Abstract
We present the precision measurement from May 2011 to May 2017 (79 Bartels rotations) of the proton fluxes at rigidities from 1 to 60GV and the helium fluxes from 1.9 to 60GV based on a total of 1×10^{9} events collected with the Alpha Magnetic Spectrometer aboard the International Space Station. This measurement is in solar cycle 24, which has the solar maximum in April 2014. We observed that, below 40GV, the proton flux and the helium flux show nearly identical fine structures in both time and relative amplitude. The amplitudes of the flux structures decrease with increasing rigidity and vanish above 40GV. The amplitudes of the structures are reduced during the time period, which started one year after solar maximum, when the proton and helium fluxes steadily increase. Above ∼3 GV the p/He flux ratio is time independent. We observed that below ∼3 GV the ratio has a long-term decrease coinciding with the period during which the fluxes start to rise.
Highlights
We present the precision measurement from May 2011 to May 2017 (79 Bartels rotations) of the proton fluxes at rigidities from 1 to 60 GV and the helium fluxes from 1.9 to 60 GV based on a total of 1 × 109 events collected with the Alpha Magnetic Spectrometer aboard the International Space Station
This measurement is in solar cycle 24, which has the solar maximum in April 2014
The amplitudes of the structures are reduced during the time period, which started one year after solar maximum, when the proton and helium fluxes steadily increase
Summary
We present the precision measurement from May 2011 to May 2017 (79 Bartels rotations) of the proton fluxes at rigidities from 1 to 60 GV and the helium fluxes from 1.9 to 60 GV based on a total of 1 × 109 events collected with the Alpha Magnetic Spectrometer aboard the International Space Station. The large acceptance and high precision of the Alpha Magnetic Spectrometer (AMS) allow us to perform accurate measurements of the fluxes as functions of time and energy This provides unique information to probe the dynamics of solar modulation, to allow the improvement of constraints for dark matter search [14,15,16,17], to investigate the processes of galactic cosmic ray propagation [18,19], and to reduce the uncertainties in radiation dose predictions for deep space human exploration [20,21]. Data analysis.—The isotropic flux Φi during a Bartels rotation in the ith rigidity bin (Ri; Ri þ ΔRi) is given by
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