Abstract
In the interstellar and interplanetary space, small objects of micrometer size—dust grains—are present. These grains are charged by impact of particles from the Sun: electrons, ions, and UV photons.
In our laboratory, we study charging of a single grain by UV irradiation. Our photon source (differentially pumped discharge lamp) works with noble gases (He in our case), and can operate with different intensity ratios of emission lines (i.e., HeI/HeII ratios).
As the first step to control the presence of HeI (21.22 eV) and HeII (40.82 eV) lines and corresponding intensity ratios, we introduce simple measurements of photoelectron energy distribution using a gridless Faraday cup (FC). In this paper, our experimental results confirm a presence of HeI line in the discharge and its dependence on the magnitude of the discharge current and on pressure conditions in the differential pumping stages of the lamp.
Measured energy distribution characteristics indicate a presence of photoemitted electrons of Maxwellian energy distribution with the temperature of about 1.6 eV and the electrons with energies in the range of 5–14 eV that probably correspond to the valence band structure of gold. A SIMION model was used to give an evidence that these electrons are not produced by a complicated configuration of the electric field within the gridless FC.