Strongly Coupled Nonneutral Ion Plasma

Radiation pressure from a laser has been used to cool and compress small nonneutral plasmas of ⁹Be⁺ ions confined by static electric and magnetic fields. A second laser has been used as a probe to measure ion densities of 2×{}10⁷ cm^-3 and ion temperatures below 100 mK. A Coulomb coupling constant, Γ, as large as 10 has been measured indicating that the plasma is strongly coupled. In the future, values of Γ large enough to observe a liquid-solid phase transition should be accessible.