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18Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2018
MODEL OF DUSTY PLASMA IN DC DISCHARGE EXPERIMENTS IN THE RANGE
OF TEMPERATURES 100—300 K V.S. Nikolaev1'2, A.V. Timofeev1,2
JIHT RAS, Moscow, Russia, e-mail: timofeevalvl@gmail.com 2MIPT, Moscow, Russia, e-mail: vladiorussia@mail.ru
Inter-particle distance in dusty plasma structures may be considered as the parameter sensitive to all important effects and forces acting on dust particles. In this work its behavior is analyzed by the method of molecular dynamics and is compared with the experiments in which this parameter was measured. For example, in the experiments [1,2] it was shown that cooling dusty plasma system down to the temperatures of the order of 100 K leads to the manifestation of two effects: (i) in some cases inter-particle distance at 100 K is 4-6 times less than at the room temperature, (ii) while in the others inter-particle distance at low temperatures is rather high and even starts to increase with further cooling of the system. The aim of this work is to explain these two effects by studying the influence of different forces on the particles of dust in molecular dynamics modeling.
In the model it is suggested that particles are placed in the stratum head which appears in the positive column of a glow discharge. Gravitational force is counterbalanced by the strong vertical electric field gradient causing two-dimensional structures appearance. Particles are kept from drifting to the walls of the discharge tube by the parabolic trap existing near the axis. Particle interaction is Yukawa-like.
In the first part of the work no assumptions about the nature of particle charging, screening length in dusty plasma system and trap appearance are made. It is found that inter-particle distance dependence on the particle charge, screening length and trap parameter is well described by power functions in conditions close to experimental ones:
r(q, Ascr, a) = (3.5 ± 0 2)q° 15±001l°c5r5±001a-0 ■ 17±0 ■ 01.
In the second part two forces are included in the model - thermophoretic force [3] which is caused by the heat emission of discharge current in the tube and ion shadowing force [4] which is caused by the attraction of the neighboring particle to the central one due to the absorption of ion flow moving to the central particle. It is shown that thermophoretic force is repulsive and grows with temperature decrease. At high values of current (>0.5 mA) it might cause the increase of inter-particle distance at low temperatures which is observed in the experiment. On the contrary, ion shadowing force causes mutual attraction between the particles and at low temperatures and high values of ion concentration in surrounding plasma might cause the decrease of average inter-particle distance by up to 50%. Model of dusty plasma including the Debye potential, parabolic trap, thermophoretic force and ion shadowing potential allows approximating values of inter-particle distance observed in the experiments.
1. Samoylov I.S., Baev V.P., Timofeev A.V., Amirov R.Kh., Kirillin A.V., Nikolaev V.S., Bedran Z.V., JETP, 151:582-591, 2017.
2. Antipov S.N., Asinovskii E.I., Fortov V.E., Kirillin A.V., Markovets V.V., Petrov O.F. and Platonov V.I. Phys.Plasmas., 14: 090701. 2007.
3. Balabanov V. V., et al. JETP, 92.1: 86-92. 2001.
4. Khrapak S. A., Morfill G. E. Phys.Plasmas., 15.8: 084502. 2008.
