Indian Institute for Plasma Research

Gandhinagar, India

Indian Institute for Plasma Research

Gandhinagar, India
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Kundu M.,Indian Institute for Plasma Research
Physics of Plasmas | Year: 2014

In this work, we re-examine collisional absorption of 800 nm wavelength laser pulses in under-dense plasma. For a given temperature and density of the plasma, most of the conventional models of the electron-ion collision frequency νei, with a Coulomb logarithm independent of the electron-ponderomotive velocity, show that νei and the corresponding fractional laser absorption α remain almost constant (or decrease slowly) up to a value Ic of the peak intensity I0 of the laser pulse, and then νei and α decrease as ≈I0-3/2 when I0 is increased beyond Ic. On the contrary, below some temperature (≲10 eV) and density, with a total-velocity (thermal velocity plus the ponderomotive velocity) dependent Coulomb logarithm, we find that νei and α grow hand in hand up to a maximum value around Ic followed by the conventional I0-3/2 decrease when I0>Ic. Such a non-conventional anomalous variation of α with I0 was observed in some earlier experiments, but no explanation has been given so far. The modified Coulomb logarithm considered in this work may be responsible for those experimental observations. With increasing temperature and density, the anomalous behavior is found to disappear even with the modified Coulomb logarithm, and the variation of νei and α with I0 approach to the conventional scenario. © 2014 AIP Publishing LLC.

Sethia G.C.,Indian Institute for Plasma Research | Sethia G.C.,Max Planck Institute for the Physics of Complex Systems | Sen A.,Indian Institute for Plasma Research
Physical Review Letters | Year: 2014

Chimera states, representing a spontaneous breakup of a population of identical oscillators that are identically coupled, into subpopulations displaying synchronized and desynchronized behavior, have traditionally been found to exist in weakly coupled systems and with some form of nonlocal coupling between the oscillators. Here we show that neither the weak-coupling approximation nor nonlocal coupling are essential conditions for their existence. We obtain, for the first time, amplitude-mediated chimera states in a system of globally coupled complex Ginzburg-Landau oscillators. We delineate the dynamical origins for the formation of such states from a bifurcation analysis of a reduced model equation and also discuss the practical implications of our discovery of this broader class of chimera states. © 2014 American Physical Society.

Misra S.,Indian Institute of Technology Delhi | Mishra S.K.,Indian Institute for Plasma Research
Monthly Notices of the Royal Astronomical Society | Year: 2013

A theoretical kinetic model for the physical understanding of the charging of dust particles in the interplanetary space plasma has been developed. in contrast to earlier studies, the present analysis incorporates (i) uniform potential theory for complex plasmas with size distribution of the dust particles, (ii) charge, number and energy balance of the constituents and (iii) appropriate expressions for photoelectric emission from a positively charged particle with inherent charge neutrality of the interplanetary space plasma. further utilizing the population balance equation (given by matsoukas and russel) for the interplanetary dust particles, the fluctuations in steady-state charge (or electric potential) has also been investigated. for the illustration purpose, the computations have been performed for the interplanetary space plasma at 1 au from the sun; for this distance, reasonably good information on the gaseous and dust components are available. as an interesting feature, the theoretical predictions are in reasonably good agreement with observations and earlier estimates. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Ashwin J.,Indian Institute for Plasma Research | Ganesh R.,Indian Institute for Plasma Research
Physical Review Letters | Year: 2010

Using "first principles" molecular dynamics simulations Kelvin Helmholtz instability has been observed for the first time at the particle level in two-dimensional strongly coupled Yukawa liquids. At a given coupling strength Γ a subsonic shear profile is superposed on an equilibrated Yukawa liquid and instability is observed. Linear growth rates computed directly from MD simulations are seen to increase with strong coupling. Vortex-roll formation in the nonlinear regime is reported. © 2010 The American Physical Society.

Pradhan S.,Indian Institute for Plasma Research
Physics Procedia | Year: 2012

The Magnet System of the Steady State Superconducting Tokamak (SST-1) has been completely refurbished under the SST-1 Mission. Since Jan 2009, a wide spectrum of refurbishment has been undertaken which, includes developing reliable designs and processes leading to the fabrication of leak tight low DC resistances in SST-1 magnet winding packs, equipping each of the sixteen SST-1 Toroidal Field (TF) magnets with a supercritical helium cooled bubble type thermal shields and testing each of the prepared TF magnets under representative conditions in cold with nominal currents along with manifolds and isolators in near representative conditions. Each of the sixteen SST-1 TF magnets has been tested fully and successfully in a dedicated test stand in nineteen campaigns during June 10, 2010 and was concluded on Jan 24, 2011. These campaigns ensured that all the sixteen TF magnets could be charged to their nominal currents of 10000 A in either two-phase or supercritical cooling conditions with leak-tight inter-double pancake resistances being in the range of 150 pico ohms to 1200 pico ohms. The supercritical helium cooled thermal shields welded in the inner bore of the TF magnets have also performed as per the design specifications. Subsequently, the assemblies of the SST-1 TF magnets and the Poloidal Field (PF) magnets in SST-1 machine shell have begun. The SST-1 TF magnets are being assembled in pairs (known as octants) together with a SST-1 vacuum vessel module, sector of 80 K bubble type thermal shields and a pair of outer-inter-coil-structures. The octant assemblies have been completed. The nine superconducting Poloidal Field (PF) magnets will shortly be assembled being supported from the TF cases. The resistive central solenoid magnets, compensating coils and the newly designed in-vessel radial control coils will be subsequently assembled. The assembled magnets inside the cryostat are expected to be cooled down starting from Jan 2012 when a detailed engineering validation of the magnet system would be undertaken. The detailed SST-1 magnet system refurbishment including some of the first-of-its-kind test results are discussed in this paper. © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.

Prajapati R.P.,Indian Institute for Plasma Research
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2011

The effect of polarization force acting on massive charged dust grains is investigated analytically on the Jeans instability of self-gravitating dusty plasma. The gravitational force acting on the massive negatively charged interstellar dust grains are considered in presence of both electrical and polarization forces. The basic equations of the problem are formulated and a general dispersion relation is obtained using plane wave approximation in low frequency wave mode. The effect of polarization force in the dispersion relation of the problem, condition of the Jeans instability and expression of the critical Jeans wave number is examined. The unstable growing modes due to self-gravitational force are studied in the situation when polarization force on the dust grain exceeds over the electrical force in magnitude. It is observed that the polarization force increases the growth rate of the system. © 2011 Elsevier B.V. All rights reserved.

Ashwin J.,Indian Institute for Plasma Research | Ganesh R.,Indian Institute for Plasma Research
Physical Review Letters | Year: 2011

Strongly coupled liquids are ubiquitous in both nature and laboratory plasma experiments. They are unique in the sense that their average potential energy per particle dominates over the average kinetic energy. Using "first principles" molecular dynamics (MD) simulations, we report for the first time the emergence of isolated coherent tripolar vortices from the evolution of axisymmetric flows in a prototype two-dimensional (2D) strongly coupled liquid, namely, the Yukawa liquid. Linear growth rates directly obtained from MD simulations are compared with a generalized hydrodynamic model. Our MD simulations reveal that the tripolar vortices persist over several turn over times and hence may be observed in strongly coupled liquids such as complex plasma, liquid metals and astrophysical systems such as white dwarfs and giant planetary interiors, thereby making the phenomenon universal. © 2011 American Physical Society.

Sinha U.,Indian Institute for Plasma Research
Physics of Plasmas | Year: 2012

Acceleration of ions using ultra-intense laser irradiated on an overdense target plasma composed of two ion species has been described using a self consistent approach. The analytical model for the steady state described here gives a complete description of the charge separation zone, i.e., ion space charge and electron sheath, created due to ponderomotive force of the laser. It successfully explains the jump in electrostatic potential or field in the laser piston responsible for a major part of the acceleration. The information about the structure of laser piston obtained from the analytical model is used for the stability analysis of the process. It has been found that the stability of the laser piston depends on the target composition. The reflection of incoming ion beams from the coulomb exploding region of the ion space charge has been described in context of the charge on the incident beam species. © 2012 American Institute of Physics.

Ranjan M.,Indian Institute for Plasma Research
Journal of Nanoparticle Research | Year: 2013

Plasmonic coupling is observed in the self-aligned arrays of silver nanoparticles grown on ripple-patterned substrate. Large differences observed in the plasmon resonance wavelength, measured and calculated using Mie-Gans theory, predict that strong plasmonic coupling exists in the nanoparticles arrays. Even though plasmonic coupling exists both along and across the arrays, but it is found to be much stronger along the arrays due to shorter interparticle gap and particle elongation. This effect is responsible for observed optical anisotropy in such arrays. Measured red-shift even in the transverse plasmon resonance mode with the increasing nanoparticles aspect ratio in the arrays, deviate from the prediction of Mie-Gans theory. This essentially means that plasmonic coupling is dominating over the shape anisotropy. Plasmon resonance tuning is presented by varying the plasmonic coupling systematically with nanoparticles aspect ratio and ripple wavelength. Plasmon resonance red-shifts with the increasing aspect ratio along the ripple, and blue-shifts with the increasing ripple wavelength across the ripple. Therefore, reported bottom-up approach for fabricating large area-coupled nanoparticle arrays can be used for various field enhancement-based plasmonic applications. © 2013 Springer Science+Business Media.

Kundu M.,Indian Institute for Plasma Research
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

In a previous paper [M. Kundu, Phys. Plasmas 21, 013302 (2014)1070-664X10.1063/1.4862038], fractional collisional absorption (α) of laser light in underdense plasma was studied by using a classical scattering model of electron-ion collision frequency νei, where total velocity v=vth2+v02 (with vth and v0 as the thermal and the ponderomotive velocity of an electron) dependent Coulomb logarithm lnΛ(v) was shown to be responsible for the anomalous (unconventional) increase of νei and α( νei) with the laser intensity I0 up to a maximum value about an intensity Ic in the low temperature (Te<15eV) regime and a conventional ≈I0-3/2 decrease when I0?Ic. One may object that the anomalous increase in νei and α were partly due to the artifact introduced in lnΛ through the maximum cutoff distance bmax v. In this work, we show similar anomalous increase in νei and α versus I0 (in the low temperature and underdense density regime) with more accurate quantum and classical kinetic models of νei without using lnΛ, but with a proper choice of the total velocity dependent inverse cutoff length kmax v2 (classical) or kmax v (quantum). For a given I0<5×1014Wcm-2, νei versus Te also exhibits so far unnoticed identical anomalous increase as νei versus I0, even if the conventional kmax vth2 or kmax vth (without v0) is chosen. The total velocity dependent kmax in the kinetic models, as proposed here, is found to explain the anomalous increase of α with I0 measured in some earlier laser-plasma experiments. © 2015 American Physical Society.

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