Looking for information

I'm hoping that someone on this list can point me to the info I'm
looking for.

About a year ago I came came across a website, I think it was NASA
affiliated, that described a technology in which energy is poured
into, I think it was a plasma, and with very little maintenance
energy, this plasma ring? served as a battery. Supposedly it had
pretty high theoretical energy density. You could pour immense
amounts of energy in, let's say at a re-fueling station in LEO, and
then use it as a means of propulsion for a sacecraft.

I've been trying to find this web reference again, but my memory is
fuzzy and I'm just not able to find the correct search terms.

Anybody else come across this same information?