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Description
The Alpha Magnetic Spectrometer (AMS), on the International Space Station (ISS) since May 2011, has acquired the largest number of particles ever measured in space by a single experiment, performing the most precise measurement of galactic cosmic rays (GCR) to-date.
The flux of all GCR species at low energy (below 100 GV) is affected by the solar activity, which varies in time with a period of about 11 years. The precise knowledge of the time variation of GCRs is crucial for a better understanding of the background to indirect searches of dark matter and for improving the modeling of the radiation environment in space, enabling safer operations for satellites and human exploration.
The detailed time variation of the proton, helium, and light nuclei fluxes was measured by AMS in the first 8.5 years of data taking, covering the maximum of solar cycle 24 and the beginning of the next solar cycle.
We observed differences in the time dependence of various GCR species, which can be related to the shape of the local interstellar spectrum and to velocity effects.
We observed recurrent flux variations with periods of 9, 13.5, and 27 days, with characteristics depending on both rigidity and time, related to the short-term solar activity.
