This project aims to investigate the orientation of plasma jet fronts in Earth's magnetotail using multi-spacecraft measurement data. The orientations are estimated by applying minimum variance analysis (MVA) and multi-spacecraft timing analysis for finding normal vectors to the jet fronts as they pass over the spacecraft. An agreement between the two analysis methods is found when applied to a data set of fronts. The obtained results are compared to measurements of the ion bulk velocities of the fronts, where a discrepancy is found. Limitations of the analysis are addressed and alternative approaches are presented. / I detta projekt undersöks riktningen hos fronter till plasma-jetstrålar i jordens magnetsvans genom analysering av mätdata från en samling rymdfarkoster. Riktningarna uppskattas genom att applicera minimum variance analysis (MVA) samt multi-spacecraft timing för att hitta normalvektorer till fronterna som passerar rymdfarkosterna. De två metoderna uppnår liknande resultat när de tillämpas på en uppsättning fronter. De erhållna normalvektorerna jämförs även med riktningen av uppmätta jonhastigheter från rymdfarkosterna där en tydlig skillnad förekommer. Begränsningar av analysmetoden påpekas och förslag på alternativa tillvägagångssätt läggs fram.

The bow shock is formed due to the abrupt deceleration of the supersonic solar wind in front of the terrestrial magnetic field. The solar wind plasma and the Interplanetary Magnetic Field (IMF) are both compressed across the shock, and according to Ampère's law a current thus flows on the bow shock at all times. The Bow Shock Current (BSC) is suggested to play an important role in solar wind-magnetosphere coupling, but there is still an open debate about its closure path. For predominantly east-west IMF, the BSC has been suggested to close to Earth's high latitude ionosphere as Field-Aligned Currents (FACs). Since the bow shock is magnetically connected to the solar wind, it must do so via open field lines through the magnetosheath. For southwards IMF with a significant east-west component, the R0 FAC flows into the ionosphere in one hemisphere, and out of it in the other. The R0 current flows on open field lines, and is thus a potential candidate to close the BSC. While a few studies have already found evidence in favour of this idea, the majority have been based on simulations. Additional observational evidence is required to confirm these findings. We used OMNI data for the IMF at the bow shock, and Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data for the FACs, to make simultaneous observations of the IMF at the bow shock and the northern hemisphere FACs, including the R0 current. We successfully identified 15 events of southwards but predominantly east-west IMF (Bz<0, |By|>|Bz|) at the bow shock, for which the northern hemisphere R0 current could be observed both in the AMPERE and DMSP data. In each of these events, the R0 current was of the correct polarity to connect to the BSC. Moreover, using Defense Meteorological Satellite Program (DMSP) and Super Dual Auroral Radar Network (SuperDARN) data, we were able to verify that part of the R0 current was flowing on open field lines. Collectively, the 15 events presented here constitute an argument in favour of at least a partial BSC closure to Earth's high latitude ionosphere as R0 FACs, for predominantly east-west IMF. Additional investigation is required to reveal the details of BSC closure.

Fusion research has been an ongoing research endeavour for many decades and it has the potential of providing an important part in the future of energy production. An important part of this process is to understand and control the various heating systems of the reactor where one of the most important systems being the Neutral Beam Injector (NBI) which injects particles at high velocities into the plasma. The number of fusion reactions caused by this process depends on the beam-target reactivity where the beam can be modelled in various ways. The aim of this report was to compare the results of two different approaches in modelling the beam-target reactivity. This was done using two models, Stix and TRANSP which has different strengths and weaknesses but they use the same input parameters. Hence it is interesting to assess how much accuracy is sacrificed when using the simpler model (Stix). The aim of this report was to compare beam-target reactivty calculations based on two different approaches for modelling the distribution of the beam ions. One approach (TRANSP) performs very detailed modelling of both the energy distribution and the distribution in pitch (i.e. the direction of the velocity with respect to the plasma magnetic field), but is also very time consuming. The other approach (Stix) is more simplistic but can only provide the distribution in energy (no pitch information). It was found that the beam-target reactivities calculated from these two modelling approaches typically differed by about 10-20 percent (a bit more a the very edge of the fusion plasma, but this is not a great concerns since very few fusion reactions happen in this region). The difference in reactivity values could be attributed to differences in the modelled energy distributions and the fact that the Stix model does not model the pitch distribution. These results provide useful insights about the merits and drawbacks of the TRANSP and Stix models. In particular, it can be useful for quantifying the uncertainty introduced by using the Stix model instead of TRANSP if the beam-target reactivity is used as input for interpreting neutron measurements from fusion plasmas.

Performing detailed simulations of plasma kinetic diffusion is a challenging task and currently requires the largest computational facilities in the world. The reason for this is that, the physics in a confined heated plasma occur on a broad range of temporal and spatial scales. It is therefore of interest to improve the computational algorithms together with the development of more powerful computational resources. Kinetic diffusion processes in plasmas are commonly simulated with the Monte Carlo method, where a discrete set of particles are sampled from a distribution function and advanced in a Lagrangian frame according to a set of stochastic differential equations. The Monte Carlo method introduces computational error in the form of statistical random noise produced by a finite number of particles (or markers) N and the error scales as αN−β where β = 1/2 for the standard Monte Carlo method. This requires a large number of simulated particles in order to obtain a sufficiently low numerical noise level. Therefore it is essential to use techniques that reduce the numerical noise. Such methods are commonly called variance reduction methods. In this thesis, we have developed new variance reduction methods with application to plasma kinetic diffusion. The methods are suitable for simulation of RF-heating and transport, but are not limited to these types of problems. We have derived a novel variance reduction method that minimizes the number of required particles from an optimization model. This implicitly reduces the variance when calculating the expected value of the distribution, since for a fixed error the  optimization model ensures that a minimal number of particles are needed. Techniques that reduce the noise by improving the order of convergence, have also been considered. Two different methods have been tested on a neutral beam injection scenario. The methods are the scrambled Brownian bridge method and a method here called the sorting and mixing method of L´ecot and Khettabi[1999]. Both methods converge faster than the standard Monte Carlo method for modest number of time steps, but fail to converge correctly for large number of time steps, a range required for detailed plasma kinetic simulations. Different techniques are discussed that have the potential of improving the convergence to this range of time steps. / QC 20120314

One of the most conspicuous problems in space physics for the last decades has been to theoretically describe how the large parallel electric fields on auroral field lines can be generated. There is strong observational evidence of such electric fields, and stationary theory supports the need for electric fields accelerating electrons to the ionosphere where they generate auroras. However, dynamic models have not been able to reproduce these electric fields. This thesis sheds some light on this incompatibility and shows that the missing ingredient in previous dynamic models is a correct description of the electron temperature. As the electrons accelerate towards the ionosphere, their velocity along the magnetic field line will increase. In the converging magnetic field lines, the mirror force will convert much of the parallel velocity into perpendicular velocity. The result of the acceleration and mirroring will be a velocity distribution with a significantly higher temperature in the auroral acceleration region than above. The enhanced temperature corresponds to strong electron pressure gradients that balance the parallel electric fields. Thus, in regions with electron acceleration along converging magnetic field lines, the electron temperature increase is a fundamental process and must be included in any model that aims to describe the build up of parallel electric fields. The development of such a model has been hampered by the difficulty to describe the temperature variation. This thesis shows that a local equation of state cannot be used, but the electron temperature variations must be descibed as a nonlocal response to the state of the auroral flux tube. The nonlocal response can be accomplished by the particle-fluid model presented in this thesis. This new dynamic model is a combination of a fluid model and a Particle-In-Cell (PIC) model and results in large parallel electric fields consistent with in-situ observations.

The γ-ray characterizing possibility of the neutron collimated flux monitor (in short, Neutron Camera) at the Mega Ampere Spherical Tokamak (MAST) is explored. Typically used to monitor neutron emission, the Neutron Camera has excellent neutron/γ-ray discrimination properties and thus presents the opportunity to measure spatially and temporally resolved γ-ray emission - a possibility of an additional fusion diagnostics method with already existing equipment. An Online Data Analysis (ODA) code was used to analyze the data on γ-rays from several plasma discharges with similar plasma parameters. A high statistics temporal distribution of the γ-ray emission and a lower statistics spatial distribution were analyzed. However, the low energy resolution and range for the Neutron Camera γ-ray measurements revealed few conclusive results on the origin of the higher energy γ-rays. Detection systems with higher energy resolution and range are suggested for an extensive analysis of γ-ray emission at MAST Upgrade.

<p>One of the most conspicuous problems in space physics for the last decades has been to theoretically describe how the large parallel electric fields on auroral field lines can be generated. There is strong observational evidence of such electric fields, and stationary theory supports the need for electric fields accelerating electrons to the ionosphere where they generate auroras. However, dynamic models have not been able to reproduce these electric fields. This thesis sheds some light on this incompatibility and shows that the missing ingredient in previous dynamic models is a correct description of the electron temperature. As the electrons accelerate towards the ionosphere, their velocity along the magnetic field line will increase. In the converging magnetic field lines, the mirror force will convert much of the parallel velocity into perpendicular velocity. The result of the acceleration and mirroring will be a velocity distribution with a significantly higher temperature in the auroral acceleration region than above. The enhanced temperature corresponds to strong electron pressure gradients that balance the parallel electric fields. Thus, in regions with electron acceleration along converging magnetic field lines, the electron temperature increase is a fundamental process and must be included in any model that aims to describe the build up of parallel electric fields. The development of such a model has been hampered by the difficulty to describe the temperature variation. This thesis shows that a local equation of state cannot be used, but the electron temperature variations must be descibed as a nonlocal response to the state of the auroral flux tube. The nonlocal response can be accomplished by the particle-fluid model presented in this thesis. This new dynamic model is a combination of a fluid model and a Particle-In-Cell (PIC) model and results in large parallel electric fields consistent with in-situ observations.</p>

<p>The Auroral Large Imaging System (ALIS) was proposed in 1989 by Åke Steen as a joint Scandinavian ground-based nework of automated auroral imaging stations. The primary scientic objective was in the field of auroral physics, but it was soon realised that ALIS could be used in other fields, for example, studies of Polar Stratospheric Clouds (PSC), meteors, as well as other atmospheric phenomena.</p><p>This report describes the design, operation and scientic results from a Swedish prototype of ALIS consisting of six unmanned remote-controlled stations located in a grid of about 50 km in northern Sweden. Each station is equipped with a sensitive high-resolution (1024 x 1024 pixels) unintensified monochromatic CCDimager. A six-position filter-wheel for narrow-band interference filters facilitates absolute spectroscopic measurements of, for example, auroral and airglow emissions. Overlapping fields-of-view resulting from the station baseline of about 50 km combined with the station field-of-view of 50° to 60°, enable triangulation as well as tomographic methods to be employed for obtaining altitude information of the observed phenomena.</p><p>ALIS was probably one of the first instruments to take advantage of unintensi- fied (i.e. no image-intensifier) scientific-grade CCDs as detectors for spectroscopic imaging studies with multiple stations of faint phenomena such as aurora, airglow, etc. This makes absolute calibration a task that is as important as it is dificult.</p><p>Although ALIS was primarily designed for auroral studies, the majority of the scientific results so far have, quite unexpectedly, been obtained from observations of HF pump-enhanced airglow (recently renamed Radio-Induced Aurora). ALIS made the first unambiguous observation of this phenomena at high-latitudes and the first tomography-like inversion of height profiles of the airglow regions. The scientific results so far include tomographic estimates of the auroral electron spectra, coordinated observations with satellite and radar, as well as studies of polar stratospheric clouds. An ALIS imager also participated in a joint project that produced the first ground-based daytime auroral images. Recently ALIS made spectroscopic observations of a Leonid meteor-trail and preliminary analysis indicates the possible detection of water in the Leonid.</p>

<p>This thesis discusses the reasons for space exploration and space science. Space plasma physics is identified as an essential building block to understand the space environment and it is argued that observation and analysis of space plasma waves is an important approach.</p><p>Space plasma waves are the main actors in many important processes. So-called broadband waves are found responsible for much of the ion heating in the auroral region. We investigate the wave properties of broadband waves and show that they can be described as a mixture of electrostatic wave modes. In small regions void of cold electrons the broadband activity is found to be ion acoustic waves and these regions are also identified as acceleration regions. The identification of the wave modes includes reconstructions of the wave distribution function. The reconstruction technique allow us to determine the wave vector spectrum, which cannot be measured directly. The method is applied to other wave events and it is compared in some detail with a similar method.</p><p>Space plasma wave are also sensitive tools for investigations of both the fine-structure and the dynamics of space plasmas. Studies of whistler mode waves observed in the boundary layer on the magnetospheric side of the magnetopause reveal that the plasma is organized in tube-like structures moving with the plasma drift velocity. The perpendicular dimension of these tubes is of the order of the electron inertial length. We present evidence that each tube is linked to a reconnection site and argue that the high density of tube-like structures indicates patchy reconnection.</p>

<p>This thesis deals with the development and calibrations of sensors to measure energetic neutral atoms (ENAs) at Mars, Venus, and the Earth. ENAs are formed in charge exchange processes between energetic, singly--charged ions and a cold neutral gas. Since ENAs can travel in long straight trajectories, unaffected by electric or magnetic fields, they can be used to remotely image plasma interactions with neutral atmospheres. ENA instrument techniques have matured over the last decade and ENA images of the Earth's ring current for example, have successfully been analyzed to extract ion distributions and characterize plasma flows and currents in the inner magnetosphere.</p><p>Three different ENA sensors have been developed to image ENAs at Mars, Venus, and the Earth. Two of them, the nearly identical Neutral Particle imagers (NPIs) are on-board the Mars Express and Venus Express spacecraft as a part of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3 and 4) instruments. The third is the Neutral Atom Detector Unit, NUADU, aboard the TC-2 spacecraft of the Double Star mission. The NPI design is based on a surface reflection technique to measure low energy (~0.3-60 keV) ENAs, while the NUADU instrument is based on a simple design with large geometrical factor and solid state detectors to measure high energy ENAs (~20-300 keV).</p><p>The calibration approach of both NPI sensors were to define the detailed response, including properties such as the angular response function and efficiency of one reference sensor direction then find the relative response of the other sensor directions. Because of the simple geometry of the NUADU instrument, the calibration strategy involved simulations to find the cutoff energy, geometrical factor and angular response. The NUADU sensor head was then calibrated to find the response to particles of different mass and energy. The NPI sensor for the Mars Express mission revealed a so-called priority effect in the sensor that lowers the angular resolution at high detector bias. During the calibration of the Venus Express NPI sensor tests were made which showed that the priority effect is a result of low amplitude (noise) pulses generated in the detector system. The conclusion is that the effect is caused by capacitive couplings between different anode sectors of the sensor. The thresholds on the preamplifiers were set higher on the Venus Express NPI, which removed the priority effect.</p><p>Two of the three ENA experiments, the Double Star NUADU instrument and the Mars Express NPI sensor, have successfully measured ENAs that are briefly described in the thesis. The first ENA measurements at Mars were performed with Mars Express. Initial results from the NPI include measurements of ENAs formed in the Martian magnetosheath and solar wind ENAs penetrating to the nightside of Mars. The first results from NUADU in Earth orbit show the expected ENA emissions from a storm time ring current. Also, together with the HENA instrument on the IMAGE spacecraft, NUADU have produced the first multi-point ENA image of the ring current.</p>