Effective Temperatures of Olivine Dust Impact Plasmas

The effective temperatures of the positive and negative charge carriers in impact plasma are measured experimentally. The measurements are performed using a dust accelerator using polypyrrole (PPy)-coated olivine dust particles impacting onto a tungsten (W) target in four velocity bins: 2–3.6, 5–6.6, 8–12, and 12–18 km/s. The setup measures the retained impact charge as a function of applied bias potential, and the temperatures are calculated by fitting the data. The effective temperatures of the cations are approximately 7 eV and independent of the impact speed. The effective temperature of the negative charge carriers changes from 1 eV for the lowest speed to values comparable to that of the cations at higher speeds. The temperature measurements presented here are significantly different from prior studies using Fe dust particles. The discrepancy is possibly due to a larger fraction of negative ions in the impact plasma that likely originates from the PPy coating.