Closed drift ion source

• US 6,919,672 B2
• Filed: 04/10/2003
• Issued: 07/19/2005
• Est. Priority Date: 04/10/2002
• Status: Expired due to Fees

• Current Assignee: General Plasma, Inc. (BASF SE)
• Original Assignee: Applied Process Technology, Inc. (Italveco Srl)
• Inventors: Madocks, John
• Primary Examiner(s): Patel, Nimeshkumar D.
• Assistant Examiner(s): RIELLEY, ELIZABETH A
• Application Number:
  US10/411,024
• Publication Number:
  US 20030230961A1
• Time in Patent Office: 831 Days
• Field of Search: 250/424, 250/425, 250/427, 250/423.F, 315/111.91, 315/111.81, 313/359.1, 313/161.1, 313/162.1, 313/231.01, 313/231.31, 313/231.41, 118/723.MW, 118/723.ME
• US Class Current: 313/359.1
• CPC Class Codes: F03H 1/0075 with an annular channel; Hall-effect thrusters with closed electron drift
• CPC Class Codes: H01J 27/143 Hall-effect ion sources with closed electron drift
• CPC Class Codes: H05H 1/54 Plasma accelerators

Abstract

A closed drift ion source which includes a channel having an open end, a closed end, and an input port for an ionizable gas. A first magnetic pole is disposed on the open end of the channel and extends therefrom in a first direction. A second magnetic pole disposed on the open end of the channel and extends therefrom in a second direction, where the first direction is opposite to the second direction. The distal ends of the first magnetic pole and the second magnetic pole define a gap comprising the opening in the first end. An anode is disposed within the channel. A primary magnetic field line is disposed between the first magnetic pole and the second magnetic pole, where that primary magnetic field line has a mirror field greater than 2.

Claims

1. A closed drift ion source, comprising:

a channel having an open end and a closed end, wherein said channel includes an input port for an ionizable gas;

a first magnetic pole disposed on said open end of said channel and extending therefrom in a first direction;

a second magnetic pole disposed on said open end of said channel and extending therefrom in a second direction, wherein said first direction is opposite to said second direction;

an anode disposed within said channel;

a primary magnetic field line disposed between said first magnetic pole and said second magnetic pole, wherein said primary magnetic field line has a mirror field greater than 2.

2. The closed drift ion source of claim 1, wherein said first and second magnetic poles comprise cathode electrodes.

3. The closed drift ion source of claim 1, wherein said first and second magnetic poles are electrically isolated.

4. The closed drift ion source of claim 1, wherein said mirror field is substantially symmetric.

5. The closed drift ion source of claim 4, wherein said first magnetic pole comprises a first distal end, and wherein said second magnetic pole comprises a second distal end, and wherein said first distal end is separated from said second distal end by a gap, wherein said primary magnetic field line comprises a minimum magnetic field strength value disposed about equidistant from said first distal end and said second distal end.

6. The closed drift ion source of claim 5, wherein said anode is disposed on a first side of said gap, further comprising a cathode disposed on a second side of said gap.

7. The closed drift ion source of claim 6, wherein said first magnetic pole comprises a top surface, and wherein said second magnetic pole comprises a top surface, further comprising:

a first coating disposed on said top surface of said first magnetic pole, wherein said first coating comprises a material having a secondary electron emission coefficient of about 1 or more; and

a second coating disposed on said top surface of said second magnetic pole, wherein said second coating comprises a material having a secondary electron emission coefficient of about 1 or more.

8. The closed drift ion source of claim 1, further comprising a first magnetic shunt disposed within said channel between said open end and said closed end, wherein said first magnetic shunt includes a bottom portion and a plurality of sides attached to and extending outwardly from said bottom portion to define an enclosure having an opening, wherein said opening of said first magnetic shunt faces said open end of said channel, wherein said anode is disposed within said first magnetic shunt.

9. The closed drift ion source of claim 8, further comprising:

a first permanent magnet attached to said first magnetic pole;

a second permanent magnet attached to said second magnetic pole; and

a second magnetic shunt attached to said first permanent magnet and to said second permanent magnet;

wherein said anode is disposed between said first permanent magnet and said second permanent magnet.

10. The closed drift ion source of claim 9, further comprising:

a third magnetic shunt disposed between said first magnetic pole and a cathode; and

a fourth magnetic shunt disposed between said second magnetic pole and a second cathode.

11. A closed drift ion source, comprising:

a first permanent magnet, where said first permanent magnet comprises a first pole having a first magnetic polarity and a second pole having a second magnetic polarity;

a second permanent magnet, wherein said second permanent magnet comprises a first pole having said first magnetic polarity and a second pole having said second magnetic polarity;

a first magnetic pole and a second magnetic pole;

wherein said first magnetic pole has a top surface, a bottom surface, a first end and a second end, wherein said bottom surface of said first magnetic pole at said first end is disposed adjacent said second end of said first permanent magnet and wherein said second end of said first magnetic pole extends from said first permanent magnet in a first direction toward said second magnetic pole;

wherein said second magnetic pole has a top surface, a bottom surface, a first end and a second end, wherein said bottom surface of said second magnetic pole at said first end is disposed adjacent to said first end of said second permanent magnet and wherein said second end of said second magnetic pole extends from said second permanent magnet in a second direction toward said first magnetic pole;

wherein said first direction is opposite to said second direction, and wherein said second end of said first magnetic pole is separated from said second end of said second magnetic pole by a gap;

a first magnetic shunt comprising a bottom portion and a plurality of sides attached to and extending outwardly from said bottom portion to define an enclosure having an opening, wherein said first magnetic shunt is disposed between said first permanent magnet and said second permanent magnet such that said opening of said first magnetic shunt faces said gap;

an anode disposed within said first magnetic shunt;

a second magnetic shunt having a first end and a second end, wherein said first end of said second magnetic shunt is attached to said first end of said first permanent magnet, and wherein said second end of said second magnetic shunt is connected to said second end of said second permanent magnet;

a primary magnetic field line disposed between said first magnetic pole extension and said second magnetic pole extension, wherein said primary magnetic field line has a mirror field greater than 2.

12. The closed drift ion source of claim 11, wherein said anode is disposed on a first side of said gap, further comprising a cathode disposed on a second side of said gap.

13. The closed drift ion source of claim 12, further comprising:

a third magnetic shunt disposed between said first magnetic pole and said cathode; and

a fourth magnetic shunt disposed between said second magnetic pole and said cathode.

14. The closed drift ion source of claim 13, wherein said mirror field is substantially symmetric.

15. The closed drift ion source of claim 14, wherein said first magnetic pole comprises a first distal end, and wherein said second magnetic pole comprises a second distal end,

wherein said primary magnetic field line comprises a minimum magnetic field strength value disposed about equidistant from said first distal end and said second distal end.

16. A method to focus a plasma, comprising the steps of:

providing an ionizable gas;

introducing said ionizable gas into a closed drift ion source comprising a first magnetic pole and a second magnetic pole separated by a gap;

producing a primary magnetic field line disposed between said first magnetic pole and said second magnetic pole, wherein said primary magnetic field line has a mirror field greater than 2; and

forming in said gap a plasma from said ionizable gas.

17. The method of claim 16, further comprising the step of producing a symmetric primary magnetic field line.

18. The method of claim 16, wherein said first magnetic pole comprises a first distal end, and wherein said second magnetic pole comprises a second distal end, and wherein said first distal end is separated from said second distal end by said gap, wherein said primary magnetic field line comprises a minimum magnetic field strength value disposed about equidistant from said first distal end and said second distal end.

19. The method of claim 16, wherein said closed drift ion source comprises:

a channel having an open end and a closed end, wherein said channel includes an input port for said ionizable gas, and wherein said first magnetic pole is disposed on said open end of said channel and extends therefrom in a first direction, and wherein said second magnetic pole is disposed on said open end of said channel and extends therefrom in a second direction, wherein said first direction is opposite to said second direction;

a first magnetic shunt disposed within said channel between said open end and said closed end, wherein said first magnetic shunt includes a bottom portion and a plurality of sides attached to and extending outwardly from said bottom portion to define an enclosure having an opening, wherein said opening of said first magnetic shunt faces said open end of said channel; and

an anode disposed within said first magnetic shunt.

20. The method of claim 19, wherein said first and second magnetic poles comprise cathode electrodes.

21. The method of claim 19, wherein said first and second magnetic poles are electrically isolated.

22. The method of claim 21, wherein said closed drift ion source further comprises:

a first permanent magnet attached to said first magnetic pole;

a second permanent magnet attached to said second magnetic pole;

a second magnetic shunt attached to said first permanent magnet and to said second permanent magnet;

a cathode disposed adjacent a first side of said gap, wherein said anode is disposed adjacent a second side of said gap;

a third magnetic shunt disposed between said first magnetic pole and said cathode; and

a fourth magnetic shunt disposed between said second magnetic pole and said cathode.