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• Holen, Gaute Arnesson; Mishra, Rinku; Miyake, Y. & Miloch, Wojciech Jacek (2026). Ion trapping around small positively charged objects in magnetized plasma. Physics of Plasmas. ISSN 1070-664X. 33(5). doi: 10.1063/5.0309574. Full text in Research Archive Show summary

  We present a novel trapping mechanism for ions around small positively charged objects in magnetized plasma. Here, the Larmor radius is larger than the object, but approximately equal to the characteristic radial length of the object's electrostatic structure. The resulting steady state solution from state-of-the-art particle-in-cell simulations shows a bipolar electric field around the object, with a density enhancement in the quasi-neutral region. Test particle simulations explore the mechanism behind the ion trapping by focusing on single-particle-motion, and transforming the particles to gyro-center, Larmor radius space. We also observe a kinetic energy gradient in the quasi-neutral region, where the ions organize themselves with respect to distance from the object according to their velocity, where the gyro-centers of particles are nearly coincident with the object's position. This leads to a shift in the velocity distribution. Analysis of test particles' temporal evolution in the gyro-center, Larmor radius space reveals regions of instability and stability, which correspondwell with the density enhancement and ion depletion. The results are similar for spherical and cylindrical objects, suggesting that the trapping mechanism is fundamental. These findings have implications for understanding plasma interactions with small objects, with potential applications in space physics, fusion devices, and plasma diagnostics.

• Holen, Gaute Arnesson; Mishra, Rinku; Miyake, Y. & Miloch, Wojciech Jacek (2026). Numerical method for dynamic dust charge in molecular dynamics simulations of laboratory and lunar dusty plasma environments. Physics of Plasmas. ISSN 1070-664X. 33(8), p. 083703-1–083703-14. doi: 10.1063/5.0320581. Full text in Research Archive
• Mishra, Rinku; Moulick, R.; Adhikari, Sayan; Marholm, Sigvald; Eklund, Anders Johan & Miloch, Wojciech Jacek (2024). Beam–plasma dynamics in finite-length, collisionless inhomogeneous systems. Physics of Plasmas. ISSN 1070-664X. 31(10). doi: 10.1063/5.0218386. Full text in Research Archive Show summary

  This study investigates the streaming instability triggered by ion motion in a plasma system that is finite in length, collisionless, and inhomogeneous. Employing numerical simulations using particle-in-cell techniques and kinetic equations, the study examines how inhomogeneity emerges from integrating a cold ion beam with a background plasma within a confined system. The findings suggest that steady ion flow can modify ion sound waves through acoustic reflections from system boundaries, leading to instability. Such phenomena are known to be a hydrodynamic effect. However, there are also signatures of the beam-driven ion sound instability where kinetic resonances play a pivotal role. The main objective is to understand the impact of a finite-length system on beam–plasma instability and to identify the wave modes supported in such configurations.

• Holen, Gaute Arnesson; Adhikari, Sayan; Mishra, Rinku & Miloch, Wojciech Jacek (2024). Self-organising phenomena in 2D complex plasma simulations withnon-mono dispersed dust size distributions. Physica Scripta. ISSN 0031-8949. 99(5). doi: 10.1088/1402-4896/ad37dd. Full text in Research Archive Show summary

  Complex plasma with a variety of continuous and discrete dust grain size distributions are simulated in 2D with molecular dynamics simulations with radial geometry to determine differences in self-organizing phenomena to more realistically represent the actual in situ variations in dust-size. The standard deviation of particle size σ(a) strongly correlates with phase separation and coupling parameter Γ for all distribution types. We observe local differences in bond order parameters and Voronoi diagrams for different size distributions, and our results suggest that phase transition is affected by continuous size distributions, particularly in the binary distribution case. Simulations with discrete size result in artifacts and discontinuities that are not found in the continuous distributions. The use of continuous distributions is observed to be beneficial both for more realistic approximation of complex plasma experiments and to study systems of strongly coupled particles in general.

• Brask, Steffen Mattias; Mishra, Rinku; Holen, Gaute Arnesson; Miyake, Y.; Usui, H. & Miloch, Wojciech Jacek (2024). Spherical Langmuir probes in magnetized plasma. A model based on particle-in-cell simulations. Physics of Plasmas. ISSN 1070-664X. 31(2). doi: 10.1063/5.0177775. Full text in Research Archive Show summary

  We present a new model for current collected by a spherical Langmuir probe in magnetized plasmas. Data are obtained using state-of-the-art fully 3D kinetic particle-in-cell simulations. We perform a dimensional analysis and use it to determine the appropriate model function. The model is then empirically derived based on the simulation data for a range of probe potentials and magnetic field values with respect to the Debye length. The final model function is applicable to most space plasmas and can easily be generalized.

• Mishra, Rinku & Dey, M (2019). Dust charging and propagation of dust-acoustic waves in a multicomponent thermal dusty plasma system. IEEE Transactions on Plasma Science. ISSN 0093-3813. 47(1). doi: 10.1109/TPS.2018.2879499. Full text in Research Archive
• Mishra, Rinku & Dey, M (2018). Propagation of electrostatic surface wave along the dust void boundary. Physica Scripta. ISSN 0031-8949. 93(8), p. 085601–085601. doi: 10.1088/1402-4896/aace66. Full text in Research Archive
• Mishra, Rinku & Dey, M (2018). Propagation of high frequency electrostatic surface waves along the planar interface between plasma and dusty plasma. Physica Scripta. ISSN 0031-8949. 93(4). doi: 10.1088/1402-4896/aaaa8d. Full text in Research Archive
• Mishra, Rinku; Adhikari, Sayan; Mukherjee, Rupak & Dey, M (2018). Correlation between two non-linear events in a dusty plasma system. Physics of Plasmas. ISSN 1070-664X. 25. doi: 10.1063/1.5066427. Full text in Research Archive
• Das, Mrinal Kumar; Borah, Debasish & Mishra, Rinku (2012). Quasidegenerate neutrinos in type II seesaw models. Physical Review D. ISSN 2470-0010. 86(9), p. 095006–095006. doi: 10.1103/PhysRevD.86.095006. Full text in Research Archive

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• Mishra, Rinku & Dey, M (2018). Dynamics of dust void boundary under the effect of dust acoustic pressure. Full text in Research Archive
• Holen, Gaute Arnesson; Miloch, Wojciech Jacek & Mishra, Rinku (2026). Plasma-object interaction in plasma environments: Numerical studies of spacecraft charging, probe accuracy and complex plasma. Universitetet i Oslo. Full text in Research Archive Show summary

  The majority of space is made up of a sea of plasma, with island of solid matter such as planets, moons, dust, spacecraft or even astronauts. Immersing any solid object in plasma results in electric charging of the object, as well as significant disturbances to the surrounding plasma. Understanding the plasma-object interaction is crucial for many situations, including reliable operation of scientific instrumentation on sounding rockets and satellites. This thesis has developed a complementary set of numerical codes to simulate and study the plasma-object interaction. These codes were used to simulate sounding rockets, probes and daughter-payloads in the ionosphere, as well as the lunar surface and ensembles of dust particles, allowing us to study the plasma-object interaction from different perspectives. We uncover a new trapping mechanism for ions in magnetized plasma interacting with an object using a new analytical approach and validate the daughter-payload instrumentation on the ICI-5b sounding rocket mission. Simulations of dusty plasmas show that its spatial and temporal evolution and resulting dust structure is sensitive to small charge changes. Our studies provide new insights to the complex dynamics of objects in plasma, both for specific applications and for the fundamental understanding of objects in plasma.

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