Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron

It is shown that in the Uragan-3M torsatron under conditions of spontaneous change of confinement mode caused by formation of an internal transport barrier, a layer with the E×B velocity shear appears at the boundary of confinement region. Appreciable changes of the edge microturbulence characterist...

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Published in:Вопросы атомной науки и техники
Date:2005
Main Authors: Sorokovoy, E.L., Grigor’eva, L.I., Chechkin, V.V., Volkov, Ye.D., Sorokovoy, Ye.L., Burchenko, P.Ya., Tsybenko, S.A., Lozin, A.V., Litvinov, A.P., Masuzaki, S., Yamazaki, K.
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Language:English
Published: Національний науковий центр «Харківський фізико-технічний інститут» НАН України 2005
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Online Access:https://nasplib.isofts.kiev.ua/handle/123456789/78419
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Cite this:Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron / E.L. Sorokovoy, L.I. Grigor’eva, V.V. Chechkin, Ye.D. Volkov, Ye.L. Sorokovoy, P.Ya. Burchenko, S.A. Tsybenko, A.V. Lozin, A.P. Litvinov, S. Masuzaki, K. Yamazaki // Вопросы атомной науки и техники. — 2005. — № 1. — С. 21-23. — Бібліогр.: 5 назв. — англ.

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Digital Library of Periodicals of National Academy of Sciences of Ukraine
id nasplib_isofts_kiev_ua-123456789-78419
record_format dspace
spelling Sorokovoy, E.L.
Grigor’eva, L.I.
Chechkin, V.V.
Volkov, Ye.D.
Sorokovoy, Ye.L.
Burchenko, P.Ya.
Tsybenko, S.A.
Lozin, A.V.
Litvinov, A.P.
Masuzaki, S.
Yamazaki, K.
2015-03-16T19:47:13Z
2015-03-16T19:47:13Z
2005
Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron / E.L. Sorokovoy, L.I. Grigor’eva, V.V. Chechkin, Ye.D. Volkov, Ye.L. Sorokovoy, P.Ya. Burchenko, S.A. Tsybenko, A.V. Lozin, A.P. Litvinov, S. Masuzaki, K. Yamazaki // Вопросы атомной науки и техники. — 2005. — № 1. — С. 21-23. — Бібліогр.: 5 назв. — англ.
1562-6016
PACS: 52.35.Ra; 52.55.Hc
https://nasplib.isofts.kiev.ua/handle/123456789/78419
It is shown that in the Uragan-3M torsatron under conditions of spontaneous change of confinement mode caused by formation of an internal transport barrier, a layer with the E×B velocity shear appears at the boundary of confinement region. Appreciable changes of the edge microturbulence characteristics and turbulence-induced particle flux in the vicinity of this layer evidence a formation of the edge transport barrier as well.
В торсатроні У-3М при зміні режиму утримання, викликаній створенням внутрішнього транспортного бар’єра, біля границі плазми виникає шар з шіром швидкості Е×В. Відповідні зміни характеристик дрібномасштабної турбулентності поблизу цього шару та викликаного турбулентністю радіального потоку частинок свідчать про створення також і крайового транспортного бар’єра.
В торсатроне У-3М при изменении режима удержания плазмы, вызванном образованием внутреннего транспортного барьера, вблизи границы плазмы появляется слой с широм скорости Е×В. Соответствующие изменения характеристик мелко-масштабной турбулентности в окрестности этого слоя и вызванного турбулентностью радиального потока частиц, свидетельствуют об образовании также и краевого транспортного барьера.
en
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
Вопросы атомной науки и техники
Magnetic confinement
Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron
Характеристики турбулентності крайової плазми при спонтанній зміні режиму утримання в торсатроні «УРАГАН-3М»
Характеристики турбулентности краевой плазмы при спонтанном изменении режима удержания в торсатроне «УРАГАН-3М»
Article
published earlier
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
title Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron
spellingShingle Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron
Sorokovoy, E.L.
Grigor’eva, L.I.
Chechkin, V.V.
Volkov, Ye.D.
Sorokovoy, Ye.L.
Burchenko, P.Ya.
Tsybenko, S.A.
Lozin, A.V.
Litvinov, A.P.
Masuzaki, S.
Yamazaki, K.
Magnetic confinement
title_short Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron
title_full Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron
title_fullStr Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron
title_full_unstemmed Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron
title_sort characteristics of edge plasma turbulence in spontaneous change of confinement mode in the uragan-3m torsatron
author Sorokovoy, E.L.
Grigor’eva, L.I.
Chechkin, V.V.
Volkov, Ye.D.
Sorokovoy, Ye.L.
Burchenko, P.Ya.
Tsybenko, S.A.
Lozin, A.V.
Litvinov, A.P.
Masuzaki, S.
Yamazaki, K.
author_facet Sorokovoy, E.L.
Grigor’eva, L.I.
Chechkin, V.V.
Volkov, Ye.D.
Sorokovoy, Ye.L.
Burchenko, P.Ya.
Tsybenko, S.A.
Lozin, A.V.
Litvinov, A.P.
Masuzaki, S.
Yamazaki, K.
topic Magnetic confinement
topic_facet Magnetic confinement
publishDate 2005
language English
container_title Вопросы атомной науки и техники
publisher Національний науковий центр «Харківський фізико-технічний інститут» НАН України
format Article
title_alt Характеристики турбулентності крайової плазми при спонтанній зміні режиму утримання в торсатроні «УРАГАН-3М»
Характеристики турбулентности краевой плазмы при спонтанном изменении режима удержания в торсатроне «УРАГАН-3М»
description It is shown that in the Uragan-3M torsatron under conditions of spontaneous change of confinement mode caused by formation of an internal transport barrier, a layer with the E×B velocity shear appears at the boundary of confinement region. Appreciable changes of the edge microturbulence characteristics and turbulence-induced particle flux in the vicinity of this layer evidence a formation of the edge transport barrier as well. В торсатроні У-3М при зміні режиму утримання, викликаній створенням внутрішнього транспортного бар’єра, біля границі плазми виникає шар з шіром швидкості Е×В. Відповідні зміни характеристик дрібномасштабної турбулентності поблизу цього шару та викликаного турбулентністю радіального потоку частинок свідчать про створення також і крайового транспортного бар’єра. В торсатроне У-3М при изменении режима удержания плазмы, вызванном образованием внутреннего транспортного барьера, вблизи границы плазмы появляется слой с широм скорости Е×В. Соответствующие изменения характеристик мелко-масштабной турбулентности в окрестности этого слоя и вызванного турбулентностью радиального потока частиц, свидетельствуют об образовании также и краевого транспортного барьера.
issn 1562-6016
url https://nasplib.isofts.kiev.ua/handle/123456789/78419
citation_txt Characteristics of edge plasma turbulence in spontaneous change of confinement mode in the URAGAN-3M torsatron / E.L. Sorokovoy, L.I. Grigor’eva, V.V. Chechkin, Ye.D. Volkov, Ye.L. Sorokovoy, P.Ya. Burchenko, S.A. Tsybenko, A.V. Lozin, A.P. Litvinov, S. Masuzaki, K. Yamazaki // Вопросы атомной науки и техники. — 2005. — № 1. — С. 21-23. — Бібліогр.: 5 назв. — англ.
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fulltext CHARACTERISTICS OF EDGE PLASMA TURBULENCE IN SPONTANEOUS CHANGE OF CONFINEMENT MODE IN THE URAGAN-3M TORSATRON E.L. Sorokovoy , L.I. Grigor’eva,V.V. Chechkin, Ye.D. Volkov, Ye.L. Sorokovoy, P.Ya. Burchenko, S.A. Tsybenko, A.V. Lozin, A.P. Litvinov, S. Masuzaki∗, K. Yamazaki∗ Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine; ∗National Institute for Fusion Science, Toki, Japan It is shown that in the Uragan-3M torsatron under conditions of spontaneous change of confinement mode caused by formation of an internal transport barrier, a layer with the E×B velocity shear appears at the boundary of confinement region. Appreciable changes of the edge microturbulence characteristics and turbulence-induced particle flux in the vicinity of this layer evidence a formation of the edge transport barrier as well. PACS: 52.35.Ra; 52.55.Hc 1. INTRODUCTION In the Uragan-3M (U-3M) torsatron with an open helical divertor (l = 3, m = 9, Ro = 1 м, a ≈ 0,12 м, Вφ = 0,7 Т, ι( a )/2π ≈ 0,3) a spontaneous transition to an improved confinement state (below – “transition”) is observed under conditions of plasma production and heating by RF fields in the ω ≤ ωci range of frequencies [1,2]. This transition is related to an internal transport barrier (ITB) formation in the layer near the τ = 1/4 rational magnetic surface [2], this having been confirmed by the form of electron density and temperature profiles as well as the existence of an E×B velocity shear in the layer considered. It has been demonstrated in [3] that the transition is accompanied by substantial changes in the diverted plasma flow (DPF) magnitude. At the initial phase of these changes being essentially non-steady-state, a reduction of all the PDF components in the spacings between the helical coils is observed, this being an evidence of plasma confinement improvement. The initial phase is terminated by an enhanced escape of thermal and suprathermal ions from the confinement volume, that is accompanied by a rise of some DPF components, thus indicating a certain degradation of confinement. It is shown in the presented paper that parallel with the ITB formation a layer with the E×B velocity shear is also formed at the plasma boundary in U-3M. In the vicinity of this layer substantial changes of the electrostatic microturbulence and assotiated radial particle flux are observed, that indicate an edge transport barrier (ETB) also to be formed. 2. EXPERIMENTAL CONDITIONS The investigations were carried out in a hydrogen plasma with the line-averaged electron density en ~ 1018 m-3 and electron temperature Te(0) ≈ 500 eV. To study the low-frequency (1-300 kHz) electrostatic turbulence in the edge plasma, an array of 4 movable probes was used. The molybdenum φ = 0.5 mm/l = 3 mm probe tips 1, 2, 3, 4 were arranged in the angles of a square 3 mm on side (see inset in Fig. 1) and orientated with the major radius. The ion saturation current (ISC) fluctuations, sI~ , were recorded by the probes 1 and 2. Also, the probe 2 measured equilibrium components of ISC, Is, and floating potential (FP), Vf, and was used for VI-characteristic measurements. The probes 3 and 4 measured the FP fluctuations, fV~ . As a recording facility, a 12 bit ADC with 1.6 µs sampling rate/channel was used. Fig. 1. Relative lay-out of helical coils I, II, III and calculated edge structure of field lines in the poloidal cross-section where measurements are made.The range of probe array LP displacement is indicated by a bold straight segment 3. DYNAMICS OF EDGE DENSITY AND POTENTIAL PROFILES DURING THE TRANSITION In Fig. 2 edge radial profiles are presented of (a) electron density (in relative units), (b) floating potential, Vf, and (c) electron temperature, Te, measured at t1 = 20 ms (before the start of transition) and t2 = 45 ms (after transition). As follows from Fig. 2, the transition is accompanied by a small broadening (∆r ~ 1 mm) of the plasma column (Fig. 2(a) and by a more distinct change of the FP profile, Vf(r), (Fig. 2(b)). As according to Fig. 2(c), the electron temperature does not change significantly with r at the plasma boundary, the radial profile of the plasma potential, Vp(r), should have qualitatively the same form as Vf(r). Then it follows from this form that a layer with a radial electric field shear Problems of Atomic Science and Technology. 2005. № 1. Series: Plasma Physics (10). P. 21-23 21 0 1 0 20 40 60 80 0 20 40 60 (m)r - before transition - after transition 0.130.120.11 (V)Vf (eV)Te en (a) (b) (c) (rel.u.) Fig. 2 occurs at the plasma boundary during the transition (Er is directed inward at r < 11.75 cm and outward at r > 11.75 cm). Hence, the velocity of plasma poloidal rotation E×B reverses its direction in this layer. As it has been shown recently [4], the ExB velocity shear seriously affects the edge turbulence, resulting in a quenching of the fluctuations, their de-correlation and a reduction of the radial turbulent flux of particles and heat. 4. CHANGES OF EDGE TURBULENCE CHARACTERISTICS DURING THE TRANSITION The time evolution of the ISC fluctuations sI~ in the vicinity of the E×B velocity shear layer (r = 11 cm) during the transition is shown in Fig. 3(b) together with the density en (Fig. 3(a)). Also, in Fig. 3(b) shown is in the sI~ (t) background the time behavior of the corresponding r.m.s. value, < sI~ >t , averaged over the 200 µs interval. It is seen that the intensity of plasma density (ISC) fluctuations is appreciably reduced with the transition. Fig. 3 As a result of a more detailed analysis, the process of transition can be divided into three phases. A fragment of the < sI~ >t time evolution in the vicinity of the transition (r = 11 cm) is shown at the top of Fig. 4. The state preceding the transition is denoted as I. The initial phase of the transition consists of two separate phases, A and B, lasting for ~ 1-2 ms, while the third phase, C, persists till the end of RF pulse. Below, in the left column of Fig. 4, shown are the normalized power spectra of the ISC fluctuations in the preceding state and three phases of the Fig. 4 transition. The percentages indicate the power fraction contained in the f > 100 kHz frequency region. The corresponding non-normalized spectra are in the right column, where the numbers indicate the total (i.e., over the entire frequency diapason) power for each phase relative to that in the preceding state (I). It follows from Fig. 4 that a considerable reduction of the total fluctuation power arises at the phase A with a simultaneous reduction of the high-frequency (f > 100 kHz) power fraction. A further reduction of the fluctuation power is observed at the phase B with some redistribution of the total power over the entire frequency region and a rise of power fraction in the high-frequency part of the spectrum. At last, at the phase C, where some deterioration of the confinement occurs, a small rise of both the total power and its high-frequency fraction takes place. The time behavior of the FP fluctuations is qualitatively the same. In Fig. 5 shown are (a) the phase spectrum between FP fluctuations recorded by the probes 3 and 4, and (b) the coherence spectrum between the density and potential fluctuations ( sI~ , probe 2; fV~ , probe 3) at the state I and at the phase C. The values of the poloidal phase velocity of the fluctuations at r = 11 cm are 5.4×105 cm/s before the transition, 8.4×105 cm/s at the phase A and 7×105 cm/s at the phase C. It is impossible to determine the phase velocity at the phase B as there is no linear section in the cross-coherence spectrum. This is possibly caused by a strong de-correlation of the fluctuations at this phase of the transition. Together with (a) the density en , Fig. 6 shows (b) the time evolution of the function )(~ tG = s ~I (t)[ 4 ~ fV (t)- 3 ~ fV (t)] that is proportional to the radial turbulent particle flux, TΓ ~ = θEn ~~ /Bφ, [5]. The 200 µs interval-averaged turbulent flux is presented in white. Below (Fig. 6(c)), a section of the averaged turbulent flux is shown in the vicinity of 22 Fig. 5 Fig. 6 transition (shaded in Fig. 6(b)). It is seen that an appreciable reduction of the flux takes place simultaneously with the reduction of the fluctuation level (cf., Fig. 4). The maximum reduction of the flux is 3.3 at the phase (B) and 2.2 at the phase (C) as compared with the preceding state (I). Like some other tokamaks and stellarators, an intermittency is inherent to the turbulent flux of particles in the U-3M torsatron. This intermittency is displayed as strong short-time separate bursts, whose amplitude can multiply exceed the average flux level [5]. The burst amplitude decreases with transition similar to the average level of the turbulent flux. However, the fraction of flux transported in the bursts does not change substantially before and after the transition. 5. SUMMARY In the U-3M torsatron under RF plasma production and heating conditions, a spontaneous change of the confinement state due to the ITB formation is also accompanied by an ETB formation in the layer of stochastisized field lines. The indications of ETB formation are: • appearance (or rise) of the radial electric field shear near the plasma boundary; • reduction of the level of plasma density and potential fluctuations; • reduction of the high frequency fraction (f >100 kHz) in the power spectra of the fluctuations (at least at the A and B phases); • reduction of the coherence between density and potential fluctuations in the high frequency region; • more than two-fold reduction of the radial turbulent particle flux near the plasma boundary. This work was carried out in collaboration with National Institute for Fusion Science (Japan) within the Program LIME. REFERENCES [1] E.D. Volkov et al.//Proc. 14th Int. Conf. on Plasma Physics and Controlled Nuclear Fusion Research, Wurzburg, 1992 / IAEA, Vienna, 1992, v. 2, p. 679. [2] E.D. Volkov et al.//Problems of Atomic Science and Technology. Series: “Plasma Physics”(9). 2003, N1, p. 3. [3] V.V. Chechkin , et al. Divertor flow and particle loss behaviors in spontaneous change of plasma confinement state in the Uragan-3M torsatron// (to be published in the next issue). [4] K.H. Burrell//Phys. Plasmas (4). 1997, p. 1499 [5] E.L. Sorokovoy et al.// Problems of Atomic Science and Technology. Series: “Plasma Physics”(8). 2002, N 5, p. 6. ХАРАКТЕРИСТИКИ ТУРБУЛЕНТНОСТИ КРАЕВОЙ ПЛАЗМЫ ПРИ СПОНТАННОМ ИЗМЕНЕНИИ РЕЖИМА УДЕРЖАНИЯ В ТОРСАТРОНЕ «УРАГАН-3М» Э.Л. Сороковой, Л.И. Григорьева, В.В. Чечкин, Е.Д. Волков, Е.Л. Сороковой, П.Я. Бурченко, С.А. Цыбенко, А.В. Лозин, А.П. Литвинов, С. Масузаки, К. Ямазаки В торсатроне У-3М при изменении режима удержания плазмы, вызванном образованием внутреннего транспортного барьера, вблизи границы плазмы появляется слой с широм скорости Е×В. Соответствующие изменения характеристик мелко-масштабной турбулентности в окрестности этого слоя и вызванного турбулентностью радиального потока частиц, свидетельствуют об образовании также и краевого транспортного барьера. ХАРАКТЕРИСТИКИ ТУРБУЛЕНТНОСТІ КРАЙОВОЇ ПЛАЗМИ ПРИ СПОНТАННІЙ ЗМІНІ РЕЖИМУ УТРИМАННЯ В ТОРСАТРОНІ «УРАГАН-3М» Е.Л. Сороковий, Л.І. Григор’єва, В.В. Чечкін, Є.Д. Волков, Є.Л. Сороковий, П.Я. Бурченко, С.А. Цибенко, О.В. Лозін, А.П. Литвинов, С. Масузакі, К. Ямазакі 23 В торсатроні У-3М при зміні режиму утримання, викликаній створенням внутрішнього транспортного бар’єра, біля границі плазми виникає шар з шіром швидкості Е×В. Відповідні зміни характеристик дрібномасштабної турбулентності поблизу цього шару та викликаного турбулентністю радіального потоку частинок свідчать про створення також і крайового транспортного бар’єра.