Beam particles, you add beam data component in particle editor.
Then you make your beam.
I found out that to give start and end points easiest is by using 2 blueprint nodes:
SetBeamTargetPoint/index.html
SetBeamSourcePoint/index.html
You can do this trough parameters, but then you lose preview in particle editor, and passing those variables over to beam emitter is kind of shaky
Ps. Do not develop your particle effects too much currently, by time most of us finishes game/project Epic will release niagara.