Abstract
The EPHIN instrument (Electron Proton Helium INstrument) forms a part of the COSTEP experiment (COmprehensive SupraThermal and Energetic Particle Analyzer) within the CEPAC collaboration on board of the SOHO spacecraft (SOlar and Heliospheric Observatory). The EPHIN sensor is a stack of six solid-state detectors surrounded by an anticoincidence. It measures energy spectra of electrons in the range 250 keV to > 8.7 MeV, and hydrogen and helium isotopes in the range 4 MeV/nuc to > 53 MeV/nuc. In order to improve the isotopic resolution, the first two detectors have been segmented: 5 sectors form a ring enclosing a central segment. This does not only allow to correct the energy-losses for particles with different path-lengths in the detectors, but allows also an estimation of the arrival direction with respect to the sensor axis. For that purpose we developed a method that allows for inferring the angle of incidence and angular distribution for ions. Here we describe the method and apply it to the November, 3, 2011 event. Due to the lack of magnetic field measurements and the restricted view cone of 83°, it is not possible to derive a real pitch angle distribution during this event. However, we can show that the particle distribution is anisotropic for several hours with a symmetry axis that deviates by about 20° from the sensor axis.
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