Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak
Tokamak plasma modes were analyzed using the Fast Fourier Transform (FFT) in presence of hot limiter biasing system in the IR-T1 Tokamak. Fourier analysis is reliable technique for mode detection in tokamaks. For this purpose we used a poloidal array of Mirnov coils and hot limiter biasing system. A...
Збережено в:
| Дата: | 2013 |
|---|---|
| Автори: | , , , , |
| Формат: | Стаття |
| Мова: | English |
| Опубліковано: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2013
|
| Назва видання: | Вопросы атомной науки и техники |
| Теми: | |
| Онлайн доступ: | http://dspace.nbuv.gov.ua/handle/123456789/109257 |
| Теги: |
Додати тег
Немає тегів, Будьте першим, хто поставить тег для цього запису!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak / M. Ghoranneviss, A. Salar Elahi, G. van Oost, R. Arvin, S. Mohammadi // Вопросы атомной науки и техники. — 2013. — № 1. — С. 8-11. — Бібліогр.: 7 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-109257 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-1092572016-11-22T03:03:51Z Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak Ghoranneviss, M. Salar Elahi, A. van Oost, G. Arvin, R. Mohammadi, S. Магнитное удержание Tokamak plasma modes were analyzed using the Fast Fourier Transform (FFT) in presence of hot limiter biasing system in the IR-T1 Tokamak. Fourier analysis is reliable technique for mode detection in tokamaks. For this purpose we used a poloidal array of Mirnov coils and hot limiter biasing system. After Fourier analysis of Mirnov coils data in presence of hot biased limiter, Power Spectral Density (PSD) diagram was plotted. PSD describes how the power of a signal is distributed with frequency. In this contribution we also determined edge safety factor and safety factor from Fourier based derived mode numbers q = m/n. We obtained the maximum MHD activity using power spectrum at the frequency 33 kHz. Also the edge safety factor was determined less than 3, and the values of obtained safety factor from the mode numbers are between 2 ≤ q ≤ 5. Results show that hot limiter biasing can be used for increasing the plasma safety factor. Моды плазмы токамака анализировались с использованием быстрого преобразования Фурье (БПФ) при наличии системы подачи напряжения на горячий лимитер в токамаке IR-T1. Использовалась полоидальная схема расположения катушек Мирнова. С помощью Фурье-анализа данных катушек Мирнова была построена диаграмма спектральной плотности мощности (СПМ), описывающая распределение мощности сигнала с частотой. Были определены величины q на краю плазмы и по данным Фурье-анализа (как отношение мод: q=m/n). Максимум активности МГД оказался на частоте 33 кГц; на краю величина q≤ 3, а найденная из номеров гармоник − 2 ≤ q ≤ 5. Результаты показали, что подача напряжения на лимитер может использоваться для увеличения плазменного коэффициента надежности. Моди плазми токамака аналізувалися з використанням швидкого перетворення Фур'є (ШПФ) за наявності системи подачі напруги на гарячий лімітер у токамаці IR-T1. Використовувалась полоїдальна схема розміщення котушок Мірнова. За допомогою Фур'є-аналізу даних з котушок Мірнова була побудована діаграма спектральної щільності потужності (СЩП), яка описує розподіл потужності сигналу з частотою. Були визначені величини q на краю плазми і по даним Фур'є-аналізу (як відношення мод: q = m/n). Максимум активності МГД виявився на частоті 33 кГц; на краю величина q ≤ 3, а знайдена з номерів гармонік – 2 ≤ q ≤ 5. Результати показали, що подача напруги на лімітер може використовуватися для збільшення плазмового коефіцієнта надійності. 2013 2013 Article Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak / M. Ghoranneviss, A. Salar Elahi, G. van Oost, R. Arvin, S. Mohammadi // Вопросы атомной науки и техники. — 2013. — № 1. — С. 8-11. — Бібліогр.: 7 назв. — англ. 1562-6016 PACS: 52.55.Fa http://dspace.nbuv.gov.ua/handle/123456789/109257 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 |
Магнитное удержание Магнитное удержание |
| spellingShingle |
Магнитное удержание Магнитное удержание Ghoranneviss, M. Salar Elahi, A. van Oost, G. Arvin, R. Mohammadi, S. Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak Вопросы атомной науки и техники |
| description |
Tokamak plasma modes were analyzed using the Fast Fourier Transform (FFT) in presence of hot limiter biasing system in the IR-T1 Tokamak. Fourier analysis is reliable technique for mode detection in tokamaks. For this purpose we used a poloidal array of Mirnov coils and hot limiter biasing system. After Fourier analysis of Mirnov coils data in presence of hot biased limiter, Power Spectral Density (PSD) diagram was plotted. PSD describes how the power of a signal is distributed with frequency. In this contribution we also determined edge safety factor and safety factor from Fourier based derived mode numbers q = m/n. We obtained the maximum MHD activity using power spectrum at the frequency 33 kHz. Also the edge safety factor was determined less than 3, and the values of obtained safety factor from the mode numbers are between 2 ≤ q ≤ 5. Results show that hot limiter biasing can be used for increasing the plasma safety factor. |
| format |
Article |
| author |
Ghoranneviss, M. Salar Elahi, A. van Oost, G. Arvin, R. Mohammadi, S. |
| author_facet |
Ghoranneviss, M. Salar Elahi, A. van Oost, G. Arvin, R. Mohammadi, S. |
| author_sort |
Ghoranneviss, M. |
| title |
Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak |
| title_short |
Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak |
| title_full |
Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak |
| title_fullStr |
Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak |
| title_full_unstemmed |
Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak |
| title_sort |
control of the edge plasma modes by hot limiter biasing in the ir-t1 tokamak |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2013 |
| topic_facet |
Магнитное удержание |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/109257 |
| citation_txt |
Control of the edge plasma modes by hot limiter biasing in the IR-T1 tokamak / M. Ghoranneviss, A. Salar Elahi, G. van Oost, R. Arvin, S. Mohammadi // Вопросы атомной науки и техники. — 2013. — № 1. — С. 8-11. — Бібліогр.: 7 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
AT ghorannevissm controloftheedgeplasmamodesbyhotlimiterbiasingintheirt1tokamak AT salarelahia controloftheedgeplasmamodesbyhotlimiterbiasingintheirt1tokamak AT vanoostg controloftheedgeplasmamodesbyhotlimiterbiasingintheirt1tokamak AT arvinr controloftheedgeplasmamodesbyhotlimiterbiasingintheirt1tokamak AT mohammadis controloftheedgeplasmamodesbyhotlimiterbiasingintheirt1tokamak |
| first_indexed |
2025-07-07T22:49:10Z |
| last_indexed |
2025-07-07T22:49:10Z |
| _version_ |
1837030233643941888 |
| fulltext |
8 ISSN 1562-6016. ВАНТ. 2013. №1(83)
CONTROL OF THE EDGE PLASMA MODES BY HOT LIMITER
BIASING IN THE IR-T1 TOKAMAK
M. Ghoranneviss1, A. Salar Elahi1, G. van Oost2, R. Arvin1, S. Mohammadi1
1Plasma Physics Research Center, Science and Research Branch, Islamic Azad University,
Tehran, Iran;
2Ghent University, Gent, Belgium
Tokamak plasma modes were analyzed using the Fast Fourier Transform (FFT) in presence of hot limiter biasing
system in the IR-T1 Tokamak. Fourier analysis is reliable technique for mode detection in tokamaks. For this
purpose we used a poloidal array of Mirnov coils and hot limiter biasing system. After Fourier analysis of Mirnov
coils data in presence of hot biased limiter, Power Spectral Density (PSD) diagram was plotted. PSD describes how
the power of a signal is distributed with frequency. In this contribution we also determined edge safety factor and
safety factor from Fourier based derived mode numbers q = m/n. We obtained the maximum MHD activity using
power spectrum at the frequency 33 kHz. Also the edge safety factor was determined less than 3, and the values of
obtained safety factor from the mode numbers are between 2 ≤ q ≤ 5. Results show that hot limiter biasing can be
used for increasing the plasma safety factor.
PACS: 52.55.Fa
INTRODUCTION
Investigation of behavior and structure of MHD is
important in tokamaks and interesting issue in plasma
physics. Besides there can be found much information
such as, plasma cross section, MHD activity, mode
numbers, magnetic islands and plasma instability.
Different diagnostics are used for plasma edge studies.
One of the commonly used diagnostics are Mirnov coils
[1]. These coils are very simple design and researcher
can utilize them easily. They can have many
applications in tokamak and also record the magnetic
fluctuations. Analysis of Mirnov coils fluctuations using
the Fast Fourier transformation (FFT) is one of the
effective methods to investigate the mode of tokamak
plasma [2, 5]. In this paper, we used the poloidal array
of 12 external Mirnov coils which are located poloidally
by 30 degrees. We determined plasma mode numbers
based on FFT. After Fourier analysis of Mirnov coils
data, we plotted the power spectrum density. We also
determined the edge safety factor and safety factor
derived from Fourier based mode numbers q = m/n for
IR-T1 tokamak.
The safety factor, q, is so called because of the role it
plays in determination of tokamak plasma stability. In
other words, higher values of q lead to greater stability.
It also appears as an important factor in transport theory.
In an axisymmetric equilibrium such as tokamak plasma
each magnetic field line has a value of q. The field line
follows a helical path as it goes around the torus on its
associated magnetic surface. Knowledge of the q profile
in a tokamak is fundamental for the understanding of
the MHD properties of plasma. Near the plasma edge, q
may be determined with accuracy from magnetic
measurements, but this becomes increasingly inaccurate
as extrapolations are made towards the plasma centre.
Several methods of determining q such as the Faraday
rotation method and a ruby laser scattering technique
have been developed [3]. In this paper, we presented an
investigation of the time evolution of the mode
numbers, edge safety factor and maximum MHD
activity on IR-T1, which is a small tokamak with large-
aspect-ratio and circular cross section (Table).
This paper is organized as follows: in section 2,
design, construction and installation of hot limiter
biasing system will be presented. In section 3 we
presented the FFT for determination of the power
spectrum density. In section 4, we presented the results
of the mode numbers of plasma using FFT. Section 5 is
for edge safety factor determined using plasma current
and toroidal magnetic field. The summary and
conclusion will be presented in section 6.
Parameters of IR-T1 Tokamak
1. DESIGN, CONSTRUCTION,
AND EXPERIMENTAL SET-UP OF THE
HOT LIMITER BIASING SYSTEM
IR-T1 is a low beta, large aspect ratio, and circular
cross-section tokamak (see Table), which has two
stainless steel grounded fully poloidal limiters with
radiuses of 12.5 cm. In the experiments described the
biased limiter position has been varied between
11.5…12.5 cm, and the bias applied between the limiter
and the vessel. This limiter consists of a stainless steel
circular head, 2 mm in radial direction (width) and 2 cm
in poloidal direction (diameter). It is inserted
approximately 1 cm past the fixed poloidal limiter into
the plasma through the low field side of the tokamak as
it is shown in Fig. 1. Also the electric circuit of limiter
biasing system used in IR-T1 is shown in Fig. 2. A
capacitor bank biases the limiter positive or negative
Parameter Value
Major radius 45 cm
Minor radius 12.5 cm
Toroidal field <1.0 T
Plasma current <40 kA
Discharge duration <35 ms
Electron density (0.7…1.5)×1013 cm-3
ISSN 1562-6016. ВАНТ. 2013. №1(83) 9
with respect to the grounded wall. The applied limiter
voltage Vbias is in the range −400…+400 V, and the bias
current Ibias is in the range -40…+40 A. The
experiments were performed in hydrogen. An edge
plasma density and temperature are in the range
(0.7…1.5)·1013 cm-3 and 20…60 eV respectively,
measured using the Langmuir probe, the toroidal
magnetic field induction BT ≈ 0.8 T, the plasma current
Ip = 25…30 kA. Also, biasing experiments were
performed in regime with ohmic heating, and
measurements of the plasma parameters were performed
using a single Langmuir probe, Mach probe, triple
magnetic probes, poloidal flux loops, and diamagnetic
flux loop.
Fig. 1. Schematic drawing of the hot limiter biasing
system on the IR-T1
Fig. 2. Electric circuit of the hot limiter biasing system used in the IR-T1
2. FFT BASED DETERMINATION
OF POWER SPECTRUM DENSITY
The FFT, representation of functions as a
superposition of sinus and cosines, has become
ubiquitous for both the analytic and numerical solution
of deferential equations and for the analysis and
treatment of communication signals [4].
To approximate a function by samples, and to
approximate the Fourier integral by the discrete Fourier
transform, it requires applying a matrix whose order is
the number sample points n. Since multiplying a n × n
matrix by a vector costs on the order of n2 arithmetic
operations, the problem gets quickly worse as the
number of sample points increases. However, if the
samples are uniformly spaced, then the Fourier matrix
can be factored into a product of just a few sparse
matrices, and the resulting factors can be applied to a
vector in a total of order n log n arithmetic operations
[4]. Power spectral density function (PSD) shows the
strength of the variations (energy) as a function of
frequency. In other words, it shows at which frequencies
variations are strong and at which frequencies variations
are weak. The unit of PSD is energy per frequency
(width) and we can obtain energy within a specific
frequency range by integrating PSD within that
frequency range. Computation of PSD is done directly
by the method FFT. PSD is a very useful tool to identify
oscillatory signals in time series data, and also it
describes how the energy or power of a signal is
distributed with frequency [6]. If ( )f t is a finite-energy
(square integrable) signal, the spectral density ( )wF of
the signal continuous Fourier transform is the square of
the magnitude of the continuous of the signal:
( ) ( ) ( ) ( )2
1 .
22
i t F F
f t e dtω ω ω
ω
ππ
∗+∞
−
−∞
Φ = =∫ (1)
( )F w is the signal continuous Fourier transform of
( )f t and is *( )F w complex conjugate. If the signal is
discrete with values fn , over an infinite number of
elements, we still have an energy spectral density:
(2)
where t is the discrete-time Fourier transform of fn.
Power can be the actual physical power, or more often,
for convenience with abstract signals, can be defined as
the squared value of the signal. This instantaneous
power is then given by: p(t) = s(t)2 for a signal s(t) [7].
Therefore according to above discussion we obtained
the PSD using FFT analysis with Mirnov coils data. For
this purpose the MP4 coil was used according to the
Fig. 3. PSD result presented in the Fig. 4, as observable,
power spectral density diagram has regular trend of
( ) ( ) ( )2
1 ,
22
i t
n
F F
f e dtω ω ω
ω
ππ
∗+∞
−
−∞
Φ = =∑
10 ISSN 1562-6016. ВАНТ. 2013. №1(83)
frequency diminution, it shows plasma has high mode
number with symmetric shape because frequencies are
near together. Also according to the appeared peaks, we
obtained the maximum MHD activity.
Fig. 3. Position of poloidally array of 12 Mirnov coils
Fig. 4. Power spectrum density of Mirnov oscillation of
IR-T1 Tokamak
3. DETERMINATION OF PLASMA MODE
NUMBERS
Tokamak plasma can support different modes. Cross
section of plasma can have different shapes, which are
designated as Roset and have M rose leaves. If the
quantity number of M was less than 3, plasma will be
stable. Mirnov coils can record current time series
caused by poloidal rotation of plasma. The external
surface of plasma is not smooth and has noises. We
plotted the polar diagram of the magnetic field
fluctuations using FFT analysis on the poloidal array of
Mirnov coils (see the Fig. 5). In these diagrams we
showed cross section of plasma at three time intervals.
First time duration is at 19.0…20.0 ms that shows the
mode number is (m=3), second interval is at
29.0…30.0 ms that mode number is (m=4) and third
interval is at 40.0…41.0 ms that mode number is (m=4).
According to above discussion, we also determined the
safety factor from mode numbers (q=m/n) at time
interval 0…35 ms, that it is discharge duration in IR-T1
tokamak, and in our experiments, toroidal number is
(n=1) (Fig. 6).
4. MEASUREMENT OF SAFETY FACTOR
PROFILE
The meaning of q dimensionless parameter is the
number of toroidal turns it takes a magnetic field line to
make a single full poloidal turn. In the case of large
aspect-ratio and circular cross-section the radial
behavior of q is simply determined by the following
equation [8]:
2
0 0 0
2
( )
rB r B
q r
R B R I
f f
q
p
m
= = , (3)
0
2
I
B
rq
m
p
= . (4)
Results of these measurements are presented in the
Figs. 7, 8. In Fig. 7 we showed (a) Mirnov coil
oscillations, (b) toroidal magnetic field, (c) loop voltage
and (d) plasma current. Also in Fig. 6 time interval edge
safety factor is presented.
Fig. 5. Polar diagram of the magnetic field fluctuations
Fig. 6. Safety factor from mode number
Fig. 7. Mirnov coil oscillations (a); toroidal magnetic
field (b); loop voltage (c) and plasma current (d)
b
a
c
d
ISSN 1562-6016. ВАНТ. 2013. №1(83) 11
Fig. 8. Time interval of edge safety factor
SUMMERY AND CONCLUSIONS
A tokamak plasma modes were analyzed using the
Fast Fourier Transform (FFT) in presence of hot limiter
biasing system in the IR-T1 Tokamak. The maximum
MHD activity was obtained using power spectrum in the
frequency of 33 kHz. We also calculated the mode
number with FFT analysis. After Fourier analysis on
Mirnov coils data, we determined the edge safety factor
and safety factor from Fourier based derived mode
numbers q = m/n. The edge safety factor determined
smaller than 3 and the value of safety factor from mode
numbers observed between 2 ≤ q ≤ 5. Experimental
results show that hot limiter biasing can be used for
increasing the plasma safety factor. Finally, it is
important to stress that the emissive limiter used on IR-
T1 proved to be a robust and valuable tool to control the
edge radial electric field for both polarities, allowing
therefore a detailed investigation of the E×B shear flow
role on the control of the edge plasma mode.
REFERENCES
1. I.H. Tan, I.L. Caldas, I.C. Nascimento, R.P. Da Silva,
E.K. Sanada, R. Braha // IEEE Trans. Plasma. Sci. PS-
14. 1986, v.3, р. 279.
2. Z. Goodarzi et al. // J. Fusion Energy. 2012, DOI:
10.1007/s10894-012-9526-4.
3. J. Wesson. Tokamaks. Clarendon, Oxford. 1997,
p. 105-131.
4. G. Paschmann. Analysis Method for Multi-Spacecraft
Data // International Space Science Ins. 2000.
5. G. Heinzel, A. Rödiger and R. Schilling. Max-
Planck-Institut für Gravitationsphysik. Teilinstitut
Hannover, February 15, 2002.
6. Dennis Ward Ricker. Echo signal processing.
Springer. ISBN 140207395X. 2003.
7. A. Salar Elahi et al. // J. Fusion Energ. 2010, DOI:
10.1007/s10894-009-9264-4.
Article received 25.12.12
УПРАВЛЕНИЕ МОДАМИ ПРИСТЕНОЧНОЙ ПЛАЗМЫ ПРИ ПОДАЧЕ НАПРЯЖЕНИЯ
НА ЛИМИТЕР В ТОКАМАКЕ IR-T1
M. Ghoranneviss, A. Salar Elahi, G. van Oost, R. Arvin, S. Mohammadi
Моды плазмы токамака анализировались с использованием быстрого преобразования Фурье (БПФ) при
наличии системы подачи напряжения на горячий лимитер в токамаке IR-T1. Использовалась полоидальная
схема расположения катушек Мирнова. С помощью Фурье-анализа данных катушек Мирнова была
построена диаграмма спектральной плотности мощности (СПМ), описывающая распределение мощности
сигнала с частотой. Были определены величины q на краю плазмы и по данным Фурье-анализа (как
отношение мод: q=m/n). Максимум активности МГД оказался на частоте 33 кГц; на краю величина q≤ 3, а
найденная из номеров гармоник − 2 ≤ q ≤ 5. Результаты показали, что подача напряжения на лимитер может
использоваться для увеличения плазменного коэффициента надежности.
УПРАВЛІННЯ МОДАМИ КРАЙОВОЇ ПЛАЗМИ ЗА ДОПОМОГОЮ ПОДАЧІ НАПРУГИ
НА ЛІМІТЕР У ТОКАМАЦІ IR-T1
M. Ghoranneviss, A. Salar Elahi, G. van Oost, R. Arvin, S. Mohammadi
Моди плазми токамака аналізувалися з використанням швидкого перетворення Фур'є (ШПФ) за наявності
системи подачі напруги на гарячий лімітер у токамаці IR-T1. Використовувалась полоїдальна схема
розміщення котушок Мірнова. За допомогою Фур'є-аналізу даних з котушок Мірнова була побудована
діаграма спектральної щільності потужності (СЩП), яка описує розподіл потужності сигналу з частотою.
Були визначені величини q на краю плазми і по даним Фур'є-аналізу (як відношення мод: q = m/n).
Максимум активності МГД виявився на частоті 33 кГц; на краю величина q ≤ 3, а знайдена з номерів
гармонік – 2 ≤ q ≤ 5. Результати показали, що подача напруги на лімітер може використовуватися для
збільшення плазмового коефіцієнта надійності.
|