Experimental Observations of a Spherical Transparent Cathode Glow Discharge

In this paper, several observations with regard to the nature of the glow discharge in a spherical inertial electrostatic-confinement device are reported. In particular, automated single and double Langmuir probe diagnostics are configured such that the ion-microchanneling phenomenon is directly verified. In addition, these measurements allow for the determination of the “star-to-jet” mode transition and show that microchanneling persists well into jet-mode regime despite its visual appearance. Conclusions about the overall discharge structure may also be drawn from spatial variations in the density and neutrality of the discharge. Finally, $I$–$V$ characteristics obtained with the double Langmuir probe indicate the presence of energetic electrons inside of the cathode-grid region.