Slit Orbit Mechanism
Figure 14: Exit Slit Selection
3.5 Single and Multichannel Detector (SCD) / (MCD)
The detector consists of the following parts:
● an arrangement of Channel Electron Multipliers (CEMs), 1 for SCD, 5 or 9 for
MCD, consisting of discrete collectors, specially screened against external HF-sig-
nals for maximum noise rejection;
● a multi-pin ceramic, high voltage vacuum feedthrough, specially designed for
low cross talk;
● SCD / MCD preamplifier;
3.5.1 Principles of Detection
Due to the spherical symmetry of the HSA, a one-to-one image of the circularly shaped
entrance slit with a radius of curvature R
0
exists in the exit plane for monochromatic
electrons with a nominal pass energy E
pass
. The images of electrons possessing different
energies within the HSA are concentric circles. In a first order approximation, the radial
image position R for electrons with kinetic energy E
k
is given by
(16)
where D is the has dispersion. The theoretical value for D is
PHOIBOS 25
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