Acceleration, Transport, and Trapping of Ultra-Heavy Ions in the Inner Zone
Tuesday, 6 March 2018: 11:45
Longshot and Bogey (Hotel Quinta da Marinha)
Geoffrey D Reeves1, Brian Larsen1, Herbert O Funsten1, Ruth M Skoug1, Philip A Fernandes1, Michael Denton2, Alex J Boyd3 and Harlan E. Spence4, (1)Los Alamos National Laboratory, Los Alamos, NM, United States, (2)New Mexico Consortium, Space Science, Los Alamos, NM, United States, (3)New Mexico Consortium, Los Alamos, NM, United States, (4)University of New Hampshire, Institute for the Study of Earth, Oceans, and Space, Durham, NH, United States
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Abstract:
We report, here, on the discovery of a population of trapped, energetic (10-50 keV), ultra-heavy (>30 AMU) ions in the inner zone of the Earth's radiation belts (L < 3). The ions are observed using the Van Allen Probes Helium, Oxygen, Proton, Electron (HOPE) plasma spectrometer [Funsten et al., 2013]. HOPE measures the energy of incoming ions using a standard electrostatic analyzer and measures the mass per charge by measuring the time of flight (TOF) of the ions at each spectrometer energy step (E). Each ion species (and charge state) falls in a specific domain of E vs TOF. The primary singly-charged ion species (Helium, Oxygen, and Protons) are reported by rate counters but HOPE also reports full E x TOF matrices at lower cadence to monitor instrument performance and identify minor ion species.
By analyzing energy vs time-of-flight (E x TOF) data over the >5 years of the Van Allen Probes mission we have identified a population of trapped ions with a most probable mass per charge of ~ 40 which would correspond to Argon; the third most abundant gas in Earth's atmosphere but not previously seen in the magnetosphere. We also consider the possibility that this new ion population corresponds to molecular species; O2 (m=32); NO (m=30); or N2O (m=44). While molecular ions have previously been observed in the magnetotail they have been no previous reports of a trapped, energetic population at L < 3.
We will consider the temporal, spatial, energy, and pitch angle distributions of this unexpected and unlikely population of ions. Important questions include: What are they? If they come from the ionosphere how are they transported to the inner zone? How are they energized to >10 keV? What are the expected lifetimes once they are trapped? and What can they tell us about other radiation belt trapping and energization processes?
