Fast ion generation and its effect on ETB formation in the U-3M torsatron
In the l=3 U-3M torsatron with RF produced and heated plasmas, a two-temperature ion energy distribution arises with a minor group of suprathermal ions. It is shown that a possible mechanism of fast ion generation is cyclotron heating and/or acceleration of ions by a strong RF field in the local A...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2006
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| Цитувати: | Fast ion generation and its effect on ETB formation in the U-3M torsatron / V.V. Chechkin, L.I. Grigor’eva, E.L. Sorokovoy, Ye.L. Sorokovoy, A.A. Beletskii, A.S. Slavnyj, P.Ya. Burchenko, A.V. Lozin, S.A. Tsybenko, A.P. Litvinov, A.Ye. Kulaga, Yu.K. Mironov, V.S. Romanov, D.V. Kurilo // Вопросы атомной науки и техники. — 2006. — № 6. — С. 34-36. — Бібліогр.: 9 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-817732025-02-09T13:59:02Z Fast ion generation and its effect on ETB formation in the U-3M torsatron Генерация быстрых ионов и её влияние на формирование КТБ в торсатроне У-3М Генерація швидких іонів та її вплив на формування КТБ в торсатроні У-3М Chechkin, V.V. Grigor’eva, L.I. Sorokovoy, E.L. Sorokovoy, Ye.L. Beletskii, A.A. Slavnyj, A.S. Burchenko, P.Ya. Lozin, A.V. Tsybenko, S.A. Litvinov, A.P. Kulaga, A.Ye. Mironov, Yu.K. Romanov, V.S. Kurilo, D.V. Magnetic confinement In the l=3 U-3M torsatron with RF produced and heated plasmas, a two-temperature ion energy distribution arises with a minor group of suprathermal ions. It is shown that a possible mechanism of fast ion generation is cyclotron heating and/or acceleration of ions by a strong RF field in the local Alfven resonance layer N|| 2≈ε1 with an additional RF field enhancement due to the coupling resonance. The observed spontaneous ETB formation is preceded by an accumulation of high energy ions in the plasma and synchronized with their burst-like outflow to the divertor. On this basis, it is believed that it is fast ion orbit loss that results in formation of a layer with Er shear and E×B velocity shear accordingly at the plasma boundary, this, in turn, resulting in a damping of turbulence and turbulence-induced anomalous transport. В 3-заходном торсатроне У-3М при ВЧ создании и нагреве плазмы образуется двухтемпературное распределение ионов по энергиям с небольшим количеством сверхтепловых ионов. Вероятным механизмом генерации быстрых ионов являются циклотронный нагрев или ускорение сильным ВЧ полем в слое локального альфвеновского резонанса при дополнительном усилении ВЧ поля вследствие резонанса связи. Спонтанное образование КТБ предваряется накоплением высокоэнергичных ионов в плазме и синхронизуется с их резким выбросом в дивертор. На этом основании считается, что образование на границе плазмы слоя с широм Еr, вызывающим подавление турбулентности и связанного с нею аномального переноса, обусловлено орбитальными потерями быстрых ионов. У 3-західному торсатроні У-3М при ВЧ створенні та нагріві плазми виникає двотемпературний розподіл іонів за енергіями з невеликою кількістю надтеплових іонів. Можливим механізмом генерації швидких іонів є циклотронний нагрів або прискорення сильним ВЧ полем у шарі локального альфвенівського резонансу при додатковому підсиленню ВЧ поля внаслідок резонансу зв’язку. Спонтанне створення КТБ випереджується накопиченням високоенергійних іонів в плазмі і синхронізується з їх різким викидом в дивертор. На цій основі вважається, що створення на границі плазми шару з широм Еr, що викликає придушення турбулентності і пов’язаного с нею аномального переносу, зумовлено орбітальними втратами швидких іонів. 2006 Article Fast ion generation and its effect on ETB formation in the U-3M torsatron / V.V. Chechkin, L.I. Grigor’eva, E.L. Sorokovoy, Ye.L. Sorokovoy, A.A. Beletskii, A.S. Slavnyj, P.Ya. Burchenko, A.V. Lozin, S.A. Tsybenko, A.P. Litvinov, A.Ye. Kulaga, Yu.K. Mironov, V.S. Romanov, D.V. Kurilo // Вопросы атомной науки и техники. — 2006. — № 6. — С. 34-36. — Бібліогр.: 9 назв. — англ. 1562-6016 PACS: 52.50.Qt; 52.55.Dy,He https://nasplib.isofts.kiev.ua/handle/123456789/81773 en Вопросы атомной науки и техники application/pdf 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 |
Magnetic confinement Magnetic confinement |
| spellingShingle |
Magnetic confinement Magnetic confinement Chechkin, V.V. Grigor’eva, L.I. Sorokovoy, E.L. Sorokovoy, Ye.L. Beletskii, A.A. Slavnyj, A.S. Burchenko, P.Ya. Lozin, A.V. Tsybenko, S.A. Litvinov, A.P. Kulaga, A.Ye. Mironov, Yu.K. Romanov, V.S. Kurilo, D.V. Fast ion generation and its effect on ETB formation in the U-3M torsatron Вопросы атомной науки и техники |
| description |
In the l=3 U-3M torsatron with RF produced and heated plasmas, a two-temperature ion energy distribution arises
with a minor group of suprathermal ions. It is shown that a possible mechanism of fast ion generation is cyclotron
heating and/or acceleration of ions by a strong RF field in the local Alfven resonance layer N||
2≈ε1 with an additional RF
field enhancement due to the coupling resonance. The observed spontaneous ETB formation is preceded by an
accumulation of high energy ions in the plasma and synchronized with their burst-like outflow to the divertor. On this
basis, it is believed that it is fast ion orbit loss that results in formation of a layer with Er shear and E×B velocity shear
accordingly at the plasma boundary, this, in turn, resulting in a damping of turbulence and turbulence-induced
anomalous transport. |
| format |
Article |
| author |
Chechkin, V.V. Grigor’eva, L.I. Sorokovoy, E.L. Sorokovoy, Ye.L. Beletskii, A.A. Slavnyj, A.S. Burchenko, P.Ya. Lozin, A.V. Tsybenko, S.A. Litvinov, A.P. Kulaga, A.Ye. Mironov, Yu.K. Romanov, V.S. Kurilo, D.V. |
| author_facet |
Chechkin, V.V. Grigor’eva, L.I. Sorokovoy, E.L. Sorokovoy, Ye.L. Beletskii, A.A. Slavnyj, A.S. Burchenko, P.Ya. Lozin, A.V. Tsybenko, S.A. Litvinov, A.P. Kulaga, A.Ye. Mironov, Yu.K. Romanov, V.S. Kurilo, D.V. |
| author_sort |
Chechkin, V.V. |
| title |
Fast ion generation and its effect on ETB formation in the U-3M torsatron |
| title_short |
Fast ion generation and its effect on ETB formation in the U-3M torsatron |
| title_full |
Fast ion generation and its effect on ETB formation in the U-3M torsatron |
| title_fullStr |
Fast ion generation and its effect on ETB formation in the U-3M torsatron |
| title_full_unstemmed |
Fast ion generation and its effect on ETB formation in the U-3M torsatron |
| title_sort |
fast ion generation and its effect on etb formation in the u-3m torsatron |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2006 |
| topic_facet |
Magnetic confinement |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/81773 |
| citation_txt |
Fast ion generation and its effect on ETB formation in the U-3M torsatron / V.V. Chechkin, L.I. Grigor’eva, E.L. Sorokovoy, Ye.L. Sorokovoy, A.A. Beletskii, A.S. Slavnyj,
P.Ya. Burchenko, A.V. Lozin, S.A. Tsybenko, A.P. Litvinov, A.Ye. Kulaga, Yu.K. Mironov,
V.S. Romanov, D.V. Kurilo // Вопросы атомной науки и техники. — 2006. — № 6. — С. 34-36. — Бібліогр.: 9 назв. — англ. |
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Вопросы атомной науки и техники |
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FAST ION GENERATION AND ITS EFFECT ON ETB FORMATION
IN THE U-3M TORSATRON
V.V. Chechkin, L.I. Grigor’eva, E.L. Sorokovoy, Ye.L. Sorokovoy, A.A. Beletskii, A.S. Slavnyj,
P.Ya. Burchenko, A.V. Lozin, S.A. Tsybenko, A.P. Litvinov, A.Ye. Kulaga, Yu.K. Mironov,
V.S. Romanov, D.V. Kurilo
Institute of Plasma Physics, NSC “Kharkov Institute of Physics and Technology”,
061108, Akademicheskaya Str. 1, Kharkov, Ukraine
In the l=3 U-3M torsatron with RF produced and heated plasmas, a two-temperature ion energy distribution arises
with a minor group of suprathermal ions. It is shown that a possible mechanism of fast ion generation is cyclotron
heating and/or acceleration of ions by a strong RF field in the local Alfven resonance layer N||
2≈ε1 with an additional RF
field enhancement due to the coupling resonance. The observed spontaneous ETB formation is preceded by an
accumulation of high energy ions in the plasma and synchronized with their burst-like outflow to the divertor. On this
basis, it is believed that it is fast ion orbit loss that results in formation of a layer with Er shear and E×B velocity shear
accordingly at the plasma boundary, this, in turn, resulting in a damping of turbulence and turbulence-induced
anomalous transport.
PACS: 52.50.Qt; 52.55.Dy,He
1. INTRODUCTION
An appreciable number of ions with energies
considerably exceeding the mean thermal energy of the
bulk ions can arise in the plasma of stellarator-type
devices, including heliotrons/torsatrons (see, e.g., [1,2]).
Apart from mechanisms of fast ion generation, studies of
their confinement in stellarators is of interest as these
particles undergo neoclassical transport in the l.m.f.p.
regime, in particular, 1/v regime typical for reactor-scale
devices [3].
In a middle-size device, the Uragan-3M (U-3M)
torsatron (l=3, m=9, R=1m, a ≈0.12 m, ι( a )≈0.3, Bφ
= 0.7 T), with RF produced and heated plasmas, a two-
temperature ion distribution in perpendicular energies
develops (Ti1~50…80eV, Ti2~250…400eV at en ~1012 cm-3,
Te(0)≈600 eV). Also, there is a minor group (<1%) of
suprathermal ions (STI) with energies >1000 eV. With
this, the hotter ions and STI (hereinafter, fast ions)
experience neoclassical diffusion in the 1/v regime (vi ~2×
102 c-1 < 23
tε υTi ι/R). Studies of mechanisms of fast ion
generation and of their confinement in U-3M is of
specific interest for the following reasons.
1. Alfven waves with ω≲ωci(0) are used for plasma
heating. The closeness of ω to ωci and strong radial non-
uniformity of the plasma can result in specific
mechanisms of wave excitation and absorbtion in the
plasma with occurrence of fast particles.
2. An open natural helical divertor is realized in
U-3M. Hence, an opportunity is offered to judge on
confinement and loss of fast ions by comparing their
behaviour in the confinement and divertor regions.
3. A spontaneous transition to the improved
confinement regime is observed in U-3M. It is of interest
to find out the effect of fast ions on the transition and to
compare their confinement in various phases of the
transition.
2. FAST ION BEHAVIOUR IN THE
CONFINEMENT AND DIVERTOR REGIONS
IN VARIOUS PHASES OF DISCHARGE
(b)
↓
(a) (d)
↓ ↓
(c)↑
Fig. 1. Time evolution of (a) RF antenna current
(envelope); (b) line-averaged electron density, en ;
(c) CX neutral flux Гn with perpendicular energy 1350 eV
(directed downward); (d) fast ion component (>500 eV)
in the divertor flow on the ion ∇B drift side, Ii
It is seen in Fig. 1 that the density en passes 3 phases
in its evolution over the RF pulse: (1) density rise at the
beginning of discharge (~3…4 ms); (2) density decay
(tens ms) which is terminated by edge Er bifurcation
toward a more negative value and ETB formation [4]; and
(3) the H-like mode phase where en stops decaying and
even can rise. At the phase (1), the flux Гn (c) exhibits a
short-time rise (maximum at 1en ≈1.2×1012 cm-3),
indicating a rise of fast ion content in the confinement
volume. Synchronously with Гn , a burst of fast ion
outflow to the divertor occurs in the phase (1) (d) as
indicated by the current Ii to the U= +500 V -biased
collector of an electrostatic charged particle energy
34 Problems of Atomic Science and Technology. 2006, № 6. Series: Plasma Physics (12), p. 34-36
0 100 200 300 400 500
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n e
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012
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-3
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(c)
(a)
(b) (d)
analyzer mounted in the divertor flow on the ion ∇B drift
side. In the phase (2), a repeat Γn rise (c) evidences an
improvement of fast ion confinement in this phase. This is
consistent with a rise of temperature Ti2 [4] and a current Ii
reduction (d). The Γn rise and Ii decay last until the Er
bifurcation. With this event the start of Γn drop and a
sharp burst of fast ion outflow to the divertor similar to
that in phase (1) are synchronized, evidencing a rise of
fast ion loss at the start of phase (3). Such a change of
confinement regime occurs at the density 2en ≈1.4×
1012 cm-3 which is close to 1en . The relation 1en ≈ 2en
~1012 cm-3 holds independent of RF power and operating gas
(hydrogen) pressure provided the bursts of fast ion outflow
occur in the phases of density rise and decay.
Fig. 2. Ii(0)-normalized ion current Ii versus retarding
voltage U plots measured in the Ii maxima in the phases
(1) (○) and (2) (●) and at the end of phase (2), before the
Ii burst (+)
It follows from Fig. 2 that the Ii(U)/Ii(0) plots taken in
the Ii maxima in phases (1) and (2) are similar. In both
cases, the contribution of ions with energies eU>500 eV
amounts 40-50%, while in the phase of en decay where
the accumulation of fast ions in the plasma is observed
(the rise of Γn) this contribution does not exceed 23%.
The closeness of 1en and 2en values and their
practical independence on the heating power and
operating gas pressure with Bφ fixed suggest an idea that
the accumulation of fast ions in the plasma and their
burst-like outflow to the divertor are governed by one
mechanism and connected with dispersion properties of
the plasma column. This suggestion is validated by a
resonance character of plots shown in Fig. 3. A possible
explanation of these plots is the effect of local Alfven
resonance, N||
2 ≈ ε1 , in an essentially non-uniform plasma
resulting in cyclotron heating/acceleration of ions in the
thin resonance layer in combination with an additional RF
field enhancement due to the coupling resonance between
the exciting antenna and plasma column. Note that other
plasma parameters also exhibit a resonance Bφ
dependence [5,6].
Fig. 3. Density 1en (○)and current Ii in its maximum in
phase (1) (●) as functions of Bφ.
3. EDGE POTENTIAL AND ITS
FLUCTUATION
1.0×10-12 cm-3
2.4×10-12 cm-3 ↓
↓
Fig. 4. Time evolution of (a) RF antenna current
(envelope), (b) density en , (c) current Ii (U=500 V) and
(c) edge floating potential, Vf. Vertical dotted lines
indicate 1st and 2nd Vf bifurcations
As is seen in Fig. 4, first, a short-time potential
increase occurs in phase (1), then it is followed by the
above mentioned burst of fast ion outflow to the divertor
(maximum at 1en ≈ 1.1×1012 cm-3). Afterwards, a state
sets in with a reduced fluctuation level, which is
terminated at en ≈ 2.4×1012 cm-3 by the first bifurcational
transition toward a higher potential Vf (in the chosen
radial location of the Langmuir probe) and a higher
fluctuation level. With this, the rise of density is slowed
down and an en decay starts (phase (2)) which lasts until
the second bifurcation at 2en ≈ 1.0×1012 cm-3 toward a
lower potential and a lower fluctuation level.
35
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po
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minor radius, r (cm)
(a)
9 10 11 12
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f (
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(b)
It follows from comparison of Figs 5(a) and 5(b) with
Fig. 4 that regimes with a stronger negative Er and Er
shear accordingly occur after the burst-like fast ion
outflow before the first bifurcation, in phase (1), and after
the second bifurcation, in phase (3). In both phases, (1)
and (3), a lower level of fluctuation is observed, this, in
turn, resulting in reduction of the anomalous transport at
the plasma boundary and in observed slowing down of the
density decay or even density rise (see, also, [4]).
Fig. 5. Equilibrium component of floating potential Vf of
a movable Langmuir probe versus minor radius r just
before the bifurcation (○) and right after it (●) in the:
a) phase (1), b) phase (3)
4. SUMMARY AND DISCUSSION
1. A possible explanation of the effect of fast ion
generation could be cyclotron heating and/or acceleration of
the ions by a strong RF field arising in the layer of non-
uniform plasma where the local Alfven resonance condition,
N||
2≈ε1, is fulfilled in combination with an additional RF field
amplification due to the coupling resonance between the
exciting antenna and the plasma column.
2. The resonance character (with respect to Bφ and
en ) of generation of fast ions and their sharp burst-like
outflow to the divertor region (Fig. 3) are combined with
indications of transition to an H-like mode (Figs 4,5). In
view of these experimental data, a scenario can be
suggested where non-ambipolar fast ion orbit loss should
be responsible for formation of a layer with an initial
small Er shear at the boundary (so-called “ion galo” [7])
in the phase (2). As the number of fast ions increases with
the total density decreasing, a critical ion collision
frequency is achieved when Er exhibits a hard
bifurcational transition to a more negative value [8]. The
observed time of potential jump, ≲10 ms, is consistent
with a theoretical estimation of the bifurcation time, τtr ~ ε
t
2ι2v-1 [9]. A reverse process, i.e., H-L-like transition, takes
place at the end of phase (1)-start of phase (2) with an
obvious hysteresis by density (Fig. 4) which is typical for
hard bifurcational transitions [9].
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Madrid, 2005. Paper P2-26
3. G. Grieger et al. //Phys. Fluids B. 1992, v. 4(7), p.
2081.
4. V.V. Chechkin et al. //Plasma Phys. Control. Fusion.
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1996, v. 38, p. 1.
ГЕНЕРАЦИЯ БЫСТРЫХ ИОНОВ И ЕЁ ВЛИЯНИЕ НА ФОРМИРОВАНИЕ КТБ В ТОРСАТРОНЕ У-3М
В.В. Чечкин, Л.И. Григорьева, Э.Л. Сороковой, Е.Л. Сороковой, A.A. Белецкий, A.С. Славный,
П.Я. Бурченко, A.В. Лозин, С.A. Цыбенко, A.П. Литвинов, A.Е. Kулага, Ю.K. Mиронов,
В.С. Рoманов, Д.В. Kурило
В 3-заходном торсатроне У-3М при ВЧ создании и нагреве плазмы образуется двухтемпературное
распределение ионов по энергиям с небольшим количеством сверхтепловых ионов. Вероятным механизмом
генерации быстрых ионов являются циклотронный нагрев или ускорение сильным ВЧ полем в слое локального
альфвеновского резонанса при дополнительном усилении ВЧ поля вследствие резонанса связи. Спонтанное
образование КТБ предваряется накоплением высокоэнергичных ионов в плазме и синхронизуется с их резким
выбросом в дивертор. На этом основании считается, что образование на границе плазмы слоя с широм Еr,
вызывающим подавление турбулентности и связанного с нею аномального переноса, обусловлено
орбитальными потерями быстрых ионов.
ГЕНЕРАЦІЯ ШВИДКИХ ІОНІВ ТА ЇЇ ВПЛИВ НА ФОРМУВАННЯ КТБ В ТОРСАТРОНІ У-3М
В.В. Чечкін, Л.І. Григор’єва, Е.Л. Сороковий, Є.Л. Сороковий, О.О. Білецький, О.С. Славний,
П.Я. Бурченко, О.В. Лозін, С.A. Цибенко, A.П. Литвинов, A.Є. Kулага, Ю.K. Mиронов,
В.С. Рoманов, Д.В. Kурило
У 3-західному торсатроні У-3М при ВЧ створенні та нагріві плазми виникає двотемпературний розподіл
іонів за енергіями з невеликою кількістю надтеплових іонів. Можливим механізмом генерації швидких іонів є
циклотронний нагрів або прискорення сильним ВЧ полем у шарі локального альфвенівського резонансу при
додатковому підсиленню ВЧ поля внаслідок резонансу зв’язку. Спонтанне створення КТБ випереджується
накопиченням високоенергійних іонів в плазмі і синхронізується з їх різким викидом в дивертор. На цій основі
36
a b
вважається, що створення на границі плазми шару з широм Еr, що викликає придушення турбулентності і
пов’язаного с нею аномального переносу, зумовлено орбітальними втратами швидких іонів.
37
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