I found a pretty good spot to farm this really quickly without any real danger of getting shot or having to avoid other enemies while trying to get this. Either load up the stage below on any difficulty or keep an eye out while you are playing the stage. Proceed through the level until you get to the part where you have to disable the Chronon Dampener and take out the enemies when you're looking for Dr. Amaral.
Once you jump down onto the platform right before the sphere (red dome) you will hit a check point making this the perfect spot to get it done really quickly. Basically all you do is walk into the dampeners field in front of you and wait for the enemy that is on the platform below you to turn around or walk up the stairs. Once he does this shoot the device (chronon harness) on his back, reload the checkpoint then rinse and repeat until your achievement pops.Difficulty:
Monarch Gala - Act 3 Part 2