The optical and electrical response of firerod in the presence and absence of dust grains

A positively biased surface attracts plasma electrons and repels ions. This differential velocity leads to positive charge accumulation near the surface. When the sheath potential exceeds the gas ionization potential, a visible glow, known as an anode spot, forms. Depending on its shape, this phenomenon is sometimes classified as a fireball or firerod. Existing research on anode spots primarily examines the conditions for formation and alternating current (AC) fluctuations using electrical signals. In this work, we mainly focus on the AC voltage fluctuation and the comparative studies between the optical and electrical signals. Additionally, we present the first investigation into the influence of dust grains on the formation and stability of firerods, detailing the resulting system changes. Finally, considering the optical signals frequencies as frequencies of ion-acoustic waves, the one-dimensional length of the firerod is also discussed. The study will be helpful for the diagnostic of such plasma systems from the outside without disturbing the pattern formed inside.