Abstract
We determine the size of argon clusters generated with a planar nozzle, based on the optical measurements in conjunction with theoretical modelling. Using a quasi-one dimensional model for the moments of the cluster size distribution, we determine the influence of critical physical assumptions. These refer to the surface tension depending on the presence of thermal equilibrium, the mass density of clusters, and different methods to model the growth rate of the cluster radius. We show that, despite strong variation in the predicted cluster size, 〈N〉, the liquid mass ratio, g, can be determined with high trustworthiness, because g is predicted as being almost independent of the specific model assumptions. Exploiting this observation, we use the calculated value for g to retrieve the cluster size from optical measurements, i.e., calibrated Rayleigh scattering and interferometry. Based on the measurements of the cluster size vs. the nozzle stagnation pressure, we provide a new power law for the prediction of the cluster size in experiments with higher values of the Hagena parameter (Γ*>104). This range is of relevance for experiments on high-intensity laser matter interactions.
Highlights
The formation of the nanometer-sized objects via the van-der-Waals aggregation of gas atoms and molecules, called cluster formation, is emerging into a highly important technique for the field of high-intensity laser-matter interactions.1 As compared to the standard gas targets made of atomic or molecular monomers, clusters provide a number of unique advantages and novel options
We have investigated argon cluster formation in a planar nozzle expansion both experimentally and theoretically with a main interest in the average cluster size, hNi
The average cluster size at a small distance downstream of the nozzle exit has been determined by combining Rayleigh scattering and interferometry data, on the one hand, and theoretically derived values for the liquid mass fraction, on the other hand, as a function of the so-called Hagena parameter, CÃ
Summary
The formation of the nanometer-sized objects via the van-der-Waals aggregation of gas atoms and molecules, called cluster formation, is emerging into a highly important technique for the field of high-intensity laser-matter interactions. As compared to the standard gas targets made of atomic or molecular monomers, clusters provide a number of unique advantages and novel options. One may either assume that the clusters have the same temperature as the surrounding gas, whereas, as mentioned above, expansive cooling of the gas and release of latent heat during cluster growth suggest that a thermal non-equilibrium model is to be applied These uncertainties show that an experimental determination of the cluster size based on the optical measurements requires an improved modelling of cluster formation in search of reliable auxiliary information. Using a model that is based on conservation of mass, momentum, and energy, and which describes the cluster size distribution via its moments, we vary the critical model assumptions These are, a thermal equilibrium vs a non-equilibrium surface tension model, a liquid vs a solid-like mass density of the clusters, and a small-cluster and Hill’s radius vs a large-cluster limit for the growth rate. The derived power law complements the prediction of the cluster size in the range of at least an order of magnitude higher CÃ than before (1:8 Â 104 < CÃ < 2:5 Â 105), i.e., well beyond the proven validity of Hagena’s relation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
