Characterizing the Magnetic Field of a Finite Octagonal Solenoid for COLTRIMS apparatus.

Coltrims (COLd Target Recoil-Ion Momentum Spectroscopy) apparatus requires a magnetic field to confine electrons in the volume of the spectrometer. This is generally achieved by using a set of large Helmholtz coils placed outside the vacuum chamber. Despite its simplicity, this approach suffers from a major drawback, though. Indeed, any magnetic parts (turbomolecular pump, gauge, …) attached to the vacuum chamber distort the magnetic field lines in the spectrometer. To circumvent this issue, we are developing a novel system where the Helmholtz coils are replaced by a solenoid directly placed around the spectrometer. In this study, we provide a comprehensive analysis of the total magnetic field generated by a finite octagonal solenoid and derive a functional form of the magnetic field. Additionally, we have simulated the trajectories of the electrons in such a non-homogeneous field, and extend the traditional Coltrims analysis procedure to this new configuration.