Measurement of the electron density in a microwave plasma torch at atmospheric pressure

The electron density in a microwave plasma torch at atmospheric pressure was measured with a Mach–Zehnder interferometer. The electron density is on the order of 1017/cm3, one order higher than that deduced from the Stark broadening of spectral lines, and increases with the increase in the microwave power. The spatial distribution of the electron density was obtained. The highest electron density locates at the symmetrical axis of the plasma torch and decreases radially. It was found that the electron density fluctuates within a range of 0.3 with the time under the same experimental conditions.