Radio-frequency plasma start-up at Uragan-3M stellarator
A double frame antenna with a broad spectrum of parallel wavenumbers (with respect to the magnetic field) is used for radio-frequency (RF) plasma production in Uragan-3M stellarator type device. The delay between the start of RF pulse and the discharge development (breakdown (delay) time) is analyze...
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| Zitieren: | Radio-frequency plasma start-up at Uragan-3M stellarator / V.E. Moiseenko, A. Lyssoivan, T. Wauters, M. Tripský, A.V. Lozin, R.O. Pavlichenko, M.M. Kozulya, M.B. Dreval, Yu.K. Mironov, V.S. Romanov, A.Ye. Kulaga, N.V. Zamanov, A.N. Shapoval, V.G. Konovalov, V.V. Chechkin, L.I. Grigor’eva, A.A. Beletskii, A.A. Kasilov, I.E. Garkusha // Вопросы атомной науки и техники. — 2017. — № 1. — С. 54-59. — Бібліогр.: 13 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1221272025-02-09T20:49:39Z Radio-frequency plasma start-up at Uragan-3M stellarator Радиочастотное создание плазмы в стеллараторе Ураган-3М Радіочастотне створення плазми в стелараторі Ураган-3М Moiseenko, V.E. Lyssoivan, A. Wauters, T. Tripský, M. Lozin, A.V. Pavlichenko, R.O. Kozulya, M.M. Dreval, M.B. Mironov, Yu.K. Romanov, V.S. Kulaga, A.Ye. Zamanov, N.V. Shapoval, A.N. Konovalov, V.G. Chechkin, V.V. Grigor’eva, L.I. Beletskii, A.A. Kasilov, A.A. Garkusha, I.E. Магнитное удержание A double frame antenna with a broad spectrum of parallel wavenumbers (with respect to the magnetic field) is used for radio-frequency (RF) plasma production in Uragan-3M stellarator type device. The delay between the start of RF pulse and the discharge development (breakdown (delay) time) is analyzed as functions of the magnetic field strength, neutral gas pressure and anode voltage of the RF generator. The reproducibility of the RF discharges is improved by the pre-ionization by the pulse of the three-half-turn antenna preceding the main RF pulse. The pre-ionization also results in shortening of the breakdown time for the frame antenna. The Langmuir probe measurements are made with two probes located at the plasma edge near and far from the double frame antenna. The measurements give rather high edge electron temperature, about 100 eV, at the initial stage of the frame antenna discharge both near and far from the antenna. The information on the plasma build-up is also given by the Hα chord measurements. Рамочная антенна с широким спектром параллельных волновых чисел (по отношению к магнитному полю) используется для высокочастотного (ВЧ) создания плазмы в установке стеллараторного типа УРАГАН-3М. Задержка между началом ВЧ-импульса и моментом развития разряда (время (задержки) пробоя) анализируется как функции величины магнитного поля, давления нейтрального газа и анодного напряжения ВЧ-генератора. Воспроизводимость ВЧ-разрядов повышается за счёт предварительной ионизации с помощью трёхполувитковой антенны, которая запускается перед основным ВЧ-импульсом. Предварительная ионизация также приводит к уменьшению времени пробоя. Измерения температуры и плотности плазмы выполнены двумя Ленгмюровскими зондами, расположенными на краю плазмы вблизи и вдали от рамочной антенны. Измерения дают достаточно высокую температуру электронов, около 100 эВ, на начальном этапе разряда как вблизи, так и вдали от антенны. Информация о создании плазмы также дают хордовые измерения линии Hα. Рамкова антена з широким спектром паралельних хвильових чисел (по відношенню до магнітного поля) використовується для високочастотного (ВЧ) створення плазми в установці стелараторного типу УРАГАН-3М. Затримка між початком ВЧ-імпульсу і моментом розвитку розряду (час (затримки) пробою) аналізується як функції величини магнітного поля, тиску нейтрального газу і анодної напруги ВЧ-генератора. Відтворюваність ВЧ-розрядів підвищується за рахунок попередньої іонізації за допомогою тринапіввиткової антени, яка запускається перед основним ВЧ-імпульсом. Попередня іонізація також призводить до зменшення часу пробою. Вимірювання температури і густини плазми виконані двома Ленгмюрівськими зондами, розташованими на краю плазми поблизу і на віддаленні від рамкової антени. Вимірювання дають досить високу температуру електронів, близько 100 еВ, на початковому етапі розряду як поблизу, так і на віддаленні від антени. Інформацію про створення плазми також дають хордові вимірювання лінії Hα. The work is supported in part by Science and Technology Center in Ukraine and National Academy of Sciences of Ukraine, grant No. 6057, and by National Academy of Sciences of Ukraine, grant П-3-22. 2017 Article Radio-frequency plasma start-up at Uragan-3M stellarator / V.E. Moiseenko, A. Lyssoivan, T. Wauters, M. Tripský, A.V. Lozin, R.O. Pavlichenko, M.M. Kozulya, M.B. Dreval, Yu.K. Mironov, V.S. Romanov, A.Ye. Kulaga, N.V. Zamanov, A.N. Shapoval, V.G. Konovalov, V.V. Chechkin, L.I. Grigor’eva, A.A. Beletskii, A.A. Kasilov, I.E. Garkusha // Вопросы атомной науки и техники. — 2017. — № 1. — С. 54-59. — Бібліогр.: 13 назв. — англ. 1562-6016 PACS: 52.50.Qt https://nasplib.isofts.kiev.ua/handle/123456789/122127 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 |
Магнитное удержание Магнитное удержание |
| spellingShingle |
Магнитное удержание Магнитное удержание Moiseenko, V.E. Lyssoivan, A. Wauters, T. Tripský, M. Lozin, A.V. Pavlichenko, R.O. Kozulya, M.M. Dreval, M.B. Mironov, Yu.K. Romanov, V.S. Kulaga, A.Ye. Zamanov, N.V. Shapoval, A.N. Konovalov, V.G. Chechkin, V.V. Grigor’eva, L.I. Beletskii, A.A. Kasilov, A.A. Garkusha, I.E. Radio-frequency plasma start-up at Uragan-3M stellarator Вопросы атомной науки и техники |
| description |
A double frame antenna with a broad spectrum of parallel wavenumbers (with respect to the magnetic field) is used for radio-frequency (RF) plasma production in Uragan-3M stellarator type device. The delay between the start of RF pulse and the discharge development (breakdown (delay) time) is analyzed as functions of the magnetic field strength, neutral gas pressure and anode voltage of the RF generator. The reproducibility of the RF discharges is improved by the pre-ionization by the pulse of the three-half-turn antenna preceding the main RF pulse. The pre-ionization also results in shortening of the breakdown time for the frame antenna. The Langmuir probe measurements are made with two probes located at the plasma edge near and far from the double frame antenna. The measurements give rather high edge electron temperature, about 100 eV, at the initial stage of the frame antenna discharge both near and far from the antenna. The information on the plasma build-up is also given by the Hα chord measurements. |
| format |
Article |
| author |
Moiseenko, V.E. Lyssoivan, A. Wauters, T. Tripský, M. Lozin, A.V. Pavlichenko, R.O. Kozulya, M.M. Dreval, M.B. Mironov, Yu.K. Romanov, V.S. Kulaga, A.Ye. Zamanov, N.V. Shapoval, A.N. Konovalov, V.G. Chechkin, V.V. Grigor’eva, L.I. Beletskii, A.A. Kasilov, A.A. Garkusha, I.E. |
| author_facet |
Moiseenko, V.E. Lyssoivan, A. Wauters, T. Tripský, M. Lozin, A.V. Pavlichenko, R.O. Kozulya, M.M. Dreval, M.B. Mironov, Yu.K. Romanov, V.S. Kulaga, A.Ye. Zamanov, N.V. Shapoval, A.N. Konovalov, V.G. Chechkin, V.V. Grigor’eva, L.I. Beletskii, A.A. Kasilov, A.A. Garkusha, I.E. |
| author_sort |
Moiseenko, V.E. |
| title |
Radio-frequency plasma start-up at Uragan-3M stellarator |
| title_short |
Radio-frequency plasma start-up at Uragan-3M stellarator |
| title_full |
Radio-frequency plasma start-up at Uragan-3M stellarator |
| title_fullStr |
Radio-frequency plasma start-up at Uragan-3M stellarator |
| title_full_unstemmed |
Radio-frequency plasma start-up at Uragan-3M stellarator |
| title_sort |
radio-frequency plasma start-up at uragan-3m stellarator |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2017 |
| topic_facet |
Магнитное удержание |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/122127 |
| citation_txt |
Radio-frequency plasma start-up at Uragan-3M stellarator / V.E. Moiseenko, A. Lyssoivan, T. Wauters, M. Tripský, A.V. Lozin, R.O. Pavlichenko, M.M. Kozulya, M.B. Dreval, Yu.K. Mironov, V.S. Romanov, A.Ye. Kulaga, N.V. Zamanov, A.N. Shapoval, V.G. Konovalov, V.V. Chechkin, L.I. Grigor’eva, A.A. Beletskii, A.A. Kasilov, I.E. Garkusha // Вопросы атомной науки и техники. — 2017. — № 1. — С. 54-59. — Бібліогр.: 13 назв. — англ. |
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ISSN 1562-6016. ВАНТ. 2017. №1(107)
54 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2017, № 1. Series: Plasma Physics (23), p. 54-59.
RADIO-FREQUENCY PLASMA START-UP AT URAGAN-3M
STELLARATOR
V.E. Moiseenko
1
, A. Lyssoivan
2
, T. Wauters
2
, M. Tripský
2
, A.V. Lozin
1
, R.O. Pavlichenko
1
,
M.M. Kozulya
1
, M.B. Dreval
1
, Yu.K. Mironov
1
, V.S. Romanov
1
, A.Ye. Kulaga
1
,
N.V. Zamanov
1
, A.N. Shapoval
1
, V.G. Konovalov
1
, V.V. Chechkin
1
, L.I. Grigor’eva
1
,
A.A. Beletskii
1
, A.A. Kasilov
1
and I.E. Garkusha
1
1
Institute of Plasma Physics of the NSC KIPT, Kharkov, Ukraine;
2
Laboratory for Plasma Physics, ERM/KMS, Brussels, Belgium
A double frame antenna with a broad spectrum of parallel wavenumbers (with respect to the magnetic field) is
used for radio-frequency (RF) plasma production in Uragan-3M stellarator type device. The delay between the start
of RF pulse and the discharge development (breakdown (delay) time) is analyzed as functions of the magnetic field
strength, neutral gas pressure and anode voltage of the RF generator. The reproducibility of the RF discharges is
improved by the pre-ionization by the pulse of the three-half-turn antenna preceding the main RF pulse. The pre-
ionization also results in shortening of the breakdown time for the frame antenna. The Langmuir probe
measurements are made with two probes located at the plasma edge near and far from the double frame antenna. The
measurements give rather high edge electron temperature, about 100 eV, at the initial stage of the frame antenna
discharge both near and far from the antenna. The information on the plasma build-up is also given by the Hα chord
measurements.
PACS: 52.50.Qt
INTRODUCTION
Plasma production at the ion cyclotron range of
frequency (ICRF) is used at a number of tokamaks and
stellarators to initiate wall conditioning discharges. At
Uragan family of stellarators (see, e.g. [1]) the ICRF
plasma production is a main tool to create target plasma
at regular shots. Several previous studies [2-5], both
theoretical and experimental, were focused on
discovering the physical nature of the plasma creation.
The points of the physical picture described in above
mentioned papers are briefly the following.
It is important that few initial charges exist in the
plasma confinement volume. They naturally appear
from the background radiation. The electrons
oscillate in the antenna near-field and make an
avalanche if the oscillating energy exceeds the
ionization threshold.
When the low density plasma is created, the process
of plasma production proceeds owing to ionization
of the neutral gas by electron impact in relatively
hot plasma. The energy losses induced by inelastic
collisions of the electrons with neutral gas are
compensated by RF heating.
At low plasma densities the RF heating is made by
the slow wave, which should be propagating.
After reaching some plasma density level, the fast
wave comes to play. Alfvén resonances, which
generate the slow wave inside the plasma core, are
important for further plasma production.
Based on this, one can build a simplified physical
picture for an atomic gas and ions in a single charged
state. Hydrogen is a molecular gas, and presence of the
molecular ions (H2
+
, H3
+
) in addition to atomic ion H
+
makes the process of wave propagations more
complicated.
A number of experiments on plasma production
were made at Uragan-3M (U-3M) stellarator type
device, which has a huge vacuum tank. When it is filled
by hydrogen with the continuous gas puff, this tank
contributes to ‘exchange’ of generated in plasma atoms
with molecules. This is confirmed by analysis of Balmer
series [6], which has molecular origin. The ‘exchange’
promotes molecular ions formation in weakly ionized
plasma. Anyway, plasma production is successful in U-
3M device.
The present U-3M experimental campaign for
plasma production studies is motivated by an
insufficient understanding of the role of molecular
plasma content in plasma production.
EXPERIMENTAL SETUP
Fig. 1. Three-half-turn (THT, top) and double frame
(bottom) antenna
ISSN 1562-6016. ВАНТ. 2017. №1(107) 55
The experiments on ICRF discharge initiation were
performed in frame of the EU (Belgium) Ukrainian
collaboration on ICRF plasma production studies. The
double frame antenna with a broad spectrum of parallel
wavenumbers (with respect to the magnetic field) [7]
(Fig. 1) was operated at f= 8.6 MHz, variable RF power
(P=15…130 kW, anode voltage of generator,
Uk1=3…9 kV), confining magnetic field
B0=0.01…0.72 T to produce RF plasma in hydrogen at a
continuous gas puff with pressure range
pH2≈7.5·10
−6
…1.5·10
−4
Torr. The three-half-turn (THT)
antenna is used for pre-ionization to increase
reproducibility of the discharges.
Fig. 2. Antenna current Ik1, Hα intensity and average
plasma density evolutions given by interferometer for
different steady magnetic field values (from up to
down): 7.1, 6.5, 5 and 3 kG. tK1=(10;25) ms,
pH2=4∙10
-5
Torr
It should be mentioned that sustaining a fully
ionized hydrogen RF plasma takes place in the Alfvén
wave range of frequencies (ω < ωci) for the given RF
generator frequency at higher magnetic fields
(B0=0.72 T). The hydrogen gas RF breakdown moment
is characterized by dominant concentration of the
hydrogen molecular ions H2
+
[8]. These result are in the
breakdown performance in the U-3M in the frequency
range ω>ωci, which allows existence of the LHR for all
tested B values.
RF PLASMA PRODUCTION
The plasma of density up to 10
19
m
-3
is created when
the frequency is in the range f=0.7-0.9 fci, where fci is the
ion cyclotron resonance frequency. When f>0.9 fci the
plasma is also produced, but with substantially lower
density (Fig. 2). This could be explained by absence of
the Alfvén resonances in the plasma column, which
possibly are responsible for further plasma density
increase. The range f<0.7 fci cannot be achieved without
tuning down the generator frequency since reaching the
upper technical limit of the confining magnetic field.
PROBE MEASUREMENTS
To measure local parameters of the boundary plasma
(floating potential Vf, electron temperature Te, electron
density ne), two movable arrays of electric (Langmuir)
probes were used. Each array includes two single probes
(diameter of probe collecting area 1 mm, length 2 mm,
molybdenum) with the distance between the probes
3 mm. One probe is used to record the floating potential,
another one – to get the I-V characteristic. One of the
arrays (“vertical probes”, VP) is inserted into the
vacuum chamber from the top in a poloidal cross-
section close to A1 (Fig. 3) and can be moved vertically,
passing at the distance of ~3 cm from the frame antenna
edge. When making measurements, this array was fixed
at the distance of 14.5 cm from the torus midplane, not
reaching 0.5 cm the calculated last closed flux surface
([9], Fig. 4,a, position “near the antenna”). Another
array (“horizontal probes”, HP) is inserted from the
outboard side of the torus in the helical period 8 (see
Fig. 1) in the poloidal cross-section 1.8 period-distant
from the cross-section D1 in which the antenna feeding
point is located.
Fig. 3. Helical coils I, II, III of U-3M. Indicated are
symmetric poloidal cross-sections A1, D1, A2, D2,…,
A9, D9 in helical periods 1, 2, …, 9, respectively,
disposition of the double frame antenna. Radial dashed
lines indicate poloidal cross-sections where movable
arrays of electric probes are inserted (VP in period 9,
near A1; HP in period 8, between D8 and A8)
This array can move horizontally parallel to the
major radius R at the distance of 2 cm over the
56 ISSN 1562-6016. ВАНТ. 2017. №1(107)
midplane. During measurements HP were fixed at the
distance of 9.25 cm from the vertical axis of the cross-
section, corresponding to the distance 0.5 cm from the
calculated plasma boundary (Fig. 4,b, position “far from
the antenna”).
Fig. 4. Disposition of movable probe arrays VP (a) and
HP (b) in poloidal cross-sections of the U-3M torus and
lines of probe displacement (dashes) relative to the
helical coils I, II, III and calculated Poincare plots of
magnetic lines of force in these cross-sections [10]
Fig. 5. Experimentally observed indications of gas
breakdown (green vertical dashed line) during RF
plasma start-up in U-3M for shot at Uk1=6 kV,
pH2=4.7∙10
−5
Torr and B0=0.72 T. Time traces of
forward (blue) and reflected (red) directional coupler
signals, average electron density, and Hα signal,
floating potential registered by the Langmuir probes,
average plasma density by interferometer and electron
temperature Te and electron density ne by LPs obtained
in a series of identical shots
The values of Vf, Te and ne were determined as a
result of processing the ion branch of the probe I-V
characteristic where the “ideal” relation (see, e.g., [10])
I(V) = Is{1-exp[(V-Vf)/Te]} was fitted to the
experimental characteristic. Here I(V) is the current to
the probe at the bias voltage V, Is 0.5Anee(2kBTe/mi)
1/2
is
the ion saturation current, A is the probe collecting area.
Fig. 5 shows the plots of the Vf(t), Te(t) and ne(t)
values derived from the I-V characteristics taken near
and far from the antenna at different time moments after
RF discharge ignition. In a qualitative consistence with
the time evolution of signals in Fig. 5, the antenna-near
floating potential Vf changes its polarity twice after
ignition and finally attains the level of ~+15 V close to
the “quasistationary” one in ~3.5 ms. The temperature
Te achives a maximum value of 80 eV (which is
remarkably high for weakly ionized plasma), drops
down to ~10 eV and stays at this level with minor
variations later. The density ne increases continuously
from values order of 10
15
m
-3
, passes (2…3)·10
16
m
-3
in
the Te maximum and achieves a “quasistationary” level
of ~7·10
17
m
-3
.
Fig. 6. Lines of sight for Ha measurements at Uragan-
3M poloidal cross-section (top). Evolution of (a) line-
averaged density and (b) Ha emission (bottom), dashed
line marks the RF power switching-on time.
UK1=5.5 kV, pH2=1∙10
-4
Torr, B0=0.72 T
The potential Vf far from the antenna, contrary to its
behavior near the antenna, does not change the polarity,
all time is positive, attains a maximum of 80 V and then
falls to ~10 V in the “quasistationary” phase. Similar to
the ne(t) behavior near the antenna, the density increases
continuously from ~10
16
m
-3
at t=1.8 ms, i.e. near the
start of Te rise, and reaches ~8·10
17
m
-3
in the
“quasistationary” stage.
Accounting for a not very high accuracy of probe
measurements, one may state that the maximum values
80 85 90 95 100 105 110 115 120
-20
-15
-10
-5
0
5
10
15
20
III
II
Z
,
cm
R, cm
I
HP
(b)a b a
ISSN 1562-6016. ВАНТ. 2017. №1(107) 57
of Te and ne obtained near and far from the antenna, as
well as the values of these parameters at the start of the
“quasistationary” stage, are close by the order of
magnitude. It seems important to note that the Te
maximum far from the antenna is ~0.2 ms delayed
relative to the maximum near the antenna.
Floating potential of VP is most sensitive to a dense
plasma appearance, and the gas breakdown time can be
calculated as a time delay between the antenna RF
voltage apply and its first (weak) reaction on the plasma
loading appearance due to SW excitation in weakly
ionized plasma, ω>ωci, (see the green dashed vertical
line in Fig. 5, also the first burst in the Hα signal clearly
seen in Fig. 6 than in Fig. 5 due to larger scale). Other
indication of the start-up could be antenna load (blue
vertical dashed line) or Hα burst. The blue vertical
dashed line in Fig. 5 indicates the second and more
prominent reaction on plasma loading by the antenna
RF signals and plasma parameters due to AW excitation
(ω < ωci) in a denser and fully ionized plasma. The
latter is confirmed by achieving a maximum in the Hα
signal in a more developed phase of the RF discharge
(see Figs. 5 and 6).
In Fig. 5 the difference between the average plasma
density, which is evaluated from the interferometer
measurements, and the edge densities is smaller at start
and larger at the end of plasma build-up. This indicates
the fact that after ignition the density radial distribution
is becoming more peaked towards the plasma core. The
radial plasma expansion from the LFS (ICRF antenna
side) towards HFS just after gas breakdown was earlier
discovered in JET with high-resolution fast CCD
camera [11].
Hα CHORD DISTRIBUTION
Hα chord distribution is measured by multi-chord Hα
detector array [12]. The scheme of measurements is
presented in Fig. 6.
Bottom part of this figure shows integral Hα and
average plasma density evolutions.
Fig. 7. Evolution of (a) Ha profile and (b) Ha profile
normalized to its maximum in every discharge instant
As it is seen in Fig. 7, the H emission profile looks
more hollow at the beginning than after plasma build-
up. However, the emission is volumetric what indicates
that plasma fills in the whole plasma volume.
PARAMETER SCAN
In the series of experiments dense plasma build-up
delay time is investigated as a function of hydrogen gas
pressure (Fig. 8).
Fig. 8. The dense plasma build-up delay time
dependence on the varying neutral gas pressure for
different generator anode voltages
The results show the existence of an optimal value
for the pressure which provides the lowest breakdown
time for each antenna voltage. This optimal pressure is
shifting towards higher pressures with the increasing
antenna load. The delay time increases before reaching
the highest and lowest pressure for each anode voltage
value. For high pressures there is a threshold anode
voltage. As it is seen from Fig. 8, e.g. for
pH2=8.25·10
-5
Torr the threshold voltage is Uk1=4 kV.
Fig. 9. The dense plasma build-up delay time
dependence on the magnetic field (top,
pH2=2.5·10
-5
Torr) and the anode voltage (bottom,
B=7.2 kG)
The delay time is almost independent on the
magnetic field value (Fig. 9). It is decreasing with
increasing magnitude of the RF voltage at antenna.
a b
58 ISSN 1562-6016. ВАНТ. 2017. №1(107)
ROLE OF PRE-IONIZATION
The reproducibility of the discharges is improved by
a pre-ionization which is made by the pulse of the three-
half-turn antenna preceding the main RF pulse. This
antenna creates the plasma of the density ne≥10
16
m
-3
.
The time between the THT antenna pulse end and the
double frame antenna start, tgap, (Fig. 10) is varied in the
experiments.
The pre-ionization results in shortening of the
plasma creation time (Fig. 11). It effects on the double
frame antenna discharge even if tgap is long.
Fig. 10. Sequence of RF pulses of THT antenna (RF-2)
and double frame antenna (RF-1)
Fig. 11. Dense plasma build-up delay time as a function
of time between RF pulses. B0=7.2 kG, pH2=2·10
-5
Torr,
UK1=6 kV, UK2=5 kV
Fig. 12. Breakdown delay time for repetitive pulses with
and without pre-ionization
Fig. 12 illustrates both shortening of the breakdown
time effect and substantial increase of discharge
repeatability.
DISCUSSIONS
The mechanism of plasma production is not fully
clear so far. The difficulties in understanding related to
existence of the molecular ions which cyclotron
frequency is lower than the heating frequency. If the
molecular ions dominate the Lower Hybrid Resonance
(LHR) appears in the plasma column at low plasma
density, ~10
15
m
-3
in our case. With increase of atomic
ion content, this density value increases. The slow wave
launched by an antenna travels to LHR position and is
absorbed there without reflections (see, e.g. [13]). Since
there are no heating behind the LHR location, the
plasma density profile should be strongly hollow or
peaked at the LFS. Following this, Hα chord profile
should also be hollow or maximized at the LFS. In
experiment we see no more than proximity of the
periphery plasma density value to the average plasma
density at the early stages of the discharge. These
witnesses rather for the volumetric plasma generation
than for plasma production only at the plasma edge with
further diffusion of it inside the confinement volume.
Similar could be concluded from the Hα emission
profile.
An important moment is that the measured electron
temperature is high when plasma density is low. For
high parallel wavenumbers in hot plasma, for the slow
wave the wave cut-off and propagation zones swap if
the parallel phase velocity of the wave is lower than the
electron thermal velocity. In such a case, a wave, being
excited by the antenna, penetrates through the cut-off
region at the plasma periphery, passes through LHR
layer with only partial damping and propagates to the
plasma core where it could be absorbed. The transition
margin to this regime is established by a certain electron
temperature, and for U-3M it is 100 eV [5]. In such a
way, the volumetric plasma production is possible.
However, more experiments are needed to clarify
whether this effect is important.
ACKNOWLEDGEMENTS
The work is supported in part by Science and
Technology Center in Ukraine and National Academy
of Sciences of Ukraine, grant No. 6057, and by National
Academy of Sciences of Ukraine, grant П-3-22.
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Article received 11.01.2017
РАДИОЧАСТОТНОЕ СОЗДАНИЕ ПЛАЗМЫ В СТЕЛЛАРАТОРЕ УРАГАН-3М
В.Е. Моисеенко, A. Lyssoivan, T. Wauters, M. Tripský, А.В. Лозин, Р.O. Павличенко, M.M. Козуля,
Н.Б. Древаль, Ю.К. Миронов, В.С. Романов, A.Е. Кулага, Н.В Заманов, A.Н. Шаповал, В.Г. Коновалов,
В.В. Чечкин, Л.И. Григорьева, A.A. Белецкий, A.A. Касилов и И.E. Гаркуша
Рамочная антенна с широким спектром параллельных волновых чисел (по отношению к магнитному
полю) используется для высокочастотного (ВЧ) создания плазмы в установке стеллараторного типа
УРАГАН-3М. Задержка между началом ВЧ-импульса и моментом развития разряда (время (задержки)
пробоя) анализируется как функции величины магнитного поля, давления нейтрального газа и анодного
напряжения ВЧ-генератора. Воспроизводимость ВЧ-разрядов повышается за счёт предварительной
ионизации с помощью трёхполувитковой антенны, которая запускается перед основным ВЧ-импульсом.
Предварительная ионизация также приводит к уменьшению времени пробоя. Измерения температуры и
плотности плазмы выполнены двумя Ленгмюровскими зондами, расположенными на краю плазмы вблизи и
вдали от рамочной антенны. Измерения дают достаточно высокую температуру электронов, около 100 эВ,
на начальном этапе разряда как вблизи, так и вдали от антенны. Информация о создании плазмы также дают
хордовые измерения линии H .
РАДІОЧАСТОТНЕ СТВОРЕННЯ ПЛАЗМИ В СТЕЛАРАТОРІ УРАГАН-3М
В.Є. Моісeєнко, A. Lyssoivan, T. Wauters, M. Tripský, О.В. Лозін, Р.O. Павліченко, M.M. Козуля,
М.Б. Древаль, Ю.К. Миронов, В.С. Романов, A.Є. Кулага, М.В. Заманов, A.М. Шаповал, В.Г. Коновалов,
В.В. Чечкін, Л.І. Грігор’єва, О.О. Білецький, A.A. Касілов та І.Є. Гаркуша
Рамкова антена з широким спектром паралельних хвильових чисел (по відношенню до магнітного поля)
використовується для високочастотного (ВЧ) створення плазми в установці стелараторного типу УРАГАН-
3М. Затримка між початком ВЧ-імпульсу і моментом розвитку розряду (час (затримки) пробою)
аналізується як функції величини магнітного поля, тиску нейтрального газу і анодної напруги ВЧ-
генератора. Відтворюваність ВЧ-розрядів підвищується за рахунок попередньої іонізації за допомогою
тринапіввиткової антени, яка запускається перед основним ВЧ-імпульсом. Попередня іонізація також
призводить до зменшення часу пробою. Вимірювання температури і густини плазми виконані двома
Ленгмюрівськими зондами, розташованими на краю плазми поблизу і на віддаленні від рамкової антени.
Вимірювання дають досить високу температуру електронів, близько 100 еВ, на початковому етапі розряду
як поблизу, так і на віддаленні від антени. Інформацію про створення плазми також дають хордові
вимірювання лінії H .
|