Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron
The study of wave processes occurring during the initial stage of RF plasma heating in the Uragan-3M torsatron was performed with using movable magnetic and electric probes. The heating was carried out by the frame antenna. The electric probe allowed to register changes of the plasma density profile...
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| Zitieren: | Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron / V.K. Pashnev, I.K. Tarasov, D.A. Sitnikov, E.L. Sorokovoy, S.A. Tsybenko, V.V. Chechkin, L.I. Grigor’eva, A.A. Beletskii, A.A. Kasilov // Вопросы атомной науки и техники. — 2017. — № 1. — С. 247-250. — Бібліогр.: 15 назв. — англ. |
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irk-123456789-1221782017-06-29T03:03:11Z Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron Pashnev, V.K. Tarasov, I.K. Sitnikov, D.A. Sorokovoy, E.L. Tsybenko, S.A. Chechkin, V.V. Grigor’eva, L.I. Beletskii, A.A. Kasilov, A.A. Диагностика плазмы The study of wave processes occurring during the initial stage of RF plasma heating in the Uragan-3M torsatron was performed with using movable magnetic and electric probes. The heating was carried out by the frame antenna. The electric probe allowed to register changes of the plasma density profile, while the magnetic probes measured amplitude and phase shifts between all magnetic field components at different points over the plasma column cross-section. The frequency spectrum of magnetic field fluctuations contains the main frequency that coincides with the RF oscillator frequency and higher harmonics. The amplitude of the 2nd harmonic in this mode can be compared with the amplitude of the basic harmonic. С помощью подвижных магнитных и электрических зондов в торсатроне Ураган-3М были изучены волновые процессы, протекающие на начальной стадии ВЧ-нагрева. Нагрев плазмы проводился с помощью “рамочной” антенны. Электрический зонд позволял регистрировать изменение профиля плотности плазмы, а магнитные зонды измеряли амплитуду и сдвиг фаз между всеми компонентами поля в различных точках по сечению плазменного шнура. Частотный спектр регистрируемых колебаний магнитного поля содержит основную частоту, совпадающую с частотой ВЧ-генератора, и более высокие гармоники. Амплитуда второй гармоники в данном режиме может быть сравнима с амплитудой основной гармоники. За допомогою рухливих магнітних і електричних зондів у торсатроні Ураган-3М були вивчені хвильові процеси, що протікають на початковій стадії ВЧ-нагріву. Нагрівання плазми проводилося за допомогою "рамкової" антени. Електричний зонд дозволяв реєструвати зміну профілю щільності плазми, а магнітні зонди вимірювали амплітуду і зрушення фаз між усіма компонентами поля в різних точках по перерізу плазмового шнура. Частотний спектр реєстрованих коливань магнітного поля містить основну частоту, яка збігається з частотою ВЧ-генератора, і більш високі гармоніки. Амплітуда другої гармоніки в даному режимі може бути порівнянна з амплітудою основної гармоніки. 2017 Article Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron / V.K. Pashnev, I.K. Tarasov, D.A. Sitnikov, E.L. Sorokovoy, S.A. Tsybenko, V.V. Chechkin, L.I. Grigor’eva, A.A. Beletskii, A.A. Kasilov // Вопросы атомной науки и техники. — 2017. — № 1. — С. 247-250. — Бібліогр.: 15 назв. — англ. 1562-6016 PACS: 52.55.Dy, 52.55.Hc http://dspace.nbuv.gov.ua/handle/123456789/122178 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Диагностика плазмы Диагностика плазмы |
| spellingShingle |
Диагностика плазмы Диагностика плазмы Pashnev, V.K. Tarasov, I.K. Sitnikov, D.A. Sorokovoy, E.L. Tsybenko, S.A. Chechkin, V.V. Grigor’eva, L.I. Beletskii, A.A. Kasilov, A.A. Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron Вопросы атомной науки и техники |
| description |
The study of wave processes occurring during the initial stage of RF plasma heating in the Uragan-3M torsatron was performed with using movable magnetic and electric probes. The heating was carried out by the frame antenna. The electric probe allowed to register changes of the plasma density profile, while the magnetic probes measured amplitude and phase shifts between all magnetic field components at different points over the plasma column cross-section. The frequency spectrum of magnetic field fluctuations contains the main frequency that coincides with the RF oscillator frequency and higher harmonics. The amplitude of the 2nd harmonic in this mode can be compared with the amplitude of the basic harmonic. |
| format |
Article |
| author |
Pashnev, V.K. Tarasov, I.K. Sitnikov, D.A. Sorokovoy, E.L. Tsybenko, S.A. Chechkin, V.V. Grigor’eva, L.I. Beletskii, A.A. Kasilov, A.A. |
| author_facet |
Pashnev, V.K. Tarasov, I.K. Sitnikov, D.A. Sorokovoy, E.L. Tsybenko, S.A. Chechkin, V.V. Grigor’eva, L.I. Beletskii, A.A. Kasilov, A.A. |
| author_sort |
Pashnev, V.K. |
| title |
Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron |
| title_short |
Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron |
| title_full |
Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron |
| title_fullStr |
Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron |
| title_full_unstemmed |
Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron |
| title_sort |
study of wave processes at the initial stage of rf-heating in the uragan-3m torsatron |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2017 |
| topic_facet |
Диагностика плазмы |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/122178 |
| citation_txt |
Study of wave processes at the initial stage of RF-heating in the Uragan-3M torsatron / V.K. Pashnev, I.K. Tarasov, D.A. Sitnikov, E.L. Sorokovoy, S.A. Tsybenko, V.V. Chechkin, L.I. Grigor’eva, A.A. Beletskii, A.A. Kasilov // Вопросы атомной науки и техники. — 2017. — № 1. — С. 247-250. — Бібліогр.: 15 назв. — англ. |
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Вопросы атомной науки и техники |
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ISSN 1562-6016. ВАНТ. 2017. №1(107)
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2017, № 1. Series: Plasma Physics (23), p. 247-250. 247
STUDY OF WAVE PROCESSES AT THE INITIAL STAGE
OF RF-HEATING IN THE URAGAN-3M TORSATRON
V.K. Pashnev, I.K. Tarasov, D.A. Sitnikov, E.L. Sorokovoy, S.A. Tsybenko, V.V. Chechkin,
L.I. Grigor’eva, A.A. Beletskii, A.A. Kasilov
Institute of Plasma Physics of the NSC KIPT, Kharkov, Ukraine
E-mail: pashnev@kipt.kharkov.ua
The study of wave processes occurring during the initial stage of RF plasma heating in the Uragan-3M torsatron was
performed with using movable magnetic and electric probes. The heating was carried out by the frame antenna. The electric
probe allowed to register changes of the plasma density profile, while the magnetic probes measured amplitude and phase shifts
between all magnetic field components at different points over the plasma column cross-section. The frequency spectrum of
magnetic field fluctuations contains the main frequency that coincides with the RF oscillator frequency and higher harmonics.
The amplitude of the 2nd harmonic in this mode can be compared with the amplitude of the basic harmonic.
PACS: 52.55.Dy, 52.55.Hc
INTRODUCTION
RF heating is one of the main methods of plasma
heating in toroidal magnetic traps due to resonance
effects of absorption of electromagnetic radiation in a
magnetized plasma. The ion cyclotron range of
frequencies (ICRF) is one of the most important
frequency ranges. Modern fusion facilities use these
frequencies in the band from one to several tens of MHz.
The ICRF includes at least two areas of resonance
absorption, namely, ion cyclotron and Alfven resonances.
The ITER tokamak which is under construction envisages
the possibilities to facilitate the breakdown using RF
techniques. The propagation of electromagnetic waves in
a magnetized plasma within this frequency range has
been studied theoretically in sufficient detail [1-4], and a
large number of experiments on ICRF plasma heating has
been conducted [5, 6].
In particular, experiments on ICRF wave generation and
plasma heating are conducted for a long time on the Uragan-
3M (U-3M) torsatron [7, 8]. With that, there are some
problems for the U-3M. First of all, these are a little
fraction of the RF power generated by the oscillator and
absorbed in the plasma and difficulties arising with
dense plasma heating (> 5×10
18
m
-3
) [9, 10].
The aim of this work was to study electromagnetic
ICRF waves exited in the U-3M plasma at the initial
stage of the RF discharge.
EXPERIMENTAL CONDITIONS AND
RESULTS
In the U-3M torsatron [11] a hydrogen plasma is
ICRF produced and heated [12]. The toroidal magnetic
field in all the experiments was B0 = 0.72 Т. The
behavior of excited electromagnetic waves was studied
at the initial stage of the RF discharge.
The pre-ionization of the fueling gas was made by
applying RF voltage to the so-called “three-half-turn
antenna” (THTA) [10] (Fig. 1, indicated as A2). As a
result, a plasma was created with the line-averaged
density (average density) of <ne> ≈ 10
16
m
-3
. A further
increase of plasma parameters was realized by
energizing the so-called “frame antenna” (FA) [8]
(indicated as A1 in Fig. 1)). The RF power fed to the FA
attained W ≈ 150 kW. The plasma obtained in this
discharge had the following parameters: the average
density <ne> ≥ 10
18
m
-3
, the electron and ion temperatures
Te ≈ Ti ≤ (300…400) eV. Plasma heating was performed at
the frequency /2 ≈ 8.8 MHz, so the condition
ω = 2πf = 0.8 ωci(0) [5], where ωci is the ion cyclotron
frequency on the geometrical axis of the device.
The following discharge parameters were recorded:
the high-frequency current in FA IRF, the Hα radiation, the
average density <ne> measured by the 2 mm
interferometer, the current in plasma measured by the
Rogowski loop Ipl, and the plasma energy content
recorded by the diamagnetic loop. The local electron
density ne was estimated from Langmuir probe
measurements. Magnetic fields of waves propagating in
the plasma were measured using two three-component
magnetic probes.
The design of the magnetic probes was as follows.
Two magnetic probes MP-1 and MP-2 were fastened to a
movable Langmuir probe (LP) one after the other
sequentially in the direction of LP motion with the
distance of 1.5 cm. Each MP could record 3 components
of the magnetic field of plasma waves. The distance
between the utmost MP and the LP was 5 cm. The MPs
were provided into the electrostatic screen and placed in a
quartz glass tube.
The magnetic probes allowed to record the BR, BZ, и
Bφ components of the fluctuating magnetic field with
the frequency of ≤ 100 MHz. The probe sensitivity
was NS = 6×10
-4
m
2
×turn in the R
direction and
NS = 3×10
-4
m
2
×turn, in the Z and φ directions. Here N
is the number of turns in the probe, S is the probe area.
Fig. 1 shows the scheme of probes layout relative to
the RF antennas and magnetic surfaces in the poloidal
cross-section where the probes are located. The dotted
line shows the direction of probe movement. The probes
are disposed at the toroidal distance of 2 helical
magnetic field periods (9 periods in total) relative to the
FA (antenna A1).
Temporal behavior of main parameters of the
discharge is given in Fig. 2 where probes are withdrawn
from the confinement area. From Fig. 2 it is clear that
within the 1st millisecond after RF voltage being
applied to the antenna A2 the current in the antenna
starts to decrease and by the 2nd millisecond (vertical
dotted line) it reaches its quasi-stationary value. Hα
during the 1st millisecond reaches its maximum and the
longitudinal current starts increasing steadily. The
248 ISSN 1562-6016. ВАНТ. 2017. №1(107)
average plasma density reaches its quasi-stationary level
in 1.5 ms. So, it could be assumed that the initial stage
of the discharge ends by the 2nd ms. Hereinafter, the
discharge was reduced up to 2 ms to be able to enter
probes to the area of plasma confinement.
Fig. 1. Helical coils I, II, III of the U-3M torsatron. The
poloidal cross-section of the torus showing positions of
helical coils, magnetic probe and vacuum magnetic
surfaces
Fig. 2. Time behavior of main discharge parameters
Time dependence of the plasma density distribution on
magnetic surfaces ‹r› (Fig. 3) was obtained basing on
measurements of the LP saturation current. In this case,
‹r› is the average radius of the magnetic surface
determined by the area of this surface S = π ‹r›
2
. The
plasma density was calculated considering the electron
temperature obtained from diamagnetic measurements
assuming that the ion temperature was Тi=0 and the
electron temperature distribution on magnetic surfaces
coincides with the saturation current distribution. Also, it
was assumed that the plasma density ne and the electron
temperature Te are constant on the magnetic surface. It is
seen that during the discharge there is a predominant
density increase on the magnetic axis (‹r› = 0 cm). During
measurements the magnetic probes were on the magnetic
surface ‹r› = 2 cm (probe MP-1) and on ‹r› = 5 сm (MP-2).
Fig. 3. Plasma density distribution on magnetic surfaces
at different times
The signals from magnetic probes were recorded
using 4-beam oscilloscopes that allowed to receive
signals with the frequency up to 200 MHz (Fig. 4). It is
seen that the signal form differs from sinusoid, i.e., the
signal spectrum has also higher harmonics. A typical
frequency spectrum of signals is given in Fig. 5.
Fig. 4. Typical oscillations of the magnetic field
components, registered by the magnetic probes:
1 Btor; 2 BR; 3 Bpol
Fig. 5. The spectrum of the magnetic field fluctuations
ISSN 1562-6016. ВАНТ. 2017. №1(107) 249
Fig. 6 shows time dependence of the first harmonic
amplitude of magnetic field fluctuations for different
spatial components that were measured near the
magnetic axis of the plasma configuration (‹r› = 2 cm,
probe MP-1). It is seen that the BR component is the
highest in value and increases with the plasma density
(Fig. 7); by the 2nd millisecond of the discharge BR
exceeds other components almost by the order of
magnitude. The maximum amplitude of this harmonic
attains BR≈ 0.6 G.
Fig. 6. Time behavior of the amplitude of the 1st
harmonic oscillation (8.8 MHz) near the axis of the
magnetic configuration (probe MP-1)
Fig. 7 shows time behaviors a) fluctuation amplitudes of
the 1st harmonic of the BR component that were measured
by different probes (MP-1 and MP-2) in different spatial
points of the plasma column; b) density trend in the area of
magnetic probes location; c) phase difference between these
fluctuations 1.5 cm separated in space.
Fig. 7. Time variations of BR components (1st harmonic)
on the magnetic surfaces<r>=2 cm and <r>=5cm; the
behavior of the local density ne and the phase shift ΔΘ
between the oscillations on these surfaces
According to the plasma density distribution (Fig. 3)
and the oscillation energy distribution (Fig. 7), the main
power is introduced into the central region of the
discharge.
CONCLUSIONS
1. Distributions of the plasma density and RF magnetic
field fluctuations were obtained in the plasma
confinement area at the initial stage of the FA driven
discharge using electrostatic and magnetic probes.
2. The phase difference between the fluctuations was
determined for different magnetic field components.
3. The density increase and the maximum level of the
energy of the magnetic field fluctuation are in the area
of magnetic axis of the plasma configuration. The main
fluctuation energy is accumulated in the BR component.
4. At the initial stage of plasma accumulation the main
power injected into the plasma volume using the frame
antenna is concentrated near central areas of the plasma
configuration.
5. Maximum fluctuation amplitude in the given
discharge attains BR ≈ 0.6 G.
6. The frequency spectrum of the RF oscillation, besides
the fundamental harmonic comprises the second and
higher harmonics.
REFERENCES
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2. R. Klima, A.V. Longinov, K.N. Stepanov. High-
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3. A.V. Longinov and K.N. Stepanov. High-frequency
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4. V.E. Golant and V.I. Fedorov. RF plasma heating in
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1989.
5. J.R. Wilson, M. Bell, A. Cavallo, et al. ICRH heating
on the TFTR tokamak for PRF up to 2.5 MW // Plasma
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10. L.I. Grigor’eva, V.V. Chechkin, V.E. Moiseenko, et
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Article received 19.01.2017
ИССЛЕДОВАНИЕ ПОВЕДЕНИЯ ЭЛЕКТРОМАГНИТНЫХ ВОЛН В НАЧАЛЬНОЙ СТАДИИ
ВЧ-РАЗРЯДА В ОБЛАСТИ УДЕРЖАНИЯ ПЛАЗМЫ В ТОРСАТРОНЕ УРАГАН-3М
В.К. Пашнев, И.К. Тарасов, Д.А. Ситников, Э.Л. Сороковой, С.А. Цыбенко В.В. Чечкин, Л.И. Григорьева,
А.А. Белецкий, А.А. Касилов
С помощью подвижных магнитных и электрических зондов в торсатроне Ураган-3М были изучены
волновые процессы, протекающие на начальной стадии ВЧ-нагрева. Нагрев плазмы проводился с помощью
“рамочной” антенны. Электрический зонд позволял регистрировать изменение профиля плотности плазмы, а
магнитные зонды измеряли амплитуду и сдвиг фаз между всеми компонентами поля в различных точках по
сечению плазменного шнура. Частотный спектр регистрируемых колебаний магнитного поля содержит
основную частоту, совпадающую с частотой ВЧ-генератора, и более высокие гармоники. Амплитуда второй
гармоники в данном режиме может быть сравнима с амплитудой основной гармоники.
ДОСЛІДЖЕННЯ ПОВЕДІНКИ ЕЛЕКТРОМАГНІТНИХ ХВИЛЬ В ПОЧАТКОВІЙ СТАДІЇ
ВЧ-РОЗРЯДУ В ОБЛАСТІ УТРИМАННЯ ПЛАЗМИ В ТОРСАТРОНІ УРАГАН-3М
В.К. Пашнєв, І.К. Тарасов, Д.А. Сiтнiков, Е.Л. Сороковий, С.А. Цибенко, В.В. Чечкін, Л.І. Григор’єва,
О.О. Білецький, А.А. Касілов
За допомогою рухливих магнітних і електричних зондів у торсатроні Ураган-3М були вивчені хвильові
процеси, що протікають на початковій стадії ВЧ-нагріву. Нагрівання плазми проводилося за допомогою
"рамкової" антени. Електричний зонд дозволяв реєструвати зміну профілю щільності плазми, а магнітні зонди
вимірювали амплітуду і зрушення фаз між усіма компонентами поля в різних точках по перерізу плазмового
шнура. Частотний спектр реєстрованих коливань магнітного поля містить основну частоту, яка збігається з
частотою ВЧ-генератора, і більш високі гармоніки. Амплітуда другої гармоніки в даному режимі може бути
порівнянна з амплітудою основної гармоніки.
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