Abstract
Capacitively coupled capillary Ar and He plasmas have been generated in a quartz tube with the inner/outer diameters of 1.0/3.0 mm at the RF (13.56 MHz) powers of 3-7 W using the externally attached parallel-plate electrodes. Plasma expansion along a tube axis was a maximum at a gas pressure of 10-20 kPa, in which Vpp was a minimum and so Paschen's minimum condition was satisfied. The capillary plasma was magnetized by a strong magnetic field of 0.4 T to sustain the plasma at a low pressure, since the plasma did not ignite at the gas pressure below 2-4 kPa. The optical emission spectrum analysis revealed that atomic excitation temperature increased with decreasing gas pressure. Furthermore, it was found that the metastable atoms play an important role in the plasma sustenance at a high gas pressure.
