Researcher in the Spotlight: Judith van Huijstee

I’m doing research on the charging of microparticles in a spatial plasma afterglow

I’m Judith van Huijstee and I’m doing research on the charging of microparticles in a spatial plasma afterglow. More specifically, I’m interested in the dynamic behavior of the particle charge: how does a particle’s charge evolve as it moves through a plasma environment and afterglow and how do the relevant experimental parameters influence this process?

From air pollution to astrophysics

My work takes place in the Elementary Processes in Gas Discharges research group of the Department of Applied Physics. The approach is to investigate the particle charge in an experimental set-up (with simple numerical simulations for comparisons). Currently, I’m measuring the particle charge by recording the particles’ trajectories in an externally-applied electric field, but I’m also investigating the possibilities for a more flexible diagnostic.

​​​​​​​"This could be used in vacuum environments, such as in advanced semiconductor production."

My research is part of a larger project on particle seal development, which is essentially split into particle generation, particle transport and particle removal. My work looks at the development of a plasma-assisted particle seal, which would use plasma to charge (airborne) contaminating particles, then use an electric field to manipulate the trajectories/movement of those particles and filter them from the gas flow. This could be used in vacuum environments, such as in advanced semiconductor production. The fundamental knowledge gathered on particle seals could also be used to create filters on exhausts that would prevent/limit air pollution, among other applications. From a broader point of view, particle charging in plasma is also relevant to planet formation in astrophysics.

Influences upon influences

There are two main challenges in our research. Firstly, there are many parameters which influence the particle charge in plasma (plasma power, gas pressure, gas flow, particle material, particle shape, etc.). These parameters (and the derived plasma parameters) are not all independent and can influence the particle charge through more than one process simultaneously. For example, changing the gas pressure changes multiple plasma parameters (that all independently influence the particle charge) as well as the particle speed (i.e., the particle-plasma interaction time, again influencing the particle charge).

The effects of the experimental parameters on particle charging are complicated and therefore not easy to untangle. Additionally, it is very hard to measure particle charge in an accurate, non-invasive and time-resolved manner (or spatially-resolved manner, as we’re interested in the particle charge at a certain position in the plasma through which it moves). This is not yet possible in our experimental set-up.

A reasonable range

In collaboration with a previous PhD student (Dr. Boy van Minderhout) and a current master’s student (Robert Rompelberg), we’ve already published several papers. Most recently, I’ve published proceedings for an SPIE conference through which we’ve shown that the charge-to-mass ratio (an important parameter that determines the efficiency of the application) in the spatial plasma afterglow is approximately equal (6% deviation) for spherical particles and non-spherical two-particle clusters (doublets) of those particles. This shows that it makes sense to study spherical particles in our experimental set-up and extrapolate the results towards non-spherical particles within a reasonable range.