Effect of wall secondary electron emission on the characteristics of double sheath near the dielectric wall in Hall thruster

To further reveal the characteristics of sheath near the dielectric wall in Hall thruster discharge channel, a one-dimensional fluid sheath model combined with the velocity distribution function of electron emitted from wall is used to study the influence of secondary electron emission yield (SEEy) σ on the characteristics of double sheath near wall. Analytic results show that because of the contribution of secondary electron flux to the density of sheath electron, the sheath presents single-layer positive ion sheath formation when σ is lower than a critical SEEy σ_dc, and also presents double-layers formation that joins with positive ion sheath and electron sheath when σ > σ_dc. However, when σ further increases to 0.999, the sheath presents the formation of three-layers that are alternated by positive ion sheath, electron sheath and positive ion sheath. Numerical results also indicate that with the increase of σ, the joining point between positive ion sheath and electron sheath moves away from wall, and the thickness of electron sheath increases obviously.