Dynamics of Fractal Ice Grains in Cryogenic Plasmas
Abstract
Ice grains formed in a cryogenically cooled plasma exhibit fractal morphologies that drive distinct collective dynamics. By measuring and quantifying the dynamics of these grains in a plasma afterglow, we observe a new fundamental dynamical regime induced by fractal scalings of ice mass and collisional cross section. In this regime, grains become more coupled to flows of gas and ions as they get larger, while the influence of gravity remains comparatively small, even as the grains reach millimeter sizes. These dynamics are unattainable by compact spheres, and thus inaccessible to dusty plasma models that assume spherical grains, challenging models for systems ranging from laboratory nanoparticle synthesis to astrophysical dust transport.
Acknowledgement (English)
This work was supported by NSF Grant No. 2308558 and the NSF/DOE Partnership in Plasma Science and Engineering via Grant No. DE-SC0020079. We thank Z. Wang (LANL, supported by DOE Fusion Energy Sciences) for the loan of a high-speed camera used in exploratory measurements, and thank R. Marshall and F. Chu for technical advice in LIF diagnostics.
Data Availability (English)
The data that support the findings of this article are openly available [37], embargo periods may apply.
Supplemental Material (English)
The document "SUPPLEMENTAL-MATERIAL-REV2.pdf" contains calculations and measurements showing the disappearance of the electrostatic and ion drag forces early in the afterglow, a lengthened computation of the gas flow regime, and methodological details for measuring the gas temperature profile, terminal velocity, and fractal parameters.
The two videos show a compilation of high-speed videos during the afterglow, slowed down by 40x. One shows the entire ice cloud using scattering, and the other shows individual grains through the long-distance microscope lens.
Files
rx5l-k7f9.pdf
Additional details
Related works
- Is supplemented by
- Dataset: 10.22002/k87vy-xqk63 (DOI)
Funding
- National Science Foundation
- 2308558
- United States Department of Energy
- DE-SC0020079
- Los Alamos National Laboratory
- Office of Fusion Energy Sciences
Dates
- Accepted
-
2025-10-09