In　this　paper,　we　study　the　quasi-neutral　limit　of　compressible　Euler-Poisson　equations　in　plasma　physics　in　the　torus　T(d).　For　well　prepared　initial　data　the　convergence　of　solutions　of　compressible　Euler-Poisson　equations　to　the　solutions　of　incompressible　Euler　equations　is　justified　rigorously　by　an　elaborate　energy　methods　based　on　studies　on　an　lambda-weighted　Lyapunov-type　functional.　One　main　ingredient　of　establishing　uniformly　a　priori　estimates　with　respect　to　lambda　is　to　use　the　curl-div　decomposition　of　the　gradient.　(c)　2010　Elsevier　Inc.　All　rights　reserved.