Electrostatic analyzer measurements of ionospheric thermal ion populations

Abstract

We define the observational parameter regime necessary for observing low‐altitude ionospheric origins of high‐latitude ion upflow/outflow. We present measurement challenges and identify a new analysis technique which mitigates these impediments. To probe the initiation of auroral ion upflow, it is necessary to examine the thermal ion population at 200–350 km, where typical thermal energies are tenths of eV. Interpretation of the thermal ion distribution function measurement requires removal of payload sheath and ram effects. We use a 3‐D Maxwellian model to quantify how observed ionospheric parameters such as density, temperature, and flows affect in situ measurements of the thermal ion distribution function. We define the viable acceptance window of a typical top hat electrostatic analyzer in this regime and show that the instrument's energy resolution prohibits it from directly observing the shape of the particle spectra. To extract detailed information about measured particle population, we define two intermediate parameters from the measured distribution function, then use a Maxwellian model to replicate possible measured parameters for comparison to the data. Liouville's theorem and the thin‐sheath approximation allow us to couple the measured and modeled intermediate parameters such that measurements inside the sheath provide information about plasma outside the sheath. We apply this technique to sounding rocket data to show that careful windowing of the data and Maxwellian models allows for extraction of the best choice of geophysical parameters. More widespread use of this analysis technique will help our community expand its observational database of the seed regions of ionospheric outflows.

Numerical simulations of a sounding rocket in ionospheric plasma: Effects of magnetic field on the wake formation and rocket potential

“…An accurate knowledge about the floating potential of spacecraft is crucial for plasma measurements, especially when the floating potential is comparable to the energy of the measured ambient plasma particles [ Olsen et al , ; Cohen et al , ]. Equally important are the effects of the charged spacecraft, and its sheath, on the trajectories of plasma particles, which can be used to determine the plasma temperature [ Comfort et al , ; Fernandes and Lynch , ]. Since the current equations presented above, equations and , are only valid for stationary, i.e., nondrifting, unmagnetized and collisionless plasmas, we will, in the following, give more accurate expressions for the ion and electron currents in the case of a drifting and magnetized plasma, which then can be used to determine the floating potential of the spacecraft.…”

The All-sky Spectrometer of Hot Cosmic Plasma

“…In particular, with its help, the plumes of charged particles generated by an ion engine in the far field are investigated by Victor et al (2006). The work by Fernandes & Lynch (2016) presents the results of observation of low-altitude ionospheric origins of high-latitude ion upflow/outflow. The main measurement problem, which was resolved within the framework of the created theoretical model, was the extremely low energy (tenths of an eV) of ions at an altitude of 200-350 km.…”