Knowledge Bank

One of the major destruction paths of ions in laboratory plasmas is the electron recombination of ions at the walls of the discharge tube. In positive column discharges, ions drift toward the wall by ambipolar diffusion. In order to analyze the chemistry in plasmas quantitatively, direct measurements of destruction rates due to this process are needed. In this work, we studied variations in $H3+$ concentration in plasmas when small amounts of $CH4,N2$ and CO are added under various discharge conditions. The concentration was measured from intensities of the $H3+$ spectra observed in a liquid nitrogen cooled positive column discharge using a color center laser and the velocity modulation method. The destruction rate due to ambipolar diffusion was obtained using a steady state model and previously reported ion-neutral reaction rate constants.