Feasibility of creating an island divertor in the Uragan-2M torsatron
The concept of an island divertor appears the only suitable idea that may be helpful to make up for the absence of a natural helical divertor in the magnetic configuration. In this context, the paper presents and discusses the measured and calculated magnetic surface structures of different configur...
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nasplib_isofts_kiev_ua-123456789-1090952025-02-23T18:17:35Z Feasibility of creating an island divertor in the Uragan-2M torsatron Возможности создания островного дивертора в торсатроне Ураган-2М Можливості створення острівного дивертора в торсатроні Ураган-2М Lesnyakov, G.G. Shapoval, A.N. Pavlichenko, O.S. Магнитное удержание The concept of an island divertor appears the only suitable idea that may be helpful to make up for the absence of a natural helical divertor in the magnetic configuration. In this context, the paper presents and discusses the measured and calculated magnetic surface structures of different configuration modes, where large magnetic islands or their remains at the edge of the plasma volume may be used for experimental implementation of the island divertor. Единственной подходящей концепцией, с помощью которой можно восполнить отсутствие естественного винтового дивертора в магнитной конфигурации, является концепция островного дивертора. В этой связи представлены и обсуждаются измеренные и вычисленные структуры магнитных поверхностей разных режимов конфигурации, в которых большие магнитные острова или их остатки на краю плазменного объема можно использовать для экспериментальной реализации островного дивертора. Єдиною придатною концепцією, за допомогою якої можна заповнити відсутність природного гвинтового дивертора в магнітній конфігурації, є концепція острівного дивертора. У зв’язку с цим наведенo та обговорюються виміряні й обчислені структури магнітних поверхонь різних режимів конфігурації, у яких великі за розміром магнітні острови або їх залишки біля краю плазмового об’єму можна використати для експериментальної реалізації острівного дивертора. 2012 Article Feasibility of creating an island divertor in the Uragan-2M torsatron / G.G. Lesnyakov, A.N. Shapoval, O.S. Pavlichenko // Вопросы атомной науки и техники. — 2012. — № 6. — С. 34-37. — Бібліогр.: 11 назв. — англ. 1562-6016 PACS: 52.55.-s; 52.55.Hc; 52.55.Rk; 52.70.Ds; 52.55.Dy https://nasplib.isofts.kiev.ua/handle/123456789/109095 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Магнитное удержание Магнитное удержание |
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Магнитное удержание Магнитное удержание Lesnyakov, G.G. Shapoval, A.N. Pavlichenko, O.S. Feasibility of creating an island divertor in the Uragan-2M torsatron Вопросы атомной науки и техники |
| description |
The concept of an island divertor appears the only suitable idea that may be helpful to make up for the absence of a natural helical divertor in the magnetic configuration. In this context, the paper presents and discusses the measured and calculated magnetic surface structures of different configuration modes, where large magnetic islands or their remains at the edge of the plasma volume may be used for experimental implementation of the island divertor. |
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Article |
| author |
Lesnyakov, G.G. Shapoval, A.N. Pavlichenko, O.S. |
| author_facet |
Lesnyakov, G.G. Shapoval, A.N. Pavlichenko, O.S. |
| author_sort |
Lesnyakov, G.G. |
| title |
Feasibility of creating an island divertor in the Uragan-2M torsatron |
| title_short |
Feasibility of creating an island divertor in the Uragan-2M torsatron |
| title_full |
Feasibility of creating an island divertor in the Uragan-2M torsatron |
| title_fullStr |
Feasibility of creating an island divertor in the Uragan-2M torsatron |
| title_full_unstemmed |
Feasibility of creating an island divertor in the Uragan-2M torsatron |
| title_sort |
feasibility of creating an island divertor in the uragan-2m torsatron |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2012 |
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Магнитное удержание |
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https://nasplib.isofts.kiev.ua/handle/123456789/109095 |
| citation_txt |
Feasibility of creating an island divertor in the Uragan-2M torsatron / G.G. Lesnyakov, A.N. Shapoval, O.S. Pavlichenko // Вопросы атомной науки и техники. — 2012. — № 6. — С. 34-37. — Бібліогр.: 11 назв. — англ. |
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34 ISSN 1562-6016. ВАНТ. 2012. №6(82)
FEASIBILITY OF CREATING AN ISLAND DIVERTOR
IN THE URAGAN-2M TORSATRON
G.G. Lesnyakov, A.N. Shapoval, O.S. Pavlichenko
Institute of Plasma Physics NSC “Kharkov Institute of Physics and Technology”,
Kharkov, Ukraine
The concept of an island divertor appears the only suitable idea that may be helpful to make up for the absence of a
natural helical divertor in the magnetic configuration. In this context, the paper presents and discusses the measured
and calculated magnetic surface structures of different configuration modes, where large magnetic islands or their
remains at the edge of the plasma volume may be used for experimental implementation of the island divertor.
PACS: 52.55.-s; 52.55.Hc; 52.55.Rk; 52.70.Ds; 52.55.Dy
INTRODUCTION
The divertor structure is necessary to control the
plasma-wall, plasma-target interactions [1, 2], and also
to provide an efficient monitoring of particles [3, 4]. In
stellarators, where the toroidal magnetic field plays a
decisive role in the formation of closed magnetic
surfaces, it is every so often difficult to create a helical
magnetic divertor structure. The conditions and required
investigations to justify the island divertor concept for
the stellarators of this kind have been adequately
formulated in refs. [1, 2]. Of first priority [1] are the
studies of the magnetic field structure, the localization
of O- and X-points of the islands outside the last closed
magnetic surface, the effect of perturbation fields on the
islands and geometry of flux bundles in the vicinity of
islands and ergodic regions.
1. SPECIAL FEATURES OF THE ISLAND
DIVERTOR CONCEPT FOR THE
“URAGAN-2M” TORSATRON
AND THE WORK OBJECTIVE
The Uragan-2M torsatron has the following
characteristics: major radius R=1.7 m and minor radius
of the toroidal vacuum chamber avc=0.34 m; helical
winding with l=2 and the number of magnetic field
periods m=4; 16 toroidal field coils; 8 compensating
vertical field coils and 4 correcting field coils. The
magnetic configuration, structure of the facility, status
and experimental program of the torsatron “Uragan-
2M” having an additional toroidal magnetic field have
been described well enough in papers [5-8].
The magnetic configuration of the Uragan-2M
torsatron having an additional toroidal magnetic field
looks complicated from the standpoint of divertor
feasibility, namely:
- practically at all configuration regimes, suitable for
operation with the plasma, the separatrix of the natural
magnetic divertor cannot fall within the vacuum
chamber dimensions;
- at numerous possible working regimes, the plasma,
which diffuses from the confinement volume, must
mainly stream along the magnetic field lines of a broad
ergodic region to the vacuum chamber wall for the
apexes of elliptically-shaped magnetic surfaces;
- practically in most cases, the separatrix of the
islands and its vicinity are generally disrupted at the
edge of the confinement volume, and then this vicinity
represents the distributed regions of the preferential
plasma outflow to the vacuum chamber wall;
- besides, the island structures can be cut off by the
vacuum chamber wall; they can break down due to
perturbations or disappear in a natural way, and these
processes can be controlled through vertical magnetic
field variation. The magnetic configuration modes in the
Uragan-2M are determined not only by variation of the
parameter kϕ, which represents the ratio of the toroidal
magnetic field of the helical winding to the total toroidal
magnetic field, but also by the ratio of the average
vertical magnetic field to the toroidal field on the
geometrical axis of the torus <B⊥/B0>.
In another variant of the concept implementation,
where the islands are located inside, but in close vicinity
to the last closed magnetic surfaces, one can use a
movable local limiter, already created and trial-tested at
the Uragan-2M [9].
That is why the only concept that is suitable to make
up for the absence of the natural helical divertor in the
Uragan-2M torsatron is the concept of the island
divertor. This concept should rely on such configuration
modes when large-in-size magnetic islands or their
remains exist at the edge of the closed magnetic surface
region, i.e., at the plasma boundary.
The present work has reduced to finding (both
experimentally and numerically) out of a vast number of
possible regimes those several regimes with the islands
at the edge, which would decide the issues of island
divertor creation.
2. MAGNETIC SURFACE STRUCTURES
MEASURED AT THE MODES THAT MEET
THE CONCEPT OF THE ISLAND
DIVERTOR
For experimental investigation of closed magnetic
surface structures in the Uragan-2M torsatron, the
earlier-tested scanning luminescent rod technique has
been used [7, 8]. The scanning luminescent rod was
placed in the poloidal section of the vacuum chamber
between the toroidal field coils at the site, where the
elliptically-shaped magnetic surfaces were arranged
vertically. In the section, where the magnetic surface
measurements were made, on the vacuum-chamber
inner surface two light-emitting diodes (LEDs) with the
known interspace between them were installed. The
horizontally-movable electron gun was placed in the
vacuum chamber section, which was clear of the
ISSN 1562-6016. ВАНТ. 2012. №6(82) 35
measurement section. It injected 40 to 50 eV electrons
on the magnetic field lines. In the present studies the
stationary magnetic field of the geometrical axis of the
torus was equal to B0= 0.1 T.
Before everything else it should be noted that during
the experiments a unique photograph was taken, which
well illustrates the operation of the island divertor
(Fig. 1).
The peculiarity of the image obtained lies in the fact
that it displays two concurrent processes. If the
luminescent rod scans the poloidal section of the
magnetic configuration, where the last closed surface is
continuously filled up with electrons from the small
gun, then all round the chamber section we observe the
discharge with a low plasma density, which is caused by
the induction electric field associated with magnetic
field oscillations. In the figure, the arrow labeled “e-
beam” shows the last closed magnetic surface, onto
which the electron beam is injected to measure its form.
The arrows bearing figures 1, 2, 3 point to three islands
of the resonance angle of rotational transform i/2π=1/3,
within which the low-density plasma is confined. The
“Sep” arrows show the dark region between the last
closed magnetic surface of the confinement volume and
the islands, where the separatrix and the field lines in its
neighborhood are broken and open, and therefore, there
is no confinement of the discharge particles. From now
on, in all the figures depicting the measured magnetic
surfaces two bright points at the edges of the figure
display the position of reference LEDs, and the (+) sign
indicated the position of the geometrical axis of the
torus.
Fig. 1. Visual demonstration of the island divertor
operation. The view of the low-density plasma
confinement region in the Uragan-2M torsatron: mode
kϕ≈0.295, <B⊥/B0>≈1.8 %; mean radius of the last
closed magnetic surface а≈16.3 cm; thickness of
separatrix region Sep≈0.45…2.5 cm; transverse
dimensions of islands δ≈2.3-4.7 cm; mean radius
of О- and Х-points of islands r≈19.6 cm
Below we show the measured Uragan-2M modes of
the magnetic configuration with islands at the edge. The
modes admit a variety of conditions making possible
studies of the island divertor and, later, its efficient use.
The changes in the islands with i/2π=1/3 at the edge of
field configurations under two modes controlled by the
vertical magnetic field can be seen in Fig. 2−Fig. 8.
Fig. 2. Magnetic surface structure at the configuration
mode with kϕ=0.31 and <B⊥/B0>=1.85 %: mean radius of
the last closed magnetic surface а≈20.4 cm; three
magnetic islands i/2π=1/3 lie near the edge; mean radius
of the island centers (O-points), r≈16.5 cm; magnetic axis
displacement from the geometrical axis of the torus
Δ≈ -5.7 cm. Hereafter, the (-) sign at the magnetic axis
shift shows that the magnetic axis is displaced inwards
relative to the geometrical axis of the torus
Fig. 3. Magnetic surface structure at the configuration
mode with kϕ=0.31 and <B⊥/B0>=1.14%: the mean
radius of the closed magnetic surface, which is adjacent
to three whiskers (1, 2, 3), i.e., remains of the broken
magnetic islands with i/2π=1/3, is а≈17.3 cm; Δ≈-9 cm
Fig. 4. Magnetic surface structure at the configuration
mode with kϕ=0.32 and <B⊥/B0>=1.58%: the mean
radius of the closed magnetic surface, which is adjacent
to the chain of magnetic islands with i/2π=1/3, is
а≈17 cm; Δ≈-6.65 cm; δ≈2.5…5 cm; island lengths are
lis≈20.6, 21 and 41 cm; the mean radius of the island
centers (O-points) is r≈13 cm
36 ISSN 1562-6016. ВАНТ. 2012. №6(82)
Fig. 5. Magnetic surface structure at the configuration
mode with kϕ=0.32 and <B⊥/B0>=1.34 %: the mean
radius of the closed magnetic surface, which is adjacent to
three whiskers (1, 2, 3), i.e., remains of the broken
magnetic islands with i/2π=1/3, is а≈14.4 cm; Δ≈-7.7 cm
Fig. 6. Magnetic surface structure at the configuration
mode with kϕ=0.33 and <B⊥/B0>=1.92 %: the mean
radius of the closed magnetic surface, which is adjacent
to two neighboring chains of magnetic islands with
i/2π=2/5 and i/2π=3/7, is а≈19 cm; Δ≈-6.4 cm
Fig. 7. Magnetic surface structure at the configuration
mode with kϕ=0.36 and <B⊥/B0>=2.03%: the mean
radius of the closed magnetic surface, which is adjacent
to two whiskers (1, 2), i.e., remains of two magnetic
islands with i/2π=1/2, is а≈14.3 cm; Δ≈-7.6 cm
Fig. 8. Magnetic surface structure at the configuration
mode with kϕ=0.295 and <B⊥/B0>=3.21 %: the mean
radius of the closed magnetic surface, which is adjacent
to a chain of five magnetic islands with i/2π=2/5, is
а≈16.8 cm; Δ≈+1.0 cm
3. THE NUMERICALLY DETERMINED
MODES OF MAGNETIC CONFIGURATION
WITH ISLANDS AT THE EDGE
To perform the computational search for the
configuration modes that would meet the formulated island
divertor concept, the earlier developed code has been
applied [10]. In the field description, the numerical code
uses real layings of bus bars of helical windings, toroidal,
compensating and correcting field coils of the Uragan-2M
torsatron. Besides, the code took into account the design-
provided geometry of helical winding detachable joints and
currentfeed connectors. The consideration of perturbations
introduced by the detachable joints and currentfeeds has
shown the formation of island structures (in addition to
natural ones) with i/2π=1/2, 1/3, 4/7, 4/6, 4/5, 8/9, etc., the
deformation of the magnetic surfaces, the violation of
magnetic configuration periodicity and symmetry [7, 10].
The numerically predicted islands and configuration
perturbations were confirmed by magnetic surface
measurements [7, 8].
Two more regimes with magnetic islands of
resonances i/2π=1/3 and 2/5 at the edge, (Figs. 9 and
10) have been found by the computational method.
140150160170180190200
R, cm
-30
-20
-10
0
10
20
30
Z,
c
m
Fig. 9. Magnetic surface structure at the configuration
mode with kϕ=0.285 and <B⊥/B0>=1.45 %: the mean
radius of the closed magnetic surface, which is adjacent to
a chain of magnetic islands with i/2π≈1/3, is а=20.5 cm;
Δ=-5.3 cm; i/2π(0)≈0.18; i/2π(а)≈1/3; δ≈1.5-4.5 cm;
a large angular length of the islands
ISSN 1562-6016. ВАНТ. 2012. №6(82 37
140150160170180190200
R, cm
-30
-20
-10
0
10
20
30
Z,
c
m
Fig. 10. Magnetic surface structure at the configuration
mode with kϕ=0.31 and <B⊥/B0>=1.5 %: the mean
radius of the closed magnetic surface, which is adjacent
to a chain of magnetic islands with i/2π=2/5, is
а≈20 cm; Δ=-6.26 cm; i/2π(0)≈0.25; i/2π(а)≈2/5
The characteristic property of these two magnetic
surface structures is the location of the islands having
the largest radial dimensions at the apexes of
elliptically-shaped magnetic surfaces.
It is pertinent to note that the two mentioned regimes
should be complemented with one more configuration
mode with kϕ≈0.375, calculated in paper [11]. In [11] it
was first suggested that the islands with i/2π=4/5 could
be used for creating the island divertor.
CONCLUSIONS
The experimental magnetic field structure studies by
the scanning luminescent rod technique as well as the
computational investigations have enabled us to find ten
modes of configurations with the islands of resonances
at the rotational transform angles i/2π=1/3, 3/7, 2/5, 1/2,
4/5, which lie outside the last closed magnetic surfaces.
The combination of the low-density plasma discharge
with the scanning luminescent rod procedure to measure
the magnetic surface has first visually demonstrated the
operation of the island divertor. It has also been shown
that by varying the vertical magnetic field value in the
configuration it is possible to provide the following
capabilities for controlling the island divertor operation:
i) to cut off the islands by the vacuum chamber wall;
ii) to use the remains of the islands already broken down
by the existing perturbations; iii) to reduce and suppress
the islands. In another variant of the island divertor
realization, when the islands are positioned inside and
close to the last closed magnetic surfaces, a movable
local limiter can be used.
REFERENCES
1. C.D. Beidler et al. Island divertor concept for the
stellarator Wendelstein 7-X and Wendelstein 7-AS // 9th
IAEA Int. Workshop on Stellarators, Garching,
Germany, 10-14 May 1993, p. 385-390.
2. E. Strumberger. Topology of field line mapping in the
ergodic region of optimized stellarator and divertor
design // 9th IAEA Int. Workshop on Stellarators,
Garching, Germany, 10-14 May 1993, p. 536-541.
3. A. Komori et al. Edge plasma control by local island
divertor in LHD // Nucl. Fusion. 2005, v. 45, p. 837-
842.
4. T. Morisaki et al. Local island divertor experiments
on LHD // J. Nucl. Materials. 2005, v. 337-339, p. 154-
160.
5. O.S. Pavlichenko. Status of “URAGAN-3M” and
“URAGAN-2M” experiments // Stellarators and other
helical confinement systems. A Collection of Papers
Presented at 9th IAEA Int. Workshop on Stellarators,
Garching, Germany, 10-14 May 1993, p. 60-77.
6. O.S. Pavlichenko et al. First results from the
URAGAN-2M torsatron // Plasma Phys. Control.
Fusion. 1993, v. 35, p. B223-B230.
7. G.G. Lesnyakov et al. Studies of magnetic surfaces in
the Uragan-2M torsatron // Contributed Papers of 23rd
EPS Conf. on Contr. Fusion and Plasma Phys. Kiev,
1996, v. 20 C, part. II (b025), p. 547-550.
8. A.A. Beletskii et al. // Problems of Atomic Science
and Technology. Series “Plasma Physics” (14). 2008,
№ 6 (58), p. 13-15.
9. G.P. Glazunov et al. First tests of the biased movable
B4C-limiter in the Uragan-2M torsatron under RF and
UHF wall conditioning // Problems of Atomic Science
and Technology. Series “Plasma Physics” (16). 2010,
№6, p. 14-16.
10. N.T. Besedin, G.G. Lesnyakov, I.M. Pankratov.
Current feed and detachable joint influence on magnetic
field configuration of the Uragan-2M torsatron // VANT.
Ser. “Termoyad. Sintez”. 1991, №1, p. 48-50 (in
Russian).
11. B. Seiwald et al. Optimization of neoclassical
transport in Uragan-2M // 31st EPS Conf. on Plasma
Phys. ECA, 2004, v. 28G, р. 5.118.
Article received 20.09.12
ВОЗМОЖНОСТИ СОЗДАНИЯ ОСТРОВНОГО ДИВЕРТОРА В ТОРСАТРОНЕ УРАГАН-2М
Г.Г. Лесняков, А.Н. Шаповал, О.С. Павличенко
Единственной подходящей концепцией, с помощью которой можно восполнить отсутствие
естественного винтового дивертора в магнитной конфигурации, является концепция островного дивертора.
В этой связи представлены и обсуждаются измеренные и вычисленные структуры магнитных поверхностей
разных режимов конфигурации, в которых большие магнитные острова или их остатки на краю плазменного
объема можно использовать для экспериментальной реализации островного дивертора.
МОЖЛИВОСТІ СТВОРЕННЯ ОСТРІВНОГО ДИВЕРТОРА В ТОРСАТРОНІ УРАГАН-2М
Г.Г. Лесняков, А.М. Шаповал, О.С. Павлiченко
Єдиною придатною концепцією, за допомогою якої можна заповнити відсутність природного гвинтового
дивертора в магнітній конфігурації, є концепція острівного дивертора. У зв’язку с цим наведенo та
обговорюються виміряні й обчислені структури магнітних поверхонь різних режимів конфігурації, у яких
великі за розміром магнітні острови або їх залишки біля краю плазмового об’єму можна використати для
експериментальної реалізації острівного дивертора.
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