Characterization of the Electron Energy Distribution Function of Plasma Sphere in the Inertial Electrostatic Confinement Device with Optical Emission Spectroscopy and Collisional-Radiative Model*

The discharge behavior within inertial electrostatic confinement (IEC) devices is not yet fully understood. A working principle based on the double-layer theory is proposed to explain the discharge mechanism. [1-3] Optical emission spectroscopy (OES) is used to evaluate the non-Maxwellian electron energy distribution function (EEDF) and the respective effective electron temperature (T_e) across the radius of the plasma sphere within the IEC. An optimized super-symmetrical cathode structure is implemented for the IEC device to reduce the uncertainty of the discharge [4] and argon is used as the demonstrating gas for the evaluation.

The prediction of the EEDF and T_e is performed through the collisional radiative model [5,6]. The x-form formula proposed by Davydov-Druyvesten is used to interpret the non-Maxwellian EEDF. [5] The line-ratio of transition 420.06 nm and 419.87 nm is used to determine the EEDF of the experimental measurement.

The T_e at the center of the plasma sphere aroud 20 eV and decays to 2 eV at the edge of plasma sphere. The T_e profile across the radius of the plasma sphere presents strong non-linearity, so as the EEDF profile. This proves the formation of a virtual anode at the center of plasma sphere, which dominates the discharge mechanism of IEC device.