The motivation behind this work emerges from a multitude of growing important applications of colliding
plasmas. Colliding Laser Produced Plasmas (LPPs) showed a viable capability for simulating many scientific
areas of great interest using laboratory-scale experiments such as the design of inertial confinement
fusion (ICF) Hohlraum.[1, 2] Plasma collisions are expected in the fusion device chambers, and
understanding the collision and subsequent interactions of the colliding plasmas is essential for using
them for various applications. In this work, colliding LPPs are generated by splitting the laser beam into
two sub-beams and then focus them onto flat or V-shaped targets. The dynamics of colliding laserproduced plasmas are investigated using fast photography and space resolved optical emission
spectroscopy. The angular distribution of ions emanating from single and colliding plasmas was also
examined by the aid of the Faraday cup detector. The seed plasmas were generated using 1064 nm, 6 ns
Nd:YAG laser ablation of the target with varied geometries.
Plasma collisions lead to formation of what is kwon as the stagnation layer which is very complex as it had
been shown that plasma stagnation can be preceded by a phase of interpenetration where the colliding
plasma plumes initially pass through each other. Many experiments have been performed on single
LPP to obtain a comprehensive understanding of its evolution and underlying formation mechanisms,
however, reports on colliding plasmas are still limited. With many simultaneous and complex processes
involved, it is critical to use comprehensive diagnostic tools to investigate the seed plasmas and the
interactions before and during the stagnation layer formation. Moreover, the plasma diagnostic tools are
necessary as they provide a more complete picture of the physical nature of colliding plasmas and the
mechanisms of stagnation which are extremely useful reference data for colliding plasma modeling
In this work, a new experimental setup to investigate the properties and potential applications of colliding
laser-produced plasmas is constructed. In this setup, the laser beam is split into two sub-beams that are
focused on flat or 90° V-shaped targets as shown in figure 1. The optical system used to split the laser
beam onto two separate foci on the target surface was similar to the one used previously. The incoming
laser beam from a nanosecond Nd:YAG laser system is split into two beams by a 0.86° wedge prism and
focused on two points on the graphite target using a 2-inch Plano-convex lens with a focal length of 40
cm creating two 500 µm spots as shown in figure 2.
The results show that colliding plasmas can generate a stagnation layer accompanied by cluster
production where a stagnation layer was observed at the interface of two, laterally or head-on, low
temperature colliding laser-produced plasmas. Brighter emission with longer lifetime was found in the
stagnation layer of the colliding plasmas compared to its seed plasma precursors. Besides, the ion
temporal profiles collected by the Faraday cup show narrower kinetic energy profiles from the colliding
region. Also, the major plasma parameters, viz., electron temperature, and density were estimated for
single graphite plasma as well as for the stagnation zone from the spectral data.
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|Affiliation||Nuclear Engineering Department Jordan University of Science & Technology P.O. Box 3030, Irbid 22110, Jordan|
|Country or International Organization||Jordan|