This thesis serves as a preliminary design study for the combination of a flight-proven ion optics system (SWIM) with a conversion surface to create a small energetic neutral atom (ENA) sensor. It is planned to use this sensor as ENA sensor for the DFP-SCIENA instrument on Comet Interceptor. Due to the nature of the Comet Interceptor mission (ESA F-class mission with a maximum launch mass of 1000 kg) the development time for a new sensor that meets the size and weight restrictions is limited. The proposed combination of SWIM with a conversion surface is based on a proven ion optics design and should result in a compact sensor design. The main goal of this thesis was to simulate different conversion surface designs and evaluate their compatibility with the SWIM instrument. During this process the different designs were optimised based on the intermediate simulation results. The simulation process was performed by using SIMION to calculate particle trajectories.  In the end, two different conversion surface designs yielded promising results. With both designs detailed simulations and data analysis were conducted to determine the different properties of the two designs. One of these designs was chosen to be further investigated for use on the Comet Interceptor mission.

Charged particles constantly stream outward from the Sun to fill the solar system. These particles, consisting mainly of protons and electrons, form a plasma called the solar wind. The solar wind interacts with every celestial body in the solar system, giving rise to different phenomena, such as the auro- ras observed at high latitudes on Earth or disruption of the systems onboard artificial satellites.  The general structure of the solar wind has been established several decades ago, however we still do not fully understand how the solar wind properties, like temperature and velocity distribution, evolve as it propagates outward in the solar system. Observations of these properties cannot be explained from a conventional fluid description. In a system approximated as a fluid, particle collisions dictate its thermodynamic state. However, the solar wind is a weakly collisional plasma that deviates from thermodynamic equilibrium. Therefore, the radial evolution of the solar wind properties must be driven by different processes. In particular, wave-particle interactions are an important regulator of the solar wind properties, because of the strong connection between the electromagnetic fields and the charged particles.  In this thesis, we probe how the velocity distribution of solar wind par- ticles evolves as it travels from the Sun to the Earth. Specifically, we study the contribution of waves on the observed solar wind properties at different distances and how these waves can affect the interplanetary environment. We focus on two types of plasma waves frequently observed in the solar wind, Langmuir and ion-acoustic waves. We present their occurrence rates at differ- ent heliocentric distances and suggest wave generation mechanisms based on Solar Orbiter observations. We show that Langmuir waves in the unperturbed solar wind are more commonly observed in regions where the magnetic field magnitude is lower than the background value. Furthermore, we also find that the occurrence rate of ion-acoustic waves is increased in the ramp regions of interplanetary shocks observed at different heliocentric distances, compared to the ion-acoustic wave occurrence rate in the unperturbed solar wind.

A few years ago, the charge-transfer reaction CO2+  +  O ⟶ O+ + CO2 was investigated experimentally for the first time since the study by Fehsenfeld et al., (1970). This new investigation was conducted by Tenewitz et al., (2018). The rate coefficient k < 6 × 10−13 cm3 s−1 , concluded by Tenewitz et al. (2018), differed substantially from the value of 9.6 × 10−11 cm3 s−1 reported by Fehsenfeld et al., (1970). Fox et al., (2021) showed that the old rate constants for the two channels of the CO2+  +  O interaction work much better than the new ones in reproducing chemical features of the Martian ionosphere. Here, we combine MAVEN/NGIMS and TIMED/SEE data to conduct model-observation comparisons of O+ concentrations in the dayside Martian ionosphere. We consider each orbit of the MAVEN Deep Dip 2 (DD2) campaign between 17-22 April 2015. In the model, we balance the production rate of O+ through the aforementioned charge transfer reaction and the photoionisation of O and CO2 , with the loss rate through the reaction O+ + CO2 ⟶ O2+ + CO. We find a better level of agreement between the modelled and the observed O+ concentrations— (i) towards closest approach altitudes (∼ 130 km), and (ii) when using the old rate constant instead of the new one for the charge transfer reaction CO2+ +  O ⟶ O+ + CO2 .

The region of space dominated by the Sun's magnetic field is called the heliosphere. It envelops the entire solar system including Earth. Therefore, a strong coupling exists between the Sun and our planet. The Sun continuously ejects particles, the solar wind, and when these high energy particles hit Earth, the magnetosphere (the region around the Earth governed by the geomagnetic field) is affected. When the solar wind is enhanced this disturbs the magnetosphere and perturbations can be seen also in ground-based observations. The upper atmosphere is subjected to solar radiation that ionise the neutral atoms and molecules, this region is referred to as the ionosphere. In the ionosphere, some of the heavier ion populations, such as O+, are heated and accelerated through several processes and flow upward. In the polar regions these mechanisms are particularly efficient and when the ions have enough energy to escape the Earth's gravity, they move outward along open magnetic field lines and may be lost into interplanetary space. Ion outflow in general has already been well studied, however, ion outflow under extreme magnetospheric conditions has not been investigated in detail. Disturbed magnetospheric conditions correlate with solar active periods, such as coronal holes or the development of solar active regions. From these regions, strong ejections called coronal mass ejections (CMEs) emerge. When these extreme events interact with Earth, they produce a compression of the magnetosphere as well as reconnection between the terrestrial magnetic field lines and the interplanetary magnetic field (IMF) lines, which most of the time leads to geomagnetic storms. The amounts of incoming solar particles and energy increase during geomagnetic storms and we also observe an increase in the O+ outflow. Our observations are made with the Cluster mission, a constellation of 4 satellites flying around Earth in the key magnetospheric regions where ion outflow is usually observed. In this thesis, we estimate O+ outflow under disturbed magnetospheric conditions and for several extreme geomagnetic storms. We find that O+ outflow lost into the solar wind increases exponentially with enhanced geomagnetic activity (Kp index) and increases about 2 orders of magnitude during extreme geomagnetic storms. / Den del av rymden som domineras av solens magnetfält kallas heliosfären. Helios-fären omfattar hela solsystemet inklusive jorden, vilket gör att det finns en starkkoppling mellan solen och jorden. Solen sänder oavbrutet ut laddade partiklar in denså kallade solvinden och när dessa energika partiklar träffar jorden påverkas mag-netosfären (det område kring jorden där det geomagnetiska fältet dominerar). Närsolvinden är starkare än vanligt uppstår störningar. I magnetosfären som ger effektersom kan uppmätas med markbaserade instrument. Den övre atmosfären utsätts för strålning från solen som joniserar atomer ochmolekyler, och formar det område som kallas jonosfären. Några av de tyngre jonpop-ulationerna i jonosfären, som till exempel syrejoner, kan hettas upp och accelererasgenom flera olika möjliga processer. Detta gör att de flödar uppåt i atmosfären. Ipolarområdena är dessa mekanismer särskilt effektiva och om tillräckligt med energitillförs jonerna kan gravitationen övervinnas, vilket gör att jonerna flödar upp längsöppna magnetfältlinjer och kan gå förlorade ut i den interplanetära rymden. Generelltsett har jonutflöde redan studerats väl, men jonutflöde under extrema magnetosfäriskaförhållanden har inte undersökts i detalj. Störda magnetosfäriska förhållanden korrelerar med då solen är aktiv, som tillexempel koronahål eller under utvecklingen av aktiva solområden. Från dessa områ-den härstammar koronamassautkastningar. När dessa extrema händelser når jordenkomprimeras magnetosfären och det geomagnetiska och interplanetära magnetiskafältet omkopplas, vilket ofta leder till geomagnetiska stormar. Under dessa införsstora mängder av partiklar i solvinden och energi till magnetosfären, och ett högresyrejonsutflöde är också observerat. Data från Clustersatelliterna har använts; dessa utgörs av fyra satelliter i for-mation i omloppsbana kring jorden. Plasmaområdena där de befinner sig är därjonutflödet vanligtvis observeras. Denna avhandling behandlar syrejonsutflöde understörda magnetosfäriska förhållanden och flera extrema geomagnetiska stormar. Detvisas att syrejonsutflödet som förloras till solvinden ökar exponentiellt med geomag-netiskt aktivitet (Kp-index) och ökar med upp till 2 storleksordningar under extremageomagnetiska stormar.

A python code was developed to compute the alpha knock-on (AKN) neutron spectrum using two already available computational tools. The code was used to calculate the AKN for a given discharge from the DTE2 JET campaign. Results showed that the beam-target contribution dominated the neutron spectra and obscured the AKN tail. A spatial profile of the AKN intensity was created which showed that the majority of the AKN reactions happen in the center of the plasma, but further analysis is needed to get a better picture of whether the AKN component will be measurable or not.

NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Ex- plorer (OSIRIS-REx) spacecraft arrived at the near-Earth rubble pile asteroid (101955) Bennu in December 2018, where it took high resolution images of the surface. The im- ages revealed that the surface is covered with boulders of various sizes. The morphology of these boulders can provide valuable information about the body’s history and the mechanical properties of the regolith. In this work, I use OSIRIS-REx images to map the outline of boul- ders on Bennu in two different geologic units: a Rugged Unit and a Smooth Unit. The two units are differentiated by surface texture, shape features and geologic features. This work was implemented using the open-source software QGIS. I compare the two units’ boulder morphology firstly in terms of boulder roughness by looking at the shape factors solidity (to what extent a boulder’s area equals that of its convex hull area) and circularity (to what extent a boulder’s perimeter is similar to the circumference of a circle with the same area). Then I study boulder compactness, by looking at the shape factors elongation (the ratio between its minor and major axis) and roundness (to what extent a boulder’s area resembles that of a circle enclosing the boulder). Despite the geologic differences, I find that there is no significant difference in the boulder roughness and compactness between the two units. Both regions’ boulders possess a large variation of values that overlap significantly. My results match well with laboratory impact experiments, implying that the regolith was created by a catastrophic impact, which is in agreement with Bennu’s status as a rubble-pile asteroid. I also find that the Smooth Unit tends to have smaller boulders (0.579 ± 0.35 m) with more boulders mapped (total 2426) than the Rugged Unit (0.711 ± 0.48 m, total 1774 boulders mapped). Finally, I show that smaller boulders tend to be rounder and less rough than larger boulders in both units. My results imply that boulder morphology is relatively uniform over the surface of Bennu, also indicating that the mechanical material properties associated with the boulder shape (such as for example tensile strength of the assembly, bulk porosity and formation history) are similar in the two units. Although the units are geologically distinct, the boulder morphology is homogeneous.

Between August 6, 2014 and September 30, 2016, the Rosetta spacecraft orbited the comet 67P/Churyumov-Gerasimenko with the purpose of observing the comet’s nucleus and the surrounding environment. The Rosetta spacecraft collected different types of data with a number of instruments, for example the Rosetta Plasma Consortium (RPC) instruments, that measured the plasma environment of the comet, and the ROSINA Comet Pressure Sensor (COPS), that measured the neutral gas environment. The aim of this study is to produce Python code to generate overview plots of data collected by the following RPC instruments: the Ion Composition Analyzer (ICA), the Ion and Electron Sensor (IES), the Fluxgate Magnetometer (MAG), the Mutual Impedance Probe (MIP), the Langmuir Probe (LAP), and the ROSINA-COPS instrument. The measurements taken by these instruments, describing the electrical, magnetic and physical properties of the plasma and gas in the cometary coma, have rarely before been visualized with uniform time axes in joint figures. A simultaneous representation of the data enables further analysis of the correlation of the instruments and of how the different plasma parameters interact in the comet’s environment. For all instruments, except ICA, the data was retrieved from ESA’s Planetary Science Archive (PSA). In the case of the ICA instrument, the data files were retrieved from IRF Kiruna’s database. The relevant data was identified and subsequently processed with various methods, such as summing over rows and columns, merging files and scaling parameters, and finally plotted in a common overview plot. The final result was a code that produces overview plots of measurements from the RPC instruments and the ROSINA-COPS instrument. With this code, overview plots of each day of the whole Rosetta mission could be generated. These overview plots are accessible through the Swedish Institute of Space Physics for future scientific use.

<p>The overall goal of the research presented in this thesis is to extend the physical understanding of the unsteady external aerodynamics associated with highly maneuverable delta-wing aircraft by using and developing novel, more efficient computational fluid dynamics (CFD) tools. More specific, the main purpose is to simulate and better understand the basic fluid phenomena, such as vortex breakdown, that limit the performance of delta-wing aircraft. The problem is approached by going from the most simple aircraft configuration - a pure delta wing - to more complex configurations. As the flow computations of delta wings at high angle of attack have a variety of unusual aspects that make accurate predictions challenging, best practices for the CFD codes used are developed and documented so as to raise their technology readiness level when applied to this class of flows.</p><p>Initially, emphasis is put on subsonic steady-state CFD simulations of stand-alone delta wings to keep the phenomenon of vortex breakdown as clean as possible. For half-span models it is established that the essential characteristics of vortex breakdown are captured by a structured CFD code. The influence of viscosity on vortex breakdown is studied and numerical results for the aerodynamic coefficients, the surface pressure distribution and breakdown locations are compared to experimental data where possible.</p><p>In a second step, structured grid generation issues, numerical aspects of the simulation of this nonlinear type of flow and the interaction of a forebody with a delta wing are explored.</p><p>Then, on an increasing level of complexity, time-accurate numerical studies are performed to resolve the unsteady flow field over half and full-span, stationary delta wings at high angle of attack. Both Euler and Detached Eddy Simulations (DES) are performed to predict the streamwise oscillations of the vortex breakdown location about some mean position, asymmetry in the breakdown location due to the interaction between the left and right vortices, as well as the rotation of the spiral structure downstream of breakdown in a time-accurate manner. The computed flow-field solutions are visualized and analyzed in a virtual-reality environment.</p><p>Ultimately, steady-state and time-dependent simulations of a full-scale fighter-type aircraft configuration in steady flight are performed using the advanced turbulence models and the detached-eddy simulation capability of an edge-based, unstructured flow solver. The computed results are compared to flight-test data.</p><p>The thesis also addresses algorithmic efficiency and presents a novel implicit-explicit algorithm, the Recursive Projection Method (RPM), for computations of both steady and unsteady flows. It is demonstrated that RPM can accelerate such computations by up to 2.5 times.</p>

The main objective of this thesis is to model the magneticstructure of interplanetary coronal mass ejections (ICME) measuredin-situ from the WIND spacecraft positioned at L1. The modeling isdone by a magnetohydrodynamic reconstruction technique based onthe GS equation with a toroidal geometry. The purpose has been toextend the application of the reconstruction program to real dataand to test its performance when different input parameters arechanged. Two events are presented; 16-17 May 2012 and 15-16 May2005 ICMEs have been successfully reconstructed with this model. The main achievements of the study are that a) the code now worksfor real data b) the important parameters that can be changed fordifferent reconstructions in the code are the number of iterationsused to find the optimal Z-axis, the plasma pressure and the orderof the polynomial fitting of the flux functional, c) if all crosssection reconstructions for different variations of theseparameters strongly resembles each other then this is anindication that the model approximation is good and that the fluxrope exists. The results have been compared and verified withpreviously published studies of these events. Using a toroidal geometry for the GS reconstruction method weobtain very similar results to the one obtained with differentreconstruction techniques.This implies that at L1, the ICMEs haveexpanded so much that a cylindrical geometry is sufficient todescribe the flux rope geometry. The toroidal Grad-Shafranovreconstruction technique is best suited for circular, or slightlyelongated, flux rope cross section profiles but have been provento work for one complex ejecta consisting of two merged fluxropes. The toroidal model might become an important asset in thefuture when data from spacecraft closer to the Sun, such as ParkerSolar Probe and Solar Orbiter, is public. When the major radius ofthe flux rope is smaller the choice of geometry will most likelyhave a larger role than for measurements at L1 and so, thetoroidal Grad-Shafranov reconstruction technique will probably bethe better alternative of the models that exists today.

<p>Waves are a fundamental feature in many parts of physics, since they transport energy without transporting matter. This is the case also in space physics. Waves are responsible for energy transport both between different parts of space and between different particles in the space plasma. They are also useful for diagnostics of the space plasma itself. The present thesis considers two different parts of the large subject of space plasma waves: Lower hybrid cavities (LHCs) and simple-pole particle distribution functions.</p><p>The LHCs are localised density depletions that have been observed by several spacecraft. They have increased wave activity in the lower hybrid frequency range, and was previously found on altitudes up to 1750 km. New observations by the Viking and Cluster satellites show that they are common magnetospheric features, at least up to an altitude of 35,000 km. Theoretical results, assuming a cylindrically symmetric density depletion, show that even though the density depletion may decrease slowly with increasing radial distance, and thus be essentially infinite in extent, there is a maximum distance within which a trapped mode, with given wave number <i>k</i><i>z</i> parallel to the geomagnetic field, may propagate. Furthermore, there is a local relation between the plasma density gradient and the lowest possible frequency that the trapped waves can have, for any monotonic density and given <i>k</i><i>z</i>. The combined theoretical and observational results indicate that the length of the cavities is larger than the width by a factor of at least 200.</p><p>Simple-pole particle distribution functions are introduced because they can model high velocity tails of the particle distribution in a way that is not possible to do with Maxwellian distribution functions. These distributions also simplify the calculations. This gives new possibilities for the physical understanding, as well as the numerical calculations, of the dispersion relations of real space plasmas. The dispersion relations of plasmas described by simple-pole distributions are examined, both for unmagnetised and for magnetised plasmas. These examples show how particle populations with the same density and mean particle energy, but with somewhat different distribution functions, have different wave propagation properties that should be observable by existing spacecraft.</p>