Experimental Observation of a Periodically Oscillating Plasma Sphere in a Gridded Inertial Electrostatic Confinement Device

The periodically oscillating plasma sphere (POPS) [] oscillation has been observed in a gridded inertial electrostatic confinement device. In these experiments, ions in the virtual cathode exhibit resonant behavior when driven at the POPS frequency. Excellent agreement between the observed POPS resonance frequency and theoretical predictions has been observed for a wide range of potential well depths and for three different ion species. The results provide the first experimental validation of the POPS concept proposed by Barnes and Nebel [].

Figure 1

Schematic of the INS-e device.

Figure 2

HV pulse operation for the POPS oscillation measurement. Solid lines indicate the grid bias and the dotted lines indicate the plasma potential measured by the emissive probe at the center of the virtual cathode.

Figure 3

(a) Temporal evolution of the plasma potential at the center of the virtual cathode with and without rf modulation. (b) Delay in the loss of the virtual cathode due to the rf modulation as a function of the modulation frequency.

Figure 4

Comparison between the experimentally measured POPS frequencies (points) and the theoretical calculations (lines) from Eq. (3) as a function of the virtual cathode well depth and the ion mass.