Spatial distribution and time evolution of correlation in ultracold neutral plasmas

National Science Foundations of China [11175227, 11304329]; Shanghai Supercomputer Center of ChinaThe correlation of ultracold neutral plasmas extracted from the pair correlation function is presented in detail. To get its spatial distribution and time evolution, a large scale simulation using a full molecular-dynamics method with open boundary condition is performed, and the expansion of an ultracold plasma is simulated. We demonstrate that the coupling strength extracted from pair correlation is a good measure for the correlation in ultracold plasma except at the very early stage. The ion-ion pair correlation arises at the timescale of omega(-1)(pi). And results imply that there is a strong coupling area at the outer plasma during the expansion