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Solar Modulation of Protons and Helium in Cosmic Rays with the Alpha Magnetic Spectrometer.

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Title:Solar Modulation of Protons and Helium in Cosmic Rays with the Alpha Magnetic Spectrometer.
Authors:Corti, Claudio
Contributors:Physics (department)
cosmic rays
solar modulation
numerical model
Date Issued:Aug 2017
Publisher:University of Hawaiʻi at Mānoa
Abstract:The search for the local interstellar spectrum (LIS) of galactic cosmic rays (GCRs) and a full
understanding of their propagation in the heliosphere are long-standing issues in the field of cosmic
rays (CRs) and heliophysics. In recent years, the increasing precision of direct CR measurements
lead to many advancements in different fields, such as acceleration and propagation processes of CRs
in the galaxy and high-sensitivity indirect searches of dark matter. The study of how GCR fluxes
change in time is also fundamental from the technological point of view: future human missions in
deep space will require better predictions of radiation doses received by astronauts and electronics
due to the long-term exposure to GCRs. The Alpha Magnetic Spectrometer (AMS) experiment,
on board the International Space Station (ISS) since May 2011, is measuring with unprecedented
accuracy the fluxes of GCRs from 0:5 GeV=n up to a few TeV=n. The large acceptance of AMS
allows to perform a detailed study of the time variation of GCRs during an entire solar cycle,
improving the understanding of the interplay between the different solar modulation processes.
In this work, AMS data have been analyzed to produce a very precise measurement of the
monthly proton and helium fluxes. A new parametrization of the proton and helium LIS has been
derived, based on the latest data from Voyager 1 and AMS. Using the framework of the forcefield
approximation, the solar modulation parameter is extracted from the time-dependent fluxes
measured by PAMELA, BESS and AMS. A modified version of the force-field approximation with
a rigidity-dependent modulation parameter is introduced, yielding better fits than the force-field
approximation. A comprehensive 3D steady-state numerical model is used to solve the Parker transport
equation of GCRs in the heliosphere and to reproduce the proton monthly fluxes observed by
AMS. The limitations of this approach in describing the modulation processes during the maximum
of solar activity are discussed.
Description:Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Physics

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