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Blog Post number 4
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publications
Experimental study of charging of dust grains in the presence of energetic electrons
Published in Physica Scripta, 2021
A low-pressure magnetized plasma is studied to find the dependency of sheath properties on ion-neutral collisions in presence of an inhomogeneous magnetic field. A self-consistent one-dimensional two-fluid hydrodynamic model is considered, and the system of equations is solved numerically. The study reveals that the width of the plasma sheath expands and space charge increases with collisions. The ion-neutral collisions and the inhomogeneous magnetic field restrict the ions to move towards the surface. The movement of the ions towards the wall can be controlled by choosing a suitable configuration of the magnetic field and ion-neutral collision frequency. A comparison between two different magnetic field configurations has been presented alongside to differentiate the commonly found scenarios in the field. The outcome of the study is supposed to help in understanding the complex dynamics of ions in plasma confinement and plasma processing of materials. Furthermore, the present work seeks to create a framework for two-fluid modeling of magnetized plasmas with any arbitrary magnetic field profiles. The analysis provided here is supposed to act as a basis for any future work in the respective field.
Recommended citation: Deka, K and Adhikari, S and Moulick, R and Kausik, SS and Saikia, BK "Effect of collisions on the plasma sheath in the presence of an inhomogeneous magnetic field", Physica Scripta 96, 075606 (2021). https://doi.org/10.1088/1361-6595/ac4c4b
Experimental study of charging of dust grains in the presence of energetic electrons
Published in Plasma Physics and Controlled Fusion, 2022
A two-electron temperature plasma is produced by the method of diffusion of two different plasmas with distinct temperatures and densities. The method is simple and provides an adequate control over the plasma parameters. The study reveals that the temperature and density of both the electron groups can be effectively controlled by just changing the discharge currents of both the plasmas. An ion-acoustic wave is excited in the plasma and is detected using a planar Langmuir probe. The damped amplitude of the wave is measured and is used as a diagnostic tool for establishing the presence of two-electron components. This production method can be helpful in controlling the hot electron density and temperature in plasma processing industries.
Recommended citation: Sharma, Gunjan and Deka, Kishor and Paul, Rupali and Adhikari, Sayan and Moulick, Rakesh and Kausik, Siddhartha Sankar and Saikia, BK "Experimental study on controlled production of two-electron temperature plasma", Plasma Sources Science and Technology 31, 025013 (2022). https://doi.org/10.1088/1361-6595/ac4c4b
Experimental study of charging of dust grains in the presence of energetic electrons
Published in Plasma Physics and Controlled Fusion, 2022
The role of hot electrons in the charging of dust grains is investigated in a two-temperature hydrogen plasma. A variety of dust particles are introduced into the system and secondary electron emission (SEE) from each of the dust grains has been reported. A cylindrical Langmuir probe is used for determining the plasma parameters and a Faraday cup is connected to an electrometer in order to measure the dust current. The electrometer readings confirm the electron emission from the dust and SEE is observed from the tungsten dust in a low-pressure experimental plasma device for the first time.
Recommended citation: Paul, Rupali and Sharma, Gunjan and Deka, Kishor and Adhikari, Sayan and Moulick, Rakesh and Kausik, Siddhartha Sankar and Saikia, BK, "Experimental study of charging of dust grains in the presence of energetic electrons", Plasma Physics and Controlled Fusion 64, 035009 (2022). https://doi.org/10.1088/1361-6587/ac44e5
Current-driven Langmuir Oscillations and Streaming Instabilities
Published in Arxiv, 2022
The Buneman and ion acoustic instabilities are usually associated with different electron and ion drift velocities, in such a way that there is a large current through the plasma. However, due to the recently discovered current-driven Langmuir oscillations (1-3), the relative drift velocity in these configurations will oscillate at the plasma frequency, and with an amplitude of at least the initial drift velocity. In contrast, the textbooks assume a constant drift velocity. Since the growth rates arrived at under that assumption are far less than the plasma frequency, several oscillation periods will take place during the linear growth phase, and this will dampen the instabilities. We provide general theoretical derivations of these oscillations, and show simulation results of the altered behavior of the instabilities. Towards the end, we hypothesize that drift-averaging might be a viable method of calculating the modified growth rates.
Recommended citation: S. Marholm, S. Adhikari, and W. J. Miloch , "Current-driven Langmuir Oscillations and Streaming Instabilities", Arxiv (2022). https://arxiv.org/pdf/2203.07467.pdf
Electron–neutral collisions effects on Langmuir probe in the lower E-region ionosphere
Published in Physics of Plasmas, 2022
We present the first set of particle-in-cell simulations including Monte Carlo collisions between charged and neutral particles used to simulate a cylindrical Langmuir probe in the electron saturation regime with a collisional electron sheath. We use a setup focused on the E-region ionosphere; however, the results of these simulations are analyzed in a general sense using dimensionless values. We find that the electron currents get enhanced as the collision frequency for electrons increases and the values of λe/λD→1, where λe is the electron mean free path and λD is the electron Debye length. In addition, we apply the simulation results to a sounding rocket experiment and show how we can correct the currents for the Investigation of Cusp Irregularities-4 sounding rocket due to collisions while it flies through the E-region.
Recommended citation: S. M. Brask, S. Marholm, F. Di Mare, S. Adhikari, A. Spicher, T. Takahashi, and W. J. Miloch , "Electron–neutral collisions effects on Langmuir probe in the lower E-region ionosphere", Physics of Plasmas 29, 033511 (2022). https://aip.scitation.org/doi/pdf/10.1063/5.0079761
Current-driven Langmuir Oscillations and Streaming Instabilities
Published in Arxiv, 2022
The Buneman and ion acoustic instabilities are usually associated with different electron and ion drift velocities, in such a way that there is a large current through the plasma. However, due to the recently discovered current-driven Langmuir oscillations (1-3), the relative drift velocity in these configurations will oscillate at the plasma frequency, and with an amplitude of at least the initial drift velocity. In contrast, the textbooks assume a constant drift velocity. Since the growth rates arrived at under that assumption are far less than the plasma frequency, several oscillation periods will take place during the linear growth phase, and this will dampen the instabilities. We provide general theoretical derivations of these oscillations, and show simulation results of the altered behavior of the instabilities. Towards the end, we hypothesize that drift-averaging might be a viable method of calculating the modified growth rates.
Recommended citation: S. Marholm, S. Adhikari, and W. J. Miloch , "Current-driven Langmuir Oscillations and Streaming Instabilities", Arxiv (2022). https://arxiv.org/pdf/2203.07467
Effect of external magnetic field and dust grains on the properties of Ion Acoustic Waves
Published in Under Review, 2022
An experimental study to investigate the effect of an external magnetic field on the propagation of ion-acoustic waves (IAWs) has been carried out in hydrogen plasma containing two-temperature electrons and dust grains. A low-pressure hot cathode discharge method is opted for plasma production. The desired two electron groups with distinct temperatures are achieved by inserting two magnetic cages with a cusp-shaped magnetic field of different surface field strengths in the same chamber. The dust grains are dropped into the plasma with the help of a dust dropper, which gain negative charges by interacting with the plasma. The IAWs are excited with the help of a mesh-grid inserted into the plasma. A planar Langmuir probe is used as a detector to detect the IAWs. The time of flight technique has been applied to measure the phase velocity of the IAWs. The results suggest that in the presence of a magnetic field, the phase velocity of IAWs increases, whereas introducing the dust particles leads to the lower phase velocity. The magnetic field is believed to have a significant effect on the wave damping. This study will aid in utilising IAWs as a diagnostic tool to estimate plasma parameters in the presence of an external magnetic field. Moreover, the study might be useful for estimating the relative ion concentrations in a two positive ion species plasma, as well as the relative concentration of the negative ions in the presence of an external magnetic field.
Recommended citation: Deka, K. and Paul, R. and Sharma, G. and Das, N. and Adhikari, S. and Moulick, R. and Kausik, S. S. and Saikia, B. K. and Chin, O. H. and Wong, C. S. . "Effect of external magnetic field and dust grains on the properties of Ion Acoustic Waves " arXiv (2022). https://arxiv.org/pdf/2203.16814.pdf
talks
Kinetic effects in magnetized plasma sheaths
Published:
An insider’s look at space missions
Published:
teaching
FYS4620 – An Introduction to Plasma Physics
Postgraduate course, University of Oslo, Department of Physics, 2022
The course covers basic principles on plasmas, waves in plasma, stability analysis of the equilibrium solutions of the equations. Examples are taken from the phenomena in the Earth’s ionosphere and magnetosphere.