Table of linksAbstract1 Introduction2 Troitsk nu-mass3 Rear wall simulation4 Results and References2 Troitsk nu-massThe experiment consists of two main components, figure 1, which are a Windowless Gaseous Tritium Source and an Electrostatic Spectrometer with Magnetic Adiabatic Collimation (MAC-E filter), reference [1]. The spectrometer entrance pitch magnet is at 7.2 T. The magnetic field in the detector location is 1.8 T. A gaseous source with freely circulating radioactive gas allows one to avoid solid state effects associated with a "substrate" or "window". The magnetic field in the WGTS has the shape of a magnetic bottle formed by the superconducting solenoids with a field value of 0.2 T in the main central part with a diameter of 50 mm and 1.2 T magnets at the edges with an inner diameter of 20 mm. To describe the motion of electrons in a magnetic field it is necessary to use a simple formula for transformation of the particle azimuthal angle 𝜃 relative to the field direction with the field strength, 𝐵\ We can estimate the maximum angle of electrons produced in the WGTS at which they will escape from the bottle. In this case 𝑠𝑖𝑛(𝜃1) = 1 and 𝜃2 = 𝑎𝑟𝑐𝑠𝑖𝑛( √︁ 𝐵2/𝐵1). With 𝐵1=1.2 T and 𝐵2=0.2 we get 23 degrees relative to the field axis. All electrons at a larger produced angle will be trapped. Electrons from the WGTS are transported to the spectrometer by a system of superconducting solenoids. A pitch solenoid at 7.2 T at the spectrometer entrance sets an additional angular cut of about 9 degrees for the 𝛽-electrons produced in the WGTS in the direction of the spectrometer. The MAC-E filter acts as an electrostatic rejector of all electrons with energy less than a given spectrometer potential. Measurement at different values of the retarding potential gives an integrated energy spectrum. A 7 pixel silicon drift detector (SDD), figure 1, with a total diameter of about 6 mm is used as an electron detector. This SDD similar to the one used in reference.:::infoAuthors:V.G. ChernovV.S. Pantuev::::::infoThis paper is available on arxiv under CC by 4.0 Deed (Attribution 4.0 International) license.:::\