Production of large resonant plasma volumes in microwave electron cyclotron resonance ion sources

• US 5,841,237 A
• Filed: 07/14/1997
• Issued: 11/24/1998
• Est. Priority Date: 07/14/1997
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Energy Research Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Energy Research Corporation (Martin Marietta Corporation)
• Inventors: Alton, Gerald D.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): VU, DAVID HUNG
• Application Number:
  US08/892,492
• Time in Patent Office: 498 Days
• Field of Search: 315/111.21, 315/111.31, 315/111.41, 315/111.51, 315/111.61, 315/111.01, 315/111.71, 315/111.81
• US Class Current: 315/111.81
• CPC Class Codes: H01J 27/18 with an applied axial magnetic field
• CPC Class Codes: H05H 1/18 wherein the fields oscillate at very high frequency, e.g. in the microwave range , e.g. using cyclotron resonance

Abstract

Microwave injection methods for enhancing the performance of existing electron cyclotron resonance (ECR) ion sources. The methods are based on the use of high-power diverse frequency microwaves, including variable-frequency, multiple-discrete-frequency, and broadband microwaves. The methods effect large resonant "volume" ECR regions in the ion sources. The creation of these large ECR plasma volumes permits coupling of more microwave power into the plasma, resulting in the heating of a much larger electron population to higher energies, the effect of which is to produce higher charge state distributions and much higher intensities within a particular charge state than possible in present ECR ion sources.

Claims

1. In an electron cyclotron resonance (ECR) ion source for producing high charge state high-intensity ion beams, said ion source having a B-minimum magnetic field for confining a plasma, and wherein said plasma is excited by microwaves from a microwave source inputted to said ion source through a waveguide, and wherein said ion source is operable to produce an electron cyclotron resonance zone to resonantly heat plasma electrons within said plasma by absorption of microwaves from said microwave source;

the improvement wherein said waveguide is a broadband waveguide having a bandwidth chosen to fall within the resonant frequency distribution of the magnetic field of said ion source; and

said microwave source comprises a microwave amplifier and a variable frequency signal generator, said microwave amplifier operable to produce microwaves and inject them into said broadband waveguide, and said variable frequency signal generator operable to input a continuously varying frequency signal to said microwave amplifier such that a large volume ECR zone is produced within said plasma.

2. The system of claim 1 wherein said microwave amplifier is a traveling wave tube amplifier.

3. The system of claim 1 further including an additional microwave amplifier and additional variable frequency signal generator, wherein both of said variable frequency signal generators are operated with frequencies phased so as to optimize the charge state distribution of said electron cyclotron resonance ion source.

4. The system of claim 3 wherein both of said variable frequency signal generators are operated with frequencies oppositely phased.

5. The system of claim 1 further including three additional microwave amplifiers and three additional variable frequency signal generators, wherein all four of said variable frequency signal generators are operated with frequencies phased 90 degrees apart so as to optimize the charge state distribution of said electron cyclotron resonance ion source.

6. In an electron cyclotron resonance (ECR) ion source for producing high charge state high-intensity ion beams, said ion source having a B-minimum magnetic field for confining a plasma, and wherein said plasma is excited by microwaves from a microwave source inputted to said ion source through a waveguide, and wherein said ion source is operable to produce an electron cyclotron resonance zone to resonantly heat plasma electrons within said plasma by absorption of microwaves from said microwave source;

the improvement wherein said waveguide is a broadband waveguide having a bandwidth chosen to fall within the resonant frequency distribution of the magnetic field of said ion source; and

said microwave source comprises a microwave amplifier and a broadband signal generator, said microwave amplifier operable to produce microwaves and inject them into said broadband waveguide; and

said broadband signal generator operable to input a broadband frequency signal to said microwave amplifier such that microwaves produced by said microwave amplifier are distributed across the bandwidth of said waveguide.

7. The system of claim 6 wherein said microwave amplifier is a traveling wave tube (TWT).

8. In an electron cyclotron resonance (ECR) ion source for producing high charge state high-intensity ion beams, said ion source having a B-minimum magnetic field for confining a plasma, and wherein said plasma is excited by microwaves from a microwave source inputted to said ion source through a waveguide, and wherein said ion source is operable to produce an electron cyclotron resonance zone to resonantly heat plasma electrons within said plasma by absorption of microwaves from said microwave source;

the improvement wherein said waveguide is a broadband waveguide having a bandwidth chosen to fall within the resonant frequency distribution of the magnetic field of said ion source; and

said microwave source is a broadband microwave source operable to produce microwaves over a wide bandwidth and inject them into said broadband waveguide such that a large volume ECR zone is produced within said plasma resulting in an ion beam with higher charge state ions and higher beam intensities within a particular charge state from said ECR ion source.

9. The system of claim 8 wherein said broadband microwave source is a plasma wave tube (PWT) amplifier.