Capacitively coupled rf coupled plasmas in N2-H2 mixtures

Abstract

This paper studies the modifications induced in low-pressure radio-frequency (rf) capacitively coupled nitrogen plasmas, by the addition of a few amount of hydrogen (up to 5%). The work is an intermediate step towards the study of N2-CH4 plasmas, for the simulation of the ionospheric chemistry of Saturn's satellite Titan. The plasmas are studied using both experiments and simulations. The experimental setup is a parallel-plate reactor (driven at 13.56 MHz frequency), surrounded by a cylindrical metallic grid to confine the discharge [1]. Electrical diagnostics allow measuring: (i) the electron density, by using a resonant cavity method; (ii) the effective rf power coupled to the plasma, by using the subtractive method [2]. Optical emission spectroscopy diagnostics are used to study the evolution, with the working conditions, of: (i) the First Negative System with the N2+ band; (ii) the atomic hydrogen Hβ line at 486.1 nm; (iii) the atomic argon line at 811.5 nm. Simulations use a hybrid code that couples a 2D (r, z) time-dependent fluid-type module, describing the transport of the charged particles, to a very complete 0D kinetic module, for the nitrogen-hydrogen mixture. Results reveal that the electron density increases with the amount of injected H2, at constant coupled power.

References [1] G. Alcouffe et al, Plasma Sources Sci. Technol. 19, 015008 (2010) [2] L.L. Alves et al, Plasma Sources Sci. Technol. (submitted, 2012)