Strongly coupled non-neutral ion plasma

The density, n /sub o/, and temperature, T, of small clouds of several hundred 9Be+ ions stored in a Penning trap have been measured. Such a system can be described as a non-neutral plasma. Radiation pressure from a laser was used to cool the ions. A second laser was used to probe the ion plasma and measure densities n /sub o/ about 2 x 107 ions/cm3 and temperatures T < 100 mK. These measurements determine a Coulomb coupling constant GAMMA is identical to e2(4πn /sub o/ /3) /sup 1/3/ /k /sub B/ T as large as ten. Theoretical calculations predict that for GAMMA greater than or equal to 2, the plasma is to exhibit liquid behavior and at GAMMA about 170 a liquid-solid phase transition is expected to take place. In the future, crystallization in a non-neutral ion plasma appears accessible