WO2023244857A1

WO2023244857A1 - Hall thruster

Info

Publication number: WO2023244857A1
Application number: PCT/US2023/025653
Authority: WO
Inventors: Benjamin JORNS; William Hurley; Thomas Marks; Matthew Byrne
Original assignee: The Regents Of The University Of Michigan
Priority date: 2022-06-17
Filing date: 2023-06-19
Publication date: 2023-12-21

Abstract

A thruster includes a mass source, an ejection outlet, and a channel forming an ejection path from the mass source to the ejection outlet. Multiple annular current paths form loops such that current flow along the loops is transverse to ion flow along the ejection path. The current paths are driven by current supply circuitry to create a selected current distribution proximate to the channel

Description

HALL THRUSTER

Priority

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63/353,298, filed June 17, 2022, titled Hall Thruster, which is incorporated herein in its entirety.

BACKGROUND

Technical Field

[0002] The disclosure relates generally to Hall thrusters.

Brief Description of Related Technology

[0003] In space travel thruster systems are used to propel vehicles to target destinations. For interplanetary space travel, thruster efficiency may guide selection of systems. Longer distance missions pose the challenge that resources, including thruster propellants and thruster energy sources, used later in the mission often may be carried by the mission vehicle from the onset. Thus, increases in thruster efficiency and improvements in the operation of high efficiency thruster designs will continue to drive adoption.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 shows a cross-sectional view of an example thruster.

[0005] Figure 2 shows an example thrust generation technique.

DETAILED DESCRIPTION

[0006] In various contexts, a Hall thruster may generate propulsion by ejecting ions from a channel as a result of a magnetic field created by cycling current proximate the channel. The magnetic field may inhibit the flow of electrons through a channel between a cathode and anode (e.g., outside and inside the channel, respectively). The buildup of electrons spiraling electrons in the channel generates an axial electric field that accelerates ions out of the channel. In some cases, a fluid (such as a noble gas, gas, or other fluid) supplied by a mass source of the thruster may be used as a source of electrons and/or ions.

[0007] To shape the magnetic field created by the current cycling, the conventional wisdom has been to rely on a ferromagnetic core (e.g., made from ferromagnetic materials, such as iron, nickel, cobalt, and/or rare earth metals, in a magnetized state) proximate to the conductive materials in which the current cycles. The conventional wisdom holds that the ferromagnetic core is necessary to generate the field strengths to support operation of a thruster.

[0008] As operating power increases, strain on the system may increase. For example, accelerated ions may crash into the various surfaces of the channel and/or other portions of the thruster. Accordingly, the accelerated ions may cause erosion on these surfaces. For example, increased operation power may be associated with increased current and/or current density. Increases in current and/or current density may increase heating due to resistance in the conductive materials (such as copper, noble metals, high temperature superconductors, and/or other high conductivity materials) used to create the current cycling proximate the channel in which the ions are accelerated. High temperatures can create challenges for any materials in the thruster. For example, ferromagnetic materials may demagnetize if the material is brought above a critical temperature for magnetization.

[0009] In some cases, high power operation may lead to saturation of the ferromagnetic core. Saturation may occur when no additional magnetic field domains within a ferromagnetic material can be aligned with the externally applied field from the cycling current. Accordingly, the field strength achievable while relying on the ferromagnetic material may be constrained as a result of this saturation.

[0010] The techniques and architectures discussed herein proceed contrary to the conventional wisdom by reducing and/or eliminating reliance on a ferromagnetic core. For example, the techniques and architectures discussed may not necessarily include a ferromagnetic core. For example, techniques and architectures discussed may operate in above-saturation modes (e.g., relying on a ferromagnetic core below saturation in a first mode and then relying on current based field shaping above saturation in a second mode). For example, the techniques and architectures discussed may operate using voids (e.g., space occupied by vacuum, gas, or other low-density occupancy).

[0011] Figure 1 shows a cross-sectional view of an example thruster 100. The cross- sectional view is along a radius of the thruster in a cylindrical space. The structure of the thruster may be realized by revolving the cross-section around the symmetry axis 199. Thus, the components (including the channel 102, current paths 1 12, 1 14, 1 16, 118, and voids 132) shown via cross-section in Figure 1 are annular in three dimensional space. The current supply circuitry 120 is shown schematically as block and is not intended to convey an annular geometry.

[0012] Current may be driven by current supply circuitry 120 through multiple current paths 112, 1 14, 116, 1 18 (e.g., made from conductive materials such as copper, noble metals, high temperature superconductors, and/or other conductive materials) forming current loops prthe channel. The current levels in the multiple current paths 1 12, 114, 1 16, 1 18 may be different, such that the spatial distribution of current cycling proximate the channel 102 may be controlled via control of the current supply circuitry 120. The positions of the current paths may be selected (e.g., selectable through fixation at the time of fabrication of the thruster and/or selectable through mechanical translation during operation/configuration) to control the distribution. Accordingly, the spatial configuration of current paths shown in the example thruster is for the purpose of illustration and other spatial configurations may be used. The cross-sectional shape of the current paths may be selected to control the distribution. Accordingly, the cross-sectional shapes shown are for the purpose of illustration and other shapes may be used. The number current paths may be selected to control the distribution. Accordingly, the number of current paths shown is for the purpose of illustration and other numbers of paths may be used. For example, up to 100 or more current paths may be used.

[0013] To create the distribution, multiple current paths may be placed at different radial and longitudinal positions around the axis of symmetry 199. For example, two different current paths may be positioned at two different radial distances from the axis of symmetry 199. As an example, two concentric current paths may be located at the same longitudinal position but at different radii with respect to the axis of symmetry 199. For example, two different current paths may be positioned at two different longitudinal distances along the axis of symmetry 199. For example, two different current paths with the same radii may be positioned at different longitudinal distances. In some cases, two example current paths may differ in both radius and longitudinal position.

[0014] The distribution of current may be selected to match (e.g., approximate to allow for operational performance interchangeable with) an existing thruster design reliant on a ferromagnetic core while implementing one or more voids 132 in place of the ferromagnetic core. Accordingly the void-based thruster may be interchanged with a thruster using the ferromagnetic core reliant design and provide consistent thrust at a lower overall thruster weight. In other words, a void may be used in lieu of a ferromagnetic core. Accordingly, the current distribution in the current paths may be selected to create a similar magnetic field within the channel that would have been created using the ferromagnetic core. In some cases, creating the same field using voids may call for use of more current than would be used in the presence of the ferromagnetic core. For example, the current used may increase up to tenfold or more.

[0015] In some cases, the current distribution may be selected to create magnetic shielding geometry in the channel. For example, the magnetic field in the channel may be selected to be strongest at the center of the channel and weakest near the wall of the channel. This shield geometry may reduce the intensity of collisions between ions and the channel wall, which may reduce material erosion and increase thruster performance/life. In other words, the magnetic shield geometry mitigates ion bombardment erosion in the channel.

[0016] The current levels in the multiple current paths may be independent from one another or dependent on one another. Accordingly, the multiple different current levels may include multiple independently controllable current levels which may be set separately each as an individual free parameter by the current supply circuitry. Additionally or alternatively, the multiple different current levels may include one or more dependently controlled current levels, where the current level in that particular dependent current path may be determined, at least in part, based on the current level in one or more other current paths.

[0017] For example, two current paths may have two independent current levels that may be selected via control of the current supply circuitry 120 without affecting one another (in some cases, the two paths may be incidentally selected to be set to the same current level).

[0018] For example, two dependent current paths may be selected to have a defined relationship between their current levels. For example, the current paths may be selected to be fixed to have the same current level. For example, the current paths may be selected to have currents in a defined ratio (or other algorithmic relationship). For example, the current paths may be selected to have current levels within a defined range of one another. Other relationships may be used. These example current levels may be characterized as dependent.

[0019] The thruster 100 may include a chassis 1 10 that may house the current paths 112, 114, 1 16, 1 18. The chassis may include voids 132 which may form ‘air cores’ as discussed below in the example implementations. The voids 132 may include portions of vacuum, gas, and/or other occupancy. The chassis 1 10 may be sealed or permeable. Accordingly, the occupancy of the voids may be fixed at the time of fabrication of the thruster or allowed to change with changes in ambient environment. In some cases, the voids 132 may allow for reduced total mass of the thruster 100 while maintaining a target footprint or overall volume for the thruster 100. Voids may allow for selectability of spacing between current paths for control of the distribution of current.

[0020] Referring now to Figure 2 which shows an example technique 200 for generation of thrust while continuing to refer to Figure 1 , the current supply circuitry 120 may drive current in current paths 112, 114, 116, 118 to generate a magnetic field 130 in the channel 102 (202).

[0021] Propellant such as gas (e.g. xenon, krypton, or other propellant gases/fluids) may be fed into the channel (204) via a mass source 101.

[0022] The magnetic field 130 may cause electrons in the channel to accelerate a collide with the propellant generating ions. The ionized electrons may increase and spiral in the channel. The increasing electrons in the channel 102 may create an electric field gradient 140 along the channel 102 (206) along an ejection path 103 towards an ejection outlet 104 of the channel 102.

[0023] The electric field gradient 140 ejects the ions from the channel 102 via the ejection outlet 104 (208) causing thrust.

[0024] In various implementations, the current paths 112, 114, 116, 118 may passively cool during operation. For example, the current paths 112, 114, 116, 118 may radiatively cool through the voids 132. In some cases (e.g., where the voids 132 have gas or other fluid occupancy) the current paths 112, 114, 116, 118 may have a convective cooling component.

[0025] In various implementations, the current paths 112, 114, 116, 118 may be actively cooled during operation. For example, coolant (such as water and/or other fluids) may be cycled through tubes proximate to (or otherwise in thermal contact with) the current paths. The coolant may be used to implement heat exchange (e.g., via compressor/evaporator, thermal electric cooling, transport to a heat sink, or other cooling scheme). For example, the current paths 112, 114, 116, 118 may be configured as bitter magnets. Accordingly the coolant may be cycled through tubes through openings in the current paths and in thermal contact with the current paths (not shown).

[0026] In various implementations, the operating temperature of the thruster may be selected to be above the critical temperatures at which various ferromagnetic materials may demagnetize. The omission of ferromagnetic materials from the thruster 100 may allow for increased operational temperature flexibility because the constraint of maintaining magnetization may be relaxed or removed.

[0027] Various implementations have been described and various other implementations are possible. Table 1 shows various examples.

[0028] The present disclosure has been described with reference to specific examples that are intended to be illustrative only and not to be limiting of the disclosure. Changes, additions and/or deletions may be made to the examples without departing from the spirit and scope of the disclosure.

[0029] The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

Claims

What is Claimed is:

1. A thruster including: a mass source; an ejection outlet; a channel forming an ejection path from the mass source to the ejection outlet; multiple annular current paths that form loops such that current flow along the loops is transverse to ion flow along the ejection path; and current supply circuitry configured to generate multiple different current levels simultaneously on the multiple annular current paths.

2. The thruster of claim 1 , including an annular void proximate to the multiple annular current paths.

3. The thruster of claim 1 , further including an annular chassis housing the multiple annular current paths.

4. The thruster of claim 1 , where the multiple different current levels include multiple independently controllable current levels.

5. The thruster of claim 1 , where the multiple different current levels include a current level dependent on at least another one of the multiple different current levels.

6. The thruster of claim 1 , where the multiple different current levels include current levels selected and/or position to generate a shield geometry, where the shield geometry mitigates ion bombardment erosion in the channel.

7. The thruster of claim 1 , where: the channel is annular; and the multiple annular current paths and the channel are disposed concentrically around an axis of symmetry.

8. The thruster of claim 7, where the multiple annular current paths are disposed at selected radial distances from the axis of symmetry.

9. The thruster of claim 7, where the multiple annular current paths are disposed at selected longitudinal position along the axis of symmetry to generate a selected current distribution proximate to the channel.

10. The thruster of claim 1 , where: the multiple annular current paths are disposed to generate a magnetic field profile matched to that of an existing design including a ferromagnetic core, where the thruster includes a core void in lieu of the ferromagnetic core.

11 . The thruster of claim 1 , where a nominal operating temperature of the thruster exceeds a critical demagnetization temperature for a ferromagnetic material.

12. The thruster of claim 1 , including cooling tubes in thermal contact with ones of the multiple annular current paths.

13. The thruster of claim 1 , where the multiple annular current paths include conductive copper paths.

14. A method including: generating thrust by ejecting ions out of a channel by: generating, via multiple annular current paths proximate the channel, a selected spatial current distribution proximate to the channel; and accelerating electrons in a spiral path within the channel thereby generating an axial electrical field to eject the ions out of the channel.

15. The method of claim 14, where generating the selected spatial current distribution includes supplying current to the multiple annular current paths to generate multiple different current levels in the multiple annular current paths.

16. The method of claim 15 where the multiple different current levels include multiple independent current levels.

17. The method of claim 15 where the multiple different current levels include a current level that is dependent on another of the multiple different current levels.

18. A method including: driving multiple current loops; and ejecting mass from a mass source down a channel forming an ejection path from the mass source to an ejection outlet, the channel forming an annulus around a core void, the channel surrounded by at least a first one of the multiple current loops.

19. The method of claim 18, where driving the multiple current loops includes driving a second one of the multiple current loops, the second one of the multiple current loops disposed within the annulus formed by the channel.

20. The method of claim 19, where the second one of the multiple current loops is disposed at least in part within the core void.