Microwave resonant cavity

1. A microwave resonant cavity, comprising:

a sidewall having a generally cylindrical hollow shape and formed of a material opaque to a microwave;

a gas flow tube disposed inside the sidewall, formed of a material transparent to a microwave, and having a longitudinal axis substantially parallel to a longitudinal axis of the sidewall;

a plurality of microwave waveguides, each said microwave waveguide having a longitudinal axis substantially perpendicular to the longitudinal axis of the sidewall and having a distal end secured to the sidewall and aligned with a corresponding one of a plurality of holes formed on the sidewall;

a top plate formed of a material opaque to a microwave and secured to one end of the sidewall; and

a sliding short circuit including:

a disk formed of a material opaque to a microwave and slidably mounted between the sidewall and the gas flow tube, the disk having an outer rim snuggly fit into the sidewall and a hole into which the gas flow tube being snuggly fit; and

at least one bar disposed inside the sidewall and arranged parallel to the longitudinal axis of the sidewall,

whereby a space defined by the top plate, sidewall, and the disk is adjusted to form a microwave resonant cavity inside the gas flow tube by moving the bar along the longitudinal direction of the sidewall.

2. A microwave resonant cavity as recited in claim 1 , wherein one end of the gas flow tube abuts the top plate and the top plate has a hole for receiving a gas that flows through the gas flow tube.

3. A microwave resonant cavity as recited in claim 1 , further comprising:

a bottom plate secured to an other end of the sidewall and having at least one hole through which the bar passes through.

4. A microwave resonant cavity as recited in claim 3 , wherein the bottom plate has a gas outlet.

5. A microwave resonant cavity as recited in claim 1 , wherein the gas flow tube passes through the top plate.

6. A microwave resonant cavity as recited in claim 1 , wherein the distal ends of the plurality of microwave waveguides are disposed at a same height along the longitudinal axis of the sidewall.

7. A microwave resonant cavity as recited in claim 1 , wherein the distal ends of the plurality of microwave waveguides are disposed at different heights along the longitudinal axis of the sidewall.

8. A microwave resonant cavity as recited in claim 1 , wherein a cross sectional shape of the sidewall is one selected from the group consisting of circle, rectangle, hexagon, and octagon.

9. A microwave resonant cavity as recited in claim 1 , wherein the longitudinal axes of the plurality of microwave waveguides are disposed on a same plane parallel to the longitudinal axis of the sidewall.

10. A microwave resonant cavity as recited in claim 1 , further comprising:

a microwave supply unit coupled to a proximal end of each said microwave waveguide.

11. A microwave resonant cavity as recited in claim 10 , wherein the microwave supply unit includes:

a microwave generator for generating microwaves; and

an isolator having a dummy load for dissipating microwaves that propagate toward the microwave generator and a circulator directing the microwaves to the dummy load.

12. A microwave resonant cavity as recited in claim 11 , wherein the microwave supply unit further includes:

a coupler for measuring a flux of microwaves; and

a tuner for reducing reflection of microwaves.