Folded waveguide coupler

• US 4,728,910 A
• Filed: 10/27/1986
• Issued: 03/01/1988
• Est. Priority Date: 10/27/1986
• 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
• Inventors: Owens, Thomas L.
• Primary Examiner(s): GENSLER, PAUL L
• Application Number:
  US06/923,540
• Time in Patent Office: 491 Days
• Field of Search: 333/24 R, 333/239, 333/99 PL, 333/248, 219/10.55 R, 219/10.55 A, 219/121 P
• US Class Current: 333/24.00R
• CPC Class Codes: H01P 7/06 Cavity resonators
• 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

A resonant cavity waveguide coupler for ICRH of a magnetically confined plasma. The coupler consists of a series of inter-leaved metallic vanes disposed withn an enclosure analogous to a very wide, simple rectangular waveguide that has been "folded" several times. At the mouth of the coupler, a polarizing plate is provided which has coupling apertures aligned with selected folds of the waveguide through which rf waves are launched with magnetic fields of the waves aligned in parallel with the magnetic fields confining the plasma being heated to provide coupling to the fast magnetosonic wave within the plasma in the frequency usage of from about 50-200 mHz. A shorting plate terminates the back of the cavity at a distance approximately equal to one-half the guide wavelength from the mouth of the coupler to ensure that the electric field of the waves launched through the polarizing plate apertures are small while the magnetic field is near a maximum. Power is fed into the coupler folded cavity by means of an input coaxial line feed arrangement at a point which provides an impedance match between the cavity and the coaxial input line.

Claims

1. A waveguide coupler for coupling rf energy at a selected operating frequency into a magnetically confined plasma within a vacuum vessel, comprising:

an electrically conductive housing having a front opening attached to a vacuum port of said vacuum vessel, a back opening, and a plurality of vanes disposed in an interleaved spaced array from opposing walls of said housing and extending axially of said housing from said front opening to said back opening thereof to form a folded, generally rectangular resonant waveguide cavity with said plurality of vanes of said housing disposed parallel to the magnetic fields confining said plasma and having a cutoff frequency substantially below said selected operating frequency and wherein the distance between the edges of said plurality of vanes is substantially equal to the distance between adjacent ones of said plurality of vanes;

an electrically conductive polarizing plate disposed over said front opening of said housing and having a plurality of rectangular openings aligned with selected alternate folds of said housing for selective propagation therethrough of rf waves having a common polarization for selective coupling of wave energy to the fast magnetosonic wave of said plasma;

an electrically conductive shorting plate means disposed over said back opening of said housing and spaced from the front opening a distance which produces maximum power transfer of rf wave energy into said plasma for establishing a wave pattern within said cavity having a small electric field component and a large magnetic field component at the apertures of said polarizing plate attached to the front of said housing to provide substantially magnetic field coupling of wave energy propagating through said polarizing plate into said plasma located adjacent to and spaced from the front of said housing; and

a transition connector means for introducing rf power at said operating frequency from a coaxial transmission line into said folded waveguide cavity formed by said housing at a transition junction providing an impedance match with said coaxial transmission line.

2. The waveguide coupler as set forth in claim 1 wherein said housing is rectangular in cross section.

3. The waveguide coupler as set forth in claim 2 wherein said transition connector means includes a coaxial coupler having an inner conductor probe segment for connection to the inner conductor of a coaxial transmission line and extending through an opening in a centralmost one of said plurality of vanes of said housing perpendicular from one sidewall of said housing into said folded waveguide cavity parallel to said vanes and a coaxial tuning stub having an outer conductor connected to the sidewall of said housing opposite said one sidewall thereof at an opening therein aligned with said opening in said centralmost vane and an inner conductor connected to said inner conductor probe of said transition connector, so that an impedance match may be obtained between the coaxial transmission input line and said transition connector means to maximize rf power transmission into said folded waveguide cavity by said inner conductor probe segment.

4. The waveguide coupler as set forth in claim 2 wherein said transition connector means includes a conductor probe segment connected at one end to the inner conductor of said coaxial transmission line and extending through a nonradiating slot in one sidewall of said housing in parallel alignment with the inward edge of a central most one of said plurality of vanes extending from the sidewall of said housing opposite said one sidewall, an electrically conductive slide means connected to the opposite end of said conductor probe segment and adapted for sliding electrical connection with said inward edge of said centralmost one of said plurality of vanes, and means for positioning said conductor probe segment along said inward edge of said centralmost one of said vanes to obtain an impedance matched connection of said coaxial transmission line to said folded waveguide cavity.

5. The waveguide coupler as set forth in claim 4 wherein said shorting plate means includes an electrically conductive member slidably disposed in said back opening of said housing for sliding electrical connection with said plurality of vanes and the sidewalls of said housing and means coupled with said electrically conductive member for selectively positioning said member along the axis of said folded waveguide cavity to vary the effective dimensions of said cavity and thereby alter the resonant frequency of said cavity to further aid impedance matching of said cavity to said transmission line input.

6. The waveguide coupler as set forth in claim 1 wherein alternate ones of said plurality of interleaved vanes are tapered along two planes from a point on the inward extending edge thereof at a selected distance from the front end of said housing toward the front end forming alternate enlarged radiating areas for the selected radiating folds of said cavity and wherein said openings in said polarizing plate are enlarged to correspond to the enlarged radiating areas provided by the tapered vanes.

7. The wave guide coupler as set forth in claim 1 wherein said housing is circular in cross section.

8. The wave guide coupler as set forth in claim 1 wherein said plurality of vanes are spaced within said housing at larger intervals near the central region of the cross section of said housing compared to the outer regions thereof and wherein the thickness of the vanes and the radius of the vane edges increases towards said central region of said housing for reducing the magnitude of the electric fields within the waveguide coupler for a selected total power operating level.

9. The waveguide coupler as set forth in claim 1 wherein said selected operating frequency is in the range of from about 50-200 MHz.