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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. Source

Pradhan S.,Indian Institute for Plasma Research
IEEE Transactions on Applied Superconductivity | Year: 2012

Testing each of the SST-1 Toroidal Field (TF) Magnets under representative conditions in cold with nominal currents was one of the primary and mandatory requisite in the refurbishment of the Steady-State Superconducting Tokamak (SST-1). Under this mandate prior to the SST-1 machine shell re-assembly, each of the 16 SST-1 TF magnets have been tested fully and successfully in a dedicated test stand. The campaign began on June 10, 2010 and was concluded on Jan 24, 2011 spanning over seven and half months without any interruption in-between. 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. Sensors and diagnostics signal conditioning and data acquisitions, magnet quench detection and magnet protection aspects in these campaigns have been precise, extensive and redundant wherever feasible. Test team had many failures as well as several learning in the course of these challenging tasks. Magnet preparations for the tests, the test designs and their executions, some exciting and confidence building experimental results as well as some failure experiences have been presented in this paper. © 2011 IEEE. Source

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. Source

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. Source

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. Source

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