Propagation of Plasma Bullet in Impurity-Controlled Working Gas: from Standard to Ultrapure Atmospheric Pressure Plasma

抄録

This study shows the variation of the characteristics of a plasma bullet generated in impurity controlled working gas. Tunable diode laser absorption spectroscopy of metastable He atoms generated in the plasma bullet was performed. The metastable He atoms are generated in the plasma bullet and are quenched by impurities. The velocity and the size of the plasma bullet are derived from the arriving time and the shape of the rising phase of the absorbance. In addition, the impurity concentration was derived from the decay time of the absorbance. The impurity concentration in the working gas is controlled in a range of more than two orders of magnitude, and the impurity concentration reaches ppb level. We have observed the impurity dependence of the velocity and size of the plasma bullet. The velocity of the plasma bullet reaches a constant value and the bullet size dramatically increase below 20 ppm of the impurities. These results show the change of the propagation mechanism of the plasma bullet in the high purity working gas. In order to distinguish the plasma generated in the high purity gas from the standard plasmas, we would call it ultrapure plasma.