Deepak Tripathi - Academia.edu (original) (raw)
Uploads
Papers by Deepak Tripathi
Physica Scripta, 2010
The nonlinear interaction of amplitude-modulated two-dimensional and three-dimensional laser beam... more The nonlinear interaction of amplitude-modulated two-dimensional and three-dimensional laser beams with a cylindrical plasma column and the generation of terahertz (THz) radiation are studied. The plasma column could be formed by a cylindrically symmetric laser pre-pulse impinging on a gas jet target. A two-dimensional Gaussian laser beam propagating through the plasma exerts a ponderomotive force on electrons, imparting on them a resonant transverse velocity at the modulation frequency, Ω, when \Omega = \omega _{\rm{p}} /\sqrt 2 , where ωp is the plasma frequency of the column. The current produces THz radiation. In the case of a cylindrically symmetric Gaussian laser beam, the electron response to ponderomotive force misses the resonance, yet the phase matching introduced by a density ripple could efficiently produce THz radiation. The power conversion efficiency of the order of the ratio of THz radiation frequency to laser frequency can be achieved at a laser intensity of ≈1015 W cm-2 at 1 μm wavelength.
Physics of Plasmas, 2011
The energy transfer between two crossed lasers (a high frequency high amplitude pump and a low fr... more The energy transfer between two crossed lasers (a high frequency high amplitude pump and a low frequency low amplitude probe beam) through the coupling with a difference frequency electrostatic mode/quasimode in a plasma is examined. The electrostatic mode in an unmagnetized plasma is a linearly damped acoustic mode, while in a magnetized plasma it is also taken to be a lower hybrid mode. It is driven by the ponderomotive force due to the pump and probe beams. The electron density perturbation associated with the electrostatic mode beats with the oscillatory velocities due to the lasers to produce nonlinear current densities facilitating the energy transfer from the high frequency laser to the probe beam. Efficient energy transfer occurs when the phase matching conditions are satisfied. Even when a finite mismatch between the lasers and the low frequency mode/quasimode exists, a significant energy transfer is possible. The theoretical results for the unmagnetized plasma are in compliance with the published experimental results. In a magnetized plasma lower hybrid wave appears to be a potential contender for facilitating energy exchange between lasers.
We observed a coronal cavity from August 8-18 2007 during a multi-instrument observing campaign o... more We observed a coronal cavity from August 8-18 2007 during a multi-instrument observing campaign organized under the auspices of the International Heliophysical Year (IHY). Here we present initial efforts to model the cavity with a geometrical streamer-cavity model. The model is based the white-light streamer model of Gibson et al. (2003), which has been enhanced by the addition of a cavity and the capability to model EUV and X-ray emission. The cavity is modeled with an elliptical cross-section and Gaussian fall-off in length and width inside the streamer. Density and temperature can be varied in the streamer and cavity and constrained via comparison with data. Although this model is purely morphological, it allows for three-dimensional, multi-temperature analysis and characterization of the data, which can then provide constraints for future physical modeling. Initial comparisons to STEREO/EUVI images of the cavity and streamer show that the model can provide a good fit to the data. This work is part of the effort of the International Space Science Institute International Team on Prominence Cavities.
A theoretical model of an analytical formalism of magnetic field generation due to an amplitude m... more A theoretical model of an analytical formalism of magnetic field generation due to an amplitude modulated intense laser beam in a plasma is developed. At plasma resonance, where modulation frequency equals the plasma frequency, significant enhancement in the magnetic field is seen. The magnetic field is found to scale directly with laser intensity and plasma frequency, while scaling inversely with laser spot size.
Coronal cavities are voids in coronal emission often observed above high latitude filament channe... more Coronal cavities are voids in coronal emission often observed above high latitude filament channels. Sometimes, these cavities have areas of bright X-ray emission in their centers (i.e. Hudson et al 1999). In this study, we use data from the X-ray Telescope (XRT) on Hinode to examine the thermal emission properties of two kinds of coronal cavities, those with and without enhanced emission at their centers. For cavities with bright X-ray emission in their centers, we find evidence for elevated temperatures in the cavity center. We find no obvious correlation between the presence of bright cavity cores and filament presence or eruption. This work is part of the effort of the International Space Science Institute International Team on Prominence Cavities
Page 27. First Order Normalization in Photogravitational Restricted Three Body Problem with Poynt... more Page 27. First Order Normalization in Photogravitational Restricted Three Body Problem with Poynting-Robertson Drag B. Ishwar'JP Sharmcr and Deepak Kumar Tripathi 1 PI DST Project2 Co-Pi DST Project3 JRF DST Project ...
Recent observational campaigns have brought together a wealth of data specifically designed to ex... more Recent observational campaigns have brought together a wealth of data specifically designed to explore the physical properties and dynamics of prominence cavities. In particular, STEREO and Hinode data have provided new perspectives on these structures. In order to effectively analyze the data in a cohesive manner, we produce overlays of several distinct and complimentary datasets including SOHO UVCS, CDS, and EIT, Hinode SOT and EIS, STEREO SECCHI, TRACE, and Nancay Radioheliograph data as well as new observations of coronal magnetic fields in cavities from the Coronal Multichannel Polarimeter. We are thus able to investigate how sensitive morphology is to the wavelength observed which details the nature of the plasma in the cavity.
We present a three-dimensional density model of coronal prominence cavities, and a morphological ... more We present a three-dimensional density model of coronal prominence cavities, and a morphological fit that has been tightly constrained by a uniquely well-observed cavity. Observations were obtained as part of an International Heliophysical Year campaign by instruments from a variety of space- and ground-based observatories, spanning wavelengths from radio to soft-X-ray to integrated white light. From these data it is clear that the prominence cavity is the limb manifestation of a longitudinally-extended polar-crown filament channel, and that the cavity is a region of low density relative to the surrounding corona. As a first step towards quantifying density and temperature from campaign spectroscopic data, we establish the three-dimensional morphology of the cavity. This is critical for taking line-of-sight projection effects into account, since cavities are not localized in the plane of the sky and the corona is optically thin. We have augmented a global coronal streamer model to include a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. We have developed a semi-automated routine that fits ellipses to cross-sections of the cavity as it rotates past the solar limb, and have applied it to Extreme Ultraviolet Imager (EUVI) observations from the two Solar Terrestrial Relations Observatory (STEREO) spacecraft. This defines the morphological parameters of our model, from which we reproduce forward-modeled cavity observables. We find that cavity morphology and orientation, in combination with the viewpoints of the observing spacecraft, explains the observed variation in cavity visibility for the east vs. west limbs.
Physics of Plasmas, 2011
Laser beat wave excitation of terahertz radiation in a rippled density clustered plasma, in the p... more Laser beat wave excitation of terahertz radiation in a rippled density clustered plasma, in the presence of an azimuthal magnetic field, is investigated. The lasers exert a beat ponderomotive force on cluster electrons, imparting them an oscillatory velocity with a significant transverse component due to the azimuthal magnetic field. The oscillatory velocity beats with the cluster density ripple and produces a nonlinear current, driving terahertz radiation. The terahertz field turns out to have ring shaped distribution. Its amplitude is enhanced by the cluster plasma resonance when 4π3nc0rc03ne/(ω2-ωpe2/3)>n0/ω2.
Physics of Plasmas, 2010
A model of relaxing ponderomotive nonlinearity is developed to study the nonstationary self-focus... more A model of relaxing ponderomotive nonlinearity is developed to study the nonstationary self-focusing of a Gaussian laser pulse in a plasma. The ponderomotive force acts on the electrons instantaneously but the plasma density redistribution via the process of ...
We have examined the stability of triangular equilibrium points in the photogravitational restric... more We have examined the stability of triangular equilibrium points in the photogravitational restricted three body problem with Poynting-Robertson drag. We consider both primaries as radiating. We have located the triangular equilibrium points of the problem, The position of triangular equilibrium points are affected by mass reduction factor and P-R drag. We have found the characteristic equation of the problem. We conclude that triangular equilibrium points remain unstable. All photogravitational and classical results of RTBP may be verified from this result.
Physica Scripta, 2010
The nonlinear interaction of amplitude-modulated two-dimensional and three-dimensional laser beam... more The nonlinear interaction of amplitude-modulated two-dimensional and three-dimensional laser beams with a cylindrical plasma column and the generation of terahertz (THz) radiation are studied. The plasma column could be formed by a cylindrically symmetric laser pre-pulse impinging on a gas jet target. A two-dimensional Gaussian laser beam propagating through the plasma exerts a ponderomotive force on electrons, imparting on them a resonant transverse velocity at the modulation frequency, Ω, when \Omega = \omega _{\rm{p}} /\sqrt 2 , where ωp is the plasma frequency of the column. The current produces THz radiation. In the case of a cylindrically symmetric Gaussian laser beam, the electron response to ponderomotive force misses the resonance, yet the phase matching introduced by a density ripple could efficiently produce THz radiation. The power conversion efficiency of the order of the ratio of THz radiation frequency to laser frequency can be achieved at a laser intensity of ≈1015 W cm-2 at 1 μm wavelength.
Physics of Plasmas, 2011
The energy transfer between two crossed lasers (a high frequency high amplitude pump and a low fr... more The energy transfer between two crossed lasers (a high frequency high amplitude pump and a low frequency low amplitude probe beam) through the coupling with a difference frequency electrostatic mode/quasimode in a plasma is examined. The electrostatic mode in an unmagnetized plasma is a linearly damped acoustic mode, while in a magnetized plasma it is also taken to be a lower hybrid mode. It is driven by the ponderomotive force due to the pump and probe beams. The electron density perturbation associated with the electrostatic mode beats with the oscillatory velocities due to the lasers to produce nonlinear current densities facilitating the energy transfer from the high frequency laser to the probe beam. Efficient energy transfer occurs when the phase matching conditions are satisfied. Even when a finite mismatch between the lasers and the low frequency mode/quasimode exists, a significant energy transfer is possible. The theoretical results for the unmagnetized plasma are in compliance with the published experimental results. In a magnetized plasma lower hybrid wave appears to be a potential contender for facilitating energy exchange between lasers.
We observed a coronal cavity from August 8-18 2007 during a multi-instrument observing campaign o... more We observed a coronal cavity from August 8-18 2007 during a multi-instrument observing campaign organized under the auspices of the International Heliophysical Year (IHY). Here we present initial efforts to model the cavity with a geometrical streamer-cavity model. The model is based the white-light streamer model of Gibson et al. (2003), which has been enhanced by the addition of a cavity and the capability to model EUV and X-ray emission. The cavity is modeled with an elliptical cross-section and Gaussian fall-off in length and width inside the streamer. Density and temperature can be varied in the streamer and cavity and constrained via comparison with data. Although this model is purely morphological, it allows for three-dimensional, multi-temperature analysis and characterization of the data, which can then provide constraints for future physical modeling. Initial comparisons to STEREO/EUVI images of the cavity and streamer show that the model can provide a good fit to the data. This work is part of the effort of the International Space Science Institute International Team on Prominence Cavities.
A theoretical model of an analytical formalism of magnetic field generation due to an amplitude m... more A theoretical model of an analytical formalism of magnetic field generation due to an amplitude modulated intense laser beam in a plasma is developed. At plasma resonance, where modulation frequency equals the plasma frequency, significant enhancement in the magnetic field is seen. The magnetic field is found to scale directly with laser intensity and plasma frequency, while scaling inversely with laser spot size.
Coronal cavities are voids in coronal emission often observed above high latitude filament channe... more Coronal cavities are voids in coronal emission often observed above high latitude filament channels. Sometimes, these cavities have areas of bright X-ray emission in their centers (i.e. Hudson et al 1999). In this study, we use data from the X-ray Telescope (XRT) on Hinode to examine the thermal emission properties of two kinds of coronal cavities, those with and without enhanced emission at their centers. For cavities with bright X-ray emission in their centers, we find evidence for elevated temperatures in the cavity center. We find no obvious correlation between the presence of bright cavity cores and filament presence or eruption. This work is part of the effort of the International Space Science Institute International Team on Prominence Cavities
Page 27. First Order Normalization in Photogravitational Restricted Three Body Problem with Poynt... more Page 27. First Order Normalization in Photogravitational Restricted Three Body Problem with Poynting-Robertson Drag B. Ishwar'JP Sharmcr and Deepak Kumar Tripathi 1 PI DST Project2 Co-Pi DST Project3 JRF DST Project ...
Recent observational campaigns have brought together a wealth of data specifically designed to ex... more Recent observational campaigns have brought together a wealth of data specifically designed to explore the physical properties and dynamics of prominence cavities. In particular, STEREO and Hinode data have provided new perspectives on these structures. In order to effectively analyze the data in a cohesive manner, we produce overlays of several distinct and complimentary datasets including SOHO UVCS, CDS, and EIT, Hinode SOT and EIS, STEREO SECCHI, TRACE, and Nancay Radioheliograph data as well as new observations of coronal magnetic fields in cavities from the Coronal Multichannel Polarimeter. We are thus able to investigate how sensitive morphology is to the wavelength observed which details the nature of the plasma in the cavity.
We present a three-dimensional density model of coronal prominence cavities, and a morphological ... more We present a three-dimensional density model of coronal prominence cavities, and a morphological fit that has been tightly constrained by a uniquely well-observed cavity. Observations were obtained as part of an International Heliophysical Year campaign by instruments from a variety of space- and ground-based observatories, spanning wavelengths from radio to soft-X-ray to integrated white light. From these data it is clear that the prominence cavity is the limb manifestation of a longitudinally-extended polar-crown filament channel, and that the cavity is a region of low density relative to the surrounding corona. As a first step towards quantifying density and temperature from campaign spectroscopic data, we establish the three-dimensional morphology of the cavity. This is critical for taking line-of-sight projection effects into account, since cavities are not localized in the plane of the sky and the corona is optically thin. We have augmented a global coronal streamer model to include a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. We have developed a semi-automated routine that fits ellipses to cross-sections of the cavity as it rotates past the solar limb, and have applied it to Extreme Ultraviolet Imager (EUVI) observations from the two Solar Terrestrial Relations Observatory (STEREO) spacecraft. This defines the morphological parameters of our model, from which we reproduce forward-modeled cavity observables. We find that cavity morphology and orientation, in combination with the viewpoints of the observing spacecraft, explains the observed variation in cavity visibility for the east vs. west limbs.
Physics of Plasmas, 2011
Laser beat wave excitation of terahertz radiation in a rippled density clustered plasma, in the p... more Laser beat wave excitation of terahertz radiation in a rippled density clustered plasma, in the presence of an azimuthal magnetic field, is investigated. The lasers exert a beat ponderomotive force on cluster electrons, imparting them an oscillatory velocity with a significant transverse component due to the azimuthal magnetic field. The oscillatory velocity beats with the cluster density ripple and produces a nonlinear current, driving terahertz radiation. The terahertz field turns out to have ring shaped distribution. Its amplitude is enhanced by the cluster plasma resonance when 4π3nc0rc03ne/(ω2-ωpe2/3)>n0/ω2.
Physics of Plasmas, 2010
A model of relaxing ponderomotive nonlinearity is developed to study the nonstationary self-focus... more A model of relaxing ponderomotive nonlinearity is developed to study the nonstationary self-focusing of a Gaussian laser pulse in a plasma. The ponderomotive force acts on the electrons instantaneously but the plasma density redistribution via the process of ...
We have examined the stability of triangular equilibrium points in the photogravitational restric... more We have examined the stability of triangular equilibrium points in the photogravitational restricted three body problem with Poynting-Robertson drag. We consider both primaries as radiating. We have located the triangular equilibrium points of the problem, The position of triangular equilibrium points are affected by mass reduction factor and P-R drag. We have found the characteristic equation of the problem. We conclude that triangular equilibrium points remain unstable. All photogravitational and classical results of RTBP may be verified from this result.