I believe I've read that it's possible (and probably necessary for even reasonably long-term efficiency) to set up the magnetic containment in a tokamak such that helium is attracted to the edges of the toroidal field, where it can be skimmed off the surface and extracted. Presumably some kind of helium skimmer block could be created, but I would imagine it would require that each time a fusion event occurs, in addition to a neutron entity you'd have to spawn a helium entity as well, which would likely lower the frequency of fusion events until skimmed off. Perhaps the skimmer functionality could be built into the injector structure, but if it's worth increasing the already high number of entities flying about to add such functionality I'm not sure.
On a related but more political note, in the future, say a few hundred years from now when we actually have working fusion reactors, they may become one of the only reliable source of helium left; practically all the helium on the planet comes from alpha decay of subterranean radioactive elements which collects in deep caves, and is usually only collected as a byproduct of natural gas extraction. Indeed, the only reason helium is perceived as being as cheap and plentiful as it is thanks to a fairly recent US government blunder; since the 1920s, the US government has hoarded enormous quantities of helium (look up the National Helium Reserve), and in 1996 Congress decided they had to be rid of it by 2005, which forced them to attempt to sell it off way below true market value. There have been partially successful attempts to save the helium reserve since, but the damage has already been done, and as a result helium isn't treated with the respect it deserves as a somewhat rare, very useful, finite resource. Joy.