First Results from the Source/loss-cone Energetic Particle Spectrometer (SEPS) on the NASA POLAR Satellite

W. L. Imhof and J. Mobilia
(Lockheed Martin Palo Alto Research Laboratory, Palo Alto, California 94304; 415-424-3252; e-mail: inhof@agena.space.lockheed.com, mobilia@agena.space.lockheed.com)

H.D. Voss
(Dept. of Physics, Taylor University, Upland, Indiana, 46989-1001; 317-998-4843; e-mail: hnvoss@tayoru.edu)

M. Walt
(STAR Laboratory, Stanford University, Stanford, California, 94305; 415-723-2690; e-mail: walt@nova.stanford.edu)

      We present high angular resolution (+/- 1.5°) energetic particle images of the source and loss cone regions using the CEPPAD Source/loss-cone Energetic Particle Spectrometer (SEPS) instrument which is mounted on the despun platform of the NASA POLAR satellite. By mapping the loss and the source cone fluxes in detail, a better understanding is obtained of pitch angle diffusion mechanisms, wave particle interactions, and direct precipitation. The detailed pitch angle measurements near the loss cone complement the other CEPPAD measurements of fluxes at large pitch angles. The SEPS instrument consists of six pinhole cameras oriented such that an ion camera and two electron cameras point in one direction while the other three cameras point in the opposite direction. Each camera has a pinhole aperture and a focal plane consisting of a solid-state detector array of 128 individually amplified sensor elements. Pulses from each sensor element are analyzed in 16 energy intervals. The overall field-of-view (f-o-v) is 48° x 24° for electrons, though for the data presented here the f-o-v is 24° x 24°. The f-o-v for ions is 22° x 22°. Over much of the POLAR orbit the despun platform is pointed towards the earth, and often during its passage through the radiation belts the SEPS f-o-v includes both the source and loss cones simultaneously. Currently we are evaluating the performance of this new type of instrument and studying the pitch angle distributions in and near the loss cones at various locations and under different geomagnetic conditions.

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