Magnetic sector analyzers use a permanent magnet or an electromagnet to cause the beam from the ion source to travel in a circular path, commonly 60 degrees. The figure illustrates a magnetic sector instrument where ions formed by electron impact are accelerated through a slit into the metal analyzer tube maintained at an internal pressure of 0.1 microtorr. Ions of different mass can be scanned across the exit slit by varying the field strength of the magnet or the accelerating potential. The ions passing through the exit slit strike a collector electrode resulting in an ion current that is amplified and recorded.