Magnetized microplasmas generated in a narrow quartz tube

Magnetized He and Ar microplasmas in a narrow quartz tube having an inner diameter of 1 mm (referred to as magnetized capillary microplasmas) are reported. A capillary microplasma can be magnetized by the occurrence of a radio frequency (rf) oscillating E×B drift motion along the tube axis, provided that the external magnetic field is perpendicular to both the rf electric field and the tube axis and that the Larmor radius of an electron is sufficiently smaller than both the electron mean free path and the tube radius. When a magnetic flux density of 0.4 T was applied, a magnetized capillary microplasma could be generated at gas pressures lower than 1.5 kPa because the electron cyclotron frequency exceeds the electron-neutral collision frequency. However, plasma ignition at low gas pressure below 4 kPa was hardly taken place without a strong magnetic field. The Ar atomic excitation temperature was estimated by optical emission spectroscopy and found to increase dramatically from 5000 to 15 000 K when the gas pressure was reduced from 4 to 0.2 kPa. This implies an increase in the electron temperature. Furthermore, Ar ionic emission (Ar II) lines were clearly observed under the magnetized plasma conditions.