Radiant energy – Ion generation – Field ionization type
Reexamination Certificate
1999-05-20
2001-07-10
Anderson, Bruce C. (Department: 2881)
Radiant energy
Ion generation
Field ionization type
C315S111210, C315S111810, C315S111910, C313S359100, C313S361100, C313S362100
Reexamination Certificate
active
06259102
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to a direct current steady-state gas-discharge Ion-Beam Source of Anode Layer type (IBSAL) for application as an ion thruster in space technology and for application in various kinds of plasma processing technology. More specifically, the present invention is related to a direct current gas-discharge Ion-Beam Source of Anode Layer type with a quadrupole magnetic system trapping an operating plasma and separating the ions from the electrons in a gas-discharge plasma produced by a quasi-closed (or closed) electron drift into crossed electric E and magnetic H fields.
BACKGROUND OF THE INVENTION
Direct current gas discharge Ion-Beam Sources with a Magnetic Layer (IBSML) and with an Anode Layer (IBSAL) are widely used in space and in an ion-beam processing technology: as thrusters in the space technology (IBSML), and as ion-beam sources in Protective Over-coats, In-situ Cleaning, Ion-assisted Deposition, Optical Coatings, Enhanced Sputtering, etc. in industrial ion beam processing technologies (IBSML, IBSAL).
These families of Ion-Beam Sources offer a simplicity in design and maintenance, increased reliability at a decreased maintenance cost, long life (theoretically an infinitesimally long life) with application of a commercially available power supply. The cross-section of an Ion-Beam Source with an Anode Layer is shown schematically in FIG.
3
. It comprises a planar long anode
1
of a conductive non-magnetic material mounted on a magnetoconductor
2
of low-carbon steel by insulators
5
, two long magnetoconductive poles
3
, and a continuation of the magnetoconductor
2
positioned symmetrically above and along the anode
1
with a permanent discharge gap between the anode surface and the poles and with a permanent magnetic gap between the mentioned poles, and a permanent magnet
4
positioned between the pole
3
and the magnetoconductor associated with the pole
2
.
The operating voltage is applied between the anode
1
and the poles
2
,
3
used as a cathodes and grounded in standard applications. The Ion-Beam Source with the cross-section shown in
FIG. 3
could be formed of any length. However, both the ends of this Ion-Beam Source should be connected to one another in order to have an uninterrupted closed magnetic gap above an uninterrupted closed anode surface under uninterrupted surfaces of the magnetic poles. This requirement of the closeness of the Ion-Beam Source elements is a consequence of the condition of a closeness of an electron drift in the crossed electrical E and magnetic H fields formed by the surface of the anode
1
together with the surfaces of the poles
2
and
3
serving as the cathodes. Indeed, if one were to form the crossed electrical E and magnetic H fields in accordance with the configuration of the electrodes and poles shown in FIG.
3
(
a
), one can expect the drift of the electrons as it shown in
FIG. 2
, i. e. along the magnetic gap shown in
FIG. 3
, because in practice, the presence of the second electrode (cathode) shown in FIG.
3
(
a
) is not necessary if one uses the magnetic poles as the cathode, due to the electric potential of the magnetic poles connection to one another by plasma, see FIG.
3
(
b
).
For a plasma ignition and for a maintenance of plasma uniformity into the magnetic (and electrical) gap, the requirements for the closeness of the electron drift and the requirements for the closeness of the magnetic and the electrical gaps must consequently be followed. These requirements create a certain obvious inconvenience in design and application of the Ion-Beam Sources with an Anode Layer. The second problem is the requirement for applying the magnetoconductor (
2
in
FIG. 3
) as the necessary element of the IBSAL. It is understood that the magnetoconductor significantly increases the weight of the IBSAL and therefore makes it impossible to consider it for space technology, and being fabricated entirely of a low-carbon steel (desirable design), it has high fabrication cost.
The present invention enables one to overcome all these considered problems by replacing the magnetic poles including the magnetoconductor in IBSAL with a corresponding quadrupole magnetic system.
SUMMARY OF THE INVENTION
The present invention pertains to an Ion-Beam Source with an Anode Layer comprising a long plane anode
1
(see
FIGS. 1 and 4
) mounted on a mounting plate
8
by insulators
5
, two long magnets of U-cross-section (formed each of two long flat bars
2
,
3
interlaced with permanent magnets
4
) positioned symmetrically above and along the anode with an invariable magnetic gap between the magnetic poles of the magnets disposed as a quadrupole system and with the invariable electrical gap between the anode surface and the corresponding surfaces of the magnetic poles
2
facing to the anode
1
serving as cathodes, a gas-distributing system formed by a plurality of holes
9
in stand-off bars
6
serving as a supports for the magnets of the quadrupole system (for example), a cooling system for the anode (shown in
FIG. 1
as squared channels into the anode body), and a cooling system for the cathode shown in
FIG. 1
in the form of the tubes
7
clamped between the poles of the quadrupole magnetic system (for example). The direction of the Ion Beam propagation is shown in
FIG. 1
by the arrows
11
.
The configuration of the electric E and magnetic H fields are shown schematically in FIG.
1
(
a
). As is seen from the field diagram presented in FIG.
1
(
a
), the direction of the magnetic field H induced by the upper pair of magnetic poles is opposite to the direction of the magnetic field induced by the near-anode pair of poles, and this direction is reversed at the special point O in FIG.
1
(
a
) where the value of the magnetic field H is equal zero. Therefore one can expect that the direction of the electron drift velocity will be opposite in the vicinity of the upper pair of magnetic poles in comparison with the near-anode vicinity, see FIG.
2
. One can expect also that the electron component of the gas-discharge plasma will be trapped at the vicinity of the point (axis for
FIG. 4
) O and will deliver the electrons into both the vicinities (near-anode and at the upper pair of magnetic poles) by diffusion. The possibility of the electrons drifting in opposite directions into the different vicinities of the quadrupole magnetic system together with the reconnection of the electron trajectories between the vicinities by the electron diffusion could be considered as a quasi-closed electron drift providing high plasma uniformity. The long life of the trapped electrons provides a significant improvement in plasma ignition and maintenance.
The magnetic field between the poles of the conventional magnetic system, see FIG.
3
(
b
), has a maximum at the point of system symmetry, and the value of this magnetic field is decreased from this point toward the anode as well as toward the opposite direction. Therefore the plasma electrons into the conventional magnetic system should have a gradient magnetic drift leading to loss in electrons. The quadrupole magnetic system has a zero value of magnetic field at the point of magnetic system symmetry (point O in FIG.
1
(
a
)), and the value of the magnetic field in this system is increased in any direction from this point. Therefore the plasma electrons are trapped into the quadrupole magnetic system providing better conditions for the ignition, generation, and maintenance of uniform plasma. As is seen from the comparison of
FIGS. 1 and 4
with
FIG. 3
, the quadrupole magnetic system does not need any heavy steel magnetoconductor for creation of the proper magnetic field, and stand-off bars
6
(
FIGS. 1 and 4
) could be designed of a non-magnetic material of a low specific weight (aluminum or titanium alloys). Thus the Ion-Beam Source of the present invention with an Anode Layer and a Quadrupole magnetic system could be considered as a thruster in competition with Ion-Beam Sources with Magnetic Layers.
REFERENCES:
patent: 4862032 (1989-08
Anderson Bruce C.
Carothers & Carothers
Wells Nikita
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