Plasma probe characteristics in low density hydrogen pulsed plasmas

TL;DR

This study combines probe diagnostics with 2D particle-in-cell simulations to evaluate plasma characteristics in low density pulsed hydrogen plasmas, revealing limitations of traditional probe theory in such regimes.

Contribution

It demonstrates that simulations can accurately model plasma probe interactions in low density pulsed plasmas, highlighting the limitations of probe theory in these conditions.

Findings

Simulations match the time evolution of probe IV characteristics.

Probe measurements overestimate plasma density in low density pulsed plasmas.

Probe theory has limited applicability in low density, transient plasma conditions.

Abstract

Probe theories are only applicable in the regime where the probe's perturbation of the plasma can be neglected. However, it is not always possible to know, a priori, that a particular probe theory can be successfully applied, especially in low density plasmas. This is especially difficult in the case of transient, low density plasmas. Here, we applied probe diagnostics in combination with a 2D particle-in-cell model, to an experiment with a pulsed low density hydrogen plasma. The calculations took into account the full chamber geometry, including the plasma probe as an electrode in the chamber. It was found that the simulations reproduce the time evolution of the probe IV characteristics with good accuracy. The disagreement between the simulated and probe measured plasma density is attributed to the limited applicability of probe theory to measurements of low density pulsed plasmas. Indeed, in the case studied here, probe measurements would lead to a large overestimate of the plasma density. In contrast, the simulations of the plasma evolution and the probe characteristics do not suffer from such strict applicability limits. These studies show that probe theory cannot be justified through probe measurements.