Magnetized microplasmas generated in a narrow quartz tube

Recently, several microplasma sources have developed for ga s chromatography detector, nanomaterial synthesis, localized etching and onsite deposition. According to Paschen´s law, microplasmas easily generate at atmospheric pressure becaus e the smaller discharge gap, the higher gas pressure. However, low pressure operation is anticipated to open up a possibility of controlling plasma parameters and radicals in a plasma gas phase. For this purpose, radio frequency (rf) He and Ar microplasmas generated in a narrow quartz tube having an inner diameter of 1 mm (referred to as capillar y microplasmas) have been magnetized by applying the stron g magnetic field, provided that the magnetic field is perpendi cular to both the rfelectric field and the tube axis and that the Larmor radius of an electron is sufficiently smaller than both the electron mean free path and tube inner radius. In this con dition, a rf oscillating EXB drift motion seems to occur along the tube axis. When a magnetic field with a magnetic flux density of 0.4 T was applied, the magnetized capillary microplasma could be generated at gas pressure lower than 1.5 kPa because the electron cyclotron frequency exceeds the electron-neutral collision frequency. The dependence of atomic excitation temperatures on gas pressure for He and Ar microplasmas generated at a constant rf power of 4 W with and without a magnetic field of 0.4 T was studied². Magnetized capillary microplasmas have generated at low gas pressure of below several kPa. The Ar atomic excitation temperature increased dramatically from 5000K to 15000K when the gas pressure was re duced from 4 to 0.2 kPa. This implies an increase in the electron temperature. In addition, plasma has not ignited without t he strong magnetic field at gas pressures below 2 kPa, even a t rf powers of 10 W or more. Furthermore, Ar ionic emission (Ar II) lines were clearly observed in the spectral range of 43 0-500 nm. It means that an increase in electron te- perature enhances the ionization and excitation efficiencies. Therefore, magnetized capillary microplasmas have the potential to be used as miniaturized ion sources.