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

Study of low pressure gas discharge plasma by using nonlocal approximation1

Jingfeng Yao1,2, Guijiang Liu1, Zijia Chu1, Chengxun Yuan1,2
School of Physics, Harbin Institute of Technology, 2 Heilongjiang Provincial Key Laboratory ofPlasma Physics and Application Technology
e-mail (speaker): yaohit@163.com

Since the realization of gas discharge plasma in thelaboratory at the beginning of the last century, the theoryof gas discharge plasma and its applications have been
fully developed. Gas discharge plasma has realized
important applications in daily life. It has madesignificant contributions to science and technology, andhas created great social wealth. With the development ofthese technologies, the control requirements of gas
discharge plasma has become more and more demanding
and needs more sophisticated theories and methods.
Currently, kinetic theory is a commonly used tool todescribe gas discharge plasma. Many applicable theories
based on the Boltzmann equation have been developed,
among which the local approximation theory has been
widely used. However, the local approximation theory
ignores the spatial gradient term when describing the gas
discharge plasma, which is difficult to apply underconditions such as low pressure. Therefore, the non-local
approximation theory has been developed to solve theproblems related to the spatial gradient, especially theinfluence of the spatial gradient on the plasma
characteristics at low pressure.
Here we present the local approximation and nonlocal
approximation kinetic theory model of gas discharge
low-temperature plasma. Firstly, based on the kinetic
theory of gas discharge plasma, using the local
approximation of the Boltzmann equation, atwo-dimensional fluid model is developed to study theeffect of pressure on the discharge characteristics of gas
discharge plasma. The distributions of the electron
density, electron temperature, electric field and mean freepath, etc., are obtained and used to discuss the discharge
characteristics and physical connotation of hollow
cathode discharge in the coaxial grid under differentpressure. It is found that, under low pressure conditions,a high-density negative glow plasma is formed inside thehollow cathode due to the hollow cathode effect. The
discharge exhibits an obvious layered structure of thecathode sheath-negative glow region. With the gradualincrease of pressure, it is observed that both the cathodesheath region and the negative glow region arecontracting and eventually the negative glow region nolonger overlaps. The Faraday dark region is formed after
the negative glow region, in which the electron density

and the excited argon atoms density decreasesignificantly. Additionally, the electron energy mean freepath is further investigated to obtain the applicability of
local approximation and nonlocal approximation atdifferent pressures (figure 1).
Then the spatially averaged Holstein-Tsendin nonlocal
approximation of the Boltzmann equation is used to
study the effects of the metastable atoms in gas discharge
plasma on the plasma electron distribution function andplasma-related reaction characteristics. The superelastic
collision between electrons and metastable atoms willstrongly affect the shape of the electron distributionfunction and the reactions rate constant. The duplicationof the electron distribution function will appear with theexcitation threshold period.
References[1] U. Kortshagen, C. Busch and L. D. Tsendin, Plasma
Sources Science & Technology 5, 1-17 (1996).
[2] C. Yuan, Z. Zhou, J. F. Yao et al., Plasma Sources
Science & Technology 28, 035017 (2019).

Figure 1. Mean free path of electron and electron energy
at low pressure (0.2 Torr) and high pressure (3.0 Torr).