Development of the system for multichannel microwave plasma probing in the torsatron U-2M
To study successfully the conditions for production and heating of the plasma, its dynamics in the process of an RF discharge in the torsatron U-2M, a multichannel system for microwave diagnostics is suggested. To obtain the electron density profiles with an asymmetric plasma cross-section in the...
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| Zitieren: | Development of the system for multichannel microwave plasma probing in the torsatron U-2M / V.L. Berezhnyj, V.L. Ocheretenko, I.B. Pinos, A.I. Skibenko, A.V. Prokopenko, Yu.V. Larin, S.M. Maznichenko, D.A. Sitnikov, M.I. Tarasov // Вопросы атомной науки и техники. — 2009. — № 1. — С. 22-24. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-881682015-11-09T03:02:10Z Development of the system for multichannel microwave plasma probing in the torsatron U-2M Berezhnyj, V.L. Ocheretenko, V.L. Pinos, I.B. Skibenko, A.I. Prokopenko, A.V. Larin, Yu.V. Maznichenko, S.M. Sitnikov, D.A. Tarasov, M.I. Магнитное удержание To study successfully the conditions for production and heating of the plasma, its dynamics in the process of an RF discharge in the torsatron U-2M, a multichannel system for microwave diagnostics is suggested. To obtain the electron density profiles with an asymmetric plasma cross-section in the l=2 torsatron, 5 fan channels and 3 longitudinal channels will be used. For these measurements a quadrature interferometer at a frequency of 140 GHz is under development. Для успішного вивчення умов створення і нагріву плазми, її динаміки в процесі ВЧ-розряду в торсатроні У-2М створюється багатоканальна система мікрохвильової діагностики. Для одержання профілів густини електронів з невісесиметричним перерізом плазми в двозаходному торсатроні буде використано п'ять віяльних і три подовжніх канали. Для цих вимірювань розробляється квадратурний інтерферометр на частоті 140 ГГц з гетеродинною індикацією фази. Для успешного изучения условий создания и нагрева плазмы, ее динамики в процессе ВЧ-разряда в торсатроне У-2М создается многоканальная система микроволновой диагностики. Для получения профилей плотности электронов с неосесимметричным сечением плазмы в двухзаходном торсатроне будет использовано пять веерных и три продольных канала. Для этих измерений разрабатывается квадратурный интерферометр на частоте 140 ГГц с гетеродинной индикацией фазы. 2009 Article Development of the system for multichannel microwave plasma probing in the torsatron U-2M / V.L. Berezhnyj, V.L. Ocheretenko, I.B. Pinos, A.I. Skibenko, A.V. Prokopenko, Yu.V. Larin, S.M. Maznichenko, D.A. Sitnikov, M.I. Tarasov // Вопросы атомной науки и техники. — 2009. — № 1. — С. 22-24. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS: 52.55.Hc http://dspace.nbuv.gov.ua/handle/123456789/88168 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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Магнитное удержание Магнитное удержание |
| spellingShingle |
Магнитное удержание Магнитное удержание Berezhnyj, V.L. Ocheretenko, V.L. Pinos, I.B. Skibenko, A.I. Prokopenko, A.V. Larin, Yu.V. Maznichenko, S.M. Sitnikov, D.A. Tarasov, M.I. Development of the system for multichannel microwave plasma probing in the torsatron U-2M Вопросы атомной науки и техники |
| description |
To study successfully the conditions for production and heating of the plasma, its dynamics in the process of an RF
discharge in the torsatron U-2M, a multichannel system for microwave diagnostics is suggested. To obtain the electron
density profiles with an asymmetric plasma cross-section in the l=2 torsatron, 5 fan channels and 3 longitudinal
channels will be used. For these measurements a quadrature interferometer at a frequency of 140 GHz is under
development. |
| format |
Article |
| author |
Berezhnyj, V.L. Ocheretenko, V.L. Pinos, I.B. Skibenko, A.I. Prokopenko, A.V. Larin, Yu.V. Maznichenko, S.M. Sitnikov, D.A. Tarasov, M.I. |
| author_facet |
Berezhnyj, V.L. Ocheretenko, V.L. Pinos, I.B. Skibenko, A.I. Prokopenko, A.V. Larin, Yu.V. Maznichenko, S.M. Sitnikov, D.A. Tarasov, M.I. |
| author_sort |
Berezhnyj, V.L. |
| title |
Development of the system for multichannel microwave plasma probing in the torsatron U-2M |
| title_short |
Development of the system for multichannel microwave plasma probing in the torsatron U-2M |
| title_full |
Development of the system for multichannel microwave plasma probing in the torsatron U-2M |
| title_fullStr |
Development of the system for multichannel microwave plasma probing in the torsatron U-2M |
| title_full_unstemmed |
Development of the system for multichannel microwave plasma probing in the torsatron U-2M |
| title_sort |
development of the system for multichannel microwave plasma probing in the torsatron u-2m |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2009 |
| topic_facet |
Магнитное удержание |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/88168 |
| citation_txt |
Development of the system for multichannel microwave plasma probing in the torsatron U-2M / V.L. Berezhnyj, V.L. Ocheretenko, I.B. Pinos, A.I. Skibenko, A.V. Prokopenko,
Yu.V. Larin, S.M. Maznichenko, D.A. Sitnikov, M.I. Tarasov // Вопросы атомной науки и техники. — 2009. — № 1. — С. 22-24. — Бібліогр.: 5 назв. — англ. |
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Вопросы атомной науки и техники |
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| fulltext |
DEVELOPMENT OF THE SYSTEM FOR MULTICHANNEL MICROWAVE
PLASMA PROBING IN THE TORSATRON U-2M
V.L. Berezhnyj, V.L. Ocheretenko, I.B. Pinos, A.I. Skibenko, A.V. Prokopenko,
Yu.V. Larin, S.M. Maznichenko, D.A. Sitnikov, M.I. Tarasov
Institute of Plasma Physics, NSC “Kharkov Institute of Physics and Technology”,
Kharkov, Ukraine
To study successfully the conditions for production and heating of the plasma, its dynamics in the process of an RF
discharge in the torsatron U-2M, a multichannel system for microwave diagnostics is suggested. To obtain the electron
density profiles with an asymmetric plasma cross-section in the l=2 torsatron, 5 fan channels and 3 longitudinal
channels will be used. For these measurements a quadrature interferometer at a frequency of 140 GHz is under
development.
PACS: 52.55.Hc
To study the conditions for production and heating of
the plasma, and its dynamics in the process of an RF
discharge in the torsatron U-2M, a multichannel system
for microwave diagnostics will be used. The main
destination of this system is to determine the electron
density spatial distribution ne and its fluctuations δne/ne.
Taking into account the installation design and plasma
column cross-section [1], the most optimum variant is the
use of five fan channels for electron density measuring
along the major plasma oval axis and three channels along
the minor plasma oval axis [2], Fig.1. For these purposes
two independent microwave interferometers with
heterodyne detection of phase (ϕ) are intended to be
designed.
In this device, operating under optimum conditions
(Кϕ = Bth/B0 = 0.32, Bth is the toroidal magnetic field
produced by the helical winding, B0 is the total toroidal
magnetic strength) the plasma density can reach the value
above 1⋅1019 m-3. With such an electron density value the
refraction at peripheral probing channels can lead to the
distortion of information obtained. For the plasma column
with a cylindrical symmetry and parabolic distribution of
the electron density ne(r) = n0[1-(r/r0)2] by probing with a
paraxial microwave beam the refraction angle will be
2
0
0
0
0
0
0 1
2
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−⋅
⋅
=
r
x
r
x
n
n
cr ε
θ , (1)
22 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2009. № 1.
Series: Plasma Physics (15), p. 22-24.
where n0 is the density on the axis, ncr is the critical
density for the given probing frequency, ε0 is the
dielectric permittivity of the plasma on the axis, x0 is the
impact parameter, r0 is the plasma radius. This formula
cannot be applied to conditions of the torsatron U-2M. In
the mode Кϕ = 0.32 the magnetic axis is shifted inwards
from the geometrical axis by ~ 5 cm. The plasma cross-
section has a form of an oval with a major axis of ~ 60 сm
and a minor axis of ~ 30 сm. Nevertheless, the analysis of
equation (1) can give general fruitful results – the less is
the n0/ncr for any given probing wavelength, the less is the
refraction angle, and θ possesses the maximum value at
x0/r0 = 0.7. Because of the beam bending, the physical
path length increases what leads to the change in the
amplitude of a signal detected S = A⋅cosϕ. On the other
side, the beam gets into the different-value density
ne = f(a) along the probing beam path (a) than it might be
in the case if the beam passes without refraction directly.
The errors due to the refraction of probing beams are of
the same order of magnitude. Displacement of probing
beam center Δx = l⋅tgθ relatively to the receiving horn
center was calculated for the equal distance l = 60 сm
from the transmitting antenna to all the receiving
antennas. From this it follows that the receiving antenna
should be installed as close to the plasma as possible. The
limits for electron density measurement by means of
microwave interferometers in the U-2M for three lengths
of probing waves with taking into account other possible
regimes of operation are given in the Table below. Here
the lower density limit is determined by the unique
determination of the phase ϕ = 2π. This limit can be
significantly decreased to sevearal degrees depending on
the type of interferometer in use. The upper limit of
plasma density is restricted by the value of critical
electron density for the given length of the probing wave.
Substantially, the upper limit of the electron density being
measured in the periphery region of the plasma is
decreased by the refraction effects. To minimize the
refraction effects, one should: optimize the construction
and arrangement of microwave elements inside the
discharge chamber [3], use the quadrature interferometers
with heterodyne phase indication, select a rather high
probing frequency with taking into account the maximal
value of ne. The quadrature interferometer has two
separate output sygnals S1 = A⋅cosϕ and S2 = A⋅sinϕ with
a phase shifted by π/2. Interpretation of quadrature
interferometer data is unambiguous even if the phase is
changing by many π/2 values. The quadrature
interferometer has not ambiguity in the determination of
the differential response dϕ/dt. As one signal approaches
an extremum, the other channel is in the middle of its
range, so that the sign of dϕ/dt is never uncertain.
Therefore, the data interpretation is unambiguous even
when the phase is changing by many orders of magnitude.
For the quadrature interferometer it is characteristic that
the constant A has one and the same time variation of
every signal, when the amplitude of the phase envelope
amplitude is changing as a result of diagnostic beam
bending because of the refraction. Thus, the algorithm of
the analysis of quadrature interferometer data
ϕ = arctg(S2/S1)+n⋅π/2 is correct even in the presence of
refraction effects [4].
Five fan probing channels are realized within the
limits of the transmitting antenna directivity diagram
(~ 40°) therefore, the input power should be sufficient to
provide measurements along the lateral probing channels.
The ratio of a power in the outer channel to that in the
central one, with taking into account the real geometry of
the torsatron U-2M, is ~ 0.5 when the open waveguide of
1.8×3.6 mm cross-section is used as a radiator (see
Fig. 1, а). The measured values of the average electron
density by five chords allow to determine its distribution
along the central part (~20 cm) of the major axis of the
plasma oval. Because of the absence of plasma column
cylindrical symmetry it is intended to carry out the
probing for the three channels along the major size of the
oval, spaced at a distance of 43 mm, in the same plasma
column section (Fig. 1a), using the diagnostic ports P65 –
P67. However, because of the inclination of these flanges
by 6° outwards the vertical axis of the plasma chamber
and the shift of the geometrical axis of the plasma oval
inwards by 5 cm in the operating mode of the installation
(Кϕ = 0.32) the external channel passes beside the plasma
column. It can be used as a control one, in the case of
variations В⊥/В0, for comparison between the data and the
probing measurements of the SOL plasma. As an
alternative, these three probing channels are
recommended to be doubled in the other plasma column
section, using the diagnostic ports Р9 – Р7 (Fig. 1b).
a b
Fig.1. Geometrical position of probing beams of the microwave interferometers at the torsatron U-2M between the
diagnostic ports: а) P66 – P64 and P65 – P67; b) P9 – P7
Refraction influence on the interferometric measurements of the electron density
in the plasma of the torsatron U-2M
N0, 1017
m-3
8 10 20 40 60 80 100 150 200 400 600 700 1000 2000 3000
23
λprobe = 8
mm
θmax, °
ΔΧ, mm
-
-
0.24
0.51
0.116
1.13 2.3 5.0
0.82
8.0
1.17
11.4
3.03
1.58
15.4 29.6
-----
-----
-----
-----
-----
-----
----- -----
------
------
------
------
------
------
-
-
------
0.057
λprobe = 4
mm
θmax, °
ΔΧ, mm
------ 0.55
0.17
0.12
1.12 1.71
0.31
0.47
0.24
2.37 3.0 4.58
1.56
0.67
6.51 15.3
2.99
29.3
-----
-----
------
------
------
------
------
------
-
λзонд = 2
mm
θmax, °
ΔΧ, mm -
------
------
------
------
0.04
0.03
0.27 0.41
0.07
0.11
0.06
0.55 0.69 1.05
0.3
0.47
0.14
1.41 2.94 4.58
0.85
2.17
0.65
6.33 8.3 21.2
------
------
In this section all the three channels traverse the
plasma column (Fig. 1b) due to displacement relatively to
the equatorial torus plane of the spatial magnetic axis of
the magnetic surfaces’ configuration. However, the
distance between the channels in this section is slightly
less (~30 mm). Measurements in the both these sections
can provide five values of the average density along the
major size of the plasma oval. Using these data, it is
possible to calculate the electron density distribution
along the minor axis of the plasma oval.
Realization of the microwave heterodyne
interferometer is based on the synchronization of the
transmitting and heterodyne oscillators by means of a
common quartz source. Moreover, for both, the
microwave oscillators [5], as well as, the corresponding
harmonics of RF oscillators can be directly used.
Simultaneously the algorithm design is under
development for automation of plasma electron density
profile construction by the results of interferometric
measurements. Some of probing channels will be used
also for measuring the electron density ne(a) and its
fluctuation ( ee nn /δ ) in the measurements on the
reflectometry and scattering of microwaves.
The above-mentioned methods of electron plasma
density diagnostics make it possible to represent the
density spatial distribution that will promote the solving
of other problems on investigations of the plasma in the
torsatron U-2M.
REFERENCES
1. G.G. Lesnyakov, D.P. Pogozhev, Yu.K. Kuznetsov,
N.T. Besedin, E.D. Volkov, O.S. Pavlichenko. Studies
of magnetic surfaces in the "Uragan-2M" torsatron //
23rd European Physical Society Conference on
Controlled Fusion and Plasma Physics, Kiev, Ukraine,
24-28 June 1996 / Contributed Papers, Part II, p. 547.
2. V.L. Berezhnyj, V.I. Kononenko, V.L. Ocheretenko,
V.А. Maslov, V.А. Svich, А.N. Topkov.
Mnogokanal'nye interferometry dalekoi infrakrasnoi
oblasti dlya izmereniya plotnosti elektronov v
stellaratore "Uragan-2M" // Fizika plazmy. 1994, v. 20,
№ 1, p. 12-14. (in Russian).
3. J.C. Hosea and F.C. Jobes. Multichannel Wave
Interferometry: Preprint MATT-1176, Princeton, New
Jersey: Princeton University, p. 36, 1975.
4. C.J. Buchenauer and A.R. Jacobson. Quadrature
interferometer for plasma density measurements // Rev.
Sci. Instrum. 1977, v. 48, № 7, p. 769-774.
5. G. Neumann and Banziger. Plasma-density
measurements by microwave interferometry and
Langmuir probes in an rf discharge // Rev. Sci. Instrum.
1993, v. 64, № 1, p. 19-25.
Article received 10.10.08
РАЗРАБОТКА СИСТЕМЫ МНОГОКАНАЛЬНОГО МИКРОВОЛНОВОГО ЗОНДИРОВАНИЯ
ПЛАЗМЫ В ТОРСАТРОНЕ У-2М
В.Л. Бережный, В.Л. Очеретенко, И.Б. Пинос, А.И. Скибенко, А.В. Прокопенко,
Ю.В. Ларин, С.М. Мазниченко, Д.А. Ситников, М.И. Тарасов
Для успешного изучения условий создания и нагрева плазмы, ее динамики в процессе ВЧ-разряда в
торсатроне У-2М создается многоканальная система микроволновой диагностики. Для получения профилей
плотности электронов с неосесимметричным сечением плазмы в двухзаходном торсатроне будет использовано
пять веерных и три продольных канала. Для этих измерений разрабатывается квадратурный интерферометр на
частоте 140 ГГц с гетеродинной индикацией фазы.
РОЗРОБКА СИСТЕМИ БАГАТОКАНАЛЬНОГО МІКРОХВИЛЬОВОГО ЗОНДУВАННЯ
ПЛАЗМИ В ТОРСАТРОНІ У-2М
В.Л. Бережний, В.Л. Очеретенко, І.Б. Пінос, А.І. Скибенко, А.В. Прокопенко,
Ю.В. Ларін, С.М. Мазніченко, Д.А. Ситников, М.І. Тарасов
Для успішного вивчення умов створення і нагріву плазми, її динаміки в процесі ВЧ-розряду в торсатроні
У-2М створюється багатоканальна система мікрохвильової діагностики. Для одержання профілів густини
електронів з невісесиметричним перерізом плазми в двозаходному торсатроні буде використано п'ять віяльних і
три подовжніх канали. Для цих вимірювань розробляється квадратурний інтерферометр на частоті 140 ГГц з
гетеродинною індикацією фази.
24
Institute of Plasma Physics, NSC “Kharkov Institute of Physics and Technology”,
Kharkov, Ukraine
|