Formation of Atomic Clusters

The onset of clustering and the size of clusters produced can be described by an empirical scaling parameter,Γ*, known as the Hagena parameter [16-TD69.pdf]:

see formula (1) in TD69.pdf

where d is the nozzle diameter (in mm), a the expansion half-angle (x = 45° for sonic nozzles, a < 45° for supersonic), po the backing pressure (in mbar), To the pre-expansion temperature (in Kelvin) and k, the condensation parameter, is a constant related to bond formation (kHe = 3:85 while kHe = 5500 17-TD69.pdf). Gas-jets with the same I* tend to form clusters of the same average size. Cluster formation is a statistical process and therefore there is usually a relatively broad distribution of cluster sizes [17–19-TD69.pdf]. In the massive condensation regime, where nearly all the atoms have condensed into clusters of greater than ~100 atoms, the average number of atoms per cluster hNci scales approximately as [17,20-TD69.pdf]

see formula (2) in TD69.pdf

By varying To and po, it is possible to control the value of I* to engineer a cluster medium of arbitrary average density and cluster size. Optical Rayleigh scattering provides a convenient technique for the in situ measurement of average cluster sizes [21–23,78-TD69.pdf page 311]. [TD69.pdf, page 311] (This is the same process Keely used and is employed in diesel injectors.)

Dense versus diffuse cluster targets
Laser–cluster interactions fall into two broad categories. One involves the interaction with a very low density cluster medium and the other with a dense cluster medium. The former provides an approximation to the interaction of intense laser pulses with single clusters, which is important for understanding the physics without the complications introduced by macroscopic effects. The latter is required for applications where a high density of clusters is needed to produce a high energy-density plasma, or where macroscopic effects are essential to the process. The study of these two density regimes demands quite different experimental approaches. To allow the laser pulses to interact with a very low density of clusters, the laser is focused many hundreds of nozzle diameters below the nozzle into a cluster beam of density of order 1010 cm-3 that is produced with a skimmer and differential pumping arrangement. Interactions with dense cluster media are more straightforward. The laser is focused a few nozzle diameters beneath the nozzle of the gas jet, where the density of clusters can be as high as 5 x 1016 cm-3.

See Also

3.14 - Vortex Theory of Atomic Motions
13.04 - Atomic Subdivision
Atomic Cluster X-Ray Emission
Atomic Clusters
Atomic Force
atomic mass
atomic number
atomic theory
atomic triplet
atomic weight
Debye length
Debye length in a plasma
Debye length in an electrolyte
Etheric Orbital Rotations
Figure 13.06 - Atomic Subdivision
Formation of Atomic Clusters
Inert Gas
Interaction of Intense Laser Pulses with Atomic Clusters - Measurements of Ion Emission Simulations and Applications TD69.pdf
Laser Cluster Interactions
Law of Atomic Dissociation
Law of Atomic Pitch
Law of Oscillating Atomic Substances
Law of Pitch of Atomic Oscillation
Law of Variation of Atomic Oscillation by Electricity
Law of Variation of Atomic Oscillation by Sono-thermism
Law of Variation of Atomic Oscillation by Temperature
Law of Variation of Atomic Pitch by Electricity and Magnetism
Law of Variation of Atomic Pitch by Rad-energy
Law of Variation of Atomic Pitch by Temperature
Law of Variation of Pitch of Atomic Oscillation by Pressure
Models of Laser Cluster Interactions
Plasma holes
Quasi-neutrality and Debye length
Violation of quasi-neutrality

Page last modified on Wednesday 05 of June, 2013 03:25:58 MDT

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