Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments
The experimental method was developed for evaluation of a hydrogen particle flux balance over a wide range of operating conditions in the Uragan-3M torsatron (U-3M) in the course of RF discharges. Standard pressure gauges were tested for measurement of non-stationary hydrogen pressure in the U-3M va...
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Pashnev, V.K. Petrushenya, A.A. Bondarenko, V.N. Sorokovoy, E.L. Ponomarenko, N.P. Ozherelyev, F.I. 2017-06-27T18:03:58Z 2017-06-27T18:03:58Z 2017 Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments / V.K. Pashnev, A.A. Petrushenya, V.N. Bondarenko, E.L. Sorokovoy, N.P. Ponomarenko, F.I. Ozherelyev // Вопросы атомной науки и техники. — 2017. — № 1. — С. 44-48. — Бібліогр.: 12 назв. — англ. 1562-6016 PACS: 52.40.Hf, 52.50.Qt, 52.55.Hc https://nasplib.isofts.kiev.ua/handle/123456789/122125 The experimental method was developed for evaluation of a hydrogen particle flux balance over a wide range of operating conditions in the Uragan-3M torsatron (U-3M) in the course of RF discharges. Standard pressure gauges were tested for measurement of non-stationary hydrogen pressure in the U-3M vacuum chamber. The average lifetime of hydrogen ions was determined for each operation mode of U-3M. Разработана экспериментальная методика оценки баланса потоков частиц водорода во время ВЧ-разрядов в торсатроне Ураган-3М (У-3М) в широком диапазоне рабочих параметров. Для измерения нестационарного давления водорода в вакуумной камере У-3М были апробированы стандартные датчики давления. Для каждого из рабочих режимов работы У-3М было определено среднее время жизни ионов водорода. Розроблено експериментальну методику оцінки балансу потоків частинок водню під час ВЧ-розрядів у торсатроні Ураган-3М (У-3М) в широкому діапазоні робочих параметрів. Для вимірювання нестаціонарного тиску водню у вакуумній камері У-3М були апробовані стандартні датчики тиску. Для кожного з робочих режимів У-3М було визначено середній час життя іонів водню. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Магнитное удержание Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments Методики измерения баланса водорода в вакуумной камере торсатрона У-3М во время плазменных экспериментов Методики вимірювання балансу водню у вакуумній камері торсатрона У-ЗМ під час плазмових експериментів Article published earlier |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| title |
Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments |
| spellingShingle |
Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments Pashnev, V.K. Petrushenya, A.A. Bondarenko, V.N. Sorokovoy, E.L. Ponomarenko, N.P. Ozherelyev, F.I. Магнитное удержание |
| title_short |
Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments |
| title_full |
Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments |
| title_fullStr |
Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments |
| title_full_unstemmed |
Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments |
| title_sort |
methods for measuring hydrogen balance in vacuum chamber of u-3m torsatron during plasma experiments |
| author |
Pashnev, V.K. Petrushenya, A.A. Bondarenko, V.N. Sorokovoy, E.L. Ponomarenko, N.P. Ozherelyev, F.I. |
| author_facet |
Pashnev, V.K. Petrushenya, A.A. Bondarenko, V.N. Sorokovoy, E.L. Ponomarenko, N.P. Ozherelyev, F.I. |
| topic |
Магнитное удержание |
| topic_facet |
Магнитное удержание |
| publishDate |
2017 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Методики измерения баланса водорода в вакуумной камере торсатрона У-3М во время плазменных экспериментов Методики вимірювання балансу водню у вакуумній камері торсатрона У-ЗМ під час плазмових експериментів |
| description |
The experimental method was developed for evaluation of a hydrogen particle flux balance over a wide range of operating conditions in the Uragan-3M torsatron (U-3M) in the course of RF discharges. Standard pressure gauges were tested for measurement of non-stationary hydrogen pressure in the U-3M vacuum chamber. The average lifetime of hydrogen ions was determined for each operation mode of U-3M.
Разработана экспериментальная методика оценки баланса потоков частиц водорода во время ВЧ-разрядов в торсатроне Ураган-3М (У-3М) в широком диапазоне рабочих параметров. Для измерения нестационарного давления водорода в вакуумной камере У-3М были апробированы стандартные датчики давления. Для каждого из рабочих режимов работы У-3М было определено среднее время жизни ионов водорода.
Розроблено експериментальну методику оцінки балансу потоків частинок водню під час ВЧ-розрядів у торсатроні Ураган-3М (У-3М) в широкому діапазоні робочих параметрів. Для вимірювання нестаціонарного тиску водню у вакуумній камері У-3М були апробовані стандартні датчики тиску. Для кожного з робочих режимів У-3М було визначено середній час життя іонів водню.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/122125 |
| citation_txt |
Methods for measuring hydrogen balance in vacuum chamber of U-3M torsatron during plasma experiments / V.K. Pashnev, A.A. Petrushenya, V.N. Bondarenko, E.L. Sorokovoy, N.P. Ponomarenko, F.I. Ozherelyev // Вопросы атомной науки и техники. — 2017. — № 1. — С. 44-48. — Бібліогр.: 12 назв. — англ. |
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| first_indexed |
2025-11-24T18:44:29Z |
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2025-11-24T18:44:29Z |
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| fulltext |
1562-6016. ВАНТ. 2017. №1(107)
44 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2017, № 1. Series: Plasma Physics (23), p. 44-48.
METHODS FOR MEASURING HYDROGEN BALANCE IN VACUUM
CHAMBER OF U-3M TORSATRON DURING
PLASMA EXPERIMENTS
V.K. Pashnev, A.A. Petrushenya, V.N. Bondarenko, E.L. Sorokovoy, N.P. Ponomarenko,
F.I. Ozherelyev
Institute of Plasma Physics of the NSC KIPT, Kharkov, Ukraine
The experimental method was developed for evaluation of a hydrogen particle flux balance over a wide range of
operating conditions in the Uragan-3M torsatron (U-3M) in the course of RF discharges. Standard pressure gauges
were tested for measurement of non-stationary hydrogen pressure in the U-3M vacuum chamber. The average
lifetime of hydrogen ions was determined for each operation mode of U-3M.
PACS: 52.40.Hf, 52.50.Qt, 52.55.Hc
INTRODUCTION
An experimental study of a hydrogen particle
balance has been carried out with standard pressure
gauges over a wide range of operating conditions in the
U-3M torsatron [1-3]: I – a mode of RF plasma heating
with a magnetic field В0 0.7 T, hydrogen pressure
P 7×10-6 Torr, average plasma density ne
1×1012 cm-3, ion and electron temperature Te,i
(200…600) eV, RF pulse length of (10…50) ms; II – a
mode of RF wall conditioning with a magnetic field
В0 0.7 T, hydrogen pressure P 4.5×10-5 Torr,
average plasma density ne 8×1012 cm-3, ion and
electron temperature Te,i 20 eV, RF pulse length of
(10…50) ms; III – a mode of RF wall conditioning with
a weak magnetic field В0 0.024 T, hydrogen pressure
P 1.3×10-4 Torr, average plasma density
ne 1.5×1012
cm-3, ion and electron temperature
Te,i 20 eV, RF pulse length of ~50 ms. The temporal
behavior of the hydrogen pressure in the vacuum
chamber of U-3M during main operation modes is
described in [4].
Two types of standard pressure sensors are used for
the measurement in the U-3M vacuum chamber. The
first type is the magnetron sensor PMM-32. The second
type is the ionization sensor PMI-2. The ionization
sensors have better inertial properties during
measurement of non-stationary pressure. This allows to
measure the behavior of pressure with temporal
resolution of a few tens of microseconds. Such sensors
are widely used in various research installations where
experiments on plasma confinement and heating [5] are
provided. They are usually fabricated and calibrated
individually for each installation taking into account
specific experimental conditions. In our case with non-
stationary magnetic fields, intensive interference from
RF antennas, and fluxes of charged particles to the walls
of the vacuum chamber of the U-3М torsatron, the
standard ionization sensors have not to be used. The
magnetron sensors are less sensitive to external
interference but they have much longer temporal inertia.
This is due to the long time changes of magnetron
discharge parameters during pressure variations.
Therefore, to measure correctly the non-stationary
pressure using such sensors, it is necessary to develop
the measurement technique which compensates their
temporal inertia.
1. MEASUREMENT OF NON-STATIONARY
PRESSURE
Locations of the magnetron pressure sensors
PMM-32 inside the U-3M vacuum chamber are shown
schematically in Fig. 1. One sensor is installed on the
roof of the vacuum chamber at a distance of 2 m above
helical coils. This sensor measures the pressure in the
main volume of the vacuum chamber. The second
sensor is installed on the upper end of a vertical tube
with an internal diameter of 24 cm and a length of
1.9 m. The lower open end of the tube is located in the
gap between helical coils. The pressure measured by the
second sensor depends on the pressure near the plasma.
This pressure, in turn, is caused by a molecular
hydrogen flux through gaps between helical coils from
the main volume of the vacuum chamber and by
hydrogen desorption from internal surfaces of helical
coils.
Fig. 1. Location of pressure sensors PMM-32 inside the
vacuum chamber of the U-3M torsatron
Pumping out of hydrogen from the vacuum chamber
during the RF discharge occurs due to absorption on
chamber walls of hydrogen atoms and ions leaving the
plasma. The pumping out rate of hydrogen from the
vacuum chamber cannot exceed a total value of
molecular conductivity of all gaps between helical coils
Ugaps 2100 m3/s because they restrict the hydrogen
flux into the plasma. Most of the molecular hydrogen
ISSN 1562-6016. ВАНТ. 2017. №1(107) 45
that flows through the gaps between helical coils is
absorbed by plasma in the confinement volume for two
reasons. Firstly, the free path length of hydrogen
molecules in the confined plasma is much smaller than
cross-sectional sizes of a plasma column. Secondly, the
hydrogen flux is considerably overlapped by the plasma
column at an exit from the gaps. This assumption is
derived from the spatial distribution of molecular fluxes
leaving the gap with the given cross-section, according
to [6].
The condition for the existence of a quasi-stationary
gas flux through the gaps between helical coils is
performed in all main operation modes:
1
LA
U
S
V , (1)
where V is the pumped volume, S is the pumping out
rate from the pumped volume through the pipeline with
a molecular conductivity U, a length L and a cross-
section A. Consequently, the temporal behavior of
hydrogen pressure in the U-3M vacuum chamber can be
described by a simple expression from a vacuum
technique, as follows:
ENDEND P
V
St
PPtP
exp)( 0
, (2)
where P(t) = nkT is the pressure in the vacuum chamber;
t – time; n – concentration of molecules; Т – gas
temperature; k – Boltzmann constant; P0 – initial
pressure. PEND is an equilibrium pressure, which is set in
the vacuum chamber, when the equality is fulfilled
between the rate of leakage from the walls and the
pumping out rate S from the chamber volume.
Condition (1) is not performed for the tube. The gas
pumping out rate from the tube volume is time-
dependent and during the RF pulse length is changing
from zero to some value that cannot exceed the value of
molecular conductivity of the tube Utube = 2.1 m3/s. The
temporal behavior of the pressure, in this case, is
determined by the hydrogen flux balance in the open
end of the tube. Such task is solved analytically in [7].
Numerical methods to solve similar tasks [6] can also be
used with regard to complex vacuum systems. In our
case, in order to describe the temporal behavior of the
pressure in the tube, one has to know the spatial
distribution of the flux of hydrogen particles that
bombard the internal surface of the tube. Formula (1)
can be used for qualitative estimation of the average
pumping rate from the tube. However, the pumping out
rate S determined from (1) in this case will be the
equivalent average rate which characterizes the pressure
change during the whole RF pulse time.
The calibration of magnetron sensors PMM-32,
based on readings of the ionization sensor PMI-2, was
performed before the start of measurement of the
hydrogen balance in the U-3M vacuum chamber. The
ionization sensor was installed on the roof of the
vacuum chamber nearby to the magnetron sensor. The
pressure in the vacuum chamber was related to readings
from magnetron sensors by the following expression:
Р = exp((U – b)/), where P is a pressure in Torr, U is a
voltage in volts on the analogue output of the
measurement unit VMB-14, b and are the coefficients
of proportionality, which are determined experimentally
for each sensor, based on the calibration curves.
It was found that the response time of the magnetron
sensor to the pressure changes was about (3…5) ms.
The time dependences of the pressure measured by
sensors PMI-2 and PMM-32 on the roof of the vacuum
chamber during a pulsed hydrogen puff are shown in
Fig. 2. In a case of the magnetron sensor the equation
(2) includes the time constant which takes into
account the time inertia of the sensor. The pumping out
rates S determined from the readings of both sensors are
close to each other. The calculation is based on
modified equation (2) shown in Fig. 2. The figure also
shows that the amplitudes of the pressure change,
measured by both sensors, are of similar value.
0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2
-5,0x10
-6
0,0
5,0x10
-6
1,0x10
-5
1,5x10
-5
2,0x10
-5
2,5x10
-5
PMM-32
PMI-2
P(t) = (P0- PEND)·exp(-S*t/ / V)+PEND (2)
PMI2
= 1;
PMM32
= 1.5;
S
PMI2, PMM32
= 650 m
3
/s; V
ch
= 65 m
3
.
P
END
P
0
P
,
T
o
rr
t, s
Fig. 2. Time dependences of hydrogen pressure
measured by the PMM-32 and PMI-2 sensors on the
roof of the vacuum chamber during a pulsed hydrogen
puff. Approximation curves calculated from modified
expression (2) for each sensor are shown as dotted lines
Sensor readings behaved differently during a fast
pressure drop in the vacuum chamber. With pumping
out rates comparable to those of outer pump line there
was no essential signal delay for the magnetron sensor
PMM-32 in relation to ionization sensor PMI-2. Fig. 3
shows the time dependences of pressure measured by
ionization and magnetron sensors on the roof of the
vacuum chamber during a fast pumping process with the
rate exceeding considerably the pumping out rate of the
outer pump line. As it is clear from Fig. 3, pressure
change amplitudes measured by both types of sensors
are also the same. However, for the magnetron sensor
there is a delay of readings in time. The time inertia of
the magnetron sensor in this case is revealed in
overestimation of the end equilibrium pressure PEND
determined from equation (2). The pumping rates for
both sensors, determined from equation (2), correspond
to each other. The time dependence of pressure
measured by the ionization sensor PMI-2 during RF
pulse has a drop caused by effect of RF interference and
charged particles bombarding the sensor casing.
When RF power is off, the readings of the ionization
sensor PMM-32 return to normal values within the
following 20 ms. The pumping stage is completed at
46 ISSN 1562-6016. ВАНТ. 2017. №1(107)
some moment after the switch-off of RF power. Starting
from this moment, hydrogen pressure increases in the
vacuum chamber. This increase is caused by hydrogen
desorption from the walls and external leakage.
The rates of hydrogen leakage determined from the
readings of both sensors are also almost the same.
However, at the stage of pressure increase, magnetron
sensor readings indicate a delay of 150 ms in time with
regard to ionization sensor readings. This peculiarity
should be taken into account during processing the
experimental dependences of hydrogen pressure in time.
Fig. 3. Time dependences of hydrogen pressure in the
vacuum chamber measured by the magnetron sensor
PMM-32 and the ionization sensor PMI-2 during and
after the RF discharge. Approximation curves
calculated from expression (2) for each sensor are
shown in dotted lines
2. HYDROGEN BALANCE IN VACUUM
CHAMBER OF U-3M TORSATRON
The hydrogen flux into the confined plasma from
the U-3M vacuum chamber during the RF discharge is
defined by molecular conductivity of gaps between
helical coils. By measuring the average pumping out
rate of hydrogen from the U-3M vacuum chamber
during the RF discharge one can determine the pressure
difference between the outside and the inside boundary
of the gaps. The pressure behind the gap near the
plasma P* is related to the pressure in the vacuum
chamber Pch by the following ratio:
U
SSU
PP
pump
ch
)(
,*
, (3)
where S is the average pumping out rate of hydrogen
from the vacuum chamber during the RF discharge; –
the transparency coefficient of gaps; U = 2100 m3/s –
the total molecular conductivity of all gaps between the
helical coils; Spump = 60 m3/s – the pumping out rate of
outer pump line. The pressure P* can be considered as
the average pressure along the outer perimeter of the
plasma. This pressure is created behind gaps by the
direct flux of hydrogen molecules from the vacuum
chamber, molecules scattered at the lateral and inner
surfaces of the helical coils, molecules, which flow
between helical coils and the plasma, and by a reverse
desorption of hydrogen molecules from the inner side
walls and helical coils. As has been shown in [4], the
temporal behavior of the hydrogen in the U-3M vacuum
chamber during RF pulse is described by expression (2).
The average flux of hydrogen molecules JH2 into
the plasma during RF pulse length tRF can be estimated
from two relations, which are approximately equal to
each other:
plHHH
ch
H AnvJ
J
J
*
2222
4
1
,
1
, (4)
where Jch = nH
2
(S – Spump) – the average flux of
hydrogen pumped out from the vacuum chamber during
the RF discharge due to absorption on the walls;
nH
2
(n0 - nH
2
/2) – the average concentration of
hydrogen molecules in the vacuum chamber during the
RF discharge; n0 – the initial concentration of hydrogen
molecules in the vacuum chamber before the RF pulse,
nH
2
– the concentration of hydrogen molecules in the
vacuum chamber at the time moment t; nH
2
– the
change of the concentration of molecular hydrogen in
the vacuum chamber during the RF discharge;
n*
H
2
= nH
2
– the concentration of hydrogen molecules
behind the gaps near the plasma at the moment t;
n*
H
2
= nH
2
– the average concentration of
molecular hydrogen behind the gap near the plasma
during the RF discharge; Vch = 65 m3 – the vacuum
chamber volume; = 2JRe
H
2
/(JH+ + JH) – the coefficient
of reverse hydrogen desorption from walls bombarded
by atoms and ions of the plasma; JRe
H2 = (SnH2 END –
Spumpn0) – the average reverse flux of hydrogen
molecules from walls into the vacuum chamber;
nH2 END = PEND/(kT) – the equilibrium concentration of
hydrogen from the expression (2); JH+
= Vpl ne / – the
average flux of hydrogen ions from the plasma to the
walls; JH – the average flux of hydrogen atoms from the
plasma to the walls; ne – the average plasma density in a
confinement volume during the RF discharge; – the
average lifetime of hydrogen ions in a confinement
volume during the RF discharge;
2Hv = (8kT/ /mH
2
)1/2 –
the average thermal velocity of hydrogen molecules;
mH
2
– the mass of a hydrogen molecule;
Apl = 42aR 4 m2 – the area of a plasma surface with
the small and the large radii a = 10.4 cm and R = 1 m,
respectively, according to [8]; Vpl = 0.213 m3 – the
volume of plasma confinement. The first expression in
(4) defines the average hydrogen flux into the confined
plasma during the RF discharge, which is measured
from the amount of hydrogen pumped out from the
vacuum chamber. The second expression in (4) defines
the molecular hydrogen flux through the outer boundary
of the plasma. If we neglect the hydrogen desorption
from walls, then JH++JH 2JH
2
. As a result,
JRe
H
2
/J H
2
= JRe
H
2
/(Jch + JRe
H
2
).
In a quasi-stationary case, when the plasma
parameters in a confinement volume are slightly varying
with time, the approximate balance of the hydrogen in a
chamber volume during the RF discharge duration can
be written, as follows:
ISSN 1562-6016. ВАНТ. 2017. №1(107) 47
RF
epl
HH
RF
H
ch
t
nV
JJ
t
n
V ))(1(
2 2
pumppuffgaspumpingwallpuffwall QQQQ 2 , (5)
where Qgas.puff = Spumpn0 – the external hydrogen puff
into the vacuum chamber; Qpump= SpumpnH
2
– pumping
out of the pump from the vacuum chamber; Qwall pumping –
wall pumping of hydrogen from the vacuum chamber;
Qwall puff – the hydrogen desorption from walls; ne – a
change of the average plasma density during the RF
discharge. An influence of radiation from the plasma on
desorption of hydrogen molecules from the walls in this
expression is not considered. Since during all operating
modes the ion and atom fluxes greatly exceed the values
of all other terms of the right-hand side of expression
(5), this expression can be simplified. Namely,
neglecting in (5) the terms of the smaller orders in
values we can estimate the average lifetime of
hydrogen ions in the plasma confinement volume during
the RF pulse length tRF from the following expression:
2
(1 )(1 )
2
pl e
RF
ch H
V n
K t
V n
, (6)
where K = JH/JH+ – the calculated ratio of the atomic JH
and ionic JН+ flux from the plasma. This expression is
correct if the ionization, charge-exchange and
dissociation of hydrogen particles do occur in the
volume of plasma confinement.
The results of Langmuir probe measurement of
plasma parameters outside of the plasma confinement
volume [9] and large enough average lifetimes of
hydrogen ions in the plasma 1 ms, according to our
estimates from (6), evidence the validity of such
assumptions. Otherwise, the average lifetime of ions
outside the plasma would be much smaller, as the
lifetime of ions outside the confinement volume is
defined by the time of flight of the ions to the walls
along the open magnetic field lines and does not exceed
(10…20) microseconds. In the case, where additional
ionization of the working gas occurs outside the
confinement volume, will characterize the average
lifetime of ions in all areas where ionization occurs.
The coefficient K can be evaluated qualitatively
from the rates of reactions and the average plasma
density for each mode. In the first mode, the electron
temperature and plasma density are Te (200…600) eV
and ne 2×1012 cm-3, respectively. In such a case the
hydrogen molecules entering into the plasma through
outer boundary are ionized to form molecular ions Н2
+,
which then immediately dissociate into ions Н+ and
atoms H, due to the high rates of ionization
H2+v (4…5)×10-8 cm3∙s-1 and dissociation
dis H2+v 1.2×10-7 cm3∙s-1, according to [10, 11]. The
free path length of hydrogen molecules in the plasma
does not exceed ~5 cm, i.e., << 2a. The dissociation
rate of hydrogen molecules, H
2
v < 9×10-9 cm3∙s-1, is
4…5.5 times lower than the rate of ionization. That is,
dissociation of hydrogen molecules in the plasma can be
neglected. The ionization rate of hydrogen atoms
H+v = (2.2…3.1)×10-8 cm3∙s-1 is almost 2 times less
than the ionization rate of molecules. The kinetic energy
of dissociated slow atoms (Franck-Condon atoms) is
E = (3…10) eV. At these energies, the average
concentration of slow atoms in the plasma column will
be much lower than the average concentration of the
molecules. Therefore, the ionization of atoms in the
plasma can also be neglected. The flux of fast charge-
exchange atoms with the kinetic energies E > 100 eV
depends on the concentration of slow hydrogen atoms in
the plasma. In turn, the concentration of slow hydrogen
atoms in the plasma is determined by dissociation of
molecular ions and also atoms reflected from the walls.
Because of gaps between helical coils and since the
reflection coefficient of atoms and ions from the walls
does not exceed ~60 %, the concentration of reflected
atoms in the plasma is 2…3 times lower than the
concentration of atoms produced by dissociation of
molecular ions. Therefore, the contribution of reflected
atoms in the ionization process in the plasma can also be
ignored. All other processes in the plasma were
negligible. In view of the above, it can be expected that
the ratio between the flux values of atoms and ions from
the plasma in the first mode K 1.
The averaged flux densities of hydrogen particles at
the plasma boundary in the case of the first mode are
shown in Fig. 4. These fluxes were computed with the
programming code KN1D [12]. In the model, used at
the quasi-stationary stage of the RF discharge, the flux
density of H2 molecules entering the plasma through its
boundary surface is balanced by the total density of
hydrogen particle fluxes leaving the plasma. The
leaving fluxes consist of H+ ions and neutrals: slow HL
atoms and fast charge-exchange HCX atoms. Other
fluxes were negligible. These results do not contradict
to the estimates presented above.
1,08
0,49
0,05
0,54
1 2 3 4
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
H
CX
H
L
H
+
j,
1
0
2
0
m
-2
s
-1
N
H
2
Fig. 4. The calculated averaged flux densities j of
hydrogen particles at the plasma boundary in the first
operation mode. №1 – flux density of hydrogen
molecules into the plasma; №2 – flux density of
hydrogen ions from the plasma; №3 – flux density of
slow hydrogen atoms from the plasma; №4 – flux
density of fast CX atoms from the plasma
In both, the second and third modes, the electron
temperature is Te 20 eV. At these electron
48 ISSN 1562-6016. ВАНТ. 2017. №1(107)
temperatures the rates of processes mentioned above are
[10, 11]: disH
2
+v 10-7 cm3∙s-1; H
2
+v 2×10-8 cm3∙s-1;
H
2
+v = 1.4×10-8 cm3∙s-1; H
2
v 9×10-9 cm3∙s-1. As
can be seen from these values, the dissociation of
hydrogen molecules and molecular hydrogen ions create
approximately the same amount of slow atoms in the
plasma. In the second mode, the plasma density is
ne 8×1012 cm-3. At this density, the free path length of
hydrogen atoms becomes comparable with the
transverse dimension of the plasma column 2a.
Therefore, the ionization of atoms begins to change
significantly the balance of hydrogen particles in the
plasma, increasing the ionic flux from plasma. In the
third mode, the ionization of atoms can be neglected.
The typical plasma density for this mode is
ne 1.5×1012 cm-3. Based on the foregoing, it can be
expected that in the second mode 1 < K 2, and in the
third mode K 2.
By measuring the temporal behavior of hydrogen
pressure in the U-3M vacuum chamber we evaluated the
average lifetime of hydrogen ions in confined plasma
for each operation mode. These times were: in the first
mode = (1…3) ms, in the second mode
= (10…20) ms, in the third mode 150 s.
CONCLUSIONS
A technique was developed to process the temporal
dependences of hydrogen pressure measured by
standard pressure sensors in the U-3M vacuum chamber
during plasma experiments. The obtained relations
allow to estimate the average lifetime of ions in the
confined plasma, the hydrogen pressure near the
plasma, as well as the value of reverse hydrogen
desorption from the walls of the U-3M vacuum chamber
during RF discharges. The lifetime of hydrogen ions in
the confined plasma was estimated for main operating
modes of U-3M.
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Article received 09.01.2017
МЕТОДИКИ ИЗМЕРЕНИЯ БАЛАНСА ВОДОРОДА В ВАКУУМНОЙ КАМЕРЕ ТОРСАТРОНА У-ЗМ
ВО ВРЕМЯ ПЛАЗМЕННЫХ ЭКСПЕРИМЕНТОВ
В.К. Пашнев, А.А. Петрушеня, В.Н. Бондаренко, Э.Л. Сороковой, Н.П. Пономаренко, Ф.И. Ожерельев
Разработана экспериментальная методика оценки баланса потоков частиц водорода во время ВЧ-
разрядов в торсатроне Ураган-3М (У-3М) в широком диапазоне рабочих параметров. Для измерения
нестационарного давления водорода в вакуумной камере У-3М были апробированы стандартные датчики
давления. Для каждого из рабочих режимов работы У-3М было определено среднее время жизни ионов
водорода.
МЕТОДИКИ ВИМІРЮВАННЯ БАЛАНСУ ВОДНЮ У ВАКУУМНІЙ КАМЕРІ ТОРСАТРОНА У-ЗМ
ПІД ЧАС ПЛАЗМОВИХ ЕКСПЕРИМЕНТІВ
В.К. Пашнєв, А.А. Петрушеня, В.М. Бондаренко, Е.Л. Сороковий, М.П. Пономаренко, Ф.І. Ожерельєв
Розроблено експериментальну методику оцінки балансу потоків частинок водню під час ВЧ-розрядів у
торсатроні Ураган-3М (У-3М) в широкому діапазоні робочих параметрів. Для вимірювання нестаціонарного
тиску водню у вакуумній камері У-3М були апробовані стандартні датчики тиску. Для кожного з робочих
режимів У-3М було визначено середній час життя іонів водню.
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