We discretize the Vlasov-Poisson system using conservative semi-Lagrangian (CSL) discontinuous Galerkin (DG) schemes that are asymptotic preserving (AP) in the quasi-neutral limit. The proposed method (CSLDG) relies on two key ingredients: the CSLDG discretization and a reformulated Poisson equation (RPE). The use of the CSL formulation ensures local mass conservation and circumvents the Courant-Friedrichs-Lewy condition, while the DG method provides high-order accuracy for capturing fine-scale phase space structures of the distribution function. The RPE is derived by the Poisson equation coupled with moments of the Vlasov equation. The synergy between the CSLDG and RPE components makes it possible to obtain reliable numerical solutions, even when the spatial and temporal resolution might not fully resolve the Debye length. We rigorously prove that the proposed method is asymptotically stable, consistent and satisfies AP properties. Moreover, its efficiency is maintained across non-quasi-neutral and quasi-neutral regimes. These properties of our approach are essential for accurate and robust numerical simulation of complex electrostatic plasmas. Several numerical experiments verify the accuracy, stability and efficiency of the proposed CSLDG schemes.

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