Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets
A compact helicon source with multi-component changeable magnetic system was studied to gain enhanced parameters of plasma and emergent ion beam. Alteration of the magnetic field configuration was found to be the main instrument for increasing the plasma density and ion beam current. The source effi...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2007
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| Назва видання: | Вопросы атомной науки и техники |
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| Цитувати: | Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets / Yu.V. Virko, V.F. Virko, K.P. Shamrai, A.I. Yakimenko // Вопросы атомной науки и техники. — 2007. — № 1. — С. 136-138. — Бібліогр.: 7 назв. — англ. |
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irk-123456789-1105122017-01-05T03:04:11Z Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets Virko, Yu.V. Virko, V.F. Shamrai, K.P. Yakimenko, A.I. Low temperature plasma and plasma technologies A compact helicon source with multi-component changeable magnetic system was studied to gain enhanced parameters of plasma and emergent ion beam. Alteration of the magnetic field configuration was found to be the main instrument for increasing the plasma density and ion beam current. The source efficiency was also critically dependent on the rf antenna position and Ar gas pressure. By optimizing these parameters, plasma outflow was greatly increased and the emergent ion beam of energy above 100 eV was produced. Досліджено компактне геліконне джерело з багатокомпонентною змінюваною магнітною системою з метою одержання поліпшених параметрів плазми та вихідного іонного пучка. Зміна магнітної конфігурації виявилась основним засобом для підвищення густини плазми та струму іонного пучка. Ефективність джерела також критично залежала від розташування ВЧ- антени та тиску аргона. Шляхом оптимізації цих параметрів був істотно підвищено вихід плазми та одержано вихідний пучок іонів з енергіями понад 100 еВ. Исследован компактный геликонный источник с многокомпонентной изменяемой магнитной ситемой с целью получения улучшенных параметров плазмы и выходящего ионного пучка. Изменение магнитной конфигурации оказалось основным средством для повышения плотности плазмы и тока ионного пучка. Эффективность источника также критически зависела от положения ВЧ- антенны и давления аргона. Путем оптимизации этих параметров был существенно повышен выход плазмы и получен выходящий пучок ионов с энергиями свыше 100 эВ. 2007 Article Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets / Yu.V. Virko, V.F. Virko, K.P. Shamrai, A.I. Yakimenko // Вопросы атомной науки и техники. — 2007. — № 1. — С. 136-138. — Бібліогр.: 7 назв. — англ. 1562-6016 PACS: 52.50.Qt, 52.75.Di, 52.80.Pi http://dspace.nbuv.gov.ua/handle/123456789/110512 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Low temperature plasma and plasma technologies Low temperature plasma and plasma technologies |
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Low temperature plasma and plasma technologies Low temperature plasma and plasma technologies Virko, Yu.V. Virko, V.F. Shamrai, K.P. Yakimenko, A.I. Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets Вопросы атомной науки и техники |
| description |
A compact helicon source with multi-component changeable magnetic system was studied to gain enhanced parameters of plasma and emergent ion beam. Alteration of the magnetic field configuration was found to be the main instrument for increasing the plasma density and ion beam current. The source efficiency was also critically dependent on the rf antenna position and Ar gas pressure. By optimizing these parameters, plasma outflow was greatly increased and the emergent ion beam of energy above 100 eV was produced. |
| format |
Article |
| author |
Virko, Yu.V. Virko, V.F. Shamrai, K.P. Yakimenko, A.I. |
| author_facet |
Virko, Yu.V. Virko, V.F. Shamrai, K.P. Yakimenko, A.I. |
| author_sort |
Virko, Yu.V. |
| title |
Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets |
| title_short |
Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets |
| title_full |
Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets |
| title_fullStr |
Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets |
| title_full_unstemmed |
Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets |
| title_sort |
characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2007 |
| topic_facet |
Low temperature plasma and plasma technologies |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/110512 |
| citation_txt |
Characterization of plasma and emergent ion beam in a compact helicon source with permanent magnets / Yu.V. Virko, V.F. Virko, K.P. Shamrai, A.I. Yakimenko // Вопросы атомной науки и техники. — 2007. — № 1. — С. 136-138. — Бібліогр.: 7 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-08T00:41:33Z |
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2025-07-08T00:41:33Z |
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| fulltext |
LOW TEMPERATURE PLASMA AND PLASMA TECHNOLOGIES
136 Problems of Atomic Science and Technology. 2007, 1. Series: Plasma Physics (13), p. 136-138
CHARACTERIZATION OF PLASMA AND EMERGENT ION BEAM
IN A COMPACT HELICON SOURCE WITH PERMANENT MAGNETS
Yu.V. Virko, V.F. Virko, K.P. Shamrai, A.I. Yakimenko
Institute for Nuclear Research, National Academy of Sciences,
Prospect Nauki 47, 03680 Kiev, Ukraine; e-mail: virko@mail.ru
A compact helicon source with multi-component changeable magnetic system was studied to gain enhanced
parameters of plasma and emergent ion beam. Alteration of the magnetic field configuration was found to be the main
instrument for increasing the plasma density and ion beam current. The source efficiency was also critically dependent
on the rf antenna position and Ar gas pressure. By optimizing these parameters, plasma outflow was greatly increased
and the emergent ion beam of energy above 100 eV was produced.
PACS: 52.50.Qt, 52.75.Di, 52.80.Pi
1. INTRODUCTION
The helicon source is one of the most efficient types
of inductively coupled plasmas. This electrodeless
discharge is intensively investigated for different
applications including electric propulsion with low [1-3]
and high [4] thrust, ion beam probing [5], etc. Helicon
sources normally operate with electromagnets, which
produce uniform or moderately nonuniform magnetic
fields, but the use of permanent magnets is preferable for
many applications. The magnetic field produced by
permanent magnets is strongly nonuniform. However, just
in the nonuniform field the discharge efficiency can be
significantly enhanced by positioning the antenna in the
region of converging magnetic field [6]. Magnetic field
nonuniformity can also result in formation of the current-
free double layer accelerating emergent ions [7].
We report on experimental results from the compact
source equipped with a two-component, changeable
magnetic system. The main idea was to enhance plasma
and ion beam characteristics by optimizing the source
performance, primarily, the magnetic configuration.
2. EXPERIMENTAL DEVICE
AND DIAGNOSTICS
The experimental device consists of two quartz
chambers. The discharge chamber of 4.5 cm inner
diameter and 32 cm length was attached to a
14.5 cm diameter drift chamber (Fig. 1). The plasma was
excited by a tree-turn (m = 0) axially movable antenna
powered from an rf generator of frequency 13.56 MHz
and power up to 1 kW. Various magnetic configurations
were produced by combining the fields of two
components of the magnetic system: the
13.5 cm outer diameter, 1.8 cm wide annular ferrite (AF)
magnetized axially; and the 12 cm long, 12 cm
inner diameter cylindrical array of ferrite bars (CFA) with
radial magnetization (Fig. 2). To investigate the effect of
the CFA field on discharge performance, we used also
more complicated, three-layered CFA that enabled to
change the magnetic field strength. Sometimes, an
electromagnetic coil (EM) was also used. All components
of the magnetic system were movable along the axis.
Axial length of the discharge chamber could be changed
with use of an axially movable quartz plate (QP). Both the
discharge and drift chambers were filled with Ar gas at
pressure varying in the range 0.5-5 mTorr. In some
experiments, a ceramic diaphragm was installed on the
outlet flange, in order to limit the source orifice and to
create a pressure drop.
Plasma parameters and the rf field characteristics were
measured by axially movable Langmuir, magnetic, and
emissive probes. The emergent ion beam was examined
with a five-grid retarding field energy analyzers (RFEA).
It was positioned in the drift chamber, 7 cm from the
outlet and could rotate over the angle of 90°, to face either
to the source outlet or to the drift chamber wall.
3. CHARACTERIZATION OF PLASMA
AND THE EMERGENT ION BEAM
We examined various magnetic configurations created
with use of the single AF, the single CFA, and a
combination of the AF with the CFA (Figs. 3 and 4).
3.1. CONFIGURATION WITH THE SINGLE AF
Axial profile of the magnetic field of the single AF
has two null points (cusps). It was found that both cusps
result in reduction of the efficiency of plasma production
and ejection. The left cusp (between the AF and the drift
chamber) prevents plasma penetration from the discharge
chamber into the drift chamber (Fig. 5).
Fig. 1. A scheme of the compact helicon plasma source
Fig. 2.The single-layer CFA (left) and the AF (right), with
magnetization directions shown by the arrows
mailto:virko@mail.ru
137
Fig. 3. Magnetic field profiles for various configuration
Fig. 4. The shapes of magnetic field lines
Maximum plasma density was found under the antenna,
it is 2×1012 cm−3 at high pressures pAr = 3-5 mTorr, and
twice smaller at lower pressure of 0.7 mTorr. Electron
temperature was 6-8 eV and 14-18 eV, whereas plasma
potential in the drift chamber 30 and 60 V, for Ar pressures
of 5 and 0.7 mTorr, respectively. Characteristics of the
RFEA facing either to the source outlet or in perpendicular
direction are similar, which implies weak plasma ejection
and the lack of accelerated ions.
3.2. CONFIGURATION WITH THE AF AND THE CFA
Adding the magnetic field of the CFA to that of the
AF eliminates the cusp between the area of maximum
magnetic field and the antenna (Fig. 3), and the magnetic
field in the discharge chamber becomes growing from the
antenna towards the outlet, which is favorable for
enhanced plasma production [7]. Indeed, plasma density
becomes higher, especially near the outlet (Fig. 5), owing
Fig. 5. Profiles of ion saturation current onto the probe
to more efficient rf power injection into the region of
strong magnetic field. The electron temperature is 9 and
15 eV, at Ar pressures of 5 and 0.7 mTorr, respectively.
The RFEA characteristics show that ion flow intensity
becomes higher by several times, as compared with the
previous configuration. Plasma potential in the discharge
chamber grows with decreasing Ar pressure, up to 120 V
at 0.37 mTorr (top Fig. 6). The plasma potential has
maximum near the entry to the AF, decreases towards the
source outlet, and makes 30–70 V in the drift chamber,
depending on pressure. The maximum energy of
accelerated ions, relative to the grounded RFEA , is equal
approximately to the maximum value of the potential in
the discharge chamber (top Fig. 7).
3.3. CONFIGURATION WITH THE SINGLE CFA
In this configuration, plasma flux is much more
intense, as long as magnetic lines are diverging gradually
into the drift chamber. The source efficiency depends
critically on the antenna position, whose optimum was
found at the left of the cusp, i.e., in the region of
converging magnetic lines (Fig. 8).
The axial distribution of the potential is, in general,
similar to that in the case with the AF and CFA; it also
grows with decreasing pressure and amounts to 110 V
inside the discharge chamber, at a pressure of 0.42 mTorr
(bottom Fig. 6). However, for reason yet unclear, the ions
with such the high energies (∼100 V) do not come to the
grounded RFEA (bottom Fig. 7).
Fig. 6. Axial distribution of the plasma potential, for the
AF+CFA (top) and the single CFA (bottom)
Fig. 7. Ion distribution functions for AF+CFA (top) and
the RFEA characteristics for the single CFA (bottom)
138
Fig. 8. Axial profiles of the ion saturation current onto the
probe, at various antenna positions marked by the arrows
4. DISCUSSION AND CONCLUSIONS
The magnetic configuration governs both the plasma
generation and the ion ejection. In optimal configurations,
the plasma density is considerably enhanced and the
emergent beam of accelerated ions arises. Configuration
with the single CFA enables to produce quite intense but
not accelerated ion flux; it is promising for materials
processing applications. In configurations with the AF,
elimination of magnetic field cusps is critical for
enhancement of plasma ejection. Removing the cusp
between the antenna and the AF, by adding the CFA field,
localizes the discharge in the region of strong field
adjoining to the source outlet, and the maximum plasma
density grows up to 5×1012 cm−3, at Ar pressures
3-5 mTorr and rf input power of 600 W. Directional
discharge burning along converging magnetic lines, i.e.,
towards the source outlet, which occurs with use of the
CFA or the CFA+AF, enables to shorten twice the
discharge chamber length without change in the discharge
modes: plasma density and ion flux characteristics remain
the same.
In conclusion, the magnetic configuration is a critical
factor for plasma production and ion acceleration, the
latter being driven not only by the electrostatic potential
but also by some other, not yet ascertained mechanisms.
ACKNOWLEDGEMENT
This work was supported by the Science and
Technology Center in Ukraine under contract # 3068.
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