Theoretical investigation of anode spot formation and its characteristics by the application of kappa distribution function as a tool for non-equilibrium steady state (NESS) plasmas

Summary form only given. Anode spots are potential structures formed by immersing an electrode into a bulk plasma and biasing the electrode to a sufficiently high electric potential. This structure is a quasineutral region which is separated from the bulk plasma by a double layer boundary. Double layer is a sheath-like region which sustains a potential difference between to different plasmas. When the anode spot forms in front of the positively biased electrode, a jump occurs in the extracted electron current to this electrode. Most of the previous theoretical and numerical studies about anode spot have considered it as a system in equilibrium and have used Maxwellian distribution in order to describe the plasma particles. These studies also have neglected the density of the electrons generated inside the anode spot and the role of these electrons on the jump of the extracted current observed by the formation of the anode spot. Present study gives a new explanation for the formation of the anode spot and its characteristics. In this study it is shown that anode spot is an out-of-equilibrium system and its nonequilibrium properties should be considered in the theoretical studies of this phenomenon. Kappa distribution, which has been developed for NESS plasma could be a handful tool for the study of the anode spot. In addition, in this study, the electrons generated inside the anode spot are indicated to be the most important particle population in terms of the extracted electron current to the biased electrode. Despite previous studies that have considered anode spot as a pathway for electrons coming from the bulk plasma and have neglected the contribution of the anode spot to the extracted current, this study identifies the anode spot as the part of the system which plays the most important role in the electron current to the biased electrode.