Patent Description:
<CIT> discloses a plasma propulsion system with no internal electrodes. Gas is flowed into an insulated axisymmetric plasma liner. A radio frequency antenna generates an inductive or helicon plasma discharge within the liner. The plasma is accelerated through a converging/diverging magnetic field out of the liner, generating thrust.

<CIT> discloses a plasma beam apparatus and method for the purpose of vacuum processing temperature sensitive materials at high discharge power and high processing rates. A gridless, closed or non-closed Hall-Current ion source is described which features a unique fluid-cooled anode with a shadowed gap through which ion source feed gases are introduced while depositing feed gases are injected into the plasma beam. The shadowed gap provides a well maintained, electrically active area at the anode surface which stays relatively free of nonconductive deposits. The anode discharge region is insulatively sealed to prevent discharges from migrating into the interior of the ion source. Thin vacuum gaps are also used between anode and non-anode components in order to preserve electrical isolation of the anode when depositing conductive coatings. The magnetic field of the Hall-Current ion source is produced by an electromagnet driven either by the discharge current or a periodically alternating current.

<CIT> discloses a Hall-type ion source for generation of ion beams for technological applications presents itself a hybrid ion source, where properties of closed drift systems and end-Hall ion sources are combined for more efficient operation. An ion source has shorter central magnetic pole than regular closed drift ion source with magnetic screens that provide positive magnetic gradient in an ion source's discharge channel. An ion source with these combined properties has higher ratio of ion beam current to discharge current than end-Hall ion source and wider range of discharge parameters than closed drift ion source.

<CIT> discloses a Hall thruster with a shared magnetic structure including a plurality of plasma accelerators establishing a transverse magnetic field in each of the plurality of plasma accelerators that creates an impedance to the flow of electrons toward the anode in each of the plurality of plasma accelerators and enables ionization of a gas moving through one or more of the plurality of plasma accelerators. The impedance localizes an axial electric field in the plurality of plasma accelerators for accelerating ionized gas through the one or more of the plurality of plasma accelerators to create thrust.

Aspects of the invention are provided according to the appended claims: specifically, the present invention provides a Hall-effect thruster assembly as defined in claim <NUM>.

Before any embodiments of the disclosure are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of the formation and arrangement of components set forth in the following description or illustrated in the accompanying drawings. The disclosure is capable of supporting other embodiments and of being practiced or of being carried out in various ways.

<FIG> illustrate a Hall-effect thruster <NUM> (HET) for spacecraft propulsion. The HET <NUM> includes a housing <NUM> having magnetic sources and material positioned therein for creating a magnetic circuit.

Referring to <FIG>, in a conventional concentric arrangement of magnetic field sources 40A-40C and magnetic field flux guides <NUM>, <NUM> within the housing <NUM>, a discharge chamber <NUM> is configured to receive propellant (e.g., Xenon, Krypton, Argon, etc.). More specifically, the propellant is introduced into the discharge chamber <NUM> through a plurality of tubes <NUM> extending through respective openings <NUM> (only one of which is shown in <FIG>). Voltage applied between a cathode (not shown) positioned at or near a first, discharge end <NUM> and an anode (not shown) positioned at or near a second end <NUM> forms an electric field extending axially relative to a longitudinal axis A within the discharge chamber <NUM>. A magnetic circuit (i.e., arrows <NUM>) including magnetic field sources 40A-40C and magnetic field flux guide material <NUM> is configured to create a radially-oriented magnetic field at the first end <NUM>. Electrons subjected to the magnetic field are used to ionize the propellant. Subsequently, the propellant ions are accelerated by the electric field for generating a thrust at the first end <NUM>. Accordingly, the magnetic field sources 40A-40C and/or the magnetic field flux guides <NUM>, <NUM> may be termed as a magnetic field generator for producing thrust of a Hall-effect thruster. In other embodiments, the magnetic field generator may represent the elements of a Hall-effect thruster that generate the magnetic field for producing the thrust.

As shown in <FIG>, the magnetic field sources 40A-40C (e.g., electromagnetic coils or permanent magnets) are oriented such that their magnetic moments are axial relative to the longitudinal axis A from proximate the first end <NUM> to proximate the second end <NUM>. The illustrated magnetic field sources 40A-40C form generally continuous annular shapes about the longitudinal axis A, but in other embodiments such sources 40A-40C may comprise a plurality of discrete or otherwise spaced sources. In the illustrated embodiment, the HET <NUM> includes three electromagnetic coils as the magnetic field sources 40A-40C, each positioned relative to the magnetic field flux guide material <NUM>. In other constructions, the magnetic circuit <NUM> may only include one of the magnetic field sources 40A-40C. Additional magnetic field flux guide material <NUM> in the form of a plate <NUM> with high magnetic relative permeability positioned at the second end <NUM> completes the magnetic circuit <NUM>.

Because of the use of the magnetic field sources 40A-40C (e.g., electromagnetic coils or permanent magnets) and magnetic field flux guide material <NUM>, the HET <NUM> produces a predetermined magnetic dipole moment (e.g., measured in Ampere square meter (A-m<NUM>)), which may now be referred to herein as the HET magnetic dipole moment. For example, the HET magnetic dipole moment may be between <NUM> A-m<NUM> and <NUM> A-m<NUM> (plus or minus (±)) in the direction of the longitudinal axis A. In some embodiments, the HET magnetic dipole moment is about <NUM> A-m<NUM> (±). This moment may interact with other magnetic fields generated from other sources to produce a torque on the HET, and ultimately on a spacecraft on which the HET <NUM> is mounted. Other magnetic fields may include, for example, Earth's magnetic field, magnetic fields produced by other components on the spacecraft, etc. For example, when the spacecraft is flying in low Earth orbit, Earth's magnetic field may interact strongly with the magnetic field of the HET <NUM>, thereby applying a significant torque to the spacecraft.

In addition, the magnetic field (magnetic dipole moment) of the HET <NUM> may be represented by a plurality of flux lines extending relative to the longitudinal axis A through the first and second ends <NUM>, <NUM>, respectively, of the HET <NUM>. The flux lines (not shown) define an overall shape of the HET magnetic field. The flux lines can be affected by other magnetic fields generated from external magnetic sources proximate the HET <NUM>.

The use of nulling magnets, shielding, or a combination of both in the HET <NUM> may reduce or achieve a near-zero net magnetic dipole moment of the HET <NUM> itself (e.g., ±<NUM> A-m<NUM>) without affecting the actual magnetic circuit <NUM> of the magnetic field sources 40A, 40B and magnetic field flux guide material <NUM>, thereby reducing the torque applied to the spacecraft by the other magnetic fields. For example, in some embodiments, the nulling magnets produce a compensating magnetic dipole moment, and a combination of the HET magnetic dipole moment and the compensating magnetic dipole moment results in a net magnetic dipole moment of the entire system of the HET <NUM>. In other embodiments, the shielding or a combination of the nulling magnets and shielding inhibit or prevent the HET magnetic dipole moment from interacting with other magnetic dipole moments outside of the HET <NUM>. Accordingly, the nulling magnets, shielding, or a combination of both in the HET <NUM> reduce an absolute value of the HET magnetic dipole moment in a direction along the longitudinal axis A. Furthermore, the nulling magnets, shielding, or a combination of both, may be positioned relative to the HET <NUM> to minimize or reduce the effect of the magnetic fields generated from the other sources on the overall shape of the magnetic field of the HET <NUM> proximate the first end <NUM> of the HET <NUM>.

<FIG> illustrates schematically an assembly <NUM> of a first HET <NUM> embodying the present disclosure, and like elements have been given the same reference numbers plus <NUM>. The assembly <NUM> includes a mount assembly <NUM> and the HET <NUM>. The HET <NUM> includes magnetic field sources 140A-140C, magnetic field flux guide material <NUM>, plate <NUM>, and a discharge chamber <NUM> defining a longitudinal axis 100A. A discharge area <NUM> of the HET <NUM> is positioned proximate a first end <NUM> of the HET <NUM>.

The mount assembly <NUM> includes a body <NUM> couplable to the HET <NUM>. More specifically, the body <NUM> includes a first side <NUM> and a second side <NUM> spaced from the first side <NUM>. A second end <NUM> of the HET <NUM> opposite the first end <NUM> is coupled to the first side <NUM> of the body <NUM>. The mount assembly <NUM> is formed of non-magnetic material (e.g., aluminum). The mount assembly <NUM> is configured to support the HET <NUM> and is configured to securably retain the HET <NUM> to the spacecraft.

The mount assembly <NUM> includes a plurality of magnetic elements <NUM> (e.g., electromagnetic coils or permanent magnets) and a structure <NUM> configured to receive or contain the magnetic elements <NUM>. In the illustrated embodiment, the plurality of magnetic elements <NUM> includes one element <NUM> positioned on the second side <NUM> of the body <NUM>. The illustrated element <NUM> in one embodiment is a single, toroidal magnet radially spaced from the longitudinal axis 100A. In other embodiments, the plurality of magnetic elements <NUM> may be one or more discrete magnets positioned relative to the longitudinal axis 100A. These discrete magnetic elements may each be formed by an arc-shaped segment, rod-like shaped segment, box-like shaped segment, etc. Still further, the magnetic elements <NUM> may be positioned at select radial positions relative to the longitudinal axis 100A.

In the illustrated embodiment, the structure <NUM> has a shape matching with or complementary of the magnetic element <NUM>. In particular, the illustrated structure <NUM> has a cylindrical shape with an outer diameter D1 and an inner diameter D2. The outer diameter D1 and the inner diameter D2 may be selected based on a diameter of the magnetic element <NUM>. Additionally, the radial position of the magnetic element <NUM> relative to the longitudinal axis 100A is based on the diameter of the magnetic element <NUM>. As such, the diameter may be selected based on positioning the magnetic element <NUM> radially closer to or farther from the longitudinal axis 100A.

In addition, the magnetic element <NUM> has a thickness T. The thickness T is the difference between the outer diameter D1 of the structure <NUM> and the inner diameter D2 of the structure <NUM>. As such, the outer diameter D1 and the inner diameter D2 may also be selected based on the thickness T of the magnetic element <NUM>.

Still further, the plurality of magnetic elements <NUM> may be one or more permanent magnets positioned radially relative to the longitudinal axis 100A. As such, the structure <NUM> may be configured to retain the one or more permanent magnets.

The plurality of magnetic elements <NUM> are collectively configured to produce an independent magnetic dipole moment and counteract the HET magnetic dipole moment produced by the magnetic field sources 140A-140C and the magnetic field flux guide material <NUM>, without significantly disrupting the magnetic field within the discharge chamber <NUM> and the discharge area <NUM> (i.e., affecting the overall shape of the magnetic field or the orientation of the magnetic field flux lines proximate the first end <NUM>). In particular, the magnitude and direction of the magnetic dipole moment of the magnetic elements <NUM> is selected for reducing the absolute value of the magnetic dipole moment of the HET <NUM> by a certain amount, one example of which may be a predetermined percentage (%) in a direction along the longitudinal axis 100A, which in some applications may result in a near-zero net magnetic dipole moment (Am<NUM>) for the system. In other embodiments, the absolute value of the magnetic dipole moment of the HET <NUM> may be reduced by a set numerical value (e.g., value having unit A-m<NUM>). Accordingly, the plurality of magnetic elements <NUM> may be referred to as null magnetic elements <NUM> or compensating elements <NUM> configured to compensate for the HET magnetic dipole moment of the HET <NUM>. The magnetic dipole moment of the magnetic elements <NUM> may be based on one or more of the following: the type of magnetic elements <NUM>, the number of magnetic elements <NUM>, the size (e.g., diameter, thickness) of the magnetic elements <NUM>, and/or the radial position of the magnetic element <NUM> relative to the longitudinal axis 100A. The magnetic elements <NUM> produce the compensating magnetic dipole moment.

In some embodiments, the plurality of magnetic elements <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between forty and ninety-five percent. In other embodiments, the plurality of magnetic elements <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between fifty and ninety-five percent. In yet other embodiments, the plurality of magnetic elements <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between sixty and ninety-five percent. In yet still other embodiments, the plurality of magnetic elements <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between seventy and ninety-five percent. For example, in the illustrated embodiment, the magnetic element <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> from about <NUM> A-m<NUM> (±) to about <NUM> A-m<NUM> (±) such that the HET magnetic dipole moment is reduced by about ninety percent.

<FIG> illustrate one example of an assembly <NUM> of the first HET <NUM> or portions thereof embodying the present disclosure, and like elements have been given the same reference numbers as the HET assembly <NUM> plus <NUM>. The assembly <NUM> includes a mount assembly <NUM> and the HET <NUM>. The HET <NUM> includes magnetic field sources, magnetic field flux guide material, and a discharge chamber (not shown; but see magnetic field sources 140A-140C, magnetic field flux guide material <NUM>, and discharge chamber <NUM> of the HET <NUM> of <FIG>) at least partially positioned within a housing <NUM>. The illustrated HET <NUM> also includes a plate <NUM>. The HET <NUM> includes the housing <NUM>, which as illustrated in <FIG> has a cylindrical shape. The HET <NUM> defines a longitudinal axis 400A. A discharge area <NUM> of the HET <NUM> is positioned proximate a first end <NUM> of the HET <NUM>.

The mount assembly <NUM> is adjacent to the housing <NUM>. The mount assembly <NUM> includes a body <NUM>. The illustrated body <NUM> is positioned proximate a second end <NUM> of the HET <NUM>, opposite the first end <NUM>. In the illustrated embodiment, the body <NUM> is coupled directly or indirectly to the plate <NUM> of the HET <NUM> (e.g., such as by fasteners). For example, the plate <NUM> or the body <NUM> includes a plurality of apertures, each aperture configured to receive a respective bolt for coupling the plate <NUM> and the body <NUM> together. In other embodiments, the body <NUM> may be coupled to the HET <NUM> by other securement means such as welding, and/or may be coupled at other locations of the HET <NUM> (e.g., magnetic flux guide material, magnetic field sources, etc.). Accordingly, the second end <NUM> of the HET <NUM> is coupled to a first side <NUM> of the body <NUM>.

With particular reference to <FIG>, the body <NUM> includes a first surface <NUM> defining the first side <NUM>. A second annular surface <NUM> at a second side <NUM> of the body <NUM> opposite the first side <NUM> faces away from the magnetic field sources and the magnetic field flux guide material. Furthermore, the illustrated body <NUM> has a generally annular shape formed by a circumferential surface <NUM> extending from the first side <NUM> to the second side <NUM>. In other words, the body <NUM> has a frustoconical shape.

The mount assembly <NUM> (i.e., the body <NUM>) is formed of non-magnetic material (e.g., aluminum). In addition, the mount assembly <NUM> is configured to support the HET <NUM> and is configured to securably retain the HET <NUM> to the spacecraft. The body <NUM> further includes a plurality of protrusions <NUM> extending away from the circumferential surface <NUM> proximate the second surface <NUM>. The protrusions <NUM> are configured to securably retain the HET <NUM> to the spacecraft. In the illustrated embodiment, the protrusions <NUM> are integral with the body <NUM>; however, in other embodiments, the protrusions <NUM> may be separate but secured to the body <NUM>. Still further, in other embodiments, the mount assembly <NUM> may include other structure that support the protrusions <NUM> or replace the protrusions <NUM> (e.g., mounting ring, brackets, etc.) for securably retaining the HET <NUM> to the spacecraft.

With particular reference to <FIG>, the body <NUM> includes a cavity <NUM> defined radially inward of the circumferential surface <NUM> and between the first and second sides <NUM>, <NUM>, respectively. The body <NUM> further includes a receptacle <NUM> positioned within the cavity <NUM> and configured to retain a plurality of magnetic elements <NUM>. In the illustrated embodiment, the mount assembly <NUM> includes twenty-four discrete magnets <NUM> positioned equidistantly and circumferentially about the longitudinal axis 400A. Each magnet <NUM> is received within a respective aperture <NUM> defined by the receptacle <NUM>. Alternatively, the plurality of magnetic elements <NUM> may be one discrete magnet, or one or more electromagnetic coils.

As shown in <FIG>, in the illustrated embodiment, the mount assembly <NUM> further includes a plurality of projections <NUM> and a retaining member <NUM> (e.g., plate). The projections <NUM> extend inwardly from the circumferential surface <NUM>. The retaining member <NUM> is coupled to the projections <NUM> by fasteners <NUM>. The illustrated projections <NUM> are axially recessed within the cavity <NUM> relative to the longitudinal axis 400A. The retaining member <NUM> is positioned proximate the second side <NUM> and configured to retain the plurality of magnets <NUM> and the receptacle <NUM> within the cavity <NUM>. More specifically, in the illustrated embodiment, the plurality of magnets <NUM> and the receptacle <NUM> are supported by the retaining member <NUM> proximate the second side <NUM> of the body <NUM>. As such, the magnets <NUM>/receptacle <NUM> are/is supported by the body <NUM>/retaining member <NUM>.

As discussed with respect to the assembly of the first HET <NUM>, the plurality of magnetic elements <NUM> of the HET <NUM> is configured to produce the compensating magnetic dipole moment. In particular, the magnitude and direction of the magnetic dipole moment of the magnetic elements <NUM> is selected for reducing the absolute value of the magnetic dipole moment of the HET <NUM> by a certain amount, one example of which may be a predetermined percentage (%) in a direction along the longitudinal axis 400A. In other words, the compensating magnetic dipole moment is configured to reduce the HET magnetic dipole moment toward the near-zero net magnetic dipole moment (A-m<NUM>). In other embodiments, the absolute value of the magnetic dipole moment of the HET <NUM> may be reduced by a set numerical value (e.g., value having unit A-m<NUM>). The plurality of magnetic elements <NUM> are configured to counteract the HET magnetic dipole moment produced by the magnetic field sources and the magnetic field flux guide material <NUM>, without significantly affecting the magnetic field within the discharge chamber <NUM> and the discharge area <NUM> (i.e., affecting the overall shape of the magnetic field or the orientation of the magnetic field flux lines proximate the first end <NUM>).

In operation, with reference to the embodiments of the first HET <NUM>, and its corresponding example of an HET <NUM> as shown in <FIG> and <FIG>, respectively, the magnetic circuit <NUM> (i.e., the magnetic field sources 140A-140C and the magnetic field flux guide material <NUM>, <NUM>) generates the HET magnetic dipole moment. The magnetic elements <NUM> generate a compensating or counteracting magnetic dipole moment, thereby reducing the HET magnetic dipole moment of the HET <NUM>, <NUM> by the predetermined percentage (%) toward the near-zero net magnetic dipole moment (A-m<NUM>).

<FIG> illustrates schematically an assembly <NUM> of a second HET <NUM> embodying the present disclosure, and like elements have been given the same reference numbers as the HET assembly <NUM> plus <NUM>. The assembly <NUM> includes a mount assembly <NUM> and the HET <NUM>. The HET <NUM> includes magnetic field sources 240A-240C, magnetic flux guide material <NUM>, plate <NUM>, and a discharge chamber <NUM> defining a longitudinal axis 200A. A discharge area <NUM> of the HET <NUM> is positioned proximate a first end <NUM> of the HET <NUM>.

The mount assembly <NUM> includes a body <NUM> coupable to the magnetic field flux guide material <NUM>/magnetic field sources 240A-240C. More specifically, the body <NUM> includes a first side <NUM> and a second side <NUM> spaced from the first side <NUM>. A second end <NUM> of the HET <NUM> opposite the first end <NUM> is coupled to the first side <NUM> of the body <NUM>. The mount assembly <NUM> is formed of non-magnetic material (e.g., aluminum). The mount assembly <NUM> is configured to support the HET <NUM> and is configured to securably retain the HET <NUM> to the spacecraft.

The HET assembly <NUM> further includes a shield assembly <NUM>. In the illustrated embodiment, the shield assembly <NUM> includes a housing <NUM> having a first portion <NUM> and a second portion <NUM> extending axially therefrom relative to the longitudinal axis 200A. The first portion <NUM> has an inner surface <NUM> in facing relationship with a side <NUM> of the body <NUM>. The first portion <NUM> further includes an outer surface <NUM>. The second portion <NUM> radially surrounds the HET <NUM> and the mount assembly <NUM> relative to the longitudinal axis 200A. Although not shown, portions of the mount assembly <NUM> may extend through the first portion <NUM> of the housing <NUM> for coupling the mount assembly <NUM> to the spacecraft.

The housing <NUM> is formed by material having high permeability (i.e., soft magnetic material such as iron, ferrite, Mu-metal, Hyperco®, etc.). The housing <NUM> is configured to shield the magnetic field sources 240A-240C and the magnetic field flux guide material <NUM> for reducing the absolute value of the HET magnetic dipole moment of the HET <NUM> by a predetermined percentage (%) in a direction along the longitudinal axis 200A. In other words, the housing <NUM> is configured to reduce the HET magnetic dipole moment toward the near-zero net magnetic dipole moment (A-m<NUM>). More specifically, the housing <NUM> is configured to inhibit or reduce interaction of the magnetic field generated by the magnetic field sources 240A-240C and the magnetic field flux guide material <NUM> with other magnetic fields (e.g., Earth's magnetic field) without significantly affecting the magnetic field within the discharge chamber <NUM> and the discharge area <NUM> (i.e., affecting the overall shape of the magnetic field or the orientation of the magnetic field flux lines proximate the first end <NUM>). Accordingly, the shield assembly <NUM> may be referred to as a shield configuration. The shielding capabilities of the shield assembly <NUM> may be based on one or more of the following: the type of material, the thickness of the first and/or second portions <NUM>, <NUM>, respectively, and/or the radial position of the second portion <NUM> relative to the longitudinal axis 200A.

In some embodiments, the shield assembly <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between thirty and seventy percent. In other embodiments, the shield assembly <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between forty and sixty percent. For example, the shield assembly <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> from about <NUM> A-m<NUM> (±) to about <NUM> A-m<NUM> (±) such that the HET magnetic dipole moment is reduced by about fifty percent.

In operation, with reference to <FIG>, the magnetic circuit <NUM> generates the HET magnetic dipole moment. The shield assembly <NUM> shields the HET magnetic dipole moment created by the magnetic circuit <NUM> (i.e., the magnetic field sources 240A-240C and the magnetic field flux guide material <NUM>), thereby reducing the HET magnetic dipole moment of the HET <NUM> by the predetermined percentage (%) toward the near-zero net magnetic dipole moment (Am<NUM>).

<FIG> illustrates schematically an assembly <NUM> of a third HET <NUM> embodying the present disclosure, and includes a combination of the magnetic elements <NUM> from the first HET assembly <NUM> and the shield assembly <NUM> from the second HET assembly <NUM>. Like elements as the first HET assembly <NUM> have been given the same reference numbers plus <NUM>, and like elements as the second HET assembly <NUM> have been given the same reference numbers plus <NUM>. The assembly <NUM> includes a mount assembly <NUM> and the HET <NUM>. The HET <NUM> includes magnetic field sources 340A-340C, magnetic field flux guide material <NUM>, plate <NUM>, and a discharge chamber <NUM> defining a longitudinal axis 300A. A discharge area <NUM> of the HET <NUM> is positioned proximate a first end <NUM> of the HET <NUM>.

The mount assembly <NUM> includes a body <NUM> coupable to the magnetic field flux guide material <NUM>/magnetic field sources 340A-340C. More specifically, the body <NUM> includes a first side <NUM> and a second side <NUM> spaced from the first side <NUM>. A second end <NUM> of the HET <NUM> opposite the first end <NUM> is coupled to the first side <NUM> of the body <NUM>. The mount assembly <NUM> is formed of non-magnetic material (e.g., aluminum). The mount assembly <NUM> is configured to support the HET <NUM> and is configured to securably retain the HET <NUM> to the spacecraft.

The mount assembly <NUM> includes a plurality of magnetic elements <NUM> (e.g., electromagnetic coils or permanent magnets). In the illustrated embodiment, the plurality of magnetic elements <NUM> includes one element <NUM> positioned proximate and spaced from the second side <NUM> of the body <NUM>. The element <NUM> is a single, cylindrical magnet positioned concentrically with the longitudinal axis 300A. In other embodiments, the plurality of magnetic elements <NUM> may be one or more discrete magnets positioned at a selected radial location relative to the longitudinal axis 300A. These discrete magnetic elements may each be formed by an arc-shaped segment, rod-like shaped segment, box-like shaped segment, etc., positioned at predetermined radial positions relative to the longitudinal axis 300A. Still further, the plurality of magnetic elements <NUM> may be one or more electromagnetic coils positioned radially relative to the longitudinal axis 300A. The plurality of magnetic elements <NUM> is configured to produce a magnetic dipole moment.

The HET assembly <NUM> further includes a shield assembly <NUM>. In the illustrated embodiment, the shield assembly <NUM> includes a housing <NUM> having a first portion <NUM> and a second portion <NUM> extending axially therefrom relative to the longitudinal axis 300A. The first portion <NUM> defines an inner surface <NUM> in facing relationship with the magnetic element <NUM>. The first portion <NUM> further includes an outer surface <NUM> in facing relationship with the second side <NUM> of the body <NUM>. The second portion <NUM> radially surrounds the magnetic element <NUM> relative to the longitudinal axis 300A. Although not shown, portions of the mount assembly <NUM> may extend around or through the shield assembly <NUM> for coupling the mount assembly <NUM> to the spacecraft.

The housing <NUM> is formed by material having high permeability (i.e., soft magnetic material such as iron, Mu-metal, Hyperco®, etc.). The magnitude and direction of the magnetic dipole moment of the plurality of magnetic elements <NUM> is selected for reducing the absolute value of the magnetic dipole moment of the HET <NUM> by a certain amount, one example of which may be a predetermined percentage (%), in a direction along the longitudinal axis 300A. In other embodiments, the absolute value of the magnetic dipole moment of the HET <NUM> may be reduced by a numerical value (e.g., value having units A-m<NUM>). Accordingly, the plurality of magnetic elements <NUM> may be referred to as null magnetic elements <NUM> or compensating elements <NUM> configured to compensate for the HET magnetic dipole moment of the HET <NUM>. The housing <NUM> is configured to shield the HET <NUM> from the magnetic element <NUM> for reducing or constraining the effect of the compensating elements <NUM> on the magnetic field (i.e., the flux lines) proximate the first end <NUM> while facilitating the reduction of the absolute value of the HET magnetic dipole moment of the HET <NUM> by a predetermined percentage (%) in a direction along the longitudinal axis 300A. In other words, the compensating magnetic elements <NUM> are configured to reduce the HET magnetic dipole moment toward the near-zero net magnetic dipole moment (A-m<NUM>), while the housing <NUM> is configured to reduce or constrain the effect of the compensating magnetic elements <NUM> on the magnetic field of the HET <NUM> proximate the first end <NUM>. The combination of the plurality of magnetic elements <NUM> and the shield assembly <NUM> is configured to counteract the HET magnetic dipole moment produced by the magnetic field sources 340A-340C and the magnetic field flux guide material <NUM>, without significantly affecting the magnetic field within the discharge chamber <NUM> and the discharge area <NUM> (i.e., affecting the overall shape of the magnetic field or the orientation of the magnetic field flux lines proximate the first end <NUM>).

In some embodiments, the plurality of magnetic elements <NUM>/shield assembly <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between forty and ninety-nine percent. In other embodiments, the plurality of magnetic elements <NUM>/shield assembly <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between fifty and ninety-nine percent. In yet other embodiments, the plurality of magnetic elements <NUM>/shield assembly <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between sixty and ninety-nine percent. In yet still other embodiments, the plurality of magnetic elements <NUM>/shield assembly <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> by between seventy and ninety-nine percent. For example, the magnetic elements <NUM>/shield assembly <NUM> is configured to reduce the HET magnetic dipole moment of the HET <NUM> from about <NUM> A-m<NUM> (±) to about <NUM> A-m<NUM> (±) such that the HET magnetic dipole moment is reduced by about ninety-eight percent.

In operation, with reference to <FIG>, the magnetic circuit <NUM> generates the HET magnetic dipole moment. The shield assembly <NUM> shields the HET magnetic dipole moment created by the magnetic elements <NUM>, thereby reducing the HET magnetic dipole moment of the HET <NUM> by the predetermined percentage (%) toward the near-zero net magnetic dipole moment (A-m<NUM>).

Thus, the disclosure provides, among other things, an HET assembly <NUM>, <NUM>, <NUM>, <NUM> configured to have a near-zero net magnetic dipole moment without significantly affecting the magnetic field within a discharge chamber <NUM>, <NUM>, <NUM>, <NUM> and the discharge area <NUM>, <NUM>, <NUM>, <NUM>, respectively. Specifically, the HET assembly <NUM>, <NUM>, <NUM>, <NUM> includes compensating elements <NUM>, <NUM> and/or a shield assembly <NUM>, <NUM> for achieving the near-zero net magnetic dipole moment. The compensating elements <NUM>, <NUM> and/or the shield assembly <NUM>, <NUM> may reduce or inhibit the interaction between the HET magnetic dipole moment of the HET <NUM>, <NUM>, <NUM>, <NUM> and magnetic dipole moments generated by other magnetic fields such that torque applied to a spacecraft may be lowered.

Claim 1:
A Hall-effect thruster assembly (<NUM>, <NUM>, <NUM>) comprising:
a Hall-effect thruster (<NUM>, <NUM>, <NUM>) including a plurality of magnetic sources (<NUM>, <NUM>) for creating a first magnetic circuit (<NUM>), the plurality of magnetic sources positioned between a first end (<NUM>, <NUM>, <NUM>) and a second, opposite end (<NUM>, <NUM>, <NUM>) of the Hall-effect thruster, the plurality of magnetic sources defining a longitudinal axis (100A, 300A, 400A) extending through the first end and the second end, the first end configured as a discharge end, the plurality of magnetic sources being configured such that during operation of the Hall-effect thruster, the plurality of magnetic sources collectively create the first magnetic circuit having a magnetic dipole moment;
a mount assembly (<NUM>, <NUM>, <NUM>) coupled to the second end, the mount assembly configured to secure the plurality of magnetic sources to a spacecraft; and
characterised by
a magnetic element (<NUM>, <NUM>, <NUM>) supported by the mount assembly, the magnetic element positioned relative to the plurality of magnetic sources by the mount assembly such that during operation of the Hall-effect thruster, the magnetic element produces a compensating magnetic dipole moment cooperative with the magnetic dipole moment of the Hall-effect thruster to reduce the absolute value of the magnetic dipole moment of the Hall-effect thruster in the direction along the longitudinal axis.