Anomalous slowdown of relaxation in an ultracold plasma

Recent experiments by T.C. Killian $et~al.$ [Phys. Rev. Lett. 83, 4776 (1999)], in which an ultracold plasma ($N_e\sim 2\times10^9$cm$^{-3}$, $T_e\sim0.1$K, and $T_i\sim10~\mu$K) with anomalously long lifetime of $\sim100~\mu$s was obtained, are explained based on a previously developed theory. The results of computer simulations of the plasma transition into a metastable state and initial heating of electrons up to several K are presented. An expression earlier obtained for the rate of the metastable plasma recombination agrees with the measured anomalously long lifetime. A conclusion is drawn that the previously predicted new physical object — a metastable overcooled plasma — is realized experimentally.