On the issue of shielding properties of plasma in the outside separatrix region of U-3M
When providing experiments on RF plasma production and heating in U-3M torsatron there was observed sudden decrease (up to two times) of mean confined plasma density during step-rise of an RF antenna voltage. Trying to analyze the reason of this effect we estimated a screening effect of the out-sepa...
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| Zitieren: | On the issue of shielding properties of plasma in the outside separatrix region of U-3M / V.G. Konovalov, V.V. Chechkin, L.I. Ggrigor’eva, A.N. Shapoval // Вопросы атомной науки и техники. — 2014. — № 6. — С. 19-21. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-811702015-05-12T03:02:11Z On the issue of shielding properties of plasma in the outside separatrix region of U-3M Konovalov, V.G. Chechkin, V.V. Ggrigor’eva, L.I. Shapoval, A.N. Магнитное удержание When providing experiments on RF plasma production and heating in U-3M torsatron there was observed sudden decrease (up to two times) of mean confined plasma density during step-rise of an RF antenna voltage. Trying to analyze the reason of this effect we estimated a screening effect of the out-separatix plasma, characteristics of which were recently measured. It was found that at the plasma confinement border the attenuation is: 6 % for H2, 1.4, 7, 6 % for C, Fe and Ti atoms correspondingly. This is much below the result of attenuation (~70 %) estimated in [1] for the flux of laser ablated C atoms. При проведении экспериментов на торсатроне У-3M при ВЧ-способе создания и нагрева плазмы наблюдалось неожиданное уменьшение (примерно двукратное) средней плотности удерживаемой плазмы при ступенчатом нарастании напряжения на ВЧ-антенне. Пытаясь установить причину этого явления, мы оценили экранирующую роль засепаратрисной области плазмы по результатам недавно проведенных измерений. Было установлено, что на границе удерживаемой плазмы ослабление потока составляет: 6 % для Н2, 1.4, 7, 6 % для C, Fe, Ti соответственно. Это значительно ниже степени ослабления (~70 %), полученной в работе [1] для потока атомов С при лазерной абляции графитовой мишени. При проведенні експериментів на торсатроні У-3М при ВЧ-способі створення та нагріву плазми спостерігалося несподіване зменшення (приблизно дворазове) середньої густини утримуваної плазми при ступінчастому наростанні напруги на ВЧ-антені. Намагаючись встановити причину цього явища, ми оцінили екрануючу роль засепаратрисної області плазми за результатами недавно проведених вимірювань. Було встановлено, що на межі утримуваної плазми ослаблення потоку становить: 6 % для Н2, 1,4, 7, 6 % для C, Fe, Ti відповідно. Це значно нижче ступеня ослаблення (~ 70 %), отриманого в роботі [1] для потоку атомів С при лазерній абляції графітової мішені. 2014 Article On the issue of shielding properties of plasma in the outside separatrix region of U-3M / V.G. Konovalov, V.V. Chechkin, L.I. Ggrigor’eva, A.N. Shapoval // Вопросы атомной науки и техники. — 2014. — № 6. — С. 19-21. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS: 52.50.Qt; 52.55.Hc 52.40.Hf http://dspace.nbuv.gov.ua/handle/123456789/81170 en Вопросы атомной науки и техники 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 Konovalov, V.G. Chechkin, V.V. Ggrigor’eva, L.I. Shapoval, A.N. On the issue of shielding properties of plasma in the outside separatrix region of U-3M Вопросы атомной науки и техники |
| description |
When providing experiments on RF plasma production and heating in U-3M torsatron there was observed sudden decrease (up to two times) of mean confined plasma density during step-rise of an RF antenna voltage. Trying to analyze the reason of this effect we estimated a screening effect of the out-separatix plasma, characteristics of which were recently measured. It was found that at the plasma confinement border the attenuation is: 6 % for H2, 1.4, 7, 6 % for C, Fe and Ti atoms correspondingly. This is much below the result of attenuation (~70 %) estimated in [1] for the flux of laser ablated C atoms. |
| format |
Article |
| author |
Konovalov, V.G. Chechkin, V.V. Ggrigor’eva, L.I. Shapoval, A.N. |
| author_facet |
Konovalov, V.G. Chechkin, V.V. Ggrigor’eva, L.I. Shapoval, A.N. |
| author_sort |
Konovalov, V.G. |
| title |
On the issue of shielding properties of plasma in the outside separatrix region of U-3M |
| title_short |
On the issue of shielding properties of plasma in the outside separatrix region of U-3M |
| title_full |
On the issue of shielding properties of plasma in the outside separatrix region of U-3M |
| title_fullStr |
On the issue of shielding properties of plasma in the outside separatrix region of U-3M |
| title_full_unstemmed |
On the issue of shielding properties of plasma in the outside separatrix region of U-3M |
| title_sort |
on the issue of shielding properties of plasma in the outside separatrix region of u-3m |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2014 |
| topic_facet |
Магнитное удержание |
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http://dspace.nbuv.gov.ua/handle/123456789/81170 |
| citation_txt |
On the issue of shielding properties of plasma in the outside separatrix region of U-3M / V.G. Konovalov, V.V. Chechkin, L.I. Ggrigor’eva, A.N. Shapoval // Вопросы атомной науки и техники. — 2014. — № 6. — С. 19-21. — Бібліогр.: 5 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT konovalovvg ontheissueofshieldingpropertiesofplasmaintheoutsideseparatrixregionofu3m AT chechkinvv ontheissueofshieldingpropertiesofplasmaintheoutsideseparatrixregionofu3m AT ggrigorevali ontheissueofshieldingpropertiesofplasmaintheoutsideseparatrixregionofu3m AT shapovalan ontheissueofshieldingpropertiesofplasmaintheoutsideseparatrixregionofu3m |
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2025-07-06T05:33:25Z |
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2025-07-06T05:33:25Z |
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1836874495373082624 |
| fulltext |
ISSN 1562-6016. ВАНТ. 2014. №6(94)
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2014, № 6. Series: Plasma Physics (20), p. 19-21. 19
ON THE ISSUE OF SHIELDING PROPERTIES OF PLASMA IN THE
OUTSIDE SEPARATRIX REGION OF U-3M
V.G. Konovalov, V.V. Chechkin, L.I. Ggrigor’eva, A.N. Shapoval
Institute of Plasma Physics National Science Center “Kharkov Institute of Physics and
Technology”, Kharkov, Ukraine
E-mail: konovalov@ipp.kharkov.ua
When providing experiments on RF plasma production and heating in U-3M torsatron there was observed
sudden decrease (up to two times) of mean confined plasma density during step-rise of an RF antenna voltage.
Trying to analyze the reason of this effect we estimated a screening effect of the out-separatix plasma,
characteristics of which were recently measured. It was found that at the plasma confinement border the
attenuation is: 6 % for H2, 1.4, 7, 6 % for C, Fe and Ti atoms correspondingly. This is much below the result of
attenuation (~70 %) estimated in [1] for the flux of laser ablated C atoms.
PACS: 52.50.Qt; 52.55.Hc 52.40.Hf
INTRODUCTION
In the l = 3 Uragan-3M (U-3M) torsatron, the
hydrogen plasma is produced and heated by supplying
RF power in the frequency range ω≤ωci to two
unshielded antennas located close the boundary of
plasma confinement volume: a frame type (FT) antenna
and a three-half-turn (THT) antenna. A very specific
feature of U-3M, distinguishing it from many other
fusion devices, is that the whole magnetic system is
placed inside a large vacuum tank, thus the ratio of
plasma volume to a gas filled volume is ~1/200. Due to
such construction, an open natural helical divertor
configuration is realized with plasma confinement
volume major radius R0 = 1 m and average plasma
radius a ≈ 0.12 m. The inner radius of helical coil
casings is 19 сm, and just these casings play the main
role of the first wall for confined plasma. Working gas
pressure (hydrogen) ≈5·10
-6
Torr.
Fig. 1. Time behavior of mean plasma density
(upper oscillogram) and anode voltage supplied to FT
antenna (lower oscillogram)
In the course of experiments it was found out that any
sudden fast rise of RF power during the discharge by
stepwise-like increase of an anode voltage, e.g., from
~6.5 by ~9 kV, results in a significant drop (factor 1.5-
2.0) of mean plasma density (measured by a microwave
interferometer), instead of ex ante density increase.
Fig. 1 demonstrates the corresponding oscillograms.
One possible explanation of this phenomenon–the
decrease of hydrogen inflow due to increase of its
ionization in a near-separatix plasma. Such a viewpoint
was mentioned long time ago [1], when discussing the
results of pulsed impurity injection by laser ablation of a
graphite target placed at the helical coil casing. As the
reason of protection from injected C atoms the authors
considered the divertor plasma layer, i.e., the region
which includes ergodic and divertor field lines with total
radial dimension ≈5 сm, although at that time there were
no data about plasma characteristics in the space
between casing and plasma confinement volume.
Using the ratio of intensities of lines CV / CII when
increasing the flux of injected atoms and suppose that at
high total flux of carbon atoms (>10
17
) the periphery
plasma temperature decreases resulting in an increase of
a penetrability, the screening ability was estimated as
≈0.7 from the level of injection.
1. ASSESSMENT OF SCREENING
EFFICIENCY
In the present paper we are trying to answer the
question about screening efficiency of the out-separatrix
plasma region for penetration of H2 molecules coming
from the space outside plasma confinement volume
through wide slits between helical coils, and H2
molecules, C, Fe, and Ti atoms coming from helical coil
casings. When considering a one-dimensional model for
penetration of indicated atoms and molecules, the data
on ne and Te spatial distributions in the space between
helical coil casings (19 cm) and the last closed magnetic
surface (10 cm in the cross section where measurements
were done) obtained from electric probe measurements
were used for the estimations. The raw data of probe
measurements of ne outside plasma confinement volume
are shown in Fig. 2 (Note that the value of ne=2·10 cm
-3
near the last closed magnetic surface, r=10 cm, was
very close to what was accepted in [1]).
As for Te(r) distribution, after some simplification of
results of probe measurements, within accuracy ±5 eV it
20 ISSN 1562-6016. ВАНТ. 2014. №6(94)
can be accepted as 30 eV in the interval 19…12 cm,
40 eV at r=11 cm and 55 eV at r=10 cm.
Toroidal magnetic field Bt was 0.72 T as distinct
from experiments in [1] provided within magnetic field
strength 0.46 T.
Fig. 2. Spatial distribution of plasma electron
density outside plasma confinement volume at anode
voltages 6.5 and 9 kV, and during L-H transition at 9 kV
2. ATTENUATION OF H2 FLUX FROM THE
VESSEL VOLUME
The most important processes can be characterized
by the use of data from the paper by Harrison [2]. For
H2 molecule disintegration at the Te range
Te=2…100 eV the following processes have to be taken
into account:
e + H2 → H + H + e - [dissociation]; (1)
e + H2 → H2
+
+ 2e - [ionisation]; (2)
e + H2 → H
+
+ H + 2e - [dissociative ionisation]. (3)
The formula for flux attenuation is:
,
where k1, k2, k3 – are the rate coefficients for processes
1, 2, 3 from [2].
The results of calculation of relative attenuation of
H2 flux are shown in Fig. 3.
Fig. 3. Relative attenuation of H2 molecular flux due to
disintegration under the influence of processes 1, 2, 3
and their sum (1+2+3)
One can see that the relative attenuation for indicated
processes amounts: 1 – 4.9%, 2 – 0.9%, and 3 – 0.25%,
i.e., ~6% in total.
3. ATTENUATION OF PARTICLE
FLUXES FROM HELICAL COIL CASINGS
The plasma-wall interaction will result in generation
of a reverse flow of hydrogen and impurities (C, Fe, Ti)
to the plasma confinement volume. For making any
estimation of penetration of these particles, important is
the knowledge of their velocity when leaving the wall
surface. Let’s compare the data from different sources.
The authors of paper [3] have found, when modeling
behavior of hydrogen neutrals in TFTR aiming to clear
up its behavior in ITER, that the peak of energy
distribution of particles sputtered under bombardment of
walls by fluxes of H, D, T, C with energies 100, 500,
1000, and 3000 eV, correspondingly, falls on 7.2 eV.
In the paper [4] the velocities were found from
measured Doppler contours.
Data from both these papers are presented in the
Table.
The velocities of the incident particles
(in cm / s)
Reference υН2 υC υFe υTi
[3] 2.6·10
6
1·10
6
1·10
6
7.9·10
5
[4] - 7.4·10
5
5·10
5
5·10
5
As follows, there are no big differences of these data.
For impurities we gave preference to data from [4], and
the estimated attenuation of them is: C – 1.4%, Fe – 7%,
Ti – 6% (Fig. 4).
Fig. 4. Relative attenuation of C, Fe, and Ti atom
fluxes on the way from casing to plasma boundary
If one supposes that C atoms have the velocity
corresponding to room temperature, (e.g., from CH4),
the attenuation factor at the edge of plasma confinement
volume will be ≈14 %.
ISSN 1562-6016. ВАНТ. 2014. №6(94) 21
CONCLUSIONS
From the above presented data the following
conclusive remarks can be drawn out:
1. In investigated U-3M RF discharges the
characteristics of out-separatrix plasma cannot provide
any significant attenuation of hydrogen or impurity
atom fluxes on the way to plasma confinement volume.
2. Therefore, the drop of plasma density during
stepwise RF power increase cannot be explained by
existence of dense plasma in the out-separatrix volume.
3. Significant attenuation could take place only with
plasma density near the last magnetic surface at the
level ≥1·10
12
сm
-3
, if distributions of out-separatix
plasma characteristics will be similar to described above.
4. The possible reason for observed drop of a mean
plasma density can be the recently disclosed effect of
strong decrease of hydrogen pressure in the U-3M tank
during RF pulse [5].
REFERENCES
1. V.L. Berezhniy, V.S. Voitsenya, Ja.Fh. Volkov, et al.
Experiments on laser injection of impurity atoms on
torsatron Uragan -3: Preprint KhPTI 89-48, 1989.
2. Physics of plasma-wall interactions in controlled
fusion / Edited by D.E. Post and R. Behrisch. Plenum
Publishing Corporation, 1986, p. 301.
3. D.P. Stotler, C.H. Skinner, R.V. Budny, A.T. Ramsey,
D.N. Ruzic, and R.B. Turkot // Phys. Plasmas. 1996,
p. 4084-4094.
4. E.D. Volkov, V.M. Zalkind, V.G. Konovalov, et al.
The behavior of light and heavy impurities in HF-
plasma heating in torsatron Uragan-3: Preprint KhPTI
89-11, 1989.
5. V.K. Pashnev, A.A. Petrushenya, E.L. Soro-
kovoy. Hydrogen recycling during the RF-plasma
heating in torsatron U-3M // Book of Abstracts ICPPCF,
Kharkiv, Ukraine, 2014, p. 29.
Article received 20.09.2014
К ВОПРОСУ ОБ ЭКРАНИРУЮЩИХ СВОЙСТВАХ ЗАСЕПАРАТРИСНОЙ ОБЛАСТИ ПЛАЗМЫ
В УСТАНОВКЕ У-3М
В.Г. Коновалов, В.В. Чечкин, Л.И. Григорьева, А.Н. Шаповал
При проведении экспериментов на торсатроне У-3M при ВЧ-способе создания и нагрева плазмы
наблюдалось неожиданное уменьшение (примерно двукратное) средней плотности удерживаемой плазмы при
ступенчатом нарастании напряжения на ВЧ-антенне. Пытаясь установить причину этого явления, мы оценили
экранирующую роль засепаратрисной области плазмы по результатам недавно проведенных измерений. Было
установлено, что на границе удерживаемой плазмы ослабление потока составляет: 6 % для Н2, 1.4, 7, 6 % для C,
Fe, Ti соответственно. Это значительно ниже степени ослабления (~70 %), полученной в работе [1] для потока
атомов С при лазерной абляции графитовой мишени.
ДО ПИТАННЯ ПРО ЕКРАНУЮЧІ ВЛАСТИВОСТІ ЗАСЕПАРАТРИСНОЇ ОБЛАСТІ ПЛАЗМИ
В УСТАНОВЦІ У-3М
В.Г. Коновалов, В.В. Чечкін, Л.І. Григор'єва, А.М. Шаповал
При проведенні експериментів на торсатроні У-3М при ВЧ-способі створення та нагріву плазми
спостерігалося несподіване зменшення (приблизно дворазове) середньої густини утримуваної плазми при
ступінчастому наростанні напруги на ВЧ-антені. Намагаючись встановити причину цього явища, ми оцінили
екрануючу роль засепаратрисної області плазми за результатами недавно проведених вимірювань. Було
встановлено, що на межі утримуваної плазми ослаблення потоку становить: 6 % для Н2, 1,4, 7, 6 % для C, Fe, Ti
відповідно. Це значно нижче ступеня ослаблення (~ 70 %), отриманого в роботі [1] для потоку атомів С при
лазерній абляції графітової мішені.
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