The Neutral Solar Wind Detector (NSWD), to be flown on board Solar Orbiter, consists of a neutral atom sensor able to detect and characterize (in terms of velocity and direction) the energetic neutrals flowing together the ionised particles within the solar wind, between ∼0.05 keV/nuc and ∼5 keV/nuc. This may be a stand-alone instrument (indicated as high priority augmentation payload in the Solar Orbiter PDD), but it is also suitable for inclusion in the solar wind particle package SWA.
The NSWD primary scientific objectives may be summarized as in the following:
• observation of neutral solar wind flux;
• velocity, density and temperature of the neutral solar wind;
• comprehension of solar Ly-α corona, i.e. deduction of solar wind plasma velocity distributions
anisotropy perpendicular and along the solar magnetic field lines from neutral solar wind
observations;
• study of the solar wind acceleration region via the detection of the neutral solar wind
hydrogen atoms and investigation of the temporal and spatial details of the solar wind using
the co-aligned movement of the Solar Orbiter spacecraft with respect to the solar rotation;
• observation of the fast and slow neutral solar wind in different solar conditions, potentially
including transitions regions and CMEs;
• resolution of the "inner source" pick-up ion puzzle thought to originate from solar wind
plasma - dust interaction in the solar atmosphere region within 0.2 AU
