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Islamabad, Pakistan

Naseer S.,University of Peshawar | Khan F.U.,Gomal University | Rehman N.U.,COMSATS Institute of Information Technology | Qayyum A.,National Tokamak Fusion Program | And 2 more authors.
EPJ Applied Physics | Year: 2010

Plasma nitriding of aluminium in a 50 Hz pulsed-dc glow discharge is studied for different ion-current densities (2.0-5.0 mA? cm-2) by keeping the corresponding discharge parameters such as treatment time, chamber pressure, substrate temperature and gas composition same. The treated samples are analysed for changes induced in surface properties using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Vickers's micro-hardness testing. XRD showed the downshift in the original diffraction peak corresponding to (111) plane reflection along with the emergence of new diffraction peak corresponding to (220) plane reflection, confirming the N-diffusion into existing Al-lattice and formation of AlN compound. Surface hardness is significantly improved which might be attributed to the diffusion of nitrogen and compound layer formation. © 2010 EDP Sciences.

Ehsan Z.,Center for Plasma Astrophysics | Ehsan Z.,Quaid-i-Azam University | Ehsan Z.,Imperial College London | Tsintsadze N.L.,Andronikashvili Institute of Physics | And 3 more authors.
Journal of Plasma Physics | Year: 2011

It is shown that nonlinear interaction between large amplitude circularly polarized EM wave and dusty plasma leads to a non-stationary ponderomotive force, which in turn produces a vortex ring and magnetic field. Then the ensuing vortex ring in the direction of propagation of the pump wave can accelerate the micron-size dust particles, which are initially at rest and eventually form a non-relativistic dust jet. This effect is purely non-stationary and unlike linear vortices, dust particles do not rotate here. Specifically, it is pointed out that the vortex ring or closed filament can become potential candidate for the acceleration of dust in tokamak plasmas. © 2010 Cambridge University Press.

Abrar M.,Quaid-i-Azam University | Abrar M.,University of Peshawar | Qayyum A.,National Tokamak Fusion Program | Gilani A.R.,Quaid-i-Azam University | And 7 more authors.
Current Applied Physics | Year: 2013

Trace rare gas optical emission spectroscopy (TRG-OES) is carried out to investigate the excitation temperature, relative densities of active species (N, N2 +) and nitrogen dissociation in inductively coupled helium admixed nitrogen plasma for different rf power (50, 100, 150 W), pressure (0.2-0.5 mbar) and helium percentage (10-90%) using Ar as an actinometer (4%). The excitation temperature is obtained from Boltzmann plot method using emission intensity of several argon lines. The dissociation of nitrogen has been investigated by both the actinometry method and the ratio (IN/IN 2) of the atomic nitrogen line emission intensity at (746.83 nm) to the vibrational band (0-0) of the N2 second positive system at 337.1 nm. The excitation temperature increases with the increase in power and helium percentage and decreases with increase in fill pressure. The nitrogen dissociation as well as the relative densities of [N] and [N2+] increases with the increase in helium percentage. © 2013 Elsevier B.V. All rights reserved.

Deeba F.,National Tokamak Fusion Program | Ahmad Z.,National Tokamak Fusion Program | Murtaza G.,Quaid-i-Azam University
Physics of Plasmas | Year: 2015

Sharifi and Parvazian have presented comments on our paper by questioning the validity of the results. The plots of different curves of kappa and (r, q) distributions produced by them are incorrect. They pretended as if we have made claim that our results are valid for large arguments of product of Bessel Function, whereas Neumann's series expansion is valid only for small arguments. In our paper, no claim is made that the results are valid for all values of b. Our results are valid only for b蠐 1. The results plotted by the commenters are incorrect and in this response we are presenting correct plots of dispersion curves. © 2015 AIP Publishing LLC.

Shafiq M.,Quaid-i-Azam University | Hassan M.,The University of Lahore | Shahzad K.,Quaid-i-Azam University | Qayyum A.,National Tokamak Fusion Program | And 3 more authors.
Chinese Physics B | Year: 2010

The carburizing of titanium (Ti) is accomplished by utilizing energetic ion pulses of a 1.5 kJ Mather type dense plasma focus (DPF) device operated in methane discharge. X-ray diffraction (XRD) analysis confirms the deposition of polycrystalline titanium carbide (TiC). The samples carburized at lower axial and angular positions show an improved texture for a typical (200)TiC plane. The Williamson-Hall method is employed to estimate average crystallite size and microstrains in the carburized Ti surface. Crystallite size is found to vary from ∼ 50 to 100 nm, depending on the deposition parameters. Microstrains vary with the sample position and hence ion flux, and are converted from tensile to compressive by increasing the flux. The carburizing of Ti is confirmed by two major doublets extending from 300 to 390 cm-1 and from 560 to 620 cm-1 corresponding to acoustic and optical active modes in Raman spectra, respectively. Analyses by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) have provided qualitative and quantitative profiles of the carburized surface. The Vickers microhardness of Ti is significantly improved after carburizing. © 2010 Chinese Physical Society and IOP Publishing Ltd.

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