Continuous wall conditioning VHF discharge without magnetic field in a toroidal device
Experiments were carried out at Uragan-2M torsaron for wall conditioning without magnetic field. Plasma discharge was created with the same antenna and VHF generator used for weak magnetic field (B0=100 G) wall conditioning. Experiment was carried out during whole wall conditioning period of Uraga...
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| Zitieren: | Continuous wall conditioning VHF discharge without magnetic field in a toroidal device / A.V. Lozin, V.E. Moiseenko, M.M. Kozulya, E.D. Kramskoj, V.B. Korovin, A.V. Yevsyukov, L.I. Grigor’eva, A.A. Beletskii, A.N. Shapoval, M.M. Makhov, A.Yu. Krasyuk, D.I. Baron and Uragan-2M Team // Вопросы атомной науки и техники. — 2016. — № 6. — С. 60-63. — Бібліогр.: 4 назв. — англ. |
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irk-123456789-1153182017-04-03T03:02:15Z Continuous wall conditioning VHF discharge without magnetic field in a toroidal device Lozin, A.V. Moiseenko, M.M. Kozulya, M.M. Kramskoj, E.D. Korovin, V.B. Yevsyukov, A.V. Grigor’eva, L.I. Beletskii, A.A. Shapoval, A.N. Makhov, M.M. Krasyuk, A.Yu. Baron, D.I. Plasma heating and current drive Experiments were carried out at Uragan-2M torsaron for wall conditioning without magnetic field. Plasma discharge was created with the same antenna and VHF generator used for weak magnetic field (B0=100 G) wall conditioning. Experiment was carried out during whole wall conditioning period of Uragan-2M experimental campaign. The dynamics of wall conditioning was obtained alongside with standard plasma parameters measurements. На торсатроне Ураган-2М был выполнен модельный эксперимент по чистке стенок вакуумной камеры без магнитного поля. Плазменный разряд создавался той же антенной и СВЧ-генератором, которые использовались для чистки в слабом магнитном поле (B0=100 Гс). Эксперимент проводился на протяжении всего периода чистки во время экспериментальной кампании Урагана-2М. Динамика чистки стенок была получена вместе со стандартными измеряемыми параметрами плазмы. На торсатроні Ураган-2М було проведено модельний експеримент із чистки стінок вакуумної камери без магнітного поля. Плазмовий розряд створювався тією самою антеною та НВЧ-генератором, що використовуються для чистки в слабкому магнітному полі (B0=100 Гс). Експеримент проводився впродовж всього періоду чистки пiд час експериментальної кампанії Урагана-2М. Динаміка чистки стінок була отримана разом із стандартними вимірюваними параметрами плазми. 2016 Article Continuous wall conditioning VHF discharge without magnetic field in a toroidal device / A.V. Lozin, V.E. Moiseenko, M.M. Kozulya, E.D. Kramskoj, V.B. Korovin, A.V. Yevsyukov, L.I. Grigor’eva, A.A. Beletskii, A.N. Shapoval, M.M. Makhov, A.Yu. Krasyuk, D.I. Baron and Uragan-2M Team // Вопросы атомной науки и техники. — 2016. — № 6. — С. 60-63. — Бібліогр.: 4 назв. — англ. 1562-6016 PACS: 52.50.Qt http://dspace.nbuv.gov.ua/handle/123456789/115318 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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| language |
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Plasma heating and current drive Plasma heating and current drive |
| spellingShingle |
Plasma heating and current drive Plasma heating and current drive Lozin, A.V. Moiseenko, M.M. Kozulya, M.M. Kramskoj, E.D. Korovin, V.B. Yevsyukov, A.V. Grigor’eva, L.I. Beletskii, A.A. Shapoval, A.N. Makhov, M.M. Krasyuk, A.Yu. Baron, D.I. Continuous wall conditioning VHF discharge without magnetic field in a toroidal device Вопросы атомной науки и техники |
| description |
Experiments were carried out at Uragan-2M torsaron for wall conditioning without magnetic field. Plasma
discharge was created with the same antenna and VHF generator used for weak magnetic field (B0=100 G) wall
conditioning. Experiment was carried out during whole wall conditioning period of Uragan-2M experimental
campaign. The dynamics of wall conditioning was obtained alongside with standard plasma parameters
measurements. |
| format |
Article |
| author |
Lozin, A.V. Moiseenko, M.M. Kozulya, M.M. Kramskoj, E.D. Korovin, V.B. Yevsyukov, A.V. Grigor’eva, L.I. Beletskii, A.A. Shapoval, A.N. Makhov, M.M. Krasyuk, A.Yu. Baron, D.I. |
| author_facet |
Lozin, A.V. Moiseenko, M.M. Kozulya, M.M. Kramskoj, E.D. Korovin, V.B. Yevsyukov, A.V. Grigor’eva, L.I. Beletskii, A.A. Shapoval, A.N. Makhov, M.M. Krasyuk, A.Yu. Baron, D.I. |
| author_sort |
Lozin, A.V. |
| title |
Continuous wall conditioning VHF discharge without magnetic field in a toroidal device |
| title_short |
Continuous wall conditioning VHF discharge without magnetic field in a toroidal device |
| title_full |
Continuous wall conditioning VHF discharge without magnetic field in a toroidal device |
| title_fullStr |
Continuous wall conditioning VHF discharge without magnetic field in a toroidal device |
| title_full_unstemmed |
Continuous wall conditioning VHF discharge without magnetic field in a toroidal device |
| title_sort |
continuous wall conditioning vhf discharge without magnetic field in a toroidal device |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2016 |
| topic_facet |
Plasma heating and current drive |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/115318 |
| citation_txt |
Continuous wall conditioning VHF discharge without magnetic field in a toroidal device / A.V. Lozin, V.E. Moiseenko, M.M. Kozulya, E.D. Kramskoj, V.B. Korovin, A.V. Yevsyukov,
L.I. Grigor’eva, A.A. Beletskii, A.N. Shapoval, M.M. Makhov, A.Yu. Krasyuk, D.I. Baron
and Uragan-2M Team // Вопросы атомной науки и техники. — 2016. — № 6. — С. 60-63. — Бібліогр.: 4 назв. — англ. |
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Вопросы атомной науки и техники |
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2025-07-08T08:35:04Z |
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| fulltext |
ISSN 1562-6016. ВАНТ. 2016. №6(106)
60 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2016, № 6. Series: Plasma Physics (22), p. 60-63.
CONTINUOUS WALL CONDITIONING VHF DISCHARGE
WITHOUT MAGNETIC FIELD IN A TOROIDAL DEVICE
A.V. Lozin, V.E. Moiseenko, M.M. Kozulya, E.D. Kramskoj, V.B. Korovin, A.V. Yevsyukov,
L.I. Grigor’eva, A.A. Beletskii, A.N. Shapoval, M.M. Makhov, A.Yu. Krasyuk, D.I. Baron
and Uragan-2M Team
Institute Institute of Plasma Physics of the NSC KIPT, Kharkov, Ukraine
E-mail: alexlozin@meta.ua
Experiments were carried out at Uragan-2M torsaron for wall conditioning without magnetic field. Plasma
discharge was created with the same antenna and VHF generator used for weak magnetic field (B0=100 G) wall
conditioning. Experiment was carried out during whole wall conditioning period of Uragan-2M experimental
campaign. The dynamics of wall conditioning was obtained alongside with standard plasma parameters
measurements.
PACS: 52.50.Qt
INTRODUCTION
The radio-frequency (RF) discharges are used for
conditioning of inner walls of vacuum chambers of
fusion devices. In the series of experiments on Uragan-
2M the Very High Frequency (VHF) discharge [0] is
investigated which needs a steady magnetic field. RF
wall conditioning without the magnetic field seems is
also useful for fusion devices in certain specific cases.
It’s complicated to switch on and off cryogenic
magnetic systems of fusion reactors. For this reason
there is a need to have wall conditioning technologies
both with and without magnetic field.
In the presence of confining magnetic field, the slow
wave which the antenna excites is substantially slowed
down in plasma that facilitates its damping. Plasma
without magnetic field slows down the electromagnetic
waves. To achieve acceptable damping of the wave,
high electron-neural collision frequency is needed.
Thus, the RF discharge may be sustained at relatively
high neutral gas pressure.
The wall conditioning is achieved due to interaction
of atomic hydrogen generated in the discharge with the
impurities accumulated at the wall surface. The
generation rate of hydrogen is proportional to the
product of neutral gas pressure and plasma density.
Thus, to keep the same rate of atomic hydrogen
generation, at higher neutral gas pressure, the plasma
density should be lower. This is a positive factor since
the probability of ionization of impurities desorbed from
the wall is lower in low density plasma.
The wall conditioning without magnetic field was
used during the 2016 experimental campaign at
Uragan- 2M. The same equipment is used as in
experiments with steady magnetic field (B0=100 G).
VHF discharge parameters were measured by means
of optical diagnostics and a Langmuir probe. The
efficiency of wall conditioning was estimated using the
cryogenic vacuum trap.
EXPERIMENTAL SETUP
The VHF wall conditioning was carried out with
continuous RF discharge at the frequency of 130 MHz
and the power about 3 kW. The RF power is launched
into plasma with the small frame antenna (Fig. 1). The
small frame antenna is made of stainless steel pipe 1 cm
in diameter and is of square shape with side length of
10 cm. Water is pumped through the pipe for antenna
cooling. To operate in steady magnetic field, the
antenna is placed 2 cm from the last closed magnetic
surface.
Fig. 1. Water cooled small frame antenna inside
torsatron Uragan-2M device during continuous wall
conditioning (top). The same antenna before mounting
into device (bottom)
When RF power is launched, plasma exists locally
only in vicinity of the small frame antenna. The size of
such plasma cloud increases with the input RF power,
but its luminosity decreases in an order of magnitude at
the distance of 1 m from the antenna (along the torus).
ISSN 1562-6016. ВАНТ. 2016. №6(106) 61
The only scenario fail was the discharge localization
inside of the ceramic insulator as at Fig. 1. That caused
sputtering of the antenna metallic parts and thin metal
film deposition at the inner surfaces of the insulator.
The deposition was prevented in further experiments
with quartz tube placed onto antenna feed-through; it
isolated antenna from the metal vacuum chamber wall
and prevented plasma discharge appearance inside of
the insulator.
OPTICAL MEASUREMENTS
During wall conditioning experiment at torsatron
Uragan-2M, hydrogen, nitrogen and hydrogen-nitrogen
mixture were used as working gases. The spectrum of
the optical emission for each plasma discharge was
measured and the results are presented in Figs. 2-4.
The Langmuir probe measurements of plasma
density and electron temperature were made in the
horizontal plane of the small frame antenna cross-
section.
The electron temperature estimated from optical
measurements with the H2 Fulcher-α band system and
Hα intensities is about 2...3 eV, which are in
correspondence with the Langmuir probe results given
further.
Fig. 2. Plasma discharge spectra for different working
gases
Fig. 3. Hydrogen plasma discharge emission spectrum.
Fig. 4. N2 and H2 mixture plasma discharge spectrum
with volume gas ratio (50/50)%
The most optimal discharge in hydrogen and
nitrogen mixture is for gas volume ratio (50/50)%. The
presence of N2
+
ion line with the wavelength 427.8 nm
showed only ionization of nitrogen molecules
(see Fig. 4) and the hydrogen spectrum indicated
hydrogen dissociation processes.
PROBE MEASUREMENTS
The probe measurements needed pulsed operation,
and the pulses were made manually by switching on/off
the VHF generator. The Langmuir probe was placed in
the same cross-section as the small frame antenna at
horizontal midplane at outer part of the torus and could
move along radius. The ion branch of the current-
voltage characteristic (I-V) was recalculated with the
formula (1) to determine the average (equilibrium) local
plasma parameters (the electron density, the electron
temperature and the floating potential):
( ) 1 exp
f
s
e
V V
I V I
T
, (1)
where V is the probe biasing voltage. The ion saturation
current can be expressed as
0,5 2 /s pr e e iI S en T m , (2)
in assumption that
i
e
ie
m
m
TT . Here Spr is the area of
the collecting probe surface, mi is the plasma ion mass.
The Langmuir probe biasing potential was changed
from -150 to +100 V to take I-V characteristics. Every
probe potential was fixed for 2-3 plasma discharges to
get average measured quantity.
It is possible to estimate the plasma density through
substitution of different ion masses in the expression
(2): mi was assumed equal 1 amu (Н
+
), 2 amu (Н2
+
),
14 amu (N
+
), or 28 amu (N2
+
)
Measurement results are represented as a table:
Langmuir probe measurements
Parameters
mixture of gases
H2 H2(50%)
+N2(50%)
H2(<10%)+
N2(~90%)
Distance of the
probe from the
chamber wall, mm
87.5 87.5 87.5
Vfl, V 50 37 64.5
Te, eV
2.7 4.1 1.8
ne (cm
-3
) by H2
+
,
mi=2 a.m.u.
5.1∙10
9
1.8∙10
9
8.6∙10
8
ne (cm
-3
) by N
+
if
mi=14 a.m.u.
− 4.8∙10
9
2.3∙10
9
ne (cm
-3
) by N2
+
if
mi=28 a.m.u.
− 6.8∙10
9
3.2∙10
9
Radial distributions parameters weren't determined,
because 150...200 plasma discharges were necessary to
obtain only a single I-V characteristic. All
measurements were made in the probe position where
the Langmuir probe floating potential was the highest.
The optimal for RF wall conditioning working gas
content was the hydrogen-nitrogen mixture with
50/50 % volume ratio, as it provided the highest plasma
density. Electron temperature 2...4 eV and of plasma
density ~4∙10
9
cm
-3
were achieved as the most suitable
for chosen wall conditioning scenario.
CRYOGENIC TRAP OPERATION
The method of vacuum chamber wall conditioning
control described in [0] was used to estimate the
conditioning efficiency. This method of conditioning
effectiveness estimation and its experimental
application is described in detail in Refs. [0,0]
According to this method, the gas pumped from the
vacuum chamber was condensed on the liquid nitrogen
trap (Fig. 5) inner surface during the RF wall
conditioning. Afterwards, the trap was cut off from the
vacuum chamber by two vacuum valves and defrosted.
The closed volume around the trap was filled with the
gas evaporated from the trap surface.
62 ISSN 1562-6016. ВАНТ. 2016. №6(106)
Fig. 5. Scheme of the liquid nitrogen trap
The liquid nitrogen trap volume together with the
outlet branch is about 52 l, the liquid nitrogen trap
volume is 32.5 l, the cooler (nitrogen) volume is 2.7 l
and inner surface area of the trap is about 0.105 m
2
. The
pressure increases in the cut off volume as the
temperature rises and the condensate evaporates from
the trap surface.
Fig. 6. Pressure in trap volume after 5-minute
exposition. Bar 1 is for gas mixture is 50 % hydrogen +
50 % nitrogen, Pchamber=3·10
-2
Torr. Bar 2 is for
background level during nitrogen pumping,
Pchamber=2.5·10
-2
Torr. Bar 3 is for background level
during hydrogen pumping, Pchamber=3·10
-2
Torr
The increment of gas pressure Pg in the closed trap
volume is proportional to the gas amount pumped from
the vacuum chamber and condensed at the liquid
nitrogen trap. The background level of the vacuum
chamber out-gassing was determined first, and the
amount of condensed gas was measured when there was
no wall conditioning and the vacuum chamber was
filled with the working gas.
Fig. 6 presents results of Pg measurements without
the RF discharge. The exposition time was 5 minutes.
The hydrogen pumping background level is higher than
the nitrogen one.
Fig. 7 presents Pg values during the RF wall
conditioning, bar 1 corresponds to the wall conditioning
at the beginning of the experimental campaign and bar 2
– after 45 hours of wall conditioning. It's seen that the
initial Pg value is greater by an order of magnitude. This
means that amount of desorbed impurities pumped from
the vacuum chamber decreased 10 times during the wall
conditioning.
Fig. 7. Pg measurements during RF wall conditioning at
the beginning of experimental campaign (1) and after
45 hours of RF wall conditioning (2)
Fig. 8 shows that gas mixtures provide 4 times more
intensive volatile substances production than a pure
hydrogen discharge.
Fig. 8. Pg values comparison for wall conditioning in
hydrogen and in 50% mixture of hydrogen and nitrogen.
Exposure time was 5 minutes. Bar 1 is for RF wall
conditioning in hydrogen, bars 2, 3 are for gas mixtures
RF conditioning: 2 – (50/50)%; 3 – (10/90)% (H2/N2)
Fig. 9 displays time evolution of the residual
pressure, Pres, in vacuum chamber during the wall
conditioning. Pres reached the minimal value
6.2·10
-2
Torr in 25 first hours of the conditioning regime
without magnetic field. Presidual was not changed until the
end of the campaign.
Fig. 9. Residual gas pressure evolution
ISSN 1562-6016. ВАНТ. 2016. №6(106) 63
CONCLUSIONS
The radio-frequency wall conditioning without
magnetic field was performed in continuous regime at
the VHF frequency 130 MHz and launched power
~3 kW. The discharge existed in high gas pressure
0.1...0.01 Torr, was located near the antenna, and did
not spread around the torus. Its parameters were
measured using the Langmuir probe and optical
diagnostics. The effect of wall conditioning was judged
by the amount of substances accumulated at the
cryogenic vacuum trap. This amount appeared by the
order of magnitude higher than without the discharge
what indicates apparently the wall conditioning.
Hydrogen, nitrogen and their mixtures had been tried as
working gases. The wall conditioning in the mixture
(50/50)% was selected as the best.
ACKNOWLEDGEMENTS
The work is supported in part by the grant П-3-22 of
National Academy of Sciences of Ukraine.
REFERENCES
1. V.E. Moiseenko et al. VHF discharges for wall
conditioning at the Uragan-2M torsatron // Nuclear
Fusion (33). 2014, p. 033009.
2. Ukrainian patent № 106462. Vacuum chamber
conditioning control method during evacuation /
V. Korovin et al.
3. D.I. Baron et al. Measurements of wall conditionaing
rate at Uragan-2M // Problems of Atomic Science and
Technology. 2013, № 1(83), p. 21-23.
4. V. Korovin et al. RF wall conditioning at the Uragan-
2M with use of high vacuum cryogenic trap // Problems
of Atomic Science and Technology. 2015, № 1(95),
p. 53-55.
Article received 28.09.2016
НЕПРЕРЫВНЫЙ ЧИСТЯЩИЙ СВЧ-РАЗРЯД БЕЗ МАГНИТНОГО ПОЛЯ
В ТОРОИДАЛЬНОЙ КАМЕРЕ
А.В. Лозин, В.Е. Моисеенко, М.М. Козуля, Е.Д. Крамской, В.Б. Коровин, А.В. Евсюков,
Л.И. Григорьева, А.А. Белетский, А.Н. Шаповал, М.М. Махов, А.Ю. Красюк, Д.И. Барон
и команда торсатрона Ураган-2М
На торсатроне Ураган-2М был выполнен модельный эксперимент по чистке стенок вакуумной камеры
без магнитного поля. Плазменный разряд создавался той же антенной и СВЧ-генератором, которые
использовались для чистки в слабом магнитном поле (B0=100 Гс). Эксперимент проводился на протяжении
всего периода чистки во время экспериментальной кампании Урагана-2М. Динамика чистки стенок была
получена вместе со стандартными измеряемыми параметрами плазмы.
БЕЗПЕРЕРВНИЙ ОЧИЩУЮЧИЙ НВЧ-РОЗРЯД БЕЗ МАГНІТНОГО ПОЛЯ
В ТОРОЇДАЛЬНІЙ КАМЕРІ
А.В. Лозін, В.Є. Моісеєнко, М.М. Козуля, Є.Д. Крамской, В.Б. Коровін, А.В. Євсюков,
Л.І. Григор’єва, А.А. Білетський, А.M. Шаповал, М.М. Махов, А.Ю. Красюк, Д.I. Барон
і команда торсатрону Ураган-2М
На торсатроні Ураган-2М було проведено модельний експеримент із чистки стінок вакуумної камери без
магнітного поля. Плазмовий розряд створювався тією самою антеною та НВЧ-генератором, що
використовуються для чистки в слабкому магнітному полі (B0=100 Гс). Експеримент проводився впродовж
всього періоду чистки пiд час експериментальної кампанії Урагана-2М. Динаміка чистки стінок була
отримана разом із стандартними вимірюваними параметрами плазми.
|