The flux emitter was a device that emitted flux energy, and was built by Citizen Brown, Emmett Brown's counterpart in 1931 in an alternate timeline. It was part of the chronometric analyser, which was a diagnostic device meant to help calibrate the time circuits. Since the timeline of the DeLorean that Edna was driving was overwritten, that DeLorean faded from existence once the time bubble protecting it popped.