INTERSTELLAR PICKUP PROTONS AT PRESSURE-BALANCED STRUCTURES

A recent attempt to measure the presence of interstellar pickup protons in the distant solar wind through their effects on the variations within pressure-balanced structures found no evidence of these particles (Burlaga et al., 1990). That study concluded that the pickup protons, expected to be correlated with the solar wind density through the charge exchange ionization process, had become smeared in the radial direction. The resulting constant pressure rendered these particles undetectable by the analysis used. This paper presents an improved analysis which takes into account the cooling of these particles in the expanding solar wind. This improvement does not change the conclusions of the previous work. The possibility that quasi-linear perpendicular diffusion is responsible for the inferred smearing across field lines is then investigated. It is shown that this mechanism can easily produce the required transport over the radial dimension of such a structure.