Method and apparatus for plasma generation
An RF-driven plasma source, including a pair of spaced-apart plasma electrodes, wherein the electrodes act as plates of a capacitor, the gas electrically discharges and creates a plasma of both positive and negative ions, in a clean process that enables efficient sample analysis, with preferred isolated sample photo-ionization, reduced-power operation and also including signal detection with modulated drive electronics.
1. A method for driving a plasma source for an ion mobility based analyzer, said plasma source including a pair of electrodes separated by a gap, said gap for formation of a plasma from a fluid, the method comprising:
applying an RF drive signal to said plasma source,
forming a plasma between said electrodes in said gap, and
modulating the drive signal to control ion formation while producing said plasma in said gap.
2. The method of claim 1 comprising stimulating said electrodes to produce ions from said fluid.
3. The method of claim 1 comprising producing said ions in packets having a frequency related to said modulated drive signal and having an average intensity linearly controlled by said modulated drive signal.
4. The method of claim 3 comprising providing an analytical electric field for analyzing said packets of ions, said analyzing being based on aspects of the mobility of said ions in said analytical electric field.
5. The method of claim 4 comprising analyzing said ions based on aspects of differential mobility of said ions in said analytical electric field.
6. The method of claim 5 comprising detecting said packets synchronously according to said modulated drive signal.
7. The method of claim 5 wherein said analyzing includes separating ions in said packets according to aspects of mobility of said ions in said analytical electric field.
8. The method of claim 7 including identifying at least one species of said separated ions according to known species behavior in said analytical electric field.
9. The method of claim 5 including detecting said packets, and reducing the signal to noise ratio of said detection by detecting said packets synchronously with said modulated drive signal.
10. The method of claim 3 comprising the step of driving said plasma with a transformer wherein said modulation circuit operates said transformer at resonance with a peak-to-peak voltage of sufficient amount to produce said packets.