Low-temperature, high-density plasmas in long micro-tubes

A low-temperature He microplasma plume generated in a micro quartz tube with the inner diameter decreasing from 245 mu m to 6 mu m is reported. The microplasma plume has a length of around 1.5 cm and reaches the position where the tube diameter is 10 mu m. Though the inner diameter of the tube is in sub-millimeter, the cross section of the tube is not fully filled with the plasma only until the tube inner diameter is down to 30 mu m. The electron density estimated from Ha stark broadening increases as the inner diameter of the tube decreases. The ignition voltage increases from 11 kV to 40 kV as the diameter of the inner quartz tube decreases from 245 mu m to 10 mu m. Further analysis shows that, in order to ignite a non-equilibrium plasma plume in 1 mu m diameter tube, the applied voltage of about 65 kV is needed and the plasma density could be as high as similar to 10(18) cm(-3). Published by AIP Publishing.