Hello, I'm

Hari

I like creating mathematical models

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Field Interest

Plasma Physics
HED Physics
Mathematical Physics

Personal Interest

Programming
Startups
Mathematical art

Completed

7 Papers
5 Conferences

Expertise

Theory
Simulation

I'm fascinated by nature and computational machines. I have combined them by simulating nature with computational machines. A quick learner with deep experience in theoretical, computational, and experimental physics. Always up for solving a challenging problem.

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Skills

Programming

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C++

Advanced
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Python

Advanced
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OpenMPI

Intermediate
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MatLab

Intermediate
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HTML

Intermediate
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CSS

Intermediate
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Javascript

Intermediate
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Fortran

Basic

Frameworks/Tools

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Qt C++

Advanced
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Nuxt JS

Advanced
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FastAPI

Intermediate
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PostgreSQL

Intermediate
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Docker

Intermediate
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git

Intermediate

Field Specific

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Particle
-in-
Cell

Advanced
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Plasma Fluid
Simulation

Advanced
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Molecular
Dynamics

Intermediate
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Perturbation/
Wave Theory

Intermediate
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Laser Diag.:
B Dot

Basic
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Laser Diag.:
Thomson
Parabola

Basic

Qualifications

Education

PhD In Aerospace Engineering

Tohoku University, Japan GPA: 3.8/4.0 2020 - 2023 (Expected)

M.Sc in Aerospace Engineering

Tohoku University, Japan GPA: 3.2/4.0 2018 - 2020

B.Tech in Aerospace Engineering

Amrita University, India GPA: 3.1/4.0 2013 - 2017

Experience

Simulation Engineer

JSOL Corporation, Tokyo, Japan 2023/4 - current

JSPS Postdoc Researcher

Tohoku University, Sendai, Japan 2023/10 - 2024/3

Undergraduate Mentor

Tohoku University, Japan 2020 - 2024

Student Research Assistant

Amrita University, India 2015 - 2017

Awards

JSPS Research Fellowship

Japan Issued by Japan Society for the Promotion of Science 2022 - 2024

MEXT Scholarship

Japan Issued by Japanese Ministry of Education, Culture, Sports, Science and Technology 2017 - 2022

Winner of One-Size-Fits-All: X-ray Plate Adapter Challenge

U.S.A/India Issued by General Electric Oil & Gas 2017

Publications

2024 | Publication | Scientific Reports |

Integrating sheath and radiation-based acceleration using scaling coefficients for tailoring radiation dominant hybrid acceleration


Kumar H S, Takahashi M, Kuramitsu Y, and Ohnishi N

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Abstract

An optimal target condition for generating GeV-energy ions with linearly polarized laser pulse is revealed by a hybrid acceleration theory based on the fractional contributions of the target normal sheath acceleration (TNSA) and the radiation pressure acceleration (RPA) mechanisms in the RPA-dominant regime. The theory is established with two scaling coefficients, which scale the TNSA and RPA velocities, and are sophisticated through two-dimensional particle-in-cell simulations where GeV-energy ions are obtained by RPA-dominant hybrid acceleration. By imposing limits on the scaling coefficients, three separate acceleration regions are obtained including a RPA-dominant acceleration region, which is optimal to generate GeV-energy ions. The past experiment/simulation results are in good agreement with the acceleration regions obtained. This RPA-dominant region is narrower than previously reported, and this region becomes even narrower with increasing material density.
https://www.nature.com/articles/s41598-024-72623-5

2024 | Publication | High Energy Density Physics |

A hybrid simulation integrating molecular dynamics and particle-in-cell methods for improved laser-target interaction


Kumar H S, Takahashi M, Kuramitsu Y, Minami T, Kiriyama H, Fukuda Y, and Ohnishi N

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Abstract

Ultra-thin targets (less than 10 nm), such as graphene, can be irradiated with relativistic intensity lasers to generate energetic ions. However, the laser prepulse can prematurely destroy these targets and significantly influence the final ion energies. Due to the limitations of the conventional hydrodynamic model, simulating the interaction between ultra-thin targets and a prepulse is infeasible. To overcome this issue, we propose a hybrid simulation technique in this study. This technique involves simulating the target-prepulse interaction using molecular dynamics (MD) simulation, which is then combined with the particle-in-cell simulation for the target-main pulse interaction, in order to accurately model the entire laser-target interaction dynamics. A realistic, experimentally measured laser intensity profile for the prepulse is used for the MD simulation, and the particle energies from this hybrid simulation are found to be in good agreement with the experiment.
https://www.sciencedirect.com/science/article/abs/pii/S1574181824000739

2024 | Publication | Chaos |

Characterization of stability of dynamic particle ensemble systems using topological data analysis


Kumar H S

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Abstract

Holes are ubiquitous structures in phase space, and their time evolution could indicate an instability in the dynamics of the system. However, the properties of these holes are difficult to study directly due to their theoretical complexity and lack of computational tools. This study proposes the use of persistent homology (PH), a technique from topological data analysis, as a computational tool for analyzing the properties of these phase-space holes, or more formally the H1 homology class according to PH. Initially, by using a toy data set, it is shown that the time evolution and the growth rate of a H1 class in phase space could be obtained by PH. For further validation, PH is applied to particle ensemble systems, such as the Hamiltonian flow and the two-stream instability (TSI). Both the stable case, where no H1 forms, and the unstable case, where H1 forms, were analyzed. It was shown that PH can distinguish between the stable and unstable cases purely from the phase-space time evolution plots. In unstable TSI, the PH also distinguished the transition of the H1 class from linear to non-linear growth. The growth rate, thus, obtained is in excellent agreement with the growth rate of the particle energy in the TSI system.
https://doi.org/10.1063/5.0177180

2022 | Conference | HEDLA |

A Coupling Simulation Integrating Molecular Dynamics and Particle-in-Cell Methods for Accurate Intense Laser-Target Simulations


Kumar H S, Takahashi M, Kuramitsu Y, Minami T, and Ohnishi N

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Abstract

The irradiation of an intense laser on thin targets generate energetic ions in experiments, which has also been replicated using particle-in-cell (PIC) simulations. However, the ion energies obtained in simulations are sometimes significantly higher than the experiments. This discrepancy was also noticed in a recent experiment involving the ultra-intense JKAREN laser (without plasma mirrors). In the corresponding PIC simulations, assumptions regarding the target expansion due to the pre-pulse had to be factored, as corrections, to obtain the experimental energies. Thus, modelling the pre-pulse is essential; but the conventional hydrodynamic pre-pulse simulations are not possible due to the ultra-thin nature of the targets. Currently, there exists no framework to successfully integrate the pre-pulse simulation with the main pulse, especially for thin targets, since the scales and the physics of the simulations involved are vastly different. In this study, we propose a coupling scheme to integrate the pre-pulse; simulated through the molecular dynamics (MD) approach, with the main pulse simulated using the PIC method. The intensity of the laser pre-pulse is usually < 1E+11 W/cm2, even for a laser like JKAREN (I = 1E+21 W/cm2) without plasma mirrors. In this regime, the atomic physics is dominant and hence the use of MD for pre-pulse simulation is reasonable. Following the experiment, a 3D graphene target was created in MD (using LAMMPS) and irradiated (energy deposition) by an experimentally obtained pre-pulse profile, leading to the target’s deformation. A section of the deformed target is then imported to the 2D PIC environment (EPOCH) through a density interpolation scheme and is simulated for the main pulse conditions. The ion energy spectrum thus obtained is in good agreement with the experiment as compared to the previous results suggesting that the proposed method realistically captures the physics behind the experiment without assuming target pre-expansion.
https://hedla.tecnico.ulisboa.pt/documents/abstracts/7IcjwPeShQ.pdf

2022 | Journal | Sci. Rep. |

Robustness of Large-Area Suspended Graphene under Interaction with Intense Laser


Kuramitsu Y, Minami T, ... Kumar H S, Ohnishi N, et al.

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Abstract

Graphene is known as an atomically thin, transparent, highly electrically and thermally conductive, light-weight, and the strongest 2D material. We investigate disruptive application of graphene as a target of laser-driven ion acceleration. We develop large-area suspended graphene (LSG) and by transferring graphene layer by layer we control the thickness with precision down to a single atomic layer. Direct irradiations of the LSG targets generate MeV protons and carbons from sub-relativistic to relativistic laser intensities from low contrast to high contrast conditions without plasma mirror, evidently showing the durability of graphene.
https://doi.org/10.1038/s41598-022-06055-4

2021 | Journal | Appl. Phys. Lett. |

Kinetic Theory of Double Layers Driven by Temperature Anisotropy in a Non-Homogeneous Magnetic Field


Kumar H S, Takahashi M, Kato C, Oshio Y, and Ohnishi N

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Abstract

A double layer (DL) is created in a plasma when the plasma is perturbed in the presence of a temperature anisotropy. We derive a new simple theory for the existence of an unstable, non-oscillatory electrostatic DL-like structure in the presence of a magnetic field gradient in a collisionless plasma with a temperature anisotropy in the direction perpendicular to the magnetic field. The DL is treated as a wave perturbation in the plasma using kinetic theory with a gyro-kinetic approximation to obtain a dispersion relation. The presence of an electron temperature anisotropy is the necessary condition to obtain an exponentially growing instability, and the corresponding growth rate is found to be the ratio of the electron kinetic energy and the electric field energy across the DL region. The theoretical predictions are then validated against a one-dimensional electrostatic particle simulation carried out in a traveling magnetic field thruster environment. An anisotropy ratio parameter was introduced, and the theoretical growth rates were found to be in good agreement with the simulation for different anisotropy ratios. An ion beam, associated with the DL dynamics, is observed within the simulation domain. A parametric study revealed that the DL-like structure loses its ambipolar shape for temperature ratios less than 10. It has been found that a stronger anisotropy is required to obtain the DL-like structure.
https://doi.org/10.1063/5.0065665

2020 | Journal | Trans. JSASS Aerospace Tech. Japan |

Numerical Simulation of Particle Acceleration in Traveling Magnetic Field Thruster


Kumar H S, Takahashi M, and Ohnishi N

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Abstract

A theoretical and numerical study has been conducted on an electrodeless thruster which uses a traveling magnetic field for effective thrust generation. The physics behind the thrust generation mechanism was studied theoretically, and the theory was validated by 1D electrostatic particle-in-cell simulations. The thrust generation was found to be due to the formation of a Double Layer (DL). The magnetic pulse pushes the electrons in the magnetic front forming a small charge separation. The localized electric fields arising due to this separation causes significant acceleration of the ions, and the electrons in opposite directions. However, this leads to further charge separation, deepening the potential well across leading to the formation of a DL which in turn generates mono-energetic ion beams. The energy required for sustaining the DL is derived from the trapped electrons in the leading front of the DL. The theory predicts a drop in the temperature of trapped electrons. This temperature decrease is confirmed by the electron thermal energy distribution obtained from the simulation.
10.2322/tastj.18.317

2020 | Conference | APS DPP |

Interaction Between a Soliton and a Double Layer in a Traveling Magnetic Field System


Kumar H S, Takahashi M, Kato C, and Ohnishi N

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Abstract

The case of a magnetic pulse traveling through a plasma is studied theoretically. Double layer (DL) and solitons were observed in this system before and it's known that certain DLs decay by emitting solitons. However, the exact trigger mechanism causing this DL-soliton transition is not understood yet. Theoretically, this transition can be treated as a DL-soliton interaction. The soliton and DL KdV equations for the traveling pulse case is derived using the Reductive Perturbation Method (RPM) by considering trapped and free electrons and free ions. RPM is used to reduce nonlinear PDEs using asymptotic expansions. This means the interaction term between the 1st order soliton and the 2nd order DL is usually lost and the system of equations is unclosed. In this study, the closure is achieved by assuming an ion density distribution in the DL and back-substituting the DL parameters into the soliton system as a higher order asymptote. The interaction term thus found is directly proportional to the trapped electron density. A higher trapped electron density means an increased DL-soliton interaction and a decreased chance of DL decay. The interaction is also solitary in nature.
2020APS..DPPJ05002K

2020 | Journal

Studies on Supersonic Cold Spray Deposition of Microparticles using a Bell-Type Nozzle


Kumar H S, Prasad K G, Kothurkar N K, and Srikrishnan A R

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Abstract

Cold spray deposition of micro-particles using a supersonic nozzle is studied using the numerical simulation of the turbulent flow field. A bell-type nozzle geometry is used for injecting the cold particle spray at supersonic velocity. The impact of driver gas pressure, temperature and particle size on critical deposition parameters is studied for transverse and axial injection. The results of the study show that particle velocity at impact is higher for axial injection in comparison to that for transverse injection under similar conditions. The approach of utilizing bell type nozzles for spray deposition is found to be beneficial with regard to the compactness of the system as well as the axial alignment of the spray.
https://doi.org/10.1016/j.surfcoat.2019.125244

Contact Me

Email

kumar.harihara.sudhan.r7@alumni.tohoku.ac.jp Write me