Magnetic diagnostics for torsatron U-2M
The features of application of magnetic diagnostics in torsatron U-2M are described. The methods to account for the influence of the metal environment and induced magnetic fields on the results of magnetic measurements are presented. During the experimental program on torsatron U-2M with help of m...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2011
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| Цитувати: | Magnetic diagnostics for torsatron U-2M / V.K. Pashnev, A.A. Petrushenya, E.L. Sorokovoy, V.V. Krasnyj // Вопросы атомной науки и техники. — 2011. — № 1. — С. 176-178. — Бібліогр.: 6 назв. — англ. |
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irk-123456789-910692016-01-07T03:03:43Z Magnetic diagnostics for torsatron U-2M Pashnev, V.K. Petrushenya, A.A. Sorokovoy, E.L. Krasnyj, V.V. Диагностика плазмы The features of application of magnetic diagnostics in torsatron U-2M are described. The methods to account for the influence of the metal environment and induced magnetic fields on the results of magnetic measurements are presented. During the experimental program on torsatron U-2M with help of magnetic diagnostics, the most important characteristics of the plasma, such as the value of the plasma energy content, the energy confinement time, the power inputted in the plasma, the value of Pfirsch-Schluter currents, the presence of magnetic islands, the shift of magnetic surfaces, the structure of MHD instabilities will be determined Описано особливості застосування магнітної діагностики в торсатроні U-2M. Представлено методи врахування впливу металевого оточення на результатах магнітних вимірювань. У ході експериментальної програми на торсатроні U-2M за допомогою магнітної діагностики визначатимуться найбільш важливі характеристики плазми, такі, як величина енерговмісту плазми, енергетичний час життя, введена в плазму потужність, величина струмів Пфірша-Шлюттера, наявність магнітних островів, зсув магнітних поверхонь, структура МГД-нестійкостей. Описаны особенности применения магнитной диагностики в торсатроне U-2M. Представлены методы учета влияния металлического окружения на результаты магнитных измерений. В ходе экспериментальной программы на торсатроне U-2M с помощью магнитной диагностики будут определяться наиболее важные характеристики плазмы, такие, как величина энергосодержания плазмы, энергетическое время жизни, введенная в плазму мощность, величина токов Пфирша-Шлюттера, наличие магнитных островов, смещение магнитных поверхностей, структура МГД-неустойчивостей. 2011 Article Magnetic diagnostics for torsatron U-2M / V.K. Pashnev, A.A. Petrushenya, E.L. Sorokovoy, V.V. Krasnyj // Вопросы атомной науки и техники. — 2011. — № 1. — С. 176-178. — Бібліогр.: 6 назв. — англ. 1562-6016 PACS: 52.55.Dy, 52.55.Hc http://dspace.nbuv.gov.ua/handle/123456789/91069 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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DSpace DC |
| language |
English |
| topic |
Диагностика плазмы Диагностика плазмы |
| spellingShingle |
Диагностика плазмы Диагностика плазмы Pashnev, V.K. Petrushenya, A.A. Sorokovoy, E.L. Krasnyj, V.V. Magnetic diagnostics for torsatron U-2M Вопросы атомной науки и техники |
| description |
The features of application of magnetic diagnostics in torsatron U-2M are described. The methods to account for the
influence of the metal environment and induced magnetic fields on the results of magnetic measurements are presented.
During the experimental program on torsatron U-2M with help of magnetic diagnostics, the most important
characteristics of the plasma, such as the value of the plasma energy content, the energy confinement time, the power
inputted in the plasma, the value of Pfirsch-Schluter currents, the presence of magnetic islands, the shift of magnetic
surfaces, the structure of MHD instabilities will be determined |
| format |
Article |
| author |
Pashnev, V.K. Petrushenya, A.A. Sorokovoy, E.L. Krasnyj, V.V. |
| author_facet |
Pashnev, V.K. Petrushenya, A.A. Sorokovoy, E.L. Krasnyj, V.V. |
| author_sort |
Pashnev, V.K. |
| title |
Magnetic diagnostics for torsatron U-2M |
| title_short |
Magnetic diagnostics for torsatron U-2M |
| title_full |
Magnetic diagnostics for torsatron U-2M |
| title_fullStr |
Magnetic diagnostics for torsatron U-2M |
| title_full_unstemmed |
Magnetic diagnostics for torsatron U-2M |
| title_sort |
magnetic diagnostics for torsatron u-2m |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2011 |
| topic_facet |
Диагностика плазмы |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/91069 |
| citation_txt |
Magnetic diagnostics for torsatron U-2M / V.K. Pashnev, A.A. Petrushenya, E.L. Sorokovoy, V.V. Krasnyj // Вопросы атомной науки и техники. — 2011. — № 1. — С. 176-178. — Бібліогр.: 6 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT pashnevvk magneticdiagnosticsfortorsatronu2m AT petrushenyaaa magneticdiagnosticsfortorsatronu2m AT sorokovoyel magneticdiagnosticsfortorsatronu2m AT krasnyjvv magneticdiagnosticsfortorsatronu2m |
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2025-07-06T19:17:35Z |
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| fulltext |
176 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2011. 1.
Series: Plasma Physics (17), p. 176-178.
MAGNETIC DIAGNOSTICS FOR TORSATRON U-2M
V.K. Pashnev, A.A. Petrushenya, E.L. Sorokovoy, V.V. Krasnyj
Institute of Plasma Physics, NSC “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
E-mail: a.petrushenya@kipt.kharkov.ua
The features of application of magnetic diagnostics in torsatron U-2M are described. The methods to account for the
influence of the metal environment and induced magnetic fields on the results of magnetic measurements are presented.
During the experimental program on torsatron U-2M with help of magnetic diagnostics, the most important
characteristics of the plasma, such as the value of the plasma energy content, the energy confinement time, the power
inputted in the plasma, the value of Pfirsch-Schluter currents, the presence of magnetic islands, the shift of magnetic
surfaces, the structure of MHD instabilities will be determined.
PACS: 52.55.Dy, 52.55.Hc
1. INTRODUCTION
Magnetic diagnostics is a set of magnetic sensors and
electronic devices, which allow to determine some of the
most important characteristics of the plasma as a result of
registration and processing of magnitudes of the magnetic
fields generated by plasma currents outside the volume
confinement [1-3]. The possibilities of magnetic
diagnostics in stellarator systems significantly enhanced
with respect to tokomaks because of existence of a
stellarator vacuum magnetic configuration. As was shown
in [4], magnetic diagnostics allow to determine the value
of the longitudinal plasma current, the value of the plasma
energy content, the power inputted in the plasma, the
energy confinement time of the plasma, shift and
deformation of magnetic surfaces, the structure of
magnetic islands, the structure of MHD instabilities, etc.
However, to obtain such information and to measure
variation of magnetic fields, a large number of magnetic
sensors should be placed outside of confinement value.
The main difficulty in carrying out magnetic
measurements is the account of the image currents arising
in the metal environment under the influence of plasma
currents.
In this paper we described the features of application
of magnetic diagnostics in the installation of torsatron
U-2M, as well as the methods to account for the influence
of the metal environment on the results of magnetic
measurements.
2. MAIN RESULTS
Vacuum chamber of torsatron U-2M consists of a set
of thin-walled sections (with wall thickness up to 5 mm)
interconnected by a silphons (with wall thickness of about
1 mm). The vacuum chamber is placed in a toroidal metal
case (with wall thickness up to 8 mm), on which the
helical coils are mounted. Estimates show that over such
metallic environment the magnetic field can penetrate
without distortions, if duration of impulse front of
magnetic field greater than 10 ms. Because the duration of
heating on torsatron U-2M is about 100 ms, placing
magnetic sensors outside the vacuum chamber will not
allow us to obtain information about magnetic fields of
plasma currents. Therefore, all the sensors of magnetic
diagnostics must be installed inside a vacuum chamber.
However, in most modes of operation of torsatron
U-2M the last closed magnetic surface can touch with
the wall of the vacuum chamber. Therefore is planned to
install limiters inside the vacuum chamber of torsatron
U-2M. These limiters will restrict the plasma at the
distance of 2 cm from the chamber walls. This distance
allows installing magnetic sensors inside the vacuum
chamber.
To carry out the program of research on torsatron
U-2M, magnetic sensors will be installed in advance in
the chamber. These sensors will register variations in the
toroidal magnetic flux, as well as variations in harmonics
of poloidal magnetic field over toroidal angle in the range
of frequencies from 10 Hz up to 200 kHz. The value of
the plasma energy content, the plasma energy
confinement time and the power inputted in the plasma
will be determine by registration of variations of toroidal
magnetic flux and zero harmonic of poloidal magnetic
field created by longitudinal plasma current. The value of
Pfirsch-Schluter currents, the shift of magnetic surfaces,
the structure of MHD instabilities, corresponding to the
first harmonic will be determine by registration of
variations of first and zero harmonics of the poloidal
magnetic field. The presence of magnetic islands, shift of
magnetic surfaces, the structure of the MHD instability,
corresponding to the second harmonic will be determined
by registration of variations of the second harmonic of the
poloidal magnetic field.
To register variations of the toroidal magnetic flux we
are planning to install diamagnetic loops inside the
vacuum chamber. To register variations of zero, first and
second harmonics of the poloidal magnetic flux over the
toroidal angle, the sets of 16 mirnov coils will be installed
in five sections of the torus.
Two diamagnetic loops covering different areas and
located in one section of the torus will be used to
compensate induced magnetic fields during the
diamagnetic measurements. With the help of an analog-
digital methods a useful signal, which is the same for each
loop, will be extracted. Block diagram of diamagnetic
measurements is shown in Fig. 1. A similar method of the
diamagnetic flux measurement has been used successfully
in torsatron U-3M. Before measuring the electronic circuit
of an analog-digital converter is tuned so that in the
absence of useful signal the resulting signal registered by
diamagnetic loops was zero. Due to this, it becomes
mailto:a.petrushenya@kipt.kharkov.ua
177
Integrator
To
ta
liz
er
2
ADC
To
ta
liz
er
1D
D
AmplifierInverter Integrator
T
ot
al
iz
er
2
ADC
T
ot
al
iz
er
1D1
D2
AmplifierInverter
10 100 1000 10000 100000
0,0001
0,0002
0,0003
0,0004
0,0005
0,0006
fscin = 500 Hz
3
2
1
0,5
(3)
(2)
(1)
U
(1)/U
(2), curve (3)
U
/(
I*f
),
cu
rv
es
(1
),(
2)
f, Hz
Fig. 1. Block diagram of diamagnetic measurements. D1 – diamagnetic loop I, D2 – diamagnetic loop II,
ADC – analog-digital converter
possible to exclude the influence of magnetic fields created
by image currents in the metal environment. To measure
variations in the poloidal magnetic field components, the
magnetic sensors installed in five sections of the torus will
be used. Provided that, when N/R << m/b (R - a large
radius, r - a small radius, N - number of periods of magnetic
field over the toroidal angle and m - number of periods of
magnetic field over small azimuthal angle, b - radius of the
surface on which is carried out magnetic measurements),
the measurements of variations in the poloidal magnetic
field component give objective information about the
structure of the longitudinal plasma current.
16 magnetic sensors will be placed in each of the five
cross-section of the torus. The real ratio is b/ ≈ 1.5. This
ratio will allow to extract poloidal harmonics with m = 0,
m = 1 and m = 2 from a common signal of the magnetic
sensors. With the help of magnetic measurements which
will be carried out in the five sections of the torus it will be
possible to measure the perturbations with N = 0 and N = 1.
Placing of magnetic sensors in special selected sections of
the torus will allow us to extract perturbations with N = 4.
As a result, it will be possible to monitor the behavior of the
fundamental harmonic of torsatron magnetic field with m =
2 and N = 4.
In total, with the help of sets of 80 magnetic sensors
installed in five sections of the torus it can be measured
following quasi-stationary and variable harmonics of
plasma currents:
1) with m=0, N=0 – longitudinal plasma current;
2) with m=1, N=0 – horizontal displacement of the
plasma current, magnetic field of Pfirsch-Schluter currents,
the vertical displacement of the plasma current and the time
variation of the radial electric field [6];
3) with m=2, N=1 – island structure of magnetic
surfaces under ι/2π=0.5 (ι – the rotational transform angle);
4) with m=1, m=2, N=4 – helical equilibrium plasma
currents.
The above mentioned magnetic sensors can register
variation in the magnetic fields at frequencies from 10 Hz
up to 200 kHz. Therefore it is possible to register MHD
fluctuations of corresponding structure with m=0, m=1,
m=2 and with N = 0, N=1, N=2, N=4.
It should be noted, that for measuring variations of the
poloidal magnetic field component with m ≠ 0 it is
necessary to take into account the influence of image
currents that flow in the metallic environment. During the
measurements of poloidal magnetic fields, the image
currents will be taken into account by using numerical
methods for processing recorded signal on the basis of
special model measurements in a vacuum chamber of
torsatron U-2M. For example, Fig. 2 shows dependence
of the ratio of the signal detected by magnetic sensors to
the frequency and the value of current of the coil
simulating the plasma current with m = 1.
Fig. 2. The dependence of ratio of the signal amplitude
U recorded by magnetic sensors to the frequency and
the value of current of the coil simulating the plasma
current with m = 1. Location of coils: (1) – inside the
metal chamber and (2) – out of the metal chamber. The
dotted line (3) shows the ratio U(1)/U(2) recorded
signals of the magnetic sensors inside and outside the
simulator of the vacuum chamber
The measurements were preformed inside and outside
the simulator of the stainless steel vacuum chamber,
which is similar to a chamber of torsatron U-2M (b/r0 ≈
0.9, r0 – radius of the metal chamber). The figure shows
that at frequencies above the skin frequency
for given configuration and thickness of the wall of the
simulator of the vacuum chamber, the recorded signal is
almost 2 times higher than one outside the simulator (c
– light speed, σ – conductivity of the metal, ∆ – wall
thickness, a – radius of the chamber). This is due to the
fact that the image currents flow in the metal chamber,
and the magnetic field of the plasma current does not
penetrate through the metallic environment. At
frequencies below the skin frequency, the magnetic
field of the plasma current penetrates through the metal
wall of the simulator of the chamber and the recorded
signal with decreasing frequency is the same inside and
outside the chamber. At frequencies above 100 kHz,
resonance effects appear related to the presence of
Hzff skin 500
8
2
=
∆
=>>
πσ
178
Fig. 3. Photos of the module with a magnetic sensor (top)
and location of constructional elements of magnetic sensors
inside the simulator of the vacuum chamber of torsatron U-
2M (photo below, in the foreground marked by the arrow,
RF antenna is visible in the background)
reactivity introduced by the metal environment in
measuring contour of the magnetic sensors.
Calculations showed that the influence of the metal
environment on the second and higher azimuthal
harmonics of poloidal magnetic field, is similar to that
of the first azimuthal harmonic.
Pictures of modules with a magnetic sensor
measuring the poloidal magnetic field components, as
well as location of constructional elements of the
magnetic sensors inside the simulator of the vacuum
chamber of torsatron U-2M are shown in Fig. 3. Due to
the modular design of elements of magnetic diagnostics,
they can be installed inside the vacuum chamber of
torsatron U-2M through vacuum ports, without
disassembling the chamber.
REFERENCES
1. V.D. Shafranov // Plasma Physics. 1971, v.13, p.757.
2. L.Ye. Zaharov, V.D. Shafranov // Zh. Tekh. Phys.
1973, v. 43, p. 225.
3. B.J. Braams: Preprint IPP s/r, Garching, 1985.
4. V.K. Pashnev, V.V. Nemov // Nuclear Fusion. 1993,
v. 33, N 3, p. 435.
5. A.I. Morozov, L.S. Solovyov // Problem of plasma
theory / M.: “GosAtomizdat”, 1963, v. 2, p. 3 (in
Russian).
6. V.K. Pashnev // VI Ukraine Conference and school
on plasma Physics and Controlled Fusion. Alushta,
(Crimea, Ukraine) September 14-20, 1998, p. 41.
Article received 14.10.10
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