Diagnosing the plasma density transition trapping experiment requires measuring the trapped beams, which have low energy (~2 MeV) and significant energy spread (~ 4% rms), as well as the higher energy drive beams (~14 MeV). In order to meet these requirements we designed and constructed a specialized spectrometer magnet. The magnet has a very long output port which allows the observation of a wide range of energies simultaneous. There is approximately a factor of 5 between the minimum and maximum observable energies. In addition, the magnet is equipped with an in-vacuum diagnostic port, which allows the electrons to travel through vacuum all the way up to the scintillator where they are detected. This feature is critical for the accurate detection of low energy electrons, which can not easily penetrate the metal foils that are often used to seal the exits of spectrometer magnets.