Simplicity and boundary behavior of spike sequences for a superlinear problem in plasma physics

We prove that spike sequences related to a nonlinear problem of Grad-Shafranov type are always simple and always converge toward interior points of the domain. This sharpens the blow-up analysis carried out by Bartolucci-Jevnikar-Wu in [2] and provides a converse to the existence result for spike sequences obtained by Wei in [21] .