Enhanced ion particle flux and momentum outward of a plasma ball

A plasma ball has been produced near the anode in a configuration that, when magnetized, operates as a radial plasma source (RPS) [1]. Plasma balls have been studied recently in different configurations [2]. We find that the plasma particle flux outward of the plasma ball is larger than that expected by the Langmuir relation in double layers [3]. The frequency of oscillations of a pendulum is larger than due to gravity only, reflecting the force by the plasma ball. The force by the plasma ball is larger than expected by the model [3]. We address these two questions: the increased ion flux and the increased force relative to the model [3]. We suggest that the Langmuir relation underestimates the ratio of ion to electron flux. We also suggest that the ions gain most of the momentum in the quasi-neutral plasma rather than in the double layer; the impulse enhancement is suggested to result from ion-neutral collisions in the plasma.\\[4pt] [1] G. Makrinich and A. Fruchtman, Phys. Plasmas 16, 043507(2009); Appl. Phys. Lett. 95, 181504 (2009); Phys. Plasmas 20, 043509 (2013).\\[0pt] [2] R. L. Stenzel, C. Ionita, and R. Schrittwieser, J. Appl. Phys. 109, 113305 (2011)\\[0pt] [3] I. Langmuir, Phys. Rev. 33, 954 (1929); B. Song, N. D'Angelo, R. L. Merlino, J. Phys D: Appl. Phys. 24, 1789 (1991).