Currently using this code on the VCM server and it lags pretty easily:

https://github.com/halvors/Nuclear-Physics/blob/1.10.2/src/main/java/org/halvors/nuclearphysics/common/entity/EntityParticle.java#L118

Code in this project is very similar. Either chunk loading or the entity collision check or both is a very expensive calculation.

A better solution than using a particle entity is what the newer version of atomic science does which is render a beam of light inside the accelerator with an intensity/size proportional to the speed