Potential of an insulated electrode in a high-energy electron flow under a gas pressure of 0.1–1.0 Pa

We analyze the variation of the floating potential of an insulated metallic electrode in a flow of electrons with an energy of up to 300 eV under a gas pressure of 0.1–1.0 Pa at a current density lower than 0.1 A/cm 2 . It is shown that the dependence of the floating potential on the initial electron energy is non-monotonic; this fact is explained by the variation of the ratio of the ion current density to the density of fast electron current in the plasma. The balance of the electron and ion currents on the surface of an insulated electrode is ensured by the cutoff of the low-energy part of the electron flow at the level determined by the magnitude of the floating potential. The maximal value of the floating potential increases upon a decrease in the gas pressure; this is due to a decrease in the ion current density. The interval of energy variation in which the floating potential decreases from the maximal value (50–250 eV) to 5–6 eV increases with the electron current density and the gas pressure. The electrode material and the type of the gas do not noticeably affect the variation of the floating potential.