Abstract

This report is the first study on the formation, stabilization and fundamental investigation of free-running helium inductively coupled plasmas (He ICPs). The plasma was operated at 600–900 W with a total helium gas flow of less than 10 L min⁻¹. The shape and the physical appearance of free-running helium plasmas differ markedly from the He ICP sources reported previously using a crystal-controlled generator. Although the free-running helium plasma appears annular, high-speed video studies reveal that the plasma rotates 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 1600–1800 K, 3800–4300 K, and 3.0 to 12 × 10¹³ cm⁻³, respectively. These fundamental characteristics are compared to those reported previously for crystal-controlled He ICPs and Ar ICPs.