1. An electromagnetic testing system for predicting a usable life of a vacuum interrupter, the electromagnetic testing system comprising: a flexible magnetic field coil configured to be placed around an installed vacuum interrupter; a power supply connected to the flexible magnetic field coil and operable to generate a DC current and to apply the DC current to the flexible magnetic field coil to generate a magnetic field to cause ion current flow across one or more gaps inside the installed vacuum interrupter; and a processor configured to measure the ion current flow across the one or more gaps inside the installed vacuum interrupter and to calculate a pressure based on a difference in measured quantity of ions flowing across the one or more gaps.