The plasma exhaust is highly ionised plasma which expands out from the spacecraft at high velocity. In fact, the velocity of the exhaust is so high that, depending on which direction you point the exhaust, it will either reach escape velocity as a stream of individual atoms, or enter the Earth’s atmosphere as a harmless trace impurity. In short, this system will not add to the space junk population, or add measurably to micrometeoroids in deep space.