K P Subramanian - Academia.edu (original) (raw)

Papers by K P Subramanian

Planetary and Space Science, 2018

The Aditya Solarwind Particle EXperiment (ASPEX) is one of the seven scientific payloads onboard ... more The Aditya Solarwind Particle EXperiment (ASPEX) is one of the seven scientific payloads onboard the Aditya-L1 mission (the forthcoming Indian solar mission), to be placed in a halo orbit around the L1 Lagrangian point of the Sun-Earth system, at a distance of 1.5 million km from the Earth, along the Sun-Earth line. ASPEX will carry out the in-situ, multi-directional measurements of the slow and fast solar wind; suprathermal particles and solar energetic particles in the energy range of 100 eV/n to 20 MeV/n. Multi-directional measurements from ASPEX will help in understanding the anisotropy in the energy distribution of particles arriving from different directions. The ASPEX payload will play a significant role in the understanding of the acceleration mechanism and generation of these energetic particles in the interplanetary medium. The ASPEX instrument has been configured as two subsystems viz. the Solar Wind Ion Spectrometer and the SupraThermal & Energetic Particle Spectrometer. This paper presents the configuration details of both the subsystems along with preliminary results obtained from the breadboard models.

Applied Spectroscopy, 2020

Stark broadening parameters have been estimated for resonant lines of Al(I) using time resolved m... more Stark broadening parameters have been estimated for resonant lines of Al(I) using time resolved measurements. The relation between the various emission line characteristics at different phases of opacity have been utilized to obtain the value of plasma temperature and Stark width parameters from the experimental data. The observed value of the center line intensity and Lorentzian component of the line width are compared against a simulated value of these parameters for optically thin case. The plasma temperature and Stark broadening parameters are obtained for the best fit condition by matching the experimentally observed and the simulated values of intensity and line widths. The time resolved measurements result in much better estimates for Stark parameters by allowing multiple points for fitting keeping the number of variables limited. The Stark shift parameters are also obtained from the slope of the plot of observed central wavelength shifts versus observed electron number densi...

Current Science, 2017

Aditya-L1, the first ever Indian scientific space mission dedicated to probe the Sun, our nearest... more Aditya-L1, the first ever Indian scientific space mission dedicated to probe the Sun, our nearest star, is slated for launch by the Indian Space Research Organisation (ISRO) most likely in 2020, the year coinciding with the expected start of the rising phase of solar cycle 25. Of the seven science payloads on-board Aditya-L1, three are in situ instruments, namely the Aditya Solar wind Particle EXperiment, the Plasma Analyser Package for Aditya and a magnetometer package. These three payloads will sample heliospheric data from the L1 Lagrangian point of the Sun-Earth system, at a distance of ~1% of the distance to the Sun, along the Sun-Earth line. This is therefore a unique opportunity for the solar physics community to gain a better understanding of the inner heliosphere and predict space weather more accurately.

Physical Review A, 2016

We present an experimental and computational analysis of dissociative double ionization of N 2 an... more We present an experimental and computational analysis of dissociative double ionization of N 2 and CO molecules under electron impact. Experiments are performed at three energies, viz. 1, 3, and 5 keV, in order to observe the effect of impact energy on the dissociative ionization kinematics. We compare the kinetic energy release (KER) distributions of the charge symmetric dissociation channels of N 2+ 2 and CO 2+ at these impact energies. An approximately linear trend between the transition energy and the expected KER values is inferred on the basis of the calculated potential energy curves of the dications. Experimentally, the normalized differential KER cross sections for these channels show an increasing trend in the low KER range and a decreasing trend in the high KER range as the electron-impact energy is increased. This observation indicates that the transition probability for excitation to different molecular ion states is not only a function of energy difference between the ground and excited states, but also a complicated function of the impact energy. In addition, nature of the observed trend in the differential KER cross sections differs significantly from their differential transition probability, which are calculated using inelastic collision model for fast-electron-impact case.

Applied optics, 2018

Composition of multielement samples is estimated by using a synthetic generated spectrum utilizin... more Composition of multielement samples is estimated by using a synthetic generated spectrum utilizing a nonlinear fitting routine. By fitting simultaneously a large number of emission lines, the error in the estimation is minimized. The procedure for synthetic spectrum generation includes self-absorption of emission lines by taking into account the number density of different species in the plasma. The Stark width of different emission lines is iteratively calculated based on the observed width and the degree of self-absorption in the individual lines. This procedure is found to be successful for achieving convergence of the retrieval algorithm even for dense spectra as well as for resolving merged lines with accuracy. This scheme was applied on a stainless steel and brass sample, and the laser-induced breakdown spectroscopy results match well with the reference value obtained from the electron probe microanalyzer measurement.

The Astrophysical Journal, 2014

Propargyl alcohol (CHCCH 2 OH) is a known stable isomer of the propenal (CH 2 CHCHO) molecule tha... more Propargyl alcohol (CHCCH 2 OH) is a known stable isomer of the propenal (CH 2 CHCHO) molecule that was reported to be present in the interstellar medium (ISM). At astrochemical conditions in the laboratory, icy layers of propargyl alcohol grown at 85 K were irradiated by 2 keV electrons and probed by a Fourier Transform InfraRed spectrometer in the mid-infrared (IR) region, 4000-500 cm −1. Propargyl alcohol ice under astrochemical conditions was studied for the first time; therefore, IR spectra of reported amorphous (85 K) and crystalline (180 K) propargyl alcohol ices can be used to detect its presence in the ISM. Moreover, our experiments clearly show benzene (C 6 H 6) formation to be the major product from propargyl alcohol irradiation, confirming the role of propargyl radicals (C 3 H 3) formed from propargyl alcohol dissociation that was long expected based on theoretical modeling to effectively synthesize C 6 H 6 in the interstellar icy mantles.

Journal of Physics B: Atomic and Molecular Physics, 1987

Page 1. Electron-helium and electron-neon scattering cross sections at low electron energies usin... more Page 1. Electron-helium and electron-neon scattering cross sections at low electron energies using a photoelectron source This article has been downloaded from IOPscience. Please scroll down to see the full text article. 1987 J. Phys. B: At. Mol. Phys. 20 2899 ...

Pramana, 1998

Abstract Absolute total electron scattering cross sections for nitrous oxide have been measured a... more Abstract Absolute total electron scattering cross sections for nitrous oxide have been measured at low electron energies using a photoelectron source. The measurements have been carried out at 19 electron energies varying from 0.739.14 eV with an accuracy of±3 ...

Trends in Atomic and Molecular Physics, 2000

Mixing of ro-vibrational levels in the excited states of certain molecules leads to elongation of... more Mixing of ro-vibrational levels in the excited states of certain molecules leads to elongation of average lifetime of excited states. The relaxation of pure adiabaticity condition of Born-Oppenheimer states allows mixing of levels in the excited state. The extent of perturbation on the emitting level by the nearby lying electronic states is ro-vibrational and is quantum number specific. This introduces variability in the anomalous lifetime as a function of the excitation wavelength. For certain wavelengths, emissions from pure unperturbed states also are observed. The radiative lifetime measurement of NO2 in the excitation region 465–490 nm is presented in this paper.

Spectroscopy Letters, 2014

Physical Review A, 2008

Fragmentation of SF 6 3+ , formed from SF 6 by absorption of soft x-ray photons, has been investi... more Fragmentation of SF 6 3+ , formed from SF 6 by absorption of soft x-ray photons, has been investigated using a momentum imaging time-of-flight spectrometer. We observe triple ion coincidences between two F + ions and SF m + where m = 0 ,. .. , 3. Strong correlation between the momentum distributions of the two F + ions is observed across all dissociation channels involving triple ion coincidences. We present a method of estimating the contribution of the neutral fragments to the kinematics of ion ejection based on the scalar triple product of the ion momentum vectors. The noncoplanarity of the three ion ejecta inferred in this manner allows us to discern the fragmentation sequence of SF 6 3+. The proposed sequence is loss of a neutral F followed by violent ejection of two F + ions and gentle removal of remaining F atoms from SF 3 + .

Journal of Quantitative Spectroscopy and Radiative Transfer, 1999

The fluorescence excitation spectra for NO have been studied and lifetimes have been measured at ... more The fluorescence excitation spectra for NO have been studied and lifetimes have been measured at the excitation photon wavelengths 465-490 nm at an interval of 0.2 nm using an excimer laser pumped dye laser as the photon source. These measurements have been carried out at several pressures ranging from 1 to 110 m Torr and three groups of lifetimes have been obtained, viz. 1-3, 20-40 and 70-120 s. The results obtained in the present experiment have been compared with other measurements, where ever possible.

Journal of Physics D: Applied Physics, 2006

... A Kumar et al A close examination of figure 3 also reveals that no appreciable shift in delay... more ... A Kumar et al A close examination of figure 3 also reveals that no appreciable shift in delay for the first component was observed for any pressure as well as for any distance from the target. This observation was in contradiction with result reported by Abhilasha et al [14] who ...

Journal of Physics B: Atomic, Molecular and Optical Physics, 2009

Page 1. Polarization dependence in non-resonant photo-triple-ionization of CO2 This article has b... more Page 1. Polarization dependence in non-resonant photo-triple-ionization of CO2 This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2009 J. Phys. B: At. Mol. Opt. Phys. 42 105201 (http://iopscience.iop.org/0953-4075/42/10/105201) ...

Journal of Physics B: Atomic, Molecular and Optical Physics, 1989

... Printed in the UK Total electron scattering cross sections for molecular oxygen at low electr... more ... Printed in the UK Total electron scattering cross sections for molecular oxygen at low electron energies KP Subramanian and Vijay Kumar Physical Research Laboratory, Navrangpura, Ahmedabad-380009, India Received 26 July 1989, in final form 26 October 1989 Abstract. ...

Journal of Applied Physics, 2007

The time- and space-resolved emission profiles of LiI and LiII emission lines from the laser-blow... more The time- and space-resolved emission profiles of LiI and LiII emission lines from the laser-blow-off plumes of a multilayered LiF–C thin film have been studied using spectroscopic technique. The evolution features were analyzed in different ambient environments ranging from high vacuum to 3mbars of argon pressures and at various fluences of the ablating laser. During the evolution of the plume, a transition region was found to exist between 4 and 6mm. Here, the plume dynamics changed from free expansion to collisional regime, where the plume experienced viscous force of the medium. The enhancement observed in neutral lines, in comparison with ionic lines, is explained in terms of the yield difference in electron impact excitation and ionization processes. Substantial difference in the arrival time distribution of the plume species was observed for LiI and LiII lines at high ambient pressures. Three expansion models are invoked to explain the evolution of the plume in different ambi...

Fusion Engineering and Design, 2005

A supersonic molecular beam injection (MBI) system for Aditya tokamak is developed in house by mo... more A supersonic molecular beam injection (MBI) system for Aditya tokamak is developed in house by modifying a piezoelectric gas inlet valve and using 400 μm diameter nozzle at 25 kg/cm 2 gas pressure. This valve is mounted directly on the Aditya vacuum vessel. Experiments ...

Physical Review A, 2006

In an experiment involving detection of a photoelectron and up to three photoions from CO 2 in co... more In an experiment involving detection of a photoelectron and up to three photoions from CO 2 in coincidence, we observe the triple ion coincidence C + :O + :O +. Moreover, we observe double coincidences between doubly charged cations and singly charged cation pairs C 2+ :O + , O 2+ :C + , O 2+ :O +. These ion triplets and pairs arise from fragmentation of the triply charged molecular ion CO 2 3+. Other ion pairs-viz., C + :O + , O + :O + , O + :CO +-arising from the doubly charged molecular ion CO 2 2+ , are also observed. From an analysis of the coincidence pattern we postulate four decay modes of the CO 2 3+ ion. Kinetic energy release in the channel leading to C + :O + :O + is measured, and its distribution is postulated to have four contributing precursor states.

Applied Optics, 2013

We propose a calibration-free algorithm for retrieval of elemental concentrations using laser-ind... more We propose a calibration-free algorithm for retrieval of elemental concentrations using laser-induced breakdown spectroscopy. This is a simple and improved version of other ratio-based algorithms as it needs only one trial parameter to estimate all other concentrations. The present algorithm has been used to estimate the composition of a brass sample, and the results agree within 1% with electron probe microanalyzer measurements.

Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray, 2016

Aditya Solar wind Particle EXperiment (ASPEX) is one of the scientific experiments onboard the Ad... more Aditya Solar wind Particle EXperiment (ASPEX) is one of the scientific experiments onboard the Aditya-L1 mission, the first Indian solar mission planned to be launched in the year of 2019. The primary objective of the ASPEX experiment is to carry out in-situ, multi-directional measurements of solar wind ions in the energy range of 100 eV/n to 5 MeV/n. ASPEX instrument has been configured into two subsystems: Solar Wind Ion Spectrometer (SWIS) and Supra Thermal & Energetic Particle Spectrometer (STEPS). SWIS will measure the angular and energy distribution of solar wind ions in the energy range of 100 eV to 20 keV and STEPS will measure the energy spectrum of high energetic particles from six directions covering the energy range of 20 keV/n to 5 MeV/n. This paper presents the overall configuration of the STEPS subsystem with preliminary results obtained from the bread board model.