Ice grain formation from negative ions in a cryogenically-cooled laboratory plasma*

Grains of ice form spontaneously when water vapor is injected into a weakly-ionized laboratory plasma with cryogenic background gas. The grains quickly grow in elongated fractal patterns, reaching tens or hundreds of microns in length [1]. The conditions for nucleation are consistent with a model for ion-catalyzed homogenous nucleation, in which anions such as OH-, created by dissociation of water vapor, attract clusters of water molecules to form stable nuclei around which grains can form [2].  The formation of clusters of water around negative ions in the plasma are measured using mass spectrometry. It is planned to compare this to observations of ice formation.

[1] Nicolov, A., Gudipati, M. S., & Bellan, P. M. (2024). Phase and morphology of water-ice grains formed in a cryogenic laboratory plasma. The Astrophysical Journal, 966(1), 66.

[2] Bellan, P. M. (2022). Mechanism for the Efficient Homogeneous Nucleation of Ice in a Weakly Ionized, Ultracold Plasma. The Astrophysical Journal, 936(1), 52.