Forward Beam Monitor for the KATRIN experiment

The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to measure the neutrino mass with a sensitivity of $0.2,eV$ ($90,%$ CL). This will be achieved by a precision measurement of the endpoint region of the $beta$-electron spectrum of tritium decay. The electrons from tritium $beta$-decay are produced in the Windowless Gaseous Tritium Source (WGTS) and guided magnetically through the beamline. In order to accurately extract the neutrino mass the source properties, in particular the activity, are required to be stable and known to a high precision. The WGTS therefore undergoes constant extensive monitoring from several measurement systems. The 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 inside the Cryogenic Pumping Section with a positioning precision of better than $0.3,mm$. The electron flux density at that position is on the order of $10^{6},s^{-1}mm^{-2}$. The detector board contains a hall sensor, a temperature gauge, and two silicon detector chips of $textit{p}$-$textit{i}$-$textit{n}$ diode type which can measure the $beta$-electron flux from the source with a precision of $0.1,%$ in less than a minute with an energy resolution of FWHM = $2,keV$.