Bragg Diffraction from Crystallized Ion Plasmas

Single crystals of a one-component plasma were observed by optical Bragg diffraction. The plasmas contained 10$^5$ to 10$^6$ single-positive beryllium-9 ions ($^9$Be$^+$) at particle densities of 10$^8$ to 10$^9$ per cubic centimeter. In approximately spherical plasmas, single body-centered cubic (bcc) crystals or, in some cases, two or more bcc crystals having fixed orientations with respect to each other were observed. In some oblate plasmas, a mixture of bcc and face-centered cubic ordering was seen. Knowledge of the properties of one-component plasma crystals is required for models of white dwarfs and neutron stars, which are believed to contain matter in that form.