7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Insight into the formation of the multi-core structure in laser-sustained plasmas.
Jinbao Liu1, Dongheyu Zhang1, Yangyang Fu1
1
Department of Electrical Engineering, Tsinghua University
e-mail (speaker): liu.jinbao@outlook.com

Laser-sustained plasma (LSP) has emerged as ahighly promising technology due to its advantageousproperties, including compact size, high energy density,and exceptional brightness. These features make LSP
suitable for a wide range of applications, such asspectrochemical analysis, space propulsion, and lightsources. Previous experimental studies have demonstrated
the potential for LSP to exhibit a multi-core structure interms of light intensity. In this study, we present acomprehensive investigation of the formation
mechanisms and characteristics of multi-core LSP
through the development of a two-dimensional multiphysics coupled model. Our model effectively simulates
the spatio-temporal evolution of LSP (Xe, 5 bar) andprovides valuable insights into the factors influencing theoccurrence of multi-core LSP.
The formation of multi-core LSP is found to beinfluenced by several key factors. Firstly, higher laser
power promotes the generation of multi-core structures.
As the laser power increases, the energy deposition
becomes more intense, resulting in higher temperaturesand increased gas ionization. Secondly, slower gas flow
facilitates the formation of multi-core LSP. The reduced
gas flow rate allows for more efficient energy transfer andaccumulation within the plasma, leading to thestabilization of multiple plasma cores. Furthermore, alarger F-number, which represents the focal length of theoptical system, encourages the occurrence of multi-core
LSP. The extended focal length provides a larger region
for energy deposition, promoting the formation ofmultiple plasma cores. Lastly, stronger ignition conditions
contribute to the generation of multi-core LSP. A more
intense initial ignition ensures a higher temperature at thefocus, allowing the remaining power of the incident laser
to ignite the gas and initiate the formation of multiple
plasma cores.
In our simulations, each core of the multi-core LSP
is initially generated at the focal point and subsequently
moves to a stable position against the direction of laser
propagation. Once stable, the multi-core LSP remains
positioned in front of the focus. Notably, the first core of

the multi-core LSP plays a crucial role in thetransformation of the incident laser from Gaussian mode
to ring mode. This transformation occurs as the first core
redistributes the laser energy, forming a ring-shapedstructure. Consequently, the first core is sustained bycentral heating, while the remaining cores are primarily
sustained by ring heating.
To gain a deeper understanding of the energy
dynamics within the multi-core LSP, we analyze theenergy terms involved. Our results indicate that thegeneration of each plasma core is contingent uponachieving a sufficiently high temperature at the focus.
This ensures that the remaining power of the incident laser
is substantial enough to ignite the surrounding gas andinitiate the formation of additional plasma cores.
Consequently, a stronger ignition significantly facilitates
the generation of multi-core LSP structures.
In summary, our study provides valuable insights
into the formation mechanisms and characteristics ofmulti-core LSP through the utilization of a twodimensional multi-physics coupled model. The
occurrence of multi-core LSP is influenced by several
factors, including laser power, gas flow rate, F-number,and ignition conditions. Understanding these factors is
crucial for optimizing the generation of multi-core LSP
structures, which hold great potential for various
applications. By shedding light on the spatio-temporal
evolution of multi-core LSP, this research contributes tothe advancement of plasma physics and enables theexploration of novel applications in fields such as
spectrochemical analysis, space propulsion, and lightsources.
References[1] Akarapu, R. et al,‘Numerical model of a lasersustained argon plasma’, Journal of Laser Applications
21, 169–175 (2009).
[2] Zimakov, V. P. et al.‘Gas laser for efficientsustaining a continuous optical discharge plasma inscientific and technological applications’, Quantum
Electronics, 39, 797-801 (2009).