# US 2019/0168895 A1 · Low-power hall thruster with an internally mounted low-current hollow cathode

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- Number: US 2019/0168895 A1
- Document ID: US20190168895A1
- Status: Published application
- Kind: A1
- Application number: 16/205,048
- Filed: 2018-11-29
- Published: 2019-06-06
- Earliest claimed: 2017-12-06
- Assignees: California Institute of Technology
- Applicants: California Institute of Technology
- Inventors: Ryan W CONVERSANO; Dan M GOEBEL; Ira KATZ; Richard R HOFER
- Web page: https://patentgrep.com/patent/US20190168895A1

## CPC

- F03H 1/0012: {Means for supplying the propellant}
- B64G 1/413: {Ion or plasma engines}
- F03H 1/0075: {with an annular channel; Hall-effect thrusters with closed electron drift}
- F03H: PRODUCING A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR (from combustion products F02K)
- B64G: COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR

## Abstract

A low-power Hall thruster gains significantly improved efficiency by a combination of features, including a single piece, h-shaped magnetic screen which enables a more efficient internal volume utilization as well as optimal magnetic shielding; an internally mounted cathode with varying diameter further decreases the footprint of the thruster; an anode with multiple baffles connected by axially oriented holes generates a highly azimuthally uniform propellant flow.

## Claims

### Claim 1

A Hall thruster comprising:
a center axis oriented from an upstream section of the Hall thruster, the upstream section housing a back pole for a magnetic circuit and a supply line for a gas propellant, to a downstream section concentric with an azimuthally-symmetrical discharge chamber; and
a single-piece azimuthally-symmetrical magnetic screen,
wherein:
the azimuthally-symmetrical discharge chamber has an annular shape,
the single-piece azimuthally-symmetrical magnetic screen has an h-shape cross section, the h-shape cross section comprising a first prong at an upstream end and two prongs at a downstream end,
the single-piece azimuthally-symmetrical magnetic screen comprises a first hollow cylinder physically contacting the back pole at a single circular point of contact,
the single-piece azimuthally-symmetrical magnetic screen comprises a second hollow cylinder and a third hollow cylinder, the second hollow cylinder being concentric to the third hollow cylinder, and
the azimuthally-symmetrical discharge chamber comprises a radially-outward wall and a radially-inward wall,
the second hollow cylinder of the single-piece azimuthally-symmetrical magnetic screen encircles the radially-inward wall of the azimuthally-symmetrical discharge chamber, and
the third hollow cylinder of the single-piece azimuthally-symmetrical magnetic screen encircles the radially-outward wall of the azimuthally-symmetrical discharge chamber, thereby forming a magnetic field protecting the radially-outward wall and the radially-inward wall of the azimuthally-symmetrical discharge chamber from erosion due to ion bombardment.

### Claim 2 (depends on 1)

The Hall thruster of claim 1, wherein the single-piece azimuthally-symmetrical magnetic screen is made of a high permeability magnetic alloy.

### Claim 3 (depends on 2)

The Hall thruster of claim 2, wherein the single-piece azimuthally-symmetrical magnetic screen is made of a material selected from: iron-cobalt-vanadium, vacuum melted low-carbon magnetic iron, and standard magnetic iron.

### Claim 4 (depends on 1)

The Hall thruster of claim 1, further comprising:
an internally-mounted cathode along the center axis, the internally-mounted cathode having a variable diameter,
wherein:
the internally-mounted cathode comprises an upstream section and a downstream section, and
the upstream section is axially longer than the downstream section.

### Claim 5 (depends on 4)

The Hall thruster of claim 4, further comprising:
an azimuthally-symmetrical anode within the azimuthally-symmetrical discharge chamber,
wherein:
the azimuthally-symmetrical anode comprises a plurality of baffles configured to increase azimuthal flow uniformity for the gas propellant,
the plurality of baffles comprises at least:
a first baffle comprising a first plurality of holes connecting the first baffle to the supply line;
a second baffle adjacent to the first baffle and connected to the first baffle through a second plurality of holes; and
a third baffle adjacent to the second baffle and connected to the second baffle through a third plurality of circular holes,
the first baffle is upstream of the second baffle,
the second baffle is upstream of the third baffle,
the first, second and third baffles are azimuthally-symmetrical,
the third baffle comprises a radially-inward surface and a radially-outward surface, and
the third baffle comprises a fourth plurality of holes on the radially-inward and radially-outward surfaces.

### Claim 6

A Hall thruster comprising:
a center axis oriented from an upstream section of the Hall thruster, the upstream section housing a back pole for a magnetic circuit and a supply line for a gas propellant, to a downstream section concentric with an azimuthally-symmetrical discharge chamber; and
an internally-mounted cathode along the center axis, the internally-mounted cathode having a variable diameter,
wherein:
the internally-mounted cathode comprises an upstream section and a downstream section, and
the upstream section is axially longer than the downstream section.

### Claim 7 (depends on 6)

The Hall thruster of claim 6, wherein the downstream section of the internally-mounted cathode comprises a cathode heater.

### Claim 8 (depends on 6)

The Hall thruster of claim 6, wherein the downstream section of the internally-mounted cathode is heaterless.

### Claim 9 (depends on 6)

The Hall thruster of claim 6, wherein the upstream section of the internally-mounted cathode has a diameter different from that of the downstream section of the internally-mounted cathode.

### Claim 10

A Hall thruster comprising:
a center axis oriented from an upstream section of the Hall thruster, the upstream section housing a back pole for a magnetic circuit and a supply line for a gas propellant, to a downstream section concentric with an azimuthally-symmetrical discharge chamber; and
an azimuthally-symmetrical anode within the azimuthally-symmetrical discharge chamber,
wherein:
the azimuthally-symmetrical anode comprises a plurality of baffles configured to increase azimuthal flow uniformity for the gas propellant,
the plurality of baffles comprises at least:
a first baffle comprising a first plurality of holes connecting the first baffle to the supply line;
a second baffle adjacent to the first baffle and connected to the first baffle through a second plurality of holes; and
a third baffle adjacent to the second baffle and connected to the second baffle through a third plurality of circular holes,
the first baffle is upstream of the second baffle,
the second baffle is upstream of the third baffle,
the first, second and third baffles are azimuthally-symmetrical,
the third baffle comprises a radially-inward surface and a radially-outward surface, and
the third baffle comprises a fourth plurality of holes on the radially-inward and radially-outward surfaces.

### Claim 11 (depends on 10)

The Hall thruster of claim 10, wherein the holes of the first plurality of holes have:
a larger total surface area than the holes of the second plurality of holes, and
a larger total surface area than the holes of the third plurality of holes.

### Claim 12 (depends on 10)

The Hall thruster of claim 10, wherein the holes of the third plurality of holes have a larger total surface area than the holes of the second plurality of holes.

### Claim 13 (depends on 10)

The Hall thruster of claim 10, wherein the holes of the fourth plurality of holes have a larger total surface area than the holes of the third plurality of holes.

### Claim 14 (depends on 10)

The Hall thruster of claim 10, wherein the holes of the second plurality of holes are equally spaced azimuthally, and azimuthally offset relative to the holes of the first plurality of holes.

### Claim 15 (depends on 10)

The Hall thruster of claim 10, wherein the holes of the third plurality of holes are equally spaced azimuthally, and azimuthally offset relative to the holes of the second plurality of holes.

### Claim 16 (depends on 10)

The Hall thruster of claim 10, wherein each hole of the third plurality of holes is aligned between two holes of the second plurality of holes with an equidistant offset from both of said two holes of the second plurality of holes.

### Claim 17 (depends on 10)

The Hall thruster of claim 10, wherein the first plurality of holes, the second plurality of holes, the third plurality of holes, or the fourth plurality of holes comprises circular holes.

### Claim 18 (depends on 10)

The Hall thruster of claim 10, wherein the first baffle, the second baffle, and the third baffle each have a rectangular cross section.

### Claim 19 (depends on 10)

The Hall thruster of claim 10, wherein the first baffle, the second baffle, and the third baffle each have a cross section selected from the group consisting of: square, pentagonal, and hexagonal.