Fundamental characteristics of pulse-operated helium inductively coupled plasma

Summary form only given. Since an inductively coupled plasma (ICP) has been introduced as an excitation and ionization source for trace elemental analysis, argon ICP has been widely used. However, argon ICP does not exhibit efficient performance for high ionization energy elements such as nonmetals, rare gases and halogens. According to Penning ionization mechanism, the ionization capability of plasma source is limited by the ionization and the metastable energy of the plasma gas species. Therefore, if helium ICP is developed, it is possible to ionize all elements effectively because helium has the larger metastable excitation energy (19.81 eV) than that of argon and the largest ionization energy (24.58 eV). We have generated and studied a stable helium ICP at the atmospheric pressure using a vortex flow enhanced torch. Though it is necessary for the high power drive (more than I kW) to derive high ionization efficiency, it can not apply because of a melting of the quartz torch. In this study, to overcome this problem, pulse-operated helium ICP, which is sustained low power (200-300 W) and applied high power pulse (more than 500 W) using amplitude modulation, is proposed and constructed (pulse frequency: 10-1000 Hz, pulse width: 25-2000 5s). The fundamental characteristics of the line emission intensity and the excitation temperature are measured for several degree of modulation.