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Rupak Mukherjee

Publications and source records attributed to Rupak Mukherjee.

At least 19 recordsLinked to original sources
arXiv2026

Direct Four-Spacecraft Measurement of Reconnection Exhaust Thickness in the Solar Wind

The thickness of a reconnecting solar wind current sheet is normally inferred from a single spacecraft as the product of the boundary-normal speed and the crossing duration. Multipoint measurements have tested this method for generic solar wind current sheets and constrained the geometry of reconnection exhausts, but a direct comparison with single-spacecraft thickness estimates for the same reconnection-associated crossings is still lacking. We analyze four current-sheet crossings observed by Magnetospheric Multiscale in the pristine solar wind on 2017 November 10 the two boundaries of a confirmed reconnection exhaust and two nearby current sheets. The tetrahedron separation was $\approx 16$ km. Cross-correlation of the magnetic-field ramps gives millisecond-level lag uncertainties, boundary normals to $4^\circ-8^\circ$ and speeds to $5\%-8\%$, while single-threshold timing at these separations is noise dominated. The exhaust edges are 29-31 ion inertial lengths ($d_i$) thick. The two edge normals differ by $22^\circ$ (68% interval [$19^\circ,26^\circ$]), resolving a nonparallel exhaust geometry. At the exhaust edges, the measured boundary speeds agree with three standard single-spacecraft estimates to 4%-15% and remain within about one Alfv\'en speed of the plasma motion. Estimating the normal from one spacecraft is the larger source of error, though the thickness is still recovered to within tens of percent when a degenerate minimum-variance solution is rejected. At the actively reconnecting sheet, the boundary speed exceeds the local plasma speed along the normal by $29\% \pm 10\%$.

physics.space-ph↗
arXiv2026

Electromagnetic Signatures of Kinetic Alfv\'{e}n Wave Turbulence at Ion Inertial Scales in Earth's High-$\beta$ Magnetosheath

We present a multi-diagnostic electromagnetic study of kinetic Alfv\'{e}n wave (KAW) activity in Earth's magnetosheath using burst-mode measurements from the Magnetospheric Multiscale (MMS) mission. We apply this analysis to a well-characterized dayside magnetosheath interval on 2015 December 28 at unusually high plasma $\beta_i \approx 14$. The identification relies on four simultaneous criteria: the normalized electric-to-magnetic field ratio $\dEperp / (\dBperp \vA)$ exceeding the ideal MHD limit (median 2.55), the presence of a finite parallel electric field $\dEpar$ (peak $3.2$~mV~m$^{-1}$), a spectral break at the ion inertial scale $\kperp d_i \approx 1$ (where $d_i = 45.0$~km is the ion inertial length, the theoretically expected transition scale at $\beta_i \gg 1$), and a kinetic-range magnetic compressibility $C_B = 0.31$ within the KAW-predicted range $[0.10, 0.40]$. All four criteria are satisfied in the same interval, providing a consistent electromagnetic identification of KAWs that does not require particle distribution measurements. A key result of this analysis is the clear identification of $d_i$ rather than the ion gyroradius $\rhoi = 170.4$~km as the relevant spectral break scale. At $\beta_i = 14.4$, the two scales differ by a factor of 3.79, making this distinction observationally testable in a way that is not possible at the more typical magnetosheath $\beta \sim 1$--$5$.

physics.plasm-ph↗
arXiv2026

Ion Channel Dynamics in Temperature-Dependent Weibel Instability Saturation

We present 1X2V continuum Vlasov-Maxwell simulations of interpenetrating plasma beams with mobile ions. While the early-time evolution is similar to the stationary-ion case, the late-time dynamics are dominated by the ion-Weibel instability. As ion channels merge, the magnetic energy increases and the magnetic structures extend further along the beam direction. Electrons rapidly reach thermal equilibrium, whereas ions retain distinct bulk velocities for much longer and thermalize more slowly. These results are relevant to collisionless shock formation in astrophysical compact objects and laser-plasma experiments. Wind/SWE observations place all four simulated cases in the firehose/Weibel-unstable region of the proton temperature anisotropy diagram, and MMS1 observations of a quasi-perpendicular bow shock ($\theta_{Bn}\approx83^\circ$, $M_A\approx27$) show a qualitatively similar electron-ion thermalization disparity.

physics.plasm-ph↗
arXiv2026

Linear-wave bound on electromagnetic energy equipartition at sub-electron scales in non-relativistic plasmas

Recent Magnetospheric Multiscale (MMS) observations report approximate equality between electric and magnetic field energy spectral densities, $\varepsilon_{0} P[\delta E]/2 \approx P[\delta B]/(2\mu_{0})$, at sub-electron scales in reconnection-driven magnetotail turbulence, interpreted as relaxation toward thermodynamic equilibrium. We derive the electric-to-magnetic energy ratio from the linear polarization of kinetic Alfv\'en waves and whistler-mode waves in the two-fluid framework and show that it saturates at $\mathcal{R}_{\infty}=(V_{A}/c)^{2}(m_{i}/m_{e})(\beta_{e}/2)$ deep in the sub-electron regime. Setting $\mathcal{R}_{\infty}=1$ yields the universal threshold $V_{A}/c \gtrsim \sqrt{2/[(m_{i}/m_{e})\beta_{e}]}$, which no non-relativistic space plasma satisfies. For typical magnetotail parameters, $\mathcal{R}_{\infty}\approx 2\times 10^{-3}$, approximately 500 times below the observed value, a discrepancy rooted in the non-relativistic ordering $(V_{A}/c)^{2}\ll 1$. Noise-floor estimates show that Search Coil Magnetometer and Electric Double Probe sensitivity convergence produces a spurious apparent equipartition throughout this regime. The observed equality likely reflects nonlinear dynamics, incoherent superposition of electromagnetic and electrostatic fluctuations, or instrumental noise contamination.

physics.plasm-ph↗
arXiv2026

Inertial-Range Suppression and Ponderomotive Density Cavitation in Broadband Sub-Alfv\'{e}nic Turbulence under Plasma Sheet Boundary Layer Conditions

Kinetic Alfv\'{e}n waves (KAWs) are among the most pervasive electromagnetic fluctuations in magnetized astrophysical plasmas, from Earth's magnetosphere to galaxy clusters. Their ponderomotive coupling to compressive density fluctuations is poorly understood in the broadband turbulent regime. We present two-dimensional pseudospectral simulations of the modified nonlinear Schr\"{o}dinger--magnetosonic (MNLS--MS) system governing KAW envelopes, initialized with a broadband power-law spectrum ($|\psi(\mathbf{k})|^2\propto k^{-5/6}$) spanning many interacting modes, at $\beta \sim 0.1$--$0.3$ representative of plasma sheet boundary layer (PSBL) conditions. A fourth-order Runge--Kutta scheme on a $256\times 256$ grid integrates the system to $t = 40$ (normalized), with total energy conserved to within $0.085\%$ in the undamped run; a damped run with dissipation loses $\sim 4\%$ of the magnetic energy over the same interval. The nonlinearity parameter $\chi_\mathrm{NL} \approx 0.25$ confirms broadband sub-Alfv\'{e}nic turbulence throughout. Magnetic field intensity and plasma density develop spatially intermittent, filamentary structures within the first few wave periods, consistent with ponderomotive density cavitation and plasma expulsion from wave-intense regions. The magnetic energy spectra show inertial-range suppression, with a rapid transition from injection ($k < 0.3$) to dissipation without an extended power-law cascade, in agreement with the moderate magnetic Reynolds number ($\mathrm{R_m} \sim 250$--$370$) of the simulation and the observationally constrained range for PSBL turbulence. These results provide numerical evidence that broadband KAW turbulence self-organizes into coherent density structures at kinetic scales, and that the spectral character of such turbulence is governed primarily by moderate-Reynolds-number constraints rather than by the wave physics alone.

physics.plasm-ph↗
arXiv2026

Weibel Instability in Collisionless Plasmas Across Astrophysical and Laboratory Shocks

We present a cold-fluid analysis of the purely transverse Weibel (current-filamentation) instability across four regimes: non-relativistic (NR) single-species, NR multi-species, relativistic single-species, and relativistic multi-species (electron--positron and electron--proton). Beginning from linearized fluid equations, we derive the dispersion relations in each regime and extract scaling laws for the maximum growth rate $\gamma_{\rm max}$ and characteristic unstable wavenumber $k_{\rm max} = \omega_{pi}/c$. Relativistic corrections suppress $\gamma_{\rm max}$ by up to 40 per cent above $v_0 \approx 0.2c$, peaking near $v_0 \approx 0.9c$. Multi-species effects are significant only for $m_e/m_i \gtrsim 1/500$. For the tabletop laser experiment of Bai et al., Nat.Commun., 16, 3770 (2025), the cold-fluid prediction gives $d_i = c/\omega_{pi} \approx 31.7\,\mu{\rm m}$, within 2 per cent of the measured filament spacing $\lambda_F \approx 31\,\mu{\rm m}$. The saturation field estimate $B_{\rm sat} \approx 2.3\times10^4$ T is an upper bound, consistent with the measured $\approx 5000$ T under kinetic suppression. Two MMS burst-mode bow shock crossings (October 16, 2015 and November 25, 2017) confirm $k_{\rm max} d_i = 1$ from FGM/FPI data. A multi-environment scatter plot spans 21 orders of magnitude in $n_i$, with all points within a factor of 3 of the 1:1 line.

physics.plasm-ph↗
arXiv2026

MMS Observations of Kinetic Alfv\'en Wave Turbulence and Steep Kinetic-Range Spectra in the Outer Plasma Sheet Boundary Layer

Energy dissipation and particle acceleration in the collisionless magnetotail plasma remain incompletely understood. We report observations of Kinetic Alfv\'en Wave (KAW) turbulence and parallel electric fields ($E_{\parallel}$) in the outer Plasma Sheet Boundary Layer (PSBL) using high-resolution burst-mode data from the Magnetospheric Multiscale (MMS) mission. For a crossing on May 31, 2017, we identify broadband KAW turbulence characterized by a normalized electric-to-magnetic field ratio $\mathcal{R}=|\delta E_{\perp}|/(v_A|\delta B_{\perp}|)=2.5\pm1.2$ exceeding the MHD limit, a spectral break near ion scales, a steep kinetic-range spectral slope ($\alpha=-3.48\pm0.13$), and low magnetic compressibility ($C_{\parallel}\approx0.03$). We observe impulsive $E_{\parallel}$ structures up to 15 mV/m and ion density fluctuations up to 68% during enhanced wave activity. The steep spectrum, compared with undamped KAW predictions ($-7/3$ to $-8/3$), is consistent with substantial energy removal at kinetic scales. The near-zero correlation between the KAW-band filtered $E_{\parallel}$ waveform (0.18 to 2.0 Hz) and ion density fluctuations ($r\approx0.04$) indicates no simple linear, zero-lag correspondence under the adopted processing. Together with bursty energy-conversion proxies, the observations are consistent with localized field-particle energy exchange and collisionless damping of KAW turbulence in the intermediate-beta outer PSBL. A specific damping channel, such as Landau damping, is not uniquely constrained by the present diagnostics.

physics.plasm-ph↗
arXiv2025

Damped Kinetic Alfv\'en Waves in Earth's Magnetosheath: Numerical Simulations and MMS Observations

The Earth's magnetosheath provides a high $\beta$ (ratio of electron thermal pressure to magnetic pressure) plasma environment where kinetic Alfv\'en waves (KAWs) strongly influence turbulence and energy dissipation. This study investigates how Landau damping modifies the nonlinear evolution of KAWs by solving a modified nonlinear Schr\"odinger equation that captures both dispersive and nonlinear effects. Without Landau damping, modulational instability drives rapid self-focusing into intense magnetic filaments, producing a turbulent cascade with $k_\perp^{-5/3}$ scaling in the inertial range ($k_\perp\rho_i<1$) that transitions to $k_\perp^{-8/3}$ at sub-ion scales ($k_\perp\rho_i>1$), here $k_\perp$ is the wavevector component perpendicular to the background magnetic field and $\rho_i$ the ion thermal gyroradius. When Landau damping is included, magnetic structures are significantly suppressed, and the spectrum steepens to $k_\perp^{-11/3}$ in the sub-ion range while the inertial range maintains $k_\perp^{-5/3}$ scaling. The damping acts across all scales through resonant wave-particle interactions, efficiently transferring energy from waves to particles. Direct comparison with Magnetospheric Multiscale (MMS) spacecraft observations shows that the observed kinetic range spectral slope falls between our undamped and damped simulation limits, consistent with an intermediate damping regime in magnetosheath turbulence. This agreement confirms that Landau damping is one of the primary mechanisms controlling turbulent energy dissipation at kinetic scales in collisionless plasmas.

physics.plasm-ph↗
arXiv2025

Suppression of two stream instability in relativistic electron-ion plasmas

This paper investigates the suppression of two stream instabilities in electron ion plasmas when the individual species attain relativistic velocities. This suppression of the growth rate of two stream instability is consistent even when the ions form a neutralizing background. It is found that the parameter space of the growth rate reasonably squeezes for relativistic electrons at higher plasma frequencies. We further report the suppression of the growth rate of the said instability as the ion electron mass ratio reaches the realistic limit. Our results have implications for high-energy plasmas, laser-plasma interactions, and relativistic particle beam physics, providing insights into the complex interplay of linear and nonlinear processes governing the two-stream instability. Our unified four-regime analysis extends previous understanding of how realistic mass ratios fundamentally modify relativistic suppression effects, providing essential scaling laws for high-energy plasma applications.

physics.plasm-ph↗
arXiv2025

Identification of phase correlations in Financial Stock Market Turbulence

The basis of arbitrage methods depends on the circulation of information within the framework of the financial market. Following the work of Modigliani and Miller, it has become a vital part of discussions related to the study of financial networks and predictions. The emergence of the efficient market hypothesis by Fama, Fisher, Jensen and Roll in the early 1970s opened up the door for discussion of information affecting the price in the market and thereby creating asymmetries and price distortion. Whenever the micro and macroeconomic factors change, there is a high probability of information asymmetry in the market, and this asymmetry of information creates turbulence in the market. The analysis and interpretation of turbulence caused by the differences in information is crucial in understanding the nature of the stock market using price patterns and fluctuations. Even so, the traditional approaches are not capable of analyzing the cyclical price fluctuations outside the realm of wave structures of securities prices, and a proper and effective technique to assess the nature of the Financial market. Consequently, the analysis of the price fluctuations by applying the theories and computational techniques of mathematical physics ensures that such cycles are disintegrated, and the outcome of decomposed cycles is elucidated to understand the impression of the information on the genesis and discovery of price and to assess the nature of stock market turbulence. In this regard, the paper will provide a framework of Spectrum analysis that decomposes the pricing patterns and is capable of determining the pricing behavior, eventually assisting in examining the nature of turbulence in the National Stock Exchange of India.

q-fin.ST↗
arXiv2025

An analysis of capital market through the lens of integral transforms: exploring efficient markets and information asymmetry

Post Modigliani and Miller (1958), the concept of usage of arbitrage created a permanent mark on the discourses of financial framework. The arbitrage process is largely based on information dissemination amongst the stakeholders operating in the financial market. The advent of the efficient market Hypothesis draws close to the M&M hypothesis. Giving importance to the arbitrage process, which effects the price discovery in the stock market. This divided the market as random and efficient cohort system. The focus was on which information forms a key factor in deciding the price formation in the market. However, the conventional techniques of analysis do not permit the price cycles to be interpreted beyond its singular wave-like cyclical movement. The apparent cyclic measurement is not coherent as the technical analysis does not give sustained result. Hence adaption of theories and computation from mathematical methods of physics ensures that these cycles are decomposed and the effect of the broken-down cycles is interpreted to understand the overall effect of information on price formation and discovery. In order to break the cycle this paper uses spectrum analysis to decompose and understand the above-said phenomenon in determining the price behavior in National Stock Exchange of India (NSE).

q-fin.ST↗
arXiv2024

Knot-detection algorithm to measure viscosity in three-dimensional MHD plasmas

This project explores the mathematical study of knots and links in topology, focusing on differentiating between the two-component Unlink and the Hopf Link using a computational tool named LINKAGE. LINKAGE employs the linking number, calculated through Barycentric Equations, Matrix Algebra, and basic topological principles, to quantify the degree of linking between two closed curves in three-dimensional space. This approach not only distinguishes between different knot structures but also has applications in understanding complex systems such as magnetic field lines in plasma physics. Additionally, this project includes an example where multiple interlinked loops were analyzed over different time stamps using the LINKAGE algorithm. By observing how these links break and evolve, the algorithm demonstrates its ability to track changes in the topological properties of the system. This dynamic analysis shows the versatility of the tool in studying evolving systems, where the topology of the components can change, providing valuable information about the underlying physical processes driving these changes.

physics.plasm-ph↗
arXiv2024

Reduced dimensional description of hydromagnetic turbulence capturing higher order fluid moments

In this paper, Chandrasekhar's deductive theory of turbulence is extended to the case of hydrodynamics and hydromagnetics, with higher order fluid moments. We include the contributions from correlation tensors at two different points of space and two different points in time to account for the energy transfer between Fourier modes with different $k$ values. We start with three governing equations using the first three moments of Vlasov equation, which gives us particle, momentum and energy conservation relations, respectively. We obtain the scalar representations of correlation tensors for hydrodynamics as well as hydromagnetics. Finally we pick an example from literature where the energy spectra alone was not capable of explaining the observations reported by the authors.

physics.flu-dyn↗
arXiv2022

Understanding the surface wave characteristics using 2D particle-in-cell simulation and deep neural network

The characteristics of the surface waves along the interface between a plasma and a dielectric material have been investigated using kinetic Particle-In-Cell (PIC) simulations. A microwave source of GHz frequency has been used to trigger the surface wave in the system. The outcome indicates that the surface wave gets excited along the interface of plasma and the dielectric tube and appears as light and dark patterns in the electric field profiles. The dependency of radiation pressure on the dielectric permittivity and supplied input frequency has been investigated. Further, we assessed the capabilities of neural networks to predict the radiation pressure for a given system. The proposed Deep Neural Network model is aimed at developing accurate and efficient data-driven plasma surface wave devices.

physics.plasm-ph↗
arXiv2020

Measurement of temperature of a dusty plasma from configuration

A new method called `Configurational Temperature' is introduced in the context of dusty plasma, where the temperature of the dust particles, submerged in the plasma, can be measured directly from the positional information of the individual dust particles and the interaction potential between the dust grains. This method does not require the velocity information of individual particles which is a key parameter to measure the dust temperature in the conventional method. The technique is initially tested using two dimensional OpenMP parallel Molecular Dynamics and Monte-Carlo simulation and then compared with the temperature evaluating from the experimental data. The experiments have been carried out in Dusty plasma experimental (DPEx) device where a two dimensional stationary plasma crystal of melamine formaldehyde particles is formed in the cathode sheath of a DC glow discharge argon plasma. The dust kinetic temperature is calculated using standard PIV technique at different pressures. The simulation results matches well with the experimental data at relatively higher pressures where the dust particles arranged into crystalline state or in a strongly coupled fluid state. An extended simulation results for three dimensional case is also presented which can be employed for the temperature measurement of three dimensional dust crystal in laboratory devices.

physics.plasm-ph↗
arXiv2019

Isothermal Equation of State of Three Dimensional Yukawa Gas

Molecular Dynamics (MD) simulation is carried out to examine the effect of particle confinement on the pressure of 3D Yukawa gas. Confinement effects are taken into account by using perfectly reflecting boundary condition in MD simulations. An equation of state relating pressure to number density is obtained. The results of the MD simulations show that in weak coupling regime pressure of confined Yukawa gas is much bigger than the kinetic pressure and scales quadratically with number density. Results are compared with earlier theories and experiments which show quadratic scaling of dust pressure with density.

physics.plasm-ph↗
arXiv2019

Coherent nonlinear oscillations in magnetohydrodynamic plasma

Single fluid magnetohydrodynamic (MHD) equations have been studied through direct numerical simulations (DNS) using pseudo-spectral methods in two as well as three spatial dimensions. At Alfvén resonance, a reversible periodic exchange of energy between kinetic and magnetic variables is observed. The oscillations are identified as nonlinear dispersionless Alfvén waves that have been predicted earlier on theoretical grounds but not observed in large scale numerical simulations. A systematic study of their occurrence for various initial conditions and a range of Alfven velocities is carried out. An analysis based on a finite mode representation of the incompressible single fluid MHD equations in two spatial dimensions reproduces the essential features of these oscillations.

physics.plasm-ph↗
arXiv2019

Study of Dynamo Action in Three Dimensional Magnetohydrodynamic Plasma with Arnold-Beltrami-Childress Flow

For a three dimensional magnetohydrodynamic (MHD) plasma the dynamo action with ABC flow as initial condition has been studied. The study delineates crucial parameter that gives a transition from coherent nonlinear oscillation to dynamo. Further, for both kinematic and dynamic models at magnetic Prandtl number equal to unity the dynamo action is studied for driven ABC flows. The magnetic resistivity has been chosen at a value where the fast dynamo occurs and the growth rate shows no further variation with the change of magnetic Reynold's number. The exponent of growth of magnetic energy increases, indicating a faster dynamo, if a higher wave number is excited compared to the one with a lower wave number. The result has been found to hold good for both kinematic and externally forced dynamic dynamos where the backreaction of magnetic field on the velocity field is no more negligible. In case of an externally forced dynamic dynamo, the super Alfvenic flows have been found to excite strong dynamos giving rise to the growth of magnetic energy of seven orders of magnitude. The back-reaction of magnetic field on the velocity field through Lorentz force term has been found to affect the dynamics of the velocity field and in turn the dynamics of magnetic field, leading to a saturation, when the dynamo action is very prominent.

physics.plasm-ph↗