arXiv subjects

Predhiman Kaw

Publications and source records attributed to Predhiman Kaw.

17 recordsLinked to original sources

arXiv2020

Propagation of slow electromagnetic disturbances in plasma

Electromagnetic (EM) waves/disturbances are typically the best means to understand and analyze an ionized medium like plasma. However, the propagation of electromagnetic waves with frequency lower than the plasma frequency is prohibited by the freely moving charges of the plasma. In dense plasmas though the plasma frequency can be typically quite high, EM sources at such higher frequency are not easily available. It is, therefore, of interest to seek possibilities wherein a low frequency (lower than the plasma frequency) EM disturbance propagates inside a plasma. This is possible in the context of magnetized plasmas. However, in order to have a magnetized plasma response one requires a strong external magnetic field. In this manuscript we demonstrate that the nonlinearity of the plasma medium can also aid the propagation of a slow EM wave inside plasma. Certain interesting applications of the propagation of such slow electromagnetic pulse through plasma is also discussed.

physics.plasm-ph↗

arXiv2019

Drift waves with dust acoustic wave coupling

Drift wave is a prominent mode of a magnetized plasma of inhomogeneous density. It plays an important role in the transport of particles, energy and momentum perpendicular to the ambient magnetic field. The frequency of this mode is governed by the inhomogeneity scale length and is much lower than the typical homogeneous plasma modes involving ions and electrons. In this work the possibility of coupling of this particular mode with the low frequency modes of a dusty plasma medium is considered.

physics.plasm-ph↗

arXiv2018

Spatial symmetry breaking in single-frequency CCP discharge with transverse magnetic field

An independent control of the flux and energy of ions impacting on an object immersed in a plasma is often desirable for many industrial processes such as microelectronics manufacturing. We demonstrate that a simultaneous control of these quantities is possible by a suitable choice of a static magnetic field applied parallel to the plane electrodes in a standard single frequency capacitively coupled plasma device. Our particle-in-cell simulations show a 60% reduction in the sheath width (that improves control of ion energy) and a four fold increase in the ion flux at the electrode as a consequence of the altered ion and electron dynamics due to the ambient magnetic field. A detailed analysis of the particle dynamics is presented and the optimized operating parameters of the device are discussed. The present technique offers a simple and attractive alternative to conventional dual frequency based devices that often suffer from undesirable limitations arising from frequency coupling and electromagnetic effects.

physics.plasm-ph↗

arXiv2018

Excitation of KdV Alfven solitons by a pulsed CO2 laser in plasma in the presence of an external magnetic field

The interaction of laser with plasmas leads to many interesting phenomena which includes laser energy absorption, mode conversion, energetic particle generation etc. In this work, the excitation of Korteweg - de Vries (KdV) Alfven solitons in plasma is demonstrated with the help of 2-D Particle - In - Cell (PIC) simulations. For this purpose, the propagation of a pulsed $CO_2$ (with a wavelength of $10 μm$) laser normally incident on an overdense plasma target is considered in the presence of an external magnetic field. The magnitude of the external magnetic field is chosen so as to have the electrons magnetized and ions unmagnetized at the laser frequency. These solitons propagate stably and are observed to be responsible for energetic electron generation as the background undisturbed electrons of the medium get reflected from its front. It is also shown that subsequently, transverse modulations appear in the structure which grow with time. With recent technological advancements in the development of short pulse $CO_2$ lasers and also on the generation of magnetic fields of the order of tens of kilo - Tesla in the laboratory, these studies have practical relevance and have a possibility of getting replicated in laboratory in near future.

physics.plasm-ph↗

arXiv2018

Fast Ignition Laser Fusion Using In-Situ Ion Acceleration With Pulsed CO2 Lasers

Fast ignition is an alternative concept of laser fusion in which the task of compressing the fusion pellet to supersolid densities is accomplished by the conventional high energy nanosecond glass lasers and the task of igniting the compressed pellet is given to a high intensity, moderate energy pico second source which can set the pellet ablaze (with DT fusion reactions) by creating an adequate size hot spot in it. In this letter, we present a conceptual method by which energy from carbon dioxide ($ CO_2 $) laser could be coupled to heat up ions produced in situ in the plasma, which in turn produces the required hot spot. An efficient conversion of $ CO_2 $ energy into ion beam energy can thus give us the required source of energy for the fast ignition laser fusion. We demonstrate by using PIC (Particle - In - Cell) simulations that the use of several Kilo Tesla of an external magnetic field in the transverse direction in an inhomogeneous plasma where a cutoff is followed by a resonance can lead to coupling of laser energy to a lower hybrid ion plasma resonance. Then ions are accelerated efficiently ($\sim 1 MeV$) by the breaking of lower hybrid waves and thereby enabling the possibility of fast ignition by ions in a convenient fashion.

physics.plasm-ph↗

arXiv2017

Evidence of new finite beam plasma instability for magnetic field generation

We demonstrate by computer simulations, laser plasma experiments, and analytic theory that a hitherto unknown instability is excited in the beam plasma system with finite transverse size. This instability is responsible for the generation of magnetic fields at scales comparable to the transverse beam dimension which can be much longer than the electron skin depth scale. This counterintuitive result arises due to radiative leakage associated with finite beam boundaries which are absent in conventional infinite periodic systems considered in earlier simulations as well as theoretical analyses and may trigger a reexamination of a hitherto prevalent idea.

physics.plasm-ph↗

arXiv2017

Energy principle for 2D electromagnetic, relativistic, interpenetrating, counter streaming plasma flows

A relativistic electron beam propagating through plasma induces a return current in the system. Such a system of counterstreaming forward and return current is susceptible to host of instabilities out of which Weibel remains a dominant mode for destabilizing the system. Weibel instability has been widely investigated in simulations, experiments, as well as, analytically using fluid and kinetic treatments. A purely growing mode like Weibel instability can also be understood by using conservation theorems and energy principle analysis. An electrostatic analog to the Weibel instability, two stream instability in a beam plasma system has already been investigated using energy principle analysis [Lashmore-Davies 2007]. A detailed analytical description of conservation theorem for 2D Weibel instability in a beam plasma system has been carried out in this manuscript.

physics.plasm-ph↗

arXiv2017

Magnetic field generation in finite beam plasma system

For finite systems boundaries can introduce remarkable novel features. A well known example is the Casimir effect [1, 2] that is observed in quantum electrodynamic systems. In classical systems too novel effects associated with finite boundaries have been observed, for example the surface plasmon mode [3] that appears when the plasma has a finite extension. In this work a novel instability associated with the finite transverse size of a beam owing through a plasma system has been shown to exist. This instability leads to distinct characteristic features of the associated magnetic field that gets generated. For example, in contrast to the well known unstable Weibel mode of a beam plasma system which generates magnetic field at the skin depth scale, this instability generates magnetic field at the scales length of the transverse beam dimension [4]. The existence of this new instability is demonstrated by analytical arguments and by simulations conducted with the help of a variety of Particle - In - Cell (PIC) codes (e.g. OSIRIS, EPOCH, PICPSI). Two fluid simulations have also been conducted which confirm the observations. Furthermore, laboratory experiments on laser plasma system also provides evidence of such an instability mechanism at work.

physics.plasm-ph↗

arXiv2015

Sub and super-luminar propagation of structures satisfying Poynting like theorem for incompressible GHD fluid model depicting strongly coupled dusty plasma medium

The strongly coupled dusty plasma has often been modelled by the Generalized Hydrodynamic (GHD) model used for representing visco-elastic fluid systems. The incompressible limit of the model which supports transverse shear wave mode is studied in detail. In particular dipole structures are observed to emit transverse shear waves in both the limits of sub and super - luminar propagation, where the structures move slower and faster than the phase velocity of the shear waves, respectively. In the sub - luminar limit the dipole gets engulfed within the shear waves emitted by itself, which then backreacts on it and ultimately the identity of the structure is lost. However, in the super - luminar limit the emission appears like a wake from the tail region of the dipole. The dipole, however, keeps propagating forward with little damping but minimal distortion in its form. A Poynting like conservation law with radiative, convective and dissipative terms being responsible for the evolution of W , which is similar to `enstrophy' like quantity in normal hydrodynamic fluid systems, has also been constructed for the incompressible GHD equations. The conservation law is shown to be satisfied in all the cases of evolution and collision amidst the nonlinear structures to a great accuracy. It is shown that monopole structures which do not move at all but merely radiate shear waves, the radiative term and dissipative losses solely contribute to the evolution of W. The, dipolar structures, on the other hand, propagate in the medium and hence convection also plays an important role in the evolution of W.

physics.plasm-ph↗

arXiv2014

Turbulence in two dimensional visco - elastic medium

The properties of decaying turbulence is studied with the help of a Generalized Hydrodynamic (GHD) fluid model in the context of two dimensional visco - elastic medium such as a strongly coupled dusty plasma system. For the incompressible case considered here however, the observations are valid for a wider class of visco - elastic systems not necessarily associated with plasmas only. Our observations show that an initial spectrum that is confined in a limited domain of wave numbers becomes broad, even when the Reynold's number is much less than the critical value required for the onset of turbulence in Newtonian fluids. This is a signature of elastic turbulence where Weissenberg's number also plays a role in the onset of turbulence. This has been reported in several experiments. It is also shown that the existence of memory relaxation time parameter and the transverse shear wave inhibit the normal process (for 2-D systems) of inverse spectral cascade in this case. A detailed simulation study has been carried out for the understanding of this inhibition.

physics.plasm-ph↗

arXiv2013

High Frequency Geodesic Acoustic Modes in Electron Scale Turbulence

In this work the finite $β$-effects of an electron branch of the geodesic acoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for el-GAMs driven non-linearly by ETG modes is derived. The ETG growth rate from the fluid model is compared to the results found from gyrokinetic simulations with good agreement. A new saturation mechanism for ETG turbulence through the interaction with el-GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared to the mixing length estimate. It is shown that the el-GAM may be stabilized by an increase in finite $β$ as well as by increasing non-adiabaticity. The decreased GAM growth rates is due to the inclusion of the Maxwell stress.

physics.plasm-ph↗

arXiv2012

High Frequency Geodesic Acoustic Modes in Electron Temperature Gradient Mode Turbulence

In this work the first demonstration of a high frequency branch of the geodesic acoustic mode (GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for high frequency GAMs driven nonlinearly by ETG modes is derived. A new saturation mechanism for ETG turbulence through the interaction with high frequency GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared to the mixing length estimate.

physics.plasm-ph↗

arXiv2011

Exact propagating nonlinear singular disturbances in strongly coupled dusty plasmas

The nonlinear longitudinal response of a strongly coupled dusty plasma system is analytically investigated using the Generalized Hydrodynamic (GHD) model. It is shown that the Galilean invariant form of the model does not have soliton solutions, but can support a variety of nonlinear singular (yet conservative) solutions like shock structures of zero strength and propagating solutions with cusp like singularities. These novel entities should be detectable in numerical simulations and experiments studying large amplitude longitudinal excitations in such systems.

physics.plasm-ph↗

arXiv2008

Stability of nonlinear one-dimensional laser pulse solitons in a plasma

In a recent one-dimensional numerical fluid simulation study [Saxena et al., Phys. Plasmas 13,032309 (2006)], it was found that an instability is associated with a special class of one-dimensional nonlinear solutions for modulated light pulses coupled to electron plasma waves in a relativistic cold plasma model. It is shown here that the instability can be understood on the basis of the stimulated Raman scattering phenomenon and the occurrence of density bursts in the trailing edge of the modulated structures are a manifestation of an explosive instability arising from a nonlinear phase mixing mechanism.

physics.plasm-ph↗

arXiv2008

Propagation of Electron Magnetohydrodynamic structures in a 2-D inhomogeneous plasma

The fully three dimensional governing equations in the electron magnetohydrodynamic (EMHD) regime for a plasma with inhomogeneous density is obtained. These equations in the two dimensional (2-D) limit can be cast in terms of the evolution of two coupled scalar fields. The nonlinear simulations for the two dimensional case are carried out to understand the propagation of EMHD magnetic structures in the presence of inhomogeneity. A novel effect related to trapping of dipolar magnetic structures in the high density plasma region in the EMHD regime is observed. The interpretation of this phenomena as well as its relevance to the problem of hot spot generation in the context of fast ignition is presented.

physics.plasm-ph↗

arXiv2005

Fluid simulation studies of the dynamical behaviour of one dimensional relativistic electromagnetic solitons

A numerical fluid simulation investigation of the temporal evolution of a special class of traveling wave solution of the one dimensional relativistic cold plasma model is reported.The solutions consist of coupled electromagnetic and plasma waves in a solitary pulse shape (Phys. Rev. Lett. 68, 3172(1992); Phys. Plasmas 9, 1820(2002)).Issues pertaining to their stability, mutual collisional interactions and propagation in an inhomogeneous plasma medium are addressed. It is found that solitary pulses that consist of a single light peak trapped in a modulated density structure are long lived whereas structures with multiple peaks of trapped light develop an instability at the trailing edge. The interaction properties of two single peak structures show interesting dependencies on their relative amplitudes and propagation speeds and can be understood in terms of their propagation characteristics in an inhomogeneous plasma medium.

physics.plasm-ph↗

arXiv2004

Nonlinear saturation of magnetic curvature driven Rayleigh Taylor instability in three dimensions

We present three dimensional fluid simulation results on the temporal evolution and nonlinear saturation of the magnetic curvature driven Rayleigh-Taylor (RT) instability. The model set of coupled nonlinear equations evolve the scalar electric field potential $ϕ$, plasma density $n$ and the parallel component of the magnetic vector potential $ψ$. The simulations have been carried out in two limits, (i) a low resistivity case in which RT is the only linearly growing mode, and (ii) a high resistivity case where the drift wave is unstable and for which the magnetic curvature parameter is set to zero to ensure the absence of the RT growth. Our simulations show nonlinear stabilization in both these limits. The stabilization mechanism is similar to that observed in earlier two dimensional simulations, namely the generation of zonal shear flows which decorrelate the radially extended unstable modes. However the nature of the saturated nonlinear state in the 3d case differs from that of 2d in some important ways such as by having significant levels of power in short scales and by the presence of electromagnetic fluctuations. Though, in the linear regime the electromagnetic effects reduce the growth rates, in the nonlinear regime their presence hinders the process of stabilization by inhibiting the process of zonal flow formation. Thus the parameter regime for which nonlinear stabilization takes place is considerably reduced in three dimensions.

physics.plasm-ph↗