arXiv subjects

Mohammad Hossein Mahdieh

Publications and source records attributed to Mohammad Hossein Mahdieh.

4 recordsLinked to original sources

arXiv2026

Multi-Objective Design of C-Shaped Targets for Energy--Divergence Control in Laser-Driven Proton Acceleration

We optimize the energy-divergence trade-off of laser-driven protons from a C-shaped target using two-dimensional particle-in-cell simulations and constrained multi-objective Bayesian optimization. Five geometry and focusing parameters are varied to maximize proton cutoff energy and minimize the RMS divergence of forward protons with E_k >= 5 MeV under a proton-only conversion-efficiency constraint of eta_H >= 9%. Of 82 designs, 60 are feasible and 15 Pareto-optimal. The Max-Energy and Min-Divergence endpoints yield 28.64 MeV at 52.51 degrees and 11.47 MeV at 11.13 degrees, respectively; a representative compromise yields 21.44 MeV at 38.44 degrees. Matched-stage diagnostics link these regimes to optical-field buildup, electron energization, charge separation, and outer-sheath organization. Numerical tests support the principal trends. Reflection timing does not support a monotonic trapping-duration law, and the charge-sheath relation remains non-local. These results establish a design-resolved route to controlling proton energy and angular quality.

physics.acc-ph↗

arXiv2026

Enhanced TNSA Ion Acceleration via Optical Confinement and Geometric Plasma Focusing in Annular Sector Targets

Enhancing the conversion efficiency and maximum energy of laser-driven ion beams is a critical challenge for applications in hadron therapy and high-energy density physics. In this work, we present a comprehensive two-dimensional Particle-In-Cell (PIC) simulation study comparing Target Normal Sheath Acceleration (TNSA) from standard flat foils and novel annular sector (C-shaped) targets. Under identical ultra-intense laser irradiation (a0=10, tau=25 fs), the annular sector geometry demonstrates a substantial enhancement in acceleration performance driven by two synergistic mechanisms: electromagnetic cavity confinement and geometric plasma focusing. Our analysis reveals that the target void acts as an optical trap, sustaining oscillating electromagnetic fields for over 300fs via multiple internal reflections. This confinement results in a total laser energy absorption of 49% (compared to 16% for flat targets), which yields a peak electron temperature of 5.1 MeV more than double the 2.2MeV observed in flat targets. Furthermore, phase space diagnostics confirm that ion bunches accelerated from the converging cavity walls superimpose at the geometric center, creating a localized high-density focal spot. Consequently, the annular target increases the proton cut-off energy to 22MeV (vs. 12MeV for flat targets) and boosts Carbon ion energies beyond 60MeV. These findings establish that tailoring target curvature to exploit optical trapping and geometric focusing offers a robust pathway for developing compact, high-efficiency laser-ion sources.

physics.plasm-ph↗

arXiv2022

The Compressive and rarefactive dust acoustic solitary waves with two different temperatures for both electrons and ions

The nonlinear propagation of dust acoustic solitary waves (DASWs) in an unmagnetized dusty plasma consisting of negatively charged dust fluid Boltzmann distributed electrons with two different temperatures Boltzmann distributed ions with two distinct temperatures are investigated. By employing the reductive perturbation technique that is valid for a small but finite amplitude limit the Korteweg de Vries (K-dV) equation have been derived. Our results reveal that the main quantities of DASWs (such as amplitude and width) are affected by two different temperatures electrons (as well as ions) temperature ratios and the number densities of two species of ions. It is shown that both positive and negative potential DASWs occur in this case.

physics.plasm-ph↗

arXiv2021

Precise design of VO2 thin films for smart windows by employing thickness dependent refractive index

Vanadium dioxide (VO2) is an adjustable refractive index material and has capability of behaving as semiconductor or conductor depending on its temperature. Such condition makes it as a material which can be employed in fabricating thermochromic smart windows. The transmission characteristics of these type of windows strongly depend on the thickness of the film. Therefore, some calculations are required to optimize the VO2 thickness. Unfortunately, refractive index of VO2 thin film is thickness dependent, therefore, in calculating the transmission of light spectrum from VO2 thin films, a unique refractive index cannot be utilized. In the present paper using three theoretical models (Lorentz-Drude oscillator, Lorentz oscillator, and Tauc-Lorentz) and employing experimental results from previous reports, we provide a collection of thickness dependent refractive index of VO2 films. More precise transmission can be achieved by using this set of refractive index data in the calculations which agree with those of experiments. These results also fairly make us capable to determine optimized film thickness for any desired transmission performance. This method is useful for design of VO2 based thermochromic smart windows.

physics.optics↗