IMAP-Ultra cutaway showing major elements: charged-particle deflection plates; front MCP assembly with two 1D start anodes servicing two entrance slits, and one 1D coincidence anode; variable aperture mechanisms servicing each entrance slit (detailed in inset); two stop MCPs imaged using 2D anodes; and a strip of SSD detectors between the two stop MCPs.

The IMAP-Ultra instrument (Ultra) images the emission of Energetic Neutral Atoms (ENAs) produced in the heliosheath and beyond, primarily in H atoms between ~3 and 300 keV, but also sensitive to contributions from He and O. Ultra is nearly identical to the Jupiter Energetic Neutral Imager (JENI), in development for flight on the European Space Agency’s JUICE mission to Jupiter and Ganymede. Ultra’s primary differences from JENI include: (1) the use of 2 identical copies, one mounted perpendicular to the IMAP spin axis (Ultra90) and one mounted at 45˚ from the anti-sunward spin axis (Ultra45) for better sky coverage and more uniform sensitivity over the heliosphere, similar to IMAP-Hi, and (2) the use of slightly thicker, UV-filtering foils covering the back plane MCPs to reduce backgrounds associated with interstellar Lyman-α photons. High resolution images covering over 50% of the heliosphere are produced every ~3 months, contributing to the understanding of the particle spectra and pressures in and beyond the heliosheath, and detecting changes in the spatial distribution of those particles on time scales sufficient to track both solar cycle as well as major active region dependencies.

Ultra will complement the measurements of IMAP-Lo and IMAP-Hi, providing over- lap in energy with IMAP-Hi for heliospheric energetic H, with comparable or better an- gular resolution, and extending the measurements through the range covered previously by Cassini/INCA with much improved sensitivity, angular resolution, and background rejection.

All schematics and numbers are preliminary as of the beginning of Phase A. Additional information about each instrument can be found in the Open Access IMAP Paper.

IMAP-Ultra Instrument Table

IMAP-Ultra Instrument Performance.