Electric lamp and discharge devices: systems – High energy particle accelerator tube – Magnetic field acceleration means
Reexamination Certificate
2001-04-13
2002-09-10
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
High energy particle accelerator tube
Magnetic field acceleration means
C313S161000
Reexamination Certificate
active
06448721
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains generally to electric plasma thrusters and more particularly to Hall field thrusters, which are sometimes called Hall accelerators.
The Hall plasma accelerator is an electrical discharge device in which a plasma jet is accelerated by a combined operation of axial electric and magnetic fields applied in a coaxial channel. The conventional Hall thruster overcomes the current limitation inherent in ion diodes by using neutralized plasma, while at the same time employing radial magnetic fields strong enough to inhibit the electron flow, but not the ion flow. Thus, the space charge limitation is overcome, but the electron current does draw power. Hall thrusters are about 50% efficient. Hall accelerators do provide high jet velocities, in the range of 10 km/s to 20 km/s, with larger current densities, about 0.1 A/cm
2
, than can conventional ion sources.
Hall plasma thrusters for satellite station keeping were developed, studied and evaluated extensively for xenon gas propellant and jet velocities in the range of about 15 km/s, which requires a discharge voltage of about 300 V. Hall thrusters have been developed for input power levels in the general range of 0.5 kW to 10 kW. While all Hall thrusters retain the same basic design, the specific details of an optimized design of Hall accelerators vary with the nominal operating parameters, such as the working gas, the gas flow rate and the discharge voltage. The design parameters subject to variation include the channel geometry, the material, and the magnetic field distribution.
A. V. Zharinov and Yu. S. Popov, “Acceleration of plasma by a closed Hall current”,
Sov. Phys. Tech. Phys.
12, 1967, pp. 208-211 describe ideas on ion acceleration in crossed electric and magnetic field, which date back to the 1950's. The first publications on Hall thrusters appeared in the United States in the 1960's, such as: G. R. Seikel and F. Reshotko, “Hall Current Ion Accelerator”,
Bulletin of the American Physical Society, II
(7) (1962) and C. O. Brown and E. A. Pinsley, “Further Experimental Investigations of Cesium Hall-Current Accelerator”,
AIAA Journal,
V.3, No 5, pp. 853-859, 1965.
Over the last thirty years, A. I. Morozov designed a series of high-efficiency Hall thrusters. See, for example, A. I. Morozov et al., “Effect of the Magnetic field on a Closed-Electron-Drift Accelerator”,
Sov. Phys. Tech. Phys.
17(3), pp. 482-487 (1972), A. I. Morosov, “Physical Principles of Cosmic Jet Propulsion”,
Atomizdat,
Vol. 1, Moscow 1978, pp. 13-15, and A. I. Morozov and S. V. Lebedev, “Plasma Optics”, in
Reviews of Plasma Physics,
Ed. by M. A. Leontovich, V.8, New York-London (1980).
H. R. Kaufman, “Technology of Closed Drift Thrusters”,
AIAA Journal
Vol. 23 p. 71 (1983), reviews of the technology of Hall field thrusters, both in the context of other closed electron drift thrusters and in the context of other means of thrusting plasma. V. V. Zhurin et al., “Physics of Closed Drift Thrusters”,
Plasma Sources Science Technology
Vol. 8, p. R1 (1999), further reviews the physics and more recent developments in the technology of Hall thrusters.
What remains a challenge is to develop a Hall thruster able to operate efficiently at low power. To reduce the cost of various space missions, there is a strong trend towards miniaturization of satellites and their components. For some of these missions, which use on board propulsion for spacecraft orbit control, this miniaturization requires development of micro electric thrusters, having a large specific impulse (1000-2000 sec), which can operate efficiently at low input power levels, that is, less than 200 watts. However, existing small Hall thrusters, which are simply scaled down by means of a linear scaling to operate at low input power, are very significantly less efficient than Hall thrusters operating at input power larger than 0.5 kW.
The conventional annular design is not well suited to scaling to small size, because the small size for an annular design has a great deal of surface area relative to the volume. A more sensible design at small size would be a cylindrical geometry design. A cylindrical design may also be useful at high power, but it may be technologically indispensable for Hall field acceleration at low power.
The present invention comprises an improvement over the prior art cited above by providing for efficient operation of a cylindrical geometry Hall thruster, in which the center pole piece of the conventional annular design thruster is eliminated or greatly reduced. The present invention discloses means of accomplishing efficient operation of such a thruster by designing magnetic fields with a substantial radial component, such that ions are accelerated in substantially the axial direction.
The present invention comprises an improvement as well as over the following prior art:
U.S. Pat. No. 4,862,032 (“End-Hall ion source”, Kaufman et al., Aug. 29, 1989) discloses specifically that the magnetic field strength decreases in the direction from the anode to the cathode. The disclosure of the above referenced patent is hereby incorporated by reference.
Other design suggestions are disclosed in U.S. Pat. No. 5,218,271 (“Plasma accelerator with closed electron drift”, V. V. Egorov et al., Jun. 8, 1993) which contemplates a curved outlet passage. The disclosure of the above referenced patent is hereby incorporated by reference. U.S. Pat. No. 5,359,258 (“Plasma accelerator with closed electron drift”, Arkhipov et al., Oct. 25, 1994) contemplates improvements in magnetic source design by adding internal and external magnetic screens made of magnetic permeable material between the discharge chamber and the internal and external sources of magnetic field. The disclosure of the above referenced patent is hereby incorporated by reference.
U.S. Pat. No. 5,475,354 (“Plasma accelerator of short length with closed electron drift”, Valentian et al., Dec. 12, 1995) contemplates a multiplicity of magnetic sources producing a region of concave magnetic field near the acceleration zone in order better to focus the ions. The disclosure of the above referenced patent is hereby incorporated by reference. U.S. Pat. No. 5,581,155 (“Plasma accelerator with closed electron drift”, Morozov, et al., Dec. 3, 1996) similarly contemplates specific design optimizations of the conventional Hall thruster design, through specific design of the magnetic field and through the introduction of a buffer chamber. The disclosure of the above referenced patent is hereby incorporated by reference.
U.S. Pat. No. 5,763,989 (“Closed drift ion source with improved magnetic field”, H. R. Kaufman Jun. 9, 1998) contemplates the use of a magnetically permeable insert in the closed drift region together with an effectively single source of magnetic field to facilitate the generation of a well-defined and localized magnetic field, while, at the same time, permitting the placement of that magnetic field source at a location well removed from the hot discharge region. The disclosure of the above referenced patent is hereby incorporated by reference.
U.S. Pat. No. 5,847,493 (“Hall effect plasma accelerator”, Yashnov et al., Dec. 8, 1998) proposes that the magnetic poles in an otherwise conventional Hall thruster be defined on bodies of material which are magnetically separate. The disclosure of the above referenced patent is hereby incorporated by reference.
U.S. Pat. No. 5,845,880 (“Hall effect plasma thruster”, Petrosov et al., Dec. 8, 1998) proposes a channel preferably flared outwardly at its open end so as to avoid erosion. The disclosure of the above referenced patent is hereby incorporated by reference.
BRIEF SUMMARY OF THE INVENTION
It is an object of this invention to provide a cylindrical Hall plasma thruster, made efficient by means of detailed control of the magnetic and electric fields.
The cylindrical configuration consists of a cylindrical ceramic channel, in which there is imposed a magnetic field strong enough to impede the motion of the electrons but not t
Fisch Nathaniel J.
Raitses Yevgeny
General Plasma Technologies LLC
Minh D A
Wong Don
LandOfFree
Cylindrical geometry hall thruster does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cylindrical geometry hall thruster, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cylindrical geometry hall thruster will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2855645