Magnet positioning system for ion source

A mass spectrometer comprising:

• a removable ionization assembly including an ionization chamber and at least one ion lens, the removable ionization assembly having a primary axis defined by the direction of an ion beam exiting the ionization assembly, the ionization chamber and the at least one ion lens arranged along the primary axis;
• an electron source aligned along the primary axis of the ionization assembly and configured to provide an electron beam parallel to the primary axis;
• and
• a magnet assembly including a magnet;
• the magnet assembly movable between a first position in which the magnet is positioned to allow removal of the ionization assembly from an ion source and a second position in which the magnet is aligned with the electron source,
• wherein the magnet assembly, ionization assembly, and the electron source are within a vacuum chamber, and movement of the magnet assembly is controlled by a component arranged outside the vacuum chamber and magnetically coupled to the magnet assembly.