arXiv subjects

Amita Das

Publications and source records attributed to Amita Das.

At least 19 recordsLinked to original sources

arXiv2026

Exploring Self-Organization of Charged Dust Dimers in Plasma

We investigate the self-organization of charged dust dimers in plasma using Molecular Dynamics (MD) simulations, with emphasis on both positional and orientational ordering. For a finite number of dimers confined by a radial electric field, the system evolves from simple arrangements to ring-like structures as the particle number increases. These rings exhibit diverse orientational states, including radial, transverse, and mixed alignments of the dimer axis, reflecting a strong coupling between spatial confinement and orientational degrees of freedom. For larger systems studied under periodic boundary conditions, bulk-like behavior emerges with coupled positional and orientational correlations. The results highlight the significance of anisotropy in determining equilibrium structures and demonstrate that orientational order plays a crucial role alongside positional ordering in complex plasmas with shaped particles. This work provides motivation for experimental studies involving shaped dust particles to explore orientational ordering phenomena beyond conventional spherical dust particle systems.

physics.plasm-ph↗

arXiv2026

Quasi mono-energetic, relativistic electron acceleration in a femtosecond, high intensity laser excited solid magnet

The interaction of ultraintense lasers with magnetized overdense plasmas reveals a fundamentally new regime of laser-driven particle acceleration. Particle-in-cell simulations demonstrate the generation of directional, quasi-monoenergetic electrons in the MeV energy range superimposed on a broad thermal electron background with the estimated acceleration gradient of 3.6 MeV/{\mu}m, which is the highest till date. In contrast to conventional laser-plasma accelerators, which rely on underdense plasmas and are therefore constrained to relatively low plasma densities and limited beam charge, the present scheme operates in plasmas with densities orders of magnitude higher, opening new possibilities for the generation of high-flux energetic electron beams. A central result of this work is the demonstration of the excitation of electron Bernstein waves during relativistic laser interaction with magnetized overdense plasmas. The subsequent Landau damping of these electrostatic warm-plasma modes selectively transfers energy to resonant electrons, leading to the emergence of quasi-monoenergetic spectral peaks at energies that can be tuned through the applied magnetic field. To support the simulation results, we experimentally demonstrate the directional emission of energetic electrons from a simple permanent-magnet target irradiated by an ultraintense laser pulse, highlighting the practical feasibility of controlled electron-beam generation in dense plasma environments. These findings establish electron Bernstein waves as an efficient mediator of laser energy coupling in overdense plasmas and introduce a new paradigm for controlled particle acceleration and energy deposition in high-energy-density plasma systems.

physics.plasm-ph↗

arXiv2026

Particle Dynamics in Constant Synthetic Non-Abelian Fields

Yang-Mills theory has extended well beyond its original role in describing the strong force and now emerges as an effective theory in condensed matter, ultracold atomic, and photonic systems. In these systems, the theory has been successful in explaining phenomena such as the spin-Hall effect, spin transport, and controlling the polarisation of light. Moreover, the ability to engineer and control synthetic non-Abelian gauge fields in these systems enables us to explore aspects of gauge dynamics inaccessible to high-energy experiments. In all the above mentioned cases, the state of the system evolves in an effective external Yang-Mills field. Thus, the study of test particle dynamics in such background fields is interesting in both the classical and quantum mechanical regimes. The background non-Abelian (color) gauge fields considered in this study are constant, and they generate uniform color magnetic fields or combined color electric and magnetic fields -- which are relevant configurations. Despite the apparent simplicity of these backgrounds, the coupled evolution of real space motion and internal color degrees of freedom results in rich, nontrivial behaviour that is qualitatively distinct from the electrodynamic (Abelian) case, such as unbounded trajectories in a constant color magnetic field. In particular, particle trajectories encode signatures of the underlying gauge sources. Finally, the classical dynamics presented in this paper serves as a precursor to the complete quantum mechanical treatment to follow.

cond-mat.str-el↗

arXiv2025

Pushing the Frontiers of Light: Magnetized Plasma Lenses and Chirp Tailoring for Extreme Intensities

In this work, an innovative scheme is proposed that exploits the response of magnetized plasmas to realize a refractive index exceeding unity for right circularly polarized (RCP) waves. Using two- and three-dimensional Particle-in-Cell (PIC) simulations with the OSIRIS 4.0 framework, it is shown that a shaped magnetized plasma lens (MPL) can act as a glass/solid-state-based convex lens, amplifying laser intensity via transverse focusing. Moreover, by integrating three key ingredients, a tailored plasma lens geometry, a spatially structured strong magnetic field, and a suitably chirped laser pulse, simultaneous focusing and compression of the pulse has been achieved. The simulations reveal up to a 100-fold increase in laser intensity, enabled by the combined action of the MPL and the chirped pulse profile. With recent advances in high-field magnet technology, shaped plasma targets, and controlled chirped laser systems, this approach offers a promising pathway toward experimentally reaching extreme intensities.

physics.plasm-ph↗

arXiv2025

Universal energy cascade and relaxation in three-dimensional inertial electron magnetohydrodynamic turbulence

Electron magnetohydrodynamics (EMHD) provides a realistic model for electron-scale heating and acceleration in weakly collisional space plasmas. A divergence-free Banerjee-Galtier type (Banerjee and Galtier, JoPA, 2017) exact relation is derived for three-dimensional homogeneous and not necessarily isotropic EMHD turbulence. By explicit calculation, it has been shown that the energy cascade is not affected by the presence of a uniform background magnetic field Bo. Using direct numerical simulations, a Kolmogorov-like energy cascade with a constant flux rate is observed across the electron inertial scale $d_e$. However, as expected, for length scales greater than $d_e$, a magnetic power spectra of $k^{-7/3}$ is obtained whereas for scales smaller than $d_e$, a $k^{-5/3}$ spectra is obtained. Similar universal cascade rate is also calculated from the scale-by-scale budget in Fourier space and is found to be equal to the one calculated using the exact law in real space. Finally, quenching the turbulence drive, the relaxation of a fully-developed EMHD turbulence is studied using the recently proposed principle of vanishing nonlinear transfers (Banerjee, Halder and Pan, PRE(L), 2023) which convincingly shows the existence of a pressure-balanced relaxed state.

physics.plasm-ph↗

arXiv2025

Electron heating in bulk overdense plasma aided by time dependent external magnetic field

This study investigates the localized electron heating in a bulk overdense plasma. The method relies on using a time dependent magnetic field. An initially high external magnetic field imposed on the overdense plasma target enables the propagation of a laser pulse inside it through the pass bands that occur in the magnetized dispersion relation. The choice of decaying external magnetic field is then tailored appropriately to achieve Electron Cyclotron Resonance (ECR) with the frequency of the laser electromagnetic field. At the resonance location, the field energy of the laser gets transferred to the electrons. These studies have been carried out with the help of the Particle-In-Cell (PIC) simulation technique on the OSIRIS4.0 platform. A detailed study has been carried out to illustrate the energy gain by electrons for a variety of temporal profiles of the magnetic field, laser intensities, and polarizations. The experiments in this regime may be within reach in the near future. For instance, the choice of long-wavelength CO$_2$ laser requires a magnetic field of about 10s of kilo Tesla to comfortably elicit a magnetized response from electrons. Recent technological advancements have shown the generation of about 1.4 kilo Tesla of magnetic field.

physics.plasm-ph↗

arXiv2025

Spatial, Spectral and Temporal Response of High Intensity Laser Plasma Mirrors- Direct Observation of the Ponderomotive Push

Plasma-based optics have emerged as a powerful platform for manipulating and amplifying ultra-intense laser pulses. However, the inherently nonlinear and dynamic nature of plasma leads to significant spatial, spectral, and temporal modulations when driven at relativistic intensities. These modifications can dramatically alter the structure of the reflected laser pulses, posing challenges for their use in applications such as vacuum ultraviolet (VUV) and X-ray generation, as well as relativistic particle acceleration. Comprehensive, multidimensional diagnostics are essential to accurately characterize these so-called `plasma mirrors' (PMs). We present a direct, \textit{in situ} measurement of the three-dimensional plasma surface evolution during femtosecond laser irradiation, achieved through simultaneous analysis of the wavefront, spectrum, and temporal profile of the reflected light. Our measurements reveal surface deformations on the order of a few hundred nanometers at relativistic intensities, in agreement with three-dimensional particle-in-cell (3D-PIC) simulations. Additionally, the PM induces substantial modifications to the pulse spectrum and temporal profile, introducing spatio-temporal couplings.

physics.plasm-ph↗

arXiv2025

10$^4$-fold amplification of a tiny magnetic field to megagauss scale in femtosecond, ultraintense laser-solid interaction

Generating a powerful and quasistatic magnetic field within the confines of a tabletop laboratory experiment has proven to be a persistent challenge. The creation of magnetized high-energy-density plasma through such experiments presents significant opportunities for exploring several terrestrial as well as astrophysical phenomena, apart from controlling relativistic electron transport, directly relevant for fusion schemes. Here we demonstrate that the modest magnetic field (10$^{-3}$ megagauss ) in a common, readily available Neodymium magnet is amplified to 10's of megagauss levels lasting a few picoseconds, when excited by an ultraintense, femtosecond laser pulse. The experimental findings are strongly supported by particle-in-cell simulations, which not only validate the observations but also unveil a potential dynamo mechanism responsible for the enhancement and amplification of the axial magnetic field. These outcomes are of utmost importance in comprehending the intricacies of relativistic electron transport and the realm of magnetized laboratory astrophysics.

physics.plasm-ph↗

arXiv2025

Experimental Signatures for Identifying Distinct Origins of Color Field Generation

Signatures for non-abelian dynamics have long been central to QCD and QGP. Equally important are they in spin systems and laser-plasma interactions, where they emerge as effective interactions. Distinguishing experimentally gauge inequivalent sources (and hence potentials) that produce the same field tensor is one major task in this endeavour. As a step in this direction, this paper investigates how physically distinct sources which produce the same color electric field (uniform and constant) may be distinguished experimentally in a gauge-invariant manner. We first study the motion of a test particle in such fields and show that the resultant trajectories are counterintuitive. We then examine the radiation emitted - both gluonic and photonic and show that each source (independent non-abelian configuration) leaves a unique signature in the energy spectra, laying the ground for application to specific physical systems.

physics.plasm-ph↗

arXiv2025

Chaos aided regime of Laser/Electromagnetic Energy Absorption by plasma

The absorption of laser energy by plasma is of paramount importance for various applications. Collisional and resonant processes are often invoked for this purpose. However, in some contexts (e.g. in vacuum and the JxB heating), the energy transfer occurs even when plasma is collisionless, and there is no resonant process involved. The energy absorption in these cases has been attributed to the sheath electrostatic fields that get generated as the electrons are pulled out in the vacuum from the plasma medium. The origin of irreversibility aiding the absorption, in these cases, remains to be understood. Particle-In-Cell (PIC) simulations using the OSIRIS 4.0 platform have been carried out. The nearby trajectories of lighter electron species involved in the interaction with the laser show exponential separation. This is confirmed by the positive Lyapunov index and also by other characterizations. The observations in these cases are contrasted with the electron cyclotron resonant case, which shows negligible chaos in the electron trajectories despite the energy absorption percentage being high.

physics.plasm-ph↗

arXiv2025

Laser pulse focusing and energetic electron generation by magnetized plasma lens

An efficient mechanism of laser pulse focusing with the help of shaped underdense plasma target immersed in inhomogeneous magnetic field has been demonstrated. These studies have been carried out with the help of 2-D Particle-In-Cell (PIC) simulation employing the OSIRIS 4.0 platform. It is shown that the divergent magnetic field profile compresses the EM wave pulse in the transverse direction. A comparative investigation with plane and lens shaped plasma geometries has also been conducted to find an optimal configuration for focusing the laser at the desirable location. Furthermore, it is also demonstrated that when the electron cyclotron resonance (ECR) layer is placed at a suitable location where the laser is focused, a highly energetic electron beam gets generated.

physics.plasm-ph↗

arXiv2024

Bulk and surface dominated phenomena and the formation of pentagonal structures in 2-D strongly coupled finite dust clusters

This paper explores the prevalence of size-dependent aspects in the context of dust clusters with the help of Molecular Dynamics (MD) simulations in two dimensions. The transition from macroscale (identified by the dominance of the number of dust particles in bulk) to microscale (where the number of particles on the surface dominates) is explored systematically. The dust particles organize in a multi-ringed structure under transverse confinement. The ring size and the number of rings increase with increasing number of dust particles. Interestingly, the formation of an additional ring is always preceded by structures with a pentagonal symmetry in the core. A detailed study of this formation has been investigated under various symmetries of the boundary condition and different values of the shielding potential.

physics.plasm-ph↗

arXiv2024

Efficient electron heating by laser in finite sized plasma micro-globular targets by repeated collisions of surface and bulk waves

A new mechanism of enhanced laser energy absorption in plasma microglobules is demonstrated with the help of two-dimensional Particle-In-Cell (PIC) simulations. The mechanism relies on the excitation of surface and bulk waves and the occurrence of repeated collisions in the confines of the finite-sized microglobular target. The episodic increase in the average particle energy correlates with the repeated collision of the surface and bulk waves that get excited by the laser on the target. It is shown that the size of the microglobular target governs the efficiency of absorption and the timings of episodic events of energy enhancement. This study thereby illustrates the novel efficient possibility that a closed plasma target provides for energy extraction. Parallels of such colliding waves creating havoc in terms of wave breaking etc. can be witnessed on the ocean surface, seismic disturbances traversing as body waves traverse reflecting and refracting in the interior of the Earth along with surface waves (propagating on the curved surface of the Earth) converge at the antipode to create destruction. Our studies here show the importance of choosing closed targets which aid in the process of repeated energy transfer to particles and often their thermalization. The waves keep propagating in the closed confines rather than getting dissipated over an extended region as would happen for extended targets.

physics.plasm-ph↗

arXiv2024

Diffusive transport of a 2-D magnetized dusty plasma cloud

Dusty plasma medium turns out to be an ideal system for studying the strongly coupled behavior of matter. The large size and slow response make their dynamics suitable to be captured through simple diagnostic tools. Furthermore, as the charge on individual particles is significantly higher than the electronic charge, the interaction amongst them can be in a strong coupling regime even at room temperatures and normal densities. Such charged dust particles are often present in several industrial plasma-based processes and can have a detrimental influence. For instance, in magnetrons, the sputtering phenomena may be affected by the accumulation of charged impurity clusters. The objective here is to understand the transport behavior of these particles in the presence of an externally applied magnetic field. For this purpose, Molecular Dynamics (MD) simulations are performed using an open-source large-scale atomic/molecular massively parallel simulator (LAMMPS). The dependence of the transport coefficient on the applied magnetic field and prevalent collisional processes has been discerned through simulations in detail.

physics.plasm-ph↗

arXiv2024

Generation of mega-gauss axial and azimuthal magnetic fields in a solid plasma by ultrahigh intensity, circularly polarised femtosecond laser pulses

The interaction of intense linearly polarized femtosecond laser pulses with solids is known to generate azimuthal magnetic fields, while circularly polarized light has been shown to create axial fields. We demonstrate through experiments and particle-in-cell simulations that circularly polarized light can generate both axial and azimuthal fields of comparable magnitude in a plasma created in a solid. Angular distributions of the generated fast electrons at target front and rear show significant differences between the results for the two polarization states, with circular polarization enforcing more axial confinement. The measurement of the spatial distribution of both types of magnetic fields captures their turbulent evolution.

physics.plasm-ph↗

arXiv2024

Evolution of Shielding Cloud Under Oscillatory External Forcing in Strongly Coupled Ultracold Neutral Plasma

This paper investigates the dynamics of crystalline clusters observed in Molecular Dynamics (MD) studies conducted earlier [Yadav, M., et al. Physical Review E, 107(5), 055214(2023)] for ultra-cold neutral plasmas. An external oscillatory forcing is applied for this purpose and the evolution is tracked with the help of MD simulations using the open source LAMMPS software. Interesting observations relating to cluster dynamics are presented. The formation of a pentagonal arrangement of particles is also reported.

physics.plasm-ph↗

arXiv2024

Enhanced plasma ion heating by lasers in inhomogeneous external magnetic field

Recent studies have shown direct ion heating (vashistha2020new,Juneja_2023) by lasers EM (Electromagnetic) wave interacting with a plasma threaded by an external uniform magnetic field. The EM wave frequency was near the lower hybrid (LH) resonance frequency. The LH resonance occurs at the edge of the pass band of the magnetized dispersion relation. The group speed of the wave is negligible at resonance. In these studies, the energy absorption remains essentially confined at the plasma surface. However, to heat the ions in the bulk plasma and at a desired location, a tailored inhomogeneous external magnetic field profile has been chosen here. The strength of the magnetic field at the plasma edge is such that the EM wave frequency lies inside the pass band, where the group velocity has a significant value. It enables the wave to enter the bulk plasma. The external magnetic field is then spatially tailored appropriately to have the LH resonance at a desired spatial location inside the plasma. The Particle-In-Cell (PIC) simulations using the OSIRIS4.0 platform have been carried out, which demonstrates that the EM wave pulse comes to a standstill at the location of the resonance. The wave pulse is observed to break down subsequently, and the energy consequently goes dominantly to the local plasma ions. The absorption is significantly enhanced compared to the case in which the magnetic field profile was homogeneous. The dependence of absorption on the choice of magnetic field profile, the laser intensity, etc., has also been carried out.

physics.plasm-ph↗

arXiv2024

Fluid Simulation for a Finite Size Plasma

Studies on finite-size plasma have attracted a lot of attention lately. They can form by ionizing liquid droplets by lasers. The dynamical behavior of such plasma droplets is, therefore, a topic of significant interest. In particular, questions related to the linear and nonlinear characteristics (associated with the inhomogeneous density typically at the edge of the droplet), the behavior of plasma expansion, etc., are of interest. A one-dimensional fluid simulation study has been carried out to investigate this behavior. It is observed that a slight imbalance in the charge density leads to oscillations that are concentrated and keep acquiring higher amplitude and sharper profile at the inhomogeneous edge region. Such oscillations lead to the expansion of the droplet. Though the fluid description breaks when the sharpness of these structures becomes comparable to the grid size, it provides a reasonable estimate of wave-breaking time. The presence of dissipative effects like diffusion is shown to arrest the sharpness of these structures. The dynamics of these structures in the presence of an externally applied oscillating electric field corresponding to a long wavelength radiation has also been studied.

physics.plasm-ph↗