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• Brask, Steffen Mattias; Marholm, Sigvald; Miloch, Wojciech Jacek & Marchand, R. (2024). Effects of guard and boom on needle Langmuir probes studied with particle-in-cell simulations. Journal of Plasma Physics. ISSN 0022-3778. 90(1). doi: 10.1017/S0022377823001411. Full text in Research Archive Show summary

  We investigate the effects of different guard geometries on the currents to needle-type Langmuir probes. The results are based on particle-in-cell numerical simulations. We show that if the guard length is less than 6–8 Debye lengths there can be a significant effect on the currents to the probe. A guard radius should not be larger than the Debye length, otherwise it can also significantly affect the currents. However, since guard radii are often close to the probe radius, the second condition is usually satisfied.

• 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.

• Brask, Steffen Mattias; Marholm, Sigvald; Mare, Francesca Di; Adhikari, Sayan; Spicher, Andres & Takahashi, T. [Show all 7 contributors for this article] (2022). Electron-neutral collisions effects on Langmuir probe in the lower E-region ionosphere. Physics of Plasmas. ISSN 1070-664X. 29(3). doi: 10.1063/5.0079761. Full text in Research Archive Show summary

  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 <i>𝜆��𝑒��/𝜆��𝐷��→1</i>, where <i>λe</i> is the electron mean free path and <i>λD</i> 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.

• Jin, Yaqi; Kotova, Daria; Xiong, Chao; Brask, Steffen Mattias; Clausen, Lasse & Kervalishvili, Guram [Show all 8 contributors for this article] (2022). Ionospheric Plasma IRregularities - IPIR - data product based on data from the Swarm satellites. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 127(4). doi: 10.1029/2021JA030183. Full text in Research Archive
• Jin, Yaqi; Xiong, Chao; Clausen, Lasse Boy Novock; Spicher, Andres; Kotova, Daria & Brask, Steffen [Show all 9 contributors for this article] (2020). Ionospheric Plasma Irregularities Based on In Situ Measurements From the Swarm Satellites. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 125(7). doi: 10.1029/2020JA028103. Full text in Research Archive Show summary

  In this study, we present global climatological distributions of ionospheric plasma irregularities based on measurements by the Swarm satellites. These first global statistics obtained by direct, in situ measurements of plasma variations with Swarm confirm the presence of three main regions of strong ionospheric irregularities: the magnetic equator extending from postsunset to early morning, in the auroral ovals (from dayside cusp to nightside), and inside the polar caps. At equatorial latitudes, ionospheric irregularities form two bands of enhanced plasma fluctuations centered around ±10° magnetic latitude. Due to different plasma processes, ionospheric irregularities at high and low latitudes show different distributions. Though the averaged intensity of plasma irregularities is weaker at equatorial latitudes than at high latitudes, the occurrence rate of significant plasma fluctuations (corresponding to extreme events) is much higher at the equator than that at high latitudes. Equatorial irregularities display clear seasonal and longitudinal variations; that is, they are most prominent over South America during the December solstice and are located over Africa during the June solstice. The magnitude of ionospheric irregularities at all latitudes is strongly controlled by the solar activity. Ionospheric irregularities become significantly weaker after 2016 during the current declining phase of solar activity. The interplanetary magnetic field Bz modulates the occurrence of ionospheric irregularities at both high and low latitudes.

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• Kotova, Daria; Jin, Yaqi; Brask, Steffen Mattias; Spogli, Luca; Wood, Alan G. & Miloch, Wojciech Jacek (2022). Comparison of electron density fluctuations measured by Swarm satellites with the ground-based scintillation data. Full text in Research Archive
• Kotova, Daria; Jin, Yaqi; Brask, Steffen; Cilliers, Pierre & Miloch, Wojciech Jacek (2020). Comparison of characteristics of electron density fluctuations from Swarm satellites with the ground-based scintillation data. Full text in Research Archive
• Miloch, Wojciech Jacek; Jin, Yaqi; Xiong, Chao; Brask, Steffen Mattias; Kotova, Daria & Kervalishvili, Guram [Show all 9 contributors for this article] (2020). Ionospheric Plasma IRregularities (IPIR data products). Full text in Research Archive
• Miloch, Wojciech Jacek; Kotova, Daria; Jin, Yaqi; Xiong, Chao; Brask, Steffen & Kervalishvili, Guram [Show all 9 contributors for this article] (2019). Ionospheric plasma irregularities studied globally with the Swarm satellites. Full text in Research Archive
• Brask, Steffen Mattias; Miloch, Wojciech Jacek; Miyake, Yohei & Usui, Hideyuki (2024). Numerical Study of Langmuir Probes: Improving Accuracy Using PIC Simulations. Universitetet i Oslo. Full text in Research Archive Show summary

  Did you know that in the vacuum of space, there is no vacuum? In fact, most of space is filled with charged particles in a plasma state. Close to Earth, Geomagnetic phenomena, space weather, and radio interference such as GPS scintillation are all explained with plasma dynamics. Space is also the largest laboratory we have for plasma physics. It is, therefore, no surprise that accurate measurements of the surrounding plasma of a spacecraft are a part of the foundation for understanding our own ionosphere. A common approach to probing a plasma is with Langmuir probes, which are conducting objects that collect an electrical current, from which we can infer plasma parameters, usually using orbital-motion-limited (OML) theory. It is known that OML will be erroneous under certain conditions. However, due to the complexity and scales of the problem, several sources of error have not been adequately studied and are therefore not well understood or accounted for. In this dissertation, we use Particle-in-Cell simulations to further our understanding by uncovering limits to the idealized OML theory and building models to correct several such error sources. The thesis focuses on charged-neutral collisional effects, the effects of imperfect geometries, and probes in magnetized plasmas.

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