Sheath structure for cylindrical probe in low-pressure electronegative discharges

Abstract

A theoretical model for collisionless and weakly collisional plasmas with cold positive ions is developed for the presheath and sheath that surround a cylindrical probe immersed in electronegative discharges. The model is solved numerically, and the spatial distributions of the normalized potential, the normalized density, and the normalized velocity and flux of positive ions are calculated for a low-pressure electronegative discharge as a function of the ratio of the negative ion density to the electron density and the ratio of the electron temperature to the negative ion temperature. As the ratio of the Debye length to the ionization length increases, it is found that the sheath width decreases, the velocity of the positive ion gets smaller, and the positive ion flux to the probe decreases. As the electronegativity increases, the sheath width decreases.