Effects of Electron Charge Fluctuations on Linear Ion-Acoustic Waves

Effects of Electron Charge Fluctuations on Linear Ion-Acoustic Waves

Sanjit Kumar Paul

Department of Basic Sciences & Humanities University of Asia Pacific, Dhaka

DOI: https://doi.org/10.51584/IJRIAS.2025.10060058

Received: 24 May 2025; Accepted: 29 May 2025; Published: 08 July 2025

ABSTRACT

The linear propagation of the ion-acoustic waves (IAWs) in a dusty plasma consisting of Boltzmann-distributed electrons and ions, mobile charge fluctuating negative dust and charge fluctuating stationary negative dust has been theoretically investigated. It has been shown that the electron charge fluctuation is a source of dissipation, and is responsible for forming IA shock waves in such a dusty plasma. The basic features of the IA shock waves have been identified in this investigation which could be useful in understanding the properties of localized space dusty plasmas. It has been proposed to design a new laboratory experiment, which will be able to identify the basic features of the ion-acoustic shock waves predicted in this theoretical investigation.

Keywords:  Charge fluctuation, linear ion-acoustic waves, dusty plasmas, shock waves.

INTRODUCTION

The wave propagation in plasmas has received much attention in recent years because of its vital role in understanding different types of collective processes in space environments, namely, lower and upper mesosphere, cometary tails, planetary rings, planetary magnetosphere, interplanetary spaces, interstellar media, etc. [1]-[6]. The dusty plasmas have also noticeable applications in laboratory devices [7]-[10]. The consideration of charge grains in plasmas does not only modify the existing plasma wave spectra [11]-[13], but also introduces a number of novel eigenmodes, such as the ion-acoustic (IA) waves, the lower-hybrid (LH) waves, the lattice waves, etc [14]-[18]. Most of the studies in dusty plasmas have been confined in considering the dust as negatively charged grains in addition to electrons and positively charged ions as the plasma species [4]-[6], [19]-[24]. It has been found that there are some plasma systems, particularly in space plasma environments, namely, cometary tails [1]-[3], [25], [26], upper mesosphere [27], Jupiter’s magnetosphere [28], etc. where positively charged dust grains play significant roles. There are three mechanisms by which the dust grains in the plasma systems mentioned above can be positively charged. These mechanisms are the following: (i) photoemission in the presence of a flux of ultraviolet (UV) photons; (ii) thermionic emission induced by radiative heating; and (iii) secondary emission of electrons from the surface of the dust grains.  In this paper, we have considered a dusty plasma containing mobile charge fluctuating negative dust, charge fluctuating stationary negative dust, Boltzmann-distributed electrons, and ions, and have studied the linear propagation of DA waves.

This paper is organized as follows. The basic equations describing our dusty plasma model are presented in Section II. I have derived the dispersion relation in Section III.I have analyzed numerically the dispersion properties of the DA wave mode in Section IV, where I have seen that negative dust-charge fluctuation is a source of linear growth instability. Finally, a brief discussion is given in Section V.

Governing Equations:

We consider an unmagnetized collisionless dusty plasma system consisting of charge fluctuating positively charged mobile dust, charge fluctuating stationary negative dust and Boltzmann-distributed electrons and ions. Thus at equilibrium , we have where n_eo (n_io) is the equilibrium electron (ion) number density, n_do^- is the negative dust number density, n_do^+ is the positive dust number density, z_do^+ is the equilibrium charge state of the positive dust component, z_do^- is the equilibrium charge state of the negative dust component. The dynamics of the DA waves of such a dusty plasma system in one-dimensional form is given by

where is the number density of the plasma species j (j equals i for ions, e for electrons), n_d^+ (n_d^-) is the number density of positive (negative) dust. u_d^+ (u_d^-) is the positive (negative) dust fluid speed. z_d^+ (z_d^-) is the charge state of the positive (negative) dust component. ϕ is the electrostatic wave potential. The electron and the ion densities are assumed to follow the Boltzmann distribution:

where k_B is the Boltzmann constant and T_e is the electron temperature, T_i is the ion temperature. We assume that dust is charged by photo-emission current(I_P^+ ), the thermionic emission current (I_t^+ )and the electron absorption current(I^- ), the electron current for negative charge dust(I_e ), the ion current for negative charge dust (I_i ) only. All other charging processes are neglected. The charge state z_d^+ component is not constant, but varies according to the following equations:

where ℏ is the Planck’s constant,T_”ph” is the photon temperature,W_e is the work function , J is the UV photon flux, Y is the yield of photons (typical values of W_e, J and Y are 2.2 eV, 5.0×1014 photons/cm2/s, and 0.1, respectively), and rd is the dust radius. Now, using q_d=+z_d^+ e (where the charge state z_d is the number of electrons residing on the dust grain space). Introducing the following normalized variables:

One can reduce equation (1) to (7) as

Derivation of the Linear Dispersion Relation

To derive a dynamical equation for the linear propagation of the DA shock waves in a dusty plasma, I first express our dependent variables Z_d^+, andZ_d^- in terms of their equilibrium and perturbed parts as

Now, substituting (18)-(22) into (13)-(17), we develop equations in various power of we have

Now assuming that all perturbed quantities are proportional to exp⁡(-iωT+ikX), i.e. taking ∂/∂T→-iω and ∂/∂X→ik, where ω and k are the wave angular frequency and the propagation constant respectively in Eqs. (23)-(27), we obtain

Now using (30)-(34), one can eliminate N_d^(+(2)),U_d^(+(2)),Z_d^(+(2)),Z_d^(-(2))and Φ^((2)), and can finally obtain the following equation:

where the nonlinear coefficient A and the dissipation coefficient C are given by

Equation (35) is the well-known Burgers equation describing the nonlinear propagation of the DA shock waves in the dusty plasma under consideration. It is obvious from (35) and (37) that the dissipative term, i.e. the right-hand side of (35) is due to the presence of the charge fluctuating dust.

Numerical Analysis:

We are now interested in looking for the stationary shock wave solution of (35) by introducing the variables ς=ξ-U_0 τ^/and τ^/=τ , where is the shock wave speed (in the reference frame) normalized by C_d , ς is normalized by λ_Dd, and τ is normalized by ω_pd^(-1). This leads us to write (35), under the steady state condition (∂/∂τ=0), as

It can be easily shown that [36], [37] that (41) describes shock waves whose speed U_0 (in the reference frame) is related to the extreme values Φ^((1)) (-∞)and Φ^((1)) (∞)by Φ^((1)) (-∞)-Φ^((1)) (∞)=2U_0/A. Thus, under the condition that Φ^((1)) is bounded atς=± ∞, the shock wave solution of (41) can be written as

are respectively, the height and thickness of the shock waves moving with the speed U_0. It is obvious from (41) to (44) that the shock waves are due to the presence of the charge fluctuating dust, and the shock structures are associated with the negative potential (A<0) as well as with positive potential (A>0).To find the parametric regimes for which positive and negative shock wave (potential) profiles exist, we have numerically analyzed A and obtain A = 0 ( 2-D ) curves for γ=”0.2to0.6″ and μ_i “= 0to3.8” . The A = 0 curve is shown in Fig.1. It shows that we can have positive shock wave (potential) profiles for the parameters whose values lie above A = 0 curve and negative shock wave (potential) profiles for the parameters whose value lie below the A = 0 curve. These are shown in Figs.2-3. Figs 2 and 3 show the positive and negative shock potential profiles respectively.

CONCLUSION

We have studied the linear propagation of IA waves in an unmagnetized dusty plasma containing Boltzmann-distributed electrons and ions, mobile charge fluctuating negative dust, and charge fluctuating stationary negative dust.  We have shown here how  the nonlinear IA waves’ basic features are modified by the charge fluctuating dust in dusty plasmas. The results, which have been obtained from this investigation, can be summarized as follows:

The dust charge fluctuation is a source of dissipation and is responsible for forming IA shock waves in the dusty plasma. The shock structures are associated with the negative potential (A<0) as well as the positive potential (A<0). It is shown that the height (normalized by k_B T_e “/e” ) of the potential structures in the form of the shock waves is directly proportional to the shock speed U_0, and it is also found that the thickness (normalized by λ_”Dd” ) of these shock structures is inversely proportional to the shock speed U_0.

The parametric regimes for the existence of positive as well as negative shock structures are shown in Fig.1.  Figs. 2 and 3 show the positive and negative shock potential profiles of shock waves respectively.

It is to be mentioned here that the parameters we have chosen in our numerical analysis are very much relevant to the plasma in the mesosphere [27]. We stress that the results of the present investigation could be useful in understanding the properties of localized DA waves of dusty plasmas in the mesosphere.

REFERENCES

1. D. A.  Mendis and M. Rosenberg, “Cosmic dusty plasma”, Annu. Rev. Astron. Astrophys., vol.32, pp. 418-463, Sep.1994.
2. M. Horanyi and D. A. Mendis, “The dynamics of charged dust in the tail of comet Giacobini-Zinner,” J. Geophys. Res., vol.91, pp. 355-361, Jan. 1986.
3. M. Horanyi, “Charged dust dynamics in the solar system”, Annu.Rev. Astrophys, vol.34, pp. 383-418, Sep.1996.
4. F. Verheest, “Waves in Dusty Plasmas”, Kluwer Academic Publishers, Dordrecht, The Netherlands. 2000.
5. P. K. Shukla, “A survey of dusty plasma physics”, Phys. Plasmas., vol. 8, no.5, pp. 1791-1803, May 2001.
6. P. K. Shukla and A. A. Mamun, Introduction to Dusty Plasma Physics, Institute of Physics Publishing Ltd., Bristol, U.K. 2002.
7. A. Barkan, R. L. Merlino, and N. D’Angelo, “Laboratory observation of the dust-acoustic mode”, Phys. Plasmas, vol. 2, no.10, pp. 3563–3565, Oct. 1995.
8. A. Barkan, N. D’Angelo, and R. L. Merlino, “Experiments on ion-acoustic waves in dusty plasmas”, Planet. Space Sci., vol 44, no.3, pp. 239-242, Mar.1996.
9. R. L. Merlino, A. Barkan, C. Thompson, and N. D’Angelo, “Laboratory studies of waves and instabilities in dusty plasmas”, Physics of Plasmas, vol. 5, no.5, pp. 1607-1614, May, 1998.
10. A. Homann, A. Melzer, S. Peters, and A. Piel, “Determination of the dust screening lengths by laser-excited lattice waves”, Phys. Rev. E, vol. 56, no.6, pp. 7138-7141, Apr. 1997.
11. P. V. Bliokh and V. V. Yaroshenko, “Electrostatic waves in Saturn rings”, Sov. Astron., vol.29, pp. 330-336, 1985. (Engl.Trasl).
12. U. de Angelis, V. Formisano, and M. Giordano, “Ion plasma waves in dusty plasmas”, J. Plasma Phys, vol.40, no.3 pp. 399-406, Dec.1988.
13. P. K. Shukla and L. Stenflo, “Stimulated scattering of electromagnetic waves in dusty plasma”, Astrophys. Space Sci., vol.190, no.1 pp 23-32, Apr.1992.
14. P. K. Shukla and V. P. Silin, “Dust ion acoustic wave”, Physica Scripta, vol. 45, pp. 508, 1992.
15. N. N. Rao, P. K. Shukla, and M. Y. Yu, “Dust-acoustic waves in dusty plasmas”, Planet. Space Sci., vol. 38, no.4 pp. 543–546, May,1990.
16. F. Melandso, “Lattice waves in dust plasma crystals”, Phys. Plasmas, Vol.3, no.11. pp. 3890-3901, Nov. 1996.
17. Y. Nakamura, H. Bailung and P. K. Shukla, “Observation of ion-acoustic shocks in a dusty plasma”, Phys. Rev. Lett., vol. 83, no.8.  pp.1602-1605, Aug. 1999
18. R. L. Merlino and J. Goree, “Dust vortex modes in a nonuniform dusty plasma”, Phys. Today, vol. 57, p.32-39, 2004.
19. M.R.Amin, and G.E.Morfill and P.K.Shukla, “Modulational   instability of dust-acoustic and dust-ion-acoustic waves”, Phys. Rev. E. Stat. Phys. Plasmas Fluids Relat. Interdiscip. Top., vol.58, no.5. p.p. 6517-6523, Feb 1998.
20. R. Bharuthram and P. K. Shukla,” Large amplitude ion-acoustic solitons in a dusty plasma”, Planet. Space Sci., vol.40, no.7, pp. 973-977, Jul.1992.
21. S. I. Popel and M. Y. Yu, “Ion acoustic solitons in impurity-containing plasmas”, Contrib. Plasma Phys.  vol.35, no 2, pp.103-108, 1995.
22. J. X. Ma and J. Liu, “Dust-acoustic soliton in a dusty plasma”, Phys. Plasmas.  vol.4, no.2, pp. 253-255, Feb. 1997.
23. A. A. Mamun, “Arbitrary amplitude dust-acoustic solitary structures in a three-component dusty plasma”, Planet. Space Sci. vol. 268, no.4, pp. 443-454, Nov.1999.
24. P. K. Shukla, M. R. Amin, and G. E. Morfill, “Instability of dust-acoustic waves in partially ionized collisional dusty gases”, Phys.Scr. vol. 59, no.5. pp.389-390,1999.
25. D. A. Mendis and M. Hor’anyi, “Dust-Plasma Interaction in the Cometary Environment”, AGU Monogr. vol.61, pp.17-25, 1991.Cometary Plasma Processes,
26. V. W. Chow, D. A. Mendis, and M. Rosenberg, “Role of grain size and particle velocity distribution in secondary electron emission in space plasmas”, J. Geophys. Res. vol. 98, no. A11, p.19065-19076, Nov. 1993.
27. O. Havnes, J. Troim. T. Blix, W. Mortensen, L. I. Naesheim, E. Thrane, and T. Tonnesen, “First detection of charged dust particles in the Earth’s mesosphere”, J. Geophys. Res.  vol. 101, no. A5, pp.10839-10848, 1996.
28. M. Hor’anyi, G. E. Morfill and E. Griin,” Mechanism for the acceleration and ejection of dust grains from Jupiter’s magnetosphere”, Nature, vol. 363, no.6425 pp.144-146, May,1993.
29. A. A. Mamun and P.K. Shukla, “Solitary potentials in cometary dusty plasmas”, Geophys. Res. Lett.  vol. 29, no.18. pp.1870-1874, Sep, 2002.
30. Fatema Sayeed and A.A. Mamun, “Solitary potential in a four-component dusty plasma”, Physics of Plasma. vol.14, no.1, pp.014501-014504, Jan, 2007.
31. A.A. Mamun, “Dust electron-acoustic shock waves due to dust charge fluctuation”, Physics Letters A, vol.372, Issue 25 pp 4610-4613.
32. S. S. Duha and A.A. Mamun, “Dust ion-acoustic waves due to dust charge fluctuation”, Physics Letters A, vol.373, Issue 14 pp 1287-1289. March’2009.
33. H. Washimi and T. Taniuti, “Propagation of ion-acoustic solitary waves of small amplitude”, Phys. Rev. Lett. Vol. 17, no.19. pp.996-998, 1966.
34. G.C.Das, C.B. Dwivedi, M. Talukdar and J. Sharma, “A new mathematical approach for shock-wave solution in a dusty plasma”, Phys. Plasmas vol.4, no.12, pp.4236-4239, Dec. 1997.
35. F. Meladso, T. K. Aslaksen and O. Havnes, “A new damping effect for the dust-acoustic wave” Planet space sci. Vol.41, no.4. pp.321-325, Apr.1993
36. V. I. Karpman, “Nonlinear Waves in Dispersive Media”, Pergamon Press, Oxford, 1975, pp. 101-105.1975
37. A. Hasegawa, “Plasma Instabilities and Nonlinear Effects”, Springer-Verlag, Berlin, 1975), p. 192.

Fig. 1. Showing A = 0 (Φvs. β) curves for the parameters P = 5.0  1013 cm-2, Q = 1.93  1028 cm-2s-1, R = 2.48  1028 cm-2s-1.

Fig. 2. Showing positive potential (Φ vs. ζ) curves for the parameters P = 5.0  1013 cm-2, Q = 1.93  1028 cm-2s-1, R = 2.48  1028 cm-2s-1 with β=38.6,

Fig. 3. Showing negative potential (Φ vs. ζ) curves for the parameters P = 5.0  1013 cm-2, Q = 1.93  1028 cm-2s-1, R = 2.48  1028 cm-2s-1 with α_i=4.77, β=38.6.