On the hysteresis in fireball formation and extinction

Abstract

A model is proposed to explain hysteresis observed in fireball formation and extinction as electrode bias is varied in partially ionized plasmas. Formation is predicted after a sufficiently deep potential well for electrons is established in the electron sheath of the electrode. Under the experimental conditions considered, once the fireball forms, the plasma potential rapidly increases, resulting in electrons being only lost to the electrode. Previous predictions suggest that once formed, the fireball double layer must maintain a potential close to the ionization potential of the neutral gas to remain in a steady state. In this paper, it is predicted that changes in electrode bias after formation result in a corresponding change in the fireball size and plasma potential. This change in plasma potential allows the double layer potential to be maintained at biases both above and below the electrode bias at onset. The fireball extinguishes when the required double layer potential can no longer be maintained with the balance of current loss of the bulk plasma. These predictions are tested experimentally and are found to be in good agreement with the measurements.