Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator
The retarding field energy analyzer (RFEA) remains the more reliable diagnostic to measure the ion temperature in the boundary plasmas of magnetic fusion devices. A compact, simple design RFEA have been developed for investigations on the tokamak ISTTOK and TJ-II stellarator. More recently a five-...
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| Zitieren: | Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator / I.S. Nedzelskiy, C. Silva, H. Fernandes, C. Hidalgo // Вопросы атомной науки и техники. — 2009. — № 1. — С. 174-176. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-886502015-11-21T03:01:40Z Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator Nedzelskiy, I.S. Silva, C. Fernandes, H. Hidalgo, C. Диагностика плазмы The retarding field energy analyzer (RFEA) remains the more reliable diagnostic to measure the ion temperature in the boundary plasmas of magnetic fusion devices. A compact, simple design RFEA have been developed for investigations on the tokamak ISTTOK and TJ-II stellarator. More recently a five-channel RFEA has been successfully tested allowing the simultaneous measurement of the ion temperature profile. The conditions of the RFEA operation in poor alignment along magnetic field are considered. Аналізатор енергії з затримуючим потенціалом (АЕЗП) залишається найбільш надійним діагностичним пристроєм для виміру температури іонів поблизу границі плазми термоядерних установок з магнітним утриманням. Компактний простий пристрій АЕЗП розроблено для досліджень на токамаці ISTTOK і стеллараторі TJ-II. Порівняно недавно п’ятиканальный АЕЗП був успішно випробуваний і дозволяє здійснювати синхронні виміри профілю температури іонів. Визначено умови роботи АЕЗП при поганій орієнтації його уздовж магнітного поля. Анализатор энергии с задерживающим потенциалом (АЭЗП) остается наиболее надежным диагностическим устройством для измерения температуры ионов вблизи границы плазмы термоядерных установок с магнитным удержанием. Компактное простое устройство АЭЗП разработано для исследований на токамаке ISTTOK и стеллараторе TJ-II. Сравнительно недавно пятиканальный АЭЗП был успешно испытан и позволяет осуществлять синхронные измерения профиля температуры ионов. Определены условия работы АЭЗП при плохой ориентации его вдоль магнитного поля. 2009 Article Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator / I.S. Nedzelskiy, C. Silva, H. Fernandes, C. Hidalgo // Вопросы атомной науки и техники. — 2009. — № 1. — С. 174-176. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS: 52.55.Fa, 52.70.-m, 52.70.Nc http://dspace.nbuv.gov.ua/handle/123456789/88650 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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Диагностика плазмы Диагностика плазмы |
| spellingShingle |
Диагностика плазмы Диагностика плазмы Nedzelskiy, I.S. Silva, C. Fernandes, H. Hidalgo, C. Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator Вопросы атомной науки и техники |
| description |
The retarding field energy analyzer (RFEA) remains the more reliable diagnostic to measure the ion temperature in
the boundary plasmas of magnetic fusion devices. A compact, simple design RFEA have been developed for
investigations on the tokamak ISTTOK and TJ-II stellarator. More recently a five-channel RFEA has been successfully
tested allowing the simultaneous measurement of the ion temperature profile. The conditions of the RFEA operation in
poor alignment along magnetic field are considered. |
| format |
Article |
| author |
Nedzelskiy, I.S. Silva, C. Fernandes, H. Hidalgo, C. |
| author_facet |
Nedzelskiy, I.S. Silva, C. Fernandes, H. Hidalgo, C. |
| author_sort |
Nedzelskiy, I.S. |
| title |
Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator |
| title_short |
Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator |
| title_full |
Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator |
| title_fullStr |
Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator |
| title_full_unstemmed |
Retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak ISTTOK and TJ-II stellarator |
| title_sort |
retarding field energy analyzers for ion temperature measurements in the boundary plasmas of the tokamak isttok and tj-ii stellarator |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2009 |
| topic_facet |
Диагностика плазмы |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/88650 |
| citation_txt |
Retarding field energy analyzers for ion temperature
measurements in the boundary plasmas
of the tokamak ISTTOK and TJ-II stellarator / I.S. Nedzelskiy, C. Silva, H. Fernandes, C. Hidalgo // Вопросы атомной науки и техники. — 2009. — № 1. — С. 174-176. — Бібліогр.: 5 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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| first_indexed |
2025-07-06T16:31:28Z |
| last_indexed |
2025-07-06T16:31:28Z |
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| fulltext |
RETARDING FIELD ENERGY ANALYZERS FOR ION TEMPERATURE
MEASUREMENTS IN THE BOUNDARY PLASMAS
OF THE TOKAMAK ISTTOK AND TJ-II STELLARATOR
I.S. Nedzelskiy, C. Silva, H. Fernandes, C. Hidalgo*
Associação Euratom/IST, Instituto de Plasma e Fusão Nuclear, Instituto Superior Técnico
1049-001 Lisboa, Portugal;
* Associacion Euratom/CIEMAT, Av. Complutence, Madrid, Spain
The retarding field energy analyzer (RFEA) remains the more reliable diagnostic to measure the ion temperature in
the boundary plasmas of magnetic fusion devices. A compact, simple design RFEA have been developed for
investigations on the tokamak ISTTOK and TJ-II stellarator. More recently a five-channel RFEA has been successfully
tested allowing the simultaneous measurement of the ion temperature profile. The conditions of the RFEA operation in
poor alignment along magnetic field are considered.
PACS: 52.55.Fa, 52.70.-m, 52.70.Nc
1. INTRODUCTION
One approach to measure an ion temperature in plasma
boundary employs a retarding field energy analyzer
(RFEA) (see, for example, [1-4]) based on selective
rejecting of plasma ions by an electric field. For
Maxwellian distribution of the analyzed ions, the
collected current as a function of retarding potential, Vr,
is given by:
Ii(Vr) = I0i, Vr ≤ Vshift, (1)
Ii(Vr) = I0iexp[-qi(Vr - Vshift)/kTi], Vr ≥ Vshift, (2)
where I0i is the ion current collected when none of the
ions is repelled by the retarding potential, and Vshift is the
potential equal to the difference between the plasma
potential and the probe ground. Calculations of ion
temperature include a least square fitting of the Vr ≥ Vshift
portion of the I(Vr) characteristics to Eq.(2).
One important requirement to the RFEA operation
strongly stated in Ref.[4] consists in alignment of the
RFEA axis exactly parallel to the local magnetic field
direction, so that it is the parallel ion velocity which is
measured and not some component of it. The exact
fulfillment of this requirement presents definite difficulty
when measure Ti profile. However, because the ions with
parallel and perpendicular to the magnetic field
velocities, moving along helical trajectories, approach
the entrance slit with equal probability inside pitch angle
cone, one may expect an effective partial compensation
of RFEA misalignment and not strongly influencing the
results of the measurements.
This work presents RFEAs elaborated for
investigations of the boundary plasmas on the tokamak
ISTTOK and TJ-II stellarator. RFEA operation in
conditions of poor alignment along local magnetic field
of the plasma device is considered with reformulation of
the alignment requirement in term of RFEA
misalignment angle range inside which the obtained
results differ within error bars of the measurements.
The paper is organized as follows. The one- and five-
channel RFEAs are described in Section 2. The RFEA
operation and examples of Ti and Te measurements on
ISTTOK with aligned RFEA are shortly presented in
Section 3. Section 4 considers dependence of the RFEA
characteristics on alignment along magnetic field.
Summary is done in Section 5.
2. RFEA DESCRIPTION
Fig.1 shows the picture and schematic of one-channel
RFEA [5]. It includes an input stainless still slit (3×0.1
mm2), three fine Nickel grids and copper collector plate,
all separated by MICA insulators (1 mm of distance
between grids). The grid and collector stack are
assembled inside boron nitride housing. The dimensions
of one-channel RFEA are 14×14×23 mm.
Fig.1. Picture and schematic of one-channel RFEA
Fig.2. Picture and schematic of five-channel RFEA
174 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2009. № 1.
Series: Plasma Physics (15), p. 174-176.
0 2 4 6 8 10
-100
-75
-50
-25
0
25
50
75
100
P
o
te
n
ti
a
l,
V
X Axis Title
0 20 40 60 80 100
-0,2
0,0
0,2
0,4
0,6
0,8
1,0 <ne> ~ 3.5*1018 m-3, Ip ~ 3.3 kA
ξ =25o: Vshift = 11 V, Ti = 15 eV (effective)
ξ =0o: Vshift = 23 V, Ti = 26 eV (real)
i/i
m
ax
U, V
Recently, a five-channel RFEA to measure
simultaneously the profile of Ti has been developed,
assembled and tested. Design of five-channel RFEA
shown in Fig.2 presents just a compilation of the one-
channel RFEA with common grids in all channels and
multiplied number of slits and collectors. Usage of
common grids sufficiently simplifies RFEA powering
and operation. The dimensions of five-channel RFEA are
20×24×55 mm, and distance between slits is 7 mm.
A standard biasing configuration is shown in the inset
of Fig.1. An operational amplifier is employed for
triangle shape biasing of the retarding grid. The current
collected by the RFEA is measured across a resistor with
isolation amplifier and acquired by ISTTOK data
acquisition system (up to 2 MHz sampling rate).
3. RFEA OPERATION
RFEAs operation has been tested in plasma of
ISTTOK (R = 0.45 m, alim = 0.078 m, avessel = 0.1 m, B =
0.5 T) with <ne> = (2…3.5)×1018 m-3, Te(0) ~ 150 eV, Ip =
(2.5…5) kA, τshot = 20 ms. RFEAs are installed in a
horizontal diagnostic port of ISTTOK and can be shot-
by-shot moved radially and rotated (±30o) by vacuum
manipulator.
Fig.3. Typical ion mode signals from two RFEA channels
(inset) and signal fitting by function of Eq. (2)
An inset in Fig.3 shows typical ion mode signals from
two channels of five-channel RFEA aligned along
magnetic field of ISTTOK. An example of ion
characteristic, as well as the respective fitting, is
presented in Fig.3.
Fig.4. Profiles of Ti and Te measured by RFEA on
ISTTOK
Fig.4 presents the profiles of Ti and Te at flat top of the
discharge measured with RFEA on ISTTOK (in electron
mode the polarity of the potentials applied to the RFEA
grids is reversed).
4. DEPENDENCE ON ALIGNMENT
ALONG MAGNETIC FIELD
In experiments on TJ-II, the RFEA expects fast
reciprocation across magnetic field surfaces, therefore
operating at slightly different angles (estimated as up to
6o range) between analyzer axis and magnetic field line.
Poor alignment conditions have been investigated with
one-channel RFEA rotated relative magnetic field line of
ISTTOK plasma.
Fig.5. Results of Ti (top), Vshift (middle) and unbiased
collected current (bottom) for different ξ
Fig.6. Example of the normalized retarding curves
at ξ ~ 0o and ξ ~ 25o
Fig. 5 present the example of obtained results of Ti
(top), Vshift (middle) and unbiased collected current
(bottom) measured for different angles, ξ, in the range of
175
0 10 20 30 40 50 60 70 80 90 100
-3
0
3
7
10
13
17
20
shot #12137, T
i
= 15 eV, V
shift
= 17-23 V
i rfe
a, a
.u
.
U
s
, V
rise
decay
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
1
10
100
λ
i
~ 0.9 cm
λ
i
~ 3.8 cm
λ e ~ 0.7 cm
λ e ~ 1.4 cm
T i
, T
e,
eV
∆ r, cm
Ti
Te
0 5 10 15 20 25 30
5
10
15
20
25
30
cos2(ξ )
T i,
eV
ξ , o
0 5 10 15 20 25
5
10
15
20
25
30
cos2(ξ )
V sh
ift
, V
ξ , o
0 10 20 30 40 50 60
0
20
40
60
80
100
I i, a
.u
.
ξ , o
ξ = (0…25o) for plasma with <ne> = 2.5×1018 m-3 and Ip =
2.5 kA. The error bars are mainly determined by noise of
the signal. Fig. 6 shows the example of the normalized
experimental retarding curves at ξ = 0o and extreme ξ =
25o demonstrating clear modifications of measured values
of Ti and Vshift. Contrary, the unchanged inside error bars
values of both Ti and Vshift in the angle range of ξ ~ ± 10o
can be identified. Fitting the unbiased collected current
data by Gaussian function gives HWFM ~ ±20o and peaks
at ξ0 ~ 9o for Ip = 2.5 kA and at ξ0 ~ 7.7o for Ip = 3.5 kA,
indicating (expected) correlation with plasma current.
Qualitatively, the observed results can be partially
understandable from idealized non-magnetized 2D model
for the parallel uniformly distributed across RFEA slit
particle flow with shifted Maxwellian distribution (Eb =
Vshift and ∆Eb = Ti). Taking into account that to cut the
particle entering into analyzer at some angle ξ relative to
the analyzer axis, the potential applied to the retarding
grid is lower on the value of ∆Vr = ∆E|| sin2ξ, Eq.(1) and
Eq.(2) can be rewritten as:
Ii(Vr) = KMI0i, Vr ≤ Vshiftcos2ξ, (3)
Ii(i)(Vr) = KMI0iexp[-qi(Vr - Vshiftcos2ξ)/kTicos2ξ],
Vr > Vshiftcos2ξ, (4)
where KM = cosξ[1 – (l/a)tgξ] is the RFEA transmission
factor in optical approximation (l is the analyzer length
from input slit to collector, and a is the analyzer aperture
after input slit), and Eq.(4) is derived from Eq.(2) by
rescaling Vr as Vr /cos2ξ.
Fig.7. Normalized retarding curves for two entering
angles of 0o and 25o calculated with Eq.4
Fig.7 (top) presents normalized retarding curves, Ii/Iimax,
calculated for two entering angles of ξ = 0o and ξ = 25o,
showing similarity with experimental results (for
comparison, cos2ξ curves are drawn in experimental data
of Fig. 5 also). Shown in Fig. 5 (bottom) the calculated
dependence of unbiased current (or KM for l = 4 mm, a =
2 mm) on entrance angle predicts fast decay in
contradiction with the experimental results. It means
(and not surprisingly) violence of linear optical
transmission approximation for magnetized particle flux.
Notice, however, quite good agreement of experimental
½(FWHM) ~ 20o with calculated complete cutting at ξ
cut = atan(a/l) = 26.6o.
5. SUMMARY
A compact, simple design one- and five-channels RFEAs
have been developed for investigations of boundary
plasmas on the tokamak ISTTOK and TJ-II stallarator.
The ion and electron temperature profiles have been
successfully measured on ISTTOK.
The investigations of dependence of the RFEA
characteristics on alignment along magnetic field of
ISTTOK show the unchanged inside the error bars results
for both Ti and Vshift in the angle range of ξ ~ ± 10o.
Presumable, the ion pitch angle could be candidate for
explanation of the observed properties.
ACKNOWLEDGEMENTS
This work has been carried out in the frame of the Contract
of Association between the European Atomic Energy
Community and Instituto Superior Técnico (IST) and of the
Contract of Associated Laboratory between Fundação para
a Ciência e Tecnologia (FCT) and IST. The content of the
publication is the sole responsibility of the authors and it
does not necessarily represent the views of the Commission
of the European Union or FCT or their services
REFERENCES
1. G.F. Matthews// J. Phys. D, 1984, v. 17, p. 2243.
2. A.S. Wan, T.F. Yang, B. Lipschultz, B. LaBombard//
Rev. Sci. Instrum. 1986, v. 57, p. 1542.
3. R. A. Pitts// Phys. Fluids B. 1991, v. 3, p. 2871.
4. G.F. Matthews, R.A. Pitts, G.M. McCracken,
P.C. Stangeby// Nucl. Fusion. 1991, v. 31, p. 1495.
5. I.S. Nedzelskiy et al// Rev. Sci. Instrum. 2006, v. 77,
p. 10E729.
Article received 22.09.08
АНАЛИЗАТОР ЭНЕРГИИ С ЗАДЕРЖИВАЮЩИМ ПОТЕНЦИАЛОМ ДЛЯ ИЗМЕРЕНИЯ ТЕМПЕРАТУРЫ
ИОНОВ НА ГРАНИЦЕ ПЛАЗМЫ В ТОКАМАКЕ ISTTOK И СТЕЛЛАРАТОРЕ TJ-II
I.S. Nedzelskiy, C. Silva, H. Fernandes, C. Hidalgo
Анализатор энергии с задерживающим потенциалом (АЭЗП) остается наиболее надежным диагностическим устройством
для измерения температуры ионов вблизи границы плазмы термоядерных установок с магнитным удержанием.
Компактное простое устройство АЭЗП разработано для исследований на токамаке ISTTOK и стеллараторе TJ-II.
Сравнительно недавно пятиканальный АЭЗП был успешно испытан и позволяет осуществлять синхронные измерения
профиля температуры ионов. Определены условия работы АЭЗП при плохой ориентации его вдоль магнитного поля.
АНАЛІЗАТОР ЕНЕРГІЇ З ЗАТРИМУЮЧИМ ПОТЕНЦІАЛОМ ДЛЯ ВИМІРУ ТЕМПЕРАТУРИ ІОНІВ НА
ГРАНИЦІ ПЛАЗМИ В ТОКАМАЦІ ISTTOK І СТЕЛЛАРАТОРІ TJ-II
I.S. Nedzelskiy, C. Silva, H. Fernandes, C. Hidalgo
Аналізатор енергії з затримуючим потенціалом (АЕЗП) залишається найбільш надійним діагностичним пристроєм для
виміру температури іонів поблизу границі плазми термоядерних установок з магнітним утриманням. Компактний простий
пристрій АЕЗП розроблено для досліджень на токамаці ISTTOK і стеллараторі TJ-II. Порівняно недавно п’ятиканальный
АЕЗП був успішно випробуваний і дозволяє здійснювати синхронні виміри профілю температури іонів. Визначено умови
роботи АЕЗП при поганій орієнтації його уздовж магнітного поля.
176
0 20 40 60 80 100
-0,2
0,0
0,2
0,4
0,6
0,8
1,0
ξ =25o: Vshift = 19 V, Ti = 21 eV (effective)
ξ =0o: Vshift = 23 V, Ti = 26 eV (real)
i/i
m
ax
Ur, V
|