The earth's magnetic field will still be there but the contents --charged particles of high energy-- will be drained, which happens naturally anyway. For military applications this might be useful to restore near earth space to somewhat usable conditions quickly after a space radiation attack.
Kinda risky for the Van Allen pants?
OK, you physicists confused this engineer. How are you shutting off the charged particle source? Is someone gonna turn off the sun? That is where all the charged particles originate from.
This idea is science fiction, and poor science fiction in my opinion.