Formation of multiple axial potential structures in expanding RF plasmas

Summary form only given. The spontaneous formation of electrostatic potential structures in geometrically and magnetically expanding plasma has great importance in development of plasma thrusters¹ as well as in ion beam production² mechanisms for various purposes. Observation of multiple axial potential structures (MAPS), with each of them separated by uniform potential regimes in helicon antenna produce radio frequency (RF) expanding plasma is reported in this presentation. Although an indirect evidence of existence of multiple double layers in expanding plasmas has been reported³, measurement of two distinct double layer potential structures separated by uniform quasineutral plasma observed in expanding RF plasma is reported for the first time to best of our knowledge. Further experiments are carried out to study the evolution of these MAPS by varying the strength of diverging magnetic field gradient as well as creating a cusp outside the throat. Emergence of second potential structure from the single double layer and their coexistence and disappearance with the magnetic field topology will be highlighted along with the comparisons of density and temperature⁴ profiles corresponding to both the cases. Strength and location of MAPS with RF power, pressure and magnetic field will also be discussed.