title: Initial measurements of O-ion and He-ion decay rates observed from the Van Allen probes RBSPICE instrument.
abstract: H-ion (∼45 keV to ∼600 keV), He-ion (∼65 keV to ∼520 keV), and O-ion (∼140 keV to ∼1130 keV) integral flux measurements, from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft B, are reported. These abundance data form a cohesive picture of ring current ions during the first 9 months of measurements. Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio. Of unique interest to ring current dynamics are the spatial-temporal decay characteristics of the two injected populations. We observe that He-ions decay more quickly at lower L shells, on the order of ∼0.8 day at L shells of 3-4, and decay more slowly with higher L shell, on the order of ∼1.7 days at L shells of 5-6. Conversely, O-ions decay very rapidly (∼1.5 h) across all L shells. The He-ion decay time are consistent with previously measured and calculated lifetimes associated with charge exchange. The O-ion decay time is much faster than predicted and is attributed to the inclusion of higher-energy (> 500 keV) O-ions in our decay rate estimation. We note that these measurements demonstrate a compelling need for calculation of high-energy O-ion loss rates, which have not been adequately studied in the literature to date.
  
  
  CONCLUSIONS
  We report initial observations of ring current ionsWe show that He-ion decay rates are consistent with theoryWe show that O-ions with energies greater than 500 keV decay very rapidly.
authors.affiliation: Center for Solar-Terrestrial Research, New Jersey Institute of Technology Newark, New Jersey, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Gerrard
authors.affiliation: Center for Solar-Terrestrial Research, New Jersey Institute of Technology Newark, New Jersey, USA.
authors.forename: Louis
authors.initials: L
authors.lastname: Lanzerotti
authors.affiliation: John Hopkins University-Applied Physics Laboratory Laurel, Maryland, USA.
authors.forename: Matina
authors.initials: M
authors.lastname: Gkioulidou
authors.affiliation: John Hopkins University-Applied Physics Laboratory Laurel, Maryland, USA.
authors.forename: Donald
authors.initials: D
authors.lastname: Mitchell
authors.affiliation: Fundamental Technologies, LLC Lawrence, Kansas, USA.
authors.forename: Jerry
authors.initials: J
authors.lastname: Manweiler
authors.affiliation: Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, California, USA.
authors.forename: Jacob
authors.initials: J
authors.lastname: Bortnik
authors.affiliation: Solar-Terrestrial Environment Laboratory, Nagoya University Nagoya, Japan.
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Keika
keywords: Van Allen Probes; inner magnetosphere; ion decay rates; spacecraft measurements