Geoscience Reference
In-Depth Information
for understanding the structure and dynamics of the magnetosphere. Since
no low-energy ion data have been obtained around Mercury, low-energy ion
data obtained by MIA together with Mercury Ion mass spectrum analyzer
(MSA) on MMO will provide us with unique opportunity to understand
detailed structure and dynamics of the Mercury magnetosphere.
3. Measurement Principle of MIA
The MIA basically employs a method of a top hat electrostatic analyzer
with toroidal deflectors as illustrated in Fig. 1. The center of FOV is
designed to be slightly inclined upward from the horizontal plane perpendic-
ular to the axis of rotational symmetry. With the spin motion of spacecraft,
3D ion distribution function is observed. The inner toroidal electrode is sup-
plied with high voltage swept between 0 V and
5 kV. Ions coming through
the collimator are attracted down toward the inner electrode by the action
of the applied potential. Only the ions with specific energy range can fur-
ther travel down to the exit of the electrodes. The ions passing through
the toroidal deflectors enter to Z-stack Micro-channel plate (MCP) and are
intensified to detectable charge pulses. In front of the MCP stack, a grid
supplied with slightly lower voltage (
−
100 V) than the front surface of the
MCP is placed in order to increase the detection eciency of ions. Finally,
the charge pulses are received by 41-channel discrete anode. The positions
where the charge pulses are detected correspond to the incident azimuthal
directions of the ions.
−
Fig. 1.
Measurement principle of MIA.
