  The \textit{KArlsruhe TRItium Neutrino} (KATRIN) experiment aims to measure
the neutrino mass with a sensitivity of \SI{0.2}{\electronvolt}
(\SI{90}{\percent} CL). This will be achieved by a precision measurement of the
endpoint region of the $\upbeta$-electron spectrum of tritium decay. The
$\upbeta$-electrons are produced in the \textit{Windowless Gaseous Tritium
Source} (WGTS) and guided magnetically through the beamline. In order to
accurately extract the neutrino mass the source activity is required to be
stable and known to a high precision. The WGTS therefore undergoes constant
extensive monitoring from several measurement systems. The \textit{Forward Beam
Monitor} (FBM) is one such monitoring system. The FBM system comprises a
complex mechanical setup capable of inserting a detector board into the KATRIN
beamline with a positioning precision of better than \SI{0.3}{\milli\metre}.
The electron flux density at that position is on the order of
\SI{e6}{\per\second\per\milli\metre\squared}. The detector board contains two
silicon detector chips of \pin diode type which can measure the
$\upbeta$-electron flux from the source with a precision of \SI{0.1}{\percent}
within \SI{60}{\second} with an energy resolution of FWHM $=$
\SI{2}{\kilo\electronvolt}. The unique challenge in developing the FBM arise
from its designated operating environment inside the Cryogenic Pumping Section
which is a potentially tritium contaminated ultra-high vacuum chamber at
cryogenic temperatures in the presence of a \SI{1}{\tesla} strong magnetic
field. Each of theses parameters do strongly limit the choice of possible
materials which e.g. caused difficulties in detector noise reduction, heat
dissipation and lubrication. In order to completely remove the FBM from the
beam tube a \SI{2}{\meter} long traveling distance into the beamline is needed
demanding a robust as well as highly precise moving mechanism.
