Description
Electrodes and other solid boundaries are invariably separated from a plasma by a non-neutral transition region known as the plasma sheath. Depending on the discharge pressure and plasma parameters, the sheath has a minimum thickness on the order of the electron Debye length.The intrinsic properties of the wall material, including its electrical conductivity, surface roughness, and chemical composition, may affect the plasma facing the wall. Macroscopic gaps, pores, or cavities in the surface are effectively filled with plasma only if their characteristic size is comparable to or larger than the sheath thickness; otherwise, the sheath may span across these features, preventing l plasma infusion.
To investigate how aeroglass [1] affects low-pressure (10 - 1000 Pa) argon plasmas, we generated a plasma inside a central millimeter-wide hole in an aeroglass cylinder. The cylinder had a height of 8 mm and a diameter of 8 mm. As the bore radius decreases, the ratio of the interface area to the plasma volume increases, thereby enhancing the relative influence of surface-related processes. Under such conditions, any material-specific effects of the aeroglass on plasma density, electron temperature, or discharge stability should become more pronounced and experimentally accessible.
Plasma diagnostic was performed using electrostatic double probes, enabling local measurements of plasma parameters without the need for an external reference electrode. At discharge pressures of < 700 Pa, we observed the emergence of a high-density plasma mode that was not present when conventional wall materials were used under otherwise identical conditions. This finding suggests that the aeroglass walls play an active role in the modification of the plasma wall interaction.
[1] Lena M. Saure et al., ACS-Nano 2023, 17, 22, 22444*22455, DOI: 10.1021/acsnano.3c05329