Tomographic imaging of electron distributions: Leveraging computing power advances to produce inexpensive, low-power, lightweight, and robust instrumentation

We describe a prototype of a novel electron spectrometer that employs a two-dimensional tomographic method to obtain the electron velocity distribution in a space plasma. The spectrometer consists of a magnetic field cavity with a single entrance aperture and a one-dimensional position sensitive microchannel plate/anode assembly electron detector. Electrons entering the instrument through the aperture which have the same component of velocity normal to the aperture plane will all strike the electron detector at the same location regardless of the magnitude of the other velocity component. Thus, the instrument performs line integrals in velocity space. By placing the instrument on a spinning spacecraft, it will provide a complete set of these integrals that may be deconvoluted using standard tomographic techniques. In many cases, basic plasma parameters can be inferred directly from the raw data without deconvolution. This instrument has advantages over conventional electrostatic analyzers: it does not require power consuming voltage stepping, makes efficient use of volume, and operates with a high duty cycle. A modified version of the instrument that is insensitive to photons and can determine three-dimensional distribution functions is also described. (C) 2003 American Institute of Physics.