Hall current plasma source having a center-mounted or a surface-mounted cathode

Patent metadata

Field	Value
Publication number	US-9934929-B1
Application number	US-201715424385-A
Country	US
Kind code	B1
Filing date	Feb 3, 2017
Priority date	Feb 3, 2017
Publication date	Apr 3, 2018
Grant date	Apr 3, 2018

Abstract

A miniature Hall current plasma source apparatus having magnetic shielding of the walls from ionized plasma, an integrated discharge channel and gas distributor, an instant-start hollow cathode mounted to the plasma source, and an externally mounted keeper, is described. The apparatus offers advantages over other Hall current plasma sources having similar power levels, including: lower mass, longer lifetime, lower part count including fewer power supplies, and the ability to be continuously adjustable to lower average power levels using pulsed operation and adjustment of the pulse duty cycle. The Hall current plasma source can provide propulsion for small spacecraft that either do not have sufficient power to accommodate a propulsion system or do not have available volume to incorporate the larger propulsion systems currently available. The present low-power Hall current plasma source can be used to provide energetic ions to assist the deposition of thin films in plasma processing applications.

First claim

What is claimed is:

1. A Hall current plasma source, comprising:
a flat end plate having a first side and an opposing second side, and a channel therethrough between the first side and the second side;
a cylindrical magnetizable core having a first end, a second end, and a first axis, the first end being attached to the second side of said flat end plate, said cylindrical magnetizable core having an outer surface and a channel therethrough between the first end and the second end along the first axis aligned with the channel in said flat end plate;
a first conducting wire coil wound around the outer surface of said cylindrical magnetizable core;
a first cylindrical magnetic screen having a second axis collinear with the first axis enclosing said first conducting wire coil, said first cylindrical magnetic screen having an outer diameter;
a hollow cathode discharge apparatus adapted to ionize a first chosen gas, comprising:
a metal tube disposed in the channel of said cylindrical magnetizable core, having a first end and a second end and an inside surface having an insert of low-work-function material attached to the inside surface of said metal tube, the first end of said metal tube passing through the channel in said flat end plate and adapted to receive the first chosen gas;
an electrical insulator attached to the first side of said flat end plate for supporting said metal tube and for electrically isolating said metal tube from both said flat end plate and said cylindrical magnetizable core; and
a metallic keeper element having a hole therethrough for permitting the first chosen gas from said metal tube to pass therethrough, said metallic keeper element being electrically isolated from said cylindrical magnetizable core and said metal tube;

a second cylinder having a third axis collinear with the first axis, comprising:
a second cylindrical magnetic screen having a fourth axis collinear with the first axis, and an inner diameter which is larger than the outer diameter of said first cylindrical magnetic screen, forming an annular region therebetween;
a second conducting wire coil disposed around said second cylindrical magnetic screen; and
a magnetizable outer cylinder having a fifth axis collinear with the first axis surrounding said second conducting wire coil, said magnetizable outer cylinder having a first end and a second end, the first end being mounted on the second side of said flat end plate;
wherein the second end of said cylindrical magnetizable core and the second end of said magnetizable outer cylinder are formed into circular pole pieces facing the annular region;

at least one cylindrical anode band disposed in the annular region;
an annular ion channel having an open end and a closed end formed in the annular region adapted to electrically isolate said first cylindrical magnetic screen and said second cylindrical magnetic screen from said at least one cylindrical anode band; and
a gas plenum adapted to receive a second chosen gas and for distributing the second chosen gas into said annular ion channel.

2. The Hall current plasma source of claim 1 , wherein said flat end plate comprises magnetizable material.

3. The Hall current plasma source of claim 1 , wherein said annular ion channel is fabricated from materials chosen from polycarbonate, polyether ether ketone, PEEK, graphite, boron nitride, and petalite ceramic.

4. The Hall current plasma source of claim 1 , wherein said low-work-function material comprises 12Ca0-7Al 2 0 3 .

5. The Hall current plasma source of claim 1 , wherein the first chosen gas and the second chosen gas comprise the same gas.

6. The Hall current plasma source of claim 1 , wherein the annular ion channel is tapered such that it is wider toward the open end thereof.

7. A Hall current plasma source, comprising:
a flat end plate having a first side and an opposing second side;
a cylindrical magnetizable core having a first end and a second end and a first axis, the first end being attached to the second side of said flat end plate, said cylindrical magnetizable core having an outer surface;
a first conducting wire coil wound around the outer surface of said cylindrical magnetizable core;
a first cylindrical magnetic screen having a second axis collinear with the first axis enclosing said first conducting wire coil, said first cylindrical magnetic screen having an outer diameter;
a second cylinder having a third axis collinear with the first axis, comprising:
a second cylindrical magnetic screen having a fourth axis collinear with the first axis, and an inner diameter which is larger than the outer diameter of said first cylindrical magnetic screen, forming an annular region therebetween;
a second conducting wire coil disposed around said second cylindrical magnetic screen; and
a magnetizable outer cylinder having a fifth axis collinear with the first axis surrounding said second conducting wire coil, said magnetizable outer cylinder having a first end and a second end, the first end being mounted on the second side of said flat end plate, and an outer surface;
wherein the second end of said cylindrical magnetizable core and the second end of said magnetizable outer cylinder are formed into circular pole pieces facing the annular region;

at least one cylindrical anode band disposed in the annular region;
an annular ion channel having an open end and a closed end formed in the annular region adapted to electrically isolate said first cylindrical magnetic screen and said second cylindrical magnetic screen from said at least one cylindrical anode band;
a gas plenum adapted to receive a first chosen gas and for distributing the first chosen gas into said annular ion channel; and
a hollow cathode discharge apparatus for ionizing a second chosen gas disposed on or outside of the outer surface of said magnetizable outer cylinder or on or above the second end of said cylindrical magnetizable core.

8. The Hall current plasma source of claim 7 , wherein said flat end plate comprises magnetizable material.

9. The Hall current plasma source of claim 7 , wherein said annular ion channel is fabricated from materials chosen from polycarbonate, polyether ether ketone, PEEK, graphite, boron nitride, and petalite ceramic.

10. The Hall current plasma source of claim 7 , wherein the first chosen gas and the second chosen gas comprise the same gas.

11. The Hall current plasma source of claim 7 , wherein the annular ion channel is tapered such that it is wider toward the open end thereof.

12. The Hall current plasma source of claim 7 , wherein said hollow cathode discharge apparatus comprises:
a base member having an outside surface and an inside surface, and an inlet therethrough for permitting the second chosen gas to flow;
a low-work function material or cathode instant start material;
an electrically insulating, gas porous insulator attached to the inside surface of said base member for supporting said low-work function material through which the second chosen gas flows around said low-work function material;
a metallic keeper having a hole therethrough through which the second chosen gas flows, and having an outer surface;
second electrically insulating material covering at least a portion of the outer surface of said metallic keeper; and
a cover member forming a chamber with said base member and having an opening therein facing said low-work function material, for receiving said second electrically insulating material, for supporting said metallic keeper in a spaced apart orientation with said low-work function material, and for enclosing said low-work function material;
wherein the second chosen gas is flowed ar

Assignees

• Univ Colorado State Res Found

Inventors

• Martinez Rafael A
• Williams John D
• Moritz Jr Joel A
• Farnell Casey C

Classifications

• H01J27/146 Primary

  End-Hall type ion sources, wherein the magnetic field confines the electrons in a central cylinder · CPC title

• H01J27/143

  Hall-effect ion sources with closed electron drift · CPC title

• F03H1/0075 Primary

  with an annular channel; Hall-effect thrusters with closed electron drift · CPC title