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

3D Molecular Dynamics Simulation of Dust Charge Dynamics in a Coulomb
Screened Plasmas
S. Kalita1,2, P. Kaur3, K. Avinash4, R. Ganesh1,2
1Institute for Plasma Research, Bhat, Gandhinagar, Gujarat 382428, India.
2
Homi Bhaba National Institute, Training School Complex, Anushaktinagar, Mumbai 400094, India.
3
Department of Chemical Physics, The Weizmann Institute of Science, Rehovot, 76100, Israel.
4
Sikkim University, Samdur, Tadong 737102, Gangtok, Sikkim, India.
e-mail (speaker): suruj.kalita@ipr.res.in

When dust particles are added to an equilibrium plasma
system, the electron flux and ion flux reaches the surfaceof the dust particles. At steady state, electron and ion
fluxes balance each other and net charge on the dust
particles is typically negative. Such Plasmas are known
as Complex Plasmas. However, depending upon thedensity of the dust particles in a plasma medium, theaverage charge on the dust grains can vary.
The two parameters, which characterize the dynamics
of dust grains are “Coulomb screening length”, λc and“Debye screening length”, λd [1]. In the low grain
density limit, in which, λc > λd , the “Debye spheres’’ ofthe individual dust grains remain isolated from the“Debye spheres’’ of the nearby dust grains. In such case,the system is in usual Debye regime and all the grains
have nearly the same mean charge. For example, in thisregime, it is well known from fluid theory [2] that themean charge of a dust grain is of the order 2.51 KTe/e (Kis the Boltzman Constant) for a Hydrogen plasma. In thehigh grain density limit, in which, λd > λc , the “Debyespheres’’ of the dust grains tend to overlap with eachother. In such case, the system is found to be in Coulomb
regime wherein a “charge reduction” and “chargedistribution’’ of the dust grains can take place dependingon the grain location. We can further combine
λc and λd to a single variable and the variable combining
λc and λd is called Havnes parameter. The Havnes
parameter is define as, H = (λd / λc)2 . When, H<1, thesystem is in “Debye regime” and when H>1, the system
is in “Coulomb regime”.
In our present work, with the help of 3D Molecular
Dynamics (MD) simulation, we have investigated thesystem in both Debye and Coulomb regimes [3]. The
average charge value that is obtained from the simulation
for particular values of λd and λc , is in good agreementwith the fluid theory [2]. Various novel results have beengenerated for various values of parameter H, including
charge distribution and charge reduction across grains,details of such results will be presented, along withdiscussion of possible application to nano-dusty plasmas[3].
When the system is in extreme “Debye regime” or inother words, H << 1, then the average charge should be
2.51 KTe/e. Considering λd = 1 and λc = 10, the averagecharge variation with time obtained from our 3D MD
simulation code MPMD-3D [4] (an extension of MPMD-

2D code [5]) is shown in Fig.1.

Figure 1: Variation of average charge with time is shown.
The mean value is around 2.47. The charge, according tofluid theory is 2.50. The deviation in the charge value
calculated by MD simulation is 1.2 %.
References[1] K. Avinash, P. K. Shukla, Physics of Plasmas 7, 2763
(2000); https://doi.org/10.1063/1.874126.
[2] C. K. Goertz, Reviews of Geophysics, Volume 27, Issue2,May 1989, Pages 271-292;
https://doi.org/10.1029/RG027i002p00271.
[3] S. Kalita, P. Kaur, K. Avinash et al, Manuscript underpreparation, 2023.
[4] S. Kalita, R. Ganesh, Phys. Fluids 33, 095118 (2021);
https://doi.org/10.1063/5.0060089.
[5] P. Kaur, R. Ganesh, PHYSICAL REVIEW E 100, 053201(2019); 10.1103/PhysRevE.100.053201.