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Dissertations / Theses on the topic 'Cosmic ray modulation'

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Published: 6 September 2023

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1

Vos, Etienne Eben. "Cosmic ray modulation processes in the heliosphere / Vos E.E." Thesis, North-West University, 2011. http://hdl.handle.net/10394/7266.

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The solar minimum of 2009 has been identified as an exceptional event with regard to cosmic ray (CR)modulation, since conditions in the heliosphere have reached unprecedented quiet levels. This unique minimum has been observed by the Earth–orbiting satellite, PAMELA, launched in June, 2006, from which vast sets of accurate proton and electron preliminary observations have been made available. These simultaneous measurements from PAMELA provide the ideal opportunity to conduct an in–depth study of CR modulation, in particular charge–sign dependent modulation. In utilizing this opportunity, a th
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2

KO, CHUNG-MING. "COSMIC-RAY MODIFIED STELLAR WINDS (ACCELERATION, MODULATION, DIFFUSION, TRANSONIC SOLUTION)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183980.

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A two fluid hydrodynamical model describing the modification of a stellar wind flow due to its interaction with galactic cosmic-rays is investigated. The two fluids consist of the thermal stellar wind gas and the galactic cosmic-rays. A polytropic one fluid model is used to describe the stellar wind gas, and the cosmic-rays modify the wind via their pressure gradient. The cosmic-rays are considered to be a hot low density gas of negligible mass flux, but with a significant pressure and energy flux compared to the thermal gas. The equations used are essentially those employed in two fluid hydro
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3

Gieseler, Jan [Verfasser]. "Understanding Galactic Cosmic Ray Modulation: Observations and Theory / Jan Gieseler." Kiel : Universitätsbibliothek Kiel, 2018. http://d-nb.info/1155760816/34.

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4

Ngobeni, Mabedle Donald. "Aspects of the modulation of cosmic rays in the outer heliosphere / by Mabedle Donald Ngobeni." Thesis, North-West University, 2006. http://hdl.handle.net/10394/97.

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A time-dependent two-dimensional (2D) modulation model including drifts, the solar wind tennination shock (TS) with diffusive shock acceleration and a heliosheath based on the Parker (1965) transport equation is used to study the modulation of galactic cosmic rays (GCRs) and the anomalous component of cosmic rays (ACRs) in the heliosphere. In particular, the latitude dependence of the TS compression ratio and injection efficiency of the ACRs (source strength) based on the hydrodynamic modeling results of Scherer et al. (2006) is used for the first time in a modulation model. The subsequent eff
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5

Krüger, Tjaart Petrus Jakobus. "The effect of a Fisk-Parker hybrid magnetic field on cosmic rays in the heliosphere / Tjaart P.J. Krüger." Thesis, North-West University, 2005. http://hdl.handle.net/10394/1205.

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The existence of a Fisk-type heliospheric magnetic field (HMF) is one of the most debated questions in cosmic-ray modulation. Recently, Burger and Hitge [2004] developed a divergence-free Fisk-Parker hybrid magnetic field model to demonstrate the behaviour of cosmic rays in the heliosphere due to such a field. This approach has been refined and the properties of the consequent field are investigated. It is found that randomly directed magnetic field diffusion in and above the photosphere significantly influences the solar magnetic field both at the solar poles and near the polar coronal hole b
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6

Krüger, Helena. "A calibration neutron monitor for long-term cosmic ray modulation studies / H. Krüger." Thesis, North-West University, 2006. http://hdl.handle.net/10394/1023.

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The propagation of high-energy cosmic rays is influenced by the time-varying heliospheric magnetic field embedded in the solar wind, and by the geomagnetic field. To penetrate through this geomagnetic field, they must have a rigidity that exceeds the geomagnetic cutoff rigidity for a given position on the earth. In the atmosphere, the primary cosmic rays interact with atmospheric nuclei, to form a cascade of secondary particles. Neutron monitors record these secondary cosmic rays, mainly the neutrons, with energies about a decade higher than detected by most spacecraft. Since neutron monitors
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7

Nndanganeni, Rendani Rejoyce. "Modelling of galactic cosmic ray electrons in the heliosphere / Nndanganeni, R.R." Thesis, North-West University, 2012. http://hdl.handle.net/10394/7034.

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The Voyager 1 spacecraft is now about 25 AU beyond the heliospheric termination shock and soon it should encounter the outer boundary of the heliosphere, the heliopause. This is set to be at 120 AU in the modulation model used for this study. This implies that Voyager 1, and soon afterwards also Voyager 2, should be able to measure the heliopause spectrum, to be interpreted as the lowest possible local interstellar spectrum, for low energy galactic electrons (1 MeV to 120 MeV). This could give an answer to a long outstanding question about the spectral shape (energy dependence) of the galactic
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8

Engelbrecht, Nicholas Eugéne. "On the heliospheric diffusion tensor and its effect on 26-day recurrent cosmic-ray variations / N.E. Engelbrecht." Thesis, North-West University, 2008. http://hdl.handle.net/10394/2052.

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9

Nkosi, Godfrey Sibusiso. "A study of cosmic ray anisotropies in the heliosphere / Godfrey Sibusiso Nkosi." Thesis, North-West University, 2006. http://hdl.handle.net/10394/1627.

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10

Strauss, Roelf du Toit. "Modelling of cosmic ray modulation in the heliosphere by stochastic processes / Roelf du Toit Strauss." Thesis, North-West University, 2013. http://hdl.handle.net/10394/10217.

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The transport of cosmic rays in the heliosphere is studied by making use of a newly developed modulation model. This model employes stochastic differential equations to numerically solve the relevant transport equation, making use of this approach’s numerical advantages as well as the opportunity to extract additional information regarding cosmic ray transport and the processes responsible for it. The propagation times and energy losses of galactic electrons and protons are calculated for different drift cycles. It is confirmed that protons and electrons lose the same amount of rigidity when t
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11

MUNINI, RICCARDO. "Solar modulation of cosmic ray electrons and positrons measured by the PAMELA experiment during the 23rd solar minimum." Doctoral thesis, Università degli Studi di Trieste, 2016. http://hdl.handle.net/11368/2908077.

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Cosmic rays (CRs) are energetic particles mainly originating outside the Solar System in extremely powerful environments like supernovae remnants (SNRs). The cosmic radiation is composed primarily of high-energy protons, helium and atomic nuclei while only a small fraction are electrons, anti-protons and positrons. During propagation through the Galaxy, CRs interact with the interstellar matter and the Galactic magnetic field. Because of these interactions CRs lose energy and change their spectral features with respect to the injection spectrum. Moreover, before reaching the Earth, CRs trave
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12

Mikuni, Vinicius Massami. "Measurement of cosmic ray electrons and positrons with the AMS-02 experiment." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-29092017-143310/.

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The Alpha Magnetic Spectrometer (AMS-02) is a high-energy particle physics detector operating on the International Space Station (ISS) since May 2011. Since its launch, the AMS-02 provided a large amount of data whose precision was never before achieved, opening a new path for the study of cosmic rays (CRs). The first published results of AMS-021-3 show tension with the current understanding of the cosmic ray theory, particularly at higher energies. These tensions are directly linked to many fundamental questions like the dark matter nature, the CR origin and their propagation through the gala
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13

Engelbrecht, Nicholas Eugéne. "On the development and applications of a three-dimensional ab initio cosmic-ray modulation model / Nicholas Eugéne Engelbrecht." Thesis, North-West University, 2012. http://hdl.handle.net/10394/8735.

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A proper understanding of the effects of turbulence on the diffusion and drift of cosmic-rays in the heliosphere is imperative for a better understanding of cosmic-ray modulation. This study presents an ab initio model for cosmic-ray modulation, incorporating for the first time the results yielded by a two-component turbulence transport model. The latter model is solved for solar minimum heliospheric conditions, utilizing boundary values chosen in such a way that the results of this model are in fair to good agreement with spacecraft observations of turbulence quantities, not only in the eclip
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14

Ghelfi, Alexandre. "Analyse des données de l'expérience AMS-02 pour la propagation du rayonnement cosmique dans la cavité solaire et la Galaxie." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY044/document.

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Le rayonnement cosmique, mis en évidence par Viktor Hess en 1912, est composé de particules chargées, créées et possiblement accélérées dans les restes de supernova, et qui se propagent dans la Galaxie. La mesure des flux du rayonnement cosmique permet de mettre des contraintes sur leurs sources et leur transport, mais aussi de se pencher sur le problème de la matière sombre.C'est pour répondre à ces questions qu'a été construit le détecteur AMS-02, mis en place sur la station spatiale internationale depuis mai 2011. Ce détecteur de haute précision mesure l'ensemble des flux de particules du r
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15

LENNI, ALEX. "Study of cosmic-ray proton and deuteron solar modulation and its relevence for indirect dark-matter searches with the PAMELA and GAPS experiments." Doctoral thesis, Università degli Studi di Trieste, 2022. http://hdl.handle.net/11368/3014975.

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Cosmic rays (CRs) are electrically charged particles accelerated by astrophysical powerful sources. CRs consists mainly of protons and helium nuclei and in minimal part of other nuclei and electrons. Among these, there are the deuterons, i.e. the deuterium nuclei, which are produced as a secondary component from interactions of CRs with the interstellar medium. During their voyage in the Galaxy, CRs experience energy losses, fragmentations in secondary products, trajectory deflections by galactic magnetic fields and generally a change of the spectral features. Before reaching the Earth, CRs p
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16

Giesen, Gaelle. "Dark Matter Indirect Detection with charged cosmic rays." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112160/document.

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Les preuves pour l'existence de la matière noire (MN), sous forme d'une particule inconnue qui rempli les halos galactiques, sont issues d'observations astrophysiques et cosmologiques: son effet gravitationnel est visible dans les rotations des galaxies, des amas de galaxies et dans la formation des grandes structures de l'univers. Une manifestation non-gravitationnelle de sa présence n'a pas encore été découverte. L'une des techniques les plus prometteuse est la détection indirecte de la MN, consistant à identifier des excès dans les flux de rayons cosmiques pouvant provenir de l'annihilation
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17

DI, FELICE VALERIA. "Low energy electron and positron measurements in space with the PAMELA experiment." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2010. http://hdl.handle.net/2108/1245.

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Questa tesi descrive lo studio di elettroni e positroni nella radiazione cosmica. Nuove misure della frazione di positroni al top dell’atmosfera tra 200 MeV e 3.0 GeV, nonché lo spettro di elettroni fino a 20 GeV, sono presentati. La misura è stata effettuata con l’esperimento PAMELA da Luglio 2006 a Dicembre 2008, periodo di minima attività solare e polarità negativa. PAMELA fornisce le prime osservazioni a lungo termine della frazione di positroni di bassa energia durante questo particolare stato della eliosfera. La grande statistica collezionata permette di studiare la variazione del flusso
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18

Minnie, Jaco. "An ab initio approach to the heliospheric modulation of galactic cosmic rays / Jaco Minnie." Thesis, North-West University, 2006. http://hdl.handle.net/10394/1258.

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In the present study we aim to further our understanding of charged particle transport in a magnetized medium. To this end, we perform direct numerical simulations of particle transport in a turbulent magnetic field. From the particle trajectories we calculate diffusion and drift coefficients. In contrast to previous numerical simulations of this nature, we also consider a background magnetic field that contains a gradient perpendicular to the magnetic field direction. By using a non-uniform background magnetic field, we can investigate the simultaneous large scale drift due to the gradient in
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19

Ndiitwani, Dzivhuluwani Christopher. "A study of the time-dependent modulation of galactic cosmic rays in the heliosphere / Dzivhuluwani C. Ndiitwani." Thesis, North-West University, 2005. http://hdl.handle.net/10394/843.

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Time-dependent cosmic ray modulation in the heliosphere is studied by using a two-dimensional time dependent modulation model. To compute realistic cosmic ray modulation a compound approach is used, which combines the effect of the global changes in the heliospheric magnetic field magnitude and the current sheet tilt angle to establish realistic time dependent diffusion and drift coefficients. This approach is refined by scaling down drifts additionally (compared to diffusion) towards solar maximum. The amount of drifts needed in the model to realistically compute 2.5 GV proton and electron an
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20

Magidimisha, Edwin. "A study of the time-dependent modulation of cosmic rays in the inner heliosphere / E. Magidimisha." Thesis, North-West University, 2010. http://hdl.handle.net/10394/4402.

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A two-dimensional (2-D) time-dependent cosmic ray modulation model is used to calculate the modulation of cosmic-ray protons and electrons for 11-and 22-year modulation cycles using a compound approach to describe solar cycle related changes in the transport parameters. The compound approach was developed by Ferreira and Potgieter (2004) and incorporates the concept of propagation diffusion barriers, global changes in the magnetic field, time-dependent gradient, curvature and current-sheet drifts, and other basic modulation mechanisms. By comparing model results with 2.5 GV Ulysses observation
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21

Manuel, Rex. "Time-dependent modulation of cosmic rays in the outer heliosphere / Rex Manuel." Thesis, North-West University, 2013. http://hdl.handle.net/10394/8740.

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The time-dependent modulation of galactic cosmic rays in the heliosphere is studied by computing intensities using a two-dimensional, time-dependent modulation model. The compound approach of Ferreira and Potgieter (2004), which describes changes in the cosmic ray transport coefficients over a solar cycle, is improved by introducing recent theoretical advances in the model. Computed intensities are compared with Voyager 1 and 2, IMP 8 and Ulysses proton observations in search of compatibility. It is shown that this approach gives realistic cosmic ray proton intensities on a global scale at Ear
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22

Langner, Ulrich Wilhelm. "Effects of termination shock acceleration on cosmic rays in the heliosphere / U.W. Langner." Thesis, North-West University, 2004. http://hdl.handle.net/10394/346.

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The interest in the role of the solar wind termination shock (TS) and heliosheath in cosmic ray (CR) modulation studies has increased sigm6cantly as the Voyager 1 and 2 spacecraft approach the estimated position of the TS. For this work the modulation of galactic CR protons, anti-protons, electrons with a Jovian source, positrons, Helium, and anomalous protons and Helium, and the consequent charge-sign dependence, are studied with an improved and extended two-dimensional numerical CR modulation model including a TS with diffusive shock acceleration, a heliosheath and drifts. The modulation is
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23

Baker, Christopher Paul. "Cosmic ray modulation in the heliosphere." Thesis, 1993. https://eprints.utas.edu.au/18946/1/whole_BakerChristopherPaul1993_thesis.pdf.

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Models describing the modulation of galactic cosmic rays in the heliosphere have been developed and investigated. These models are numerical solutions of the cosmic ray transport equation under idealized heliospheric conditions. Primarily, the models were used to predict the radial gradient g r of galactic cosmic rays in the vicinity of the Earth during solar-minimum conditions specified by a flat neutral sheet and no propagating shock disturbances. It was found that g r was not sensitive to the assumed value of the cosmic ray distribution at the Sun, but was very sensitive to (a) the di
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24

Raath, Jan Louis. "A comparative study of cosmic ray modulation models / Jan Louis Raath." Thesis, 2015. http://hdl.handle.net/10394/15516.

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Until recently, numerical modulation models for the solar modulation of cosmic rays have been based primarily on finite difference approaches; however, models based on the solution of an appropriate set of stochastic differential equations have become increasingly popular. This study utilises such a spatially three-dimensional and time-stationary model, based on that of Strauss et al. (2011b). The remarkable numerical stability and powerful illustrative capabilities of this model are utilised extensively and in a distinctly comparative fashion to enable new insights into the processes of modul
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25

Hall, DL. "Modulation of high energy cosmic rays in the heliosphere." Thesis, 1995. https://eprints.utas.edu.au/19632/7/whole_HallDamianLindsay1995.pdf.

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The distribution of galactic cosmic ray particles in the heliosphere is influenced (modulated) by the Sun's interplanetary magnetic field (IMF) and the solar wind. The particles diffuse inward, convect outward and have drifts in the motion of their gyro-centres. They are also scattered from their gyro-orbits by irregularities in the IMF. These processes are the components of solar modulation and produce streaming (anisotropies) of particles in the heliosphere. The anisotropies can be investigated at Earth by examining the count rates of cosmic ray detectors. The anisotropic streams appea
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26

Ngobeni, Mabedle Donald. "Modeling of galactic cosmic rays in the heliosphere / Mabedle Donald Ngobeni." Thesis, 2015. http://hdl.handle.net/10394/15476.

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The modulation of galactic cosmic ray (GCR) Carbon in a north-south asymmetrical heliosphere is studied, using a two-dimensional numerical model that contains a solar wind termination shock (TS), a heliosheath, as well as particle drifts and diffusive shock re-acceleration of GCRs. The asymmetry in the geometry of the heliosphere is incorporated in the model by assuming a significant dependence on heliolatitude of the thickness of the heliosheath. As a result, the model allows comparisons of modulation in the north and south hemispheres during both magnetic polarity cycles of the Sun, and from
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