SF6 breakdown characteristics with a specially-designed cathode

A high-voltage photocathode design recently introduced for breakdown studies in compressed-gas and high-field conditions is used in a study of SF₆. The experiment was carried out for N×d ranging from 0.25 to 3.3×10¹⁹ cm^-2, N and d being, respectively, the molecular density and gap length. Statistical scattering of data was low, on average within 2 and 3%, respectively, for uniform and nonuniform conditions. Measured breakdown values were found to fall into two categories, Paschen and non-Paschen data, depending on the parametric couple (N,d) considered. Paschen data are in full agreement with values calculated using a streamer breakdown criterion. Local nonuniformity produced by the device seems to affect the Paschen behavior slightly at very short gap length and higher densities. Departure from the Paschen curve and growing deviation as N×d increases characterize the other category. The couples (N_s, d_s) at which departures set in are determined by numerically fitting the data. When displayed assuming a linear relationship, experimental d_s scales inversely with its corresponding N_s, illustrating the highly consistent behavior of the active deviation mechanisms, particularly in relation to reproducibility