Formation and fundamental characteristics of novel free-running helium inductively coupled plasmas

This report is the first study on the formation, stabilization and fundamen tal investigation of free-running helium inductively coupled plasmas (He IC Ps). The plasma was operated at 600-900 W with a total helium gas flow of l ess than 10 L min(-1). The shape and the physical appearance of free-runnin g helium plasmas differ markedly from the He ICP sources reported previousl y using a crystal-controlled generator. Although the free-running helium pl asma appears annular, high-speed video studies reveal that the plasma rotat es at a frequency of 75-275 Hz. Lateral profiles of emission spectra of the free-running discharge viewed end-on provide rotational temperature (T-rot ), excitation temperature (T-exc), and electron number density (n(e)) of 16 00-1800 K, 3800-4300 K, and 3.0 to 12 x 10(13) cm(-3), respectively. These fundamental characteristics are compared to those reported previously for c rystal-controlled He ICPs and Ar ICPs.