Enhanced vortex flow torch for a helium ICP

Abstract

Aiming at generating a helium plasma source for the analysis of aqueous samples, a new torch for a helium inductively coupled plasma (He-ICP) was developed. By utilizing flow visualization along with a spark-tracing method, it was found that with a conventional torch for Ar-ICP an adequate helium gas vortex flow to sustain a stable plasma doesn't form in the plasma-generating region. To enhance the vortex flow, compared with that using the Ar-ICP torch, the new He-ICP torch has the following two characteristics : (a) a smaller diameter gas inlet and (b) a shorter distance from the gas inlet to the plasma-generating region. As a result of this change, a stable doughnut-type helium plasma can be produced when using 40.68 MHz RF input power that is >500 W, a plasma gas flow rate >161 min^-1, and a carrier gas flow rate >1.01 min^-1. A spatial measurement of the helium emission intensity was performed, and the generation of a doughnut-type plasma was confirmed.