Medium Energy Neutral Atom (MENA) Imager for the IMAGE Mission

C. J. Pollock (1), K. Asamura (2), J. Baldonado (3), M. M. Balkey (4), 
P. Barker (3), J.L. Burch (1), E. J. Korpela (8), J. Cravens (1), 
G. Dirks (1), M.-C. Fok (5), H. O. Funsten (3), M. Grande (6), M. Gruntman (7), 
J. Hanley (1), J.-M. Jahn (1), M. Jenkins (1), M. Lampton (8), 
M. Marckwordt (8), D. J. McComas (3), T. Mukai (2), G. Penegor (8), 
S. Pope (1), S. Ritzau (3), M. L. Schattenburg (9), E. Scime (4), R. Skoug (3), 
W. Spurgeon (3), T. Stecklein (1), S. Storms (3), C. Urdiales (1), 
P. Valek (1),(10), J.T.M van Beek (11), S. E. Weidner (1), and M. Wuest (1), 
M.K. Young (1), C. Zinsmeyer (1)

1 Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166; 
2 Institute Of Space and Astronautical Sciences, 3 1 1 Yoshinodai Sagamihara, 
  Kanagawa 229-8510 , Japan; 
3 Los Alamos National Laboratory, CSSE/NIS-1,, Los Alamos, NM 87545; 
4 West Virginia University, Department of Physics, Box 6315, Morgantown, 
  WV 26506;   
5 Universities Space Research Association, NASA GSFC, Greenbelt MD, 20771; 
6 Rutherford Appleton Laboratory, Oxfordshire OX11 0QX, England; 
7 University of Southern California, Department of Aerospace Engineering, 
  Los Angeles, CA, 90089;
8 University of California at Berkeley, Space Sciences Laboratory, 
  Centennial Drive at Grizzly Peak Blvd, Berkeley, CA, 94720; 
9 MIT Center for Space Research, 77 Massachusetts Ave, Cambridge, MA, 02139; 
10 Auburn University, Department of Physics, 206 Allison Laboratory, Auburn, 
   AL, 36849; 
11 Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindoven, 
   The Netherlands

  
           The Medium Energy Neutral Atom (MENA) imager was developed in
response to the Imaging from the Magnetopause to the Aurora for Global
Exploration (IMAGE) requirement to produce images of energetic neutral
atoms (ENAs) in the energy range from 1 to 30 keV. These images will be
used to infer characteristics of magnetospheric ion distributions. The MENA
imager is a slit camera that images incident ENAs in the polar angle (based
on a conventional spherical coordinate system defined by the spacecraft
spin axis) and utilizes the spacecraft spin to image in azimuth. The speed
of incident ENAs is determined by measuring the time-of-flight (TOF) from
the entrance aperture to the detector. A carbon foil in the entrance
aperture yields secondary electrons, which are imaged using a
position-sensitive Start detector segment. This 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 incident ENA on the 1D
position-sensitive Stop detector segment provides both a Stop-timing signal
and the location that the ENA impacts the detector. The ENA incident polar
angle is derived from the measured Stop and Start positions. 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 degree x 4 degree angular resolution over a field of view 
140 degrees x 360 degrees, over an energy range from 1 keV to 30 keV. Thus, 
the MENA imager is well suited to conduct measurements relevant to the Earth's 
ring current, plasma sheet, and (at times) magnetosheath and cusp.

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Space Science Reviews, IMAGE Special Issue, Vol. 91, pp. 113-154, February, 2000