Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron
First observations of plasma fluctuations in the frequency range of 1…20 kHz in various plasma conditions of the URAGAN-2M (U-2M) torsatron are presented. Observed fluctuations of the Hα emissivity are coherent with the line-averaged density fluctuations measured by the 140 GHz heterodyne interferom...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2016
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| Цитувати: | Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron / M.B. Dreval, R.O. Pavlichenko, A.M. Shapoval, F.I. Ozherelyev, Yu.K. Mironov, V.S. Romanov, M.M. Makhov, N.V. Zamanov, A.E. Kulaga // Вопросы атомной науки и техники. — 2016. — № 6. — С. 15-18. — Бібліогр.: 9 назв. — англ. |
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irk-123456789-1152272017-03-31T03:02:28Z Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron Dreval, M.B. Pavlichenko, R.O. Shapoval, A.M. Ozherelyev, F.I. Mironov, Yu.K. Romanov, V.S. Makhov, M.M. Zamanov, N.V. Kulaga, A.E. Magnetic confinement First observations of plasma fluctuations in the frequency range of 1…20 kHz in various plasma conditions of the URAGAN-2M (U-2M) torsatron are presented. Observed fluctuations of the Hα emissivity are coherent with the line-averaged density fluctuations measured by the 140 GHz heterodyne interferometer. Bursts of 1…2 kHz, m=1 oscillations, localized in the central region of the plasma column, are always observed at the heating degradation stage of the crankshaft antenna operation in “standard” U-2M discharges (B₀=0.35 T). For this “standard” discharges with low RF power 10…15 kHz plasma density fluctuations are strongly localized at the region of substantial Hα emissivity gradients. Transient burst of 6 kHz central fluctuations are also observed in the medium magnetic field (B₀=0.067 T) discharges. Strong m = 1 fluctuations in the frequency range of 10…20 kHz are observed in the plasma conditioning discharges with low temperature and magnetic field (B₀=0.01 T). These fluctuations are localized in the central part of the plasma. Direction of poloidal rotation of the mode which causes fluctuations is reversed during the discharge simultaneously with its substantial amplitude increase and frequency decrease from 20 to 10 kHz. The fluctuations observed in standard U-2M discharges have frequency below the geodesic acoustic mode (GAM) frequency and can be caused by drift plasma modes. The frequency of fluctuations in the plasma conditioning discharges is observed in the range near the GAM frequency or higher. Представлены первые наблюдения флуктуаций в диапазоне частот 1…20 кГц в плазме торсатрона УРАГАН-2М (У-2М) с различными параметрами. Наблюдаемые колебания эмиссии линии Hα когерентны с флуктуациями среднехордовой плотности, измеренными с помощью 140 ГГц интерферометра. Всплески 1…2 кГц, m=1 колебаний, локализованные в центральной области плазменного столба, всегда наблюдаются на стадии деградации нагрева плазмы антенной коленвального типа в стандартных разрядах У-2М (B₀ = 0,35 Tл). В разрядах У-2М низкой ВЧ-мощности и B₀=0.35 Tл флуктуации плотности плазмы на частоте 10…15 кГц сильно локализованы в области существенных градиентов свечения Hα. Вспышка 6 кГц колебаний в центральной области также наблюдается в разрядах со средним магнитным полем (B₀ = 0,067 Tл). Сильные m=1 колебания в диапазоне частот 10…20 кГц наблюдаются в плазме чистящего разряда с низкой температурой и магнитным полем B₀ = 0,01 Tл. Эти колебания локализованы в центральной части плазмы. Направление полоидального вращения моды, вызывающей колебания, меняется во время разряда одновременно с существенным увеличением амплитуды колебаний и снижением частоты с 20 до 10 кГц. Колебания, наблюдаемые в стандартных разрядах У-2М, имеют частоту ниже частоты геодезической акустической моды (ГАМ) и могут быть вызваны дрейфовыми модами. Частота колебаний плазмы в чистящих разрядах наблюдается в области частоты ГАМ или превышает её. Представлені перші спостереження флуктуацій в діапазоні частот 1…20 кГц у плазмі торсатрона УРАГАН- 2М (У-2М) з різними параметрами. Коливання емісії лінії Hα, що спостерігалися, мають когерентність з флуктуаціями середньо-хордовою густини, що вимірювалась за допомогою 140 ГГц інтерферометра. Сплески 1…2 кГц, m=1 коливань, що локалізовані в центральній області плазмового стовпа, завжди спостерігаються на стадії деградації нагріву плазми антеною коленвального типу в стандартних розрядах У-2М (B₀ = 0,35 Tл). У розрядах У-2М низькою ВЧ-потужності і B₀=0,35 Tл флуктуації густини плазми на частоті 10…15 кГц сильно локалізовані в області істотних градієнтів світіння Hα. Спалах 6 кГц коливань в центральній області також спостерігається в розрядах із середнім магнітним полем (B₀ = 0,067 Tл). Сильні m=1 коливання в діапазоні частот 10…20 кГц спостерігаються в плазмі розряду, що чистить, з низькою температурою і магнітним полем (B₀ = 0,01 Tл). Ці коливання локалізовані в центральній частині плазми. Напрямок полоідального обертання моди, що викликає коливання, змінюється під час розряду одночасно з істотним збільшенням амплітуди коливань та зниженням частоти з 20 до 10 кГц. Коливання, які спостерігаються в стандартних розрядах У-2М, мають частоту нижче частоти геодезичної акустичної моди (ГАМ) і можуть бути викликані дрейфовими модами. Частота коливань плазми в розрядах, що застосовують для чистки, спостерігається в області частоти ГАМ або перевищує її. 2016 Article Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron / M.B. Dreval, R.O. Pavlichenko, A.M. Shapoval, F.I. Ozherelyev, Yu.K. Mironov, V.S. Romanov, M.M. Makhov, N.V. Zamanov, A.E. Kulaga // Вопросы атомной науки и техники. — 2016. — № 6. — С. 15-18. — Бібліогр.: 9 назв. — англ. 1562-6016 PACS: 52.55.Hc; 52.70.La http://dspace.nbuv.gov.ua/handle/123456789/115227 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 Dreval, M.B. Pavlichenko, R.O. Shapoval, A.M. Ozherelyev, F.I. Mironov, Yu.K. Romanov, V.S. Makhov, M.M. Zamanov, N.V. Kulaga, A.E. Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron Вопросы атомной науки и техники |
| description |
First observations of plasma fluctuations in the frequency range of 1…20 kHz in various plasma conditions of the URAGAN-2M (U-2M) torsatron are presented. Observed fluctuations of the Hα emissivity are coherent with the line-averaged density fluctuations measured by the 140 GHz heterodyne interferometer. Bursts of 1…2 kHz, m=1 oscillations, localized in the central region of the plasma column, are always observed at the heating degradation stage of the crankshaft antenna operation in “standard” U-2M discharges (B₀=0.35 T). For this “standard” discharges with low RF power 10…15 kHz plasma density fluctuations are strongly localized at the region of substantial Hα emissivity gradients. Transient burst of 6 kHz central fluctuations are also observed in the medium magnetic field (B₀=0.067 T) discharges. Strong m = 1 fluctuations in the frequency range of 10…20 kHz are observed in the plasma conditioning discharges with low temperature and magnetic field (B₀=0.01 T). These fluctuations are localized in the central part of the plasma. Direction of poloidal rotation of the mode which causes fluctuations is reversed during the discharge simultaneously with its substantial amplitude increase and frequency decrease from 20 to 10 kHz. The fluctuations observed in standard U-2M discharges have frequency below the geodesic acoustic mode (GAM) frequency and can be caused by drift plasma modes. The frequency of fluctuations in the plasma conditioning discharges is observed in the range near the GAM frequency or higher. |
| format |
Article |
| author |
Dreval, M.B. Pavlichenko, R.O. Shapoval, A.M. Ozherelyev, F.I. Mironov, Yu.K. Romanov, V.S. Makhov, M.M. Zamanov, N.V. Kulaga, A.E. |
| author_facet |
Dreval, M.B. Pavlichenko, R.O. Shapoval, A.M. Ozherelyev, F.I. Mironov, Yu.K. Romanov, V.S. Makhov, M.M. Zamanov, N.V. Kulaga, A.E. |
| author_sort |
Dreval, M.B. |
| title |
Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron |
| title_short |
Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron |
| title_full |
Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron |
| title_fullStr |
Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron |
| title_full_unstemmed |
Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron |
| title_sort |
observation of 1…20 khz fluctuations in the uragan-2m torsatron |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2016 |
| topic_facet |
Magnetic confinement |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/115227 |
| citation_txt |
Observation of 1…20 kHz fluctuations in the Uragan-2M torsatron / M.B. Dreval, R.O. Pavlichenko, A.M. Shapoval, F.I. Ozherelyev, Yu.K. Mironov,
V.S. Romanov, M.M. Makhov, N.V. Zamanov, A.E. Kulaga
// Вопросы атомной науки и техники. — 2016. — № 6. — С. 15-18. — Бібліогр.: 9 назв. — англ. |
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Вопросы атомной науки и техники |
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ISSN 1562-6016. ВАНТ. 2016. №6(106)
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2016, № 6. Series: Plasma Physics (22), p. 15-18. 15
OBSERVATION OF 1…20 kHz FLUCTUATIONS IN THE URAGAN-2M
TORSATRON
M.B. Dreval, R.O. Pavlichenko, A.M. Shapoval, F.I. Ozherelyev, Yu.K. Mironov,
V.S. Romanov, M.M. Makhov, N.V. Zamanov and A.E. Kulaga
Institute of Plasma Physics of the NSC KIPT, Kharkov, Ukraine
E-mail: mdreval@kipt.kharkov.ua
First observations of plasma fluctuations in the frequency range of 1…20 kHz in various plasma conditions of the
URAGAN-2M (U-2M) torsatron are presented. Observed fluctuations of the Hα emissivity are coherent with the
line-averaged density fluctuations measured by the 140 GHz heterodyne interferometer. Bursts of 1…2 kHz, m=1
oscillations, localized in the central region of the plasma column, are always observed at the heating degradation
stage of the crankshaft antenna operation in “standard” U-2M discharges (B0=0.35 T). For this “standard” discharges
with low RF power 10…15 kHz plasma density fluctuations are strongly localized at the region of substantial Hα
emissivity gradients. Transient burst of 6 kHz central fluctuations are also observed in the medium magnetic field
(B0=0.067 T) discharges. Strong m = 1 fluctuations in the frequency range of 10…20 kHz are observed in the
plasma conditioning discharges with low temperature and magnetic field (B0=0.01 T). These fluctuations are
localized in the central part of the plasma. Direction of poloidal rotation of the mode which causes fluctuations is
reversed during the discharge simultaneously with its substantial amplitude increase and frequency decrease from
20 to 10 kHz. The fluctuations observed in standard U-2M discharges have frequency below the geodesic acoustic
mode (GAM) frequency and can be caused by drift plasma modes. The frequency of fluctuations in the plasma
conditioning discharges is observed in the range near the GAM frequency or higher.
PACS: 52.55.Hc; 52.70.La
INTRODUCTION
Alfvén eigenmodes (AE), which are observed in
various tokamaks and stellarators, have been
extensively studied both experimentally and
theoretically [1]. Set of modes with lower than AE
frequencies is also observed. One of extensively
studied low frequency modes is the geodesic acoustic
mode (GAM) [2]. In addition, set of different low
frequency branches arising from coupling of Alfvén and
acoustic continuum waves, geodesic curvature,
modification of Alfvén and acoustic waves by drift
effects have been observed [3-6]. Experimental
determination of the mode type, its behavior and its
drier provide important information for the physics of
eigenmodes in stellarators and tokamaks.
In the hot plasma the Soft X-ray array set provides
appropriate information for the plasma fluctuations
identification. On the contrary in the case of the cold
plasma the SXR emission cannot be observed, thus, the
multiline Hα diagnostics can replace its role in the mode
determination. Amplitude of fluctuations of the spectral
line emission
~
I depends on electron density fluctuations
~
en as : dlTnI e
l
e )(
~~~
, where )(
~
eT represent a
function from effective cross-sections of the spectral
line excitation and densities of hydrogen molecules and
atoms in the Hα case. Fluctuations of electron density is
expected under influence of the set of low frequency
eigenmodes under investigation, and therefore
fluctuations of the Hα emission brightness consequently
is also should be observed. New 10-channels camera for
Hα measurement with a temporal resolution of about 20
μs has been designed and successfully applied for the
noisy URAGAN-3M (U-3M) plasma conditions. It was
used for studies of the RF breakdown in U-3M and for
the plasma fluctuations [7]. It allows localize plasma
fluctuations radially, allow determine poloidal mode
number and the direction of the rotating plasma modes
[7]. This camera was recently installed in URAGAN-2M
(U-2M) and used in our work. Strong suppression of the
RF noise and 50 kHz bandwidth of the diagnostics
opens technical possibility for studies of the low
frequency (up to 50 kHz) fluctuations.
Observation of 20…400 kHz fluctuations in the U-3M
torsatron has been published recently [8]. The excitation
conditions of these modes depend on the radio
frequency antenna type and the plasma density, the
appearance of the modes correlating with the presence
of both suprathermal electrons and high-energy ions in
the plasma, which supports common opinion that the
modes are excited by energetic particles. Raw estimates
show that toroidicity-induced Alfvén eigenmodes could
be responsible for the 150…400 kHz fluctuations. Low-
frequency 20…70 kHz bursts in U-3M are observed
during plasma confinement transitions. This m = 2,
20 kHz mode rotated in the electron diamagnetic
rotation direction with a frequency lower than the
geodesic acoustic mode frequency and was identified as
a drift-sound-type mode [8]. Low-frequency 1…5 kHz
fluctuations were also observed in different U-3M
plasma conditions by our 10-channels Hα camera [7]. In
our work we continue studies of plasma fluctuations in
the Alfvén-wave-heated plasmas, started in U-3M, and
extend it to the U-2M torsatron.
1. 10-CHANNELS CAMERA SETUP
The Hα camera consists of a 10 channels linear array
of photodiodes BPW34. The camera is viewing
vertically, as it is shown in Fig. 1. The amplifiers with
50 kHz bandwidth combined with STM32F4
microprocessor-based digitizers are used in the
16 ISSN 1562-6016. ВАНТ. 2016. №6(106)
diagnostics. Original electronics design of the camera
allows to suppress successfully high level RF noise and
to register Hα distribution from low density plasma [7].
Fig. 1. Lines of sight the 10-channels camera across the
U-2M cross-section and last close magnetic surface
The camera lens was replaced to the short focal distance
one (long focal distance is used in U-3M) in order to
project the U-2M plasma cross-section onto the slit of
camera. In the short focal distance case, the distance
from the point in plasma to the focal plane is
substantially varied. Therefore, in contrast to the simple
pinhole camera or the long focal distance case,
measured signal cannot be approximated by simple
integration over the solid viewing angle. Accurate data
analysis is required for local emissivity distribution
restoration from the integrated measurements.
2. FLUCTUATIONS IN THE
CONDITIONING DISCHARGES
Fig.2 shows fluctuations in the conditioning
discharge. These low magnetic field (B0=0.01 T, ω ››
ωci) low temperature (Te=1…20 eV) RF discharges are
routinely used for U-2M and U-3M wall conditioning.
The Hα emissivity fluctuations are coherent with the
line-averaged density fluctuations measured by the
single chord 140 GHz heterodyne interferometer, as it is
seen from the Fig. 2. Simultaneously with arising of the
fluctuations amplitude, its frequency decrease from
20 to 10 kHz as it is shown in the top frame of the
Fig. 2. Due to clear systematic phase shift between
fluctuations of Hα emission measured from different
channels, these fluctuations can be excited by the
rotated poloidally plasma mode [7]. Under this
assumption, the evolution of the space structure of the
fluctuations (see in the inserts of Fig. 2) is caused by the
m=1 plasma mode. According to the mode space
structure data, direction of its poloidal rotation is
reversed simultaneously with the amplitude arising, as it
seen from the two inserts comparison. It can be caused
by the Doppler effect (due to the plasma rotation itself)
or can be caused by the excitation of different plasma
modes during the discharge. The frequency of geodesic
acoustic mode (GAM) separates different types of the
plasma eigenmodes. According to the probe
measurements, electron temperature in this type of the
U-2M conditioning discharges is near 5…10 eV,
therefore the GAM frequency
i
m
e
TR
GAM
f
0
22
is not exceed 10 kHz [8]. Thus, observed fluctuations
can be caused by the GAM mode itself, where the m = 1
mode of the density perturbation is expected [9], or can
be caused by Alfvén eigenmodes with frequencies
higher than the GAM one. At the present time no fast
particles is observed in the U-3M and U-2M
conditioning discharge (according to the neutral particle
analyzer and probes measurements), thus, common for
AE driver is not present in these discharges.
Fig. 2. Fluctuations of Hα and line-averaged density in
the conditioning discharge. Dominant frequency and
space distributions of the mode at two discharge stages
3. FLUCTUATIONS IN THE В0=0.06…0.35 T
DISCHARGES
Plasma fluctuations are also observed in U-2M RF
discharges with “standard” magnetic field B0= 0.35 T
(ω<ωci). In the low RF input power discharges the
density fluctuations are observed in some symmetric
lines of sight of the Hα camera but substantially
decrease in the inner regions and absent in outer regions
(Fig. 3).
Fig. 3. Fluctuations of Hα and line-averaged density.
Space distribution in the insert
ISSN 1562-6016. ВАНТ. 2016. №6(106) 17
In these discharges 10…15 kHz plasma density
fluctuations are strongly localized in the region of
substantial Hα emissivity gradients.
Bursts of 1…2 kHz, m=1 oscillations caused by the
rotating modes are always observed at the heating
degradation stage of the crankshaft antenna operation
(Fig. 4). They appear at the decrease stage of the SXR
emission and disappear when the SXR signal is
dropping close to the zero level in “standard” U-2M
discharges (B0=0.35 T). They are localized in the central
region of the plasma column as it seen from the Fig. 4
insert.
Fig. 4. Fluctuations of Hα and line-averaged density.
Space distribution in the insert
Fig. 5. Fluctuations of Hα and line-averaged density.
Space distribution in the insert
Frequency of these fluctuations is definitely lower
than the GAM frequency and therefore these
fluctuations should have the drift nature. It is also
expected strong modification of the plasma parameter
gradients at the discharge degradation stage (due to the
substantial cooling of the plasma). This modification of
the gradients can cause the drift modes excitation.
Similar transient burst of the low frequency fluctuations
is observed in the U-3M too [8]. Transient burst are also
observed in the medium magnetic field discharges in U-2M.
An example of the transient burst of 6 kHz central
fluctuations at B0=0.067 T is shown in Fig. 5.
Fast line-averaged density rise at 22 ms (see Fig. 5)
coincides with the burst. The space structure of the
mode is more complex in this case (additional
considerations are required for the mode structure
determination from our line-integrated data).
Nevertheless, transient appearance at the time of
expected gradients modification and sub-GAM
frequency confirm drift nature of this fluctuations.
SUMMARY AND CONCLUSIONS
The 1…20 kHz fluctuations have been observed in
various U-2M discharges. Observed Hα fluctuations are
coherent with the line-averaged density fluctuations.
The fluctuations have frequency below the geodesic
acoustic mode (GAM) frequency and can be caused by
drift plasma modes in standard U-2M discharges. The
transient bursts of the fluctuations in this case coincide
with the strong modifications of the discharge. This is
also indicate that they are caused by the caused by drift
modes. The frequency of fluctuations in the plasma
conditioning discharges is observed in the range near
the GAM frequency or higher in contrast to the standard
discharges.
ACKNOWLEDGEMENTS
The U-3M Team is gratefully acknowledged for
useful discussions. The authors thank the U-3M Team
and especially to A.V. Lozin, V.K. Pashnev,
V.V. Chechkin and V.E. Moiseenko for providing the
U-3M experimental conditions. This work has been
supported in part by National Academy Science of
Ukraine Project No. X-4-1/2016.
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Article received 12.10.2016
18 ISSN 1562-6016. ВАНТ. 2016. №6(106)
НАБЛЮДЕНИЯ ФЛУКТУАЦИЙ С ЧАСТОТАМИ 1…20 кГц В ТОРСАТРОНЕ УРАГАН-2М
Н.Б. Древаль, Р.О. Павличенко, А.Н. Шаповал, Ф.И. Ожерельев, Ю.К. Миронов, В.С. Романов,
М.М. Махов, Н.В. Заманов и А.Е. Кулага
Представлены первые наблюдения флуктуаций в диапазоне частот 1…20 кГц в плазме торсатрона
УРАГАН-2М (У-2М) с различными параметрами. Наблюдаемые колебания эмиссии линии Hα когерентны с
флуктуациями среднехордовой плотности, измеренными с помощью 140 ГГц интерферометра. Всплески
1…2 кГц, m=1 колебаний, локализованные в центральной области плазменного столба, всегда наблюдаются
на стадии деградации нагрева плазмы антенной коленвального типа в стандартных разрядах У-2М
(B0 = 0,35 Tл). В разрядах У-2М низкой ВЧ-мощности и B0=0.35 Tл флуктуации плотности плазмы на
частоте 10…15 кГц сильно локализованы в области существенных градиентов свечения Hα. Вспышка 6 кГц
колебаний в центральной области также наблюдается в разрядах со средним магнитным полем (B0 =
0,067 Tл). Сильные m=1 колебания в диапазоне частот 10…20 кГц наблюдаются в плазме чистящего разряда
с низкой температурой и магнитным полем B0 = 0,01 Tл. Эти колебания локализованы в центральной части
плазмы. Направление полоидального вращения моды, вызывающей колебания, меняется во время разряда
одновременно с существенным увеличением амплитуды колебаний и снижением частоты с 20 до 10 кГц.
Колебания, наблюдаемые в стандартных разрядах У-2М, имеют частоту ниже частоты геодезической
акустической моды (ГАМ) и могут быть вызваны дрейфовыми модами. Частота колебаний плазмы в
чистящих разрядах наблюдается в области частоты ГАМ или превышает её.
СПОСТЕРЕЖЕННЯ ФЛУКТУАЦІЙ З ЧАСТОТОЮ 1…20 кГц У ТОРСАТРОНІ УРАГАН-2М
М.Б. Древаль, Р.О. Павличенко, А.М. Шаповал, Ф.І. Ожерельєв, Ю.К. Миронов, В.С. Романов,
М.М. Махов, М.В. Заманов і А.Є. Кулага
Представлені перші спостереження флуктуацій в діапазоні частот 1…20 кГц у плазмі торсатрона УРАГАН-
2М (У-2М) з різними параметрами. Коливання емісії лінії Hα, що спостерігалися, мають когерентність з
флуктуаціями середньо-хордовою густини, що вимірювалась за допомогою 140 ГГц інтерферометра. Сплески
1…2 кГц, m=1 коливань, що локалізовані в центральній області плазмового стовпа, завжди спостерігаються на
стадії деградації нагріву плазми антеною коленвального типу в стандартних розрядах У-2М (B0 = 0,35 Tл). У
розрядах У-2М низькою ВЧ-потужності і B0=0,35 Tл флуктуації густини плазми на частоті 10…15 кГц сильно
локалізовані в області істотних градієнтів світіння Hα. Спалах 6 кГц коливань в центральній області також
спостерігається в розрядах із середнім магнітним полем (B0 = 0,067 Tл). Сильні m=1 коливання в діапазоні
частот 10…20 кГц спостерігаються в плазмі розряду, що чистить, з низькою температурою і магнітним полем
(B0 = 0,01 Tл). Ці коливання локалізовані в центральній частині плазми. Напрямок полоідального обертання
моди, що викликає коливання, змінюється під час розряду одночасно з істотним збільшенням амплітуди
коливань та зниженням частоти з 20 до 10 кГц. Коливання, які спостерігаються в стандартних розрядах У-2М,
мають частоту нижче частоти геодезичної акустичної моди (ГАМ) і можуть бути викликані дрейфовими
модами. Частота коливань плазми в розрядах, що застосовують для чистки, спостерігається в області частоти
ГАМ або перевищує її.
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