Effect of Ionization on Void Formation in an RF Discharge under Microgravity Conditions

An analysis of the formation of a void in the PK3 setup in dusty plasma with 3.4-μm-diameter melamine–formaldehyde particles—in an RF discharge in argon at a pressure of 12–50 Pa under microgravity conditions at the ISS is presented. The uniform state of the plasma can only be obtained at a voltage close to the discharge extinction voltage. The application of a low-frequency voltage of 20–50 Hz stabilizes the state of the dusty plasma and shifts the void formation threshold towards higher RF voltages. It is shown that the formation of a void is associated with non-local ionization of the plasma at the center of the discharge by fast electrons, which are heated in the near-electrode layers.