Design and simulation of a magnetic bottle time of flight spectrometer with an ExB system to measure the kinetic energy of positron-induced electrons.

We investigate the ability of a magnetic bottle time of flight spectrometer attached to a low-energy positron beam to measure the kinetic energy of positron-induced electrons

accurately. In our magnetically guided positron beam system, low energy positrons (<1eV) reach the sample after they are bent around a microchannel plate electron detector using an ExB system. Positrons reaching the sample result in electron emission through secondary processes or following the Auger decay of positron annihilation-induced holes. The ejected electrons travel through a field-free region before they are drifted up to the electron detector by the ExB system. A permanent magnet is placed behind the sample to produce an adiabatically varying magnetic field that parallelizes the electron trajectories and thus improves the TOF system's energy resolution. The low-energy positron beam system also employs transverse magnetic fields to cancel any stray magnetic fields and steer the positron beam to the sample. We simulate the trajectory of the positrons and electrons through the system by solving the governing differential equations. The electric fields are computed employing standard PDE solvers, whereas the magnetic fields are calculated using analytical forms available for finite Helmholtz coils. Through our simulation, we aim to investigate the parameters that determine the accuracy with which the positron-induced electrons' endpoint or maximum kinetic energy can be measured.