Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices
The peculiarities of applying cathodes made of reversible getter hydride-forming alloys in the gasdischarge devices with crossed ExH fields have been revealed. It has been shown that the availability of such electrodes allows to realize a correlation between the intensity of working gas releasing an...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2000
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| Цитувати: | Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices / V.N. Borisko, I.A. Rudaya, I.N. Sereda // Вопросы атомной науки и техники. — 2000. — № 1. — С. 82-85. — Бібліогр.: 11 назв. — рос. |
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irk-123456789-816162015-05-19T03:02:31Z Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices Borisko, V.N. Rudaya, I.A. Sereda, I.N. Газовый рaзряд, ППР и их применения The peculiarities of applying cathodes made of reversible getter hydride-forming alloys in the gasdischarge devices with crossed ExH fields have been revealed. It has been shown that the availability of such electrodes allows to realize a correlation between the intensity of working gas releasing and the discharge parameters. The possibility for controlling erosion processes and heat regimes for the cathode materials has been shown to exist by initiating a controlled hydrogen desorption from the electrodes. 2000 Article Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices / V.N. Borisko, I.A. Rudaya, I.N. Sereda // Вопросы атомной науки и техники. — 2000. — № 1. — С. 82-85. — Бібліогр.: 11 назв. — рос. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/81616 533.9 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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Газовый рaзряд, ППР и их применения Газовый рaзряд, ППР и их применения |
| spellingShingle |
Газовый рaзряд, ППР и их применения Газовый рaзряд, ППР и их применения Borisko, V.N. Rudaya, I.A. Sereda, I.N. Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices Вопросы атомной науки и техники |
| description |
The peculiarities of applying cathodes made of reversible getter hydride-forming alloys in the gasdischarge devices with crossed ExH fields have been revealed. It has been shown that the availability of such electrodes allows to realize a correlation between the intensity of working gas releasing and the discharge parameters. The possibility for controlling erosion processes and heat regimes for the cathode materials has been shown to exist by initiating a controlled hydrogen desorption from the electrodes. |
| format |
Article |
| author |
Borisko, V.N. Rudaya, I.A. Sereda, I.N. |
| author_facet |
Borisko, V.N. Rudaya, I.A. Sereda, I.N. |
| author_sort |
Borisko, V.N. |
| title |
Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices |
| title_short |
Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices |
| title_full |
Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices |
| title_fullStr |
Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices |
| title_full_unstemmed |
Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices |
| title_sort |
peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2000 |
| topic_facet |
Газовый рaзряд, ППР и их применения |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/81616 |
| citation_txt |
Peculiarities of applying reversible hydrogen getters as materials for athodes in gas discharge devices / V.N. Borisko, I.A. Rudaya, I.N. Sereda // Вопросы атомной науки и техники. — 2000. — № 1. — С. 82-85. — Бібліогр.: 11 назв. — рос. |
| series |
Вопросы атомной науки и техники |
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2025-07-06T06:48:50Z |
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2025-07-06T06:48:50Z |
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| fulltext |
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ 2000. №1.
Серия: Плазменная электроника и новые методы ускорения (2), с. 82-85.
82
UDK 533.9
PECULIARITIES OF APPLYING REVERSIBLE HYDROGEN GET-
TERS AS MATERIALS FOR CATHODES IN GAS DISCHARGE
DEVICES
V. N. Borisko, I. A. Rudaya, I. N. Sereda
Kharkov National University. Physical technical department.
61108, 31 Kurchatov av., Kharkov,Ukraine
The peculiarities of applying cathodes made of reversible getter hydride-forming alloys in the gas-
discharge devices with crossed ExH fields have been revealed. It has been shown that the availability of
such electrodes allows to realize a correlation between the intensity of working gas releasing and the dis-
charge parameters. The possibility for controlling erosion processes and heat regimes for the cathode ma-
terials has been shown to exist by initiating a controlled hydrogen desorption from the electrodes.
In systems of gas feeding for various plasma and
energy physical devices using hydrogen isotopes as a
working gas, the gas is generally injected into a dis-
charge chamber from a tank through Pd or Ni accu-
mulators which clean hydrogen from various gaseous
impurities [1]. Recently, in the above systems, solid-
state gas generators based on binary hydrides of such
metals as Ti, Zr, Sc, Er, U, etc. have been widely used
[2]. First of all, the advantages of those generators are a
high purity of the gas injected (99,99 – 99,999%),
along with the safety and compactness in storage. How-
ever, intermetallic compounds of the ST-707 and ST-
172 type based on Zr-V, Zr-V-Fe, capable to absorb
hydrogen reversibly, which were developed in Italy by
“SAES Getters” Company [3, 4], allow to design uni-
versal gas supplying systems that combine the functions
of not only a working-gas generator but a getter as well.
At room temperatures, such intermetallic compounds
exhibit the equilibrium pressure not exceeding 1 – 10
Pa, the dynamics of sorption-desorption and hydrogen
capacity being improved. The decomposition of the
hydride phases of the above materials allows to provide
for filling hydrogen isotopes in the range of working
temperatures 400 – 900 K, and t
he gas itself releases uniformly. The feature pecu-
liar to those compounds is a decrease in the ionization
potential of hydrogen generated by 0,3 – 0,5 eV caused
by the recombination of hydrogen atoms at the metal-
hydride surface following by the desorption of the
molecules in the excited and thermodynamically non-
equilibrium state [5, 6].
In recent years, the possibility for applying such
materials as electrodes in gas discharge devices has
been investigated [2, 7]. It has been found that the
availability of the metal-hydride electrodes saturated
with hydrogen decreases the combustion voltage in the
self-maintained glow discharge which results from
increasing in the hydrogen ionization cross-section by a
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U
(V
)
H (Oe)
200 300 400 5
50
100
150
200
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300
21
I (
m
A)
U (V)
Fig.1a. The ignition curves of reflecting dis-
charge.
1 – cathode from metal-hydride.
2 – cathode from stainless steel.
Fig.1b. Current–voltage characteristics of mag-
netron discharge.
1 – cathode from stainless steel.
2 – cathode from metal-hydride.
a
b
83
factor of 1,3 to 1,5 as compared to common molecular
hydrogen from a tank. It has been also shown by mass-
spectrography methods that in this case, the properties
of the discharge gas phase change: the shares of H+
and H+
3 enhance relative to the content of the molecular
ions H+
2. However, the plasma parameters and the
processes in plasma have not been studied. Besides, the
investigations were only performed in the glow
discharge, and some of the experimental results
obtained were not simply interpreted and are of a
contradictory character. Here, we summarize the
experimental data presented on the influence of the
metal-hydride cathode saturated with hydrogen on the
gas-discharge characteristics, as well as the influence of
the discharge plasma on the gas-emission properties of
that electrode. The investigations were carried out in
the discharges with crossed electrical and magnetic
fields: the Penning and planar magnetron discharges.
The discharge cathodes were made of the getter
hydride-contained alloy Zr55V40Fe5 modified with 3
mass percent B2O3 . For reference measurements, the
cathodes from molybdenum or stainless steel were
used. The two types of the discharge were investigated
in the hydrogen medium, both in self-consistent in
pressure regime [8, 9], in which case the increase in
discharge current due to the power introduced into the
discharge results in the increase in the hydrogen
pressure inside the chamber, and the decrease in the
above current lowers the pressure; and in the flow of
hydrogen. Studies on the conditions for the existence of
the discharge of both types in cases of applying the
cathodes made of metal-hydrides or stainless steel,
revealed that, unlike the findings of the previous
authors, while the external parameters being the same,
the ignition of the discharge with metal-hydride
cathodes was worse than that with stainless steel ones,
and the discharge voltage exceeded a similar value for
the reference discharge (Fig. 1). The reasons are as
follows. The cross-section for the process of
dissociative adhesion of the low-energy electrons to the
oscillatory excited molecules of the working gas is
inversely proportional to the electron energy and
increases also with increasing the oscillation quantum
number of molecules [10]. Near the cathode, electrons
have a minimal energy which fact is connected with
turning the trajectories of the oscillating electrons in the
reflecting discharge, as well as with the emission of the
low-energy secondary electrons resulting from the ionic
bombardment of the cathode. On the other hand, the
metal-hydride cathode saturated with hydrogen
desorbes the molecules which are already in the
oscillatory excited state. Therefore, these processes
near the cathode lead to the significant increase in the
cross-section for generating the negative ions and, as a
consequence, to the deterioration of the ignition and
increase in the discharge-supporting voltage. To verify
the above assumption, a possibility for creating a
source of the negative hydrogen ions which could use
the reflective discharge with a metal-hydride cathode
for a plasma-forming stage has been investigated [11].
The comparative analysis performed on the negative
hydrogen ions yield in case of using the cathodes made
of a hydride-forming material and stainless steel
showed that the usage of the above intermetallic
compounds allowed to enhance significantly the current
in the H-beam. The mass-spectrometry of the neutral
plasma component in the magnetron discharge burning
in hydrogen atmosphere which is desorbed from the
metal-hydride cathode showed that the insertion of such
a compound into the cathode of a gas-discharge device
changed markedly the composition of not only the main
plasma gas component but also the impurity one, i. e. in
this case, various plasma-chemical reactions involving
hydrogen are stimulated [9]. The changes in the com-
position of the gas-phase impurities are not connected
with the emission of the hydrogen atoms from the
0 20 40 60 80 100
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(P
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I (mA)
Fig.2a. Magnetron discharge. Dependence of
hydrogen pressure in gas discharge devices.
1 – cathode from metal-hydride.
2 – cathode from stainless steel.
Fig.2b. Reflecting discharge. Dependence of
hydrogen pressure (P) and metal-hydride cath-
ode temperature (T) on the discharge current
value.
a b
84
metal-hydride cathode surface, i. e. such a cathode also
features the catalytic activity in reactions accompanied
with the hydrogen transmission.
Fig. 2 displays the dependence’s of the working-
gas pressure on the discharge current for discharges
operating in the autostable in pressure regimes. For
comparison, in Fig. 2a, curve 2, the change in the
hydrogen pressure in the discharge chamber with a
stainless steel cathode is plotted. From Fig. 2 it can be
seen that in a magnetron discharge, the presence of a
metal-hydride cathode leads to the significant change in
pressure in the discharge chamber, and the dependence
itself is linear. For the reflecting discharge, when one of
the cathodes was made of the metal-hydride saturated
with hydrogen and the other was made of stainless
steel, the above dependence is non-linear at low
discharge currents (up to 50mA) and near - linear at Id >
50mA. The reason is that the mechanism of the
interaction between cathodes and discharge gas phase is
changed. Within the low discharge current range, the
dispersion of the cathode material made of stainless
steel by high-energy particles and the absorption of
hydrogen by the resultant film are crucial. However, as
the discharge current and, consequently, the
temperature of the cathodes enhance, the role of the
hydrogen desorption from the metal-hydride cathode is
growing (Fig. 2b) The plasma parameters for the
discharges of both types were determined by the probe
technique. In the planar magnetron discharge, the
measurements were performed at the height of 0,5cm
under the anode section in the points positioned under
the area of plasma beam location.
The electron temperatures in the discharges with
the cathodes of both types appeared to be the same: Te
~ 2eV. However, the dependence’s of the plasma den-
sity on the discharge current significantly differed (Fig.
3).
In case of discharge with the metal-hydride cath-
ode, the plasma density was monotonously growing as
the discharge current increased, whereas for the refer-
ence discharge, the tendency for saturation was ob-
served.
The presence of the metal-hydride cathode causes
the gas density within the near-cathode region to be
determined by the dynamical equilibrium between
sorption and desorption processes which depends on
the temperature and hydrogen-sorbing characteristics of
the hydride-forming material. Therefore, in this regime,
increasing the hydrogen pressure, as the discharge
current is rised, is accompanied by increasing the gas
density in the discharge chamber. The resultant gain in
the rate of collisions between electrons
and neutral particles leads both to the intensive ioniza-
tion processes and to the enhancement of the diffusive
electron flow from the area of the plasma beam local-
ization. For this reason, the increase in the discharge
current with the metal-hydride cathode is accompanied
by the rise in the plasma density beyond the electro-
magnetic trap. The investigation on the spatial distribu-
tion of the plasma parameters within interelectrode
clearances in the Penning discharge for
cathodes made of stainless steel and hydrogen-saturated
metal-hydride showed that both the space potentials
and the electron temperature did not depend on the
cathode material. However, within the near-cathode
areas, the plasma densities are observed to differ by a
factor of 2 - 3. In the area of the metal-hydride cathode,
the plasma density is slightly lower which fact seems to
be connected with the processes of recharging positive
ions at the molecules of hydrogen desorbed from that
cathode.
The explorations on the dispersing of the metal-
hydride cathodes in the regime of hydrogen desorption
were carried out. The cathodes were irradiated with
argon and hydrogen ions with energies (0,5 - 5) keV
and current densities (10 - 100) mA/cm2
. The analysis
revealed the significant decrease in the erosion as com-
pared to the dispersion of the same materials with no
desorption. As can be seen from Fig. 2, the hydrogen
desorption from the metal-hydride cathodes has a
unique functional dependence on the discharge current.
In other words, the bombardment of the discharge of
the metal-hydride cathode with high-energy plasma
particles is an effective tool for controlling the gas-
emission regime of its operating. As a result, close to
the cathode surface, the protective gas target is formed
which reduces markedly the erosion of the material due
to the dissipation on it of the particle-beam energy.
In the Penning discharge, the temperature of the
cathodes was controlled by thermocouples, one of the
electrodes being made of the metal-hydride saturated
with hydrogen and the other being made of stainless
steel. The increase in the discharge current was ob-
served to slow down the growth in the temperature of
the metal-hydride cathode (Fig. 2b, curve T). The
analysis of the thermal balance showed that the major
portion (up to 70%) of the heat energy released at the
0 100 200
0
5
10 2
1
n
x
10
9 (
c
m
-3 )
I (mA)
Fig.3. Dependence of plasma density on the
discharge current value.
1 – control discharge.
2 – discharge with metal-hydride cathode.
85
cathode was expended on the desorption of gaseous
hydrogen. Such a softening of the thermal regime dur-
ing the operation of the electrodes made using reversi-
ble hydrogen sorbents with high rates and large thermal
effects of sorption-desorption was achieved due to both
the heat decomposition of the hydride phases and en-
ergy dissipation of the particle beams on the gas target
which was formed with the hydrogen desorbed.
Fig.4. Dependence of metal-hydride temperature
(1) and difference of temperatures between cath-
odes (2 – metal-hydride – stainless steel, 3 – metal-
hydride – metal-hydride) on the exposition time.
The dependence of the difference between the op-
erating temperatures for the cathodes on the exposition
time for the bombarding the hydrogen particles with the
energy 2,5 kV and current density 5 mA/cm2
plotted in
Fig. 4 shows that the temperature of the metal-hydride
cathode is significantly lower than that of the stainless
steel one, and in case of using two metal-hydride cath-
odes, a minor temperature difference is observed only
during the first 15 minutes of the discharge operation,
then it completely disappears.
As a result of the studies performed, it has been
shown that applying the reversible sorbents of hydro-
gen at a low pressure with high rates and large thermal
effects of sorption-desorption allows to reduce signifi-
cantly the rates of their dispersion by the plasma ions as
well as to lower the heat load for those materials. The
above effect is achieved due to creating the protective
gas target as a result of both thermal decomposition of
the metal-hydride and ionic stimulated desorption. The
influence of the plasma beams upon those cathodes
stimulates the hydrogen desorption from the electrode
immediately into the operation zone of the plasma-
forming stage which fact provides a return coupling
between the intensity of the gas emission and parame-
ters of the gas discharge.
The application of the reversible hydrogen getters
as cathodes for the plasma sources of the negative ions
permits to enhance significantly the negative ion yield
owing to the desorption of the molecules in the oscil-
latory excited state from those materials.
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ionov vodoroda // Visnik HGU, Ser. Yadra, chastinki,
polya. №421, p. 146–148.
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