Simulations of Argon Plasma Decay in a Thermionic Converter

TL;DR

This study uses particle-in-cell simulations to analyze argon plasma decay in thermionic diodes, revealing dimensional effects on plasma behavior and proposing a new method to measure work function differences.

Contribution

The paper introduces a comparative analysis of 1D and 2D plasma decay in thermionic diodes and suggests a novel technique for measuring work function differences.

Findings

2D plasma decay shows gradual electrostatic potential change.

1D plasma fluctuations cause large potential fluctuations.

Maximum current occurs at flat-band condition, enabling work function measurement.

Abstract

The dynamics of an argon plasma in the gap of a thermionic diode is investigated using particle-in-cell (PIC) simulations. The time-averaged diode current, as a function of the relative electrical potential between the electrodes, is studied while the plasma density depletes due to recombination on the electrode surfaces. Simulations were performed in both 1D and 2D and significant differences were observed in the plasma decay between the two cases. Specifically, in 2D it was found that the electrostatic potential gradually changes as the plasma decays, while in 1D fluctuations in the plasma led to large potential fluctuations which changed the plasma decay characteristics relative to the 2D case. This creates significant differences in the time-averaged diode current. Furthermore, it was found that the maximum time-averaged current is collected when the diode voltage is set to the flat-band condition, where the cathode and anode vacuum biases are equal. This suggests a novel technique of measuring the difference in work functions between the cathode and anode in a thermionic converter.