Method and apparatus for preventing cyclotron breakdown in partially evacuated waveguide

• US 4,687,616 A
• Filed: 01/15/1986
• Issued: 08/18/1987
• Est. Priority Date: 01/15/1986
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Department of Energy (Government of the United States of America)
• Inventors: Moeller, Charles P.
• Primary Examiner(s): Walsh, Donald P.
• Application Number:
  US06/818,946
• Time in Patent Office: 580 Days
• Field of Search: 376/123, 376/140, 376/133, 376/131, 376/132
• US Class Current: 376/123
• 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

Cyclotron breakdown is prevented in a partially evacuated waveguide by providing a section of waveguide having an axial cut therein in order to apply a potential across the two halves of the waveguide. This section is positioned in the waveguide crossing the area of electron cyclotron resonance. The potential applied across the waveguide halves is used to deflect seed electrons into the wall of the waveguide in order to prevent ionization of gas molecules and creation of more electron ion pairs which would result in cyclotron breakdown. Support means is also disclosed for electrically isolating the waveguide halves and transition means is provided between the section of the waveguide with the axial cut and the solid waveguide at either end thereof.

Claims

1. A method of preventing cyclotron breakdown in a partially evacuated waveguide used to insert microwave energy for electron cyclotron heating in a plasma magnetic confinement device comprising the steps of, applying a static magnetic field for confining the plasma in said device and applying an electrostatic field in order to remove electrons to prevent ionization of gas molecules and creation of more electron ion pairs in said waveguide.

2. The method of claim 1 wherein said electrostatic field has a substantial component along said static magnetic field.

3. The method of claim 2 wherein said electrostatic field is applied along said static magnetic field in order to run said seed electrons into the wall of said waveguide.

4. The method of claim 3 wherein said seed electrons are run into said wall in a time short compared to the time for ionization of the gas molecules in said waveguide by accelerated electrons.

5. In a magnetic plasma confining device including a torroidally shaped vacuum vessel having field coils wound around said vessel in order to generate a static magnetic field for plasma confinement, a waveguide running from the low magnetic field side of said vacuum vessel across a portion wherein cyclotron resonance occurs to the high field side of said vacuum vessel, a launch means positioned at the end of said waveguide to reflect microwave energy back across said vessel into said plasma, and means for applying microwave energy through said waveguide against said launch means, the improvement comprising means for applying a static electric field across a portion of said waveguide in the area crossing said cyclotron resonance whereby seed electrons are removed in order to prevent ionization of gas molecules and creation of more electron ion pairs.

6. The device of claim 5 wherein said static electric field has a substantial component along said static magnetic field.

7. The device of claim 6 wherein said means for applying a static electric field includes an axial cut in said portion of said waveguide in the plane of the microwave rf electric field.

8. The device of claim 7 wherein said means for applying a static electric field includes insulating support means for joining the two sides of said portion of said waveguide defined by said axial cut.

9. The device of claim 8 wherein transition means is provided between the ends of said portion of said waveguide and the remainder of said waveguide.

10. The device of claim 9 wherein said transition means includes an insulating gap defined by a metal shim and has alternating quarter wavelength radial waveguides cut in the faces of the solid waveguide sections.