Multi-point in situ measurements of thermal ions during the KiNET-X mission

The Kinetic-scale Energy and momentum Transport eXperiment (KiNET-X) sounding rocket explored the coupling of injected barium ions (Ba+) to the ambient ionospheric plasma at two altitudes by releasing two canisters of barium neutrals, each forming an ionized cloud. KiNET-X had instruments on the main payload and on two small deployed subpayloads (Bobs) to measure the Ba+ density (nBa+). The main payload observed nBa+ at a nearly fixed pitch angle to the local geomagnetic field (B→), whereas the Bobs scanned a range of pitch angles. A simple model based on tracing each cloud's particles agreed with the main payload's observed nBa+ profile from the first release; however, for the second release, non-ideal “skidding” motion was required to capture features of the observed nBa+ profile. This paper is a companion to Moses et al. [Phys. Plasmas 32, 042109 (2025)] that analyzes the Bobs' nBa+ profiles. Comparison between the Bobs' measured and modeled nBa+ profiles indicate that pitch angle scattering occurred in each release. Non-idealized pitch angle distributions may arise in the Ba+ clouds from the presence of electric fields parallel to B→ or wave–particle pitch angle diffusion. Pitch angle scattering processes can be proxied in our model by increasing the field-of-view for the density calculation. These different model configurations capture different portions of the measured subpayloads' density and pitch angle profiles. There is perhaps a combination of skidding and scattering that is not easily represented in our model.