Electron sources for plasma electronics and different technological application
There are the following advantages of applying electron guns with plasma cathodes in devices exciting microwave radiation: stability of their parameters, high density of current, relative insensitivity to ion bombardment and the possibility of operating over a wide range of pressure values of a plas...
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| Zitieren: | Electron sources for plasma electronics and different technological application / V.S. Antipov, I.A. Bez’yazyshny, I.V. Berezhnaya, E.A. Kornilov // Вопросы атомной науки и техники. — 2002. — № 4. — С. 155-157. — Бібліогр.: 4 назв. — англ. |
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irk-123456789-803102015-04-15T03:02:21Z Electron sources for plasma electronics and different technological application Antipov, V.S. Bez’yazyshny, I.A. Berezhnaya, I.V. Kornilov, E.A. Plasma electronics There are the following advantages of applying electron guns with plasma cathodes in devices exciting microwave radiation: stability of their parameters, high density of current, relative insensitivity to ion bombardment and the possibility of operating over a wide range of pressure values of a plasma-generating gas [1-5]. The given work aims at constructing the guns with the parameters necessary for the excitation of microwaves of high amplitudes in the slow-wave structures: the beam energy is 20-30 kV, the current is up to 5 A, and the pulse duration is 0,11÷1 ms. The principal problem arising during construction of heavy-current electron sources with plasma emitters consists in the following: it is necessary to provide such conditions of the gas volume, under which the discharge firing would be stable and the emissive plasma generation be effective, whereas a gas breakdown in the accelerating gap must be eliminated. 2002 Article Electron sources for plasma electronics and different technological application / V.S. Antipov, I.A. Bez’yazyshny, I.V. Berezhnaya, E.A. Kornilov // Вопросы атомной науки и техники. — 2002. — № 4. — С. 155-157. — Бібліогр.: 4 назв. — англ. 1562-6016 PACS: 52.80.-s; 52.77.-j http://dspace.nbuv.gov.ua/handle/123456789/80310 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Plasma electronics Plasma electronics |
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Plasma electronics Plasma electronics Antipov, V.S. Bez’yazyshny, I.A. Berezhnaya, I.V. Kornilov, E.A. Electron sources for plasma electronics and different technological application Вопросы атомной науки и техники |
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There are the following advantages of applying electron guns with plasma cathodes in devices exciting microwave radiation: stability of their parameters, high density of current, relative insensitivity to ion bombardment and the possibility of operating over a wide range of pressure values of a plasma-generating gas [1-5]. The given work aims at constructing the guns with the parameters necessary for the excitation of microwaves of high amplitudes in the slow-wave structures: the beam energy is 20-30 kV, the current is up to 5 A, and the pulse duration is 0,11÷1 ms. The principal problem arising during construction of heavy-current electron sources with plasma emitters consists in the following: it is necessary to provide such conditions of the gas volume, under which the discharge firing would be stable and the emissive plasma generation be effective, whereas a gas breakdown in the accelerating gap must be eliminated. |
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Article |
| author |
Antipov, V.S. Bez’yazyshny, I.A. Berezhnaya, I.V. Kornilov, E.A. |
| author_facet |
Antipov, V.S. Bez’yazyshny, I.A. Berezhnaya, I.V. Kornilov, E.A. |
| author_sort |
Antipov, V.S. |
| title |
Electron sources for plasma electronics and different technological application |
| title_short |
Electron sources for plasma electronics and different technological application |
| title_full |
Electron sources for plasma electronics and different technological application |
| title_fullStr |
Electron sources for plasma electronics and different technological application |
| title_full_unstemmed |
Electron sources for plasma electronics and different technological application |
| title_sort |
electron sources for plasma electronics and different technological application |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2002 |
| topic_facet |
Plasma electronics |
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http://dspace.nbuv.gov.ua/handle/123456789/80310 |
| citation_txt |
Electron sources for plasma electronics and different technological application / V.S. Antipov, I.A. Bez’yazyshny, I.V. Berezhnaya, E.A. Kornilov // Вопросы атомной науки и техники. — 2002. — № 4. — С. 155-157. — Бібліогр.: 4 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT antipovvs electronsourcesforplasmaelectronicsanddifferenttechnologicalapplication AT bezyazyshnyia electronsourcesforplasmaelectronicsanddifferenttechnologicalapplication AT berezhnayaiv electronsourcesforplasmaelectronicsanddifferenttechnologicalapplication AT kornilovea electronsourcesforplasmaelectronicsanddifferenttechnologicalapplication |
| first_indexed |
2025-07-06T04:16:37Z |
| last_indexed |
2025-07-06T04:16:37Z |
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1836869639850688512 |
| fulltext |
ELECTRON SOURCES FOR PLASMA ELECTRONICS AND DIF-
FERENT TECHNOLOGICAL APPLICATION
V.S. Antipov, I.A. Bez’yazyshny, I.V. Berezhnaya, E.A. Kornilov
Institute of Plasma Electronics and New Methods of Acceleration NSC KIPT
There are the following advantages of applying electron guns with plasma cathodes in devices exciting microwave
radiation: stability of their parameters, high density of current, relative insensitivity to ion bombardment and the possi-
bility of operating over a wide range of pressure values of a plasma-generating gas [1-5]. The given work aims at con-
structing the guns with the parameters necessary for the excitation of microwaves of high amplitudes in the slow-wave
structures: the beam energy is 20-30 kV, the current is up to 5 A, and the pulse duration is 0,1 ÷ 1 ms.
The principal problem arising during construction of heavy-current electron sources with plasma emitters consists
in the following: it is necessary to provide such conditions of the gas volume, under which the discharge firing would
be stable and the emissive plasma generation be effective, whereas a gas breakdown in the accelerating gap must be
eliminated.
PACS: 52.80.-s; 52.77.-j
DETERMINING EMISSIVE PROPERTIES OF
PLASMA CATHODES
Hybrid plasma structures operate under the gas pres-
sure 10-4-10-3 mm Hg, whereas the thermocathode can
function under the pressure 10-6 mm Hg. Hence, some ad-
ditional powerful pumping out is required. Firing of the
gas discharge - in order to produce the plasma cathode un-
der the pressure 10-4-10-3 mm Hg - makes it necessary to
realize conditions for oscillations of electrons. As it is
planned to locate the plasma source inside the solenoid
of magnetic field, oscillations of electrons become possi-
ble only in the magnetron-type system of coaxial elec-
trodes [3]. The main our attention is given to investiga-
tions of this type of plasma sources from the viewpoint of
finding the optimal conditions for its steady operation in
the range of pressure values 10-4-10-3 mm Hg, which is re-
quired for the hybrid HF tube. The scheme of experimen-
tal investigations is presented in Fig. 1.
Fig 1. The scheme of experimental investigations.
1 is the magnetron anode, 2 is the magnetron cath-
ode, 3 is the butt-end emissive electrode,4 is the anode in
the accelerating gap, 5 is the collector, L1 is the longitudi-
nal size of the magnetron cell, L2 is the anode length; D1
and D2 are the cathode and anode diameters, correspond-
ingly; d0 is the accelerating gap size, and δ is the width of
annular emissive aperture.
The magnetron cell of discharge (discharge in the
crossed fields HE⊥ ) is formed with the stainless-steel
cylindrical cathode (the diameter 80 mm), the butt-end
electrodes and the anode. Sizes of the latter (its diameter
d and the length L ) are variable during the experiment.
The process of gas discharge burning is under control
through varying of electric voltage and the ballast resis-
tance in anode-cathode circuit, pressure and the kind of
gas, magnetic field voltage, the ratios d d1 2/ and
L L2 1/ as well as through connecting of the emissive
emitter 3 either to the cathode of magnetron or its anode.
The experiments are conducted in two regimes: 1. -
when d d1 2/ = l,14 and L L2 1/ = 0,9, and 2. -when
d d1 2/ = 4 and L L2 1/ = 0,9 ÷ 0,5. If L L2 1〈 〈 and the
electrode 3 is coupled with the anode 1, the regime of hol-
low cathode comes into existence in which magnetic field
is unnecessary for the electron oscillations. In the hollow
cathode, we have succeeded in firing of the discharge un-
der the pressure ~10-2 mm Hg, but high voltage ~5 kV is
necessary for its emergence. The requirement of high volt-
age and relatively high pressure for realization of the dis-
charge burning in the hollow cathode makes this device to
stay in the background. The attention is mostly paid to the
discharge firing in the coaxial magnetron cell. Regarding
the electron emission from the magnetron cell, it would be
better to get the same positive potential at both the exter-
nal and butt-end electrodes. Therefore, attempts are made
to firing of discharge in the modification where the cath-
ode is placed inside the anode. However, increase of volt-
age with the source available up to 5 kV causes discharge
firing only under the pressure ≥ 10-2 mm Hg in this case.
If the external electrode of magnetron cell is under the
negative potential (the inverse magnetron), the discharge
is easily set on fire under the field durability ≤ 1 kV in
the pressure range 10-4 - 10-3 mm Hg, in which we are in-
terested.
All facts considered, investigation of self-sustained
discharge of the «inverse- magnetron type» in crossed
E H⊥ fields deserves cardinal attention as in this case
the conditions for multiplying and oscillations of electrons
are the best. This discharge can be fired even in high vac-
uum (down to 10-10 mm Hg and its the most suitable for
our goal to obtain the electron beam with plasma emitter
operating under the gas pressure 10-4 mm Hg.
In Fig. 2, the curves of pressure- and gas-kind depen-
dences of the discharge voltage are presented for various
ratios of the cathode- to anode diameters. The curves 1, 2
Problems of Atomic Science and Technology. 2002. № 4. Series: Plasma Physics (7). P. 155-157 155
and 3 are obtained when d d1 2/ =1,14 and the curves 4,
5 and 6 are obtained when d1 /d2=4 ( for He, N2 and Ar,
correspondingly). As the graphs indicate, the minimum
pressure, under which the low-voltage glow discharge is
burning U b ≤ 500 V, decreases with the increase of the
ratio d1 /d2 and with the growth of the atomic number of
the working gas. In our experiment, it’s reduced down to
10-4 mm Hg in argon when d1 /d2=4. Under these condi-
tions the butt-end electrodes are mechanically and electri-
cally connected with the magnetron cathode - i. e., there is
the case of the magnetoelectrostatic confinement of elec-
trons generated in the discharge because of the gas ioniza-
tion and secondary electron emission from the cathode.
This regime is characteristic for the magnetrons applied as
vacuum meters [6] and electromagnetic traps.
0
500
1000
U , V
1
2
3
4
5
6
P ,
H
mmH g
10-4 10-3 10-2 10-1
Fig. 2. The dependence of the discharge voltage ver-
sus the plasma-generating gas pressure.
Experiments shows that when d1 /d2 =4, not only the
working pressure is decreasing, but also the magnetic field
voltage goes down; its minimum is 200 Oe. Thus, for this
discharge the magnitude of ( )pd
еf in Pashen curve
makes 0,1-1 - i.e., if p=10-4 mm Hg, the effective path
length of the electron reaches 103-104 cm. The current-
versus-voltage characteristic (CVC) of the discharge in
the heavy-current regime is demonstrated in Fig. 3 when
the pressure is 3*10-4 mm Hg and the parameters p, H and
d1 /d2 are optimized.
Duration of the diffusive stage of burning of the dis-
charge δ t is in the inverse proportion to the discharge
current (if t ≥ δ t , the discharge enters the arc stage).
As a matter of fact, for currents ≤ 10 A, the magnitude of
δ t could reach the value 10-3 sec after prolonged de-
gassing of the electrodes with discharges. For currents 〉
10 A, as a rule, the discharge duration doesn't exceed 50
µ s.
So, it’s found that the minimum pressure necessary
for discharge firing decreases as the ratio d1 /d2 increases;
it nonmonotonically depends on the magnetic field
strength. This is explicable with the fact that, as the d1/d2
increases, not only the distance between the electrodes
varies, but also the ratio of the anode- to cathode arias (in
our case, S Sa c/ =0,15 ).
0 4 8 12 16 20
0
400
800
1200
I , A
U, V
Fig. 3. The current-versus-voltage characteristic of
the discharge in the heavy-current regime.
Probably, diminution of the anode area can cause
prolongation of the electron life-time and, hence, the ion-
ization effectiveness increases as well. The following fact
also affirms this statement: the minimum pressure for the
discharge firing decreases as the L 2/L1 diminishes. How-
ever, it should be noted that the decrease of L2 / L1 down
to the value ≤ 0,5 worsens the characteristics of burning.
This could be conditioned by the fact that in this case the
discharge is burning only in the anode gap.
The results presented in this subsection demonstrate
that it’s easy to fire the gas discharge in the system of the
«inverse magnetron» -type in the low-voltage (U ≤ 1000
V) regime under low pressures (down to values of the or-
der of 10-4 mm Hg). In the gas discharge, plasma density
reaches the value ≈ 1012 cm-3 when the discharge cur-
rent is ~ 50 A. This plasma density can provide the elec-
tron emission with the current density ≈ 5 A/cm2 , which
is no worse than in modern powerful thermocathodes. Re-
alization of discharges under the given pressure is possi-
ble only in the case when the butt-end electrodes serve as
reflectors of electrons - i.e., in the regime of the magneto-
static confinement of plasma.
So, principal results of the investigations consist in
the following: a possibility of maintaining a self-sustained
gas discharge under pressures over the range 10-4-10-3 mm
Hg, which makes the necessary condition for operation of
hybrid plasma- filled slow-wave structures, does really ex-
ist. Hence, in principle, construction of the isobaric HF
tube with plasma cathode is possible.
The electron emission from a plasma cathode is real-
ized by applying a high voltage across the area between
the discharge cell and the accelerating electrode (the latter
is a grounded fine-mesh grid) through an opening in the
butt-end electrode (the discharge gap cathode) - see Fig.
2 in the section 2. The experiments are carried out in both
the cases when δ r ≤ lc d. . and δ r 〉 lc d. . ( δ r is the
aperture size). As it’s found, when the emission annular
aperture is ≈ 2-3 mm, is comparable with the size of lc d. .
, any essential emission of electrons from the magnetron
discharge isn’t observed. As a matter of fact, in the isobar-
156
ic gas regime under the pressure ≤ 10-3 mm Hg, the emis-
sion has been detected only when the circular aperture
with the diameter > 10 mm has been used - i.e., in the case
when δ r 〉 lc d. . . This regime corresponds to the emission
from a free plasma boundary. Another regime (when δ
r ≤ lc d. .
) could provide emission only by virtue of the
dip of the accelerating electrode voltage.
The curves in Fig. 3 depict the emissive ability of the
PSE of the inverse-magnetron type in the case of the in-
jection through the butt-end electrode under the cathode
voltage. The curves demonstrate the dependence of the
emission current versus the accelerating voltage for vari-
ous values of the discharge current. The curves 1, 2, 3 and
4 are obtained when Id = 2, 4, 6, and 8 A, corresponding-
ly (the emissive aperture diameter is 10 mm). The
injection efficiency, determined as α = I Iem d weakly
depends on the discharge current, being of the order of 0.2
- 0.25. The practically achievable duration of the injection
pulse varies from 0.5 ms up to 0.05 ms under the dis-
charge currents 10 A and ≥ 50 A, correspondingly. In the
latter case, the injection pulse duration is restricted by the
development of the discharge in the accelerating gap. The
discharge transition into an uncontrollable arc phase has
been observed under the discharge currents ≥ 100 A; it
doesn’t influence the injection pulse duration.
0 2 4 6 8 10
0.0
0.5
1.0
1.5
2.0
2.5
U ,k V
I , A
1
2
3
4
Fig. 4. The dependence of emission current versus
the accelerating voltage.
The empirical scaling j tem ⋅ ≤∆ 5*10-5 А/сm2*sec
is obtained. Under this conditions the emitter can reliably
operate in the pulse-periodic regime. So, with the plasma
cathode submitted, the current density 0.1-1 A/cm2 is
achievable, which suits the experimental investigations of
temperate-power microwave devices.
CONCLUSION
The results of the work can be formulated as follows:
1. In the systems of the «hollow cathode» - and «in-
verse magnetron» -types, the experiments on firing a gas
discharge and controlling its parameters are carried out.
They permit to determine the principal parameters of gas
discharges in the systems mentioned and optimize them
with respect to the minimum expenditure of the plasma-
generating gas and the minimum magnitudes of the elec-
tric and magnetic fields which are necessary for the dis-
charge burning. In the system of the «inverse
magnetron»-type, the firing and steady burning of the dis-
charge is realized: currents are up to 50 A in the low-volt-
age regime (U b ≤ 1000 V) under the gas pressure ≈ 10-4
mm Hg. Realization of such discharges is found to be pos-
sible only in the case when the butt-end electrodes reflect
electrons - i.e., in the regime of magnetoelectric retention
of electrons.
2. Experiments on electron emission from a plasma
discharge of the « classical inverse magnetron»-type have
been carried out. It’s demonstrated that under the low
pressure 10 -4 mm Hg the discharge can be used for con-
structing a plasma cathode of a circular aperture in the
butt-end electrode only in the case when the latter is con-
nected with the magnetron cathode in the case of the elec-
tron emission from the plasma free boundary. The emis-
sion through a circular aperture of the diameter 10 mm in
the butt-end has been obtained, the emissive current being
2 A under the voltage 20 kV. Such a system may be rec-
ommended for applying in a slow-wave structure of the
«chain of coupled cavities»-type in the investigations of
the isobaric mode of operation.
3. An annular electron beam of a large diameter has
been excited (the diameter is 80 mm, the rim is 5 mm); its
power is up to 200 kW (the accelerating voltage is 25 kV;
the injection current is 8 A) under relatively low pressures
of the working gas (~5*10-4 mm Hg).
4. These experiments are of the independent value
because the plasma cathodes are examined with respect to
their application in generators of microwave radiation and
other electron devices. As it should be especially noted,
the experimental data indicate that, in general, it’s possi-
ble to use plasma cathodes for realization of the isobaric
mode of operation of the microwave device when the plas-
ma-generating gas pressures could be equal in both the ar-
eas of discharge burning and beam-plasma interaction (hy-
brid slow-wave structures). This permits to construct a
hermetic modification of a powerful microwave device
without applying any of additional effective vacuum
pumps.
REFERENCES
1. Kervalishvili N.A., Jarinov A.V. //Sov. Phys.;
JTF, 35 (12), 2194-2201 (1965).
2. Gavrilov N.V., Zavialov M.A., Nikulin S.L.,
Ponomarev A.V. //Sov. Phys.: Pisma v JTF, 19
(21) (1993).
3. Ox E.M., Chaghin A.A. //Sov. Phys.: JTF, 61(6),
204-206 (1991).
4. Redhead P.A. \\Can. J. Phys, v. 43, 1965, p. 1001.
4. Azovsky Yu.S., Karpoukhin V.I., Lavrentiev O.A. //
Plasma Phys., v.6, №2, 256-262 (1980).
157
Determining emissive properties of plasma cathodes
Conclusion
References
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