A ``plasmascope'' using light emitter diodes

A ``plasmascope'' device which permits visual display of the floating potentials from a 7 × 7 matrix of Langmuir probes immersed in a low-density plasma is described. The probe potential, which is proportional to the plasma space potential, is sampled through a high impedance FET circuit. These potentials are displayed by a matrix of light emitter diodes such that the light intensity at a point on the matrix is proportional to the corresponding probe floating potential. This device is useful to determine the qualitative location of the plasma, its configuration, and slow motion.