Distinguishing 3He and 4He with the Electron Proton Telescope (EPT) on Solar Orbiter

Abstract:

The Electron Proton Telescope (EPT) is one of the sensors of the Energetic Particle Detector (EPD) for the Solar Orbiter mission, which will provide key measurements to address particle acceleration at and near the Sun. The EPD suite consists of four different sensors (STEP, SIS, EPT and HET) which together will resolve the energetic particle spectrum from 2 keV to 20 MeV for electrons, 3 keV to 100 MeV for protons and circa 100 keV/nuc to 100 MeV/nuc for heavier ions.
EPT itself is primarily designed to cleanly separate and measure electrons in the energy range from 20 - 400 keV and protons from 20 - 7000 keV.
To achieve this, EPT uses two back-to-back solid state detectors with a magnet system to deflect electrons on one side and a Polyimide foil to stop protons below ~400 keV on the other side. The two detectors then serve as each other's anti-coincidence.
Additionally this setup also allows us to measure penetrating particles with deposited energies in the 1 MeV to 40 MeV range. Looking at the ratio of deposited energy in the two detectors versus total deposited energy allows us to differentiate between protons and alpha particles.
Distinguishing ³He from ⁴He will be challenging, but possible provided good knowledge of the instrument, high-fidelity modeling and a precise calibration of EPT. Here, we will present feasibility studies leading to a determination of the ³He / ⁴He ratio with EPT.