Well, they can operate on just DD, so they can start from no 3He and make 3He.
This video of a presentation by Helion's Kirtley at Princeton has a slide where the reactivity vs. energy loss is shown for a DD system at beta=1. That system will make 3He directly, and also make tritium by two modes (directly from DD, and by capture of neutrons on 6Li in a blanket.) The net result would be production of 1.5 3He nuclei per DD fusion, on average. It takes a while for some of those 3He to be produced though, as the tritium has to decay (halflife of 12 years.)
This video of a presentation by Helion's Kirtley at Princeton has a slide where the reactivity vs. energy loss is shown for a DD system at beta=1. That system will make 3He directly, and also make tritium by two modes (directly from DD, and by capture of neutrons on 6Li in a blanket.) The net result would be production of 1.5 3He nuclei per DD fusion, on average. It takes a while for some of those 3He to be produced though, as the tritium has to decay (halflife of 12 years.)
https://mediacentral.princeton.edu/media/JPP08December2022_D...