National Tokamak Fusion Program

Islamabad, Pakistan

National Tokamak Fusion Program

Islamabad, Pakistan
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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.


Deeba F.,National Tokamak Fusion Program | Deeba F.,The University of Lahore | Ahmad Z.,National Tokamak Fusion Program | Murtaza G.,Salam University
Physics of Plasmas | Year: 2010

A generalized dielectric constant for the electron Bernstein waves using non-Maxwellian distribution functions is derived in a collisionless, uniform magnetized plasma. Using the Neumann series expansion for the products of Bessel functions, we can derive the dispersion relations for both kappa and the generalized (r,q) distributions in a straightforward manner. The dispersion relations now become dependent upon the spectral indices κ and (r,q) for the kappa and the generalized (r,q) distribution, respectively. Our results show how the non-Maxwellian dispersion curves deviate from the Maxwellian depending upon the values of the spectral indices chosen. It may be noted that the (r,q) dispersion relation is reduced to the kappa distribution for r=0 and q=κ+1, which, in turn, is further reducible to the Maxwellian distribution for κ→∞. © 2010 American Institute of Physics.


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.


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.


Hassan M.,Quaid-i-Azam University | Hassan M.,Nanyang Technological University | Qayyum A.,National Tokamak Fusion Program | Ahmad S.,National Tokamak Fusion Program | And 6 more authors.
Applied Surface Science | Year: 2014

Amorphous hydrogenated carbon (a-C:H)/diamond-like carbon (DLC) coatings have been achieved on AISI 304 stainless steel (SS) substrates by employing energetic ions emitted from a repetitive plasma focus operated in CH4 discharge. The Raman spectroscopy of the coatings exhibits the evolution of a-C:H/DLC coatings with clearly observed D and G peaks centered about 1320-1360 and 1560-1620 cm-1 respectively. The diamond character of the coatings is influenced by the ion flux and repetition rate of the focus device. The repetitive discharge mode of plasma focus has led to the formation of a-C:H/DLC coatings in short duration of time. The coatings transform from a-C to a-C:H depending upon substrate angular position. X-ray diffraction (XRD) analysis confirms the formation of DLC coating owing to stress-induced restructuring in SS. The estimated crystallite size is found to be ∼40-50 nm. Field emission scanning electron micrographs exhibit a layered granular surface morphology of the coatings. The Vickers surface hardness of the DLC coated SS samples has been significantly improved. © 2014 Elsevier B.V.


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.


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.


Qayyum A.,National Tokamak Fusion Program | Ahmad S.,National Tokamak Fusion Program | Ahmad N.,National Tokamak Fusion Program | Deeba F.,National Tokamak Fusion Program | Hussain S.,National Tokamak Fusion Program
Journal of Fusion Energy | Year: 2015

Triple Langmuir probe (TLP) technique is used to measure local and time-resolved plasma parameters in pulsed capacitive discharge. This technique allows the instantaneous measurement of plasma parameters in transient discharges and obviates the need of any voltage or frequency sweep. In TLP configuration, two probes are differentially biased to acquire ion-saturation current whereas third probe is kept floating into plasma to measure floating potential. Thus TLP technique enables to measure electron temperature Te, electron number density ne, floating potential Vf, and their fluctuations as a function of time in rapidly time-varying plasmas. The results presented here demonstrate the progression of capacitive discharge for different fill pressures. This technique would be useful in measuring the temporal behavior of rapidly-time varying plasmas, such as the turbulence in the edge region of magnetically confined fusion plasma of GLAST Spherical Tokamak. © 2014, Springer Science+Business Media New York.


Qayyum A.,National Tokamak Fusion Program | Ahmad N.,National Tokamak Fusion Program | Ahmad S.,National Tokamak Fusion Program | Deeba F.,National Tokamak Fusion Program | And 2 more authors.
Review of Scientific Instruments | Year: 2013

Triple Langmuir probe (TLP) diagnostic system with its necessary driving circuit is developed and successfully applies for time-resolved measurement of plasma parameters in the negative glow region of pulsating-dc discharge. This technique allows the instantaneous measurement of electron temperature "T-", electron number density "n-" as well as plasma fluctuations without any voltage or frequency sweep. In TLP configuration two probes are differentially biased and serve as a floating symmetric double probe whereas the third probe is simply floating into plasma to measure floating potential as a function of time and thus incorporates the effect of plasma fluctuations. As an example of the application to time-dependent plasmas, basic plasma parameters such as floating potential, electron temperature, and electron number density in low pressure air discharge are determined as a function of time for different fill pressure. The results demonstrate temporal evolution of plasma parameters and thus plasma generation progression for different fill pressures. © 2013 AIP Publishing LLC.


PubMed | National Tokamak Fusion Program
Type: Journal Article | Journal: The Review of scientific instruments | Year: 2014

Triple Langmuir probe (TLP) diagnostic system with its necessary driving circuit is developed and successfully applies for time-resolved measurement of plasma parameters in the negative glow region of pulsating-dc discharge. This technique allows the instantaneous measurement of electron temperature [T_], electron number density [n_] as well as plasma fluctuations without any voltage or frequency sweep. In TLP configuration two probes are differentially biased and serve as a floating symmetric double probe whereas the third probe is simply floating into plasma to measure floating potential as a function of time and thus incorporates the effect of plasma fluctuations. As an example of the application to time-dependent plasmas, basic plasma parameters such as floating potential, electron temperature, and electron number density in low pressure air discharge are determined as a function of time for different fill pressure. The results demonstrate temporal evolution of plasma parameters and thus plasma generation progression for different fill pressures.

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