WO2016149082A1

WO2016149082A1 - Hall thruster with exclusive outer magnetic core

Info

Publication number: WO2016149082A1
Application number: PCT/US2016/021973
Authority: WO
Inventors: Benjamin Allen WELANDER
Original assignee: Aerojet Rocketdyne, Inc.
Priority date: 2015-03-15
Filing date: 2016-03-11
Publication date: 2016-09-22

Abstract

A Hall thruster includes an annular discharge channel, a cathode, an exclusive outer magnetic core disposed asymmetric to the annular discharge channel, and an outer magnetic pole between the cathode and the annular discharge channel. The outer magnetic core circumscribes at least a portion of the cathode.

Description

HALL THRUSTER WITH EXCLUSIVE OUTER MAGNETIC CORE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present disclosure claims priority to United States Provisional Patent

Application No. 62/133,424, filed March 15, 2015.

BACKGROUND

[0002] Ion accelerators with closed electron drift are also known as Hall-effect thrusters or Hall thrusters. Hall thrusters can be used on space vehicles for propulsion, station-keeping, orbit changes, or counteracting drag, for example. Hall thrusters generate thrust by supplying a gas to an annular channel. The annular channel has a closed end with an anode and an open end through which the gas is discharged. A cathode introduces free electrons into the area of the open end. The electrons are induced to drift circumferentially in the annular channel by a generally radially extending magnetic field in combination with a longitudinal electric field, but the electrons eventually migrate to the anode. The electrons collide with the gas atoms to create ions. The longitudinal electric field accelerates the ions from the open end of the annular channel to generate a reaction force that produces thrust. In general, Hall thrusters come in wide range of discharge power configurations.

SUMMARY

[0003] A Hall thruster according to an example of the present disclosure includes an annular discharge channel, a cathode, an exclusive outer magnetic core disposed asymmetric to the annular discharge channel, and an outer magnetic pole circumscribing the annular discharge channel.

[0004] In a further embodiment of any of the foregoing embodiments, the outer magnetic core includes a permanent magnet.

[0005] In a further embodiment of any of the foregoing embodiments, the outer magnetic core is a hollow tube, and the hollow tube circumscribes at least a portion of the cathode.

[0006] A further embodiment of any of the foregoing embodiments includes an outer coil that circumscribes at least a portion of the outer magnetic core. [0008] A Hall thruster according to an example of the present disclosure includes an inner magnetic pole defining a central axis, and an outer magnetic structure having an outer magnetic pole and an exclusive outer magnetic core. The outer magnetic pole circumscribes the inner magnetic pole. The outer magnetic pole and the inner magnetic pole define an annular region there between. The outer magnetic pole is of a non-axisymmetric shape with respect to the central axis. The outer magnetic core radially is displaced from the annular region. The outer magnetic core is disposed asymmetric to the central axis.

[0009] In a further embodiment of any of the foregoing embodiments, the outer magnetic core is a hollow tube and the outer magnetic pole includes an orifice concentric to the hollow tube.

[0010] A further embodiment of any of the foregoing embodiments includes a cathode disposed at least partially in the hollow tube.

[0011] In a further embodiment of any of the foregoing embodiments, the outer magnetic pole includes a protrusion between the orifice and the annular region.

[0012] The Hall thruster as recited in claim 5, further comprising a coil circumscribing at least a portion of the outer magnetic core.

[0013] In a further embodiment of any of the foregoing embodiments, the outer magnetic structure includes a permanent magnet.

[0014] In a further embodiment of any of the foregoing embodiments, the outer magnetic pole tapers in width from the annular region.

[0015] A Hall thruster according to an example of the present disclosure includes an annular discharge channel, a cathode, and an exclusive outer magnetic structure disposed asymmetric to the annular discharge channel.

[0016] In a further embodiment of any of the foregoing embodiments, the outer magnetic structure includes a permanent magnet.

[0017] In a further embodiment of any of the foregoing embodiments, the outer magnetic structure includes a hollow tube, and the hollow tube circumscribes at least a portion of the cathode.

[0018] A further embodiment of any of the foregoing embodiments includes an outer coil that circumscribes at least a portion of the outer magnetic structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.

[0020] Figure 1 illustrates an example Hall thruster.

[0021] Figure 2 illustrates an isometric view of a magnetic circuit of a Hall thruster.

[0022] Figure 3 illustrates an axial view of a magnetic circuit of a Hall thruster.

DETAILED DESCRIPTION

[0023] Figure 1 schematically illustrates an example Hall thruster 20. As will be described, the Hall thruster 20 has a single, exclusive asymmetric outer magnetic core, which can potentially reduce thruster size and reduce the amount of power consumed in comparison to Hall thrusters that utilize multiple outer cores arranged symmetrically around the annular channel.

[0024] In the example shown, the Hall thruster 20 includes a magnetic circuit 22. The magnetic circuit 22 is also shown in isolation in Figure 2 and in an axial view in Figure 3. In Figure 2 and Figure 3, the optional magnetic coils have been omitted from the magnetic circuit 22. The magnetic circuit 22 includes an inner magnetic structure 24 that is disposed along, and defines, a central axis (A). In this example, the inner magnetic structure 24 includes an inner magnetic pole 24a and a cylindrical inner core 24b. The inner magnetic pole 24a is an enlarged region, or cap, coupled at the end of the inner core 24b.

[0025] The magnetic circuit 22 also includes an outer magnetic structure 26. The outer magnetic structure 26 includes an outer magnetic pole 26a. The outer magnetic pole 26a circumscribes the inner magnetic pole 24a. Thus, the inner magnetic structure 24 and the outer magnetic structure 26 define an annular region 28 between the inner and outer poles 24a/26a.

[0026] The outer magnetic structure 26 also includes an outer (magnetic) core 30 that is displaced radially outward from the annular region 28. In this example, the outer core 30 is a hollow tube and is cylindrical. In a modified example, the outer core 30 is solid rather than hollow. The outer core 30 has an axial length that is approximately equal to the axial length of the inner core 24b.

[0027] The magnetic circuit 22 further includes a magnetic connector 32, which magnetically couples the inner magnetic structure 24 and the outer magnetic structure 26. That is, the magnetic connector 32, along with the outer core 30 and the inner core 24b, form a magnetic flux path between the inner and outer magnetic poles 24a/26a. In the example shown, the magnetic connector 32 is a plate.

[0028] The magnetic circuit 22 is of a non-axisymmetric shape with respect to the central axis (A). For example, at least the outer magnetic pole 26a of the outer magnetic structure 26 is non-rotationally symmetric about the central axis (A). In further examples, the outer core 30 and/or the magnetic connector 32 are also of non-axisymmetric shapes with respect to the central axis (A).

[0029] Referring also to the axial view of the magnetic circuit 22 in Figure 3, the non-axisymmetric shape of the outer magnetic pole 26a in this example tapers in width (as represented at 34) from the annular region 28. In the example shown, the taper results in a "tear-drop" geometry that has a narrow end at the outer core 30 and an opposed wide end at the annular region 28. As will be appreciated given this disclosure, the outer magnetic pole 26a may have other non-axisymmetric shapes. The thickness of the outer magnetic pole 26a may vary so as to efficiently transmit magnetic flux and provide a uniform magnetic field in the annular region 28. As used herein, length is the longest dimension of a structure, thickness is the shortest orthogonal dimension, and width is an intermediate orthogonal dimension. In this example, the thickness of the outer magnetic pole 26a is parallel to the central axis (A) and the length is between the wide and narrow ends of the tear-drop shape.

[0030] The magnetic circuit 22 may be primarily formed of a ferromagnetic material. Portions of the magnetic circuit 22 may be formed of a permanent magnetic material to enhance efficiency. For example, the outer core 30 may be formed of a permanent magnetic material, while other portions or the remainder of the magnetic circuit 22 are formed of non-permanent magnetic material (e.g., a material that does not generate a persistent magnetic field).

[0031] Referring again to Figure 1, the magnetic circuit 22 in the given example also includes an optional inner coil 40 and an optional outer coil 42. If used, the inner coil 40 is arranged about the central axis (A) and circumscribes at least a portion of the inner core 24b. If used, the outer coil 42 is arranged about the outer core 30. In this regard, the outer coil 42 circumscribes at least a portion of the outer core 30. The outer coil 42 is also disposed asymmetric to the annular discharge channel 46. In this regard, the outer coil 42 is not coiled about the annular discharge channel 46, but rather is coiled about a different axis, which in the illustrated example is the axis of the outer core 30. [0032] The outer core 30 and, optionally, the outer coil 42 are "exclusive" with respect to any other outer magnetic cores and outer coils of the Hall thruster 20. That is, aside from the outer core 30 and optionally the outer coil 42, there is no other magnetic core or coil radially outwards of the annular discharge channel 46 that is operable to generate and transmit magnetic flux between the magnetic connector 32 and the outer magnetic pole 26a.

[0033] The Hall thruster 20 includes a cathode 44 arranged, in this example, in at least a portion of the outer core 30. The outer core 30 circumscribes at least a portion of the cathode 44. The cathode 44 is thus integrated into the Hall thruster 20 rather than being mounted as an external component.

[0034] The Hall thruster 20 further includes an annular discharge channel 46. The annular discharge channel 46 is arranged about the central axis (A) and is defined in this example by a radially inner wall 46a, a radially outer wall 46b, and a bottom wall 46c. The annular discharge channel 46 defines an open exit at the annular region 28.

[0035] In the illustrated example, the Hall thruster 20 also includes an ionizable gas source 48 and an electric field source/anode 50. The ionizable gas source 48 and electric field source/anode 50 may be of similar configuration as those already known in Hall thrusters and are thus not described in further detail herein.

[0036] The operation of the Hall thruster 20 is discussed below with regard to features disclosed herein. The description of the operation or functionality is not representative of the full operation of the Hall thruster 20, and the Hall thruster 20 may have additional components and functionalities consistent with known Hall thrusters.

[0037] The magnetic circuit 22 produces a magnetic field. A portion of the magnetic field is shown by magnetic field lines (F) in Figure 1. The magnetic field shape is dictated by the magnetic circuit 22 such that the magnetic field lines extend radially across the exit at the annular region 28. The magnetic field line (F) allows free electrons to flow magnetically unimpeded from the cathode 44 toward the inner magnetic pole 24a and cross the thruster plume (TP) emanating from the exit at the annular region 28, as shown in Figure 1.

[0038] Symmetric outer structures and multiple outer coils or a single outer coil arranged symmetrically about the central axis were heretofore thought to be necessary for generating an axisymmetric magnetic field across the exit at the annular region 28. However, the particular geometry of the magnetic circuit 22 of the disclosed Hall thruster 20 can likewise generate an axisymmetric magnetic field across the exit at the annular region 28. Thus, despite the asymmetric outer magnetic pole 26a, asymmetric magnetic connector 32 and exclusive outer core 30, the Hall thruster 20 generates a magnetic field geometry in the open exit at the annular region 28 that is symmetric about the central axis (A). For example, the outer magnetic pole 26a has a relatively thick cross-section, a high magnetic saturation point, and a high magnetic permeability. These properties permit the outer magnetic pole 26a to readily transmit magnetic field flux and, in turn, generate the desired axisymmetric, radial magnetic field across the exit at the annular region 28.

[0039] With the elimination of multiple outer magnetic cores and coils, the Hall thruster 20 can potentially lower power requirements, and thereby potentially increase efficiency. The elimination of multiple outer coils also permits the Hall thruster 20 to be more compact, reduce the overall number of components, and reduce assembly steps.

[0040] The location of the cathode 44 in the outer core 30 in one example permits free electrons generated by the cathode 44 to travel freely along magnetic field lines (F) towards the plasma plume emanating from the open annular region 28. A magnetic field providing a free electron path between the cathode and the plasma plume may lower the potential difference between the cathode and the plasma plume and increase thruster efficiency.

[0041] The location of the cathode 44 in the outer core 30 in one example also protects the cathode 44 from ion bombardment. For further protection from bombardment, the cathode 44 may be recessed into the outer core 30. This protection may also extend cathode life, alleviate the need for sputter-resistant cathode materials or alleviate the need for a second cathode. In a further example, the outer magnetic pole 26a defines an orifice 30a displaced radially outward from the open annular region 28 and concentric with the outer core 30. The outer magnetic pole 26a may additionally include a protrusion 52 between the orifice 30a and the annular region 28. The protrusion 52 may serve to further protect the cathode 44 from ion bombardment. The protrusion 52 may extend only on one side of the orifice 30a adjacent the annular region 28 or the protrusion 52 may be configured as a full ring around the orifice 30a. The protrusion 52 may be formed of a ceramic material or other durable barrier material. Example materials may include, but are not limited to, boron nitride and graphite.

[0042] Additionally, the configuration of the Hall thruster 20 may permit enhanced cooling. Most of the heat generated in a Hall thruster originates at or near the annular discharge channel 46. Here, with the use of the exclusive outer core 30 and non- axisymmetric magnetic circuit 22, heat generated at or near the annular channel 46 can readily radiate away from the Hall thruster 20 because there is less blocking structure surrounding the annular channel 46.

[0043] Although specific combinations of features are shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.

[0044] The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.

Claims

CLAIMS What is claimed is:

1. A Hall thruster comprising:

an annular discharge channel;

a cathode;

an exclusive outer magnetic core disposed asymmetric to the annular discharge channel; and

an outer magnetic pole circumscribing the annular discharge channel.

2. The Hall thruster as recited in claim 1, wherein the outer magnetic core includes a permanent magnet.

3. The Hall thruster as recited in claim 1, wherein the outer magnetic core is a hollow tube, and the hollow tube circumscribes at least a portion of the cathode.

4. The Hall thruster as recited in claim 1, further comprising an outer coil that circumscribes at least a portion of the outer magnetic core.

5. A Hall thruster comprising:

an inner magnetic pole defining a central axis; and

an outer magnetic structure having an outer magnetic pole and an exclusive outer magnetic core, the outer magnetic pole circumscribing the inner magnetic pole, the outer magnetic pole and the inner magnetic pole defining an annular region there between, the outer magnetic pole being of a non-axisymmetric shape with respect to the central axis, the outer magnetic core radially displaced from the annular region, and the outer magnetic core disposed asymmetric to the central axis.

6. The Hall thruster as recited in claim 5, wherein the outer magnetic core is a hollow tube and the outer magnetic pole includes an orifice concentric to the hollow tube.

7. The Hall thruster as recited in claim 6, further comprising a cathode disposed at least partially in the hollow tube.

8. The Hall thruster as recited in claim 7, wherein the outer magnetic pole includes a protrusion between the orifice and the annular region.

9. The Hall thruster as recited in claim 5, further comprising a coil circumscribing at least a portion of the outer magnetic core.

10. The Hall thruster as recited in claim 5, wherein the outer magnetic structure includes a permanent magnet.

11. The Hall thruster as recited in claim 5, wherein the outer magnetic pole tapers in width from the annular region.

12. A Hall thruster comprising:

an annular discharge channel;

a cathode; and

an exclusive outer magnetic structure disposed asymmetric to the annular discharge channel.

13. The Hall thruster as recited in claim 12, wherein the outer magnetic structure includes a permanent magnet.

14. The Hall thruster as recited in claim 12, wherein the outer magnetic structure includes a hollow tube, and the hollow tube circumscribes at least a portion of the cathode.

15. The Hall thruster as recited in claim 12, further comprising an outer coil that circumscribes at least a portion of the outer magnetic structure.