As of a few years ago, the DOE started making Plutonium again in partnership with NASA [0]. And as of last year that appeared to be still happening [1]. And this Plasma magnet still would need something like an RPS to get past Jupiter, according to the article:

>Using a steady, nuclear power or beamed power source, such a craft could accelerate to the heliopause, allowing interstellar precursor missions, such as Kuiper belt exploration and the FOCAL mission within a short time frame.

[0]https://www.popsci.com/plutonium-238-is-produced-in-america-...

[1]https://rps.nasa.gov/news/21/a-step-forward-in-reestablishin...