Galactic and Anomalous Cosmic Rays in the inner heliosphere : HELIOS E6 results

Over 40 years ago, the HELIOS mission was launched with the goal to improve our understanding of the inner heliosphere as well. In this work, the measurements of the Experiment 6 ( E6 ), one of three particle instruments on-board HELIOS was revisited and re-analysed. The E6 was capable of measuring electrons in the low MeV and elements from hydrogen to magnesium in the MeV to GeV range. The data were completely recalibrated by using a sophisticated model of the instrument as well as taking into account effects like degrading of the detectors, complex temperature dependent behaviour and non-linearities of the detectors. All of these effects have been quantified and the properties of the installed optical detector have been obtained. It is shown that with these data energy spectra of the different elements can be obtained in dependence of time and radial distance from the spacecraft to the Sun. From the hydrogen spectra the modulation parameter for the analysed time period was determined, which agrees with expectations for the analysed period of time. The gradient for anomalous oxygen was determined for the first time in the inner heliosphere and is with (48 ± 12)%/AU much larger than expected from measurements in the outer heliosphere. It agrees qualitatively with recent models of solar modulation. The gradient of galactic hydrogen above 200 MeV was determined to be (2 ± 2.5)%/AU. This value agrees well with other measurements and predictions. With the obtained recalibration it is also possible to analyse Solar Energetic Particle ( SEP ) events as well as spectra of elements heavier than helium up to very high energies.


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