Nonlinear vertical oscillations of a particle in a sheath of a rf discharge

A new simple method to measure the spatial distribution of the electric fie ld in the plasma sheath is proposed. The method is based on the experimenta l investigation of vertical oscillations of a single particle in the sheath of a low-pressure radio-frequency discharge. It is shown that the oscillat ions become strongly nonlinear as the amplitude increases. The theory of an harmonic oscillations provides a good quantitative description of the data and gives estimates for the first two anharmonic terms in an expansion of t he sheath potential around the particle equilibrium.