Observations of quiet-time suprathermal ions and electrons (the "superhalo") at 1 AU and beyond find that the suprathermal tails of the solar wind are always present, suggesting that continuous acceleration is taking place in the solar wind and/or in the corona. Fisk and Gloeckler (2006) have suggested that the ubiquitous suprathermal ion tails can result from thermal particles interacting with compressional turbulence embedded in the solar wind. This mechanism predicts a power-law steady state spectrum with an index of -1.5, consistent with a number of ion observations at 1 AU and in the outer heliosphere. However, the mechanism of the acceleration takes time, so it is likely that the suprathermal spectrum will not be fully developed and more variable inside 1 AU.
(As described, this is in situ only.)
However SPICE could be used to observe non-thermal electron distributions at the limb, e.g in combination with SPP in quadrature (TBC). (Up to which electron energies can SPICE observe? If this cannot reach the superhalo energies, then SPICE is not needed here.)