arXiv subjects

Bhooshan Paradkar

Publications and source records attributed to Bhooshan Paradkar.

9 recordsLinked to original sources

arXiv2026

Revisiting Electron Heating in Capacitively Coupled Plasma (CCP) Discharges: A Nonlinear Dynamics Perspective

Despite decades of research, the electron heating mechanisms in capacitively coupled plasma (CCP) discharges over a wide range of operating conditions is not fully understood. Although stochastic heating is generally regarded as the dominant collisionless heating mechanism at low pressures, the inherently nonlinear electron dynamics responsible for this process have not been fully quantified. These nonlinear interactions drive stochastic heating, a mechanism considered crucial for energy transfer in CCPs, yet its quantitative impact on plasma parameters remains insufficiently explored. In this work, we investigate electron dynamics in steady-state CCP discharges and demonstrate that electron motion in the plasma bulk exhibits intrinsically chaotic behavior. The onset of chaos is identified using Poincare sections and quantified through Lyapunov exponent analysis. To further quantify this behavior, we map the spatial distribution of the Lyapunov exponent-normalized by the electron-neutral collision frequency-across the plasma bulk for different pressures and RF voltages. The normalized Lyapunov exponent increases systematically with decreasing pressure and increasing RF voltage, indicating enhanced stochasticity and a stronger sensitivity of electron trajectories to initial conditions. These results establish the Lyapunov exponent as a quantitative measure of effective stochastic scattering in collisionless CCPs and provide a direct comparison with the classical stochastic collision frequency proposed by Popov and Godyak [Journal of Applied Physics 57, 53-58 (1985)]. The present analysis offers a unified nonlinear dynamical framework for understanding stochastic electron heating in low-pressure RF plasmas.

physics.plasm-ph↗

arXiv2026

Quasi-static transverse electric field driven electron acceleration in relativistic laser matter interaction

Achieving significant energy gain in laser-driven relativistic electron beams remains challenging due to dephasing between the accelerating laser field and the electrons. We show that transverse electric fields, when aligned with the plane of laser polarization, can mitigate dephasing and enable substantial energy gain without compromising beam directionality. As a practical realization, we propose a two-laser scheme in which one laser generates the transverse field while the other drives electron acceleration. By tailoring the interaction geometry, this configuration sustains phase locking, enhances energy transfer, and opens a pathway toward compact, high-efficiency electron accelerators.

physics.plasm-ph↗

arXiv2026

Collisionless Bulk Electron Heating in Resonant Low-Voltage Capacitively Coupled Plasmas

We investigate collisionless power absorption in resonant, low$-$pressure capacitively coupled plasmas (CCPs). In these radio-frequency (RF) discharges, the sheath capacitance almost exactly balances the plasma inductance, driving the total RF discharge voltage down to just a few volts. However, plasma persists not only in this ultra$-$low$-$voltage regime; it also generates ions that strike the electrodes with kinetic energies substantially exceeding the amplitude of the applied RF voltage. This counterintuitive behavior arises from the presence of a pronounced electrostatic potential well of approximately 40 V within the plasma bulk, which confines electrons while simultaneously accelerating ions toward the electrodes. We show that, under these resonant conditions, collisionless electron heating exhibits a fundamentally different behavior from the conventional paradigm of stochastic sheath heating mediated by electron$-$sheath interactions. Instead, the predominant energy transfer mechanism is bulk electron heating in RF electric fields via a primarily collisionless process that emerges from the synergistic action of: (i) a strongly amplified RF electric field within the plasma bulk, (ii) electron oscillatory motion (bouncing) within the plasma potential well, and (iii) electron scattering resulting from collisions with neutral atoms. Collectively, these phenomena give rise to a pronounced high$-$energy tail in the electron energy distribution function and thereby lead to a substantial enhancement of the ionization rates. As the gas pressure rises, the resonance is disrupted. At the same time, the region of maximum power absorption moves from the plasma core toward the edges and the sheath, which is accompanied by the disappearance of the high$-$energy electron population and a corresponding decrease in ionization rates

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↗

arXiv2026

Multigrid Poisson Solver for Complex Geometries Using Finite Difference Method

We present an efficient numerical method, inspired by transformation optics, for solving the Poisson equation in complex and arbitrarily shaped geometries. The approach operates by mapping the physical domain to a uniform computational domain through coordinate transformations, which can be applied either to the entire domain or selectively to specific boundaries inside the domain. This flexibility allows both homogeneous (Laplace equation) and inhomogeneous (Poisson equation) problems to be solved efficiently using iterative or fast direct solvers, with only the material parameters and source terms modified according to the transformation. The method is formulated within a finite difference framework, where the modified material properties are computed from the coordinate transformation equations, either analytically or numerically. This enables accurate treatment of arbitrary geometric shapes while retaining the simplicity of a uniform grid solver. Numerical experiments confirm that the method achieves second-order accuracy , and offers a straightforward pathway to integrate fast solvers such as multigrid methods on the uniform computational grid.

math.NA↗

arXiv2025

Resonantly Driven Electron Bernstein Waves in Magnetized Low-Pressure Capacitive Discharges

The physics of capacitively coupled plasma (CCP) discharges is investigated in a mildly magnetized regime, defined by $1 \le f_{ce}/f_{rf} < 2$, where $f_{ce}$ and $f_{rf}$ denote the electron cyclotron frequency and the applied radio-frequency (RF), respectively. A distinctive feature of this regime is the excitation of electron Bernstein waves (EBWs) that propagate into the bulk plasma. As the applied magnetic field increases, notable changes in the discharge characteristics occur, with EBWs observed to propagate along the plasma density gradient inside the bulk. The underlying physics of CCP operation in this regime is analyzed in detail using particle-in-cell Monte Carlo collisions (PIC-MCC) simulations.

physics.plasm-ph↗

arXiv2025

Simulation Studies of Resonant Excitation of Electron Bernstein Waves in Capacitive Discharges

The behavior of capacitive coupled plasma (CCP) discharges is investigated in a mildly magnetized regime, defined by the condition 1 $\leq$ $f_{ce}/f_{rf}$ $\lt$ 2, where $f_{ce}$ and $f_{rf}$ are the cyclotron and radio-frequencies (RF), respectively. This regime exhibits complex and distinctive plasma dynamics due to the interplay between RF fields and the externally applied magnetic field. Two prominent phenomena are observed in this regime. First, the plasma density profile becomes asymmetric across the discharge, deviating from the typical symmetric distribution seen in unmagnetized CCPs. Second, electron Bernstein waves (EBWs), high-frequency electrostatic waves, are excited and propagate within the bulk plasma, particularly along steep electron density gradients. As the strength of the magnetic field increases within this regime, the CCP discharge undergoes a transition from a symmetric configuration to an asymmetric one, and then returns to a symmetric profile at higher field strengths. Notably, the excitation and propagation of EBWs are strongly correlated with the presence of discharge asymmetry and localized density gradients. These waves play a significant role in energy transport and electron heating under mildly magnetized conditions. To gain deeper insight into the underlying physics, detailed numerical simulations are carried out using the particle-in-cell Monte Carlo collision (PIC-MCC) technique. These simulations capture the kinetic behavior of electrons and ions, including the collisionless effects and sheath dynamics essential to understanding the excitation of EBWs and the evolution of discharge symmetry. The study thus sheds light on the role of weak magnetic fields in shaping plasma behavior and highlights the importance of wave-particle interactions in magnetized CCPs.

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↗

arXiv2023

Novel Instabilities in Counter-Streaming Nonabelian Fluids

The dynamics of strongly interacting particles are governed by Yang-Mills (Y-M) theory, which is a natural generalization of Maxwell Electrodynamics (ED). Its quantized version is known as quantum chromodynamics (QCD) and has been very well studied. Classical Y-M theory is proving to be equally interesting because of the central role it plays in describing the physics of quark-gluon plasma (QGP)-which was prevalent in the early universe and is also produced in relativistic heavy ion collision experiments. This calls for a systematic study of classical Y-M theories. A good insight into classical Y-M dynamics would be best obtained by comparing and contrasting the Y-M results with their ED counterparts. In this article, a beginning has been made by considering streaming instabilities in Y-M fluids. We find that in addition to analogues of ED instabilities, novel nonabelian modes arise, reflecting the inherent nonabelian nature of the interaction. The new modes exhibit propagation/ growth, with growth rates that can be larger than what we find in ED. Interestingly, we also find a mode that propagates without getting affected by the medium.

physics.plasm-ph↗