arXiv subjects

Prabhakar Srivastav

Publications and source records attributed to Prabhakar Srivastav.

6 recordsLinked to original sources

arXiv2025

On the enhanced Balmer emission of hydrogen in helium Capacitively Coupled Radio Frequency (CCRF) plasma

The present study investigates the observation and enhancement in the intensity of the hydrogen Balmer series emission in a He CCRF plasma using optical emission spectroscopy (OES). In addition to the characteristic line emission of He atoms, the Balmer series of hydrogen and the molecular emission of N2 are also observed in the He discharge. These emissions were primarily attributed to the presence of water vapor in the chamber. In order to confirm the role of He, the study is also performed using air and Ar where no such Balmer series emissions is seen. Experimental evidence suggests that He metastables transfer energy to trace amount of water content present in the vacuum chamber. The results point towards the hypothesis that energy exchange between metastable He and water molecules could be the underlying mechanism. Since the energy of He metastables exceeds the ionization energy of H or H2O molecule, Penning ionization is expected to occur upon their interaction. The H ions formed as a result, consequently recombine with electrons in the plasma, emitting the Balmer series. Furthermore, the emission intensity of the Balmer series of H depends on the electron density of the He plasma. Experiments also show significant deviations in the intensity ratios of the Balmer series from conventional discharges, indicating difference in the underlying population mechanism. A Collisional Radiative (CR) model for measured plasma parameters was used to estimate the metastable population density to understand the mechanism behind the enhancement of the emission intensity. The increase in the metastable densities as well as the radiative recombination cross section appear to be responsible for the observed enhancement. We believe these results will be significant in terms of applications, in addition to providing a fundamental understanding of energy transfer between metastables of He and H2O.

physics.plasm-ph↗

arXiv2025

Shock wave bending around a dusty plasma void

We report on experimental observations of the bending of a dust acoustic shock wave around a dust void region. This phenomenon occurs as a planar shock wavefront encounters a compressible obstacle in the form of a void whose size is larger than the wavelength of the wave. As they collide, the central portion of the wavefront, that is the first to touch the void, is blocked while the rest of the front continues to propagate, resulting in an inward bending of the shock wave. The bent shock wave eventually collapses, leading to the transient trapping of dust particles in the void. Subsequently, a Coulomb explosion of the trapped particles generates a bow shock. The experiments have been carried out in a DC glow discharge plasma, where the shock wave and the void are simultaneously created as self-excited modes of a three-dimensional dust cloud. The salient features of this phenomenon are reproduced in molecular dynamics simulations, which provide valuable insights into the underlying dynamics of this interaction.

physics.plasm-ph↗

arXiv2024

Observation of Kolmogorov turbulence due to multiscale vortices in dusty plasma experiments

We report the experimental observation of fully developed Kolmogorov turbulence originating from self-excited vortex flows in a three-dimensional (3D) dust cloud. The characteristic -5/3 scaling of three-dimensional Kolmogorov turbulence is universally observed in both the spatial and temporal power spectra. Additionally, the 2/3 scaling in the second-order structure function further confirms the presence of Kolmogorov turbulence. We also identified a slight deviation in the tails of the probability distribution functions for velocity gradients. The dust cloud formed in the diffused region away from the electrode and above the glass device surface in the glow discharge experiments. The dust rotation was observed in multiple experimental campaigns under different discharge conditions at different spatial locations and background plasma environments.

physics.plasm-ph↗

arXiv2019

ETG Turbulence Induced Energy flux in the Large Laboratory Plasma

The Large Volume Plasma Device (LVPD) has successfully demonstrated excitation of Electron Temperature Gradient (ETG) driven turbulence in finite plasma beta condition , where the threshold condition for ETG turbulence is satisfied. The observed mode follows wave-vector scaling and frequency ordering of ETG turbulence. Simultaneous measurement of fluctuations in electron temperature, $δT_e $, plasma density, $δn_e $ and potential,$δV_f $ are obtained. Strong negative correlation with correlation coefficients $ C_{δn_e δϕ_f}\sim -0.8 $ and $ C_{δT_e δϕ}\sim -0.9 $ are observed between density and potential and temperature and potential fluctuations, respectively. These correlated density, temperature and potential fluctuations lead to generation of turbulent heat flux. The measured heat flux is compared with theoretically estimated heat flux from ETG model equations. The experimental result shows that net heat flux is directed radially outward.

physics.plasm-ph↗

arXiv2019

Observation of Electromagnetic Fluctuation Induced Particle Transport in ETG Dominated Large Laboratory Plasma

The Large Volume Plasma device(LVPD), a cylindrically shaped, linear plasma device of dimension( $ϕ=2m $, $ L =3m $) have successfully demonstrated the excitation of Electron Temperature Gradient(ETG) turbulence[ Mattoo et al.,[1]]. The observed ETG turbulence shows significant power between $ω\sim (25-90 krad/s )> Ω_{ci}(= 8 krad/s )$, corresponding to the wavenumber, $ k_y ρ_e ~ (0.1- 0.2)$ where, $ Ω_{ci}$ and $ρ_e(=5 mm ) $, ion cyclotron frequency and electron Larmor radius, respectively. The observed frequency and wave number matches well with theoretical estimates corresponding to Whistler-ETG mode. We investigated electromagnetic (EM) fluctuations induced plasma transport in high beta ( $ β\sim 0.01 - 0.4 $ ) ETG mode suitable plasma in LVPD. The radial electromagnetic (EM) electron (ion) flux ( $ Γ^{e,i}_{em} $) results primarily from the correlation between fluctuations of parallel electron current ($δJ_{\parallel ,e,i}$ ) and radial magnetic field ($ δB_r $ ). The electromagnetic particle flux is observed to be much smaller than the electrostatic particle flux,$ Γ_{em}\approx 10^{-5} Γ_{es} $ .The EM flux is small but finite contrary to the conventional slab ETG model. The electromagnetic flux is non-ambipolar. A theoretical model is obtained for the EM particle flux in straight homogeneous magnetic field geometry. The theoretical estimates are seen to compare well with the experimental observations. Sluggish parallel ion response is identified as the key mechanism for generation of small but finite electromagnetic flux.

physics.plasm-ph↗

arXiv2017

Observation of Radially Inward Turbulent Particle Flux in ETG dominated Plasma of LVPD

Radially inward turbulent particle flux is observed in the core region of target plasma of Large Volume Plasma Device(LVPD). The region satisfy conditions for ETG turbulence, i.e. threshold condition, $ η_e = L_{n_e} / L_{T_e} > 2/3 $ , where density scale length, $ L_{n_e} \sim 300 cm $ and temerature scale length, $ L_{T_e} \sim 50cm $[S.K. Mattoo et al., Phys. Rev. Lett., 108, 255007(2012)\cite{Mattoo_PRL}]. The measured flux is dominantly electrostatic ($Γ_{es} \approx 10^{5} Γ_{em}$) although the nature of the measured turbulence is electromagnetic($β\approx 0.6 $). The turbulence has been established as a consequence of electron temperature gradient (ETG) driven modes. Experimental observations of phase angle between density ($ n_e $) and potential ($ϕ$) fluctuations, $ θ_{\tilde{n}_e, \tildeϕ} $ and electrostatic particle flux, $ Γ_{es} $ shows good agreement with the corresponding theoretical estimates for ETG turbulence.

physics.plasm-ph↗