Generating of low energy intensive ion streams in conditions of low pressure
In the work the method of forming of low energy ion streams near the sample surface with separating the generation area of plasma and the acceleration area of ion is offered. It allows to lower pressure in acceleration area essentially (0.01 Pa and below). The separating of the areas takes place at...
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| Date: | 2000 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2000
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| Cite this: | Generating of low energy intensive ion streams in conditions of low pressure / D.V. Zinoviev, A.F. Tseluyko, A.G. Chunadra, N.N. Yunakov // Вопросы атомной науки и техники. — 2000. — № 6. — С. 103-105. — Бібліогр.: 3 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860004914145525760 |
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| author | Zinoviev, D.V. Tseluyko, A.F. Chunadra, A.G. Yunakov, N.N. |
| author_facet | Zinoviev, D.V. Tseluyko, A.F. Chunadra, A.G. Yunakov, N.N. |
| citation_txt | Generating of low energy intensive ion streams in conditions of low pressure / D.V. Zinoviev, A.F. Tseluyko, A.G. Chunadra, N.N. Yunakov // Вопросы атомной науки и техники. — 2000. — № 6. — С. 103-105. — Бібліогр.: 3 назв. — англ. |
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| container_title | Вопросы атомной науки и техники |
| description | In the work the method of forming of low energy ion streams near the sample surface with separating the generation area of plasma and the acceleration area of ion is offered. It allows to lower pressure in acceleration area essentially (0.01 Pa and below). The separating of the areas takes place at the expense of vacuum resistance in a plasma generating device. The dependence of plasma parameters on exterior parameters of the device is determined and the way of the further decreasing of working pressure in the modification area up to 10⁻³ – 10⁻⁴ Pa are shown.
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| first_indexed | 2025-12-07T16:38:24Z |
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103 Problems of Atomic Science and Technology. 2000. № 6. Series: Plasma Physics (6). p. 103-105
UDC 533.915
GENERATING OF LOW ENERGY INTENSIVE ION STREAMS IN
CONDITIONS OF LOW PRESSURE
Zinoviev D.V., Tseluyko A.F., Chunadra A.G., Yunakov N.N.
Kharkov National University, 31 Kurchatov ave., Kharkov, 61108, Ukraine
In the work the method of forming of low energy ion streams near the sample surface with separating the
generation area of plasma and the acceleration area of ion is offered. It allows to lower pressure in acceleration area
essentially (0.01 Pa and below). The separating of the areas takes place at the expense of vacuum resistance in a
plasma generating device. The dependence of plasma parameters on exterior parameters of the device is determined
and the way of the further decreasing of working pressure in the modification area up to 10-3 – 10-4 Pa are shown.
INTRODUCTION
In resent years the range of ion source application in
various fields of science and industry has been
extended. In this connection the active research work in
making and perfecting of ion sources with different
parameters is being carried out.
Ion sources of low energies (with energy up to
1000 eV) are of great interest. It is linked, from the one
hand, with wide implementation of new materials in
industry, which handling owing to radiative damages
does not allow use of high-energy ion beams. On the
other hand, the energy of reacting particles at a level of
tens electron-volt is necessary for synthesis of new
materials with unique properties in conditions of
plasma-chemical conversion.
One of the simplest ways of making intensive low
energy ion beams is the method of ion stream forming
from plasma immediately at a modified surface. In this
case ion stream is formed at the expense of a potential
difference between plasma and negatively charged
surface [1].
Main problem at use of this method is making dense
plasma in working volume. As a rule, for this purpose
the plasma generators based on some type of gas
discharge are used. For steady-state combustion of the
discharge it is necessary to support increased working
pressure in the modification region, that is an essential
limitation of this method.
So, for the extraction of intensive ion streams (with
the ion current density about tens mA/cm2) it is
necessary to create the dense plasma (with the
concentration 1012–1013 particles/cm3) in the plasma
generator. In this connection the working gas pressure
in the device is necessary to support at a level 10-3 Torr.
Such pressure for many problems is intolerably high.
The decreasing of working gas pressure leads first, to
astable burning of the discharge and second, to reducing
of plasma concentration, and consequently to reducing
of ion current density.
In this paper for decreasing working pressure in the
modification region with keeping of ion stream intensity
on a surface the method is offered, in which the zone of
plasma production and zone of ion stream formation are
separated in plasma production volume through the
vacuum resistance. On the basis of theoretical and
experimental results the efficiency of application of this
method for forming low energy ion streams is shown.
PRINCIPLE OF THE DEVICE OPERATION
The principle scheme of the device operation is
submitted in Figure. The working gas ionization is
carried out in a metal discharge tube of the extended
configuration and the diameter of 40 mm through a
primary electron beam. The primary electron beam is
formed by an electron gun with hot cathode, which is
located in a discharge tube end face. The gun anode is a
discharge tube wall, which is under an earth potential.
For decreasing losses of electrons on the discharge tube
walls the plasma column is contained by a longitudinal
magnetic field with intensity maximum in the middle of
discharge tube. A primary electron beam forming takes
place in a double electrical layer at the hot cathode
surface.
The working gas is inleted into the electron gun
area. The gas pumping is yielded through a vacuum
chamber. At the expense of vacuum resistance of a
discharge tube interior cavity there is a pressure
Figure. The principle scheme of the device
operation
EG
Electron gun Discharge tube
Modification
zone
Р
Pressure distribution
L0
Н
Plasma
column
Pumping
Gas inlet
Ji(0) J Li( )z
104
difference between an electron gun and vacuum
chamber. The discharge tube length was chosen such,
that at known pump speed of the used high-vacuum
device to ensure a pressure drop between an electron
gun field and modification area in 15 times. Such
difference is explained by that the working range of
pressures for the discharge with hot cathode is at a level
10-3 Torr, and necessary in our case pressure is
10–4 Torr and lower in a modification zone.
In the assumption of a molecular mode of gas flow
the estimation of anode cavity vacuum resistance was
yielded with the help of expression for gas conductance
of the round section short tube [2]
( )ldMTdU aa += 33,11,38 3 , (1)
where U is gas conductance of the tube [m3/s], d is the
tube internal diameter [m], l is the tube length [m], Та is
the gas temperature [°К], Ма is the gas molecular weight
[atomic mass unit].
To pressure drop p = рg – рm between the electron
gun zone рg and the modification area рm corresponds
the gas stream Q = U (рg – рm). For pump speed of the
high-vacuum device S and pressure рm the stream Q is
determined by expression Q = S⋅рm. Using relations (1),
we gain
d
M
T
p
p
S
dl
a
a
3
411,38
m
g
3
−
−= . (2)
In our case for an argon at a pressure drop pg/pm = 15
and the vacuum chamber pump speed S = 380 L/s the
anode tube length value is l = 19 cm.
In a longitudinal nonhomogeneous magnetic field at
presence of a great concentration gradient plasma runs
out into the vacuum chamber working volume in
reduced pressure area. The carried out measurings have
shown, that on an exit from a discharge tube ion current
density was 15–20 mA/cm2 at the discharge current of
2–3 A and the discharge voltage 30–400 V.
DEVICE WORK EFFICIENCY
The efficiency of ion use in this type plasma
generator is viewed in magnetoplasmadynamics
approach for one-dimensional case. Thus it was taken
into account, that the ion generation in volume happens
both at the expense of beam primary electrons, and at
the expense of plasma electrons. It was supposed that
the ion drifting from a disruptive gap happens only
through end faces of the system along a magnetic field.
The electron drifting in a radial direction can be
neglected, as the magnetic field hold electrons well in a
transverse direction, and those, in turn, by bulk charge
retain ions from a transverse displacement. For viewing
simplicity the magnetic field inhomogeneity in an anode
tube disruptive gap was not taken into account.
From the account of the entered assumptions the
continuity equation for a stationary case looks like
( ) peipbeibii nnvn γ+γ=
!
div , (3)
where ni is the ion density in a sectional space point; iv!
is the ion velocity; γib is the frequency of neutral gas
ionization by beam electrons; nbe is the beam electron
density; γip is the frequency of neutral gas ionization by
plasma electrons; npe is the plasma electron density.
As γib = vbe/λbe and λbe = 1/ n0(z)⋅ iσ , where vbe is
the beam electron velocity; λbe is the ionization free
length; n0(z) neutral gas atom concentration; iσ is the
medial section of neutral atom ionization by beam
electrons, so
( ) bebeibei nvznn σ=γ 0 .
Considering, that the plasma is quasi-neutral, i.e. npe
≈ ni from (3) it follows
( ) ( ) ( )znnvznvn iipbebeiii γ+σ= 0div
! . (4)
In view of that vbe nbe = Je/e, where Je is the current
density of primary electrons from a hot cathode, е is the
electron charge, and Jbe from a Langmuir relation for a
double layer is defined as
( ) eipibe mMJJ 0β= , (5)
where Jpi is the ion current density through a double
layer; Mi is the ion mass; me is the electron mass; β is
the coefficient taking into account free and not free
modes of discharge burning (0 < β < 1) [3], and as in the
assumption, that the ion drifting across a magnetic field
is missed, the equation (4) becomes
( ) ( ) ( ) iipieiiizi neJmMznvn
zd
d
γ+σβ= 00 . (6)
After integration on z from 0 up to L, where L is the
discharge tube length
( ) ( ) dzndzzn
m
M
e
J
vn
L
iip
L
e
ii
i
L
izi ∫∫ γ+σβ=
00
00
0
, (7)
( ) ( ) ( ) ( )
( ) ( ) ( ) ( )dvvfvvznzn
dvvfvvznzn
epep
v
ii
epepi
v
iip
ie
ie
∫
∫
∞
∞
σ=
=σ=γ
0
0
.
Taking into account, that
e
J
vn i
izi = and
( ) Lndzzn
L
0
0
0 =∫ , where Ji is common ion stream (on
the cathode and in a vacuum chamber) and at a linear
relation of neutral atom concentration on the discharge
tube length ( ) ( )( ) 20000 nLnn += ( 0n is the average
on length neutral atom concentration), equation (7)
becomes
105
( ) ( )( ) ( ) ( ) ( ) dznndvvfvvnL
m
M
J
e
JLJ
e
L
iepep
v
i
e
i
iiii
ie
0
0
2
00101
∫⋅∫ σ+σβ=+
∞
,
where Ji (L) is the ion stream on the discharge tube exit, Ji (0) is the ion stream at the cathode. Or,
( )
( ) ( ) ( ) ( ) dz
J
nne
dvvfvvnL
m
M
J
LJ L
i
i
epep
v
i
e
i
i
i
i
ie
∫∫ ⋅σ+−σβ=
∞
0
0
2
0 0
1
0
As well as ( ) ( ) akTLpLn =0 , ( ) ( ) akTpn 000 = and ( ) ( )( ) 20000 nLnn += we receive
( )
+=
U
S
kT
Lpn ’
a 2
10 .
Then the last equation becomes
( )
( )
( ) ( ) ( ) ( ) dz
J
nne
dvvfvv
U
S
kT
LpL
m
M
J
LJ L
i
i
epep
v
i
ae
i
i
i
i
ie
∫∫ ⋅σ+−
+σβ=
∞
0
0
2
0
1
2
1
0
.
As the last term of the expression is always more then 0,
the account of ionization at the expense of plasma
electrons increases a relation Ji (L) /Ji (0). Without the
account of the contribution of plasma electrons into
ionization the simplified estimate of the bottom of ion
use efficiency looks like
( )
( )
( )
1
2
1
0
−
+σβ=
U
S
kT
Lp
m
ML
J
LJ
ae
i
i
i
i . (8)
RESULTS AND DISCUSSION
The expression (8) displays the relation of an ion
stream on the exit from the plasma generator to an ion
stream on the gun cathode necessary for the discharge
maintenance (forming of a double layer at the cathode).
It is well visible, that Ji(L) directly proportional depends
on sorts of working gas, the discharge tube length, and
the pressure on the exit from the plasma generator and
the vacuum chamber pump speed.
Knowing Ji(0), it is possible to estimate
quantitatively the ion current density Ji(L). At a
thermionic current equal 2 A and cathode diameter of
18 mm the ion current density on the cathode for a free
mode of the discharge combustion (β = 1) in argon
medium from (7) in our case makes ∼ 3 mA/cm2. Then
from (9) for the discharge tube length L = 19 cm,
pressure in the chamber p(L) = 2⋅10-4 Torr and the pump
speed S = 0,38 m3/s ion current density on the exit Ji(L)
makes 550 mA/cm2.
The overflow of a theoretical estimation above
experimental values is stipulated by that the ion streams
of great intensity are obtained experimentally to not free
mode of discharge combustion, when the Langmuir
relation is not executed (β << 1). At use of a discharge
free mode the theoretical estimations almost coincide
with the experimental ones, but the ion stream intensity
on the exit in this case made less than 1 mA/cm2.
Thus, in the work the simple method of forming of
intensive ion beams in conditions of low pressure in a
modification zone (10-4 Torr and below) is offered. At
increasing of pump speed or discharge tube length it is
possible to decrease pressure essentially (up to 10-6 Torr
and below). In our experiments, at increasing of pump
speed for a short time (up to 15 s) at the expense of
thermal evaporation of metal in the vacuum chamber,
ion current density on the exit was steadily supported at
a level of 20 mA/cm2 at pressure 2⋅10-6 Torr.
REFERENCES
1. D.V. Zinoviev, A.F Tseluyko et al. The formation of
low energy ion beams in the arc discharge // J. Tech.
Phys. XL. 1999, .№ 1, P. 263.
2. E.S. Frolov and V.E. Minaichev. Vacuum
Technology. Moskow: “Mashinostroenie”, 1985, p. 38.
3. S. D. Gvozdover, in Electric current in gas. Steady-
state current, edited by V. L. Granovski. Moskow:
“Nauka”, 1971, pp. 336-341.
UDC 533.915
Kharkov National University, 31 Kurchatov ave., Kharkov, 61108, Ukraine
I
INTRODUCTION
PRINCIPLE OF THE DEVICE OPERATION
RESULTS AND DISCUSSION
REFERENCES
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| id | nasplib_isofts_kiev_ua-123456789-78537 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T16:38:24Z |
| publishDate | 2000 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Zinoviev, D.V. Tseluyko, A.F. Chunadra, A.G. Yunakov, N.N. 2015-03-18T18:38:15Z 2015-03-18T18:38:15Z 2000 Generating of low energy intensive ion streams in conditions of low pressure / D.V. Zinoviev, A.F. Tseluyko, A.G. Chunadra, N.N. Yunakov // Вопросы атомной науки и техники. — 2000. — № 6. — С. 103-105. — Бібліогр.: 3 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/78537 533.915 In the work the method of forming of low energy ion streams near the sample surface with separating the generation area of plasma and the acceleration area of ion is offered. It allows to lower pressure in acceleration area essentially (0.01 Pa and below). The separating of the areas takes place at the expense of vacuum resistance in a plasma generating device. The dependence of plasma parameters on exterior parameters of the device is determined and the way of the further decreasing of working pressure in the modification area up to 10⁻³ – 10⁻⁴ Pa are shown. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Plasma dynamics and plasma-wall interaction Generating of low energy intensive ion streams in conditions of low pressure Article published earlier |
| spellingShingle | Generating of low energy intensive ion streams in conditions of low pressure Zinoviev, D.V. Tseluyko, A.F. Chunadra, A.G. Yunakov, N.N. Plasma dynamics and plasma-wall interaction |
| title | Generating of low energy intensive ion streams in conditions of low pressure |
| title_full | Generating of low energy intensive ion streams in conditions of low pressure |
| title_fullStr | Generating of low energy intensive ion streams in conditions of low pressure |
| title_full_unstemmed | Generating of low energy intensive ion streams in conditions of low pressure |
| title_short | Generating of low energy intensive ion streams in conditions of low pressure |
| title_sort | generating of low energy intensive ion streams in conditions of low pressure |
| topic | Plasma dynamics and plasma-wall interaction |
| topic_facet | Plasma dynamics and plasma-wall interaction |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/78537 |
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