Measuring the plasma-wall charge by infrared spectroscopy

TL;DR

This paper introduces a novel infrared spectroscopy method to measure plasma-induced charge accumulation on dielectric surfaces by detecting shifts in surface plasmon resonance, enabling non-contact charge sensing.

Contribution

It presents a new approach using surface plasmon resonance in infrared spectroscopy to quantify plasma-wall charge accumulation non-invasively.

Findings

Reflectivity dips depend strongly on incident angle near Berreman resonance.

Charge-induced shifts are measurable with attenuated total reflection setups.

The method allows non-contact, in situ measurement of plasma-wall charges.

Abstract

We show that the charge accumulated by a dielectric plasma-facing solid can be measured by infrared spectroscopy. The approach utilizes a stack of materials supporting a surface plasmon resonance in the infrared. For frequencies near the Berreman resonance of the layer facing the plasma the reflectivity dip--measured from the back of the stack, not in contact with the plasma--depends strongly on the angle of incidence making it an ideal sensor for the changes of the layer's dielectric function due to the polarizability of the trapped surplus charges. The charge-induced shifts of the dip, both as a function of the angle and the frequency of the incident infrared light, are large enough to be measurable by attenuated total reflection setups.