M S Qaisar

Energy loss of charged projectiles in dusty plasmas

The analytical and numerical results for the slowing down of two heavy projectile ions passing through a multicomponent dusty plasma are presented. Within the linear dielectric approach, the electrostatic potential and the stopping power of the two projectiles are computed for different values of KD (the normalized effective wave number) and R (the separation between the two projectiles) retaining two-ion-correlation effects. The enhancement in the energy loss is observed, and it is compared with that of a single ion projectile case. These results are useful to explain the crystallization of dust grains in astrophysical and laboratory plasmas.

Energy loss of a test charge in partially ionized dusty plasmas

The energy loss of a test charge particle in an unmagnetized dusty plasma is estimated, by incorporating the dust–neutral collisions. A slowly damping large amplitude wake field is observed which moves ahead of the test charge position for large dust–neutral collision frequencies. A critical test charge velocity is determined for a particular dust–neutral collision frequency below which the test charge gains energy instead of losing. The collisions enhance the energy loss only for the test charge velocities greater than the dust acoustic speed.

Shielding of N×M projectiles in a collisional, self-gravitating, generalized Lorentzian dusty plasma

The shielding potential of N×M projectiles passing through a collisional, self-gravitating dust contaminated plasma is studied by mean of linearized dielectric theory for a generalized Lorentzian plasma. The correlation and interference effects of projectiles on the shielded potential as well as on the energy loss are presented. The amplitude of the shielded potential is enhanced with the increase of dust Jeans frequency for separation less than the effective Debye length. The dust charge fluctuations produce a potential well for slow charge relaxation rate and the energy is gained by the test charge projectiles. However, for fast charge relaxation rate with a fixed value of Jeans frequency, the energy loss is enhanced. The dust neutral collisions also enhance the energy loss for the test charge velocities greater than the dust acoustic speeds.

Effect of grain-size distribution on the energy loss of a pair of charged projectiles in a dust-contaminated plasma

Analytical and numerical results are presented for the slowing down of a pair of heavy test charge projectiles through a multicomponent, dust-contaminated plasma. The correlation and interference effects of two collinear and noncollinear projectiles on electrostatic potential and energy loss are studied for a Maxwellian distribution and a special class of physically reasonable size distributions. The energy loss behavior versus projectile velocity of noncollinear projectiles is also examined for various orientations. It is found that the energy loss for Maxwellian distribution (for large value of spectral index κ) is larger compared to that for generalized Lorentzian distribution. It is also observed that for smaller values of κ, the test charge projectile gains energy instead of losing. These results would be useful for the understanding of the energy loss mechanism, which might be responsible for the coagulation of dust particles in molecular clouds, in the ion-beam driven inertial confinement fusion sc...

Delocalized heat flux for low Z plasmas

Abstract In local theory, the finite Z effect on electron heat conduction in plasmas is well established. We investigate that effect for nonlocal heat transport by solving the reduced Fokker-Planck equation for moderately low Z plasma. It is found that the classical Spitzer-Harm heat flux expression is recovered along with the usual finite Z correction factor, in the gentle gradient limit. Similarly in the nonlocal case, the maximum heat flux expression is also multiplied by a finite Z correction factor which results in substantial reduction of heat flux. For typical parameters Th = 10Tc, nh=0.1nc and Z=5, the free streaming heat flux value corresponds to a flux limiting factor ƒ≈0.07 in contrast with 0.21 of our previous nonlocal model.

Electron thermal conduction for steep temperature gradients

A new delocalized heat transport formula has been derived by solving the reduced Fokker-Planck equation and by using the nondiffusive approximation for the electron distribution function. The authors have found that for moderately high-Z plasmas, the maximum heat flow expression is modified in the steep gradient limit and is found to be in good agreement with the numerical Fokker-Planck simulation results. Also, in the gentle gradient limit, the usual classical Spitzer-Harm heat flux expression is recovered.

Effect of self-gravitation on the energy loss of pair of projectiles in dusty plasma

The effect of self-gravitation of massive dust grains is investigated on the shielded potential and the energy loss of pair of charged projectiles passing through a dust-contaminated plasma. Analytical general expressions are derived for the shielded potential and for the energy loss by incorporating two-body correlation effects. An interference contribution of these projectiles to the shielded potential and energy loss is observed that depends upon their orientation and separation distance. It is found that for two collinear projectiles the potential is enhanced by increasing dust Jeans frequency for separation less than Debye length and the energy loss versus projectile velocity decreases with the increase of Jeans frequency for arbitrary separation. The effect of inclination of two noncollinear projectiles on energy loss is also investigated for a fixed value of Jeans frequency ωjd=4×10−4ωpd. The contribution to the energy loss due to the interference term has been separately calculated for a typical J...

Heat transport formula in strongly inhomogeneous plasmas

Abstract A nonlocal heat transport formula has been derived by solving the reduced Fokker-Planck equation for strongly inhomogeneous laser produced plasmas. The formula derived by Albritton et al. is modified by taking into account the electrostatic potential. The maximum heat flow expression takes a new form in the steep temperature gradient case and is in good agreement with the numerical Fokker-Planck simulation results while the classical Spitzer-Harm result is recovered in the gentle gradient limit.

Role of inverse bremsstrahlung absorption and electrostatic potential on energy transport mechanism in laser produced plasmas

An analytical nonlocal heat transport formula has been derived from the reduced Fokker-Planck equation for a strongly inhomogeneous laser produced plasma including inverse-bremsstrahlung absorption as well as the electrostatic potential. It is found that while the former contributes an additive term to the heat flux, enhancing its value for both steep- and gentle-gradient situations, the latter effect introduces an exponential term which significantly reduces the electron thermal transport. Our calculations also show that for a moderately intense laser field, the maximum heat flux for steep gradients situations corresponds to flux inhibition factor f ~ 0.15-0.17.

Thermal transport in the presence of steep gradients and strong ambipolar field

A kinetic treatment to incorporate the effect of a strong ambipolar field on nonlocal heat transport in laser-produced plasmas is presented. The numerically calculated nonlocal propagators are found to be significantly modified and consequently the flux inhibition factor for steep thermal and density gradients turns out to be much lower than predicted previously. The classical Spitzer-Harm result is also recovered in the local case.