Medium Energy Neutral Atom (MENA) imager for the IMAGE mission

The Medium Energy Neutral Atom (MENA) imager was developed in response to t he Imaging from the Magnetopause to the Aurora for Global Exploration (IMAG E) requirement to produce images of energetic neutral atoms (ENAs) in the e nergy range from 1 to 30 keV. These images will be used to infer characteri stics of magnetospheric ion distributions. The MENA imager is a slit camera that images incident ENAs in the polar angle (based on a conventional sphe rical coordinate system defined by the spacecraft spin axis) and utilizes t he spacecraft spin to image in azimuth. The speed of incident ENAs is deter mined by measuring the time-of-flight (TOF) from the entrance aperture to t he detector. A carbon foil in the entrance aperture yields secondary electr ons, which are imaged using a position-sensitive Start detector segment. Th is provides both the one-dimensional (1D) position at which the ENA passed through the aperture and a Start time for the TOF system. Impact of the inc ident ENA on the 1D position-sensitive Stop detector segment provides both a Stop-timing signal and the location that the ENA impacts the detector. Th e ENA incident polar angle is derived from the measured Stop and Start posi tions. Species identification (H vs. O) is based on variation in secondary electron yield with mass for a fixed ENA speed. The MENA imager is designed to produce images with 8 degrees x4 degrees angular resolution over a fiel d of view 140 degrees x360 degrees, over an energy range from 1 keV to 30 k eV. Thus, the MENA imager is well suited to conduct measurements relevant t o the Earth's ring current, plasma sheet, and (at times) magnetosheath and cusp.