A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry
Results of experiment modeling backscattering of microwaves from rotating plasma layer perturbed by fluctuations are presented. It was shown that auto- and crosscorelation of reflected power have a periodicity equal to rotation period. Such periodicity was observed by microwave reflectometry in expe...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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| Zitieren: | A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry / O.S. Pavlichenko, A.I. Skibenko, I.P. Fomin, I.B. Pinos, V.L. Ocheretenko, V.L. Berezhniy // Вопросы атомной науки и техники. — 2000. — № 6. — С. 172-174. — Бібліогр.: 5 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859655789073924096 |
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| author | Pavlichenko, O.S. Skibenko, A.I. Fomin, I.P. Pinos, I.B. Ocheretenko, V.L. Berezhniy, V.L. |
| author_facet | Pavlichenko, O.S. Skibenko, A.I. Fomin, I.P. Pinos, I.B. Ocheretenko, V.L. Berezhniy, V.L. |
| citation_txt | A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry / O.S. Pavlichenko, A.I. Skibenko, I.P. Fomin, I.B. Pinos, V.L. Ocheretenko, V.L. Berezhniy // Вопросы атомной науки и техники. — 2000. — № 6. — С. 172-174. — Бібліогр.: 5 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | Results of experiment modeling backscattering of microwaves from rotating plasma layer perturbed by fluctuations are presented. It was shown that auto- and crosscorelation of reflected power have a periodicity equal to rotation period. Such periodicity was observed by microwave reflectometry in experiments on RF plasma production on U-3M torsatron and was used for measurement of plasma poloidal rotation velocity.
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| first_indexed | 2025-12-07T13:39:39Z |
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172 Problems of Atomic Science and Technology. 2000. № 6. Series: Plasma Physics (6). p. 172-174
UDC 533.9
A SIMPLE METHOD OF POLOIDAL ROTATION VELOCITY
MEASUREMENT IN TOROIDAL PLASMAS VIA MICROWAVE
REFLECTOMETRY
O.S.Pavlichenko, A.I.Skibenko, I.P.Fomin, I.B.Pinos, V.L.Ocheretenko, V.L.Berezhniy
Institute of Plasma Physics of NSC KhIPT, Kharkov 61108, Ukraine
Results of experiment modeling backscattering of microwaves from rotating plasma layer perturbed by
fluctuations are presented. It was shown that auto- and crosscorelation of reflected power have a periodicity equal to
rotation period. Such periodicity was observed by microwave reflectometry in experiments on RF plasma
production on U-3M torsatron and was used for measurement of plasma poloidal rotation velocity.
1. Introduction
One of key issues of confinement studies in
stellarators now is an understanding of role of the radial
electric field. Heavy ion beam probe (HIBP) technic is
being used (CHS) or prepared (TJ-II, LHD) for
measurement of plasma potential. This technic needs
special ports on device and is expensive. Indirect
method of electric field measurement is observation of
poloidal plasma rotation in crossed radial electric and
toroidal magnetic fields. Change exchange spectroscopy
(CHXS) is being used for observation of Doppler shift
of ion spectral lines and calculation of poloidal rotation
velocity (W7-AS, CHS). This diagnostic needs a special
diagnostic neutral beam or uses plasma heating neutral
beam. Therefore any new and possibly more simple
diagnostics for observation of poloidal plasma rotation
with a good spatial resolution are welcomed.
Microwave reflectometry is a well-known technic
for measurement of electron density profiles and its
fluctuations. It has a rather good spatial resolution (few
mm). Microwave reflectometry is being extensively
used on Uragan-3M (U-3M) torsatron for radial electron
density and its fluctuation profiles measurements [1-2].
Microwave (O- and X- mode) reflectometry setup on U-
3M uses 3 monostatic (launch/receive) antennas ported
in one of toroidal crossections of l=3 torsatron between
helical conductors (Fig.1). This setup allows to study
crosscorrelation between microwave signals reflected in
different poloidal locations and was used for
measurement of poloidal propagation velocity of plasma
fluctuations in experiments on RF plasma
production/heating in U-3M torsatron [3]. It was
observed that both auto (AC)- and crosscorrelation (CC)
of signals had periodical structures. Closer look showed
that period of modulation of both AC and CC is
proportional to the time delay of CC between signals of
different antennas. To understand this phenomenon we
performed a model experiment on observation of
microwave reflection from rotating rippled surface
metallic cylinder. It was shown that the period of both
AC and CC modulation is equal to the period of rotation
of cylinder. This conclusion became a basis of simple
measurement of poloidal rotation velocity of plasma via
microwave reflectometry in U-3M torsatron.
In this paper we present results of this model
experiment along with explanation (II), compare them
with data obtained on U-3M torsatron (III) and conclude
(IV) that modulation of AC of microwave power
reflected from plasma in tilted antenna geometry can be
used for measurement of poloidal rotation velocity in
toroidal magnetically confined plasmas.
II. Model experiment
The experiment was performed using the 37.5 GHz
fixed frequency homodyne reflectometer similar to that
Fig.1 Reflectometry setup at U-3M
Fig.2 Model experiment setup and photo
173
one installed on U-3M torsatron. Up to 10 mW cw
incident power was launched via a 20 dB standard gain
horn on the rippled rotating metallic surface. The same
antenna received reflected power. The reflecting rippled
surface was formed from 0.2-mm-thick stainless shim
mounted on the surface of grooved Al cylinder
(diameter of 240 mm and height of 40 mm). This
cylinder was previously used as the phase shifter of
λ=337 mkm laser interferometer and had a triangular
shaped grooves (period = 0.3 mm , height =0.3 mm).
The shim was pressed to form a periodical structure
with triangular teeth (period = 16 mm, height=3 mm).
This shim was mounted on cylinder surface without of
special care about saving periodicity of teeth and could
cover 90 % of cylinder circumference or total cylinder
surface. The cylinder was rotating with frequency of 6
Hz.
0
200
400
600
800
0 200 400 600 800
re
fle
ct
ed
p
ow
er
, a
.u
.
t,ms
-0.4
-0.2
0
0.2
0.4
0.6
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0 200 400 600 800
autocorelation
t , m s∆
Fig.3 Reflection from grooved cylinder (left-
detector signal, right- AC)
0
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400
600
800
0 200 400 600 800
re
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ct
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p
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re
fle
ct
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ow
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.u
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-0.6
-0.4
-0.2
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0.6
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0 200 400 600 800
re
fle
ct
ed
p
ow
er
, a
.u
.
autocorelation
autocorelation
autocorelation
t,ms
t,ms
t,ms t,ms∆
t,ms∆
t,ms∆a)
b)
c)
Fig.4 Reflection from 90% shim for different
antenna tilt angle α [a) α=0o, b) α=6o, c) α=16o]
The antenna was put on a distance of 30 mm from
reflecting surface along a horizontal line intersecting
cylinder center and could be moved vertically on a
distance up to 33 mm. This movement resulted in a tilt
of antenna to cylinder surface up to 16o (Fig.2).
The signal of microwave detector was digitized
with ADC (τ= 4 mks) and stored. The typical signals of
detector along with crosscorelation of signals are shown
on Fig. 3-4.
It was observed that in all cases : no shim (Fig.3),
90 % shim (Fig.4) and 100 % shim – the signal of
reflectometer exhibit periodical changes corresponding
to rotation period. These changes result in a well-
pronounced periodicity of crosscorrelation. As for as in
the case when the reflective surface was definitely
inhomogeneous (90 % shim) the periodicity of reflected
signal corresponds to the cylinder rotation period, one
can conclude that the period of crosscorrelation
modulation is equal to the cylinder rotation period.
This observation is general. Changes in rippled
surface shape and antenna tilt angle resulted only in
reflected power change. For shorter periodicity of
reflecting surface perturbations the modulation of
reflected power was smaller. More oblique wave launch
resulted in smaller backward reflection.
These observations are in a very good
correspondence with data of G.D.Conway [4] and one
can use all his arguments for explanation of backward
reflection of microwaves from rippled reflecting surface
as a result of Bragg diffraction. The novelty of our
experiment is in using of a rotating rippled surface and
showing that the periodicity in crosscorrelation of
reflected power is equal to reflecting surface rotation
period.
The periodic structure on autocorrelation can be
understood if to take into account a fact that the
frequency of microwaves reflected from moving surface
is Doppler shifted. This was clearly shown in
experiment on W7AS stellarator [5]. In homodyne
reflectometer this results in modulation of output signal
with frequency of Doppler shift. This modulation is
reflected in modulation of autocorrelation of output
signal.
III. Experiment on U-3M
Periodical structures in both auto and
crosscorrelation of signals were observed previously on
U-3M torsatron [1]. The typical forms of AC and CC
observed at simultaneous probing of plasma by antennas
2 and 3 are shown on Fig.5. The observed periodicity
can be interpreted now as result of poloidal rotation of
plasma reflecting layer with frequency F ≈ 10 kHz. This
rotation results in a corresponding time lag in
crosscorrelation between signals of 2 antennas.
Autocorrelation approach is now used in reflectometry
system of U-3M torsatron for measurement of plasma
poloidal rotation velocity. One of the data obtained is
shown on Fig.6. This figure presents the radial
distribution of poloidal rotation velocity obtained at
simultaneous plasma probing with both inside and
outside antennas with probing frequency change on
shot-to-shot basis. The most striking feature of this
observation is existence of strong poloidal velocity
shear in outer plasma.
174
0
1
-0.3 -0.2 -0.1 0 0.1 0.2 0.3
τ,ms
-0.5
0
0.5
1
-0.3 -0.2 -0.1 0 0.1 0.2 0.3
AC
CCτ13
Fig.5 Typical autocorelation and crosscorelation
(between antennas 1 and 3) on U-3M
-10
-5
0
5
10
-10 -5 0 5 10 15r, cm
po
lo
id
al
r
ot
at
io
n
ve
lo
ci
ty
, K
m
/s
Fig.6 Radial distribution of plasma poloidal rotation
velocity for RF produced plasma in U-3M torsatron
measured from AC and CC
IV. Conclusion
It was shown that when microwaves are
launched in tilted antenna geometry and are
backscattered from rotating rippled plasma cut-off layer,
both auto and crosscorrelations of output of homodyne
reflectometer have the periodicity corresponding to
rotation period. This gives a very simple and cost
effective way of measurement of plasma poloidal
rotation velocity. If plasma probing is being performed
in one poloidal location, one can measure the value of
poloidal rotation velocity only. A direction of rotation
can be measured if one can port 2 antennas in different
poloidal locations and use crosscorelation.
The radial distribution of poloidal rotation velocity
can be measured in both tokamaks and stellarators by
using multi-frequency homodyne reflectometers similar
to that one used on many toroidal magnetic systems.
References
1. A.I.Skibenko, O.S.Pavlichenko et al., 23rd EPS
Conference on Controlled Fusion and Plasma
Physics, Contr.Papers., Kiev (1996), part III,
p.1124
2. V.L.Berezhniy, E.D.Volkov et al., Problems of
Atomic Science and Technology, Series: Plasma
Physics, Kharkov (1999), issues 3-4, p.43
3. O.S.Pavlichenko, A.I.Skibenko et al., XII
International Stellarator Conference, Contr.Papers,
Madison (1999)
4. G.D.Conway, Rev.Sci.Instrum, 64(10) , 2782
(1993)
5. C.Christou, J.Baldzuhn et al., 25th EPS Conference
on Controlled Fusion and Plasma Physics,
Contr.Papers., Praha (1998), ECA Vol.22C (1998),
1466-1469
O.S.Pavlichenko, A.I.Skibenko, I.P.Fomin, I.B.Pinos, V.L.Ocheretenko, V.L.Berezhniy
In this paper we present results of this model experiment along with explanation (II), compare them with data obtained on U-3M torsatron (III) and conclude (IV) that modulation of AC of microwave power reflected from plasma in tilted antenna geometry can
II. Model experiment
III. Experiment on U-3M
Fig.6 Radial distribution of plasma poloidal rotation velocity for RF produced plasma in U-3M torsatron measured from AC and CC
IV. Conclusion
References
|
| id | nasplib_isofts_kiev_ua-123456789-78565 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T13:39:39Z |
| publishDate | 2000 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Pavlichenko, O.S. Skibenko, A.I. Fomin, I.P. Pinos, I.B. Ocheretenko, V.L. Berezhniy, V.L. 2015-03-18T19:27:06Z 2015-03-18T19:27:06Z 2000 A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry / O.S. Pavlichenko, A.I. Skibenko, I.P. Fomin, I.B. Pinos, V.L. Ocheretenko, V.L. Berezhniy // Вопросы атомной науки и техники. — 2000. — № 6. — С. 172-174. — Бібліогр.: 5 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/78565 533.9 Results of experiment modeling backscattering of microwaves from rotating plasma layer perturbed by fluctuations are presented. It was shown that auto- and crosscorelation of reflected power have a periodicity equal to rotation period. Such periodicity was observed by microwave reflectometry in experiments on RF plasma production on U-3M torsatron and was used for measurement of plasma poloidal rotation velocity. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Plasma diagnostics A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry Article published earlier |
| spellingShingle | A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry Pavlichenko, O.S. Skibenko, A.I. Fomin, I.P. Pinos, I.B. Ocheretenko, V.L. Berezhniy, V.L. Plasma diagnostics |
| title | A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry |
| title_full | A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry |
| title_fullStr | A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry |
| title_full_unstemmed | A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry |
| title_short | A simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry |
| title_sort | simple method of poloidal rotation velocity measurement in toroidal plasmas via microwave reflectometry |
| topic | Plasma diagnostics |
| topic_facet | Plasma diagnostics |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/78565 |
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