The need for accurate measurements of thermal velocity distribution functions in the solar wind

The current state of the art thermal particle measurements in solar wind are insufficient to address many long standing, fundamental physical processes. is a weakly collisional ionized gas experiencing collective effects due long-range electromagnetic forces. Unlike collisionally mediated fluid like Earth’s atmosphere, not thermodynamic or equilibrium. For that reason, exhibits multiple populations for each species. We can mostly resolve three major electron (e.g., core, halo, strahl, and superhalo) wind. ions, we sometimes separate proton core from secondary beam heavier ion species alpha-particles. However, as becomes cold hot, our ability these more difficult. Instrumental limitations have prevented us properly resolving features within population. This destroys examine energy budgets across transient, discontinuous phenomena shock waves) evolution velocity distribution functions. Herein illustrate both instrumentation why higher resolutions necessary kinetic physics accomplished by directly comparing some observations with calculations moments inaccuracy incompleteness poor resolution data.