Looks to be the Synth Field Helmet, which you get off synths.
Source: I have one and use it all the time.

I wish you could change the color on it, or loot the black ones that some synths wear. What is it with Bethesda games and always having badass looking armor that is unlootable? Oblivion had the same thing with the white and gold guard armor.

I think they do that to annoy players.

Same. A black synth field helmet would look badass, especially with the Courser uniform

I wear the synth field helmet with full heavy combat armour, but that's only cuz I can't find a combat helmet, plus I like the full face cover it provides.

I dropped it for a combat helmet thinking I'd be able to use the lamp on it, but apparently I can't. Still, I have the combat helmet, skull bandana, and wrap around goggles with the armored Railroad coat mk 2

During the quest Battle for Bunker Hill you can loot some, as well as when the Brotherhood attacks the Railroad . Also good places to get full sets of T-60 Power Armor if you arent with the Brotherhood