Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Patent
1995-01-12
1996-12-03
Pascal, Robert
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
31511141, 31511161, 31323131, 3133591, 3133621, 3133611, 60202, H01J 152, H05H 100, F03H 100
Patent
active
055811558
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to plasma accelerators applied in particular to space propulsion, and more particularly to plasma accelerators of the type having closed electron drift, also known as stationary plasma accelerators, or in the United States of America as "Hall-current accelerators".
PRIOR ART
Electric accelerators are designed essentially for space propulsion applications. As sources of ions or of plasma, they are also used in terrestrial applications, in particular for ion machining. Because of their high specific impulse (1500 s to 6000 s) they make considerable mass savings possible on satellites compared with accelerators that make use of chemical propulsion.
One of the typical applications of accelerators of this type is north-south control of geostationary satellites where they make a mass saving of 10% to 15% possible. They can also be used for compensating drag in low orbit, for maintaining a heliosynchronous orbit, and for primary interplanetary propulsion.
Ion thrusters can be divided into several categories.
A first type of ion thruster is thus constituted by an accelerator in which ionization is performed by bombardment, also known as a Kaufman accelerator. Examples of thrusters of that type are described, in particular, in documents EP-A-0 132 065, WO 89/05404, and EP-A-0 468 706.
In an accelerator making use of ionization by bombardment, atoms of thrust gas are injected at low pressure into a discharge chamber where they are bombarded by electrons emitted by a hollow cathode and collected by an anode. The ionization process is magnified by the presence of a magnetic field. A certain number of the atom-electron collisions cause a plasma to be created in which the ions are attracted by the acceleration electrodes (outlet grids), themselves at a potential that is negative relative to the potential of the plasma. The electrodes concentrate and accelerate the ions which leave the thruster in the form of widely spreading radiation. The ion radiation is then neutralized by a flux of electrons emitted from an external hollow cathode called a "neutralizer".
The specific impulse (I.sub.sp) obtained from thrusters of that type is of the order of 3000 seconds and above.
The power requirement is about 30 W per mN of thrust.
Other types of ionization accelerator are constituted by accelerators using radiofrequency ionization, accelerators using ionization by contact, or field emission accelerators.
Those various ionization accelerators, including accelerators using ionization by bombardment share the common feature of having their ionization function clearly separated from their ion-acceleration function.
They also share in common the fact of presenting current density in the ion optics that is limited by the space charge phenomenon, which density is limited in practice to 2 mA/cm.sup.2 to 3 mA/cm.sup.2 in accelerators using ionization by bombardment, and thus of presenting thrust per unit area that is rather low.
In addition, such accelerators and bombardment accelerators in particular require a certain number of electricity feeds (in the range 4 to 10), thereby leading to the implementation of rather complex electronic circuits for conversion and control.
Accelerators are also known, in particular from an article by L. H. ARTSIMOVITCH et al., published in 1974 and concerning the program for developing the stationary plasma accelerator (SPD) and tests on the "METEOR" satellite, which accelerators are of the "closed electron drift" type, also known as "stationary plasma" accelerators, which differ from the other categories by the fact that ionization and acceleration are not distinguished and the acceleration zone includes equal numbers of ions and of electrons, thereby making it possible to eliminate any space charge phenomenon.
A closed electron drift accelerator as proposed in the above-specified article by L. H. ARTSIMOVITCH et al. is described below with reference to FIG. 2.
An annular channel 1 defined by a part 2 made of insulating material is placed in an elec
REFERENCES:
patent: 4841197 (1989-06-01), Takayama et al.
patent: 4862032 (1989-08-01), Kaufman et al.
patent: 5218271 (1993-06-01), Egorov et al.
patent: 5475354 (1995-12-01), Valentian et al.
"Technology of Closed-Drift Thrusters" by H. Kaufman AIAA Journal, vol. 23, No. 1, pp. 78-87.
"Open Single-Lens Hall-Current Accelerator", V. N. Dem'yanenko, et al, vol. 21, No. 8, Aug. 1976, Soviet Physics Technical Physics, New York, pp. 987-988.
Bougrova Antonina I.
Dessijatskov Alexei V.
Morozov Alexei I.
Niskine Valentine T.
Valentian Dominique
Kinkead Arnold
Pascal Robert
Societe Europeene de Propulsion
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