Dust acoustic solitary waves in dusty plasma with nonthermal ions

The problem of arbitrary amplitude electronacoustic solitary (EAS) waves in a plasma having cold fluid electrons, hot superthermal electrons and stationary ions is addressed. The domain of their allowable Mach numbers enlarges as the spectral index κ increases revealing therefore that the "maxwellisation" process of the hot component favors the propagation of the EAS waves. As the superthermal character of the plasma is increased, the potential pulse amplitude increases while its width is narrowed, i.e, the superthermal effects makes the electron-acoustic solitary structure more spiky. As the spectral index κ decreases, the hot electrons are locally expelled and pushed out of the region of the soliton's localization. A decrease of the fractional number density of the hot electrons relative to that of the cold ones number density would lead to an increase of the depth as well as the width of the localized EAS wave. Our results should help to understand the salient features of large amplitude localized structures that may occur in the plasma sheet boundary layer and may provide an explanation for the strong spiky waveforms that have been observed in auroral electric fields.

Section: Theoretical Model and Basic Equationssupporting

confidence: 93%

Arbitrary amplitude electron-acoustic solitary waves in the presence of excess superthermal electrons

Younsi

Tribeche

2010

“…In a recent paper Pakzad (2009) studied the occurrence of large-amplitude solitary waves in a dusty plasma with cold negatively charged dust, nonthermal positive ions and Boltzmann distributed electrons, using a Sagdeev pseudopotential method. He discussed the influence of the parameters characterizing the degree of nonthermality, the ion-to-electron temperature ratio and the relative species' densities on the existence domains where negative solitary waves can occur.…”

Section: Dear Editormentioning

confidence: 99%

“…He discussed the influence of the parameters characterizing the degree of nonthermality, the ion-to-electron temperature ratio and the relative species' densities on the existence domains where negative solitary waves can occur. The main result claimed by Pakzad (2009) seems to be that for some values of the nonthermality parameter the minimum and maximum Mach numbers coincide, which prevents the existence of negative solitary wave solutions. The possibility that there might be positive solitary structures was not mentioned nor investigated.…”

Section: Dear Editormentioning

confidence: 99%

Comment on the paper “Dust acoustic solitary waves in dusty plasma with nonthermal ions”

Verheest

2010

Dear Editor,In a recent paper Pakzad (2009) studied the occurrence of large-amplitude solitary waves in a dusty plasma with cold negatively charged dust, nonthermal positive ions and Boltzmann distributed electrons, using a Sagdeev pseudopotential method. He discussed the influence of the parameters characterizing the degree of nonthermality, the ion-to-electron temperature ratio and the relative species' densities on the existence domains where negative solitary waves can occur. The main result claimed by Pakzad (2009) seems to be that for some values of the nonthermality parameter the minimum and maximum Mach numbers coincide, which prevents the existence of negative solitary wave solutions. The possibility that there might be positive solitary structures was not mentioned nor investigated.Unfortunately for the author, not only was exactly the same problem (finding large-amplitude dust-acoustic solitary waves) for exactly the same plasma configuration (cold negatively charged dust, nonthermal positive ions and Boltzmann distributed electrons) treated by us (Verheest and Pillay 2008) with exactly the same Sagdeev pseudopotential method, but this was done in much greater detail and with more attention to the physical limitations on the existence of solitary structures in compositional parameter and Mach number space. We never claimed to be the only or first ones in combining nonthermal species with dust, but we tried to discuss the specific problem and plasma configuration in a thorough way. Our paper was published a year and a half before Pakzad submitted his work, but it is not even cited in the reference list.We found that one should not limit the treatment to negative solitary waves, the existence of which is bounded in Mach number from above by infinite dust compression, and showed that there can also be a range of positive solitary waves, the existence of which ends when a positive double layer is encountered. The double layer Mach numbers then provide the upper bounds on the positive polarity side. There are even regions in compositional parameter space where both negative and positive structures can coexist.To be more specific about our own work, we clearly indicated that, depending on the relative densities of the negative species (dust and electrons), negative solitary waves were not possible when the ionic nonthermality parameter exceeds a critical maximum, as shown in Figs. 2 and 3 of Verheest and Pillay (2008) and mentioned in the discussion thereof. Critical values for the nonthermality parameter are encountered whenever the lower Mach number curve (translating the required convexity condition for the Sagdeev pseudopotential to admit solitary waves) crosses the upper Mach number curve, seemingly Pakzad's main result.Such crossings, however, occur in many plasma models, given changes in one or more compositional parameters, when existence domains for solitary structures are plotted. This is illustrated, e.g., by Fig. 6 of McKenzie et al. (2004), to quote just one among many papers in the literature, ...

“…Exact pseudo-potential derived from analytical form and numerical solution have shown that the nonthermal distribution modified solitary waves (Chatterjee and Roychaudhury 1995;Cairns et al 1995a). For some values of the nonthermal parameter there is no soliton (Pakzad 2009). The ion temperature changes the minimum value of the nonthermal parameter as well as the Mach number for the coexistence of compressive and rarefactive ion-acoustic solitary waves (Mamun 1997).…”

Section: Introductionmentioning

confidence: 99%

On existence conditions of dust-acoustic solitary waves in a plasma with positively charged dust

Marif

Djebli

2011

Dust acoustic (DA) solitary wave existence conditions are investigated for positively charged dust particles in the presence of nonthermal electrons. Once Sagdeev pseudo-potential derived through fluid equations, for large amplitude DA waves, the lower limit on Mach number is calculated analytically using the necessary condition for the solitary waves existence. The double layers conditions provides the upper limit on Mach number. This allowed us to numerically investigate the effect of the temperature, density and nonthermal parameters on the solitary waves' characteristics. The present study is devoted to a complex plasma subject to ultraviolet radiations such as the one in the lower earth's ionosphere.