Experimental Observation of Coulomb Screening and Coulomb Acoustic Wave in Nanodusty Plasmas

Nanodusty plasma, composed of electrons, ions and nanometer sized dust grains, can result in a highly dense dusty plasma where the ratio of dust to ion densities i.e., Havnes parameter becomes very high, P»1. Due to high dust density, the nanodust particles float at a small potential resulting in a reduced average dust charge. In nanodusty plasmas, self-excited dust density waves dominate the cloud dynamics in most of the experimental scenarios. It has been shown theoretically by Avinash et al. [1],[2] that in high dust density regime, dust particles screen each other not by usual Debye screening but by a new screening mechanism called “Coulomb Screening”. This is shown to cause dust charge reduction. A characteristic scale length, λ_c²=1/4πn_dr_d for Coulomb screening is obtained where n_d and r_d, are the dust density and dust radius, respectively. It is shown that Coulomb Screening gives rise to a new acoustic mode called Coulomb acoustic mode in high density nanodusty plasma. In this particular work, the observations and results of an experiment [3] on the propagation of a self-excited dust density wave under strong Havnes effect will be presented based on these theoretical predictions. For the parameters of the experiment, the Coulomb screening dominates over the Debye screening i.e., λ_c«λ_d. The dispersion relation is experimentally measured and compared with a theoretical dispersion which includes Debye as well as Coulomb screening. Based on this comparison the experimentally observed mode is identified as the “Coulomb Acoustic mode”.

References:

[1] Avinash K., Shukla P. K. // Physics of Plasmas. 2000. V. 7. No. 7. P. 2763-2765.

[2] Avinash K., Bhattacharjee A., Merlino R. // Physics of Plasmas. 2003. V. 10. No. 7. P. 2663-2666.

[3] Chutia B., Deka T., Bailung Y., Sharma D., Sharma S. K., Bailung H. // Physics of Plasmas. V. 28. No. 12. P. 123702.