Performance Analysis of the Nano Dust Analyzer Under Solar UV Illumination

Abstract:

The Nano Dust Analyzer (NDA) is a linear time-of-flight mass analyzer developed to measure the distribution and elemental composition of nanometer-sized dust particles originating in the inner Heliosphere. The temporal variability of the flux and angular distribution is governed by the complex interaction with the interplanetary magnetic field within 1 AU and provides the means also to learn about solar wind conditions. As part of a heliospheric mission, measurements made by the NDA will determine the size-dependent flux of nano-dust and its variations, it will characterize the composition of nano-dust, and may determine their source processes. The nano-dust particles arrive at 1 AU approximately from the direction of the Sun, thus, the NDA is designed specifically to operate while being exposed directly to solar UV radiation. Here, we report on the performance analysis of the NDA under UV illumination. Solar UV radiation is most likely the largest source of noise for the instrument. A fraction of incident photons will scatter into the ion detector and generate background noise, reducing the instrument's sensitivity. The detailed modeling is conducted using a commercial ray-tracing program. The instrument's performance while exposed to UV radiation is optimized in terms of instrument geometry and surface materials/optical properties, and the requirements on all optical surfaces that are necessary to reduce the effect of UV to the required level are defined and presented here.