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

Applications of “Energy Tree” Concept on Active Control of Some KeyParameters in Collision-Dominated Low-Temperature Plasmas
He-Ping Li1, Zi-Ming Zhang1, Lu-Xiang Zhao2, Heng-Xin Zhao1, Chuan Fang1
1
Department of Engineering Physics, Beijing, China
2
Department of Mechanical Engineering, Beijing, Chinae-mail (speaker): liheping@tsinghua.edu.cn

In recent years, with dramatic development of numerous
applications of collision-dominated low-temperatureplasmas (CD-LTPs), e.g., plasma biochemical engineering,clinical medicine, agriculture, low-dimensional materials
synthesis, environmental protection and energy saving,
etc., specific or even extreme demands on certain plasma
parameters, e.g., electron energy and number density,
heavy-particle temperature, characteristic scale like
plasma action distance, area or volume, heat flux density
to a treated workpiece, have become one of the importantresearch aspects in the field of plasma science andtechnology. In our opinion, it is indispensable tounderstand deeply to the complex physiochemical
processes in plasmas with energy transfer as the main line
for achieving active control of key plasma parameters.
In this paper, based on our previously proposed “EnergyTree” concept [1], the synergistic non-equilibriumtransport mechanisms are analyzed focusing on the massmomentum-energy (MME)-coupling transport processes
in several typical CD-LTPs. And then, examples arepresented to show the applications of the preceding
theoretical analyses for the active control of some key
plasma parameters.
For the RF-APGD plasmas generated using a baremetallic electrode configuration, the specific energytransfer channel is discovered, i.e., energy deposition
through electron Joule heating process (Valve 1: EJoule,E)→ energy transfer from electrons to heavy particles via
elastic collisions (Eel) → energy loss to the metal electrodethrough the heavy-species heat conductive process (Valve2: Econd). Consequently, a novel approach is proposed togenerate the RF-APGDs with independently controlled
gas temperature and electron number density bycontrolling the energy valves mentioned above. And thehelium RF-APGD plasmas are produced with a quasiindependent variation of the spatiotemporally averaged
gas temperatures from −33.7 to 49.5 °C and the plasma
densities from 2.7×1016 to 6.3×1016 m-3 on the radiofrequency gas discharge plasma experimental platform(RPX) [2].
For the atmospheric-pressure direct-current arc
discharges, based on the analyses on the MME-couplingtransfer processes, on the one hand, it is found that theconvective and/or conductive heat transfer of heavy
particles are the major energy transfer processes inside theheavy-particle subsystem itself and the dissipative
processes to the environment, and thus, would play a keyrole for controling the non-equilibrium level of theplasmas [3]. And consequently, an argon arc plasma withlow gas temperature, high electron number density andlarge volume non-equilibrium region is produced due tothe enhancement of the convective energy transfer process
in the arc core region with the introduction of a counterflow cold gas through an annular anode on a free-burningarc plasma experimental platform (APX) [4]. On the otherhand, it is revealed that the operating pressure also plays
an important role by influencing the elastic collisionenergy exchange between electrons and heavy particles
and the convective heat transfer process [3]; thus, the gas
temperature, and consequently, the heat flux density to atreated workpiece may be modulated. Therefore, based on
the principle of consistent heat flux density and heatingtime with real flight conditions, the ground simulation
method for materials ablation has been developed on themulti-phase gas discharge plasma experimental platform(MPX). The experimental result show that the proposed
ground simulation method can be used as a pre-test
approach for effectively simulating the surface thermal
environment of the component of high-speed re-entry
spacecraft before costly wind tunnel experiments [5].
Based on the preceding discussions, it is indispensable toestablish a model collision-dominated plasma system(mCDPS) not only for investigating the complex
synergistic MME-coupling non-equilibrium transportmechanisms in CD-LTPs, but also for promoting existingor even creating novel applications of plasmas in thefuture.
Acknowledgement: This work has been supported by theNational Natural Science Foundation of China (Nos.
12205163, 11475103, 10972119), Tsinghua Precision
Medicine Foundation (Nos. 10001020119, 2022TS015),
Tsinghua University Initiative Scientific Research
Program (Nos. 20182000306, 20229990132).
References[1] He-Ping Li, Kostya (Ken) Ostrikov, Wenting Sun,
Phys. Rep., 2018, 770-772: 1[2] Jing Li, Chuan Fang, Jian Chen, et al., Plasma Sources
Sci. Technol., 2022, 31: 055015[3] Chuan Fang, Jian Chen, Jing Li, et al., Plasma Sources
Sci. Technol., 2022, 31: 015015[4] Chuan Fang, Zi-Ming Zhang, Yao-Ting Wang, et al., J.
Phys. D: Appl. Phys., 2023, 56: 11LT01[5] Chuan Fang, Ph. D. Thesis, Tsinghua University, 2023