Including sheath effects in the interpretation of planar retarding potential analyzer’s low-energy ion data

Abstract

The interpretation of planar retarding potential analyzers (RPA) during ionospheric sounding rocket missions requires modeling the thick 3D plasma sheath. This paper overviews the theory of RPAs with an emphasis placed on the impact of the sheath on current-voltage (I-V) curves. It then describes the Petite Ion Probe (PIP) which has been designed to function in this difficult regime. The data analysis procedure for this instrument is discussed in detail. Data analysis begins by modeling the sheath with the Spacecraft Plasma Interaction System (SPIS), a particle-in-cell code. Test particles are traced through the sheath and detector to determine the detector's response. A training set is constructed from these simulated curves for a support vector regression analysis which relates the properties of the I-V curve to the properties of the plasma. The first in situ use of the PIPs occurred during the MICA sounding rocket mission which launched from Poker Flat, Alaska in February of 2012. These data are presented as a case study, providing valuable cross-instrument comparisons. A heritage top-hat thermal ion electrostatic analyzer, called the HT, and a multi-needle Langmuir probe have been used to validate both the PIPs and the data analysis method. Compared to the HT, the PIP ion temperature measurements agree with a root-mean-square error of 0.023 eV. These two instruments agree on the parallel-to-B plasma flow velocity with a root-mean-square error of 130 m/s. The PIP with its field of view aligned perpendicular-to-B provided a density measurement with an 11% error compared to the multi-needle Langmuir Probe. Higher error in the other PIP's density measurement is likely due to simplifications in the SPIS model geometry.

Electrostatic analyzer measurements of ionospheric thermal ion populations

“…The spacecraft potential is determined by a current balance model [Siddiqui et al, 2011] which uses the float potential and electron temperature as inputs. Both of these input quantities were well measured on MICA, and the resulting spacecraft potential is consistent with in situ thermal ion measurements by two different instruments Fisher et al, 2016]. Quantities arising from analysis include the…”

Inference of plasma parameters from fixed-bias multi-needle Langmuir probes (m-NLP)

“…In space, it was suggested that temperature estimates be obtained from the International Reference Ionosphere (IRI) model [5] or incoherent scatter radar measurements. The article also reports comparisons of inferred densities with those obtained from the IRI model, and independent measurements in a laboratory plasma [10]; both being deemed satisfactory, and constituting an improvement over estimates made with Jacobsen's original technique.…”

Spatiotemporal Limitations of Data‐Driven Modeling: An ISINGLASS Case Study

“…The main payload of ISINGLASS B included the energetic electron instrument Acute Precipitating Electron Spectrometer (APES) (Michell et al., 2016), the COrnell Wire BOom Yo‐yo System (COWBOYS) electric field instrument (Klatt et al., 2005), a retarding potential analyzer sensor Petite Ion Probe (PIP) (Fisher et al., 2016; Fraunberger et al., 2020), and a thermal electron plasma sensor Electron Retarding Potential Analyzer (ERPA) (Cohen et al., 2016; Frederick‐Frost et al., 2007). Multi‐point measurements were also made using PIPs carried by 4 sub‐payloads, known as BOBs (Roberts, Lynch, Clayton, Disbrow, et al., 2017, Roberts, Lynch, Clayton, Weiss, et al., 2017), ejected from the main payload.…”