Plasma enhanced gas reactor

1. A plasma enhanced gas reactor apparatus comprising a reaction chamber, means for coupling microwave radiation into the chamber, a pair of opposed field enhancing electrodes for concentrating microwave energy for forming plasma in a localized region between the electrodes, gas passages for passing a gaseous medium into and out of the chamber so that the gaseous medium passes through said localized region of plasma, electrode holders located in a wall of the chamber, the electrodes comprising electrically conducting tubes held in said electrode holders located in the chamber wall, the electrode tubes being removable and replaceable from outside of the apparatus.

2. Apparatus as claimed in claim 1 , wherein the electrodes comprise tungsten tubes.

3. Apparatus as claimed in claim 2 , wherein at least one of the electrode tubes is clamped in position by means of a collet positioned around the electrode tube and squeezed between a shoulder provided in the electrode holder and a sleeve screwed into the electrode holder to apply longitudinal pressure to the collet, the consequential radial expansion of the collet serving to clamp the electrode tube in position.

4. Apparatus as claimed in claim 2 , wherein at least one of the electrode tubes has a threaded portion of larger diameter than the remainder of the tube, the threaded portion on the tube cooperating with a threaded portion of the electrode holder and secured at its chosen location by a locknut.

5. Apparatus as claimed in claim 1 , wherein at least one of the electrode tubes is clamped in position by means of a collet positioned around the electrode tube and squeezed between a shoulder provided in the electrode holder and a sleeve screwed into the electrode holder to apply longitudinal pressure to the collet, the consequential radial expansion of the collet serving to clamp the electrode tube in position.

6. Apparatus as claimed in claim 1 , wherein at least one of the electrode tubes has a threaded portion of larger diameter than the remainder of the tube, the threaded portion on the tube cooperating with a threaded portion of the electrode holder and secured at its chosen location by a locknut.

7. Apparatus as claimed in claim 1 , wherein the reaction chamber is formed by the space between two plate members having side wall portions to form a shape in cross-section in the form of an elongated letter “n” and secured together with the side wall portions of one plate member in abutment with the side wall portions of the other plate member.

8. Apparatus as claimed in claim 7 , wherein the said space between the two plate members is closed at one end by a closure plate and at the other end is adapted for connection to a waveguide for supplying microwave radiation into the reaction chamber.

9. Apparatus as claimed in claim 1 , wherein one or both of the electrode holders has or have a hollow interior which communicates with the hollow interior of the associated electrode tube, to provide a passageway for gaseous medium into and/or out of the reaction chamber, and a further passageway for gaseous medium into and/or out of the reaction chamber is provided through a wall of the chamber.

10. A plasma enhanced gas reactor apparatus comprising a reaction chamber, means for coupling microwave radiation into said chamber, a pair of opposed field enhancing electrodes for concentrating microwave energy for forming plasma in a localized region between the electrodes, gas passages for passing a gaseous medium into and out of said chamber for passing the gaseous medium through said localized region, electrode holders located in a wall of the chamber, said electrodes comprising electrically conducting tubes held in said electrode holders, and means for removing and replacing said electrode tubes from outside of said apparatus.