Patent ID: 8110993

Claim:
A method for tracking a variable resonance condition in a plasma coil during creation of plasma from a gas flowing in a plasma torch adjacent to the plasma coil, comprising: providing a radio-frequency (RF) power source comprising: a power amplifier that generates a radio-frequency power signal with an adjustable operating frequency, said power amplifier also generating a reference phase signal derived from said radio-frequency power signal; an impedance match that provides said radio-frequency power signal to the plasma coil; a phase probe positioned adjacent to said plasma coil to generate a coil phase signal corresponding to said adjustable operating frequency; and a phase-locked loop device that generates a drive signal to said power amplifier to control said adjustable operating frequency, said drive signal being based upon a phase relationship between said reference phase signal and said coil phase signal, such that said adjustable operating frequency tracks said variable resonance condition; providing a high-voltage ignition charge from said RF power source to the gas in plasma torch so as to create an electrical discharge through said gas so as to create a test sample comprising a partial plasma state within said plasma torch; and applying an RF power signal from said plasma coil to said test sample in said plasma torch, wherein said adjustable operating frequency of said power amplifier tracks said variable resonance condition of said plasma coil such that said test sample in the plasma torch achieves a full plasma state.