, I.K. |
| title |
Oscillatory and wave activity in the runaway electrons flow |
| title_short |
Oscillatory and wave activity in the runaway electrons flow |
| title_full |
Oscillatory and wave activity in the runaway electrons flow |
| title_fullStr |
Oscillatory and wave activity in the runaway electrons flow |
| title_full_unstemmed |
Oscillatory and wave activity in the runaway electrons flow |
| title_sort |
oscillatory and wave activity in the runaway electrons flow |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2016 |
| topic_facet |
Magnetic confinement |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/115232 |
| citation_txt |
Oscillatory and wave activity in the runaway electrons flow / I.K. Tarasov, M.I. Tarasov, D.A. Sitnikov, V.V. Olshansky, V.M. Lystopad, N.V. Lymar,
M.V. Gnidenko // Вопросы атомной науки и техники. — 2016. — № 6. — С. 29-32. — Бібліогр.: 8 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-08T08:22:34Z |
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| fulltext |
ISSN 1562-6016. ВАНТ. 2016. №6(106)
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2016, № 6. Series: Plasma Physics (22), p. 29-32. 29
OSCILLATORY AND WAVE ACTIVITY IN THE RUNAWAY
ELECTRONS FLOW
I.K. Tarasov, M.I. Tarasov, D.A. Sitnikov, V.V. Olshansky, V.M. Lystopad, N.V. Lymar,
M.V. Gnidenko
Institute of Plasma Physics of the NSC KIPT, Kharkov, Ukraine
E-mail: itarasov@ipp.kharkov.ua
The presence of the accelerated particles flow (the flow of runaway electrons) in the plasma confinement volume
may case a number of different instabilities. In this work we investigate the spectrum of fluctuations in a flow of
charged particles to identify the oscillatory and wave processes observed. Besides, we pay special attention to the
interaction between the flow particles and plasma fluctuations. The main evidence of such interaction is the presence
of modulation in the particles flow with the corresponding characteristic modulation frequency. Namely, the
modulation frequency in such cases corresponds to the frequency of characteristic oscillations of the discharge
plasma. Basing on this, we carried out the experimental investigations of spectrum of oscillations observed in the
circuits of edge electrostatic probes during the microwave pumping pulse and also on the back edge of the magnetic
field pulse.
PACS: 52.59.Rz, 52.70.Nc, 52.70.La
INTRODUCTION
In this work we study the oscillatory and wave
activity of the U-3M torsatron edge plasma during a
hyper thermal electrons flow formation and propagation
[1, 2]. The measurements were carried out at the
magnetic field pulse edges and during the RF-heating
pulse which was applied at the stage of stationary
magnetic field.
The flow influence on the plasma stability was
widely studied on tokamaks. Thus the investigation of
the edge plasma wave dynamics in presence of a hyper
thermal electrons flow in stellarators represents special
interest [3]. In our case the flow was generated by the
magnetic field intensity variation at the edges of the
magnetic field pulse (plasma confinement is performed
by generation of a confining magnetic field
configuration which was created by applying a current
pulse to the magnetic field coils) [4, 5]. An
accompanying X-ray output was also registered during
the flow formation and the particles acceleration [6, 7].
Here we also continue our studies of the conditions
under which a parametrical excitation of the Bernstein
modes takes place. This work contains some additional
information about its parameters.
EXPERIMENTAL SETUP AND
DIAGNOSTIC ELEMENTS
Experiments were performed on U-3M device.
U-3M is a l = 3, m = 9 torsatron with open helical
divertor. The main parameters of plasma and magnetic
field are R = 1 m, a = 0.13 m, B ≤ 1.6 T. In this
experiment the magnetic field was B = 0.72 T. Plasma
in U-3M is produced by absorption of a RF power (f =
8…8.6 MHz, P ≤ 200 kW) from 2 antennas placed
inside of the helical winding near the last closed
magnetic surface. Frame aerials are used to excite the
RF wave in plasma.
A set of capacitive probes (3 probes) was used as the
signal detectors. The probes were placed at the
periphery of the confinement volume. Each probe
represented a square 5×5 cm. plate of stainless steel
with the thickness Δ = 0.2 cm. The plates were attached
to ceramic stays and placed symmetrically on the inner
surface of the magnetic field coil. The probes were
placed in one cross-section of the plasma filament.
Probe 1 is situated on the inner side of the torus.
Probes 2 and 3 are placed on the outer side with the
120° poloidal offset.
The signals from each of detectors were transmitted
by the microwave coaxial cable to the spectrum
analyzer (C4-59, С4-60). A constant bias voltage was
applied on the probes through the same coaxial lines
using a stabilized voltage source.
The measurements of radiation output in the sub
millimeter and infrared spectral areas were carried out
by the LiNbO3 pyrometric detectors placed at the
plasma edge.
THE MAGNETIC FIELD VARIATION
CAUSES THE RUNAWAY FLOW
X-ray radiation output was observed in the absence
of RF-heating at the edge of the pulse of magnetic field
(Fig. 1) [8]. At the same time the particles ejection on
the probes at the edge of the torus was detected. The
ejection was accompanied by Hα and ECE radiation
outputs. Thus, the flow of hyper thermal particles is
formed at the edges of magnetic field pulse. This
runaway flow is presumably created by the toroidal
electric field which is induced by the variation of the
intensity of magnetic field.
The flow intensity is sensitive to the working gas
pressure. At the low pressures, the flow exists not only
at the pulse edges but also during the phase of stationary
magnetic field.
SYNCHROTRON RADIATION OUTPUT
A synchrotron radiation output was observed during
the RF-power injection into the main confinement
volume (Fig. 2). The amplitude level depended strongly
on the radiation frequency.
30 ISSN 1562-6016. ВАНТ. 2016. №6(106)
The spectral measurements were carried out for the
frequency range from 5 to 40 GHz (Fig. 3). It was
shown that the signal level increased together with the
frequency in the range from 5 to 20 GHz which
included the range of the plasma waves frequency
(~10…20 GHz).
The measurements of radiation output in the sub
millimeter and infrared spectral areas were carried out
by the LiNbO3 pyrometric detectors placed at the
plasma edge (Fig. 4).
The results have shown a strong noise level during
the whole magnetic field pulse. On this “noisy”
background a number of spikes corresponded to the
RF-heating pulse and the magnetic field pulse edges
were observed.
Fig. 1. The measurements carrier out without applying
RF-heating at different working gas pressures
Fig. 2. The dynamics of level of synchrotron radiation
observed during the RF-heating pulse
Fig. 3. The amplitude of synchrotron radiation observed
during the RF-heating pulse versus the radiation
frequency (f = 5…40 GHz)
Fig. 4. Ultrahigh frequency radiation
(f = 10…1000 GHz) during the whole magnetic field
pulse
MICROWAVE ACTIVITY
The measurements of the diamagnetic flow
dynamics and the microwave activity level (12 GHz)
dynamics during the RF-heating pulse have shown a
correlation in fluctuations dynamics in these two
channels (Fig. 5). Such correlation may be considered as
a sign of the fan instability development
Fig. 5. Dynamics of microwave components of the
current on the peripheral probe and the intensity of the
diamagnetic current
It was also estimated that the microwave signal
reacts noticeably on the discharge transition to the
improved confinement mode just like the probe current
or radiometry signal (Fig. 6) [8].
Fig. 6. Correlation of fluctuations in the signals on the
peripheral current probe: its microwave components
and microwave signal of reflektometer
WAVE ACTIVITY
Finally the results of experiments carried out at the
vicinity of the fourth harmonic of RF-heating frequency
have shown that the signal in the probe circuit passes
ahead of the X-ray output. The measurements carried
ISSN 1562-6016. ВАНТ. 2016. №6(106) 31
out for narrow frequency bands (Δf = 300 kHz) with
different values of the average frequency has shown that
the time shift between the X-ray output beginning and
the probe current pulse reduces together with the
average frequency growth (Fig. 7).
Fig. 7. Signals corresponded to different frequencies
representing different harmonics of the pumping
frequency appeared on the probes with different offsets
according to the moment of hard X-ray output. Usually,
the offsets for higher harmonics were smaller
The application of electrostatic potential of different
polarities to the probes located at the system edge was
also performed during the RF-heating. It caused much
weaker effect but the potential polarity influence was
similar to that observed in the previous case. The most
pronounced influence was observed at the low-
frequency area (Fig. 8).
These results give a particularly answer on the
question about the way in which the fluctuations are
registered by the probes. Now we can say that the
information about the fluctuations is carried by an
electron flow which propagates from the plasma volume
to the periphery.
CONCLUSIONS
The set of oscillograms of signals from the edge
electrostatic probes confirms that the runaway electrons
flow interacts with the high-frequency fluctuations in
plasma. As result, the particles flow experiences strong
non-linear high-frequency modulation. Actually the
modulation shows itself in the fact that we detect
charged particles in the confinement configuration
during 1.5…2 s after turning off the microwave heating.
It is also remarkable that the particles which are
modulated by higher harmonics of pumping frequency
leave confinement volume faster than those modulated
by lower harmonics.
This fact represents an evidence of wave-particle
interaction because higher frequency corresponds to
higher phase velocity. Consequently, particles with
higher velocities leave the confinement volume faster
while the confining magnetic field is decreasing (back
front of the magnetic field pulse). Thus the particles
modulated by higher frequencies reach edge
electrostatic probes faster.
The observed behaviour could be explained as a
result of generating of non-dumping modes (BGK-
wave, Van-Kampen wave).
After interaction with the RF-plasma the flow
becomes modulated by the particles density and
velocity. Thus the spectrum of the flow current contains
Fig. 8. The flow formation may be caused by
development of plasma instabilities
the RF-heating frequency harmonics together with the
parametric instability spectral components.
The presence of the fan instability is proved by
increased oscillatory activity at the Langmuir frequency.
These oscillations correlate with the signal from the
diamagnetic loop.
The information about the oscillations observed by
the edge probes during the RF-pumping pulse is carried
by electron flows directed to the systems periphery. The
formation of such flows is presumably the result of the
plasma instability development.
In particular the synchrotron radiation (5…44 GHz)
output was observed during the RF-heating pulse. At the
same time an ultrahigh frequency (10…1000 GHz)
radiation was registered during the whole magnetic field
pulse.
Special attention was paid to hard X-ray outputs
observed predominately on the edges of magnetic field
pulse. The radiation energy reaches 2 MeV which
proves the suggestion about formation of a high
energetic particles flow of the magnetic field pulse.
REFERENCES
1. V.V. Olshansky, K.N. Stepanov, I.K. Tarasov,
M.I. Tarasov, D.A. Sitnikov, A.I. Skibenko,
E.D. Volkov // Problems of Atomic Science and
Technology. Series “Plasma Physics”. 2009, № 1,
p. 43-45.
2. K.N. Stepanov, V.V. Olshansky, M.I. Tarasov,
D.A. Sitnikov // Plasma Physics. 2010, v. 36, № 10,
p. 916-925.
3. M.I. Tarasov. Streams of charged particles in plasma
and their fluctuations in linear and toroidal magnetic
configurations // Thesis. Kharkov. 2011, p. 140.
4. V.V. Alikaev, Yu.I. Arseniev, G.A. Bobrovskiy,
А.А. Kondratiev, K.А. Razumova // Jornal of Technical
Physics. 1975, v. XLV, № 3, p. 515-522.
5. H. Dreicer. Electron and ion runaway in a fully
ionized gas // Phys. Rev. 1960, v. 117, № 2, p. 329-342.
6. B.B. Kadomtsev, O.P. Pogutse // JETP. 1967, v. 53,
№ 6 (12), p. 2025-2033.
32 ISSN 1562-6016. ВАНТ. 2016. №6(106)
7. S.V. Mirnov. Physical processes in tokamak plasma.
M.: “Energoatomizdat”, 1983 (in Russian).
8. M.I. Tarasov, I.K. Tarasov, D.A. Sitnikov,
A.S. Slavnyi, A.E. Kulaga, R.O. Pavlichenko, et al. // 5-
th ITER International Summer School, P 31 MHD and
Energetic Particles. June 20-24, 2011, Provence,
France.
Article received 27.09.2016
КОЛЕБАТЕЛЬНАЯ И ВОЛНОВАЯ АКТИВНОСТИ В ПОТОКЕ УБЕГАЮЩИХ ЭЛЕКТРОНОВ
И.К. Тарасов, М.И. Тарасов, Д.А. Ситников, В.В. Ольшанский, В.М. Листопад, Н.В. Лымарь,
М.В. Гниденко
Присутствие в объёме удержания плазмы потока ускоренных электронов (убегающих электронов) может
приводить к раскачке разного рода неустойчивостей. В данной работе речь идёт об исследовании спектра
флуктуаций в потоке, а также идентификации наблюдаемых колебательных и волновых процессов. Кроме
того, уделено особое внимание взаимодействию частиц потока с флуктуациями плазмы. В качестве
основного признака такого взаимодействия можно рассматривать наличие в потоке убегающих электронов
модуляции с частотами, соответствующими характерным частотам волновых процессов в плазме разряда.
Основываясь на этих соображениях, были проведены исследования спектра колебаний тока в цепи
периферийных электростатических зондов как во время импульса ВЧ-накачки, так и на заднем фронте
импульса магнитного поля.
КОЛИВАЛЬНА І ХВИЛЬОВА АКТИВНОСТИ В ПОТОЦІ ВТIКАЮЧИХ ЕЛЕКТРОНIВ
І.К. Тарасов, М.І. Тарасов, Д.А. Сiтнiков, В.В. Ольшанський, В.М. Листопад, М.В. Лимар, М.В. Гніденко
Присутність в обсязі утримання плазми потоку прискорених електронів (втікаючих електронів) може
призводити до розгойдування різного роду нестiйкостей. У даній роботі мова йде про дослідження спектра
флуктуацій в потоці, а також ідентифікації спостережуваних коливальних і хвильових процесів. Крім того,
приділено особливу увагу взаємодії часток потоку з флуктуаціями плазми. В якості основної ознаки такої
взаємодії можна розглядати наявність в потоці втікаючих електронів модуляції з частотами, відповідними
характерним частотам хвильових процесів у плазмі розряду. Грунтуючись на цих міркуваннях, були
проведені дослідження спектра коливань струму в ланцюзі периферійних електростатичних зондів як під
час імпульсу ВЧ-накачки, так і на задньому фронті імпульсу магнітного поля.
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