Effect of Secondary Electron Emission on Electron Cross-Field Current in \textit{E$\times$B} Discharges

This paper reviews recent experimental, theoretical, and numerical studies of plasma-wall interaction in a weakly collisional magnetized plasma bounded with channel walls made from different materials [1-3]. A low-pressure \textit{E $\times $ B} plasma discharge of the Hall thruster was used to characterize the electron current across the magnetic field and its dependence on the applied voltage and the electron-induced secondary electron emission (SEE) from the channel wall [1]. The presence of a depleted anisotropic electron energy distribution function with beams of secondary electrons was predicted to explain the enhancement of the electron cross-field current observed in experiments. Without the SEE, the electron cross-field transport can be reduced from anomalously high to nearly classical collisional level. The suppression of the SEE was achieved using an engineered carbon-velvet material for the channel walls [3]. Both theoretically and experimentally, it is shown that the electron emission from the walls can limit the maximum achievable electric field in the magnetized plasma. \\[4pt] [1] Y. Raitses, et al, IEEE Trans. on Plasma Scie. \textbf{39}, 995 (2011). \\[0pt] [2] M. D. Campanell, et al, Phys. Rev. Lett. \textbf{108}, 235001 (2012). \\[0pt] [3] Y. Raitses, et al, \textit{J.Appl. Phys.} \textbf{99}, 036103 (2006).