Measurement of the Plasma Width in a Ring Cusp

A pure, fully ionized, ${\mathrm{D}}_2$ plasma of 2×${10}^{19}$ ions, generated from free-falling ${\mathrm{D}}_2$ pellets with use of a 100-J Nd-glass laser pulse followed by a 1000-J C${\mathrm{O}}_2$ laser pulse, is used to fill ($\beta =1\mathrm{}$) a cusp-configured magnetic field. The width of the plasma escaping through the ring cusp is determined by laser scattering, chamber wall light and chemical deposits, and plasma lifetime. The ring cusp is an ion gyroradius wide, in contrast to recent experiments that have indicated a considerably narrower cusp width.