I created this quick file for you to learn from that does what you want

Instead of animating an emitter along the path of a circle, I simply created a sphere named "hydrogen" that rotates around a larger sphere called "Nucleus".

The small sphere rotates via a simple "time" expression applied to its' Y rotation attribute, rather than keyframing it along a path etc.

I then applied a simple surface emitter to the smaller sphere so particles would emit from it as it rotates around the larger sphere.

I then reduced the length of the "tail" by simply reducing the particle's lifespan.
So now the tail dies long before it reaches back around itself again

To get the tail to "fade", I leave that learning lesson up to you
HINT: "opacityPP"

Good luck!