description: Field saving refers to writing the simulation fields to disk in such a way that
they can be reloaded in subsequent runs. At this time, it saves only the time-dependent field
components, not the external fields defined with define_solenoid or constant_fields.
This command results in saving of the fields at 1ns intervals starting at simulated time of 5ns to file
”gunRun.fsave”. Successive saves are placed in successive SDDS pages.