Electron drift velocity in acetylene and carbon dioxide determined from rf breakdown curves

In this work, we investigated the ignition of radio-frequency capacitive discharge in acetylene and in carbon dioxide. RF breakdown curves were measured in the range of distances between the flat electrodes from 4.5 mm to 30 mm in acetylene and from 5 mm to 40 mm in carbon dioxide at the frequency of 13.56 MHz. In the RF voltage range up to 2000 V, the diffusion-drift and Paschen’s branches are present in the breakdown curves. Diffusion-drift branches have a region of ambiguous dependence of the RF breakdown voltage on the gas pressure and, accordingly, the turning point. From the measured coordinates of the turning points on the diffusion-drift branches of the RF breakdown curves, the electron drift velocity was determined in the reduced electric field range 319 Td < E/N < 3409 Td (1 Townsend = 10⁻¹⁷ Vcm²) in acetylene and 272 Td < E/N < 6240 Td in carbon dioxide from turning points on the measured breakdown curves. The measured values of Pinhão et al. [PSST, 2020, 29, 045009] bulk drift velocity in C₂H₂, as well as their results of Monte Carlo simulation (“bulk” solution) are in good agreement with the data of other authors in the range E/N = 20 – 300 Td, but in a stronger reduced electric field they deviate towards the higher values of electron drift velocity. Our results for CO₂ are approximately 1.15–1.2 times higher than the data of paper by H. Schlümbohm [Zeitschrift für Physik 182 (1965) 317].