ИСТИНА

The ultracold plasmas created in the magneto-optical traps, the study of which began in the early 2000's, were considered initially as a promising candidate for realization of the strongly-coupled Coulomb's systems. Unfortunately, this was found to be precluded by the anomalous heating immediately after the ionization, which nature remains unclear till now. Here, we explore the hypothesis that such a heating is caused by the clusterization of ions in ultracold plasmas. (Namely, the first ionized atom shifts the ionization threshold of nearby atoms and, thereby, facilitates their subsequent ionization; so that the ions are formed in groups.) If this is the case, such clusters should act as the multiply-charged ions and attract simultaneously a few electrons, thereby stimulating the multi-electron scattering with the efficient exchange of energy. To verify this hypothesis, we performed the molecular-dynamic simulations, which distinctive feature was the initial distribution of ions with both enhanced and suppressed clusterization. As a result, it was found that a suppressed clusterization has no appreciable effect on the electron temperature, while the enhanced clusterization can lead to the considerable increase in this temperature, up to an order of magnitude. Therefore, the clusterized distribution of ions after the ionization could really be a cause for the anomalous electron heating. However, such heating can be avoided if the ultracold plasmas are produced in two steps: firstly, the neutral atoms are excited to the blockaded Rydberg states and, secondly, they are ionized by a narrow-band laser radiation. Then, the resulting ions will be well separated from each other, and the anomalous heating should be absent.