| definition |
- The Fast Plasma Investigation
observes the fast-moving plasma.
Incoming particles pass through a filter
which cherry picks certain particle
speeds and directions and allows them
to pass through to a sensor plate.
When an incoming particle hits the
sensor plate, some million electrons
come out the other side, so the
instrument can detect the event. The
whole process takes several
nanoseconds. By separately
measuring electrons and ions, and by
filtering for specific energies, FPI can
count the number of particles of each
kind entering the instrument from a
range of directions at different energies
during any given time span.
Past plasma detectors have relied on
the spin of the spacecraft to gain a full
view of its environment, but with only a
journey of a fraction of a second
through any given magnetic
reconnection site, FPI must be much
faster. Four sensors are used to detect
the negatively charged electrons and
another four for the positively charged
ions. Each sensor is made of two
spectrometers whose field of view is
separated by 45 degrees, each of
which can scan through a 45-degree
arc for a larger panorama. All together
the sensors can observe the entire sky.
The box for each dual sensor and its
components is as big as a small
toaster oven, weighing in at about 15
pounds.
In combination, FPI – consisting of the
four dual electron spectrometers, the
four dual ion spectrometers, and one
data processing unit -- will produce a
three-dimensional picture of the ion
plasma every 150 milliseconds and of
the electron plasma every 30
milliseconds. These frame rates are
similar to those used in video and a
factor of 100 times faster than what
has been accomplished before for
electrons.
The dual electron spectrometers and
the processing unit, or IDPU, were built
at NASA Goddard. The dual ion
spectrometers were built by Meisei
Electric in Gunma, Japan, under the
direction of the Institute of Space and Aeronautical
Sciences, a part of the Japanese
Aerospace Exploration Agency.
|
