Low-energy Energetic Neutrals Atom imaging of Jovian icy moons by PEP/JNA on JUICE
Authors: Shimoyama Manabu , Pontoni Angèle , Karlson Stefan , Asamura Kazushi , Wurz Peter , Wieser Martin , Barabash Stas 
Published: September 2022

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&lt;li&gt;&lt;sup&gt;1&lt;/sup&gt;Swedish Institute of Space Physics, Solar System Physics and Space Technology, Kiruna, Sweden (shimoyama@irf.se)&lt;/li&gt;
&lt;li&gt;&lt;sup&gt;2&lt;/sup&gt;Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Kanagawa, Japan&lt;/li&gt;
&lt;li&gt;&lt;sup&gt;3&lt;/sup&gt;University of Bern, Bern, Switzerland&lt;/li&gt;
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&lt;p&gt;&lt;strong&gt;Summary&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;Jovian Neutrals Analyzer (JNA) is one of six sensors in the Particle Environment Package (PEP) onboard the JUICE mission to Jovian system. The JNA provides the low-energy (10 eV &amp;#8211; 3.3 keV) energetic neutral atom (ENA) images originating from the Jovian magnetospheric plasma interaction with the surface/magnetosphere of the Galilean icy moons, and Io torus images through ENA emissions generated from charge-exchange between the corotating plasma and the neutral torus for the first time. While the design is inherited from successful predecessors, the JNA is highly-optimized for a harsh radiation environment in Jupiter. In this paper, we discuss the calibrated performance of JNA flight and flight spare models as well as possible science cases that JNA will address.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt; &lt;/strong&gt;&lt;strong&gt;ENA imaging technique&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;A technique for space plasma imaging using Energetic Neutral Atoms (ENAs) is a powerful tool to remotely study global plasma phenomena [Wieser, 2010]. ENAs are primarily generated by ion neutralization through charge-exchange processes or ion interaction with various space objects, such as planets, moons, comets or asteroid, via backscattering, sputtering or recoiling processes. Since ENAs as neutrals are not affected to electromagnetic field, we can remotely observe ion properties where they are born by detecting ENAs.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt; &lt;/strong&gt;&lt;strong&gt;Icy moon observation&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;Jovian Neutrals Analyzer (JNA) is designed to detect low-energy ENAs with energy from 10 eV to 3.3 keV produced in the Jovian system. ENA images of the moons directly display plasma precipitation patterns on the moon&amp;#8217;s surface and make it possible to visualize the magnetic field structure of Ganymede&amp;#8217;s magnetosphere and to investigate how Callisto affects magnetic environment in Jupiter&amp;#8217;s magnetosphere. The plasma precipitation maps also give clues to understanding surface weathering processes of Ganymede and Callisto. JNA also aims to detect LENAs from charge-exchange of the co-rotating hot plasma and neutral tori of Io and Europa in the inner magnetosphere. For Io torus imaging, the Io torus is not visible in high-energy ENAs due to low energetic ion fluxes in these regions (Futaana, 2015).&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Instrument&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;The JNA detects ENAs by converting neutrals to ions on a charge conversion surface. Ionized neutrals, namely ions, are subsequently guided through the electrostatic energy analyzer and subjected to time-of-flight (TOF) analysis (Figure 1). Combination of energy- and TOF-analysis provides information on mass discrimination. Whereas the design is based on successful predecessors, i.e. Chandrayaan/CENA and BepiColombo/ENA instruments, a TOF system is heavily optimized to mitigate extremely harsh radiation environment in the Jovian system. JNA uses 11 Ceramic Channel Electron Multipliers (CCEMs) for start signal detection and 11 CCEMs for stop signal detection for the TOF measurement, which allow us to substantially suppress background noises originating in radiation by a single coincidence scheme.&lt;/p&gt;
&lt;p&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;360&quot; height=&quot;260&quot; /&gt;&lt;/p&gt;
&lt;p&gt;Figure 1: JNA measurement principle&lt;/p&gt;
&lt;p&gt;&lt;strong&gt; &lt;/strong&gt;&lt;strong&gt;Calibration&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;JNA flight and flight spare models were calibrated at the calibration facility of the Swedish Institute of Space Physics. The JNA was mounted on the 4-axis turntable in the vacuum chamber with the particle beam source. Species used for calibrations were H, H&lt;sub&gt;2&lt;/sub&gt;, N and Ar. The beam energies were varied from 100 eV to 15 keV. Based on the whole set of calibration data, instrument performance such as angular response, energy response, mass response and sensitivity is verified. The summary of the performance is listed in the table 1. Performance of the charged particle deflector was also verified with high energy ion beams. For JNA flight spare model, advanced calibrations were carried out at University of Bern with focus on the response to relevant species (O and S) and low energy beams (&lt; 300 eV).&lt;/p&gt;
&lt;p&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;360&quot; height=&quot;275&quot; /&gt;&lt;/p&gt;
&lt;p&gt;Figure 2: JNA flight model&lt;/p&gt;
&lt;p&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;360&quot; height=&quot;232&quot; /&gt;&lt;/p&gt;
&lt;p&gt;Figure 3: Calibration setup&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;Table 1: JNA performance&lt;/p&gt;
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&lt;td&gt;Parameters&lt;/td&gt;
&lt;td&gt;&amp;#160;Values&lt;/td&gt;
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&lt;td&gt;Energy range&lt;/td&gt;
&lt;td&gt;&amp;#160;10 eV - 3.3 keV&lt;/td&gt;
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&lt;td&gt;Energy resolution&lt;/td&gt;
&lt;td&gt;&amp;#160;80 - 100 %&lt;/td&gt;
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&lt;td&gt;Mass range&lt;/td&gt;
&lt;td&gt;&amp;#160;1 - 40 amu&lt;/td&gt;
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&lt;td&gt;Mass resolved&lt;/td&gt;
&lt;td&gt;&amp;#160;1, heavy&lt;/td&gt;
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&lt;td&gt;Angular resolution&lt;/td&gt;
&lt;td&gt;
&lt;p&gt;&amp;#160;15-25&amp;#176; (azimuth),&lt;/p&gt;
&lt;p&gt;&amp;#160;7&amp;#176; (elevation)&lt;/p&gt;
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&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Acknowledgements&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;The project is supported by Swedish National Space Agency.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;Futaana, Y., et al. (2015), Low-energy energetic neutral atom imaging of Io plasma and neutral tori, Planet. Space Sci., https://doi.org/10.1016/j.pss.2014.12.022.&lt;/p&gt;
&lt;p&gt;Wieser, M., et al. (2010), First observation of a mini-magnetosphere above a lunar magnetic anomaly using energetic neutral atoms, Geophys. Res. Lett., doi:10.1029/2009GL041721.&lt;/p&gt;
&lt;p&gt;Kazama, Y., et al. (2006), Energetic neutral atom imaging mass spectroscopy of the Moon and Mercury environments, Adv. Space Res., https://doi.org/10.1016/j.asr.2005.05.047.&lt;/p&gt;
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