Measurement of correlation-enhanced collision rates using pure ion plasmas

This paper presents the first direct experimental measurements of the Salpeter enhancement of collisions due to particle correlations. The perpendicular-to-parallel collision rate νperpendicular|| is measured in laser-cooled pure ion plasmas, spanning the regimes from weak to strong magnetization, and from weak to strong particle correlations. The abrupt suppression of collisions in the strongly magnetized regime of T < or approx. 10-3 eV is observed, mitigated by the Salpeter enhancement when correlation effects become significant. This νperpendicular|| enhancement due to correlations is directly analogous to the enhancement of fusion collisions in hot dense stellar plasmas. The measured collisional enhancement is approximately exp(Γ), where Γ is the correlation parameter, and this is quantitatively consistent with analytical estimates based on thermal equilibrium shielding and correlations.